Namon Nassef

Photo courtesy of Namon Nassef

Namon Nassef, inventor of the Zero Liquid Discharge Sewage Elimination System.

Sewage is nasty work, but Namon Nassef has built his career on finding innovative ways to clean it up. The 64-year-old engineer is the inventor of the Zero Liquid Discharge (ZLD) system, a product that will revolutionize how transportation systems dispose of human waste.

The machine uses excess engine heat to break down sewage from boats, buses, recreational vehicles, trains and airplanes and convert that fluid into clean water vapor. Think of it like a miniature wastewater treatment plant, except it leaves behind no odors, solids or other chemicals that pollute the environment. 

Nassef's product was recognized by Popular Science magazine in 2011 as one of the “Top Inventions of the Year.” The model he's working with today is even cleaner and more compact.  

“It’s a green technology because it reuses energy that would be discarded. By making that one gallon of diesel fuel or jet fuel do something more than just move the vehicle — the train, boat or aircraft — you've also eliminated sewage that was generated on board,”  Nassef explains. “This is completely different than anything out there.”

We think so, too.


ZLF prototype

Photo courtesy of Namon Nassef

The first ZLD prototype.

The first ZLD prototype was about the size of an office desk, dreamed up by Nassef while in graduate school at the University of Oklahoma in the early 1970s.

The objective was to use waste energy to eliminate sewage. But the technology, things like microprocessors and computers, was not readily available. "It took a while for the technology to develop,” he said. 

In the meantime, Nassef got to work on building his own company, Nassef Engineering & Equipment.

He also got around to purchasing a small recreational boat for his family to go water skiing. When the boat broke and needed its engine replaced, Nassef remembered the patent he had worked on in college. He thought, why not adapt the new engine to the ZLD system? So Nassef went back to his office, sketched up a diagram and carried it to a machine shop.

Twenty years, eleven prototypes and several thousand dollars later, the environmental engineer has a production unit that can eliminate up to 300 gallons of sewage per day. The model is about 8 inches tall, 15 inches wide and 24 inches long, or about the size of a medium suitcase. It weighs less than 100 pounds.  


Any vehicle that’s equipped with a toilet or sink has a sewage holding tank. The tank is used as means of temporary storage before the sewage can be dumped at a municipal plant. By evaporating sewage, the small, lightweight ZLD unit eliminates the needs for large holding tanks (freeing up space and making the vehicle lighter), and in turn, reduces the load on sewage treatment plants.

The only thing the technology depends on is a machine that produces sufficient waste heat. This is heat for which no other application is found, typically produced from generators or the burning of transport fuels (See how the ZLD system turns wastewater into water vapor). 

Thus, the system can be installed anywhere from tour buses and ocean liners (the technology has already been certified by the U.S. Coast Guard and the Environmental Protection Agency for use on ships) to offshore platforms and remote military bases where generators supply power to several hundred men in temporary quarters. But nowhere will the benefits of ZLD be more clearly seen than in the commercial airline industry.



Photo courtesy of Namon Nassef

The ZLD unit in a demonstration trailer.

Currently, the only way to get rid of sewage on an airplane is to store it on the aircraft. Keep in mind that waste generated on a plane is about seven times more concentrated than waste dumped at a municipal plant. That’s because it’s typically flushed with urine instead of water. This creates a great deal of work when the plane lands. It requires someone to suck out all the waste from the tank, clean it and finally use a myriad of disinfectants so the waste won’t smell.

Now imagine an aircraft equipped with Nassef’s ZLD unit. If you’re able to eliminate sewage as the plane is flying, that plane gets lighter and lighter (both because the tank is smaller and there’s less stuff in the tank). If that plane could be made lighter, it would get better fuel economy. And now, when the plane lands, it doesn’t need someone to empty the holding tank or chemicals to keep it from stinking up the aircraft. It also increases the capacity of the municipal plant where that load would normally be dumped.

“Airplanes generate so much waste energy from the exhaust that they’re not using. That energy could be used to completely eliminate sewage before the plane ever lands,” Nassef said.

For perspective, a small aircraft engine produces 3 million cubic feet of exhaust gas per minute. The ZLD system only needs around 1,000 cubic feet of exhaust gas per minute to convert solid waste in water vapor.

“If you look at the number of aircraft in the world, it would make a tremendous impact – millions of dollars a year in fuel savings alone.”   

This isn’t even counting the impact of smaller holding tanks, reduced chemical and labor costs, and less time on a tarmac as a result of an easier loading and unloading process.


ZLD demo trailerNassef is currently looking for investors to go into full-scale manufacturing. The first markets he plans to pursue are tour buses and RVs. The next would be the marine industry, including tugs boats, ferry boats and cruise ships. Airplanes would be down the line — although Nassef says if he were able to find investors in the next two months, he could physically put a unit on an aircraft within a year. 

For now, Nassef continues to travel around the country with his demonstration trailer, hoping that other visionaries will see the application of his invention.

“There are no examples where technology is being used right now,” said Nassef. “We have the opportunity to produce a product in United States that nobody else has, but is applicable worldwide.”

See how the ZLD system works >
