Energy efficiency assessment of China wastewater treatment plants by unit energy consumption per kg COD removed

Unit energy consumption per kg pollutant removed (kWh/kgCOD_removed) is used for the first time in assessing and ranking the sustainability of main treatment technologies of 1215 wastewater treatment plants (WWTPs) in China. The metric better measures the sustainability of main treatment technologies in WWTPs than unit energy consumption per cubic meter treated (kWh/m³). The energy consumption data of these WWTPs were selected from the database of 1399 WWTPs to evaluate the energy efficiency of different treatment technologies. 80.3% of the WWTPs applied anaerobic-oxic plus anaerobic–anoxic–oxic, oxidation ditch, and sequencing batch reactor as main technologies. Statistical analysis shows that the unit energy consumption of WWTPs decreases with increasing design flow rate, operation loading rate, and influent COD concentration. For example, the average unit energy consumption of SBR decreases from 2.76 kWh/kgCOD_removed to 0.83 kWh/kgCOD_removed when the design flow rate increases from less than 10,000 m³/d to 100,000–200,000 m³/d. The mean unit energy consumption of SBR decreases from 1.71 kWh/kgCOD_removed to 1.32 kWh/ kgCOD_removed and 2.85 kWh/ kgCOD_removed to 0.63 kWh/kgCOD_removed as the operation loading rate and COD removal increase from 40% to 100% and from less than 150 mg/L to over 450 mg/L, respectively. SBR has the lowest unit energy consumption among all the technologies. Therefore, SBR might be the most appropriate technology in small and medium-scale WWTPs in China. Regression equations were developed to predict the unit energy consumption for sustainable design treatment trains by input variables such as design flow rate, operation loading rate, and influent COD concentration.

本研究首次采用每去除1千克化学需氧量（Chemical Oxygen Demand, COD）的单位能耗（kWh/kgCOD_去除），对中国1215座污水处理厂（wastewater treatment plants, WWTPs）的主流处理工艺可持续性开展评估与排序。相较于每处理1立方米污水的单位能耗（kWh/m³），该指标更能精准衡量污水处理厂主流处理工艺的可持续性水平。本次研究选取的1215座污水处理厂能耗数据源自1399座污水处理厂的数据库，用于评估不同处理工艺的能源利用效率。其中80.3%的污水处理厂采用厌氧-好氧（anaerobic-oxic）+厌氧-缺氧-好氧（anaerobic-anoxic-oxic）、氧化沟（oxidation ditch）以及序批式反应器（sequencing batch reactor, SBR）作为主流处理工艺。统计分析结果显示，污水处理厂的单位能耗随设计处理规模、运行负荷率以及进水COD浓度的升高而降低。例如，当设计处理规模从不足10000 m³/d提升至100000~200000 m³/d时，序批式反应器的平均单位能耗从2.76 kWh/kgCOD_去除降至0.83 kWh/kgCOD_去除；当运行负荷率从40%提升至100%、进水COD浓度从不足150 mg/L升至450 mg/L以上时，序批式反应器的平均单位能耗分别从1.71 kWh/kgCOD_去除降至1.32 kWh/kgCOD_去除、从2.85 kWh/kgCOD_去除降至0.63 kWh/kgCOD_去除。在所有处理工艺中，序批式反应器的单位能耗最低，因此其或许是中国中小型污水处理厂的最优适配工艺。本研究还构建了回归方程，可通过设计处理规模、运行负荷率以及进水COD浓度等输入变量，预测可持续设计处理流程的单位能耗。