Research On Environmental Impact Assessment And Energy Recovery Optimization Of Wastewater Treatment Plant Based On LCA

Sewage treatment is an environmental protection project.The sewage containing high pollutants is discharged after being treated to meet the standards,reducing the discharge of pollutants and protecting the water environment.However,sewage treatment is a high-energy-consuming project,which consumes a lot of energy and produces other secondary pollution.The traditional environmental impact assessment method of sewage treatment plants fails to fully consider the total load on the environment at different stages,and has certain limitations.Life Cycle Assessment（LCA）,as an internationally popular and standardized scientific assessment method,is a technology that quantifies the environmental impact of research objects at all stages.LCA not only considers the overall material and energy input and output flow,but also considers the evaluation of the potential environmental impact of the system throughout the life cycle.When applying LCA to the environmental impact assessment of sewage treatment plants,LCA is not limited to a certain stage or a certain index,but can also cover the entire life cycle of the sewage treatment plant,which helps to find the root cause of environmental problems in the sewage treatment process.Conducive to the overall process control of sewage treatment.In view of this,this study selected LCA,with the aid of life cycle Ga Bi software,taking a sewage treatment plant in Jilin Province as a case,collecting and sorting out various relevant data of the CAST process and A²/O-MBR process before and after the upgrading of the sewage treatment plant.Analyze and evaluate the environmental impact of the sewage treatment plant upgrading project;at the same time,under the existing sewage treatment process conditions,add efficient energy recovery means to evaluate the improvement significance of its comprehensive environmental impact on the sewage treatment plant,so as to finally achieve the sustainable development goal.The research results are as follows:1)Targeted sewage treatment plant acidification potential（AP）,eutrophication potential（EP）,freshwater ecotoxicity potential（FAETP）,global warming potential（GWP）,human toxicity potential（HTP）,ozone depletion potential（ODP）,Photochemical smog production potential（POCP）and terrestrial ecotoxicity potential（TETP）8 environmental impact category weight values are 0.24,0.17,0.09,0.33,0.05,0.03,0.02 and 0.06.Among them,GWP has the highest weight value and POCP has the lowest weight value.2)Before and after the upgrade of the target sewage treatment plant,the CAST process and A²/O-MBR process,the potential value of comprehensive environmental impact increased from 2.27x10^-6/FU before the transformation to 3.77x10^-6/FU after the transformation,an increase of 66.52%.Among the eight environmental impact categories,the potential value of other environmental impacts except EP is greater than that before the transformation,that is,after the sewage treatment plant is upgraded,the increased negative environmental impact is greater than the environmental benefit brought by the improvement of water quality.Therefore,while ensuring the quality of effluent water,it is necessary to reduce environmental impact through technical improvements in energy saving and consumption reduction or energy recovery.3)Among the 8 environmental impact categories of the target sewage treatment plant,except for the ODP sludge treatment stage of the CAST process before the transformation>the biological treatment stage>the pretreatment stage,the CAST process and the A²/O-MBR process of the other environmental impact categories are both before and after the transformation.It is biological treatment stage>sludge treatment stage>pretreatment stage.GWP,HTP,EP and AP are the main environmental impact categories of the target sewage treatment plant.Among them,the impact of GWP,HTP and AP mainly comes from the biological treatment electricity of sewage treatment plants,while the impact of EP mainly comes from the biological treatment process.The main sources of environmental impact are CO₂and CH₄,HTP is arsenic and nickel,EP is P,N and COD in effluent discharge,and AP is acidified gas such as SO₂and NO_X.4)Based on the A²/O-MBR process of the current target sewage treatment plant,and on the premise of making up for the electricity consumption deficit before and after the upgrade,a high-efficiency energy recovery scheme with water source heat pump and anaerobic digestion is proposed.The environmental impact potential value of the sewage treatment plant after the implementation of energy recovery has dropped from 3.77x10^-6/FU before recovery to 1.79x10^-6/FU,which is a 52.59%decrease.Among them,the environmental impact category with the largest reduction is GWP,followed by HTP,and ODP has the smallest reduction.Compared with the CAST process before the upgrade,the potential value of environmental impact after energy recovery is also reduced by 21.05%,and the reduction is mainly from the environmental impact categories of EP and ODP.When the energy recovery plan meets the effluent quality standards,the overall environmental impact has also been improved.Therefore,in the future operation of the sewage treatment plant,attention should be paid to energy recovery to improve the environmental impact of the sewage treatment plant.