Water-energy-pollutant nexus assessment of water reuse strategies in urban water systems using metabolism based approach

In this study a combined water-energy-pollutant nexus and water metabolism assessment was developed to study the impacts of implementing water reuse in an Urban Water System (UWS). The model was based on the WaterMet2 tool which was able to track down water, energy and eutrophication flows over the main components of the UWS. The suggested method was demonstrated in a real case study in Mexico. Eight hypothetical reuse strategies including six greywater (GW) recycling options (decentralised) and two reclaimed water distribution (centralised) were simulated and compared with Business As Usual (BAU) strategy ('do nothing') over a long-term planning (30 years). The intervention options were set up at either 10% or 50% of adoption rates (proportional to household and demands within the UWS) to be implemented at years 10 and 20. The analysis showed that centralised strategies consume less energy but produce more eutrophication emissions than the BAU as opposed to GW strategies. The treatment technologies (efficiency, energy consumption) and adoption rates are key variables in selecting the least impacting reuse strategy. Combining GW strategies using low-energy treatment (such as wetlands) with high adoption rates the system outperforms the rest of the options in all of the impact categories. The proposed metabolic-nexus approach was able to provide useful information about the performance and environmental impacts of centralised and decentralised water reuse options to support management decisions.