WP2

Composting – matter recovery; The aim of the proposed research related to WP2 is the estimation of effects of the composting and vermicomposting process to change of PAHs concentration and transformation of chemical forms of heavy metals in relation to batch composition. Dewatered sludge and organic fraction of municipal waste will be used as compost components. The principal parameters characterizing composting mass will be the proportion between total organic carbon, total nitrogen and organic phosphorus treated as variables.


 Highlights


  • Proper raw materials selection in the feedstock allows to obtain good quality of  compost
  • The use of biopreparations improve the composting process efficiency and leads to a higher degree of  organic matter decomposition
  • Vermicomposting of different sewage sludge exhibiting various contamination levels
  • Eisenia andrei employed in the process of decomposition of organic matter
  • Removal of total heavy metals and polycyclic aromatic compounds
  • Heavy metals and PAHs accumulation in earthworms' bodies

Executive summaries of WP2 results


 All three following tasks were implemented: 2.1 The term of parameterAT4-respiration activity; 2.2 To carry out the composting process; 2.3 Vermi-composting experiment on the products obtained from the second task. In order to carry out the tasks provided in the WP2 numerous laboratory tests were conducted. The aim of the task 2.1. was: firstly, to determine the changes in physico-chemical parameters during composting different biodegradable wastes, secondly to study of main parameter of this work, the respiration activity during composting process. Raw materials used for this study were collected from a regional municipal landfill (OFMSW), sewage sludge (SS), bulking agents (BA) Miscanthus, green waste (GW), waste from markets (WM) in the form of grass were used as a co-substrate for experiments. Mixtures for composting experiment were prepared by adding different quantities of co-substrates. AT4 oxygen consumption test during composting process was provided by means of OxiTop system. From M.21.1. milestone it was observed a reduction in oxygen demand of materials composted at a time. The values of oxygen demand after 40 days of composting ranged between 16.24 - 541.91 g O2/kg d.m. In the first two to four weeks after the start of composting processes there is intense microbial growth that is due to decomposition of easily biodegradable fraction of composted material. In further stages decreasing the amount of organic matter in compost - thus the demand for oxygen in composted material is lower. It was found that mixtures with 65% and 71% sewage sludge addition were most stabile of the tested samples. However only for the sample with 65% content of sewage sludge the respiration activity was on the level 10,78 g O2/kg d.m. which indicates that this compost can be use in agriculture with taking into account physical – chemical properties. The aim of the 2.2 To carry out the composting process was to identify and quantify the changes in physico-chemical parameters taking place during composting different biodegradable wastes. It is also investigated how different bulking agents affected the composting process. Raw materials used for this study were: 1) sewage sludge (SS1) from regional municipal wastewater treatment plant, sewage sludge (SS2) from co-digestion, organic fraction of municipal solid waste (OFMSW) selectively collected from households, 2) bulking agents (BA): miscanthus, willow, maize straw, barley straw and 3) grass (G) from green urban areas. In this experiment four types of bulking agents were tested. Individual components of compost were collected and added to the reactor for the lab-scale incubation experiment are shown in Table 1.1. From the M2.2.1 Composting process it was fund that efficiency of the aerobic stabilisation process depends on the composition of composting mixture. One of the most important parameter which affects the microbial activity directly, the compost temperature and hence the rate of decomposition is moisture. The moisture content in the initial compost mixtures were within 65–80%, and values of that parameter decreased during composting process due to evaporation as a result of microbial heat generation as well as aeration. In the final product, moisture content was between 52-70%, and was too high in all samples with maize straw. The N-Kieldahl concentration in the composting mass increased in all composts in the end of the process. pH in composting mixes ranges between 5.10 – 5.70. After 70 days of composting process pH in all samples increased to the values of 5.8 – 6.12. The total carbon contents of all mixtures decreased during the composting process. The TC changes in sample R23 were on the highest level (29.31%), and achieved the reduction level of 28.7%. 28.35%. 27.03% for R24, R15 and R17, respectively. The lowest reduction of TC content was observed in R10 and R18 sample with the 20% addition of SS1. For the samples R10 willow was used as a bulking agent while sample R18 a maize straw. In all other samples the decrease of TC was observed at similar levels around 25%. The C/N ratio was used by many authors as one of the most important indicators of compost maturity. The C/N of all mixtures decreased during the composting process to value 11.88 – 14.29. In all composted samples a decrease in C/N ratio was observed, which indicates a proper direction of decomposition process. Table 1. Percentage composition of co-substrates in composting process: 1) sewage sludge (SS1) from regional wastewater treatment plantl, sewage sludge (SS2) from co-digestion, organic fraction of municipal solid waste (OFMSW) selectively collected from households, 2) bulking agents (BA): miscanthus (M), willow (W), maize straw (MS), barley straw (BS) and 3) grass (G) from green urban areas.

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This C/N ratio value is typical for mature compost. The lowest value C/N ratio observed for R16 sample (12.54). this compost consists of 20% SS2 and has miscanthus as a bulking agent. In turn. the lowest value C/N ratio reported for R23 sample (11.88) this compost consists of 30% SS1 and barley straw as a bulking agent. The decrease of total P content was observed at the end of the process. The loss of organic P is likely due to the mineralization of organic phosphorus and its consumption by microorganisms. During the composting process the concentration of heavy metals was also monitored. The concentration of cadmium was low in all samples and slight increase of Cd content was observed in the final products. Cadmium is one of the most bioavailable and soluble metals. An increase in the concentration of almost all metals during the process was observed. The only exception was observed in the case of Co in mixture R11, where decrease was observed. Polish law regulates only four metals (Cd, Cr, Ni, Pb) to qualify composts as organic fertilizer. In the most cases the obtained products were characterized by a low content of heavy metals and proper content from the requirements of the Minister of Agriculture and Rural Development to Act on fertilizers and fertilization posed organic fertilizers. Studies have shown that composting is a good method for the disposal of different organic wastes. The aim of the task Task. 2.3 Vermicomposting experiment on the products obtained from the second task was to evaluate the effects of the vermicomposting on the quality of final products. The part of the composts from task 2.2. were chosen in order to perform the series of experiments. In this context, vermicomposting was understood as a stabilization step, that allows to improve the quality of the product. Earthworms influence the physical and chemical parameters of substratum by direct and indirect actions, showing the ability to remediate some dangerous contaminants, like PAH’s, heavy metals and some pathogens (i.e. Escherichia coli and Salmonella). The main aims of the realised part of task 2.3. was to study the dynamic of the degradation of polycyclic aromatic hydrocarbons (PAHs) during sewage sludge vermicomposting. The concentration of 16 priority PAHs was examined before and after the vermicmposting step. Adult (clitellated) E. andrei worms provided by the Lille 1 University laboratory were introduced in three composts obtained in pre-composting step. The total PAHs content was reduced significantly in all analyzed mixtures. After 5 weeks of vermicomposting, PAHs concentration was reduced from the initial value of 3965.86 µg kg-1 to 565.45 µg kg-1 in mixture A (85.75 % removal), from 9244.56 to 3896.27 µg kg-1 in mixture B (57.88 % removal) and from 2945.91 to 1129.76 µg kg-1 in mixture C (61.65 % removal). Even though an important decrease of PAHs was observed in all analysed mixtures, only a slight ability of bioconcentration of this compound in worm’s bodies was noted (body accumulation factor; BAF<1). Similar phenomenon was observed in the case of 2,4-Dichlorophenoxyacetic acid herbicide, which encourages to investigate the possible mechanisms involved in the removal of dangerous compounds in the presence of worms. Vermicomposting can be considered as a tool for bioremediation of soil contaminated with heavy metals and hydrocarbons. While heavy metal concentrations fluctuated mildly in substratum, several metals clearly accumulated in earthworms bodies. Body Accumulation Factors could be ranked as follow (Cd>Cu>Zn>Ni>Cr>Pb). From M.2.3.1. it was found that vermicomposting has recently been appreciated as a modern biotechnology of degradation of biosolids, in which earthworms play an important role as natural bioreactors in the process of decomposition of organic matter. Some of earthworm species are able to transform a variety of organic wastes, which constitute 46% of global solid wastes , like solid paper mill waste, human feaces , domestic waste , sugar production wastes and sewage sludge into a valuable product named vermicompost. Vermicomposting may constitute an interesting alternative or complementation for classical composting process. Combined composting-vermicomposting processes has been investigated for various organic wastes. Two to four weeks of precomposting step may be crucial to obtain the proper parameters of the substratum and to remove ammonia and inorganic salts or other substances, potentially toxic or earthworms. Being a relatively environmentaly-friendly method of waste management, vermicomposting is also known as a low-cost strategy, with more revenues comparing to traditional composting. Vermicomposting process may constitute an interesting alternative for the existing waste treatment strategies, mostly for small municipalities. The economical and environmental costs are relatively low comparing to the possible gains of employing earthworms into the process. Moreover, earthworms can accumulate some heavy metals in their bodies in non-linear way, with higher Body Accumulation Factors (BAFs) at lower concentrations. Earthworms are also recently claimed to enhance the biodegradation of another dangerous contaminants, like polycyclic aromatic hydrocarbons, known as ubiquitous cancerogenic, teratogenic and ecotoxic pollutants. Funding has been used for laboratory and field tests carried out in Polish-Norwegian cooperation, organization of training courses (LCA training research visit at NTNU Industrial Ecology), intership and participation in conferences.