Biological pretreatment of non-flocculated sludge augments the biogas production in the anaerobic digestion of the pretreated waste activated sludge

Abstract

High-efficiency resource recovery from municipal solid waste (MSW) has been a focus of attention. The objective of this research is to develop a bio-pretreatment process for application prior to the anaerobic digestion of MSW to improve methane productivity. Bacillus licheniformis was used for pretreating MSW (non-flocculated with 0.07% citric acid), followed by anaerobic digestion. Laboratory-scale experiments were carried out in semi-continuous bioreactors, with a total volume of 5 L and working volume of 3 L. Among the nine organic loading rates (OLRs) investigated, the OLR of 0.84 kg SS m⁻³ reactor day⁻¹ was found to be the most appropriate for economic operation of the reactor. Pretreatment of MSW prior to anaerobic digestion led to 55% and 64% increase of suspended solids (SS) and volatile solids reduction, respectively, with an improvement of 57% in biogas production. The results indicate that the pretreatment of non-flocculated sludge with Bacillus licheniformis which consumes less energy compared to other pretreatment techniques could be a cost-effective and environmentally sound method for producing methane from MSW.

Keywords:

• anaerobic digestion
• methane production
• municipal solid waste
• biochemical methane potential
• bacterial pretreatment

Acknowledgements

The authors are thankful to the Department of Biotechnology, India, for financial assistance to this project (BT/PR13124/GBD/ 27/192/2009) under their scheme Rapid Grant for Young Investigator.