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Investigation of biogas generation from the wastes of a vegetable market of Bangladesh under daily feed condition
Md Abdul Jalil, Santosh Karmaker, Md Samiul Basar and Md Shamsul Hoque
Biogas generation based on market wastes is a promising technology to manage the solid wastes of the markets. This paper
presents the results of two sets of laboratory experiments on biogas generation from the wastes of a rural vegetable market of
Bangladesh under daily feed condition at ambient temperature. The easily biodegradable wastes were used as the feed for biogas
generation. Cow dung, cauliflower stick, papaya and potato were the major biodegradable wastes. Daily average composition of
the wastes was used as substrate for the experiments after cutting the wastes into small pieces (less than 4 mm in size). The total
solids (TS) and volatile solids (VS) of the biodegradable portion of the market wastes were 17.84% and 13.85% respectively. The
experimental setups were placed in a large closed chamber and were operated at ambient temperature as controlling temperature
within a bioreactor at rural set up is very difficult. A 5 L reactor was initially loaded with 750 g waste and inoculum was added to
make the effective volume of 2 L (single chamber reactor) in the first set. In the second set, two digesters of 1.5 L volume each
were connected in series near the bottom to have a double chamber reactor. It was initially fed with 750 g wastes (350 g in each
digester) and inoculum was added to make the effective volume of 1 L for each digester. Both the reactors were operated for 40
days. Considering the hydraulic retention time as 40 days, from the 2nd day of operation, the single chamber reactor was fed daily
one time with a mixture of 18.75 g waste and required volume of tap water (natural groundwater) to make the total volume of 50
mL after dispensing equal volume of slurry from the reactor through the outlet. For the double chamber reactor, the first chamber
of the reactor was fed daily with the same mixture as that of the single chamber reactor after taking out 50 mL slurry from the
second chamber. The daily biogas production was measured by water displacement method and the daily temperature within the
enclosed chamber was recorded with a thermometer. During the experiments, it was observed that the daily average temperature
varied in between 19 and 27oC and it did not affect the rate of biogas production. The results of the experiments revealed that the
stable rate of gas production was 0.25 m3/m3/d at the organic loading rate (OLR) is 1.42 g VS/L/d. The outlet chamber produced
roughly double volume of gas in total compared to the inlet chamber of the double chamber reactor. But the stable rate of biogas
generation was 0.25 m3/m3/d for the double chamber reactor at the OLR of 1.42 g VS/L/d. Consequently, the stable biogas
generation was same for both the reactors in terms of organic loading and it was 0.18 m3/kg of VS added.
