Financial analysis of decentralized water reuse systems in mission critical facilities at U.S. Army installations

Abstract

Given increased frequency of droughts and other extreme events exacerbated by climate change, decentralized water reuse is being increasingly considered as a key opportunity for increasing resiliency and sustainability by reducing net municipal water demand and emergency resupply needs. Initial building scale approaches, such as onsite treatment and reuse of wastewater for toilet flushing has not been economically favorable in many cases. Return on investment (ROI) of such projects is limited by the capital and annual expenditures relative to the cost savings. This study applied integrated building scale cost models to assess the potential economic benefits of more advanced decentralized water reuse frameworks (e.g., reclaimed gray water for shower and laundry, reclaimed gray water for server cooling), with the ultimate aim of providing more economical approaches to increase sustainability and resiliency of buildings at U.S. Army installations. This study developed life cycle cost models of different building water reuse frameworks to characterize associated life cycle costs of systems and benefits in terms of return on investment. In an existing barracks building occupied with 500 personnel, both gray and black water treatment and reuse systems for toilet flushing do not provide economic benefit within system design life of 20 years. Incorporating broader water end uses such as shower and laundry resulted in a financial benefit after 26 years, with greater benefits at higher building occupancies. Also, economically favorable water reuse opportunities exist at Army data centers that require 130 kgal per day for server cooling. By performing sensitivity analysis over a range of key parameters – unit price of water, system capital costs, discount rate, and wastewater recovery percentage – the most important drivers of ROI were identified. In the context of current Army Directive 2020-03 Installation Energy and Water Resiliency Policy, the results support financially viable approaches for implementation of water reuse in military facilities that can also reduce resupply demands in grid-down or other emergency scenarios.