Energy and GHG accounting for wastewater infrastructure

Abstract

Ensuring water and energy security and lowering the emissions of Greenhouse Gases (GHGs) are now priority areas for urban planners. However, most studies considered different components of urban wastewater infrastructure in isolation. This paper calculates the total energy and GHG footprints of wastewater infrastructure, including the energy consumption of, and GHG emissions from, the transport and treatment of wastewater, taking Delhi as a case study. The net energy consumed by wastewater infrastructure was conservatively estimated at 0.26kWh/m3 (σ=0.101kWh/m3). Operating the infrastructure claimed 70% of the total energy, and electricity accounted for about 55% of the total energy. Nearly two-third of the total energy was used for treating the wastewater. The infrastructure for transporting wastewater claimed a greater share of the embodied energy of materials. Net GHG emissions from the wastewater infrastructure were estimated at 1.426kg CO2-eq/m3 (σ=0.41kg CO2-eq/m3). Fugitive emissions contributed 53% of the total daily GHG emissions. The study revealed a trade-off between energy savings and environmental and GHG implications of wastewater infrastructure. Unlined open drains had lower GHG emissions and negligible energy use but an adverse impact on the environment and public health. Decentralized wastewater infrastructure is energy efficient in terms of the amount of pollutants removed but consumes more energy per unit volume of wastewater treated. Producing energy from the biogas generated in the process lowered the energy and GHG footprints of wastewater infrastructure by 0.10kWh/m3 (σ=0.01kWh/m3) and 0.08kg CO2-eq/m3 (σ=0.01kg CO2-eq/m3) respectively.