Life Cycle Assessment and Cost Analysis of Ozone-Biologically Activated Carbon and Reverse Osmosis-Based Direct Potable Reuse
Citation:
Morelli, B., S. Arden, K. McGaughy, Cissy Ma, M. Jahne, AND J. Garland. Life Cycle Assessment and Cost Analysis of Ozone-Biologically Activated Carbon and Reverse Osmosis-Based Direct Potable Reuse. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-24/214, 2024.
Impact/Purpose:
This study assesses the life cycle environmental and cost impacts for a series of indierect potable reuse (IPR) and direct potable reuse (DPR) water treatment system configurations in Gwinnett County. The analyses advances the understanding of the environmental impacts and benefits of different water reuse strategies, especially commonly used DPR treatment trains relying on Reverse Osmosis (RO) vs an Ultraviolet Advanced Oxidation Process (UV AOP). The results shew light on the local specificity, environmental impacts and cost consideration in planning and designing DPR.
Description:
This is a life cycle assessment (LCA) and life cycle cost analysis (LCCA) case study that estimates the environmental impact and cost of an existing indirect potable reuse (IPR) water system in Gwinnett County, Georgia, compared to four hypothetical direct potable reuse (DPR) scenarios. One DPR treatment configuration is the fully advanced treatment (FAT) system, widely used in California for DPR, which relies on reverse osmosis (RO) and an ultraviolet advanced oxidation process (UV AOP). The second DPR treatment configuration consists of a modified ozone-biologically activated carbon (ozone-BAC) treatment process with enhanced biological nitrogen removal and high-dose UV. Two blend ratio scenarios are examined for each DPR treatment system, representing 50% and 80% reuse rates. Blend ratio blend ratio refers to the fraction of influent to the drinking water treatment facility that is sourced directly from the water resource recovery facility. This research was carried out as a partnership between Gwinnett County and the U.S. Environmental Protection Agency with the goal of advancing understanding of the environmental impacts and benefits of DPR and IPR, as well as the potential comparative environmental and cost advantages of ozone-BAC systems that have greater feasibility in inland regions where RO brine management can be difficult or costly. This project builds on a report released in 2018 by the Water Research Foundation that documents the results of a pilot project evaluating the feasibility of non-RO DPR at Gwinnett County’s wastewater and drinking water treatment facilities. This analysis expands on the scope of that project to include an assessment of life cycle environmental impacts while addressing water quality exceedances observed at higher blend ratios. The treatment configurations have been updated to address water quality issues related to nitrate, bromate, N-nitrosodimethylamine, cyanide, and total dissolved solids (TDS). Study results suggest that local context is important when considering the feasibility, cost, and environmental impact of DPR projects. Even with the presence of a low-TDS blending source (Lake Lanier), ozone-BAC DPR is only feasible in Gwinnett County at the 50% blend scenario; at the 80% blend scenario, side stream RO is needed to keep TDS from accumulating to unacceptable levels in the potable supply. In all DPR scenarios, the need for additional nutrient and TDS removal results in higher costs and environmental impacts relative to the IPR baseline in all environmental impact categories except eutrophication potential and water scarcity, though water scarcity benefits are small and due to the very low water scarcity of Gwinnet County. Environmental impacts in acidification potential, climate change potential, cumulative energy demand, fossil resource scarcity, particulate matter formation and smog formation potential increase by 10–30% in the ozone-BAC 50% blend scenario, 45–65% in the ozone-BAC 80% blend scenario, and 80–160% in the RO DPR scenarios. Adopting DPR systems leads to 55–95% reductions in eutrophication potential associated with the addition of denitrification filters and RO processes. The energy required to operate the RO treatment and brine management processes is the primary driver of increased environmental impacts for RO DPR, whereas both chemicals and energy tend to drive impacts of ozone-BAC DPR. Given the importance of energy inputs, the local electricity grid can have a considerable effect on environmental impacts. Results of one sensitivity analysis show that the U.S. grid region can affect baseline environmental impact results by −70% to +185% depending on the impact category and grid region selected.