Study On Upgrading And Reconstruction Analysis And Path Optimization Of Class ⅠB Standard Wastewater Treatment Plants

In order to protect inland water bodies and coastal environments,various provinces and cities have successively issued local wastewater discharge standards.The standards stipulate that the effluent discharge of wastewater treatment plants needs to be upgraded from Class ⅠB level of the Pollutant Discharge Standards for Urban Wastewater Treatment Plants to Class ⅠA or Quasi-IV standard.There are often multiple ways to upgrade wastewater treatment plants,but it is difficult to choose the most ideal way to treat wastewater in specific upgrading scenarios from a series of upgrading schemes.Furthermore,there are environmental impacts and costs associated with building materials,energy,and chemical use while improving water quality.Based on the above issues,this article uses model-based simulation,life cycle assessment,life cycle cost,and multi-attribute decision-making methods to quantify the environmental impacts and costs of upgrading paths under different scenarios.The article also selects the optimal paths through multi-attribute decision-making to provide decision support for managers and facilitate the sustainable development of regional environments.The main contents of this article are as follows:Based on a wide range of case studies,several representative upgrading processes for wastewater treatment plants were selected,including high-efficiency sedimentation tanks,activated sand filters,denitrification deep-bed filters,and constructed wetlands.The design calculations for each process unit in the upgrading path were conducted in combination with engineering cases and design manuals.The GPS-X software and regression equations were used to establish and simulate the operation process of each upgrading path.The size design parameters and relevant operating parameters were input into the software.The results showed that the upgrading paths designed in this study could meet the requirements of corresponding scenarios.The simulation results provided a basis for subsequent attribute analysis.The open LCA software was used to establish a life cycle assessment model for the construction and operation stages under two scenarios.The upgrading processes included improved AAO,activated sand filters,denitrification filters,constructed wetlands,and combined processes.Based on actual data from the wastewater treatment plant and the life cycle inventory,the life cycle costs of each upgrading path were calculated,including construction costs,operation costs,maintenance costs,and land requirements.The results showed that in the scenario of upgrading from Class ⅠB to Class ⅠA,the BAP2(improved AAO + high-efficiency sedimentation tank+ activated sand filter)had the smallest environmental impacts,BAP3(AAO +constructed wetland)had the lowest economic cost,and BAP1(AAO +high-efficiency sedimentation tank + denitrification deep-bed filter)had the smallest land requirement.In the scenario of upgrading from Class ⅠB to Class IV,the BSP4(improved AAO + high-efficiency sedimentation tank + activated sand filter)had the smallest environmental impacts,BSP5(improved AAO + constructed wetland)had the lowest economic cost,and BSP1(AAO + high-efficiency sedimentation tank +denitrification deep-bed filter)had the smallest land requirement.Based on the quantitative results of the attributes related to various upgrading paths,the TOPSIS model in multi-attribute decision-making was applied to evaluate the advantages and disadvantages of each upgrading path.Three sets of attribute weights with regional characteristics were obtained through interviews with decision-makers in Northeast,East China,and Southwest regions,respectively,and the final rankings of upgrading paths in different regions were obtained accordingly.The results show that for the scenario of upgrading from Level B to Level A,in the Northeast region,the optimal upgrading path calculated is BAP3(AAO + constructed wetland),while in East China and Southwest region,the optimal upgrading path calculated is BAP2(improved AAO + high-efficiency sedimentation tank + activated sand filter).For the scenario of upgrading from Level B to quasi-Class IV,the optimal upgrading path calculated in the Northeast,East China,and Southwest regions is BSP4(improved AAO + high-efficiency sedimentation tank + activated sand filter +constructed wetland).Moreover,the results show that the attribute weights in different regions may affect the selection of the optimal path,indicating that regional characteristics should be taken into consideration when selecting upgrading schemes for sewage treatment plants.