Achieving low-carbon and sustainable wastewater treatment by controlling the flow of pollutants: A pilot scale investigation on reducing greenhouse gas emissions and enhancing resource recovery

To achieve the carbon peaking and carbon neutrality goals, the greenhouse gas (GHG) emission reduction of wastewater treatment plants (WWTPs) has aroused widespread concern in the society. This study calculated and evaluated the carbon footprint of mainstream anaerobic/anoxic/aerobic (AAO) process WWTPs. A coagulationsedimentation + microalgae and anaerobic digestion + land application (CSM-ADLA) process was developed for wastewater treatment. The new process rearranged pollutants control and employed treatment techniques of low GHG emissions according to the intergovernmental panel on climate change (IPCC) rules. Most of the organic pollutants (78.7 % of chemical oxygen demand) and organic nitrogen compounds (49.4 % of total nitrogen) were captured in sludge and lowered the loads of microalgae, and then the sludge underwent AD degradation. These designs avoided the above-mentioned pollutants from entering the biological treatment process, thereby reducing GHG emissions. A microalgae treatment featured with natural light source and no aeration was employed to refine the product water. The carbon emission of the CSM-ADLA process (i.e., 0.298 kg carbon dioxide equivalent/m3 wastewater) was 32.6 % of that of the conventional AAO process. Meanwhile, the CSMADLA process enhanced capture and utilization of carbon, nitrogen and phosphorus. Resource recycling provides an effective way for carbon emission reduction and avoids resource waste. In general, this process could be considered as a low-carbon, cost-effective and sustainable wastewater treatment technology.