Impactof Revising Discharge Standard On WWTP’s Operational Decision

To alleviate the serious water pollutionissue, Chinese government has frequently and significantly tightenedwater pollutantsdischarge standards in the past 15 years. As a result, thedischarge violation rateand discharge fee ofwastewater treatment plant(WWTP)both went up. In order to meet the increasingly stringent discharge standards, WWTP could make full use of its current treatment capability by optimizing operation conditions. We use multi-objective decisionmodels to optimize WWTP’s operational decisions, to help WWTP meet varying discharge standards with minimal total cost(TC) or minimal life cycle environmental impacts(LCEI).And weevaluate current environmental protection policies by comparing and discussing the Pareto solutions of the multi-objectivedecision models based on different discharge standards.Simulating the wastewater treatment process in WWTPis the foundation of optimizing WWTP’s operational decision.We modify the influent data and key process parameters of Benchmark Simulation Model 2(BSM2), thenuse the modified BSM2 model as the simulation tool.In our study, the multi-objectivedecision models are estabilished through the following 4 steps. Firstly, based on Chinese Pollution Charge Policy and real discharge standards, we establish new fomulations ofdischarge violation rate and discharge fee. Secondly, we assess the life cycle impacts of WWTP and take it into account as one of the threeobjectives. Thirdly, webuild the multi-objectivedecision model from the view of operation,minimize the violation rate and the TCsimultaneously. Fourthly, webuild the multi-objectivedecision model from the view of environmental protection, minimize the violation rate and the LCEIof WWTP at the same time.At last, we compare anddiscuss the Pareto solutions of the multi-objectivedecision modelsbased on the 4-stage discharge standards of Shandong Xiaoqing River basin. Main conclusions are sumarried as follows:(1). Compared to the default operational decisions,WWTP could drasticallyreduce the TC or LCEI by implementing the Pareto solutions as operational decision. And the decision model could provide enough decision information for WWTP tocontrolarbitrary violation rates with minimal TC or minimal LCEI.(2). Under existing Pollution Charge Policy, frequently and significantly tightening the discharge standards will lead to a decrease in WWTP’s willingness to control violation rate and an increase in WWTP’s environmental damage. Besides, tightening the discharge standards will change the synergic relationship between controlling violation rate and reducing environmental damage. This synergic relationship, however, is the basic logic of environmental protection and wastewater treatment process.