F. Thailand

Thailand produced about 20 million tons of cassava in 1988. A typical Thai tapioca starch factory discharges approximately 15-23 m³ wastewater per ton of starch. The COD (chemical oxygen demand) of the wastewater is high and is in the range of 15,000 to 45,000 mg/l which can be a serious pollution problem. In the early 1980s there was a strong interest in producing ethanol from cassava and in 1983, a pilot plant was set up with a capacity of 1500 litres of ethanol per day to study the feasibility of ethanol from tapioca starch. The plant yield was in the range of 185-200 litres ethanol per ton of fresh cassava, and the production cost of ethanol (99.5 per cent v/v) was estimated to be about $0.48/litre (at 1987 prices), including factory operation and depreciation costs (Thomas, 1990).

However, in spite of the technical success of the project, it seems unlikely that fuel ethanol will be produced from cassava, at least in the near future, with the prevailing oil prices. Instead biogas from wastewater treatment looks more promising and efforts are being made to this end. Laboratory and pilot plant studies have shown that it is technically and economically possible to produce biogas from the wastewater in a fixed-bed reactor. The pay-back period of the anaerobic digester system is estimated to be less than three years for a factory producing 70-80 tons of starch per day (Tanticharoen, 1990). The biogas produced from wastewater is estimated to be able to save $11,860 per month (at 1988 prices) in factory fuel costs.