News | May 20, 2019

Army engineers: heat sewage with tailpipe, recover drinking water

System can recover up to a gallon of water per minute, using less than 40 watt-hours of energy per gallon

Marines toss a re-supply of water cases off a combat vehicle at a patrol base in Afghanistan.

USMC photo

Clean drinking water can be hard to find for expeditionary forces but a research team at the Army Corps of Engineers has figured out how to efficiently get it back from the sewage tank.

Corps engineers Jedediah Alvey, Martin Page, and Axy Pagan-Vasquez are repurposing the exhaust from a diesel generator, otherwise wasted heat, to power a sewage dryer. The evaporated water coming off the sewage is picked up by an air stream created by a blower.

But to reduce energy usage further, the air stream’s dew point is dropped by a desiccant filter before it enters a cooling interface where the clean water condenses and is collected.

News Article Image of Army engineers: heat sewage with tailpipe, recover drinking water

A Navy seaman adjusts the frequency of a 10-kilowatt generator at a firebase in Afghanistan.

Navy photo

“The desiccant containment apparatus is a wheel structure consists of a circular honeycomb matrix of heat-absorbing material, according to the Army’s patent application that was made public on May 16.

“The desiccant wheel [is] slowly rotated within the process and regeneration air streams of an air-handling system. As the thermal wheel rotates, moisture is picked up from the process air stream in one half of the rotation and given up to the regeneration air stream in the other half of the rotation. Thus, moisture from the process air stream is transferred to the matrix material and then from the matrix material to the regeneration air stream, raising the humidity of the regeneration air stream (raising this stream’s dew point), while decreasing the humidity of the process stream (lowering this stream’s dew point).”

For the last two decades, U.S. military outposts in Afghanistan and Iraq, known as forward operating bases or contingency bases, have required lots of water, especially drinking water. Typically, pallets of one or two-liter water bottles are delivered by truck or helicopter over great distances. The delivery trucks become a target for attack by enemy forces thus requiring an armed escort.

Diesel generators almost exclusively power those same bases. So, tapping into their waste heat in order to significantly reduce orders for bottled water and the number of resupply missions just makes sense.

And according to the patent application, the “system can recover up to a gallon of water per minute, using less than 40 watt-hours of energy per gallon.” That’s 1,440 gallons per day at a cost that beats the similar Atmospheric Water Generation Unit, which needs about 310 watt-hours of energy to make a quart of drinking water.

TechLink, the Department of Defense’s national partnership intermediary, which helps connect businesses to military labs, is now guiding private companies through the evaluation and licensing of the Army Corps of Engineers’ invention portfolio for the purposes of commercial production and sales.

Quinton King, a senior technology manager at TechLink, said efficiency is the water recovery system’s top attribute and noted that the accelerated evaporation processes and desiccant materials could also pull clean water from brine or sludge.

“Flexible, sustainable water solutions for base camp operations makes this attractive for military customers,” King said. “But anyone who uses generators could put this to work on otherwise inaccessible water sources.”


Company inquiries can be sent to Quinton King at quinton.king@montana.edu or he can be reached at 406-994-7795.