Study On Energy-saving And Emission-reduction Of Coal Chemical Wastewater Treatment Based On Life Cycle Assessment

Coal chemical wastewater is a kind of typical industrial wastewater with high ammonia nitrogen and difficult to be treated,which has a wide range of sources and different water quality,high pollutant concentration and high toxicity,rich organic matter species and difficult to biodegrade.Therefore,the treatment of coal chemical wastewater is bound to be a process of high energy consumption,high material consumption and high discharge.At present,most of the studies focus on how to improve the removal effect of pollutants,while ignoring the negative environmental benefits caused by the process itself due to energy consumption and greenhouse gas emission.Based on life cycle assessment(LCA),this study analyzes the environmental impact of coal chemical wastewater treatment system itself,and studies the coal chemical wastewater treatment system from two aspects: pollutant removal efficiency and life cycle environmental impact.On the premise of ensuring removal efficiency,the energy saving and emission reduction space of coal chemical wastewater treatment is further excavated,and the energy saving and emission reduction scheme is put forward and the benefit analysis is carried out.The main research contents and conclusions are as follows:(1)Taking coking wastewater as the research object,the pollution removal capacity of its treatment system is analyzed.The results show that the NH4+-N concentration in raw water of coking wastewater is as high as 4000~5000 mg/L,and the average removal rate of steamed ammonia unit reaches 97.6%.The effluent NH4+-N concentration of both AOAO unit and AOO unit can be below 15 mg/L,but there are significant differences in TN removal capacity.The average TN removal rate of AOAO unit with segmentalized influent is 93.4%,while that of AOO unit is only 26.4%.The LCA modeling of coking wastewater treatment system shows that the total impact of each unit on the environment is as follows: AOO unit > segmented water intake AOAO unit >steamed ammonia unit > coagulation treatment unit > pretreatment unit > effluent discharge > sludge treatment unit.The contribution of the AOO unit to the 11 environmental impact indicators is greater than that of the segmented water intake AOAO unit.From the carbon footprint perspective,steamed ammonia is the largest carbon footprint contribution unit,accounting for 44.7%,followed by the AOO unit and the segmented water inlet AOAO unit,and the smallest sludge treatment unit.(2)Taking coal gasification wastewater as the research object,the pollution removal ability of its treatment system is analyzed.The results show that the denitrification efficiency of CANON unit is better than that of AO unit.If the deep denitrification unit adopts the SBR process,the total nitrogen reaches the standard rate high.The whole system has good stability,and the average total removal rates of NH4+-N and TN are 99.18% and 94.70%,respectively.The COD concentration of effluent after pretreatment unit was reduced to 151.41 mg/L,which met the discharge standard.The LCA modeling of coal gasification wastewater treatment system shows that the total impact of each unit on the environment is as follows: AO unit >CANON unit > pretreatment unit,effluent discharge unit,advanced denitrification unit > sludge treatment unit.If the anaerobic reaction is used as the means of pre-biological treatment,it can produce obvious environmental benefits.The contribution of CANON unit to 11 influencing indexes was smaller than that of AO unit,and the contribution of CANON unit was about 47.5% less than that of AO unit.(3)Analytic hierarchy process(AHP)was used to compare the biological nitrogen removal processes of 4 kinds of coal chemical wastewater.The results show that segmented water intake AOAO process is optimal from the point of view of technical performance,CANON process is optimal from the point of view of economic performance and environmental impact,and the best choice is to CANON process from three aspects.Based on the above research,this paper puts forward the energy saving and emission reduction scheme of coal chemical wastewater.Through the benefit analysis,it is found that the energy saving and emission reduction scheme has obvious energy consumption benefit and environmental benefit in coking and coal gasification industries respectively.