Performance of a high-rate activated sludge-integrated vertical-flow constructed wetland for municipal wastewater treatment

High-rate activated sludge (HRAS) coupled with constructed wetland (CW) processes is attracting growing interest in the carbon emissions reduction of wastewater treatment. However, the service effectiveness of CW for low-carbon performance of the HRAS-CW process is still vague, particularly in treating low carbon-to-nitrogen ratio municipal wastewater. In this study, a pilot-scale HRAS-integrated vertical-flow CW (HRAS-IVCW) demonstration plant was established to investigate its performance with respect to water quality, energy consumption and carbon emissions. Through the improved function of CWs, the HRAS-IVCW system achieved satisfactory treatment performance under influent conditions of low organic loading. Moreover, the electrical energy consumption for HRAS-IVCW system operation was 193.2 ± 6.2 mL CH₄/g COD, and 32.8 % could be compensated by energy recovery from excess sludge containing high organic content. In addition, an optimized redox environment in the IVCW module using dissolved oxygen allocation and metal oxide addition improved the element flow path and effectively enhanced the simultaneous nutrient removal and carbon emissions of the HRAS-IVCW system, resulting in 8.1–82.3 % lower carbon emissions than those of a similar process under equal TN removal. This study advances the practical application of the HRAS-CW process in the low-carbon design and operation of municipal wastewater treatment plants.