Optimize The Urban Water System From A Perspective Of Water-Greenhouse Co-benefits

Water-energy-greenhouse gases are vital and closely related to human survival.Due to the rapid economic development,China has serious water shortage problems,outstanding water pollution problems,energy shortages,and huge pressure on greenhouse gas emission reduction.At the same time,the increase in reclaimed water applications and the improvement of wastewater treatment standards will result in more direct and indirect greenhouse gas emissions than direct wastewater discharge and conventional wastewater treatment processes.This shows that higher standards of effluent quality,less natural water supply and less greenhouse gas emissions have a multi-directional constraint on the construction of urban water systems.Therefore,under the premise of ensuring the water quality and quantity of water required by users,building an urban water system with balanced water and greenhouse gas emission reduction in water resources,water environment protection and water production process is a necessary condition for achieving sustainable development.To this end,this study established a greenhouse for water resources,water environmental protection and urban water production processes by quantitatively analyzing the relationship between water-energy-greenhouse gas emissions in urban water supply systems and sewage treatment systems(collectively referred to as urban water production processes).The urban water system management method and the water-energy collaborative management method aiming at the gas emission reduction and win-win situation.Based on the water flow in the urban water system,this study used a multi-source data at the regional scale to construct a quantitative relationship model between the water quantity,energy consumption and greenhouse gas emissions in the urban water production process for China.The local sensitivity analysis method was used to quantitatively analyze the impact of internal factors of water systems in China on urban water production energy consumption and greenhouse gas emissions.The results show that from the national scale,the energy consumption of urban water production mainly comes from the water supply subsystem.The greenhouse gas emissions from urban water production mainly come from the sewage treatment subsystem.From the regional scale,water consumption and long-distance water supply affect urban production.The main parameters of water energy consumption,and the proportion of thermal power in the local total power generation is the main parameter affecting the greenhouse gas emissions of urban water production.Based on the above model and key influencing factors,using the non-dominated sorting genetic evolution algorithm(NSGA II),this study proposes a method for constructing urban water systems from the perspective of water-greenhouse gas emission reduction.Firstly,the urban water supply system and sewage treatment system are taken as the research object,and the optimization model aiming at water saving and energy saving win-win,and the optimization model aiming at the win-win of wastewater pollutant emission and greenhouse gas emission reduction are respectively constructed.Secondly,the comprehensive system consisting of water supply system,sewage treatment system and electric power production system is taken as the research object,and the three-objective optimization model of water saving,wastewater pollutant emission reduction and greenhouse gas emission reduction is constructed.Taking the urban water production process in Tianjin as an example,the trial calculation and inspection were carried out.The results show that the optimization results can quantify and intuitively reflect the contradiction and synergy between water and greenhouse gas emissions in urban water production,and provide decision makers with a series of water-greenhouse gas emission reduction and win-win urban water system quantification.The results also show that synergistic optimization of urban water systems and local power production structures can achieve better results.Finally,this study coordinated the optimization of urban water systems and local power production structures in 31 provinces and cities across the country with the goal of water saving,wastewater pollutant emission reduction and greenhouse gas emission reduction.The optimization results confirm that the optimization model is versatile and effective throughout the country.This paper also proposes a quantitative control plan to achieve the goal of achieving a win-win situation for water-greenhouse gas emission reduction in response to the characteristics of water resources in various regions.The results suggest that for water-deficient areas,improving the sewage treatment rate of livestock and poultry farming in the sewage system is the first choice for regulation and control.In its water supply system,the use of decentralized reclaimed water and desalinated water to replace concentrated supply of long-distance water is an effective way,but not all areas of reclaimed water use are appropriate,but based on local water resources and energy conditions.There is an optimal upper limit for the use of recycled water.This result also demonstrates the need for water management using this optimization model.