Water is a critical measure for Department of Defense (DoD) sustainability and security. In the recent Executive Order 13693, DoD installations are required to further reduce potable water consumption by 2% each year until 2015, relative to 2007 baseline levels, setting the total reduction target at 36%. Many DoD installations aim to reduce water use intensity by more than 50%. To achieve 50% reduction in water use intensity, conservation and efficient fixtures alone are generally not sufficient. Reuse of wastewater to offset consumption of potable water needs to be integrated into the approach. The use of local, distributed wastewater reuse systems can enable specific opportunities with maximum return on investment to be targeted, but as more water reuse opportunities are pursued, the required levels of water treatment can also increase to protect health, environment, and infrastructure.

The objective of this project is to demonstrate and validate the performance of an energy-efficient gray water treatment and reuse system. Specifically, the following aspects will be demonstrated and validated:

• Energy efficient treatment of gray water from showers to generate water that is suitable for reuse in showering, shaving, and toilet flushing.
• Recovery of waste heat from shower drains to reduce water heating requirements.
• A relatively simple and scalable retrofit design concept that is minimally invasive and can apply to gang latrine buildings common to DoD training facilities.

The gray water treatment system is comprised of a Low Energy Advanced Primary Membrane BioReactor (LEAP-MBR) followed by Ultra-Low-Energy Reverse Osmosis (ULERO) purification. These technologies were developed by GE Water and GE Global Research and tested successfully for gray water treatment as part of SERDP project ER-2238. These technologies will be coupled with a heat exchanger system to maximize energy efficiency of the gray water reuse process. For the demonstration, a minimally-invasive sump system will be installed into an existing dedicated gang shower drain that supports 60 showers. The shower water will be pumped to a containerized unit that contains the heat exchanger, water storage tanks, and the LEAP-MBR ULERO treatment system. The heat exchanger will transfer the waste heat from the shower drain (gray water) to preheat the influent water that is going into the boiler for heating. The cooled gray water will then be treated in the LEAP-MBR chamber to remove/degrade the organic and particulate contaminants in the water. The LEAP-MBR applies controlled aeration to use less energy than conventional aerobic biodegradation technology. It also provides high fidelity separation of particulates using advanced membranes. Effluent from the LEAP-MBR will be further purified using an advanced ULERO technology, which purifies water at about half of the operating pressure of competing brackish water reverse osmosis membranes, saving energy.

Given that the DoD still uses approximately 90 billion gallons of water per year, the incorporation of water reuse technologies is becoming increasingly important as installations try to further reduce their net water demand levels.  The LEAP-MBR ULERO provides new concepts for integrated gray water and waste heat recovery that increase the return on investment. The system increases the fraction of reusable gray water from plumbing systems and provides a process and data collection requirements for high tier gray water reuse in buildings. (Anticipated Project Completion - 2020)

Lalley, J., S.G. Zetterholm, S. Waisner, E. Martinez-Guerra, M. Wamsley, L. Gurtowski, R. Wade, S. Pragner, and C. Griggs. Source Separated Graywater: Chemistry, Unit Operations, and Criteria Towards Re-Use. Journal of Water Process Engineering, 53(2023): 103736. doi.org/10.1016/j.jwpe.2023.103736.