Management of various organic fractions of municipal solid waste via recourse to VFA and biogas generation

Abstract

A hybrid anaerobic solid–liquid system was used for anaerobic digestion of organic fraction of municipal solid waste (OFMSW) consisting of mixed food + fruit waste and vegetable waste. Hydrolysis and acidogenesis potential of the above wastes were evaluated with the aim of producing value-added products in the form of volatile fatty acids (VFAs) and biogas recovery. Efficient hydrolysis and acidogenesis of mixed food + fruit waste was observed at a hydraulic retention time (HRT) of 1–3 d with a five-fold increase in soluble chemical oxygen demand (SCOD) followed by VFA production consisting of 50–75% acetic acid. Longer time was required for hydrolysis of vegetable waste with optimum hydrolysis and SCOD generation at 9 d HRT followed by VFA synthesis consisting of 45% acetic acid. Higher inoculum:substrate ratios resulted in improved hydrolysis and acidogenesis rates for vegetable waste in shorter time of 6 d with higher VFA production and increase in acetic acid content to 70%. When acidogenic leachate was fed into methanogenic reactors, detectable biogas production was observed after 25 d with 37–53% SCOD removal from leachate from mixed food + fruit waste and methane production of 0.066–0.1 L g⁻¹ SCOD removed and methane content of 38%. Though biogas yield from acidogenic leachate from vegetable waste was lower, nearly 94% volatile solids (VS) removal was observed in the reactors thereby providing methane yield of 0.13–0.21 L g⁻¹ VS consumed. Thus, the study provided a method for generation of value-added products from an otherwise misplaced resource in the form of OFMSW.

Keywords:

• municipal solid waste
• organic waste
• hydrolysis and acidogenesis
• inoculum to substrate ratio
• biogas

Acknowledgements

AAK duly acknowledges the financial support in the form of the Lien Environmental Fellowship Award, provided by the Lien Foundation-NTU Environmental Endeavour (EE2), Singapore for carrying out the study at Nanyang Technological University (NTU), Singapore.