A process plant for nitrification using the DynaSand^® Oxy, nitrification process.

The water to be nitrified enters the DynaSand^® Oxy through an inlet distributor. As the water flows upwards through the filter bed, ammonia is converted into nitrate by bacteria - Nitrosomonas and Nitrobacter - which form a layer on the surfaces of the filter grains. The bacteria, which are autotrophic and thus live only on inorganic materials, produce new biomass out of carbon dioxide.

• Continuous process as DynaSand^® with the addition of ammonia removal.
• Ammonia, suspended solids and BOD removal in a single stage.
• Low ammonia consents achieved.
• Peak inlet concentrations handled.
• Efficient, easy operation.
• Stand alone addition to the works.
• Proven technology.
• Free Standing - 'built-in' concrete basin units available. 

The DynaSand^® Oxy filter, like the DynaSand^® filter, is based on the counter flow principle.  The water to be treated (red arrow) is admitted through the inlet distributor (1) in the lower section of the unit and is cleaned as it flows upwards through the media bed, prior to discharge (blue arrow) through the filtrate outlet (2) at the top. 

To ensure that the autotrophic nitrifying bacteria have sufficient oxygen and carbon dioxide to convert ammonia to nitrates, aeration hoods fed by process air (green arrow)are sited within the upper layer of media to provide sufficient aeration.  The resultant nitrates remain dissolved in the water.

The media containing the entrapped solids is conveyed from the tapered bottom section of the unit (3), by means of an airlift pump (4), to the media washer (5) at the top. 

Cleaning of the media commences in the pump itself where impurities are separated from the media grains by the turbulent mixing action.  The contaminated media spills from the pump outlet into the washer labyrinth (6) in which it is washed by a small counter current flow of clean water.  The separated solids and sloughed biomass (brown arrow) are discharged through the wash water outlet (7), while the grains of clean media (which are heavier) are returned to the media bed (8).  As a result, the bed is in slow, constant downward motion through the unit.  Compressed air for the air lift pump is provided via the air distribution panel.

Thus, water purification and media washing both take place continuously enabling the filter to remain in service without interruption.

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Frequently Asked Questions

Q. What is the difference between a DynaSand^® and a DynaSand^® Oxy?

A DynaSand^® Oxy has an aeration ring within the filter to boost the dissolved oxygen content, such that the nitrifying bacteria have an oxygen supply. The media can also be changed such that it is better able to support a microbial population, and the bed depth is often different such that sufficient volume of media is present to treat the wastewater.

Q. Can a DynaSand^® Oxy remove BOD?

Yes, but it should not be used as the main BOD removal process, and the solids generated by carbonaceous BOD removal can block the filter. Small amount of excess BOD can be removed as part of the nitrification process.

Q. Why use different media in a DynaSand^® Oxy?

The media used in the DynaSand^® Oxy has a slightly rough surface texture, this allows the biomass to better adhere to the media, and stops it being removed in the washing section.

Q. Why are DynaSand^® Oxy filter so tall?

The sizing of the filters is based both on the hydraulic and organic load rates, the hydraulic rate determines the number of filters and the organic rate determines the bed volume, these two aspects combine to give the bed height, which is often in excess of that required for straight filtration.