![\"\"](\"data:image\/svg+xml;base64,PHN2ZyB3aWR0aD0iMSIgaGVpZ2h0PSIxIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPjwvc3ZnPg==\")
<\/a><\/h6>\nFig.\u00a01. Composting containers used for community composting (left); one of the\u00a0final compost mixtures for the\u00a0pot experiments (right)<\/h6>\n
In the\u00a0first year, two composts were created in plastic composters with a\u00a0volume of 500\u00a0litres: one with sludge from the\u00a0domestic activated WWTP (marked K-A) and the\u00a0other with sludge from the\u00a0reed bed plant (marked 1\u00a0K-K). In the\u00a0case of sludge from the\u00a0reed bed plant, one more experimental pile of material was prepared in the\u00a0form of a\u00a0trapezoidal pile under foil, with a\u00a0volume of 4,000\u00a0litres. The\u00a0compost was marked as 2\u00a0K-K. Layers of sludge in a\u00a0total volume that corresponded to the\u00a0principles established by the\u00a0SN regarding composting (i.e. a\u00a0maximum sludge content of up to 40\u00a0% of the\u00a0pile) were interspersed with layers of grass from mowing, layers of chips from processed wood matter and, in the\u00a0case of a\u00a0reed bed plant, also with additional layers of macrophyte vegetation from reed bed filters of the\u00a0plant (reed with an admixture of iris and great manna grass). The\u00a0ratio of input materials corresponded to the\u00a0requirement for the\u00a0recommended C\/N ratio, which is reported in the\u00a0range of 20\u00a0to 30\/1\u00a0[17, 18], while the\u00a0addition of green and wood matter during sewage sludge composting aimed to increase the\u00a0C\/N ratio [19].<\/p>\n
In the\u00a0second year, composts were established in trapezoidal piles covered with PE black impermeable foil with a\u00a0volume of about 300\u00a0litres using sludge from two sizes of reed bed plants (domestic\u00a0\u2013 compost K-3\u00a0and municipal\u00a0\u2013 compost K-4). The\u00a0layers were placed as follows: bottom layer 10\u00a0cm\u00a0\u2013 wilted grass, above it a\u00a05\u00a0cm layer of sludge from the\u00a0reed bed plant (dry sludge about 14\u00a0%), above that a\u00a015\u00a0cm layer\u00a0\u2013 wilted grass, then a\u00a05\u00a0cm layer of sludge from the\u00a0reed bed plant (dry sludge about 14\u00a0%) and the\u00a0upper layer consisted of a\u00a010\u00a0cm layer of wilted macrophytes. The\u00a0description of the\u00a0municipal reed bed plant is given in Rozkon et al. [20].<\/p>\n
During the\u00a0composting process, the\u00a0ambient air temperature and the\u00a0temperature and humidity of the\u00a0environment in the\u00a0compost were monitored.<\/p>\n
During composting, mixed samples of the\u00a0resulting compost were taken to analyse the\u00a0current level of microbiological contamination (enterococci, faecal coliform bacteria) and the\u00a0content of nutrients and macroelements (N, P, K, Ca, Mg, Na) and heavy metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn). Dry matter, loss by annealing, and the\u00a0content of culturable microorganisms at 22\u00a0\u00b0C were also monitored. Sampling took place for composts established in the\u00a0first year after four and twelve months from establishment; for composts established in the\u00a0second year after four, seven and twelve months from establishment. The\u00a0length of the\u00a0composting process corresponded to experience with the\u00a0course of extensive small-volume (domestic, community) composts, which are characterized by a\u00a0longer period of maturation and stabilization.<\/p>\n
Assessment of the\u00a0effect of composts on the\u00a0production of selected crops<\/h3>\n
Assessment of the\u00a0effect of composts on the\u00a0production of selected crops was carried out using pot experiments. Among the\u00a0studied crops (also on the\u00a0basis of research), crops representing different types of vegetables (leaf, fruit) were selected: lettuce (Lactuca sativa L.)\u00a0\u2013 Maralus variety (Fig.\u00a02<\/em>) and tomato (Lycopersicon esculentum Mill.)\u00a0\u2013 Tornado F1\u00a0variety (Fig.\u00a03<\/em>). Lettuce is one of the\u00a0most commonly consumed raw leafy vegetables [24] and is classified as a\u00a0plant sensitive to heavy metals [21\u201323]. Tomatoes are the\u00a0second most important vegetable in the\u00a0world after potatoes; in 2016, annual global production was 177\u00a0million tons grown on almost 4.8\u00a0million ha of land [24].<\/p>\n<\/a>\nFig.\u00a02. View of part of the\u00a0containers from the\u00a0lettuce planting pot experiments; mixing of compost with soil in the\u00a0upper layer of about 5\u00a0cm is evident<\/h6>\n<\/a>\nFig.\u00a03. View of part of the\u00a0containers from the\u00a0tomato planting pot experiments<\/h6>\n
<\/p>\n
Pot experiments for growing selected types of vegetables<\/h3>\n
Pot experiments were designed using the\u00a0same five-litre plastic pots with a\u00a0surface area of 0.031\u00a0m2. All sets were placed in the\u00a0same location and under the\u00a0same conditions. Two (experiment 1\u00a0year) or three repetitions (experiment 2\u00a0year) were prepared for each variant of the\u00a0substrate (soils, composts, mixtures of soils and composts). Substrates were chosen to include comparative soils\u00a0\u2013 fertile garden soil (chernozem\u00a0\u2013 Hustopesko region), designated as ZZ in the\u00a0experiments, and degraded eroded field soil (chernozem\u00a0\u2013 Hustopesko region), designated as EZ in the\u00a0experiments. Then there were mixtures of these soils with composts, and only composts. Soils and composts were homogenized by mixing before being filled into containers, and portions were subsequently placed into individual containers. The\u00a0materials were prepared in a\u00a0rainless period with the\u00a0following humidity levels: first year experiment\u00a0\u2013 soils about 94\u00a0% dry matter, composts about 73\u00a0%; second year experiment\u00a0\u2013 soil about 94\u00a0% dry matter, composts about 74\u00a0%. Mixtures of field soil with composts were prepared in such a\u00a0way that the\u00a0proportion of compost corresponded to the\u00a0theoretical field dose of 80\u00a0tons of compost per hectare. After conversion, it was 260\u00a0g in one five-litre container. The\u00a0amount of soil in the\u00a0mixture weighed about 3\u00a0kg. The\u00a0proportion of compost in the\u00a0mixtures was about 8\u00a0%. The\u00a0compost was always mixed with the\u00a0soil individually when filling each container, incorporating it into the\u00a0upper layer of the\u00a0soil to a\u00a0depth of about 5\u00a0cm (Fig.\u00a02<\/em>).<\/p>\nProcessing and analysis of vegetable, soil, and compost samples<\/h3>\n
Lettuce was harvested about one month after planting the\u00a0seedlings (May), at\u00a0the\u00a0time of full maturity of the\u00a0lettuce heads before their transition to the\u00a0phase of flower formation (Fig.\u00a04<\/em>). Tomato plants were planted on the\u00a0same dates as the\u00a0lettuce. Harvesting of tomato fruits took place from the\u00a0first appearance of ripening fruits (July) until the\u00a0end of production of ripening fruits (September, October). Lettuce samples were dried at room temperature, finely crushed, and homogenized. Harvested tomato fruits were weighed fresh and stored in a\u00a0freezer. At the\u00a0end of the\u00a0harvest, all fruits from a\u00a0given plant were mixed, processed in the\u00a0laboratory into a\u00a0homogeneous mixture, and freeze-dried to take sample portions for analysis. To determine Al, As, Cd, Cr, Cu, Ni, Pb, Na, K, Ca, Mg, Fe, Mn and Zn, each sample (about 1g) was mineralized in a\u00a0Teflon container by MLS-1200\u00a0MEGA device using 3\u00a0ml of concentrated HNO3\u00a0and 1\u00a0ml of 30% H2O2. The\u00a0containers were sealed for the\u00a0mineralization cycle to take place. After cooling, the\u00a0contents of the\u00a0container were transferred into a\u00a0100\u00a0ml volumetric flask. The\u00a0determination of Al, As, Cd, Cr, Cu, Ni, and Pb was carried out by the\u00a0method of atomic absorption spectrometry\u00a0\u2013 electrothermal atomization (AAS-ETA) on a\u00a0PERKIN ELMER AANALYST 600. The\u00a0determination of Na, K, Ca, Mg, Fe, Mn and Zn was carried out by the\u00a0method of flame atomic absorption spectrometry (AAS-flame) on a\u00a0PERKIN ELMER AANALYST 400. The\u00a0calibration curve method was used to determine the\u00a0content of individual metals. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Determination of Hg was carried out on an AMA-254\u00a0mercury analyser, calibrated according to the\u00a0manufacturer\u2019s\u00a0manual. Approximately 0.1\u00a0g was weighed from the\u00a0pre-treated sample. The\u00a0Hg content determined always corresponded to the\u00a0average of two to three simultaneous determinations. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Homogenized samples of composts and soils were freeze-dried and then processed in a\u00a0manner identical to the\u00a0processing of biomass samples. Total phosphorus was determined using the\u00a0cuvette test LCK 348 (HACH-LANGE) on a\u00a0DR 3900\u00a0spectrophotometer with a\u00a0tungsten lamp (Vis). Total nitrogen was determined by the\u00a0modified Kjeldahl method according to SN\u00a0ISO\u00a011261.<\/p>\n<\/a>\nFig.\u00a04. View of part of the\u00a0planting pot experiment containers; in the\u00a0left part, lettuce heads and tomato plants with fruits in a\u00a0substrate with compost, in the\u00a0right part in a\u00a0substrate without compost<\/h6>\nAssessment of phytotoxicity of composts using the\u00a0seed germination test<\/h3>\n
In the case of using sludge from small sources (domestic and small municipal WWTPs) for horticultural and agricultural purposes, the main interest of the user is also to reduce the contamination of the resulting sludge and to ensure that the substrates used that contain sludge or compost do not pose a health risk and a danger to the environment in terms of toxicity. This fact can be verified, for example, by phytotoxicity tests or earthworm escape tests [25]. Phytotoxicity tests exist in the form of directives issued by major environmental agencies, such as the US EPA (United States Environmental Protection\u00a0Agency), OECD (Organization for Economic Co-operation and Development), ISO (International Standards Organization), ASTM (American Society for Testing and Materials), and others. Papers from 2011\u00a0and 2019\u00a0give an overview of phytotoxicity tests [26, 2].<\/p>\n
The seed germination test, which was chosen for our study, is a\u00a0method of evaluating the\u00a0intensity of decomposition of organic materials and the\u00a0maturity of the\u00a0resulting compost, which was developed at the\u00a0Crop Research Institute\u00a0Prague for use in composting practice. It is a\u00a0biological method of evaluating the\u00a0phytotoxicity of a\u00a0sample leachate using the\u00a0germination index of a\u00a0sensitive plant\u00a0\u2013 garden cress (Lepidium sativum) [27].<\/p>\n
The resulting germination index can be obtained from the\u00a0following equation:<\/p>\n<\/a>\n <\/p>\n
<\/p>\n
<\/p>\n
<\/p>\n
where:<\/p>\n
kv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 is\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the\u00a0germination rate of the\u00a0sample [%]<\/p>\nkk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 control germination [%]<\/p>\nlv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of the\u00a0sample [mm]<\/p>\nlk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of control [mm]<\/p>\nAt values up to 50\u00a0%, the\u00a0index states that the\u00a0compost is unusable for direct application, from 60\u00a0to 80\u00a0% it gives the\u00a0possibility of application with a\u00a0certain risk of damage to sensitive plants, and at values of 80\u00a0% and higher it declares mature compost. If the\u00a0germination index is between 60\u00a0and 80\u00a0%, it can be said that the\u00a0compost is in the\u00a0conversion phase and has the\u00a0best fertilizing effect. Above 80\u00a0%, this effect decreases, and the\u00a0influence of humus is stronger, which means that nutrients are more bound. The\u00a0release of N and P is slower and there is no leaching of nutrients into groundwater [28].<\/p>\n
Statistical analyses were performed using available tools in MS Office Excel 2016\u00a0and SW R-4.\u00a03.\u00a02. for Windows using ANOVA analysis of variance after pre-screening the\u00a0data sets for standard distribution. The\u00a0choice of procedure and statistical methods corresponded to the\u00a0procedures that were used in a\u00a0similar experiment focused on the\u00a0effect of addition of sewage sludge composts to substrates for horticultural purposes [29]. In the\u00a0case of pot experiments, the\u00a0evaluation was carried out by calculating statistical characteristics for individual variants of substrates and crops from two (first year) and three repetitions (second year).<\/p>\n
RESULTS AND DISCUSSION<\/h2>\nComposition and contamination of used soils and\u00a0composts<\/h3>\n
The contents of heavy metals and arsenic in the\u00a0soils used in the\u00a0experiments in both years did not exceed the\u00a0preventive and indicative values according to National Decree No. 153\/2016\u00a0Coll. Of the\u00a0composts used in the\u00a0first year, all composts exceeded both the\u00a0proposed limit value for Cu in the\u00a0framework of the\u00a0EU technical report [30] and the\u00a0given national standard. The\u00a0composts also exceeded both limit values for Zn, and in the\u00a0case of K-A compost, the\u00a0limit value for this element was also exceeded according to SN 465735\u00a0[31]. K-3\u00a0and K-4\u00a0composts used in the\u00a0second year did not exceed any of the\u00a0limit values proposed within the\u00a0EU and given by the\u00a0SN 465735\u00a0standard. Lower concentrations of Cu and Zn in these composts (on average 218\u00a0mg\/kg Zn and 65.9\u00a0mg\/ kg Cu compared to the\u00a0values of 1,016\u00a0mg\/kg Zn and 386\u00a0mg\/kg Cu in the\u00a0composts in the\u00a0first year) were probably caused by the\u00a0lower proportion of used sludge in the\u00a0input mixture for composting. Sludge load can be affected by the\u00a0connection to the\u00a0sewage system, which also brings rain wash rich in these metals due to the\u00a0corrosion of roofing materials.<\/p>\n
Regarding the\u00a0assessment of microbial contamination, it was carried out using standard analytical methods for the\u00a0determination of indicator organisms (Salmonella sp., enterococci, thermotolerant coliform bacteria) in the\u00a0input sludge and in the\u00a0resulting substrates from composting. Microbial contamination of sewage sludge from domestic WWTPs ranged from 2\u00a0\u00a0103\u00a0to\u00a04.2\u00a0\u00a0103\u00a0KTJ\/g of dry matter of samples in the\u00a0case of enterococci and 1.6\u00a0\u00a0104\u00a0to 6\u00a0\u00a0104\u00a0KTJ\/g of dry matter of samples in the\u00a0case of thermotolerant coliform bacteria. The\u00a0amount of thermotolerant coliform bacteria in the\u00a0sludge from the\u00a0municipal reed bed plant was in the\u00a0range of 1\u00a0\u00a0105\u00a0to 2\u00a0\u00a0106\u00a0KTJ\/g of dry matter and the\u00a0number of enterococci in the\u00a0range of 1\u00a0\u00a0104\u00a0to 6\u00a0\u00a0106\u00a0KTJ\/g of dry matter. Microbial contamination in fresh substrates from composts before their use in pot experiments was zero for composts K-3, K-4\u00a0and 1\u00a0K-K (zero detection of KTJ per gram of dry matter) for both indicators. For composts\u00a01\u00a0K-A and 2\u00a0K-K in tens of KTJ per gram of dry matter for enterococci and in lower hundreds of KTJ per gram of dry matter for FC. For all composts, it would be acceptable when assessed with the\u00a0limits listed in the\u00a0SN as \u201cComposting\u201d. The\u00a0presence of Salmonella sp. was not detected even in the\u00a0input sludge.<\/p>\n
Phytotoxicity test results<\/h3>\n
Mixed samples were taken from the\u00a0set of composts established in the\u00a0second year (K-3\u00a0and K-4) and supplemented with a\u00a0control sample (seeds germinated only on distilled water) for phytotoxicity seed germination test. Compost samples were already stabilized, they did not show changes in microbial contamination and content of heavy metals and macroelements. The\u00a0garden cress test was performed in two dilutions, namely 5\u00a0\u00a0and 10\u00a0\u00a0dry weight (%). For each sample, 10\u00a0Petri dishes with 8\u00a0seeds were used, for a\u00a0total of 80\u00a0seeds. After 24\u00a0hours, the\u00a0number of germinated seeds in each Petri dish was determined and the\u00a0lengths of all roots were measured.<\/p>\n
Some vegetative responses, such as the\u00a0seed germination test or the\u00a0elongation of root and seedling growth, are commonly used to assess the\u00a0excess toxicity of organic and inorganic compounds in various substrates [32]. The\u00a0average germination rate in our experiment was found to be 7.5, 7.5, 7.7, and 7.8\u00a0seeds out of 10\u00a0for individual prepared mixtures of composts and soils, and 7.8\u00a0for the\u00a0control set. ANOVA analysis showed that the\u00a0null hypothesis of equality of mean values of the\u00a0mixtures and the\u00a0control set could not be rejected at the\u00a0significance level of\u00a0 = 0.05\u00a0(p < 0.05). The\u00a0spread of root lengths between the\u00a0minimum and maximum values for the\u00a0prepared mixtures was generally in the\u00a0same interval of 4.0\u00a0to 9.0\u00a0cm with average values of 6.6, 6.8, 6.2, and 5.8\u00a0cm. The\u00a0smallest average length (5.4\u00a0cm) was achieved by sprouts from the\u00a0control set. The\u00a0results of the\u00a0phytotoxicity test show that the\u00a0mixtures used were stabilized, without a\u00a0negative impact on the\u00a0germination of garden cress seeds. The\u00a0IK index values ranged from 107\u00a0to 118\u00a0for all four mixtures.<\/p>\n
Effect of compost application on change in yield of useful parts of crops<\/h3>\n
In the case of containers with lettuce seedlings, the difference in the weight of the above-ground part (leaves) of the grown head of lettuce without damaged and dry leaves on the edge was monitored. In both years, a statistically significant difference in fresh biomass weight was demonstrated (ANOVA, alpha level 0.05). In the first year, the average weight of the fresh head of lettuce was 15.7 g when using the EZ soil and 61.2 g when using the ZZ soil. In containers with 100% compost substrates, the average weight of fresh heads of lettuce was\u00a077.5\u00a0g (1\u00a0K-K), 82.8\u00a0g (1\u00a0K-A), and 99.1\u00a0g (2\u00a0K-K). An 8% admixture of compost to poor-quality soil contributed to a\u00a0substantial increase in yield. The\u00a0average weights of fresh heads were 104\u00a0g (mixture with 1\u00a0K-A), 105\u00a0g (mixture with 1\u00a0K-K), and 95.2\u00a0g (2\u00a0K-K). This is an increase of up to 85\u00a0% compared to EZ soil, and 36\u00a0to 41\u00a0% compared to high-quality ZZ soil. An experiment in the\u00a0second year confirmed these results. The\u00a0average weight of a\u00a0fresh head of lettuce when using EZ was 81.4\u00a0g, i.e., much higher than in the\u00a0first year. However, the\u00a0EZ used in this year contained 38\u00a0% more organic matter compared to the\u00a0EZ used in the\u00a0first year. In containers with 100% compost substrates, the\u00a0average fresh weights of lettuce heads were 154\u00a0g (K-3) and 108\u00a0g (K-4). When using compost K-3, the\u00a0average yield increased by 47\u00a0% when using compost K-4\u00a0by 25\u00a0%. An\u00a08% admixture of composts to the\u00a0soil meant an increase in average yields by 27\u00a0% (compost K-3) and by 14\u00a0% (compost K-4) to values of 111\u00a0g (K-3) and 95.3\u00a0g (K-4). Fig.\u00a04<\/em>\u00a0shows the\u00a0difference in the\u00a0size of the\u00a0lettuce heads as a\u00a0result of the\u00a0use of compost in growing substrates.<\/p>\nIn the\u00a0case of tomato plants, the\u00a0influence of cultivation in 100% compost substrates and in soils with admixture of these substrates on the\u00a0number of fruits obtained during the\u00a0growing season and the\u00a0total weight of the\u00a0fruits was assessed. Fruits were harvested ripe continuously throughout the\u00a0season, weighed and stored to prepare the\u00a0resulting mixture for analyses. From the\u00a0pot experiment in the\u00a0first year, it appears that tomatoes grown in low-quality EZ soil had the\u00a0lowest number of fruits (about13\u00a0fruits per plant). The\u00a0yield from ZZ chernozem (about 25\u00a0fruits per plant on average) was comparable to the\u00a0yield of tomatoes growing in a\u00a0substrate of 100% compost (about 30\u00a0fruits per plant on average for all composts used). An 8% admixture of composts to the\u00a0EZ soil increased the\u00a0average yield from 13\u00a0fruits to 20\u00a0fruits per plant. A\u00a0pot experiment in the\u00a0second year confirmed the\u00a0highest average yields from 100% compost substrates, approximately 25\u00a0fruits per plant. The\u00a0yield from EZ was around 15\u00a0fruits. Compared to the\u00a0results from the\u00a0first-year experiment, the\u00a0addition of compost substrates to this soil did not significantly increase the\u00a0yield. Average yields from these mixtures remained at around 15\u00a0fruits per plant. In the\u00a0first year, fruits from plants grown in eroded soil had the\u00a0lowest total weight (about 300\u00a0g per plant on average). In 100% compost substrates, the\u00a0average fruit weight per plant was 645\u00a0g for K-A, 755\u00a0g for 1\u00a0K-K, and 650\u00a0for 2\u00a0K-K. The\u00a0admixture of all types of composts to EZ increased the\u00a0average mass yields to values of 410\u00a0to 495\u00a0g, i.e. to the\u00a0level of quality chernozem ZZ (450\u00a0g per plant on average). The\u00a0fruit weight analysis from the\u00a0second-year experiment replicated the\u00a0findings from the\u00a0fruit number analysis. For 100% compost mixtures, average fruit weights per plant were 700\u00a0to 800\u00a0g.<\/p>\n
Content of selected nutrients and elements in useful parts of crops<\/h3>\n
Evaluation was done for P, N, K, Na, Ca, and Mg. The\u00a0element content was measured in dried or lyophilized samples (see above) and determined per kg of dry matter. Subsequently, these values were recalculated using the\u00a0values of dry matter to fresh matter, both for the\u00a0biomass of lettuce leaves and for the\u00a0biomass of fruits from tomato plants. In tomato fruits, a\u00a0statistically significant difference in content was found for P, Ca, K, Na (both pot experiments of the\u00a0first and second year) and for N and Mg (pot experiment from the\u00a0second year). In lettuce leaves, a\u00a0statistically significant difference in content was found for K\u00a0and Ca (pot experiment from the\u00a0first year), but this was not confirmed in the\u00a0experiment in the\u00a0following year. In contrast, in this year a\u00a0statistically significant difference was found for N, P, and Na.<\/p>\n
Tab. 1. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0first-year pot experiment (in mg\/kg of fresh matter)<\/p>\n<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 3.<\/h6>\n
The content of nutrients in the\u00a0leaves from heads of lettuce (Figs. 5<\/em>\u00a0and\u00a07<\/em>) and also in the\u00a0tomato fruits (Figs. 6<\/em>\u00a0and 8<\/em>) was comparable in both pot experiments. The\u00a0contents of selected nutrients differ between the\u00a0biomass of heads of lettuce and the\u00a0biomass of fruits from tomato plants in total numbers mainly because both biomasses have very different dry matter. In the\u00a0case of lettuce biomass, the\u00a0dry matter is around an average value of 91\u00a0%, in the\u00a0case of tomato biomass around an average value of 8\u00a0% (7\u00a0to 11\u00a0%). The\u00a0differences in nutrient content in lettuce and tomato biomass from containers with individual substrates can be seen from the\u00a0graphs in Figs. 5\u20138<\/em>. Due to the\u00a0conversion to fresh mass, the\u00a0differences (e.g. in N and K\u00a0content) are higher in lettuce biomass. The\u00a0use of substrates from composting resulted in a\u00a0demonstrably higher content of P, Na and, conversely, a\u00a0lower content of Ca in tomato fruits in the\u00a0case of using compost as an admixture. In the\u00a0pot experiment in the\u00a0second year, this difference was found only in clean substrates from composting. This was also related to the\u00a0increase in N content in the\u00a0biomass (Fig.\u00a08<\/em>). Similarly, a\u00a0significantly higher content of all elements with the\u00a0exception of Ca (a\u00a0decrease in its content) was found in lettuce biomass from the\u00a0pot experiment in the\u00a0second year (Fig.\u00a07<\/em>).<\/p>\n<\/a>\nFig. 5. Average content of nutrients in lettuce heads grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 6. Average content of selected nutrients in tomatoes grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 7. Average content of nutrients in lettuce heads grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 8. Average content of selected nutrients in tomatoes grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\nContent of risk elements in useful parts of crops<\/h3>\n
The assessment was carried out for the\u00a0following heavy metals and elements: Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn. The\u00a0analytical procedure for determining the\u00a0content in biomass and conversion to evaluable results for fresh matter was the\u00a0same as in the\u00a0case of the\u00a0elements listed in the\u00a0previous sub-chapter.<\/p>\n
These results were compared with the\u00a0limit contents established in the\u00a0following regulations:<\/p>\n
Commission Regulation (EC) No. 1881\/2006\u00a0(hereinafter referred to as the\u00a0\u201cRegulation\u201d) setting limits of 0.2\u00a0mg\/kg Cd, 0.3\u00a0mg\/kg Pb.<\/p>\n
National regulation Decree No. 53\/2002\u00a0Coll. (hereinafter referred to as the\u00a0\u201cDecree\u201d), setting limits (in mg\/kg of fresh matter): 0.5\u00a0As, 0.2\u00a0Cd, 0.2\u00a0Cr, 10\u00a0Cu, 50\u00a0Fe, 0.03\u00a0Hg, 2.5\u00a0Ni, 0.3\u00a0Pb, 25\u00a0Zn. The\u00a0Decree was repealed due to accession to the\u00a0European Community on 1st August 2004. However, it still allows to assess and compare the\u00a0level of contamination for more metals than the\u00a0Commission Regulation, where limits are set only for Cd and Pb.<\/p>\n
For tomato fruits, no exceedance of the\u00a0limit values given by the\u00a0Regulation for either Cd or Pb was detected for individual plants, in both pot experiments. Also, it was not detected that the\u00a0older, no longer valid limits given by the\u00a0Decree were exceeded for any monitored element. A\u00a0comparison of the\u00a0average values for individual substrate variants (Tab. 1<\/em>\u00a0and 2<\/em>) shows that no limit contents of risk elements were exceeded either. In tomato fruits, a\u00a0statistically significant difference in content was found for Zn, Cu, and Cr (both pot experiments), for Ni, Mn, and Cd (pot experiment from the\u00a0second year), and for Al (pot experiment from the\u00a0first year).<\/p>\nTab. 2. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0second-year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 4<\/em>.<\/h6>\nTab. 3. Average values of heavy metals and arsenic in lettuce grown in the first year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nTab. 4. Average values of heavy metals and arsenic in lettuce grown in the second year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nAn analysis comparing only container fills consisting entirely of soil or composts determined a\u00a0statistically significant difference in content for Cd (pot experiment from the\u00a0second year) and for Al, As, and Zn (pot experiment from the\u00a0first year). However, in the\u00a0case of the\u00a0analysis for the\u00a0first-year experiment, the\u00a0analysis was affected by the\u00a0size of the\u00a0variance of the\u00a0two values from the\u00a0crop pairs, with the\u00a0mean values lying close to each other.<\/p>\n
Limit values were exceeded for lettuce leaves in all leaf samples for Cd from the\u00a0second-year pot experiment and in all samples from the\u00a0first-year pot experiment, with the\u00a0exception of containers filled with K-A compost and K-K compost. The\u00a0exceedance was valid for samples from all input soils. It was probably caused by the\u00a0loading of these soils with Cd. When evaluating according to the\u00a0limits from the\u00a0Decree, an exceedance was determined in both pot experiments for Zn, Fe, Cr, and from the\u00a0samples of the\u00a0second year also in several cases for Ni and Hg. In the\u00a0case of Hg, these were samples from containers using K-4\u00a0compost in mixtures. In the\u00a0case of Ni, these were two samples out of three from a\u00a0set of containers with input soil and two samples out of three containers with a\u00a0mixture of input soil and K-4\u00a0compost. In contrast to the\u00a0experiment from the\u00a0second year, two samples of the\u00a0experiment from the\u00a0first year were determined to exceed the\u00a0limit value for Cu and Hg. However, it was always only one sample from a\u00a0pair. It cannot therefore be concluded that some substrate mixtures showed a\u00a0higher transfer of the\u00a0given elements to the\u00a0leaves. In the\u00a0case of a\u00a0comparison of average values from individual substrate variants (Tabs.\u00a03\u00a0and 4), it follows that the\u00a0limit contents of Cr and Zn were exceeded in all substrate variants. Ni exceeded the\u00a0average values for eroded soil and the\u00a0mixture of eroded soil and K-4\u00a0compost from the\u00a0second-year experiment. Overall, the\u00a0most problematic was the\u00a0occurrence of Cd values above the\u00a0limit. In this case, the\u00a0limit value in the\u00a0leaves was already exceeded for the\u00a0input soils in both experiments. This was also reflected in exceeding the\u00a0limit value for mixtures of soil and compost. Paradoxically, in the\u00a0case of 100% compost substrates, the\u00a0average Cd contents were below the\u00a0limit in four out of five cases. Therefore, it is not possible to unequivocally prove the\u00a0negative effect of the\u00a0application of composted sludge. Of the\u00a0other risk elements with limits, Pb, Cu, As proved to be unproblematic.<\/p>\n
A\u00a0statistically significant difference in content was found in lettuce leaves for Cd and Mn (both pot experiments), Cu (pot experiment from the\u00a0first year) and Hg with Zn (pot experiment from the\u00a0second year). An analysis comparing only container fills consisting of 100\u00a0% soil or composts determined a\u00a0statistically significant difference in content for Zn (both pot experiments) and Cd and Mn (pot experiment from the\u00a0second year).<\/p>\n
The results from the\u00a0pot experiments can be compared with the\u00a0results of a\u00a0number of similar studies and experiments that have been carried out in practically all parts of the\u00a0world. The\u00a0aim of these studies and experiments is to verify the\u00a0possibility of replacing substrates from peat and other non-renewable sources with substrates from composting, including composts used recycle sewage sludge. In the\u00a0study [22], the\u00a0authors conducted a\u00a0pot experiment to investigate the\u00a0effect of composted sewage sludge (KKOV) applied alone and mixed with chemical fertilizer on the\u00a0growth and accumulation of heavy metals in lettuce grown on two soils (Xanthi-Udic Ferralosol and Typic Purpli-Udic Cambosol). The\u00a0experiment included a\u00a0control (fertilizer containing N, P and K); a\u00a0composted sludge applied at a\u00a0rate of 27.54\u00a0(KKOV), 82.62\u00a0(3KKOV), 165.24\u00a0(6KKOV) t\/ha; and a\u00a0mixture of composted sludge and chemical fertilizer (1\/2\u00a0KKOV + 1\/2\u00a0NPK). Application doses were determined according to local recommended doses. Application of KKOV increased biomass; content of Cu, Zn, and Pb in lettuce; total metals and metals extracted with DTPA in soil. KKOV at doses of 27.54\u00a0and 82.62\u00a0t\/ha increases plant biomass less than NPK fertilizer alone.<\/p>\n
Another study [32] was conducted with the\u00a0aim of evaluating the\u00a0potential possibility of using composted sewage sludge (KKOV) as an alternative to expensive peat (PE) for the\u00a0cultivation of lettuce (Lactuca sativa L.). Five substrates were prepared with different percentages of KKOV and PE in the\u00a0growth medium. The\u00a0percentage of KKOV addition to PE was 0\u00a0%, 15\u00a0%, 30\u00a0%, 50\u00a0%, and 70\u00a0%. The\u00a0growth media KKOV + PE had very good physical and chemical properties and significant content of plant nutrients, especially P, K, Ca, and Mg. The\u00a0greatest growth increments and yields were achieved in the\u00a0growth medium with 30% KKOV and 70% PE from the\u00a0total volume. Shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight obtained from the\u00a0growth medium with 30% KKOV and 70% PE were increased by 56.53\u00a0%, 43.93\u00a0%, 29.46\u00a0%, and 67.24\u00a0% in comparison with peat substrate. The\u00a0addition of KKOV as a\u00a0component of the\u00a0growth medium increased the\u00a0concentrations of nutrients (N, P, K, Mg, Ca, Cu, Mn, Zn, and Pb) in the\u00a0lettuce plant. However, trace element levels in tissues were much lower than phytotoxic levels.<\/p>\n
As part of the\u00a0study [23], a\u00a0greenhouse experiment was conducted with four lettuce cultivars comparing composted municipal waste with perlite (MSWC + P), composted sludge with perlite (KKOV + P), and peat with perlite (peat + P). Plant biometric parameters measured after 72\u00a0days of growth showed that the\u00a0yield of plants cultivated on KKOV + P was similar to control plants, independent of the\u00a0cultivar. In contrast, the\u00a0MSWC + P mixture generally suppressed the\u00a0formation of biomass, especially in the\u00a0Murai and Patagonia cultivars. Compared to the\u00a0peat + P mixture, both compost substrates reduced the\u00a0accumulation of heavy metals in leaves, with a\u00a0large effect in the\u00a0Maximus cultivar. The\u00a0amounts of Cd and Pb in the\u00a0edible part were always below the\u00a0limits set by European regulations.<\/p>\n
The authors of the\u00a0research published in the\u00a0study [34] prepared a\u00a0field test in which they grew tomatoes on soil enriched with sludge, soil fertilized with NPK fertilizer, and untreated soil. On soils enriched with the\u00a0addition of sludge, a\u00a0higher amount of Cd contained in the\u00a0above-ground part of tomatoes was found compared to soil with inorganic fertilization. The\u00a0Cd accumulation in the\u00a0fruits was low compared to the\u00a0other analysed plant parts and did not obviously differ depending on the\u00a0type of soil. The\u00a0amount of Cd in tomato fruits was an order of magnitude lower than in leaves.<\/p>\n
The availability of metals and their accumulation in tomatoes with increasing addition of sludge to the\u00a0soil was the\u00a0subject of a\u00a0study published in the\u00a0paper of Elloumi et al. [35]. Results showed that soil pH decreased, while salinity, organic C, total N, available P, and reactive forms of Na, Ca, K, and heavy metals increased significantly with increasing sludge application rates. Of the\u00a0three heavy metals Zn, Cu and Cr, Zn had the\u00a0greatest ability to transfer from soil to plants. Low translocation of metals from roots to leaves was observed. The\u00a0use of a\u00a0dose of 2.5\u00a0to 5\u00a0% of sewage sludge appeared in the\u00a0experiment as an effective and cost-effective method for restoring soil fertility.<\/p>\n
Zhou et al. [36] found distinct differences in heavy metal concentrations in the\u00a0edible parts of various vegetables grown in soil contaminated with heavy metals (Pb, Cd, Cu, Zn, and As). Heavy metal concentrations decreased as follows: leafy vegetables > stem vegetables\/root vegetables\/fruit vegetables\u00a0>\u00a0leguminous vegetables\/melon vegetables. The\u00a0ability of leafy vegetables to absorb and accumulate heavy metals was the\u00a0highest and that of melon vegetables was the\u00a0lowest.<\/p>\n
The mentioned studies will make it possible to assess the\u00a0risks in the\u00a0use of substrates from composting sewage sludge from the\u00a0point of view of the\u00a0content of risk elements, especially heavy metals, which was also the\u00a0subject of our experiments. Due to the\u00a0accumulation of these elements in soils and in biomass during the\u00a0transfer from sludge to compost, it is necessary to find suitable application doses of substrates that ensure compliance with limit values in soils and biomass, as well as limit the\u00a0possible risk of phytotoxicity. A\u00a0study focused on horticultural substrates [29] worked with a\u00a0dose of composted sludge of only 2\u00a0kg of compost with sewage sludge of 2\u00a0to 4\u00a0kg per 1\u00a0m2, which had a\u00a0positive effect on soil properties and nutrient supply for cultivated vegetables. In our experiments, we verified the\u00a0benefits and risks of doses of 8\u00a0kg of 100% compost per 1\u00a0m2, when the\u00a0risks were below the\u00a0limit when used for growing tomatoes. In contrast, the\u00a0use of similar substrates for leafy vegetables appears inappropriate.<\/p>\n
In addition to the risks caused by the content of the studied heavy metals and arsenic, it is not possible to ignore the risks associated with the occurrence of other foreign substances and micropollutants in sewage sludge. In the paper [16], our research team presents an overview of drug residues and other micropollutants in sludge before and after composting. It is obvious that, for many of these substances, composting means their reduction or elimination. Styszko et al. [37] monitored changes in the content of selected drugs in sludge during their processing with the aim of safe use. In addition to composting, other methods of processing sludge for substrates usable in agriculture and\u00a0reclamation are being studied, for example in the\u00a0form of biochar preparation (e.g. [38, 39]). With the\u00a0correct dosage, these procedures appear to be promising both from the\u00a0point of view of eliminating a\u00a0number of foreign substances (using thermal processes) and from the\u00a0point of view of enriching the\u00a0soil with organic matter and nutrients with gradual release.<\/p>\n
CONCLUSION<\/h2>\n
The presented study was focused on checking the\u00a0possible benefits and risks associated with the\u00a0use of sludge from domestic and small WWTPs of two main technologies (activation WWTP, reed bed WWTP) within the\u00a0local circular economy as a\u00a0source of nutrients for growing selected crops after their processing by composting, which simulated domestic and community small-scale composting conditions. The\u00a0aim was to verify the\u00a0possible effects and thus provide information for decision-making in the\u00a0process of dealing with this sludge. The\u00a0predominant process is the\u00a0transfer of sludge to a\u00a0larger WWTP with sludge management. The\u00a0study was also carried out with regard to the\u00a0increasing number of questions about the\u00a0possibilities of local composting of this sludge and the\u00a0subsequent use of composts.<\/p>\n
Literature reviews of similar studies show that the\u00a0use of composts to improve soil properties, including composts that include sludge from municipal wastewater treatment, contributes to the\u00a0support of yields of crops and trees, including various types of vegetables. At appropriate doses, there is no transfer of risk elements to these crops, or only to an extent that complies with the\u00a0regulations. Both of the\u00a0presented pot experiments confirmed these assumptions for tomatoes; however, in the\u00a0case of growing lettuce, the\u00a0content of some risk elements in the\u00a0biomass was found to be exceeded. However, this was also influenced by the\u00a0load on the\u00a0used soils. The\u00a0results thus show that local composting with the\u00a0inclusion of sludge can theoretically achieve quality products that can be used in growing plants, but for selected groups of vegetables it is not suitable (e.g. for leafy vegetables such as lettuce) and excessive contamination of the\u00a0consumed parts can occur.<\/p>\n
The study yielded findings from which it is possible to set appropriate conditions and limits for the\u00a0use of composts with the\u00a0addition of sludge from the\u00a0mentioned groups of WWTPs, considering the\u00a0content and transfer of risk elements. Microbiological contamination was not monitored as the\u00a0input analysis of the\u00a0composts did not show above-limit contamination, or it was zero for most of the\u00a0composts used. For practical use, however, it would be necessary to conduct a\u00a0study of the\u00a0content and transfer of other groups of pollutants, such as drug residues and microplastics.<\/p>\n
Acknowledgements<\/h3>\n
The article was written with the\u00a0financial support of the\u00a0project SS02030008\u00a0\u201cCentre of Environmental Research: Waste Management, Circular Economy and Environmental Security\u201d and using the\u00a0results of the\u00a0project TH02030532\u00a0\u201cNew procedures for the\u00a0treatment and stabilization of sewage sludge from small municipal sources\u201d as part of its implementation.<\/em><\/p>\nThe Czech version of this article was peer-reviewed, the English version was translated from\u00a0the Czech original by Environmental Translation Ltd.<\/p>\n","protected":false},"excerpt":{"rendered":"
The aim of the study, the results of which are presented in this article, was to assess the possibility of simplifying treatment and stabilisation procedures of sewage sludge from small municipal sources of pollution (domestic and small WWTPs up to about 1,000 EP) at the place of their origin and their subsequent use through extensive composting. The results demonstrated the benefit of the application of composts from a material base containing sludge from small WWTPs in increasing the production of the monitored types of vegetables. However, especially with lettuce, there was a higher transmission of selected risk elements. We therefore do not recommend the use of composts with sludge for growing leafy green vegetables. In contrast, this risk did not arise with fruit and vegetables. For practical use, it is still necessary to assess the rate of transfer of other pollutants, such as drug residues and microplastics.<\/p>\n","protected":false},"author":8,"featured_media":28052,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[90,89,92],"tags":[3416,3413,3417,2624,3415,3414,3418],"coauthors":[187,188],"class_list":["post-27929","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-waste-management","category-water-technology-water-supply-waste-water-treatment","category-main","tag-compost-utilization","tag-domestic-wastewater-treatment-plant","tag-pot-experiments","tag-sewage-sludge","tag-sludge-composting","tag-small-wastewater-treatment-plant","tag-vegetables"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=27929"}],"version-history":[{"count":14,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions"}],"predecessor-version":[{"id":32930,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions\/32930"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/28052"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=27929"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=27929"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=27929"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=27929"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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<\/a>\nFig.\u00a02. View of part of the\u00a0containers from the\u00a0lettuce planting pot experiments; mixing of compost with soil in the\u00a0upper layer of about 5\u00a0cm is evident<\/h6>\n<\/a>\nFig.\u00a03. View of part of the\u00a0containers from the\u00a0tomato planting pot experiments<\/h6>\n
<\/p>\n
Pot experiments for growing selected types of vegetables<\/h3>\n
Pot experiments were designed using the\u00a0same five-litre plastic pots with a\u00a0surface area of 0.031\u00a0m2. All sets were placed in the\u00a0same location and under the\u00a0same conditions. Two (experiment 1\u00a0year) or three repetitions (experiment 2\u00a0year) were prepared for each variant of the\u00a0substrate (soils, composts, mixtures of soils and composts). Substrates were chosen to include comparative soils\u00a0\u2013 fertile garden soil (chernozem\u00a0\u2013 Hustopesko region), designated as ZZ in the\u00a0experiments, and degraded eroded field soil (chernozem\u00a0\u2013 Hustopesko region), designated as EZ in the\u00a0experiments. Then there were mixtures of these soils with composts, and only composts. Soils and composts were homogenized by mixing before being filled into containers, and portions were subsequently placed into individual containers. The\u00a0materials were prepared in a\u00a0rainless period with the\u00a0following humidity levels: first year experiment\u00a0\u2013 soils about 94\u00a0% dry matter, composts about 73\u00a0%; second year experiment\u00a0\u2013 soil about 94\u00a0% dry matter, composts about 74\u00a0%. Mixtures of field soil with composts were prepared in such a\u00a0way that the\u00a0proportion of compost corresponded to the\u00a0theoretical field dose of 80\u00a0tons of compost per hectare. After conversion, it was 260\u00a0g in one five-litre container. The\u00a0amount of soil in the\u00a0mixture weighed about 3\u00a0kg. The\u00a0proportion of compost in the\u00a0mixtures was about 8\u00a0%. The\u00a0compost was always mixed with the\u00a0soil individually when filling each container, incorporating it into the\u00a0upper layer of the\u00a0soil to a\u00a0depth of about 5\u00a0cm (Fig.\u00a02<\/em>).<\/p>\nProcessing and analysis of vegetable, soil, and compost samples<\/h3>\n
Lettuce was harvested about one month after planting the\u00a0seedlings (May), at\u00a0the\u00a0time of full maturity of the\u00a0lettuce heads before their transition to the\u00a0phase of flower formation (Fig.\u00a04<\/em>). Tomato plants were planted on the\u00a0same dates as the\u00a0lettuce. Harvesting of tomato fruits took place from the\u00a0first appearance of ripening fruits (July) until the\u00a0end of production of ripening fruits (September, October). Lettuce samples were dried at room temperature, finely crushed, and homogenized. Harvested tomato fruits were weighed fresh and stored in a\u00a0freezer. At the\u00a0end of the\u00a0harvest, all fruits from a\u00a0given plant were mixed, processed in the\u00a0laboratory into a\u00a0homogeneous mixture, and freeze-dried to take sample portions for analysis. To determine Al, As, Cd, Cr, Cu, Ni, Pb, Na, K, Ca, Mg, Fe, Mn and Zn, each sample (about 1g) was mineralized in a\u00a0Teflon container by MLS-1200\u00a0MEGA device using 3\u00a0ml of concentrated HNO3\u00a0and 1\u00a0ml of 30% H2O2. The\u00a0containers were sealed for the\u00a0mineralization cycle to take place. After cooling, the\u00a0contents of the\u00a0container were transferred into a\u00a0100\u00a0ml volumetric flask. The\u00a0determination of Al, As, Cd, Cr, Cu, Ni, and Pb was carried out by the\u00a0method of atomic absorption spectrometry\u00a0\u2013 electrothermal atomization (AAS-ETA) on a\u00a0PERKIN ELMER AANALYST 600. The\u00a0determination of Na, K, Ca, Mg, Fe, Mn and Zn was carried out by the\u00a0method of flame atomic absorption spectrometry (AAS-flame) on a\u00a0PERKIN ELMER AANALYST 400. The\u00a0calibration curve method was used to determine the\u00a0content of individual metals. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Determination of Hg was carried out on an AMA-254\u00a0mercury analyser, calibrated according to the\u00a0manufacturer\u2019s\u00a0manual. Approximately 0.1\u00a0g was weighed from the\u00a0pre-treated sample. The\u00a0Hg content determined always corresponded to the\u00a0average of two to three simultaneous determinations. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Homogenized samples of composts and soils were freeze-dried and then processed in a\u00a0manner identical to the\u00a0processing of biomass samples. Total phosphorus was determined using the\u00a0cuvette test LCK 348 (HACH-LANGE) on a\u00a0DR 3900\u00a0spectrophotometer with a\u00a0tungsten lamp (Vis). Total nitrogen was determined by the\u00a0modified Kjeldahl method according to SN\u00a0ISO\u00a011261.<\/p>\n<\/a>\nFig.\u00a04. View of part of the\u00a0planting pot experiment containers; in the\u00a0left part, lettuce heads and tomato plants with fruits in a\u00a0substrate with compost, in the\u00a0right part in a\u00a0substrate without compost<\/h6>\nAssessment of phytotoxicity of composts using the\u00a0seed germination test<\/h3>\n
In the case of using sludge from small sources (domestic and small municipal WWTPs) for horticultural and agricultural purposes, the main interest of the user is also to reduce the contamination of the resulting sludge and to ensure that the substrates used that contain sludge or compost do not pose a health risk and a danger to the environment in terms of toxicity. This fact can be verified, for example, by phytotoxicity tests or earthworm escape tests [25]. Phytotoxicity tests exist in the form of directives issued by major environmental agencies, such as the US EPA (United States Environmental Protection\u00a0Agency), OECD (Organization for Economic Co-operation and Development), ISO (International Standards Organization), ASTM (American Society for Testing and Materials), and others. Papers from 2011\u00a0and 2019\u00a0give an overview of phytotoxicity tests [26, 2].<\/p>\n
The seed germination test, which was chosen for our study, is a\u00a0method of evaluating the\u00a0intensity of decomposition of organic materials and the\u00a0maturity of the\u00a0resulting compost, which was developed at the\u00a0Crop Research Institute\u00a0Prague for use in composting practice. It is a\u00a0biological method of evaluating the\u00a0phytotoxicity of a\u00a0sample leachate using the\u00a0germination index of a\u00a0sensitive plant\u00a0\u2013 garden cress (Lepidium sativum) [27].<\/p>\n
The resulting germination index can be obtained from the\u00a0following equation:<\/p>\n<\/a>\n <\/p>\n
<\/p>\n
<\/p>\n
<\/p>\n
where:<\/p>\n
kv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 is\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the\u00a0germination rate of the\u00a0sample [%]<\/p>\nkk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 control germination [%]<\/p>\nlv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of the\u00a0sample [mm]<\/p>\nlk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of control [mm]<\/p>\nAt values up to 50\u00a0%, the\u00a0index states that the\u00a0compost is unusable for direct application, from 60\u00a0to 80\u00a0% it gives the\u00a0possibility of application with a\u00a0certain risk of damage to sensitive plants, and at values of 80\u00a0% and higher it declares mature compost. If the\u00a0germination index is between 60\u00a0and 80\u00a0%, it can be said that the\u00a0compost is in the\u00a0conversion phase and has the\u00a0best fertilizing effect. Above 80\u00a0%, this effect decreases, and the\u00a0influence of humus is stronger, which means that nutrients are more bound. The\u00a0release of N and P is slower and there is no leaching of nutrients into groundwater [28].<\/p>\n
Statistical analyses were performed using available tools in MS Office Excel 2016\u00a0and SW R-4.\u00a03.\u00a02. for Windows using ANOVA analysis of variance after pre-screening the\u00a0data sets for standard distribution. The\u00a0choice of procedure and statistical methods corresponded to the\u00a0procedures that were used in a\u00a0similar experiment focused on the\u00a0effect of addition of sewage sludge composts to substrates for horticultural purposes [29]. In the\u00a0case of pot experiments, the\u00a0evaluation was carried out by calculating statistical characteristics for individual variants of substrates and crops from two (first year) and three repetitions (second year).<\/p>\n
RESULTS AND DISCUSSION<\/h2>\nComposition and contamination of used soils and\u00a0composts<\/h3>\n
The contents of heavy metals and arsenic in the\u00a0soils used in the\u00a0experiments in both years did not exceed the\u00a0preventive and indicative values according to National Decree No. 153\/2016\u00a0Coll. Of the\u00a0composts used in the\u00a0first year, all composts exceeded both the\u00a0proposed limit value for Cu in the\u00a0framework of the\u00a0EU technical report [30] and the\u00a0given national standard. The\u00a0composts also exceeded both limit values for Zn, and in the\u00a0case of K-A compost, the\u00a0limit value for this element was also exceeded according to SN 465735\u00a0[31]. K-3\u00a0and K-4\u00a0composts used in the\u00a0second year did not exceed any of the\u00a0limit values proposed within the\u00a0EU and given by the\u00a0SN 465735\u00a0standard. Lower concentrations of Cu and Zn in these composts (on average 218\u00a0mg\/kg Zn and 65.9\u00a0mg\/ kg Cu compared to the\u00a0values of 1,016\u00a0mg\/kg Zn and 386\u00a0mg\/kg Cu in the\u00a0composts in the\u00a0first year) were probably caused by the\u00a0lower proportion of used sludge in the\u00a0input mixture for composting. Sludge load can be affected by the\u00a0connection to the\u00a0sewage system, which also brings rain wash rich in these metals due to the\u00a0corrosion of roofing materials.<\/p>\n
Regarding the\u00a0assessment of microbial contamination, it was carried out using standard analytical methods for the\u00a0determination of indicator organisms (Salmonella sp., enterococci, thermotolerant coliform bacteria) in the\u00a0input sludge and in the\u00a0resulting substrates from composting. Microbial contamination of sewage sludge from domestic WWTPs ranged from 2\u00a0\u00a0103\u00a0to\u00a04.2\u00a0\u00a0103\u00a0KTJ\/g of dry matter of samples in the\u00a0case of enterococci and 1.6\u00a0\u00a0104\u00a0to 6\u00a0\u00a0104\u00a0KTJ\/g of dry matter of samples in the\u00a0case of thermotolerant coliform bacteria. The\u00a0amount of thermotolerant coliform bacteria in the\u00a0sludge from the\u00a0municipal reed bed plant was in the\u00a0range of 1\u00a0\u00a0105\u00a0to 2\u00a0\u00a0106\u00a0KTJ\/g of dry matter and the\u00a0number of enterococci in the\u00a0range of 1\u00a0\u00a0104\u00a0to 6\u00a0\u00a0106\u00a0KTJ\/g of dry matter. Microbial contamination in fresh substrates from composts before their use in pot experiments was zero for composts K-3, K-4\u00a0and 1\u00a0K-K (zero detection of KTJ per gram of dry matter) for both indicators. For composts\u00a01\u00a0K-A and 2\u00a0K-K in tens of KTJ per gram of dry matter for enterococci and in lower hundreds of KTJ per gram of dry matter for FC. For all composts, it would be acceptable when assessed with the\u00a0limits listed in the\u00a0SN as \u201cComposting\u201d. The\u00a0presence of Salmonella sp. was not detected even in the\u00a0input sludge.<\/p>\n
Phytotoxicity test results<\/h3>\n
Mixed samples were taken from the\u00a0set of composts established in the\u00a0second year (K-3\u00a0and K-4) and supplemented with a\u00a0control sample (seeds germinated only on distilled water) for phytotoxicity seed germination test. Compost samples were already stabilized, they did not show changes in microbial contamination and content of heavy metals and macroelements. The\u00a0garden cress test was performed in two dilutions, namely 5\u00a0\u00a0and 10\u00a0\u00a0dry weight (%). For each sample, 10\u00a0Petri dishes with 8\u00a0seeds were used, for a\u00a0total of 80\u00a0seeds. After 24\u00a0hours, the\u00a0number of germinated seeds in each Petri dish was determined and the\u00a0lengths of all roots were measured.<\/p>\n
Some vegetative responses, such as the\u00a0seed germination test or the\u00a0elongation of root and seedling growth, are commonly used to assess the\u00a0excess toxicity of organic and inorganic compounds in various substrates [32]. The\u00a0average germination rate in our experiment was found to be 7.5, 7.5, 7.7, and 7.8\u00a0seeds out of 10\u00a0for individual prepared mixtures of composts and soils, and 7.8\u00a0for the\u00a0control set. ANOVA analysis showed that the\u00a0null hypothesis of equality of mean values of the\u00a0mixtures and the\u00a0control set could not be rejected at the\u00a0significance level of\u00a0 = 0.05\u00a0(p < 0.05). The\u00a0spread of root lengths between the\u00a0minimum and maximum values for the\u00a0prepared mixtures was generally in the\u00a0same interval of 4.0\u00a0to 9.0\u00a0cm with average values of 6.6, 6.8, 6.2, and 5.8\u00a0cm. The\u00a0smallest average length (5.4\u00a0cm) was achieved by sprouts from the\u00a0control set. The\u00a0results of the\u00a0phytotoxicity test show that the\u00a0mixtures used were stabilized, without a\u00a0negative impact on the\u00a0germination of garden cress seeds. The\u00a0IK index values ranged from 107\u00a0to 118\u00a0for all four mixtures.<\/p>\n
Effect of compost application on change in yield of useful parts of crops<\/h3>\n
In the case of containers with lettuce seedlings, the difference in the weight of the above-ground part (leaves) of the grown head of lettuce without damaged and dry leaves on the edge was monitored. In both years, a statistically significant difference in fresh biomass weight was demonstrated (ANOVA, alpha level 0.05). In the first year, the average weight of the fresh head of lettuce was 15.7 g when using the EZ soil and 61.2 g when using the ZZ soil. In containers with 100% compost substrates, the average weight of fresh heads of lettuce was\u00a077.5\u00a0g (1\u00a0K-K), 82.8\u00a0g (1\u00a0K-A), and 99.1\u00a0g (2\u00a0K-K). An 8% admixture of compost to poor-quality soil contributed to a\u00a0substantial increase in yield. The\u00a0average weights of fresh heads were 104\u00a0g (mixture with 1\u00a0K-A), 105\u00a0g (mixture with 1\u00a0K-K), and 95.2\u00a0g (2\u00a0K-K). This is an increase of up to 85\u00a0% compared to EZ soil, and 36\u00a0to 41\u00a0% compared to high-quality ZZ soil. An experiment in the\u00a0second year confirmed these results. The\u00a0average weight of a\u00a0fresh head of lettuce when using EZ was 81.4\u00a0g, i.e., much higher than in the\u00a0first year. However, the\u00a0EZ used in this year contained 38\u00a0% more organic matter compared to the\u00a0EZ used in the\u00a0first year. In containers with 100% compost substrates, the\u00a0average fresh weights of lettuce heads were 154\u00a0g (K-3) and 108\u00a0g (K-4). When using compost K-3, the\u00a0average yield increased by 47\u00a0% when using compost K-4\u00a0by 25\u00a0%. An\u00a08% admixture of composts to the\u00a0soil meant an increase in average yields by 27\u00a0% (compost K-3) and by 14\u00a0% (compost K-4) to values of 111\u00a0g (K-3) and 95.3\u00a0g (K-4). Fig.\u00a04<\/em>\u00a0shows the\u00a0difference in the\u00a0size of the\u00a0lettuce heads as a\u00a0result of the\u00a0use of compost in growing substrates.<\/p>\nIn the\u00a0case of tomato plants, the\u00a0influence of cultivation in 100% compost substrates and in soils with admixture of these substrates on the\u00a0number of fruits obtained during the\u00a0growing season and the\u00a0total weight of the\u00a0fruits was assessed. Fruits were harvested ripe continuously throughout the\u00a0season, weighed and stored to prepare the\u00a0resulting mixture for analyses. From the\u00a0pot experiment in the\u00a0first year, it appears that tomatoes grown in low-quality EZ soil had the\u00a0lowest number of fruits (about13\u00a0fruits per plant). The\u00a0yield from ZZ chernozem (about 25\u00a0fruits per plant on average) was comparable to the\u00a0yield of tomatoes growing in a\u00a0substrate of 100% compost (about 30\u00a0fruits per plant on average for all composts used). An 8% admixture of composts to the\u00a0EZ soil increased the\u00a0average yield from 13\u00a0fruits to 20\u00a0fruits per plant. A\u00a0pot experiment in the\u00a0second year confirmed the\u00a0highest average yields from 100% compost substrates, approximately 25\u00a0fruits per plant. The\u00a0yield from EZ was around 15\u00a0fruits. Compared to the\u00a0results from the\u00a0first-year experiment, the\u00a0addition of compost substrates to this soil did not significantly increase the\u00a0yield. Average yields from these mixtures remained at around 15\u00a0fruits per plant. In the\u00a0first year, fruits from plants grown in eroded soil had the\u00a0lowest total weight (about 300\u00a0g per plant on average). In 100% compost substrates, the\u00a0average fruit weight per plant was 645\u00a0g for K-A, 755\u00a0g for 1\u00a0K-K, and 650\u00a0for 2\u00a0K-K. The\u00a0admixture of all types of composts to EZ increased the\u00a0average mass yields to values of 410\u00a0to 495\u00a0g, i.e. to the\u00a0level of quality chernozem ZZ (450\u00a0g per plant on average). The\u00a0fruit weight analysis from the\u00a0second-year experiment replicated the\u00a0findings from the\u00a0fruit number analysis. For 100% compost mixtures, average fruit weights per plant were 700\u00a0to 800\u00a0g.<\/p>\n
Content of selected nutrients and elements in useful parts of crops<\/h3>\n
Evaluation was done for P, N, K, Na, Ca, and Mg. The\u00a0element content was measured in dried or lyophilized samples (see above) and determined per kg of dry matter. Subsequently, these values were recalculated using the\u00a0values of dry matter to fresh matter, both for the\u00a0biomass of lettuce leaves and for the\u00a0biomass of fruits from tomato plants. In tomato fruits, a\u00a0statistically significant difference in content was found for P, Ca, K, Na (both pot experiments of the\u00a0first and second year) and for N and Mg (pot experiment from the\u00a0second year). In lettuce leaves, a\u00a0statistically significant difference in content was found for K\u00a0and Ca (pot experiment from the\u00a0first year), but this was not confirmed in the\u00a0experiment in the\u00a0following year. In contrast, in this year a\u00a0statistically significant difference was found for N, P, and Na.<\/p>\n
Tab. 1. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0first-year pot experiment (in mg\/kg of fresh matter)<\/p>\n<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 3.<\/h6>\n
The content of nutrients in the\u00a0leaves from heads of lettuce (Figs. 5<\/em>\u00a0and\u00a07<\/em>) and also in the\u00a0tomato fruits (Figs. 6<\/em>\u00a0and 8<\/em>) was comparable in both pot experiments. The\u00a0contents of selected nutrients differ between the\u00a0biomass of heads of lettuce and the\u00a0biomass of fruits from tomato plants in total numbers mainly because both biomasses have very different dry matter. In the\u00a0case of lettuce biomass, the\u00a0dry matter is around an average value of 91\u00a0%, in the\u00a0case of tomato biomass around an average value of 8\u00a0% (7\u00a0to 11\u00a0%). The\u00a0differences in nutrient content in lettuce and tomato biomass from containers with individual substrates can be seen from the\u00a0graphs in Figs. 5\u20138<\/em>. Due to the\u00a0conversion to fresh mass, the\u00a0differences (e.g. in N and K\u00a0content) are higher in lettuce biomass. The\u00a0use of substrates from composting resulted in a\u00a0demonstrably higher content of P, Na and, conversely, a\u00a0lower content of Ca in tomato fruits in the\u00a0case of using compost as an admixture. In the\u00a0pot experiment in the\u00a0second year, this difference was found only in clean substrates from composting. This was also related to the\u00a0increase in N content in the\u00a0biomass (Fig.\u00a08<\/em>). Similarly, a\u00a0significantly higher content of all elements with the\u00a0exception of Ca (a\u00a0decrease in its content) was found in lettuce biomass from the\u00a0pot experiment in the\u00a0second year (Fig.\u00a07<\/em>).<\/p>\n<\/a>\nFig. 5. Average content of nutrients in lettuce heads grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 6. Average content of selected nutrients in tomatoes grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 7. Average content of nutrients in lettuce heads grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\n<\/a><\/h6>\nFig. 8. Average content of selected nutrients in tomatoes grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\nContent of risk elements in useful parts of crops<\/h3>\n
The assessment was carried out for the\u00a0following heavy metals and elements: Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn. The\u00a0analytical procedure for determining the\u00a0content in biomass and conversion to evaluable results for fresh matter was the\u00a0same as in the\u00a0case of the\u00a0elements listed in the\u00a0previous sub-chapter.<\/p>\n
These results were compared with the\u00a0limit contents established in the\u00a0following regulations:<\/p>\n
Commission Regulation (EC) No. 1881\/2006\u00a0(hereinafter referred to as the\u00a0\u201cRegulation\u201d) setting limits of 0.2\u00a0mg\/kg Cd, 0.3\u00a0mg\/kg Pb.<\/p>\n
National regulation Decree No. 53\/2002\u00a0Coll. (hereinafter referred to as the\u00a0\u201cDecree\u201d), setting limits (in mg\/kg of fresh matter): 0.5\u00a0As, 0.2\u00a0Cd, 0.2\u00a0Cr, 10\u00a0Cu, 50\u00a0Fe, 0.03\u00a0Hg, 2.5\u00a0Ni, 0.3\u00a0Pb, 25\u00a0Zn. The\u00a0Decree was repealed due to accession to the\u00a0European Community on 1st August 2004. However, it still allows to assess and compare the\u00a0level of contamination for more metals than the\u00a0Commission Regulation, where limits are set only for Cd and Pb.<\/p>\n
For tomato fruits, no exceedance of the\u00a0limit values given by the\u00a0Regulation for either Cd or Pb was detected for individual plants, in both pot experiments. Also, it was not detected that the\u00a0older, no longer valid limits given by the\u00a0Decree were exceeded for any monitored element. A\u00a0comparison of the\u00a0average values for individual substrate variants (Tab. 1<\/em>\u00a0and 2<\/em>) shows that no limit contents of risk elements were exceeded either. In tomato fruits, a\u00a0statistically significant difference in content was found for Zn, Cu, and Cr (both pot experiments), for Ni, Mn, and Cd (pot experiment from the\u00a0second year), and for Al (pot experiment from the\u00a0first year).<\/p>\nTab. 2. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0second-year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 4<\/em>.<\/h6>\nTab. 3. Average values of heavy metals and arsenic in lettuce grown in the first year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nTab. 4. Average values of heavy metals and arsenic in lettuce grown in the second year pot experiment (in mg\/kg of fresh matter)<\/h5>\n<\/a>\nAn analysis comparing only container fills consisting entirely of soil or composts determined a\u00a0statistically significant difference in content for Cd (pot experiment from the\u00a0second year) and for Al, As, and Zn (pot experiment from the\u00a0first year). However, in the\u00a0case of the\u00a0analysis for the\u00a0first-year experiment, the\u00a0analysis was affected by the\u00a0size of the\u00a0variance of the\u00a0two values from the\u00a0crop pairs, with the\u00a0mean values lying close to each other.<\/p>\n
Limit values were exceeded for lettuce leaves in all leaf samples for Cd from the\u00a0second-year pot experiment and in all samples from the\u00a0first-year pot experiment, with the\u00a0exception of containers filled with K-A compost and K-K compost. The\u00a0exceedance was valid for samples from all input soils. It was probably caused by the\u00a0loading of these soils with Cd. When evaluating according to the\u00a0limits from the\u00a0Decree, an exceedance was determined in both pot experiments for Zn, Fe, Cr, and from the\u00a0samples of the\u00a0second year also in several cases for Ni and Hg. In the\u00a0case of Hg, these were samples from containers using K-4\u00a0compost in mixtures. In the\u00a0case of Ni, these were two samples out of three from a\u00a0set of containers with input soil and two samples out of three containers with a\u00a0mixture of input soil and K-4\u00a0compost. In contrast to the\u00a0experiment from the\u00a0second year, two samples of the\u00a0experiment from the\u00a0first year were determined to exceed the\u00a0limit value for Cu and Hg. However, it was always only one sample from a\u00a0pair. It cannot therefore be concluded that some substrate mixtures showed a\u00a0higher transfer of the\u00a0given elements to the\u00a0leaves. In the\u00a0case of a\u00a0comparison of average values from individual substrate variants (Tabs.\u00a03\u00a0and 4), it follows that the\u00a0limit contents of Cr and Zn were exceeded in all substrate variants. Ni exceeded the\u00a0average values for eroded soil and the\u00a0mixture of eroded soil and K-4\u00a0compost from the\u00a0second-year experiment. Overall, the\u00a0most problematic was the\u00a0occurrence of Cd values above the\u00a0limit. In this case, the\u00a0limit value in the\u00a0leaves was already exceeded for the\u00a0input soils in both experiments. This was also reflected in exceeding the\u00a0limit value for mixtures of soil and compost. Paradoxically, in the\u00a0case of 100% compost substrates, the\u00a0average Cd contents were below the\u00a0limit in four out of five cases. Therefore, it is not possible to unequivocally prove the\u00a0negative effect of the\u00a0application of composted sludge. Of the\u00a0other risk elements with limits, Pb, Cu, As proved to be unproblematic.<\/p>\n
A\u00a0statistically significant difference in content was found in lettuce leaves for Cd and Mn (both pot experiments), Cu (pot experiment from the\u00a0first year) and Hg with Zn (pot experiment from the\u00a0second year). An analysis comparing only container fills consisting of 100\u00a0% soil or composts determined a\u00a0statistically significant difference in content for Zn (both pot experiments) and Cd and Mn (pot experiment from the\u00a0second year).<\/p>\n
The results from the\u00a0pot experiments can be compared with the\u00a0results of a\u00a0number of similar studies and experiments that have been carried out in practically all parts of the\u00a0world. The\u00a0aim of these studies and experiments is to verify the\u00a0possibility of replacing substrates from peat and other non-renewable sources with substrates from composting, including composts used recycle sewage sludge. In the\u00a0study [22], the\u00a0authors conducted a\u00a0pot experiment to investigate the\u00a0effect of composted sewage sludge (KKOV) applied alone and mixed with chemical fertilizer on the\u00a0growth and accumulation of heavy metals in lettuce grown on two soils (Xanthi-Udic Ferralosol and Typic Purpli-Udic Cambosol). The\u00a0experiment included a\u00a0control (fertilizer containing N, P and K); a\u00a0composted sludge applied at a\u00a0rate of 27.54\u00a0(KKOV), 82.62\u00a0(3KKOV), 165.24\u00a0(6KKOV) t\/ha; and a\u00a0mixture of composted sludge and chemical fertilizer (1\/2\u00a0KKOV + 1\/2\u00a0NPK). Application doses were determined according to local recommended doses. Application of KKOV increased biomass; content of Cu, Zn, and Pb in lettuce; total metals and metals extracted with DTPA in soil. KKOV at doses of 27.54\u00a0and 82.62\u00a0t\/ha increases plant biomass less than NPK fertilizer alone.<\/p>\n
Another study [32] was conducted with the\u00a0aim of evaluating the\u00a0potential possibility of using composted sewage sludge (KKOV) as an alternative to expensive peat (PE) for the\u00a0cultivation of lettuce (Lactuca sativa L.). Five substrates were prepared with different percentages of KKOV and PE in the\u00a0growth medium. The\u00a0percentage of KKOV addition to PE was 0\u00a0%, 15\u00a0%, 30\u00a0%, 50\u00a0%, and 70\u00a0%. The\u00a0growth media KKOV + PE had very good physical and chemical properties and significant content of plant nutrients, especially P, K, Ca, and Mg. The\u00a0greatest growth increments and yields were achieved in the\u00a0growth medium with 30% KKOV and 70% PE from the\u00a0total volume. Shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight obtained from the\u00a0growth medium with 30% KKOV and 70% PE were increased by 56.53\u00a0%, 43.93\u00a0%, 29.46\u00a0%, and 67.24\u00a0% in comparison with peat substrate. The\u00a0addition of KKOV as a\u00a0component of the\u00a0growth medium increased the\u00a0concentrations of nutrients (N, P, K, Mg, Ca, Cu, Mn, Zn, and Pb) in the\u00a0lettuce plant. However, trace element levels in tissues were much lower than phytotoxic levels.<\/p>\n
As part of the\u00a0study [23], a\u00a0greenhouse experiment was conducted with four lettuce cultivars comparing composted municipal waste with perlite (MSWC + P), composted sludge with perlite (KKOV + P), and peat with perlite (peat + P). Plant biometric parameters measured after 72\u00a0days of growth showed that the\u00a0yield of plants cultivated on KKOV + P was similar to control plants, independent of the\u00a0cultivar. In contrast, the\u00a0MSWC + P mixture generally suppressed the\u00a0formation of biomass, especially in the\u00a0Murai and Patagonia cultivars. Compared to the\u00a0peat + P mixture, both compost substrates reduced the\u00a0accumulation of heavy metals in leaves, with a\u00a0large effect in the\u00a0Maximus cultivar. The\u00a0amounts of Cd and Pb in the\u00a0edible part were always below the\u00a0limits set by European regulations.<\/p>\n
The authors of the\u00a0research published in the\u00a0study [34] prepared a\u00a0field test in which they grew tomatoes on soil enriched with sludge, soil fertilized with NPK fertilizer, and untreated soil. On soils enriched with the\u00a0addition of sludge, a\u00a0higher amount of Cd contained in the\u00a0above-ground part of tomatoes was found compared to soil with inorganic fertilization. The\u00a0Cd accumulation in the\u00a0fruits was low compared to the\u00a0other analysed plant parts and did not obviously differ depending on the\u00a0type of soil. The\u00a0amount of Cd in tomato fruits was an order of magnitude lower than in leaves.<\/p>\n
The availability of metals and their accumulation in tomatoes with increasing addition of sludge to the\u00a0soil was the\u00a0subject of a\u00a0study published in the\u00a0paper of Elloumi et al. [35]. Results showed that soil pH decreased, while salinity, organic C, total N, available P, and reactive forms of Na, Ca, K, and heavy metals increased significantly with increasing sludge application rates. Of the\u00a0three heavy metals Zn, Cu and Cr, Zn had the\u00a0greatest ability to transfer from soil to plants. Low translocation of metals from roots to leaves was observed. The\u00a0use of a\u00a0dose of 2.5\u00a0to 5\u00a0% of sewage sludge appeared in the\u00a0experiment as an effective and cost-effective method for restoring soil fertility.<\/p>\n
Zhou et al. [36] found distinct differences in heavy metal concentrations in the\u00a0edible parts of various vegetables grown in soil contaminated with heavy metals (Pb, Cd, Cu, Zn, and As). Heavy metal concentrations decreased as follows: leafy vegetables > stem vegetables\/root vegetables\/fruit vegetables\u00a0>\u00a0leguminous vegetables\/melon vegetables. The\u00a0ability of leafy vegetables to absorb and accumulate heavy metals was the\u00a0highest and that of melon vegetables was the\u00a0lowest.<\/p>\n
The mentioned studies will make it possible to assess the\u00a0risks in the\u00a0use of substrates from composting sewage sludge from the\u00a0point of view of the\u00a0content of risk elements, especially heavy metals, which was also the\u00a0subject of our experiments. Due to the\u00a0accumulation of these elements in soils and in biomass during the\u00a0transfer from sludge to compost, it is necessary to find suitable application doses of substrates that ensure compliance with limit values in soils and biomass, as well as limit the\u00a0possible risk of phytotoxicity. A\u00a0study focused on horticultural substrates [29] worked with a\u00a0dose of composted sludge of only 2\u00a0kg of compost with sewage sludge of 2\u00a0to 4\u00a0kg per 1\u00a0m2, which had a\u00a0positive effect on soil properties and nutrient supply for cultivated vegetables. In our experiments, we verified the\u00a0benefits and risks of doses of 8\u00a0kg of 100% compost per 1\u00a0m2, when the\u00a0risks were below the\u00a0limit when used for growing tomatoes. In contrast, the\u00a0use of similar substrates for leafy vegetables appears inappropriate.<\/p>\n
In addition to the risks caused by the content of the studied heavy metals and arsenic, it is not possible to ignore the risks associated with the occurrence of other foreign substances and micropollutants in sewage sludge. In the paper [16], our research team presents an overview of drug residues and other micropollutants in sludge before and after composting. It is obvious that, for many of these substances, composting means their reduction or elimination. Styszko et al. [37] monitored changes in the content of selected drugs in sludge during their processing with the aim of safe use. In addition to composting, other methods of processing sludge for substrates usable in agriculture and\u00a0reclamation are being studied, for example in the\u00a0form of biochar preparation (e.g. [38, 39]). With the\u00a0correct dosage, these procedures appear to be promising both from the\u00a0point of view of eliminating a\u00a0number of foreign substances (using thermal processes) and from the\u00a0point of view of enriching the\u00a0soil with organic matter and nutrients with gradual release.<\/p>\n
CONCLUSION<\/h2>\n
The presented study was focused on checking the\u00a0possible benefits and risks associated with the\u00a0use of sludge from domestic and small WWTPs of two main technologies (activation WWTP, reed bed WWTP) within the\u00a0local circular economy as a\u00a0source of nutrients for growing selected crops after their processing by composting, which simulated domestic and community small-scale composting conditions. The\u00a0aim was to verify the\u00a0possible effects and thus provide information for decision-making in the\u00a0process of dealing with this sludge. The\u00a0predominant process is the\u00a0transfer of sludge to a\u00a0larger WWTP with sludge management. The\u00a0study was also carried out with regard to the\u00a0increasing number of questions about the\u00a0possibilities of local composting of this sludge and the\u00a0subsequent use of composts.<\/p>\n
Literature reviews of similar studies show that the\u00a0use of composts to improve soil properties, including composts that include sludge from municipal wastewater treatment, contributes to the\u00a0support of yields of crops and trees, including various types of vegetables. At appropriate doses, there is no transfer of risk elements to these crops, or only to an extent that complies with the\u00a0regulations. Both of the\u00a0presented pot experiments confirmed these assumptions for tomatoes; however, in the\u00a0case of growing lettuce, the\u00a0content of some risk elements in the\u00a0biomass was found to be exceeded. However, this was also influenced by the\u00a0load on the\u00a0used soils. The\u00a0results thus show that local composting with the\u00a0inclusion of sludge can theoretically achieve quality products that can be used in growing plants, but for selected groups of vegetables it is not suitable (e.g. for leafy vegetables such as lettuce) and excessive contamination of the\u00a0consumed parts can occur.<\/p>\n
The study yielded findings from which it is possible to set appropriate conditions and limits for the\u00a0use of composts with the\u00a0addition of sludge from the\u00a0mentioned groups of WWTPs, considering the\u00a0content and transfer of risk elements. Microbiological contamination was not monitored as the\u00a0input analysis of the\u00a0composts did not show above-limit contamination, or it was zero for most of the\u00a0composts used. For practical use, however, it would be necessary to conduct a\u00a0study of the\u00a0content and transfer of other groups of pollutants, such as drug residues and microplastics.<\/p>\n
Acknowledgements<\/h3>\n
The article was written with the\u00a0financial support of the\u00a0project SS02030008\u00a0\u201cCentre of Environmental Research: Waste Management, Circular Economy and Environmental Security\u201d and using the\u00a0results of the\u00a0project TH02030532\u00a0\u201cNew procedures for the\u00a0treatment and stabilization of sewage sludge from small municipal sources\u201d as part of its implementation.<\/em><\/p>\nThe Czech version of this article was peer-reviewed, the English version was translated from\u00a0the Czech original by Environmental Translation Ltd.<\/p>\n","protected":false},"excerpt":{"rendered":"
The aim of the study, the results of which are presented in this article, was to assess the possibility of simplifying treatment and stabilisation procedures of sewage sludge from small municipal sources of pollution (domestic and small WWTPs up to about 1,000 EP) at the place of their origin and their subsequent use through extensive composting. The results demonstrated the benefit of the application of composts from a material base containing sludge from small WWTPs in increasing the production of the monitored types of vegetables. However, especially with lettuce, there was a higher transmission of selected risk elements. We therefore do not recommend the use of composts with sludge for growing leafy green vegetables. In contrast, this risk did not arise with fruit and vegetables. For practical use, it is still necessary to assess the rate of transfer of other pollutants, such as drug residues and microplastics.<\/p>\n","protected":false},"author":8,"featured_media":28052,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[90,89,92],"tags":[3416,3413,3417,2624,3415,3414,3418],"coauthors":[187,188],"class_list":["post-27929","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-waste-management","category-water-technology-water-supply-waste-water-treatment","category-main","tag-compost-utilization","tag-domestic-wastewater-treatment-plant","tag-pot-experiments","tag-sewage-sludge","tag-sludge-composting","tag-small-wastewater-treatment-plant","tag-vegetables"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=27929"}],"version-history":[{"count":14,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions"}],"predecessor-version":[{"id":32930,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions\/32930"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/28052"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=27929"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=27929"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=27929"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=27929"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Processing and analysis of vegetable, soil, and compost samples<\/h3>\n
Lettuce was harvested about one month after planting the\u00a0seedlings (May), at\u00a0the\u00a0time of full maturity of the\u00a0lettuce heads before their transition to the\u00a0phase of flower formation (Fig.\u00a04<\/em>). Tomato plants were planted on the\u00a0same dates as the\u00a0lettuce. Harvesting of tomato fruits took place from the\u00a0first appearance of ripening fruits (July) until the\u00a0end of production of ripening fruits (September, October). Lettuce samples were dried at room temperature, finely crushed, and homogenized. Harvested tomato fruits were weighed fresh and stored in a\u00a0freezer. At the\u00a0end of the\u00a0harvest, all fruits from a\u00a0given plant were mixed, processed in the\u00a0laboratory into a\u00a0homogeneous mixture, and freeze-dried to take sample portions for analysis. To determine Al, As, Cd, Cr, Cu, Ni, Pb, Na, K, Ca, Mg, Fe, Mn and Zn, each sample (about 1g) was mineralized in a\u00a0Teflon container by MLS-1200\u00a0MEGA device using 3\u00a0ml of concentrated HNO3\u00a0and 1\u00a0ml of 30% H2O2. The\u00a0containers were sealed for the\u00a0mineralization cycle to take place. After cooling, the\u00a0contents of the\u00a0container were transferred into a\u00a0100\u00a0ml volumetric flask. The\u00a0determination of Al, As, Cd, Cr, Cu, Ni, and Pb was carried out by the\u00a0method of atomic absorption spectrometry\u00a0\u2013 electrothermal atomization (AAS-ETA) on a\u00a0PERKIN ELMER AANALYST 600. The\u00a0determination of Na, K, Ca, Mg, Fe, Mn and Zn was carried out by the\u00a0method of flame atomic absorption spectrometry (AAS-flame) on a\u00a0PERKIN ELMER AANALYST 400. The\u00a0calibration curve method was used to determine the\u00a0content of individual metals. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Determination of Hg was carried out on an AMA-254\u00a0mercury analyser, calibrated according to the\u00a0manufacturer\u2019s\u00a0manual. Approximately 0.1\u00a0g was weighed from the\u00a0pre-treated sample. The\u00a0Hg content determined always corresponded to the\u00a0average of two to three simultaneous determinations. The\u00a0correctness of the\u00a0determined concentrations was verified using the\u00a0simultaneous analysis of internal and reference material. Homogenized samples of composts and soils were freeze-dried and then processed in a\u00a0manner identical to the\u00a0processing of biomass samples. Total phosphorus was determined using the\u00a0cuvette test LCK 348 (HACH-LANGE) on a\u00a0DR 3900\u00a0spectrophotometer with a\u00a0tungsten lamp (Vis). Total nitrogen was determined by the\u00a0modified Kjeldahl method according to SN\u00a0ISO\u00a011261.<\/p>\n In the case of using sludge from small sources (domestic and small municipal WWTPs) for horticultural and agricultural purposes, the main interest of the user is also to reduce the contamination of the resulting sludge and to ensure that the substrates used that contain sludge or compost do not pose a health risk and a danger to the environment in terms of toxicity. This fact can be verified, for example, by phytotoxicity tests or earthworm escape tests [25]. Phytotoxicity tests exist in the form of directives issued by major environmental agencies, such as the US EPA (United States Environmental Protection\u00a0Agency), OECD (Organization for Economic Co-operation and Development), ISO (International Standards Organization), ASTM (American Society for Testing and Materials), and others. Papers from 2011\u00a0and 2019\u00a0give an overview of phytotoxicity tests [26, 2].<\/p>\n The seed germination test, which was chosen for our study, is a\u00a0method of evaluating the\u00a0intensity of decomposition of organic materials and the\u00a0maturity of the\u00a0resulting compost, which was developed at the\u00a0Crop Research Institute\u00a0Prague for use in composting practice. It is a\u00a0biological method of evaluating the\u00a0phytotoxicity of a\u00a0sample leachate using the\u00a0germination index of a\u00a0sensitive plant\u00a0\u2013 garden cress (Lepidium sativum) [27].<\/p>\n The resulting germination index can be obtained from the\u00a0following equation:<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n where:<\/p>\n kv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 is\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the\u00a0germination rate of the\u00a0sample [%]<\/p>\n kk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 control germination [%]<\/p>\n lv<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of the\u00a0sample [mm]<\/p>\n lk<\/sub>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 average root length of control [mm]<\/p>\n At values up to 50\u00a0%, the\u00a0index states that the\u00a0compost is unusable for direct application, from 60\u00a0to 80\u00a0% it gives the\u00a0possibility of application with a\u00a0certain risk of damage to sensitive plants, and at values of 80\u00a0% and higher it declares mature compost. If the\u00a0germination index is between 60\u00a0and 80\u00a0%, it can be said that the\u00a0compost is in the\u00a0conversion phase and has the\u00a0best fertilizing effect. Above 80\u00a0%, this effect decreases, and the\u00a0influence of humus is stronger, which means that nutrients are more bound. The\u00a0release of N and P is slower and there is no leaching of nutrients into groundwater [28].<\/p>\n Statistical analyses were performed using available tools in MS Office Excel 2016\u00a0and SW R-4.\u00a03.\u00a02. for Windows using ANOVA analysis of variance after pre-screening the\u00a0data sets for standard distribution. The\u00a0choice of procedure and statistical methods corresponded to the\u00a0procedures that were used in a\u00a0similar experiment focused on the\u00a0effect of addition of sewage sludge composts to substrates for horticultural purposes [29]. In the\u00a0case of pot experiments, the\u00a0evaluation was carried out by calculating statistical characteristics for individual variants of substrates and crops from two (first year) and three repetitions (second year).<\/p>\n The contents of heavy metals and arsenic in the\u00a0soils used in the\u00a0experiments in both years did not exceed the\u00a0preventive and indicative values according to National Decree No. 153\/2016\u00a0Coll. Of the\u00a0composts used in the\u00a0first year, all composts exceeded both the\u00a0proposed limit value for Cu in the\u00a0framework of the\u00a0EU technical report [30] and the\u00a0given national standard. The\u00a0composts also exceeded both limit values for Zn, and in the\u00a0case of K-A compost, the\u00a0limit value for this element was also exceeded according to SN 465735\u00a0[31]. K-3\u00a0and K-4\u00a0composts used in the\u00a0second year did not exceed any of the\u00a0limit values proposed within the\u00a0EU and given by the\u00a0SN 465735\u00a0standard. Lower concentrations of Cu and Zn in these composts (on average 218\u00a0mg\/kg Zn and 65.9\u00a0mg\/ kg Cu compared to the\u00a0values of 1,016\u00a0mg\/kg Zn and 386\u00a0mg\/kg Cu in the\u00a0composts in the\u00a0first year) were probably caused by the\u00a0lower proportion of used sludge in the\u00a0input mixture for composting. Sludge load can be affected by the\u00a0connection to the\u00a0sewage system, which also brings rain wash rich in these metals due to the\u00a0corrosion of roofing materials.<\/p>\n Regarding the\u00a0assessment of microbial contamination, it was carried out using standard analytical methods for the\u00a0determination of indicator organisms (Salmonella sp., enterococci, thermotolerant coliform bacteria) in the\u00a0input sludge and in the\u00a0resulting substrates from composting. Microbial contamination of sewage sludge from domestic WWTPs ranged from 2\u00a0\u00a0103\u00a0to\u00a04.2\u00a0\u00a0103\u00a0KTJ\/g of dry matter of samples in the\u00a0case of enterococci and 1.6\u00a0\u00a0104\u00a0to 6\u00a0\u00a0104\u00a0KTJ\/g of dry matter of samples in the\u00a0case of thermotolerant coliform bacteria. The\u00a0amount of thermotolerant coliform bacteria in the\u00a0sludge from the\u00a0municipal reed bed plant was in the\u00a0range of 1\u00a0\u00a0105\u00a0to 2\u00a0\u00a0106\u00a0KTJ\/g of dry matter and the\u00a0number of enterococci in the\u00a0range of 1\u00a0\u00a0104\u00a0to 6\u00a0\u00a0106\u00a0KTJ\/g of dry matter. Microbial contamination in fresh substrates from composts before their use in pot experiments was zero for composts K-3, K-4\u00a0and 1\u00a0K-K (zero detection of KTJ per gram of dry matter) for both indicators. For composts\u00a01\u00a0K-A and 2\u00a0K-K in tens of KTJ per gram of dry matter for enterococci and in lower hundreds of KTJ per gram of dry matter for FC. For all composts, it would be acceptable when assessed with the\u00a0limits listed in the\u00a0SN as \u201cComposting\u201d. The\u00a0presence of Salmonella sp. was not detected even in the\u00a0input sludge.<\/p>\n Mixed samples were taken from the\u00a0set of composts established in the\u00a0second year (K-3\u00a0and K-4) and supplemented with a\u00a0control sample (seeds germinated only on distilled water) for phytotoxicity seed germination test. Compost samples were already stabilized, they did not show changes in microbial contamination and content of heavy metals and macroelements. The\u00a0garden cress test was performed in two dilutions, namely 5\u00a0\u00a0and 10\u00a0\u00a0dry weight (%). For each sample, 10\u00a0Petri dishes with 8\u00a0seeds were used, for a\u00a0total of 80\u00a0seeds. After 24\u00a0hours, the\u00a0number of germinated seeds in each Petri dish was determined and the\u00a0lengths of all roots were measured.<\/p>\n Some vegetative responses, such as the\u00a0seed germination test or the\u00a0elongation of root and seedling growth, are commonly used to assess the\u00a0excess toxicity of organic and inorganic compounds in various substrates [32]. The\u00a0average germination rate in our experiment was found to be 7.5, 7.5, 7.7, and 7.8\u00a0seeds out of 10\u00a0for individual prepared mixtures of composts and soils, and 7.8\u00a0for the\u00a0control set. ANOVA analysis showed that the\u00a0null hypothesis of equality of mean values of the\u00a0mixtures and the\u00a0control set could not be rejected at the\u00a0significance level of\u00a0 = 0.05\u00a0(p < 0.05). The\u00a0spread of root lengths between the\u00a0minimum and maximum values for the\u00a0prepared mixtures was generally in the\u00a0same interval of 4.0\u00a0to 9.0\u00a0cm with average values of 6.6, 6.8, 6.2, and 5.8\u00a0cm. The\u00a0smallest average length (5.4\u00a0cm) was achieved by sprouts from the\u00a0control set. The\u00a0results of the\u00a0phytotoxicity test show that the\u00a0mixtures used were stabilized, without a\u00a0negative impact on the\u00a0germination of garden cress seeds. The\u00a0IK index values ranged from 107\u00a0to 118\u00a0for all four mixtures.<\/p>\n In the case of containers with lettuce seedlings, the difference in the weight of the above-ground part (leaves) of the grown head of lettuce without damaged and dry leaves on the edge was monitored. In both years, a statistically significant difference in fresh biomass weight was demonstrated (ANOVA, alpha level 0.05). In the first year, the average weight of the fresh head of lettuce was 15.7 g when using the EZ soil and 61.2 g when using the ZZ soil. In containers with 100% compost substrates, the average weight of fresh heads of lettuce was\u00a077.5\u00a0g (1\u00a0K-K), 82.8\u00a0g (1\u00a0K-A), and 99.1\u00a0g (2\u00a0K-K). An 8% admixture of compost to poor-quality soil contributed to a\u00a0substantial increase in yield. The\u00a0average weights of fresh heads were 104\u00a0g (mixture with 1\u00a0K-A), 105\u00a0g (mixture with 1\u00a0K-K), and 95.2\u00a0g (2\u00a0K-K). This is an increase of up to 85\u00a0% compared to EZ soil, and 36\u00a0to 41\u00a0% compared to high-quality ZZ soil. An experiment in the\u00a0second year confirmed these results. The\u00a0average weight of a\u00a0fresh head of lettuce when using EZ was 81.4\u00a0g, i.e., much higher than in the\u00a0first year. However, the\u00a0EZ used in this year contained 38\u00a0% more organic matter compared to the\u00a0EZ used in the\u00a0first year. In containers with 100% compost substrates, the\u00a0average fresh weights of lettuce heads were 154\u00a0g (K-3) and 108\u00a0g (K-4). When using compost K-3, the\u00a0average yield increased by 47\u00a0% when using compost K-4\u00a0by 25\u00a0%. An\u00a08% admixture of composts to the\u00a0soil meant an increase in average yields by 27\u00a0% (compost K-3) and by 14\u00a0% (compost K-4) to values of 111\u00a0g (K-3) and 95.3\u00a0g (K-4). Fig.\u00a04<\/em>\u00a0shows the\u00a0difference in the\u00a0size of the\u00a0lettuce heads as a\u00a0result of the\u00a0use of compost in growing substrates.<\/p>\n In the\u00a0case of tomato plants, the\u00a0influence of cultivation in 100% compost substrates and in soils with admixture of these substrates on the\u00a0number of fruits obtained during the\u00a0growing season and the\u00a0total weight of the\u00a0fruits was assessed. Fruits were harvested ripe continuously throughout the\u00a0season, weighed and stored to prepare the\u00a0resulting mixture for analyses. From the\u00a0pot experiment in the\u00a0first year, it appears that tomatoes grown in low-quality EZ soil had the\u00a0lowest number of fruits (about13\u00a0fruits per plant). The\u00a0yield from ZZ chernozem (about 25\u00a0fruits per plant on average) was comparable to the\u00a0yield of tomatoes growing in a\u00a0substrate of 100% compost (about 30\u00a0fruits per plant on average for all composts used). An 8% admixture of composts to the\u00a0EZ soil increased the\u00a0average yield from 13\u00a0fruits to 20\u00a0fruits per plant. A\u00a0pot experiment in the\u00a0second year confirmed the\u00a0highest average yields from 100% compost substrates, approximately 25\u00a0fruits per plant. The\u00a0yield from EZ was around 15\u00a0fruits. Compared to the\u00a0results from the\u00a0first-year experiment, the\u00a0addition of compost substrates to this soil did not significantly increase the\u00a0yield. Average yields from these mixtures remained at around 15\u00a0fruits per plant. In the\u00a0first year, fruits from plants grown in eroded soil had the\u00a0lowest total weight (about 300\u00a0g per plant on average). In 100% compost substrates, the\u00a0average fruit weight per plant was 645\u00a0g for K-A, 755\u00a0g for 1\u00a0K-K, and 650\u00a0for 2\u00a0K-K. The\u00a0admixture of all types of composts to EZ increased the\u00a0average mass yields to values of 410\u00a0to 495\u00a0g, i.e. to the\u00a0level of quality chernozem ZZ (450\u00a0g per plant on average). The\u00a0fruit weight analysis from the\u00a0second-year experiment replicated the\u00a0findings from the\u00a0fruit number analysis. For 100% compost mixtures, average fruit weights per plant were 700\u00a0to 800\u00a0g.<\/p>\n Evaluation was done for P, N, K, Na, Ca, and Mg. The\u00a0element content was measured in dried or lyophilized samples (see above) and determined per kg of dry matter. Subsequently, these values were recalculated using the\u00a0values of dry matter to fresh matter, both for the\u00a0biomass of lettuce leaves and for the\u00a0biomass of fruits from tomato plants. In tomato fruits, a\u00a0statistically significant difference in content was found for P, Ca, K, Na (both pot experiments of the\u00a0first and second year) and for N and Mg (pot experiment from the\u00a0second year). In lettuce leaves, a\u00a0statistically significant difference in content was found for K\u00a0and Ca (pot experiment from the\u00a0first year), but this was not confirmed in the\u00a0experiment in the\u00a0following year. In contrast, in this year a\u00a0statistically significant difference was found for N, P, and Na.<\/p>\n Tab. 1. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0first-year pot experiment (in mg\/kg of fresh matter)<\/p>\n The content of nutrients in the\u00a0leaves from heads of lettuce (Figs. 5<\/em>\u00a0and\u00a07<\/em>) and also in the\u00a0tomato fruits (Figs. 6<\/em>\u00a0and 8<\/em>) was comparable in both pot experiments. The\u00a0contents of selected nutrients differ between the\u00a0biomass of heads of lettuce and the\u00a0biomass of fruits from tomato plants in total numbers mainly because both biomasses have very different dry matter. In the\u00a0case of lettuce biomass, the\u00a0dry matter is around an average value of 91\u00a0%, in the\u00a0case of tomato biomass around an average value of 8\u00a0% (7\u00a0to 11\u00a0%). The\u00a0differences in nutrient content in lettuce and tomato biomass from containers with individual substrates can be seen from the\u00a0graphs in Figs. 5\u20138<\/em>. Due to the\u00a0conversion to fresh mass, the\u00a0differences (e.g. in N and K\u00a0content) are higher in lettuce biomass. The\u00a0use of substrates from composting resulted in a\u00a0demonstrably higher content of P, Na and, conversely, a\u00a0lower content of Ca in tomato fruits in the\u00a0case of using compost as an admixture. In the\u00a0pot experiment in the\u00a0second year, this difference was found only in clean substrates from composting. This was also related to the\u00a0increase in N content in the\u00a0biomass (Fig.\u00a08<\/em>). Similarly, a\u00a0significantly higher content of all elements with the\u00a0exception of Ca (a\u00a0decrease in its content) was found in lettuce biomass from the\u00a0pot experiment in the\u00a0second year (Fig.\u00a07<\/em>).<\/p>\n The assessment was carried out for the\u00a0following heavy metals and elements: Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn. The\u00a0analytical procedure for determining the\u00a0content in biomass and conversion to evaluable results for fresh matter was the\u00a0same as in the\u00a0case of the\u00a0elements listed in the\u00a0previous sub-chapter.<\/p>\n These results were compared with the\u00a0limit contents established in the\u00a0following regulations:<\/p>\n Commission Regulation (EC) No. 1881\/2006\u00a0(hereinafter referred to as the\u00a0\u201cRegulation\u201d) setting limits of 0.2\u00a0mg\/kg Cd, 0.3\u00a0mg\/kg Pb.<\/p>\n National regulation Decree No. 53\/2002\u00a0Coll. (hereinafter referred to as the\u00a0\u201cDecree\u201d), setting limits (in mg\/kg of fresh matter): 0.5\u00a0As, 0.2\u00a0Cd, 0.2\u00a0Cr, 10\u00a0Cu, 50\u00a0Fe, 0.03\u00a0Hg, 2.5\u00a0Ni, 0.3\u00a0Pb, 25\u00a0Zn. The\u00a0Decree was repealed due to accession to the\u00a0European Community on 1st August 2004. However, it still allows to assess and compare the\u00a0level of contamination for more metals than the\u00a0Commission Regulation, where limits are set only for Cd and Pb.<\/p>\n For tomato fruits, no exceedance of the\u00a0limit values given by the\u00a0Regulation for either Cd or Pb was detected for individual plants, in both pot experiments. Also, it was not detected that the\u00a0older, no longer valid limits given by the\u00a0Decree were exceeded for any monitored element. A\u00a0comparison of the\u00a0average values for individual substrate variants (Tab. 1<\/em>\u00a0and 2<\/em>) shows that no limit contents of risk elements were exceeded either. In tomato fruits, a\u00a0statistically significant difference in content was found for Zn, Cu, and Cr (both pot experiments), for Ni, Mn, and Cd (pot experiment from the\u00a0second year), and for Al (pot experiment from the\u00a0first year).<\/p>\n An analysis comparing only container fills consisting entirely of soil or composts determined a\u00a0statistically significant difference in content for Cd (pot experiment from the\u00a0second year) and for Al, As, and Zn (pot experiment from the\u00a0first year). However, in the\u00a0case of the\u00a0analysis for the\u00a0first-year experiment, the\u00a0analysis was affected by the\u00a0size of the\u00a0variance of the\u00a0two values from the\u00a0crop pairs, with the\u00a0mean values lying close to each other.<\/p>\n Limit values were exceeded for lettuce leaves in all leaf samples for Cd from the\u00a0second-year pot experiment and in all samples from the\u00a0first-year pot experiment, with the\u00a0exception of containers filled with K-A compost and K-K compost. The\u00a0exceedance was valid for samples from all input soils. It was probably caused by the\u00a0loading of these soils with Cd. When evaluating according to the\u00a0limits from the\u00a0Decree, an exceedance was determined in both pot experiments for Zn, Fe, Cr, and from the\u00a0samples of the\u00a0second year also in several cases for Ni and Hg. In the\u00a0case of Hg, these were samples from containers using K-4\u00a0compost in mixtures. In the\u00a0case of Ni, these were two samples out of three from a\u00a0set of containers with input soil and two samples out of three containers with a\u00a0mixture of input soil and K-4\u00a0compost. In contrast to the\u00a0experiment from the\u00a0second year, two samples of the\u00a0experiment from the\u00a0first year were determined to exceed the\u00a0limit value for Cu and Hg. However, it was always only one sample from a\u00a0pair. It cannot therefore be concluded that some substrate mixtures showed a\u00a0higher transfer of the\u00a0given elements to the\u00a0leaves. In the\u00a0case of a\u00a0comparison of average values from individual substrate variants (Tabs.\u00a03\u00a0and 4), it follows that the\u00a0limit contents of Cr and Zn were exceeded in all substrate variants. Ni exceeded the\u00a0average values for eroded soil and the\u00a0mixture of eroded soil and K-4\u00a0compost from the\u00a0second-year experiment. Overall, the\u00a0most problematic was the\u00a0occurrence of Cd values above the\u00a0limit. In this case, the\u00a0limit value in the\u00a0leaves was already exceeded for the\u00a0input soils in both experiments. This was also reflected in exceeding the\u00a0limit value for mixtures of soil and compost. Paradoxically, in the\u00a0case of 100% compost substrates, the\u00a0average Cd contents were below the\u00a0limit in four out of five cases. Therefore, it is not possible to unequivocally prove the\u00a0negative effect of the\u00a0application of composted sludge. Of the\u00a0other risk elements with limits, Pb, Cu, As proved to be unproblematic.<\/p>\n A\u00a0statistically significant difference in content was found in lettuce leaves for Cd and Mn (both pot experiments), Cu (pot experiment from the\u00a0first year) and Hg with Zn (pot experiment from the\u00a0second year). An analysis comparing only container fills consisting of 100\u00a0% soil or composts determined a\u00a0statistically significant difference in content for Zn (both pot experiments) and Cd and Mn (pot experiment from the\u00a0second year).<\/p>\n The results from the\u00a0pot experiments can be compared with the\u00a0results of a\u00a0number of similar studies and experiments that have been carried out in practically all parts of the\u00a0world. The\u00a0aim of these studies and experiments is to verify the\u00a0possibility of replacing substrates from peat and other non-renewable sources with substrates from composting, including composts used recycle sewage sludge. In the\u00a0study [22], the\u00a0authors conducted a\u00a0pot experiment to investigate the\u00a0effect of composted sewage sludge (KKOV) applied alone and mixed with chemical fertilizer on the\u00a0growth and accumulation of heavy metals in lettuce grown on two soils (Xanthi-Udic Ferralosol and Typic Purpli-Udic Cambosol). The\u00a0experiment included a\u00a0control (fertilizer containing N, P and K); a\u00a0composted sludge applied at a\u00a0rate of 27.54\u00a0(KKOV), 82.62\u00a0(3KKOV), 165.24\u00a0(6KKOV) t\/ha; and a\u00a0mixture of composted sludge and chemical fertilizer (1\/2\u00a0KKOV + 1\/2\u00a0NPK). Application doses were determined according to local recommended doses. Application of KKOV increased biomass; content of Cu, Zn, and Pb in lettuce; total metals and metals extracted with DTPA in soil. KKOV at doses of 27.54\u00a0and 82.62\u00a0t\/ha increases plant biomass less than NPK fertilizer alone.<\/p>\n Another study [32] was conducted with the\u00a0aim of evaluating the\u00a0potential possibility of using composted sewage sludge (KKOV) as an alternative to expensive peat (PE) for the\u00a0cultivation of lettuce (Lactuca sativa L.). Five substrates were prepared with different percentages of KKOV and PE in the\u00a0growth medium. The\u00a0percentage of KKOV addition to PE was 0\u00a0%, 15\u00a0%, 30\u00a0%, 50\u00a0%, and 70\u00a0%. The\u00a0growth media KKOV + PE had very good physical and chemical properties and significant content of plant nutrients, especially P, K, Ca, and Mg. The\u00a0greatest growth increments and yields were achieved in the\u00a0growth medium with 30% KKOV and 70% PE from the\u00a0total volume. Shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight obtained from the\u00a0growth medium with 30% KKOV and 70% PE were increased by 56.53\u00a0%, 43.93\u00a0%, 29.46\u00a0%, and 67.24\u00a0% in comparison with peat substrate. The\u00a0addition of KKOV as a\u00a0component of the\u00a0growth medium increased the\u00a0concentrations of nutrients (N, P, K, Mg, Ca, Cu, Mn, Zn, and Pb) in the\u00a0lettuce plant. However, trace element levels in tissues were much lower than phytotoxic levels.<\/p>\n As part of the\u00a0study [23], a\u00a0greenhouse experiment was conducted with four lettuce cultivars comparing composted municipal waste with perlite (MSWC + P), composted sludge with perlite (KKOV + P), and peat with perlite (peat + P). Plant biometric parameters measured after 72\u00a0days of growth showed that the\u00a0yield of plants cultivated on KKOV + P was similar to control plants, independent of the\u00a0cultivar. In contrast, the\u00a0MSWC + P mixture generally suppressed the\u00a0formation of biomass, especially in the\u00a0Murai and Patagonia cultivars. Compared to the\u00a0peat + P mixture, both compost substrates reduced the\u00a0accumulation of heavy metals in leaves, with a\u00a0large effect in the\u00a0Maximus cultivar. The\u00a0amounts of Cd and Pb in the\u00a0edible part were always below the\u00a0limits set by European regulations.<\/p>\n The authors of the\u00a0research published in the\u00a0study [34] prepared a\u00a0field test in which they grew tomatoes on soil enriched with sludge, soil fertilized with NPK fertilizer, and untreated soil. On soils enriched with the\u00a0addition of sludge, a\u00a0higher amount of Cd contained in the\u00a0above-ground part of tomatoes was found compared to soil with inorganic fertilization. The\u00a0Cd accumulation in the\u00a0fruits was low compared to the\u00a0other analysed plant parts and did not obviously differ depending on the\u00a0type of soil. The\u00a0amount of Cd in tomato fruits was an order of magnitude lower than in leaves.<\/p>\n The availability of metals and their accumulation in tomatoes with increasing addition of sludge to the\u00a0soil was the\u00a0subject of a\u00a0study published in the\u00a0paper of Elloumi et al. [35]. Results showed that soil pH decreased, while salinity, organic C, total N, available P, and reactive forms of Na, Ca, K, and heavy metals increased significantly with increasing sludge application rates. Of the\u00a0three heavy metals Zn, Cu and Cr, Zn had the\u00a0greatest ability to transfer from soil to plants. Low translocation of metals from roots to leaves was observed. The\u00a0use of a\u00a0dose of 2.5\u00a0to 5\u00a0% of sewage sludge appeared in the\u00a0experiment as an effective and cost-effective method for restoring soil fertility.<\/p>\n Zhou et al. [36] found distinct differences in heavy metal concentrations in the\u00a0edible parts of various vegetables grown in soil contaminated with heavy metals (Pb, Cd, Cu, Zn, and As). Heavy metal concentrations decreased as follows: leafy vegetables > stem vegetables\/root vegetables\/fruit vegetables\u00a0>\u00a0leguminous vegetables\/melon vegetables. The\u00a0ability of leafy vegetables to absorb and accumulate heavy metals was the\u00a0highest and that of melon vegetables was the\u00a0lowest.<\/p>\n The mentioned studies will make it possible to assess the\u00a0risks in the\u00a0use of substrates from composting sewage sludge from the\u00a0point of view of the\u00a0content of risk elements, especially heavy metals, which was also the\u00a0subject of our experiments. Due to the\u00a0accumulation of these elements in soils and in biomass during the\u00a0transfer from sludge to compost, it is necessary to find suitable application doses of substrates that ensure compliance with limit values in soils and biomass, as well as limit the\u00a0possible risk of phytotoxicity. A\u00a0study focused on horticultural substrates [29] worked with a\u00a0dose of composted sludge of only 2\u00a0kg of compost with sewage sludge of 2\u00a0to 4\u00a0kg per 1\u00a0m2, which had a\u00a0positive effect on soil properties and nutrient supply for cultivated vegetables. In our experiments, we verified the\u00a0benefits and risks of doses of 8\u00a0kg of 100% compost per 1\u00a0m2, when the\u00a0risks were below the\u00a0limit when used for growing tomatoes. In contrast, the\u00a0use of similar substrates for leafy vegetables appears inappropriate.<\/p>\n In addition to the risks caused by the content of the studied heavy metals and arsenic, it is not possible to ignore the risks associated with the occurrence of other foreign substances and micropollutants in sewage sludge. In the paper [16], our research team presents an overview of drug residues and other micropollutants in sludge before and after composting. It is obvious that, for many of these substances, composting means their reduction or elimination. Styszko et al. [37] monitored changes in the content of selected drugs in sludge during their processing with the aim of safe use. In addition to composting, other methods of processing sludge for substrates usable in agriculture and\u00a0reclamation are being studied, for example in the\u00a0form of biochar preparation (e.g. [38, 39]). With the\u00a0correct dosage, these procedures appear to be promising both from the\u00a0point of view of eliminating a\u00a0number of foreign substances (using thermal processes) and from the\u00a0point of view of enriching the\u00a0soil with organic matter and nutrients with gradual release.<\/p>\n The presented study was focused on checking the\u00a0possible benefits and risks associated with the\u00a0use of sludge from domestic and small WWTPs of two main technologies (activation WWTP, reed bed WWTP) within the\u00a0local circular economy as a\u00a0source of nutrients for growing selected crops after their processing by composting, which simulated domestic and community small-scale composting conditions. The\u00a0aim was to verify the\u00a0possible effects and thus provide information for decision-making in the\u00a0process of dealing with this sludge. The\u00a0predominant process is the\u00a0transfer of sludge to a\u00a0larger WWTP with sludge management. The\u00a0study was also carried out with regard to the\u00a0increasing number of questions about the\u00a0possibilities of local composting of this sludge and the\u00a0subsequent use of composts.<\/p>\n Literature reviews of similar studies show that the\u00a0use of composts to improve soil properties, including composts that include sludge from municipal wastewater treatment, contributes to the\u00a0support of yields of crops and trees, including various types of vegetables. At appropriate doses, there is no transfer of risk elements to these crops, or only to an extent that complies with the\u00a0regulations. Both of the\u00a0presented pot experiments confirmed these assumptions for tomatoes; however, in the\u00a0case of growing lettuce, the\u00a0content of some risk elements in the\u00a0biomass was found to be exceeded. However, this was also influenced by the\u00a0load on the\u00a0used soils. The\u00a0results thus show that local composting with the\u00a0inclusion of sludge can theoretically achieve quality products that can be used in growing plants, but for selected groups of vegetables it is not suitable (e.g. for leafy vegetables such as lettuce) and excessive contamination of the\u00a0consumed parts can occur.<\/p>\n The study yielded findings from which it is possible to set appropriate conditions and limits for the\u00a0use of composts with the\u00a0addition of sludge from the\u00a0mentioned groups of WWTPs, considering the\u00a0content and transfer of risk elements. Microbiological contamination was not monitored as the\u00a0input analysis of the\u00a0composts did not show above-limit contamination, or it was zero for most of the\u00a0composts used. For practical use, however, it would be necessary to conduct a\u00a0study of the\u00a0content and transfer of other groups of pollutants, such as drug residues and microplastics.<\/p>\n The article was written with the\u00a0financial support of the\u00a0project SS02030008\u00a0\u201cCentre of Environmental Research: Waste Management, Circular Economy and Environmental Security\u201d and using the\u00a0results of the\u00a0project TH02030532\u00a0\u201cNew procedures for the\u00a0treatment and stabilization of sewage sludge from small municipal sources\u201d as part of its implementation.<\/em><\/p>\n The Czech version of this article was peer-reviewed, the English version was translated from\u00a0the Czech original by Environmental Translation Ltd.<\/p>\n","protected":false},"excerpt":{"rendered":" The aim of the study, the results of which are presented in this article, was to assess the possibility of simplifying treatment and stabilisation procedures of sewage sludge from small municipal sources of pollution (domestic and small WWTPs up to about 1,000 EP) at the place of their origin and their subsequent use through extensive composting. The results demonstrated the benefit of the application of composts from a material base containing sludge from small WWTPs in increasing the production of the monitored types of vegetables. However, especially with lettuce, there was a higher transmission of selected risk elements. We therefore do not recommend the use of composts with sludge for growing leafy green vegetables. In contrast, this risk did not arise with fruit and vegetables. For practical use, it is still necessary to assess the rate of transfer of other pollutants, such as drug residues and microplastics.<\/p>\n","protected":false},"author":8,"featured_media":28052,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[90,89,92],"tags":[3416,3413,3417,2624,3415,3414,3418],"coauthors":[187,188],"class_list":["post-27929","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-waste-management","category-water-technology-water-supply-waste-water-treatment","category-main","tag-compost-utilization","tag-domestic-wastewater-treatment-plant","tag-pot-experiments","tag-sewage-sludge","tag-sludge-composting","tag-small-wastewater-treatment-plant","tag-vegetables"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=27929"}],"version-history":[{"count":14,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions"}],"predecessor-version":[{"id":32930,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/27929\/revisions\/32930"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/28052"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=27929"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=27929"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=27929"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=27929"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}<\/a>\nFig.\u00a04. View of part of the\u00a0planting pot experiment containers; in the\u00a0left part, lettuce heads and tomato plants with fruits in a\u00a0substrate with compost, in the\u00a0right part in a\u00a0substrate without compost<\/h6>\n
Assessment of phytotoxicity of composts using the\u00a0seed germination test<\/h3>\n
<\/a>\nRESULTS AND DISCUSSION<\/h2>\n
Composition and contamination of used soils and\u00a0composts<\/h3>\n
Phytotoxicity test results<\/h3>\n
Effect of compost application on change in yield of useful parts of crops<\/h3>\n
Content of selected nutrients and elements in useful parts of crops<\/h3>\n
<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 3.<\/h6>\n
<\/a>\nFig. 5. Average content of nutrients in lettuce heads grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n
<\/a><\/h6>\nFig. 6. Average content of selected nutrients in tomatoes grown within the\u00a0first-year pot experiment in g\/kg of fresh biomass<\/h6>\n
<\/a><\/h6>\nFig. 7. Average content of nutrients in lettuce heads grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\n
<\/a><\/h6>\nFig. 8. Average content of selected nutrients in tomatoes grown within the\u00a0second-year pot experiment in g\/kg of fresh biomass<\/h6>\n
Content of risk elements in useful parts of crops<\/h3>\n
Tab. 2. Average values of heavy metals and arsenic in tomatoes grown in the\u00a0second-year pot experiment (in mg\/kg of fresh matter)<\/h5>\n
<\/a>\nNote: the\u00a0limit values used for the\u00a0assessment of contamination are listed in Tab. 4<\/em>.<\/h6>\n
Tab. 3. Average values of heavy metals and arsenic in lettuce grown in the first year pot experiment (in mg\/kg of fresh matter)<\/h5>\n
<\/a>\nTab. 4. Average values of heavy metals and arsenic in lettuce grown in the second year pot experiment (in mg\/kg of fresh matter)<\/h5>\n
<\/a>\nCONCLUSION<\/h2>\n
Acknowledgements<\/h3>\n