Investigation of Biogas Generation from the Waste of a Vegetable and Cattle Market of Bangladesh

Abstract

The results of a study on the type and quantity of solid wastes generated in a rural vegetable and cattle market, and biogas generation from the waste are presented in this paper. The market wastes were collected; individual items were separated and measured on both normal days and haat days. During a normal day, it was found that very insignificant amount of waste was generated. But on a haat day, a large amount of wastes was found to be generated. On average, the amount of easily biodegradable waste was 589 kg out of the total waste of 1004 kg on a haat day. Cow dung, fish waste, ginger, cursed lobe, guava, and banana leaf were the major biodegradable wastes. Other biodegradable wastes were goat dropping, bitter melon, pointed gourd, dhundul and brinjal. The total solids (TS) and volatile solids (VS) of the biodegradable portion of the market waste were determined and were found to be 17.94% and 13.87% respectively. Laboratory experiments were run in order to generate biogas in anaerobic digesters using the same composition of the market waste. They were placed in a large closed chamber and room heaters were used to maintain the temperature of the chamber at a constant value. Two types of experiments (batch and daily feed) were carried out in two phases. In the first phase of the experiments, 500 g and 750 g waste were added in 2.5 L digesters separately and inoculum was added to make the effective volume of 2.1 L for each digester. The experiments were operated for 46 days (hydraulic retention time – HRT) and the average temperature was found to be 34.7°C. In the second phase of the experiments, one single chamber reactor was initially fed with 750 g waste having the effective volume of 2.2 L. Another double chamber (two digesters connected in series) reactor was initially fed with 750 g waste having the effective volume of 2.7 L. Then a mixture of daily feed of 18.75 g waste and required volume of water was fed after dispensing equal volume of slurry from the reactor. The experiments were run for 40 days and the average temperature was 35.1°C. The results of the 1st phase of experiments revealed that the daily biogas generation rate was 0.273 and 0.389 m3/kg of VS added for the organic loading rate (OLR) of 0.83 and 1.24 g VS/L/d respectively for 40 days retention time. The results of the 2nd phase of experments revealed that for HRT of 40 days, the rate of biogas producton was 0.244 and 0.30 m3/kg of VS added for the