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Bacteria to help meet the ammonia wastewater challenge

Nitrifying bacteria can play a key role in tackling the challenge of ammonia discharges from wastewater treatment works, writes Dr John Lear

Preventing the discharge of ammonia into water bodies is a significant issue, as it is not only highly toxic to fish and other wildlife but also causes considerable oxygen depletion in receiving waters. Consent limits can be lower than 5 mg/L, so it is essential that ammonia is removed in the wastewater treatment plant (WWTP).

Ammonia is removed both in nature and in the WWTP by nitrification and this process is carried out by nitrifying bacteria. These specialised microbes are chemolithotrophs, meaning that unlike most bacteria, they use inorganic substances as an energy source. They are also obligate aerobes - they require oxygen to survive and grow. The addition of nitrifying bacteria to the WWTP is a highly effective way of optimising ammonia removal and meeting consent limits, avoiding costly fines.

The nitrification process takes place in two stages: 1) the oxidation of ammonia to hydroxylamine, then conversion to nitrite, carried out by species such as Nitrosomonas; and 2) the oxidation of nitrite to nitrate by species such as Nitrobacter.

Nitrifying bacteria do not form spores and are extremely sensitive to physical and chemical challenges. They cannot be dried or freeze-dried into powders and die rapidly if stored in liquid form at ambient temperatures. Care should be taken with commercial products that claim to contain true nitrifiers but instead utilise other species of bacteria which are more suited to removing organic matter in the treatment plant and can provide little or no ammonia or nitrite removal.

Biological Preparations uses a bespoke in-house fermentation process to produce and supply Nitrosomonas and Nitrobacter in concentrated liquid form. Each batch is activity-tested before dispatch and the products are shipped in refrigerated containers for immediate use or storage in a fridge where they have a shelf life of up to 6 months.

Nitrifying bacteria are extremely slow-growing as the amount of energy that can be generated from nitrification is low – their doubling time may between 7 and 20 hours. But this means that they have evolved to become extremely efficient at oxidising ammonia and nitrite. Our standard products have an activity of 5000mg ammonia or nitrite oxidised per kg product per hour.

The bacteria are normally added to the nitrifying zone of the WWTP and ammonia and/ or nitrite removal begins immediately. They may be used to establish activity in newly constructed or seasonally operated plants, to reseed a plant after toxic shock or to improve the ability of the existing biomass to meet ammonia consent levels.

Nitrifiers have fairly exacting growth requirements in terms of dissolved oxygen, temperature, pH and levels of organic matter, which are normally present or readily achievable in the WWTP. Biocides and other inhibitory substances should also be absent. We can advise on optimising conditions and given information on ammonia loading, effluent flow and hours of operation, can devise a dosing programme in order for operators to take full advantage of these remarkable bacteria.

For more information on our nitrifying products please contact our offices on 029 2067 4090.


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