A recirculating vertical flow constructed wetland for the treatment of domestic wastewater

A recirculating vertical flow constructed wetland (RVFCW) has been developed for the treatment of grey water. The overall aim of this research was to apply the RVFCW, a decentralized, small-scale system, to the treatment of domestic wastewater (DWW), modifying it, where necessary, to produce effluents that conform to Israeli regulations for urban landscape irrigation. Two RVFCWs were operated with and without a soil-plant component and with various recirculation flow rates (RFR) and treatment times. Without plants, at a RFR of 4.5 m³ h^-1 and 12 h treatment time, the average biological oxygen demand (BOD₅) and total suspended solids concentrations of the treated effluent were 5 and 10 mg l^-1, respectively. A kinetic analysis showed that even 6 h were sufficient to achieve the required effluent quality. Addition of the soil-plant component, which necessitated a reduction in the RFR, caused no changes in effluent quality, and its role in the treatment remained undetermined. In all operational modes, counts of E. coli were reduced from the order of 10⁶ to 10³ CFU 100 ml^-1, and further reduction to less than 10 CFU 100 ml^-1 was attained with a UV irradiation unit. In conclusion, the RVFCW produces high quality effluents, and can treat DWW at a potential organic load of over 120 g BOD₅ m^-2 d^-1.