Anaerobic Degradation Pattern of Urban Solid Waste Components

INTRODUCTION

Resource recovery and treatment of organic fraction of waste material has received considerable attention primarily due to the large fraction of organic waste generated in most of the Indian cities and the environmental problems associated with alternative disposal methods. Bangalore city is one among the five metros in India which produces more than 3500 tons per day of municipal solid waste (MSW) and a major fraction is contributed by organic biodegradable waste of 72% (Chanakya et al., 2009). From general observations it appears that approximately, half of the total waste generated in the city generally reaches these authorized waste disposal sites whereas a small fraction of wastes are composted and rest of the wastes are dumped in unauthorized places without any treatment. This approach is permitted as a stop gap arrangement but is environmentally unsatisfactory (Shwetmala et al., 2012).

Possible treatment methods for organic waste treatment are aerobic composting and anaerobic biomethanation. The investigation of decomposition of organic materials is essential for an understanding of the relative worth of different materials. Waste degradation process has also been considered in aerobic composting (Chanakya et al., 2007a, Hamoda et al., 1998) and in anaerobic biomethanation (Barlaz et al., 1989, Chanakya et al., 2007b). Waste decomposition in these processes requires monitoring of biodegradation rates. To determine the waste biodegradation rate and to generate a usable measure for the loss of organic matter, it is necessary to determine process kinetics using experimental data obtained under controlled conditions.

Organic waste type and its chemical composition have long been considered as a critical factor in determining the extent and rate of decay (Singh and Gupta, 1977). The content of pectin, cellulose, hemicellulose and lignin and the C/N ratio are the most important controlling factors in the rate of the decomposition process. All fractions of organic waste substrates do not degrade at the same rate; especially when relative content of pectin, cellulose, hemicellulose and lignin vary from one substrate to another. Typically there are two classes of degradability among the fractions, the rapidly degradable with a higher rate constant and the slowly degradable with a low decay constant. In experimental studies the degradation rates may be split into a rapid early decay followed by a slower second phase of digestion (Chanakya et al, 2009).

Therefore, in this study a two phase first order kinetic model is used to measure the rate of anaerobic decomposition of ten specific types of fermentable fractions commonly occurring in urban solid waste in Bangalore. These estimated biodegradation kinetic rate constants can be used to predict degradation rate of organic matter during anaerobic treatment.

Table 1: Fresh weights of individual samples used for experiment

Table 2: TS and moisture content in waste substrates


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