A pilot scale high-rate contact stabilization process with primary sedimentation for energy-neutral wastewater treatment

Abstract

This study investigates the organic carbon removal performance and carbon recovery potential of a pilot-scale high-rate contact stabilization (HiCS) process with primary sedimentation (PS+HiCS), implemented at an advanced biological wastewater treatment plant (WWTP). COD fractionation of the grit chamber effluent revealed particulate, colloidal, and dissolved COD fractions of 74, 2, and 24 %, respectively. The PS+HiCS process was operated continuously at a flow rate of 1 m(3)/h for 214 days, with SRTs ranging from 0.63 to 2 days. HRTs were maintained at 23 min in the contact tank (CT) and 72 min in the stabilization tank (ST). Dissolved oxygen (DO) concentrations in both tanks were controlled at 1-3 mg/L, except for the SRT of 0.63 days when CT was intentionally kept non-aerated. A total COD removal efficiency of 85 % was achieved, and the COD oxidation reduced to 12.5 %. COD was captured with an efficiency of up to 65 % at 1 day of SRT. At an SRT of 0.88 days, the process demonstrated a net energy gaining potential of 0.32 kWh/m(3) with < 100 mg/L effluent COD. This study highlights that domestic wastewater can be treated in an energy-neutral or energy-positive manner using the proposed PS+HiCS process, providing a sustainable solution for wastewater management.