Carbon Footprint And Reduction Potential Of Chinese Wastewater Treatment Sector

Tackling global climate change calls for the joint efforts of all sectors and industries to reduce greenhouse gas(GHGs)emission.Wastewater is an important source of greenhouse gases.During wastewater treatment,the degradation of carbon(C)and nitrogen(N)was accompanied with formation and emission of GHGs,including methane(CH4).nitrogen dioxide(N2O)and carbon dioxide(CO2.).In addition,indirect GHGs emissions are caused due to the intensive consumption of electricity and chemicals during wastewater treatment.The United States and the European countries have done many researches in estimation of wastewater-associated GHGs emission.However,this field has been paid less attention in China,which owns the world’s largest and still growing wastewater sector.In particular,information about the emission sources,spatial distribution,influence factors and carbon emission reduction potential in the wastewater sector is still lacking.In this thesis,the development status of China’s wastewater sector was first evaluated and a life cycle analysis about the transformation and fates of C、N elements during wastewater collection and treatment was performed.Then,the GHGs emissions of municipal wastewater sector were estimated using Monte Carlo simulation method based on the official activity level data and the corrected emission factors were determined based on the literature.The results show that the GHGs emission of the municipal wastewater sector in China reached 54.14 million tons carbon dioxide equivalent(Mt CO2e)in 2016.The whole wastewater treatment sector produced 197 Mt CO2e GHGs,accounting for 1.71%of the national total emission.Wastewater treatment plant(WWTP)is the biggest emission unit in municipal wastewater sector(contributed to 60%of the total emission),followed by sludge disposal units(21%contribution).The GHG emissions are regionally unbalanced.Guangdong,Shandong,Jiangsu and Zhejiang were the four provinces that emitted most GHGs emissions in China.The carbon density of China’s municipal wastewater sector stabilized at about 0.92 kg CO2e/m3,indicating the WWTPs with activated sludge process is a non-negligible source of GHGs emission in China.The future trends of GHGs emission in China’s wastewater sector were estimated based on the possible implementation of three alternative wastewater treatment paradigms.If activated sludge process continues to be used as the main treatment process,China’s municipal wastewater sector is expected to produce 83.16 Mt CO2e GHGs in 2030.The whole wastewater treatment sector will emit 365 Mt CO2e GHGs,accounting for 2.95%of national carbon emissions.Such GHGs emission may be alleviated by shifting to more sustainable treatment paradigms.The first paradigm adopts high rate activated sludge process coupled with anaerobic ammonium oxidation,which may enable energy self-sufficiency in WWTPs and thus reduce around 79%of carbon emissions.However,this process still results in considerable N2O emissions.The second paradigm is anaerobic membrane bioreactor coupling ion exchange technology,which enables energy recovery and resource recovery simultaneously.This process will reduce 106%of carbon emissions,thereby hopefully turning the wastewater treatment sector from a GHG source to a sink.This work may provide valuable implications for guiding the future sustainable development of the wastewater sector and for completing the carbon emission assessment models,and will also promoting better knowledge and action on global warming control.