Application of Emergy Analysis to the Sustainability Evaluation of Municipal Wastewater Treatment Plants

Municipal wastewater treatment plants consume much energy and manpower, are expensive to run, and generate sludge and treated wastewater whilst removing pollutants through specific treatment regimes. The sustainable development of the wastewater treatment industry is therefore challenging, and a comprehensive evaluation method is needed for assessing the sustainability of different wastewater treatment processes, for identifying the improvement potential of treatment plants, and for directing policymakers, management measures and development strategies. This study established improved evaluation indicators based on Emergy Analysis that place total wastewater, resources, energy, economic input and emission of pollutants on the same scale compared to the traditional indicators. The sustainability of four wastewater treatment plants and their associated Anaerobic-Anoxic-Oxic (A2O), Constant Waterlevel Sequencing Batch Reactor (CWSBR), Cyclic Activated Sludge Technology (CAST) and Biological Aerated Filter (BAF) treatment processes were assessed in a city in northeast China. Results show that the CWSBR process was the most sustainable wastewater treatment process according to its largest calculated value of Improved Emergy Sustainable Index (2.53 × 100), followed by BAF (1.60 × 100), A2O (9.78 × 10−1) and CAST (5.77 × 10−1). Emergy Analysis provided improved indicators that are suitable for comparing different wastewater treatment processes.