Evaluating sludge management strategies using wastewater treatment plant simulations and life cycle assessment

Abstract

The goal of this study is to compare the environmental and energy performance of three sludge management scenarios at a wastewater treatment plant in Mexico, using process simulations and life cycle assessment (LCA) to assess energy use, environmental impacts, and costs. The functional unit is one cubic meter of treated influent wastewater, including sludge treatment and disposal. Screw press, thermal drying, and anaerobic digestion (AD) were assessed for energy use and environmental impacts, focusing on global warming potential, terrestrial acidification, freshwater eutrophication, and fossil resource scarcity. The Base Case scenario assumes a 50/50 distribution of wastewater flow between two biological treatment lines (anoxic/oxic and conventional activated sludge), with sludge equally treated by drying and screw pressing. The Best-Case scenario directs all flow to the anoxic/oxic line and treats all sludge through AD with electricity and heat recovery. Compared with the Base Case, the Best-Case scenario reduced energy use by 14%, corresponding to a specific energy savings of 0.04 kWh/m³, and achieved annual cost savings of 35,891 USD. The key challenges included limited data on sludge characteristics and disposal practices in Mexico, which required careful adaptation. LCA was enabled through process simulation, which provided site-specific inventory data despite limited regional reporting.