Effects of C/N ratio and earthworms on greenhouse gas emissions during vermicomposting of sewage sludge

Abstract

The emissions of greenhouse gases (CO2, CH4, and N2O) during bio-stabilization of sewage sludge under different C/N ratios with/without Eisenia fetida were evaluated in this study. Vermicomposting led to the more significant reductions of pH, TOC and C/N ratio compared to the control treatment without earthworms. C/N ratio had a significant effect on the emission of N2O, whereas its influences on CO2 or CH4 emission were not obvious. Earthworms reduced the CH4 emission greatly, although the CO2 emission was not affected by earthworms. Furthermore, a higher emission of N2O was observed in vermicomposting compared to the control. Both the C/N ratios and earthworms exerted statistically significant effects on the total GHG emission. Vermicomposting could enhance the degradation of organics and accelerate the mineralization process of nitrogen, whereas the increase in the C/N ratio could reduce GHG emission during vermicomposting of sewage sludge.