Comparison of alternative wastewater treatment plants using life cycle assessment (lca)

Abstract

This work aims to assess potential negative impacts of two non-conventional wastewater treatment plants (WwTP) through Life Cycle Assessment (LCA) methodology. Since such systems are designed to minimize environmental impacts of sanitary or industrial sewage disposal, they must be chosen and engineered taking into account overall impacts of its own construction, operation and maintenance. In this context, a powerful decision making tool to be used is LCA, since it carries a detailed study of potential emissions generated by a process or product. Collected data regarding two pilot WwTP led to construction of life cycle inventory (LCI) for a constructed wetland system and a system consisting of septic tank, submerged aerated filter and secondary decanter. Design of both systems aimed at secondary treatment of sewage. Chosen tools were ecoinvent 3.4 database, open source software openLCA 1.7 and ReCiPe 2019 Midpoint (H) method for data interpretation. Considering all 18 impact categories available, the wetland system generated higher potential emissions to the environment and in more categories when compared to the septic tank-filter-decanter system. Main categories of impact were terrestrial ecotoxicity, climate change, scarcity of fossil resources, human (non-carcinogenic) toxicity and water consumption for both systems, although not of the same relevance. However, the septic tank-filter-decanter system had significantly greater impact on terrestrial ecotoxicity when compared to all other categories of impact, being 3 times higher than the second most significant category (climate change) for this system. When compared to the wetlands, impact was 3.5 time higher. Results showed that materials used in the construction of both systems caused greater environmental impacts, especially glass fiber used for septic tank, filter and decanter, responsible for 79% of the impact in terrestrial ecotoxicity. Another significantly contributing flow was electricity consumption, responsible for impacts on water consumption, which was more significant in the septic tank-filter-decanter system due to pumping and aeration equipment.