Analysis And Comparison On The Life Cycle Environmental Imapcts Of Wastewater Treatment Process

In recent years, various provinces and cities have promulgated new local wastewater discharge standards which stipulate that the effluent of wastewater treatment plants should meet the standard of Class A. The wastewater treatment plants generally take some methods such as improving treatment process or increasing dosage of chemicals to make the effluent quality reach to new standard, however, those approaches would reducing ending discharge environmental impact and increase energy consumption in the front at the same time resulting the transfer of environmental problems. Therefore the problems of how the environmental impact of different wastewater treatment processes is and how the wastewater treatment plant environmental impact change before and after the new policy implementation on the base of effluent quality reach to Class A which are the wastewater treatment plants facing. Based on the above problem, this paper used life cycle assessment (LCA) which based on input-output theory to assessed different wastewater treatment processes and the results would provide decision support for managers and good for regional environment sustainable development.The main contents of this paper are as follows:(1) Gabi 5.0 software was used to build the wastewater treatment operation stage life cycle assessment model of wastewater treatment plants of A and B which treatment processes are Biological Aerated Filter (BAF) and Constant Waterlevel Sequencing Batch Reactors (CWSBR). Water reuse factor was considered into evaluation and the results showed that the environmental impacts of CWSBR were lower than those of BAF. Both of two processes the results of Marine Aquatic Ecotoxicity Potential (MAETP) were the largest and the result of Ozone Creation Potential (ODP) were the smallest which can be ignored when compared with other types of impacts.(2) Wastewater treatment plant A was chosen as the object to compare its the original process and new technological environment before and after implementation new standard. The results showed that after implemented new policy the environmental impacts of new process were increased than before.(3) This paper pointed out the conception of net variables (Net Variable Quantity, NVQ) in order to calculated the whole environmental impacts and find the better water reuse rate. Took wastewater treatment plant A as example, calculated the NVQ of different water reuse rate from 40% to 100%, The results indicated that when the reuse rate between 60% and 70%, the value of NVQ changed from positive to negative,namely the water reuse can reduce total environmental impacts.