Maturity and Stability Evaluation of Composted Municipal Solid Wastes

Composting process is a feasible biological treatment for the recycling of municipal solid wastes as a soil amendment. The principal requirement of compost for it to be safely used in soil is a high degree of stability or maturity, which implies stable organic matter content as well as the absence of phytotoxic compounds and plant or animal pathogens. At the present study, the maturity and stability of composted municipal solid wastes at a biocompost plant was evaluated. For the assessment of compost maturity, important parameters including temperature, moisture content, pH, electrical conductivity, carbon-to-nitrogen (C/N) ratio, microbial parameters including Salmonella, total and fecal coliforms were measured during the composting process (80 days). In addition, phytotoxicity as seed germination index and heavy metals concentration (Zn, Cu, Cr, Ni, Cd and Pb) was determined at the end of the composting time. The results showed that the C/N ratio decreased during the composting process (reached to 15.6) due to the loss of carbon and the increase in nitrogen content per unit material; also, the NH4+/NO3 ratio decreased with increase in the time of composting and reached to 1.08. In addition, the microbial parameters including Salmonella and total and fecal coliforms decreased significantly at the end of the composting period and reached to standard values. Furthermore, germination index (GI) increased during the composting process and the compost samples at the end of the composting phase had GI values greater than 90. The produced compost in this study was mature and ready for use as an agricultural substrate or soil conditioner after 80 days of composting