Venturi Aerator reduces Ammonia

Ammonia levels needn’t become a problem

Here’s how to handle them using a Venturi Aerator

Higher than anticipated ammonia levels at this WWTP,  due to higher than anticipated organic loadings on the system was a problem that needed to be resolved.

Ammonia from the DC influent to the primary septic tank ranged between 55 mg/L and 85 mg/L depending on the time of year. It was discovered that the water going into the trickling filter was also void of DO, low in pH, and had ammonia two to three times higher than the design loadings of 25-30 mg/L.

Flows ranged from 76,000 to 135,000 litre per day [L/D]. Further, there was insufficient alkalinity to support the metabolic reductions of ammonia by the resident bacteria in the wastewater and on the filter media.

A 15,000 litre poly tank was placed on-site as an aeration tank along with a two-inch Venturi Aerator unit with a small centrifugal pump.  The Venturi -Aerator unit is designed to add dissolved oxygen (DO) from an ambient air source.

During the cold winter months the Venturi added DO up to 8.0 to 9.5 mg/L and in the very hot summer months DO ranged from 3.5 to 5.0 mg/L. This difference is due to water temperature and the reduced solubility of oxygen in warm and hot water.

The Venturi Aerator was placed in a slightly submerged discharge (600mm) so the kinetic energy of the discharge would spin and mix the contents of the tank.  Liquids were pumped into the top of the tank at 60 litres per minute [L/M]  displacing an equal volume of treated effluent out of the bottom of the tank.

The pH was also being raised by some stripping of CO2 by the Venturi Aerator from 6.7-6.9 up to 7.2-7.5. This allowed nitrification to occur in the aeration tank, which has a 4 hour hydraulic retention time before being transferred into treatment trains.

A siphon break was added and used to add the required additional alkalinity.  A total of 7kg of bicarbonate was added daily and dosing was controlled by a small peristaltic metering pump.

The entire treatment process time was two days from when the wastewater was pumped into the aeration tank until it reached a very large leaching field.

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