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This study examined the feasibility of applying a membrane bioreactor to small wastewater treatment using a pilot-scale plant. The operation was continued for 336 days. From the start to 251st day, the operation was continued without membrane washing. During the latter term of the operation, however, suction pressure increased rapidly corresponding to the increase of sludge viscosity. Because sludge viscosity increase occurred right after the suspension of sludge wasting, excess sludge must be wasted at regular intervals in order to keep low sludge viscosity. More than 90 % of organic matter, suspended solids, and coliform bacteria were successfully removed. As far as nitrogen removal was concerned, denitrification was the rate determining step in this system. To enhance denitrification, the following three points should be considered: i) to concentrate inflow of raw sewage at the beginning of anoxic period, ii) to shorten aeration time, and iii) to maintain high MLSS concentration.

Bioethanol production from rice-straw is carbon neutral and less competitive with food supplies, so it provides great possibilities for resolving global issues. This study aims to conduct economic and environmental evaluations on rice-straw bioethanol production in Vietnam, where huge amounts of unused rice-straw are available, by a top-down life-cycle assessment by means of an inputoutput table. The economic impacts are evaluated by total costs, total production, and total added value; the environmental impacts are assessed by greenhouse gas emissions with consideration of life-cycle, i.e., the plant construction phase, production phase, and plant scrapping phase. Three technology scenarios are assumed: (1) present technology, (2) advanced technology with higher conversion rates, and (3) innovative technology with a new production method and economies of scale. The results demonstrate that, first, rice-straw bioethanol production can reduce annual gasoline consumption by more than 20 %, and plant construction costs account for 8-22 % of the total investment in Vietnam. Second, under the present technology, both economic and environmental net benefits are negative. However, the innovative technology makes both benefits positive. Third, under the advanced technology, the environmental net benefit is positive, while the economic net benefit is negative. This implies that satisfying economic viability is more difficult than attaining environmental viability in rice-straw bioethanol production. Therefore, technological development and transfer are necessary to make rice-straw bioethanol production feasible.