Experimental studies and mathematical modeling of a semibatch bio-digester using municipal market waste as feed stock

Abstract

An anaerobic digester of 10 dm³capacity has been operated in batch mode at an optimum temperature of 40^oC and <i style="">p</i>H 6.8 using vegetable market-waste as the feed material. The effect of slurry concentration and that of the concentration of carbohydrate, protein and fat in the slurry on the biogas production rate and methane concentration in the biogas have been studied<b style="">. </b>A maximum concentration of methane in the order of 80% has been obtained. The liquid medium of a running digester based on vegetable market waste has been used as seed culture. Both acidogenic and methanogenic bacterial strains have been isolated from the broth. Growth kinetics of acidogenic bacteria have been determined using carbohydrate, fat and protein individually as limiting substrates. Kinetics of exponential growth of methanogenic bacteria have been determined using different volatile fatty acids and long chain fatty acids as substrates. In all the cases, Monod type model has been observed to fit well with the experimental growth patterns. The performance of the digester has been studied using slurry concentration and concentration of carbohydrate, protein and fat in the slurry as parameters. A deterministic mathematical model has been developed using the suitable growth parameters of isolated bacterial strains to explain the transient behaviour of the digester. The model predictions have been compared successfully with the experimental findings.