As both a bioreactor and effluent filter, TETRA Denite combines filtration and denitrification to achieve a high level of process synergy. Simultaneous removal of total suspended solids and nitrate-nitrogen achieves 1ppm NO3-N and 3 ppm total nitrogen or less. Fundamental to this process is the specially sized and shaped granular media used in the fixed-film biological filters. The high solids loading capacity of the media is ideal for retaining biological solids produced by the denitrification process, and the powerful backwash of the TETRA Denite filter system removes these solids periodically. The surface area of the 3mm diameter sand particles is very large, providing 1000m2 per cubic meter contact between the wastewater supply and the biomass.

During the denitirification process, wastewater is forced to flow around nitrogen gas bubbles that accumulate in media voids in the filtration vessel, improving biomass contact and filtration efficiency. Effective removal of nitrogen generated from the nitrate is undertaken by introducing methanol using the patented TetraPace™ automatic dosing control. Severn Trent Services employs a “bump” operation to remove or purge accumulated gas- nitrogen or air- that can potentially build up on the filter media. If desired, this “bumping” can be accomplished without removing the reactor from service using the patented SpeedBump™, which applies backwash water to the bottom of the filter, releasing the entrapped gas into the atmosphere and reducing head loss.

The denitrified solids – along with other suspended solids such as phosphorous and heavy metals removed in the process – are retained within the media. The solids are backwashed out of the filter by a simultaneous injection of air and water, and returned to the upstream biological treatment units at the end of each cycle. By operating down flow, excellent levels of solids removal are achieved, eliminating the need for clarifiers and additional effluent polishing filters.

A key feature of the Denite system is the ease with which an existing TETRA Deep Bed Filter plant, originally installed to meet suspended solids, BOD and phosphorous standards, can be readily upgraded to denitrify in Denite mode and thus meet new total nitrogen standards.

Severn Trent Services Managing Director, Dr. Mike Ashley, commented, “We are aware of more than one hundred wastewater treatment plants where the use of methanol is the preferred choice for denitrification. The independent Methanol Institute has cited an example where the Denite process has more than halved the previous discharge level.

“Our TETRA Denite system has demonstrated, time and time again, its efficiency and cost effectiveness in an increasingly demanding and price-conscious industry.”

For more information on the TETRA Denite® System, email info@severntrentservices.com.

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