Decentralized graywater treatment by a combination of sequencing batch reactor and advanced oxidation processes for reuse in Vietnam

The availability of sufficient clean water has become an increasing problem even in regions with generally humid climates such as Vietnam due to rising water consumption, particularly in densely populated urban areas. The associated problems, such as an increasing scarcity of groundwater, pose major challenges for water management. Appropriate treatment and reuse of graywater, which accounts for a high proportion of total wastewater in households, can contribute significantly to solving this problem. In the present study, a combination of a biologically active sequencing batch reactor (SBR) and subsequent treatment by advanced oxidation processes (AOP) for decentralized graywater treatment is described as a promising option for water reuse in Vietnam. Treatment of synthetic graywater in a model reactor has shown that SBR is a suitable approach for efficient removal of bioavailable organic matter (BOD5 removal >95%), but that the resulting effluent does not meet the required quality criteria for reuse in terms of microbiological contamination, color and micropollutant levels. However, the subsequent AOP remedies these deficiencies. Thus, the number of coliforms could be reduced from 1320 to <1 MPN/100 mL, turbidity to <2 NTU and color by 75% to 4-6 Pt/Co-units. With the exception of terbutryn, the graywater-relevant micropollutants considered could be removed to such an extent by the subsequent UV/H₂O₂ treatment step within 60 min of treatment time that the requirements of the corresponding Environmental Quality Standard (EQS) values are met. Therefore, a combination of both methods enables efficient graywater treatment for a variety of reuse purposes. PRACTITIONER POINTS: For laboratory investigations, a synthetically produced greywater was produced on the basis of various literature references, which is representative of the Southeast Asia region under consideration. Aerobic biological treatment resulted in a significant improvement in water quality in terms of color and typical general wastewater parameters such as chemical oxygen demand (COD), BOD5, and ammonium. In contrast, the biological stage only insufficiently removed turbidity, coliforms, total P, total N, and a number of selected organic trace substances typical of greywater. Only subsequent treatment using a AOP process (VUV irradiation and peroxide) reduced all the parameters and studied pollutants to such an extent that the water can be reused, for example, for irrigation purposes or for groundwater recharge.