Investigating Impacts Reclaimed Water Utilization And Sludge Disposal Ways On Comprehensive Performance Of Municipal Wastewater Treatment Systems Based On Emergy,Carbon Emissions And Economic Analysis

Sewage treatment is one of important measures for solving issues,related to water resource security and water resource sustainable utilization.Through reducing water pollution,sewage treatment can improve urban natural environment and watershed water quality.In recent years,the number of urban sewage treatment facilities of China has showed the fast-increasing trend and most of them have carried out crafts upgrading,which consumes lots of resources and energy sources and thus produces some negative effects on the surroundings.At the same time,the issues including low sewage resource utilization level,irregular harmless sludge disposal practices,weak operation and maintenance capacities are existed.Therefore,relevant research is needed to investigate impacts of reclaimed water and sludge disposal methods on the performance of sewage treatment systems,providing a basis for decision-making.According to characteristics of sewage treatment systems,this paper adopted improved emergy analysis,accompanied by carbon emission accounting and economic analysis,to compare effects of reclaimed water and sludge disposal methods as well as sewage treatment technologies on comprehensive performance of sewage treatment systems.Therein,based on considering pollutant emissions’ impacts,emergy analysis was used to evaluate environmental sustainability and Net emergy profit per unit sewage disposal(NEPU).Meanwhile,carbon emissions accounting method was applied to quantification of carbon emission intensity and carbon neutrality level,and economic analysis was used to assess Rate of return on investment(ROI)and Net economic profit per unit sewage disposal(NPU).Finally,an index-Synergistic index(SI),based on improved emergy sustainability index(IESI)and Carbon neutralization rate(CNR)as well as Rate of return on investment(ROI),was constructed to investigate synergistic effect among the three performance indicators.Two urban sewage treatment plants(A sewage treatment plant and B sewage treatment plant),located in Da-zhou city,Sichuan Province,as study cases,were studied using the proposed approach and related indictor systems based on their four scenarios,which were attained through different combinations of reclaimed water and sludge disposal methods.The main study results show that:(1)Results from emergy evaluation show that,emergy based indicators of scenarios of A sewage treatment plant are all superior to those of scenarios of B sewage treatment plant.Reclaimed water reuse and sludge-coupled incineration power generation can improve emergy-based environmental performance,and have more obvious effectiveness on scenarios of B sewage treatment.Sewage treatment technologies,reclaimed water and sludge disposal methods can all influence emergy based indicators;therein,sludge disposal methods have the largest effect on improved emergy yield rate(IEYR),and reclaimed water disposal methods have the greatest impact on improved environmental load rate(IELR)and IESI.Scenario 4 and Scenario 8 is the most sustainable scheme for A sewage treatment plant and B sewage treatment plant,respectively.(2)Results from carbon emission analysis reflect that,carbon emission related indicators of scenarios of A sewage treatment are all superior to those of corresponding scenarios of B sewage treatment plant.Reclaimed water reuse and sludge-coupled incineration power generation greatly raise carbon neutrality level and reduce carbon emission intensity.Sewage treatment technologies,treated water and sludge disposal methods can all affect carbon emission related indicators.Scenario 4 and Scenario 8 is the best scheme for A sewage treatment plant and B sewage treatment plant,respectively,according to carbon emissions and carbon neutrality level.(3)Results from economic analysis illustrate that,economic benefit of scenarios of A sewage treatment is all superior to that of corresponding scenarios of B sewage treatment plant.Reclaimed water reuse and sludge-coupled incineration power generation improve economic benefit of sewage treatment systems to varying degrees,especially for scenarios of B sewage treatment plant.Sewage treatment technologies,treated water and sludge disposal methods can all affect economic benefit of sewage treatment systems,especially sludge disposal methods.Scenario 4 and Scenario 8 has the best economic benefit for A sewage treatment plant and B sewage treatment plant,respectively.(4)Results from SI show that,comprehensive performance of scenarios of A sewage treatment plant is better than related scenarios of B sewage treatment plant.Reclaimed water reuse and sludge-coupled incineration power generation can enhance comprehensive performance of sewage treatment systems to varying degrees relative to original schemes,especially for scenarios of B sewage treatment plant.Sewage treatment technologies,treated water and sludge disposal methods can all affect comprehensive performance of sewage treatment systems,especially treated water disposal methods.Comprehensive performance improvement of sewage treatment systems should emphasize CNR and IESI.Scenario 4 and Scenario 8 has the best comprehensive performance for A sewage treatment plant and B sewage treatment plant,respectively.(5)One single evaluation method can reveal some specific advantages and disadvantages of each scenario,but results of based on diverse single evaluation methods could conflict one another during ranking different scenarios.In practice,generally decision-makers should consider environmental sustainability,carbon emission and economic benefit simultaneously.Compared with one single evaluation method,the proposed SI index and related methods can provide more complete decision-making information.Generally,comprehensive performance of A sewage treatment plant is superior to that of B sewage treatment plant.Therefore,A sewage treatment plant operates more mature and efficient in this region.Since reclaimed water reuse and sludge-coupled incineration power generation can better enhance comprehensive performance of B sewage treatment plant than A sewage treatment plant,so B sewage treatment plant should be considered when upgrading the existing sewage treatment plants.Sewage treatment technologies,treated water and sludge disposal methods can all affect performance indicators of sewage treatment systems to different degrees,so feasible study and performance evaluation should be carefully implemented before sewage treatment engineering projects being constructed.