Abstract
The aim of this study was to assess the degree of stabilization of composted sewage sludge (SSC) during maturation using tests in aerobic and anaerobic conditions, determining the potential for biogas formation and its composition, as well as changes of mobile and bioavailable forms of metals in SSC after treatment. The samples were taken in the second phase of composting, during the maturation process. The biological stability of SSC samples was determined by detecting an incubation test (GS21) and respiration index (AT4). The potential for biogas formation and composition changes of SSC during maturation were analyzed. It was found that the chemical composition of the tested samples depended on the degree of their maturity. It was found that the both tested methods (AT4, GS21) of assessing the stability of waste are sufficient. Treatment under anaerobic conditions did not significantly change the composition of the samples, with the exception of total organic carbon (TOC). A high percentage of methane in biogas for samples at the beginning of the maturation process indicates a high content of biodegradable organic matter in SSC. In addition, the decrease of mobile and bioavailable forms of heavy metals percentage, during the SSC maturation, was found. In order to confirm the results of current study, a long-term field studies should be carried out on the effects of SSCs tested on soils and plants.Graphic
Highlights
Sewage sludge (SS) used in agriculture is the one of the recommended recycling routes
Whereas the degree of stabilization of waste after biological treatment of mechanical–biological treatment (MBT) is determined in order to assess the potential for decomposition in a landfill
The results indicate that the tested Sewage sludge compost (SSC) contained degradable organic matter, which was used by microorganisms during maturation
Summary
Sewage sludge (SS) used in agriculture is the one of the recommended recycling routes. The stability of compost is an important index for determining the potential impact on the nitrogen and oxygen availability in the soil [10] For this reason, a suitable composting process management is necessary to obtain a quality product [11]. The stability of compost is related to microbial activity and to the degree of organic matter decomposition Each of these parameters, maturity and stability, is assessed using different tests e.g. germination index (GI), production rates of O 2 uptake or C O2, physico–chemical parameters or microbial activity [11, 13,14,15,16,17,18,19,20,21]. Biochemical test methods are commonly used, which are based on aerobic respiration indices adopted from assessing the stability of waste after mechanical–biological treatment (MBT) or composted waste [18]. Measurement of biogas composition gives an estimation of anaerobic biodegradability and helps in assessing the impact of compost to the environment
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