Optimization and mechanism of coupling process between algal ponds and constructed wetlands for wastewater polishing and nutrient recovery

Abstract

Due to the lack of influent carbon source and the limited adsorption of the substrate, constructed wetlands (CW) could not achieve satisfactory removal of nitrogen and phosphorus. In this study, the coupling process between algal ponds (AP) and constructed wetlands (AP-CW) was proposed to enhance wastewater purification performance. The results showed that when 10.6 mg/(L‧d) microalgae were added into the CW, the best TN removal reached 90.3% and 1 g microalgae averagely promoted 0.291 g N removal in CW. In addition, a coupled model of AP-CW was established to find the optimal range of critical parameters. Based on effluent purification and nutrient recovery, the optimal parameters were determined as: 5 d HRT of AP and 0.4% microalgae reuse rate. With optimal parameters in AP-CW, the TN and TP removal were 94.18% and 85.80% respectively. For the engineering application, the microalgae suspended-attached mixed culture in AP was presented and the microalgae production was increased by 32.1%. Moreover, microalgae were suggested to be consecutively added to the CW daily to reduce the fluctuation of effluent pollutants. Based on the above optimization conditions, the nitrogen and phosphorus removal of optimized AP-CW increased by 110.4% and 416.4% respectively compared with a single CW, and 55.6% TN and 83.9% TP were recovered as bioresource. This study provides theoretical guidance and technical support for efficient sewage purification and nutrient recovery.