The decentralized wastewater management utilizing existing infrastructure and low-cost natural treatment processes has a large potential in Vietnam. Centralized wastewater collection and treatment systems are often not affordable. Currently the septic tank is the most common on-site wastewater treatment facility in Vietnam. Nevertheless it has a limited treatment performance. The Improved Septic Tank, also known as Baffled Septic Tank with or without Anaerobic Filter (BASTAF or BAST) 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 3-chamber BAST followed by Anaerobic Filter significantly increased the removal efficiencies in terms of BOD, COD and TSS in comparison with a conventional septic tank of the same size. Average treatment efficiencies of 80–90% in terms of BOD, COD and TSS can be achieved. Another component of the study showed that post-treatment of BASTAF effluent in a 2-stage vertical flow constructed wetland (CW) planted with locally available macrophytes allowed the achievement of level A, Vietnamese standard for wastewater discharge in terms of COD, BOD5, TSS, TN, NH4-N and T-P. Results of this study are now being implemented in different provinces inVietnam.

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