Audio Summary

In field operating environments, military units must ensure access to a critical water supply to maintain mission readiness. Increasing complexity of logistics and costs to transport water in addition to climate change are driving the development and demonstration of water treatment units. The objective of this project was to demonstrate and validate the performance of an energy-efficient gray water treatment and reuse system that utilizes ultrafiltration (UF) and reverse osmosis (RO) membrane technologies with a disinfection step to treat low strength graywater. Specifically, the following aspects were 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.

Technology Description

The gray water treatment system was 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 were coupled with a heat exchanger system to maximize energy efficiency of the gray water reuse process. For the demonstration, a minimally-invasive sump system was installed into an existing dedicated gang shower drain that supports 60 showers. The shower water was pumped to a containerized unit that contains the heat exchanger, water storage tanks, and the LEAP-MBR ULERO treatment system. The heat exchanger transferred 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 was then 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 was 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.

Graywater for the primary testing was supplied by two battalion training events occurring during this demonstration over a period of six months. Samples used were collected from human shower sampling events. During the demonstration greater than 100,000 gallons were treated from training rotations over the six-month period and characterization of the source graywater continued throughout the system demonstration. Based on what was found in the literature, these are among the largest source-separated graywater sampling events to date. The data from this event is valuable because it represents the range of feedwater characteristics for normal sink and shower water use practices by a military unit.

Demonstration Results

The combined treatment train of UF and RO met all compliance metrics for all analytes of interest for potability and met non-potable metrics except for special use cases in three states. All water treated met standards for un-restricted reuse in all other cases where guidelines are established. In addition, when reusing water, the additional water gained is more than just the recovery rate achieved by the RO unit. The ultimate multiplier effect is many times higher due to the water being used many times. A water recovery rate of 85% multiplies the effective volume of useable water by a factor of 6.5 creating a significant reduction in the volumes required.

Implementation Issues

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 demonstrated system 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. Both the quality of the treated water and the effective volume gains from the multiplier effect directly support Department of Defense water sustainment goals for both installations and operational environments. (Project Completion - 2022)

Project Summary


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