Anaerobic Digestion of Lignocellulosic Wastes

T, Anas (2014) Anaerobic Digestion of Lignocellulosic Wastes. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

One of the major problems faced by modern society is the shortage of energy supply. On the other hand, a large amount of energy-rich organic material is discharged into the environment as waste. Anaerobic digesters are considered as sustainable sources for alternate energy. Yard waste and other green waste constitute a major portion of municipal solid waste (MSW). Lignocellulosic biomass feed stocks, in particular yard waste, are highly desired for anaerobic digestion as they are widely available. High concentration of lignin presents a major challenge for utilizing yard wastes as a feedstock for anaerobic digestion as lignin is resistent towards anaerobic degradation . Therefore, additional steps are necessary to increase the biodegradability of yard waste. This research assessed the potential of application of anaerobic digester in managing lignocellu- losic wastes. The main focus was to increase the methane production of yard waste by co-digesting with widely available food waste and to study on degradation of lignocellulosic components. The food waste and yard waste obtained from IIT Hyderabad mess and lawn respectively, were co-digested in the ratios of 1:0, 1:0.5, 1:1, 1:1.5, 1:2, 1:3, 1:4 and 0:1. The reactor responses at four solid retention times (SRTs) - 30day, 20 days, 12 days, and 6 days, were studied. The research was performed in semi-batch mode using a respirometer. The reactors were initially inoculated with sludge obtained from a running anaerobic digester. A biochemical methane potential test was done in order to nd the methane potential of sub- strates. The methane potential obtained for food waste was 472.19 L/kg VS and that for yard waste was 265.71 L/kg VS. The destruction of volatile solids, lignin, cellulose, hemicellulose and volatile fatty acids were studied. Methane production showed a decreasing trend with increase in yard waste content.However, the performance of the reactor, in terms of biogas production and volatile solids destruction, was observed to be the best at a food to yard waste ratio of 1:0.5. Also a SRT of 20 days showed a positive increment to gas production and ber degradation compare to other SRTs.Volatile solids degradation decreased with increase in VS loading. Similarly, the degradation of lignin, cellu- lose and hemicellulose also decreased with increase in VS loading. A maximum degradation of 21% in lignin, 32% in cellulose and 27% in hemicellulose was observed. The volatile fatty acids were high in food waste, as the food waste facilitates faster fermentation. Acetic acid concentration showed an inverse relationship with methane production. Concentrations of propionic and butyric acids, which indicate the health of reactors, increased with increase in VS loading . Consequently, pH decreased. Carbon mass balance was performed at each SRT. Unaccounted was obtained to be within 10%.

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