Effect of Carbon/Nitrogen on Elimination of Coliforms during Composting of Sewage Sludge, Dairy Manure and Sawdust

Abstract

Composting is a solid waste management alternative to reduce potential hazards in the converting of sewage sludge into reusable material on land. But inefficiency of traditional composting process rate lowers its demand. In-vessel system could provide more effective pathogens reduction and produce pathogen-free soil amendments in comparison with traditional composting systems. In order to achieve successful composting process environmental factors such as temperature, moisture, aeration and nutrients should be sufficiently controlled. This study was undertaken to assess the effect of the carbon/nitrogen (C/N) ratio on reduction or elimination of total and fecal coliforms in co-composting of sewage sludge with dairy manure and sawdust using an in-vessel system under controlled conditions. Temperature, pH and C/N values were used for consideration of the stabilization of the composting process. In this study the minimum temperature of composting process was set to 40 oC by temperature controlled external heater. Initial mesophilic phase occurred within 2 days followed by the thermophilic phase, which lasted for about 10 days. Monitored parameters featured reaction trends to those obtained changes in the mesophilic, thermophilic and maturation phases. A high C/N reduction observed for high initial C/N mixtures (30 and 40) within 7 days of composting. Low initial C/N mixture (20) showed slightly C/N reduction during composting. A higher ratio of C/N preparations led to a higher stabilization rates but higher coliforms reduction achieved with low C/N ratios.