Sewage treatment isn't rocket science - except when it is

It’s a case of finding a use for what was thought of as waste. Sewage treatment processes produce methane and nitrous oxide, both greenhouse gasses, while leaving undesirably high levels of nitrogen in the discharged water. On their own, all three of these things are harmful to the environment.

A conventional aeration based sewage treatment plant:

Stanford University reports that a team at their Woods Institute for the Environment has found a way to take those unwanted waste gasses and use them to 1) reduce the amount of nitrogen in the water, 2) produce an alternative energy source and 3) dispose of the nitrous oxide cleanly – by using it as rocket fuel, in fact.

The process seems fairly simple – reduce the amount of oxygen in the sewage treatment process, and the anaerobic microbes that promote the production of nitrous oxide and methane flourish, resulting in more of these gasses. The problem would normally be that these gasses are harmful, and producing more of them would be the last thing you would want. That’s where the rocket science comes in.

Brian Cantwell, a professor of Aeronautics and Astronautics joined the team of a professor of Civil and Environmental Engineering, Craig Criddle, to help solve the problem.

According to an article in the Stanford University News, ‘The result was a novel design with the potential for treating the world’s wastewater: First, reduce oxygen levels at the treatment plant to encourage the production of nitrous oxide and methane gas. Then use the extra methane to power the plant and a small rocket thruster to break down the nitrous oxide into clean, hot air. ‘A single thruster about the size of a basketball could potentially consume every ounce of nitrous oxide produced by a typical treatment plant,’ Cantwell said.”

A nitrous oxide rocket thruster, like would be used in the sewage treatment plant:

The design has several benefits:

The anaerobic treatment process is less expensive than the conventional aeration method.

The methane produced could be used to power the treatment plant itself, further reducing the cost, and making it possible to build treatment facilities where no other power source exists, such as in developing countries.

Nitrogen, a serious environmental pollutant and human health threat, and a major problem within current sewage treatment systems, is removed from the wastewater, making plant effluent cleaner.

The nitrous oxide can be burned by a rocket engine with no polluting consequences. When nitrous oxide burns, it is separated into pure nitrogen and oxygen. Nitrogen gas is beneficial in the atmosphere, where excess nitrogen in the water is harmful.

The Nitrogen Cycle: there should be a balance between nitrogen in the air and nitrogen in the ground. It’s a balance that has been broken by human activity:

And cleaner air and water is good for everyone!

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