Analysis of the Water-Energy Nexus of Treated Wastewater Reuse at a Municipal Scale

Treated wastewater has the potential to be a feasible alternative to supply non-potable uses and avoid water scarcity in urban areas, but it is important to understand and compare the associated energy consumption and CO2 emissions. This study presents a comparative analysis of the water-energy nexus associated with the traditional water supply and to the alternative reuse of treated wastewater, both for non-potable purposes. A case study of a Portuguese municipality was considered, regarding golf course irrigation and municipal gardens irrigation. A balance between production and demand was established, and the energy consumption and CO2 emissions were calculated considering the supply with drinking water and with treated wastewater. Three scenarios were defined to analyze the water-energy nexus for different configurations of the potential end-uses: (1) golf course supply, (2) municipal irrigation supply and (3) simultaneous supply to the golf course and to municipal irrigation. A quality analysis was also carried out by comparing the records from discharged wastewater quality parameters with the limits presented in the legislation for each proposed non-potable use. The results show that all scenarios present significant annual savings from using treated wastewater instead of drinking water from the public network, especially scenarios 1 and 3, that consider the golf course irrigation (water costs decrease by about 60,000.00 EUR/year). Regarding the water-energy nexus, this study reveals that treated wastewater spends less energy on its production and supply and produces fewer CO2 emissions. The energy savings can reach an average value of about kWh/year, with 5300 fewer kg of CO2 emitted in the best scenario.