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Life Cycle Assessment and Cost Analysis of Mixed Wastewater and Graywater Distributed Treatment for Water Reuse in San Francisco
Cashman, S., B. Morelli, Xin Ma, J. Garland, AND M. Jahne. Life Cycle Assessment and Cost Analysis of Mixed Wastewater and Graywater Distributed Treatment for Water Reuse in San Francisco. AWWA 2019 Sustainable Water Management Conference, Tucson, AZ, March 31 - April 03, 2019.
To explore the environmental impacts and life cycle cost of decentralized wastewater treatment coupled with on-site, non-potable reuse (NPR) as a strategy for alleviating water scarcity. The stakeholders that would be interested in this study and apply the results including local communities; utilities, OW; OWM; Regions; LCA practitioners, decision makers, academia; experts.
Communities such as San Francisco, CA are promoting decentralized wastewater treatment coupled with on-site, non-potable reuse (NPR) as a strategy for alleviating water scarcity. This research uses life cycle assessment (LCA) and life cycle cost analysis (LCCA) to evaluate several urban building and district scale treatment technologies based on a suite of environmental and cost indicators. The project evaluates aerobic membrane bioreactors (AeMBRs), anaerobic membrane bioreactors (AnMBRs), and recirculating vertical flow wetlands (RVFWs) treating both mixed wastewater and source separated graywater. Life cycle inventory (LCI) data were compiled from published, peer reviewed literature and generated using GPS-X™ wastewater modeling software. Several sensitivity analyses were conducted to quantify the effects of system scale, reuse quantity, AnMBR sparging rate, and the addition of thermal recovery on environmental and cost results. Results indicate that the volume of treated graywater is sufficient to provide for on-site NPR applications, and that net impact is lowest when the quantity of treated wastewater provides but does not considerably exceed NPR demand. Of the treatment options analyzed, the AeMBR and RVFW both demonstrated similarly low global warming potential (GWP) impact results , while the AeMBR had the lowest estimated system net present value (NPV) over a 30-year operational period. The addition of thermal recovery considerably reduced GWP impact for the AeMBR treatment process it was applied to, and similar benefits should be available if thermal recovery were applied to other treatment processes. The AnMBR treatment system demonstrated substantially higher GWP and cumulative energy demand (CED) results compared to the other treatment systems, due primarily to the need for several post-treatment processes required to prepare the effluent for disinfection. When the quantity of treated wastewater closely matches NPR demand, the environmental benefit of avoiding potable water production and distribution (for non-potable applications) leads to net environmental benefits for the AeMBR and RVFW treatment systems. The same benefit is possible for the AnMBR if intermittent membrane sparging can successfully prevent membrane fouling.