Supply-chain environmental effects of wastewater utilities
This letter describes a comprehensive modeling framework and the Wastewater-Energy Sustainability Tool (WWEST) designed for conducting hybrid life-cycle assessments of the wastewater collection, treatment, and discharge infrastructure in the United States. Results from a case study treatment plant which produces electricity using methane offgas are discussed. The case study system supplements influent with 'high-strength organic waste' to augment electricity production. The system balance is 55 kg of greenhouse gases per million liters of wastewater. Sensitivity analysis confirms that reusing biogas from anaerobic digestion for electricity reduces life-cycle greenhouse gas emissions by nine times. When biogas is captured and reused for electricity, material production (e.g., chemicals and pipes) and the corresponding supply chains, rather than energy production, are responsible for most of the environmental effects. When biogas is flared, the material and energy production contributions are similar.