Life cycle impact analysis of tertiary treatment alternatives to treat secondary municipal wastewater for reuse in cooling systems

Life cycle impacts have been evaluated to compare and assess six tertiary treatment alternatives for secondary treated municipal wastewater for reuse in thermo-electric power plant cooling systems. Impacts during construction and operation of tertiary treatment processes using databases and characterization tools embedded in the process-based life cycle assessment (LCA) software, Simapro v7.3, and the Carnegie Mellon economic input-output LCA (EIO-LCA) 2002 model were estimated. Infrastructure cost estimates from life cycle cost analysis were used as inputs to the EIO-LCA model. Inputs to the process-based analysis included chemical doses added during and after tertiary treatment, approximate transport distance of chemicals from producer to treatment site, and energy generation to operate major equipment during treatment. Impacts considered included global warming potential (in kg CO₂ eq.), acidification (in kg SO₂ eq.), eutrophication (in kg N eq.) and ecotoxicity (in kg 2,4-D eq.) - estimated using TRACI model characterization factors. The environmental impacts analysis showed that manufacture of chemicals for tertiary treatment and conditioning, and electric power generation were the main processes that contribute to environmental impacts. Thus, alternatives with no or less tertiary treatment are recommended from an environmental impact perspective for reuse of secondary treated wastewater in cooling systems.