Seasonal variation induced stability of municipal solid waste compost: an enzyme kinetics study

Abstract

An investigation was carried out in laboratory to find out the effect of ambient temperature and different treatments on passive bin composting of municipal solid waste (MSW). A potent cellulase degrading inoculum (Bacillus subtilis, B. amyloliquefaciens, B. nakamurai and B. velezensis) sourced from dumpsite soil and cow dung slurry was used as addon to MSW composters. Treatments were tested during summer (26–45 °C) and winter (5–22 °C) season to profile the physio-chemical, enzymatic and microbial changes during 90-day study. In addition, a kinetics model for MSW composting was derived for the rate of organic load degradation deducing the first order kinetics rate (Kr), limiting velocity (Km) and dissociation constant (Kd). The results of the present investigation revealed that ambient temperature hastened the degradation of organic substrates in case of MSW amended with microbes and cow dung (60 days) as indicated by the achieved maximum kinetics reaction rate, 0.0131 day−1 (R2 = 0.993) and reduced C/N ratio (11.6%). Also, enzymatic profiles; dehydrogenase (170.1 µg TPF g−1 day−1), cellulase (96.1 µg glucose g dwt−1 h−1) and urease (539.1 μg NH4+–Ng dwt−1 h−1) with a high temperature profile (47–63 °C) in the finished summer compost, Cs4 supported the results. Whereas, winter composting could not attain the desired results and produced immature compost even after 90 days. Statistical analysis (proximal cluster analysis, hierarchical cluster analysis and ANOVA) and kinetics study showed that ambient temperature in collaboration with addons significantly influenced the compost maturity.