The decentralized wastewater management approach has a true potential in Vietnam, also in urban and peri-urban areas where centralized wastewater collection and treatment systems are often not affordable. In urban areas of Vietnam, the conventional septic tank is the most common on-site wastewater treatment facility. However, the system has a limited treatment performance, and can not provide the treatment required to reach national effluent standards and to avoid water pollution. This paper presents an innovative way to improve the treatment efficiency of septic tanks. The Improved Septic Tank, also known as Baffled Septic Tank with or without Anaerobic Filter (BAST or BASTAF), developed and studied at the Centre for Environmental Engineering of Towns and Industrial areas (CEETIA), Hanoi University of Civil Engineering, represents a valuable and promising alternative to the conventional septic tank. Results of laboratory-and pilot-scale research on BAST and BASTAF systems show that at a hydraulic retention time (HRT) of 2 days, the BAST(AF) significantly increased the removal efficiencies in terms of BOD, COD and TSS compared with a conventional septic tank without any significant increase in construction expenses. The results indicated that a reactor combining one sedimentation/equalizing chamber followed by two up-flow chambers could efficiently treat domestic toilet wastewater. Average treatment efficiencies of 80–90% in terms of BOD, COD and TSS could be achieved. The addition of an anaerobic filtration chamber filled with charcoal or local-made recycled plastic balls (VABCO-K) could further increase removal efficiencies by 10% and prevent sludge wash out. Despite its virtues, the BAST(AF) system was not able to reach the strict wastewater discharge standards of Vietnam. Therefore a second study was conducted aiming at investigating post-treatment of BAST(AF) effluent with a vertical-flow constructed wetland. The study showed that treatment of BASTAF effluent in 2-stage vertical flow constructed wetland planted with locally available macrophytes, e.g. Typha Orientalis, Phragmites communis, and Dracaena fragrans allowed achievement of level A, Vietnamese standard for wastewater TCVN 5945-2005 in terms of COD, BOD 5 , TSS, TN, NH 4 -N and T-P.
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