Energy Consumption Modeling And Energy Balance Evaluation Of Wastewater Treatment Plant

Wastewater treatment plants?WWTPs?are energy-intensive facilities,and managers are paying more and more attention to energy consumption in wastewater treatment processes.Previous studies have shown that the energy consumption varies significantly between different wastewater treatment processes,which indicates that for different treatment processes,the influence variables of energy consumption are also different.Exploring the variables affecting energy consumption in different treatment processes and predicting energy consumption are of great value to policy makers in planning new WWTPs and developing management plans to improve the energy efficiency of wastewater treatment.In addition,effectively utilizing the potential energy of the sewage treatment plant and realizing energy production is also one of the effective ways to achieve energy saving of the WWTP.Previous studies have shown that under certain conditions,WWTPs can achieve energy balance or even net energy production.However,information on the energy consumption and energy recovery potential of WWTPs as a function of wastewater influent characteristics is still very limited,and the need to assess the energy balance of WWTP has become an issue of increasing concern.Through statistical analysis of 832 wastewater treatment plant samples with a total of six treatment processes,this paper establishes an energy consumption model and uses a stepwise regression method to screen out key variables that affect energy consumption.The established energy consumption prediction models of six different processes show that the influent flow plays a very important role in the energy consumption of the WWTP using AAO,oxidation ditch,SBR and CASS processes,which means the energy consumption of these processes Affected by the scale of WWTPs.However,AO and CAST processes are less affected by the scale of WWTPs.Other variables,such as the amount of COD reduction,ammonia nitrogen reduction,and BOD₅ reduction,are important to further explain the energy consumption model.It is worth noting that the pollutant removal rate has little effect on the energy consumption of WWTPs.In addition,the correlation between COD-related variables and BOD₅-related variables is high.To avoid the problem of collinearity,one of the variables is often eliminated in the stepwise regression modeling process.The determination coefficients of the energy consumption models established by the new cost function are all above 0.6,and the determination coefficients of most process energy consumption models can reach above 0.8.Generally,the model is considered acceptable when the determination coefficient value is greater than 0.5.Therefore,the energy consumption model established is suitable for the energy consumption prediction in actual operation and provides relevant suggestions for the optimal operation of WWTPs.For the AAO process,a novel net energy consumption?NEC?model was developed for predicting the energy self-sufficiency level of WWTPs.From our results,exponential regression showed a high accuracy in predicting the annual energy consumption,the annual excess sludge production and the bioreactor surface area in WWTPs.Wastewater with more internal energy?determined by influent COD concentration and inflow rate?not only leads to higher energy consumption in WWTPs,but also results in an increase in the excess sludge production,bioreactor surface area and wastewater volume.This means that the WWTPs could achieve energy saving or even net energy production by incorporating sludge incineration,PV generation and thermal energy recovery.By combing regression analysis with theoretical formula,the annual net energy demand of WWTPs reached-0.187-0.466 k Wh·m^-3 in the range of wastewater condition studied(the influent COD concentration range of 60-800 mg·L^-1 and the inflow rate range of 1296-100000 m³·d^-1).The NEC model reveals that the net zero energy consumption may be achieved by integrating the better understandings wastewater internal energy,energy conversion methods and environmental media energy,which is of value to policy makers for the planning of new WWTPs and provides theoretical support for the selection of available energy recovery methods.