Effluent quality and reuse potential of domestic wastewater treated in a pilot-scale hybrid constructed wetland system

Abstract

The study investigates treatment and reuse potential of domestic wastewater of a small community of about 30 people sequentially by anaerobic pretreatment followed by horizontal (HSSF-CW) and vertical (VSSF-CW) sub-surface flow constructed wetlands operated in series. The organic and suspended solids load to the hybrid wetland system was decreased by anaerobic pretreatment. HSSF-CW mainly removed organic matter and supported denitrification whereas VSSF-CW mainly obtained nitrification and phosphorus removal. Recirculation of the effluent increased particularly total nitrogen removal in the wetland system. The study involves evaluation of the whole system in terms of effluent quality. It was achieved on average >95% organic matter and >90% nitrogen removal in the hybrid constructed wetland system with anaerobic pretreatment at a specific wetland surface area of only about 1 m(2) per person. Average mass removal rates were 21.17 gCOD/m(2)day, 5.58 gBOD5/m(2)day, 2.78 gTKN/m(2)day, 1.35 gTN/m(2)day, 0.44 gTP/m(2)day and 5.21 gTSS/m(2)day throughout the total duration of the operation. Consequently, the effluent met the regulations for discharge limits for organic matter and suspended solids. COD and TN concentrations decreased to below 20 mg/L in the effluent. It was also shown that effluent of the system could be reused for irrigation if it is disinfected properly.

Keywords: Anaerobic pretreatment; Domestic wastewater; Horizontal sub-surface flow constructed wetland; Vertical sub-surface flow constructed wetland; Water reuse.