Comparative evaluation of different operation scenarios for a full-scale wastewater treatment plant: Modeling coupled with life cycle assessment

All inputs and outputs of a technical system can be interpreted from an environmental point of view and some modifications, that are less harmful to the environment, can be incorporated into the system by using the life cycle assessment (LCA) approach. The energy footprint of wastewater treatment plants (WWTPs) is one of the most important environmental indicators. The sustainability of wastewater treatment systems can be evaluated in terms of energy consumption based on LCA. The aim of this study was to determine the environmental performance of a biological nutrient removal (BNR) plant in conjunction with mathematical modeling and the LCA approach based on three scenarios, which would reduce the net electricity consumption of the treatment plant by 10%. Three scenarios were constructed by the combinations of different values in dissolved oxygen (DO) concentration, sludge retention time (SRT) and internal recirculation (IR) parameters. A mathematical modeling study was carried out in order to determine the values of those parameters that decreased the net electricity consumption by 10%. Scenario 0 was developed based on a reference WWTP with default DO concentration, SRT and IR. The pairs of SRT and IR; SRT and DO; IR and DO were analyzed in Scenario 1, 2 and 3, respectively. The results showed that the global warming impact category has approximately the same values in Scenario 0 and Scenario 1 and these scenarios have the best performances in this category. Scenario 0 is also the best environmental performing with respect to marine eutrophication, while it has the highest environmental loads in terrestrial ecotoxicity and fossil resource scarcity categories. In freshwater eutrophication, Scenario 1 has the best environmental performance while the highest environmental burden in marine eutrophication is occurred in Scenario 1. Moreover, Scenario 1 and Scenario 2 have the same values and the worst environmental performances in the terrestrial acidification impact category. Scenario 1 and 2 have much better performances in fossil resource scarcity impact than in other scenarios while Scenario 2 is the worst environmental performing with respect to the global warming besides terrestrial acidification. Scenario 3 has a worse environmental performance in the freshwater eutrophication category in comparison to other scenarios, while it has the best environmental performances in the terrestrial acidification and terrestrial ecotoxicity categories. Scenario 1, 2 and 3 have better environmental performances in energy-related impact categories compared to the baseline scenario.