Embodied energy and greenhouse gas emissions from wastewater reuse strategies in Indian Himalayan region

Increasing water stress and high energy requirements in urban water systems (UWSs) makes it imperative to reduce water demand by adopting wastewater reuse. However, there is a gap in the existing literature about analysing the operation of hilly urban water systems (UWSs) and suggesting energy efficient and environmentally benign wastewater reuse strategies. The objective of this study is to investigate the water-energy-greenhouse gas (GHG) nexus for different wastewater reuse strategies in UWS located in the Indian Himalayan region. Potential scenarios for the direct potable and non-potable reuse in the region were analysed. The system boundary consisted of the construction and operation phase inputs. The functional unit of the study was 1 m3 of water supplied to the UWS. The data inventory was developed using process designs, site specific information, engineering calculations and commercial databases. The total embodied energy and total GHG emissions were estimated using the existing models based on mass balance approach. The hilly UWS uses 17.6 kWh/m3 of total embodied energy and emits 6.2 kgCO2eq/m3 GHG emissions in its present operation. Over 90% of energy and GHG emissions were associated with pumping, which is required to cover over 1000 m of elevation head. The combined reuse scenario comprising both non-potable and direct potable reuse had the lowest embodied energy use and GHG emissions with a magnitude of 12.9 kWh/m3 and 4.3 kgCO2eq/m3. By comparative assessment of potential reuse scenarios, the study provides rationale for adopting appropriate strategy based on water savings, energy use, and environmental interventions.