Life Cycle Assessment of a wastewater treatment plant in an urban area using the environmental footprint method

This study evaluated the environmental impacts of a wastewater treatment plant (WWTP) in the city of San Luis Potosi (Mexico) using the environmental footprint method in the life cycle analysis (LCA). The functional unit established was 1 m3 of treated water, considering a WWTP lifetime of 25 years. LCA integrated a detailed inventory of the evaluated system, incorporating the materials and energy inputs used in the WWTP infrastructure, operation and maintenance, and heavy metal concentrations in sludge. Likewise, the entire wastewater treatment train was included. SimaPro 9.3 software was used to model the processes, and the Ecoinvent v3.0 database provided the background data, assessing sixteen impact categories. Results revealed that the infrastructure and the tertiary treatment contribute to the impact categories of land use and ozone depletion, respectively. However, the operation contributes with values higher than 90% for 15 indicators, of which ten were due to the use of electric energy and the energy production form in Mexico. Heavy metal concentrations in the sludge contribute to human health effects and freshwater toxicity categories. These impacts could be decreased (up to 80%) if the sludge was not placed in the soil to be sun-dried. Therefore, improvement opportunities are based on reducing the distance between the pretreatment area and the WWTP to decrease the electrical energy consumption demanded by the pumping, using an alternate energy source to supply the demand of the WWTP, and sludge management in a controlled landfill or biogas production and use it in the lighting of the WWTP.