Comparison of the Composting Performance of Four Different Sewage Sludge Amendments

Abstract

ABSTRACT.High moisture content of sewage sludge is a major constraint in composting, and therefore sewage sludge needs to be mixed with bulking agents that have a high water absorption ratio and better structural stability. In this study, dewatered sludge has been mixed with four different bulking agents in terms of physicochemical properties, with a 1:1 (v/v) proportion of sawdust (SW), hazelnut husk (HH), corn straw (CS), or pine litter (PL), and the composting performances of bulking agents were investigated by considering temperature rise, CO2, H2S evolution, organic matter (OM) removal, C/N ratio, and dissolved organic carbon (DOC) removal. Three of the mixtures, namely, HH, PL, and SW, provided better initial composting conditions, ensuring an appropriate water–air balance within the compost matrix. CS was not able to supply sufficient porosity due to the smaller water absorption ratio and higher degradation rate, which induced anaerobic conditions. Among the mixtures, a higher and faster temperature rise (max 56.5°C) and CO2 release was provided by HH, while OM removal (53%) and DOC degradation were higher with the CS mixture, despite the low temperature rise and low peak value of CO2 release. Relatively low degradable carbonaceous contents of SW delayed all the composting indicators measured in the study. HH significantly enhanced bioreactions and accelerated the stability of sludge compost by providing both structural stability and a readily available carbon source, significantly shortening the composting time.