This System Recovers Heat Energy from Sewage

Our planet is facing a potentially devastating climate emergency, partly due to the fact that the infrastructure we have set up to deliver food, energy and water is incredibly wasteful at every step of the process. A full 40 percent of the food produced in this country is wasted before it can be consumed. That waste occurs at the farm, delivery, retail and consumer levels. The same thing is true for energy. Inefficient power plants deliver electricity to a transmission and distribution system that wastes 6 percent of that energy before it reaches our homes, where a whole lot more is wasted. All totaled, we waste over 60 percent of the energy we produce.

The good news in this, if there is any, lies in the numerous opportunities that are emerging to do something about this. Whether this is a matter of closing the barn door after the horse has escaped is a philosophical one, but the fact is: As you read this, horses are still escaping.

A vast amount of this wasted energy is given off as heat -- heat that we could be using instead of paying more for additional energy that is turned into heat. Recovering some of that heat as it is literally washed down the drain is the idea behind a system from Canadian firm International WasteWater.

The idea is somewhat similar to that of a heat recovery ventilator (HRV) that pulls heat out of air that is being exhausted from a building, and sends it back inside. The difference between an HRV and the two systems produced by International Wastewater, the Sharc and the Piranha, is that they pull heat from the waste water leaving a building through the sewer line rather than exhausted air.

According to the DOE, some 400 billion kilowatt-hours of energy are literally washed down the drain in the U.S. every year. To get an idea of the magnitude of this waste problem: The city of Denver found itself in trouble because the temperature of its wastewater discharge is too high -- potentially threatening the aquatic environment, said Lynn Muller, founder of International Wastewater. The city is now installing a number of Muller's systems to remove some of that heat and put it to good use.

While an HRV uses a heat exchanger to grab heat, the International Wastewater System products use heat pumps, which are far more effective in collecting heat. The heat pumps then use that heat to produce more hot water.

It’s a little more complicated than that, but not much. The system also requires pumps, storage tanks, filters and something called a macerator to make sure that the sewage keeps flowing (video). Because of the cost of the equipment, the systems make sense economically in larger, multi-family residential buildings, where there is lots of heat to be captured and lots of hot water required. Once the heat has been extracted, the sewage continues on its journey to the treatment plant.

The Sharc system is recommended for larger apartment or townhouse complexes with multiple buildings. It has also been installed in college dormitories. The smaller Piranha is designed for a single building. Either one will meet all the domestic hot water needs of residents with only a small amount of additional energy needed to run the heat pump. But with sewage temperatures running at approximately 80 degrees (depending on conditions) the heat pump efficiency will be very high.

Energy savings are impressive. A recent project involving 60 townhouse units achieved energy savings of 75.2 percent compared to a comparable natural gas system.Other systems have achieved comparable results.

Image credit: International WasteWater