Field-scale decentralized domestic wastewater treatment system: Effect of dynamic loading conditions on the removal of organic carbon and nitrogen.

The field-scale decentralized wastewater treatment system (DWTS) was developed with an anaerobic baffled reactor (ABR) and a newly configured hybrid constructed wetland (HCW) vegetated with Typha angustifolia and Canna indica to treat 42 kLd of domestic wastewater. Biorack baffled constructed wetland (BBCW) and baffled vertical flow constructed wetland (BVFCW) were used in the first and second stage of HCW respectively. DWTS was assessed for its efficiency to remove COD, BOD and TKN under high (varying flow and varying COD) and moderate (constant flow and varying COD) dynamic loading conditions. The tracer study and pertinent computation showed the good performance of DWTS in its hydraulic efficiency. COD of raw wastewater was the treatment-limiting step in ABR. BBCW sustained larger fluctuations in loading rates [hydraulic (0.43-10.29 m/m2.d) and organic (0.08-2.30 kgCOD/m2.d)]. The draining (unsaturated) conditions enhanced COD and BOD removal in BVFCW. DWTS was found to be efficient for the average removal of COD (70-90%) and TKN (40-65%). HCW contributed 50-60% and 70-80% to COD and TKN removal respectively. The quantification of impacts on treatment efficiency and sustainability of DWTS was demonstrated at field-scale under high and moderate dynamic conditions.