A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1987

Bench scale experiments were conducted to determine the biodegradability of the tapioca starch and the vegetable oil wastewaters. Two batch digesters and three semi-continuous digesters were operated for each run. The batch digesters were filled with influent mixtures of digested sludge: wastewater at 70:30 and 50: 5 0 ratio. The first run of the semi-continuous digesters was fed with tapioca starch wastewater at organic loadings of 0.4, 1 and 2 kg COD/m3 -d , corresponding to hydraulic retention times (6) of 21.6, 8.7 and 4.3 days, respectively. The vegetable oil wastewater was used during the second run at organic loadings of 0.2, 0 .5 and 1.0 kg COD/m3 -d corresponding to a of 7, 2.8 and 1.4 days, respectively. Gas production was shown to increase with retention time and with increasing influent concentration. The maximum CH4 production a nd COD reduction recorded were 0.09 m3 /m3 -d a nd 88 %, respectively, at a loading of 0.4 kg COD/m3 -d for tapioca wastewater a nd similarly for vegetable oil wastewater, CH4 production was 0.04 m3 /m3 -d and COD reduction was 80% at 0.2 kg COD/m3 -d. The results indicated that only the tapioca starch wastewater was satisfactorily applicable for kinetic analysis. In both batch and semi-continuous systems, the results indicated that the degradation of tapioca starch wastewater was better than the vegetable oil wastewater in relation to gas production and COD removal efficiency.