Energy Consumption And Environmental Impacts Of Wastewater Treatment System In China:a Hybrid Input-Output Analysis

Rapid urbanization and increasingly serious water pollution pose new challenges for the low-carbon and sustainable development of a city.One of the indispensable aspects of China's urbanization is the construction of urban wastewater infrastructure.With an inevitable rise in energy intensity and environment pollutions,the urban wastewater infrastructure must incorporate energy accounting and environment management into its wastewater planning to help it reduce the urban wastewater system's environmental footprint allowing it to pursue low-pollution sustainable development.This study proposed an input-output-based hybrid model of urban wastewater system,calculating life cycle energy and environmental pollution(including EP and GHG)in national wastewater systems.This approach is more comprehensive and less labor intensive than the traditional life cycle assessment.Additionally,this model is flexible in terms of data availability.Given more site-specific data,the model can also avoid the main defect of the input-output method.Conventional methods used in wastewater treatment plants(WWTPs)emphasizing removal of detrimental substances from wastewater are essential for protection of the aquatic environment and public health.However,they are associated with costs in terms of environmental problem shifting,such as energy consumption,solid waste production,and greenhouse gas emissions.An improved approach involving wastewater-derived resource recovery in WWTPs is recognized as one potential solution.However,the environmental impacts and benefits of such a substantial change remain uncertain.Based on input-output-based hybrid model of urban wastewater system,this study analyzed life cycle energy consumption and environmental footprint of four scenarios with two scenarios under the traditional substance elimination approach and two under the resource recovery approach.Results show that compared with the traditional approach,the energy consumption and environmental impact of the resource recovery approach were performed very well,especially the scenario2 of recovering nutrients via excess-sludge composting,GHG,EP and energy consumption of which was reduced by 88%,61%and 95%respectively compared with the scenario 1 of traditional approach.Within traditional approach,the scenario2 adopted sludge anaerobic digestion perfomed far better than the scenariol,GHG and energy consumption reduced by 28%and 19.7%respectively.WWTPs have varied performance at different treatment levels with varying effects on the natural environment.The WWTPs considered under the improved and conventional approaches were each hypothesized to treat municipal wastewater to several different sets of effluent standards for comparative investigation of the potential environmental impacts and benefits of the resource recovery approach for WWTPs.Three increasingly stringent discharge limits from Chinese discharge regulations(class 2,class 1B,and class 1A)were selected.Results show that for the traditional approach,secnario2 adopting sludge anaerobic digestion performs better under class 1B whilst scenario 1 better under class 2.For the resource recovery approach,senario2 recovering nutrient performs better underclass 1A whist scenariol better under class 1B.It is concluded in the overall estimation that the lower sustainability of wastewater treatment contributed by increasingly stringent discharge demands was offset and mitigated by the resource-recovery scenarios involved,and the scenario of recovering nutrients via excess-sludge composting was of more benefit.These results suggest that implementation of this transition for WWTPs should be studied carefully in different temporal and spatial contexts.