Defining a wastewater treatment plant design to improve environmental performance using the life cycle assessment methodology

Abstract

Although materials recovery is presented as a green solution for Wastewater Treatment Plants, recovery systems have material and energy use, and environmental impacts. Few articles were found performing the Life Cycle Assessment of nexus Wastewater Treatment Plants and even fewer performing impacts mitigation. This work aims to o mitigate a water-energy-food nexus Wastewater Treatment Plant impacts through the use of the Life Cycle Assessment methodology. As the base scenario, this work considered the following systems: 1) Water-line: Upflow Anaerobic Sludge Blanket followed by High Rate Aerobic System, microalgae biomass system (coagulationflocculation-sedimentation), sand filter and chlorination; 2) Sludge line: dewatering, anaerobic digestion, sludge bed and liming; 3) Biogas line: gasometer, biogas purification, and heat and power co-generation. The alternative scenarios considered: use of ferric chloride for coagulation, thermal and alkaline hydrolysis, CO2 recirculation in the High Rate Aerobic Pond, a combination of thermal hydrolysis and CO2 recirculation, membrane system, a system with no resource recovery, a system only with water recovery, and a system with biogas recovery. The Proknow-C methodology was used for the literature review and Life cycle assessment to mitigate environmental impacts. The present contribution considered the content of ISO 14040 and ISO 14044 (2006) to carry out the research. Additionally, the software openLCA 1.9, and the database Ecoinvent 3.5 were chosen. The following categories were evaluated: Global Warming Potential and Global Temperature Potential (IPCC 2013); Cumulative Energy Demand (CED); Acidification, Human Toxicity, Marine and freshwater Eutrophication and marine, freshwater and terrestrial Ecotoxicity (ReCiPe (H) 1.13 2008). Regarding the review study, the primary conclusion relies on the gaps found in the literature: lack of a specific ISO norm and lack of replicable works that can be used to be compared in future papers. Results showed that the best environmental performance was obtained in the scenario that presents CO2 recirculation and thermal hydrolysis, which offers the highest energy and biosolids production. Moreover, most of the environmental impacts from all systems were derived from the transportation and manufacture of chemical products needed in the wastewater treatment (coagulants, sodium hydroxide, chlorine, and others). The sensitivity analysis did not show significant modifications in the impacts measured by the systems, except for transportation variation in scenario 5, since this scenario had high distance transportation in the base scenario