A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Eng.) - Asian Institute of Technology, 1968

The physical, chemical, and biochemical characteristics of wastewater from a tapioca starch processing plant were assessed, and the biological treatability of the raw waste was evaluated in anaerobic digesters and anaerobic stabilization ponds. The effect of pH, alkalinity adjustment, nutrient addition, and loading on efficiencies of the two systems were studied. The results obtained indicated for both anaerobic digestion and anaerobic stabilization in ponds, that nitrogen and phosphorus supplementation, as well as pH adjustment of the raw waste were found to be beneficial precursors of anaerobic treatment of tapioca starch waste. However, alkalinity adjustment was found to be more essential, and the combination of nutrients and alkalinity gave best results, based on removals of BOD$ and volatile solids. In the case of anaerobic digestion, the efficiency of the system, based on gas production rate and removals of BOD$ and volatile solids, decreased with increasing organic loading, or with shortening detention period. This statement was also true in the studies on anaerobic stabilization of the waste in the ponds. The highest efficiency for anaerobic digestion over the entire study period was obtained in the digester fed with raw waste to which nutrients and alkalinity were added, at the longest detention time of 30 days. For pond studies, the highest efficiency was obtained in the pond having the same feeding conditions as the mentioned digester, but with a detention period of 27 days. Based on the same hydraulic loading, it was found that the efficiency of the pond was higher than that of the digester and, in addition, the pond would, in practice, be much easier to operate and maintain than the digester.