Carbon Dioxide and Methane Emissions during the Composting and Vermicomposting of Sewage Sludge under the Effect of Different Proportions of Straw Pellets

Abstract

The aim of this study was to evaluate the carbon dioxide (CO2) and methane (CH4) emissions during the composting and vermicomposting of sewage sludge under the effect of different proportions of straw pellets. Four treatments, including a control with three replicates, were designed to mix the initial sewage sludge with varying rates of pelletized wheat straw (0, 25%, 50%, and 75% (w/w)). Over a 60-day period, vermicomposting with Eisenia andrei treatments and composting were carried out. The results indicated that both composting and vermicomposting produce a significant (p < 0.001) amount of CO2 and CH4 emissions from all treatments. Vermicomposting significantly reduced CH4 emissions by 18%, 34%, and 38% and increased CO2 emissions by 75%, 64%, and 89% for the treatments containing 25%, 50%, and 75% straw pellets, respectively, compared to composting. However, CO2 emissions decreased and CH4 emissions increased during composting compared to vermicomposting. As a result of this finding, both composting and vermicomposting processes are recommended as an additive of pelletized wheat straw, depending on the target gas to be reduced.