Nitrogen removal system uses less energy, no carbon source

Nitrogen removal system uses less energy, no carbon source
DEMON nitrogen removal system from World Water Works

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The DEMON nitrogen removal system from World Water Works is designed for municipal and industrial wastewater streams with high ammonia concentrations (greater than 200 mg/L). The system’s two-step process uses ammonia oxidizing bacteria (AOB) that convert half the ammonia to nitrite. A second biological process uses anaerobic ammonium oxidizing bacteria (anammox) to convert the nitrite and remaining ammonia into nitrogen gas, reducing energy usage by 60 percent. The system also produces 90 percent less biomass than traditional nitrogen removal processes. This is all accomplished in a single tank.

“The DEMON system is a shortcut in nitrogen removal,” says Chandler Johnson, chief technology officer for World Water Works. Unlike conventional activated biomass processes that convert ammonia into nitrate, the DEMON (an acronym for DEamMONification) process requires no carbon source, such as methanol. “It’s a very cost-effective upgrade for handling the side-stream treatment of high ammonia-laden streams coming from the dewatering step in the wastewater treatment pipe,” he says.

Once dewatered, centrate is collected in a buffer tank and pumped into the DEMON reactor, where it is aerated and mixed. During the aeration period, ammonia is converted into nitrite and acid is formed. When pH drops approximately 0.02 to 0.05 units, aeration is stopped. Under anaerobic conditions, nitrites, combined with the remaining ammonia, are converted into nitrogen gas.

The conversion process causes pH to rise. When pH rises approximately 0.02 to 0.05 units, aeration is restarted. After six hours, the process is stopped, allowing bacteria to separate from the centrate. A 30-minute settling process leaves a clear supernatant, which is discharged. Settled bacteria remain in the reactor. The nitrogen removal cycle takes approximately eight hours.

“One of the key features is the biomass separation step that allows us to retain the slow-growing anammox granules and waste the AOB and NOB [nitrite-oxidizing bacteria], which we don’t want to accumulate in the system,” Johnson says.

Suitable for both new plant construction and retrofits, systems have been designed to handle flows from approximately 78,000 gpd of centrate up to 1.1 mgd of filtrate, depending on the size of the system, with even larger flows possible.

Simple to operate and maintain, the system has a blower that provides air and a mixer that helps combine the contents of the tank. “The technology is based on a sequencing batch reactor [SBR],” Johnson says, with the number of reactors – one, two or three – determined by the size of the treatment facility. 800/607-7973;


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