WPL's SAF Technology for UK Water Projects

WPL has installed an innovative new type of wastewater treatment plant for a UK Water Company.  With ever tightening Environment Agency consent standards water companies are upgrading their works to meet these consents.

Working with WPL Limited, specialists in wastewater treatment solutions, this is the first UK Water Company to use WPL’s innovative HIPAF Anoxic N-SAF modules, the first system to incorporate denitrification in a Submerged Aerated Filter plant. This new technology is to serve a population equivalent of over 5000 in the local area.

The ability to denitrify within a SAF is a ground breaking new technology that has been developed by WPL’s engineering department.  WPL is the first company to have supplied such a technology as a capital project solution to a UK Water Company. 

Gary Tasney, WPL’s Operations Manager, says “Denitrification in a SAF had long been considered to be biochemically unworkable due to a constant air demand required to maintain scour of the media pack and to prevent sedimentation within the biozone. We have successfully overcome these technical barriers with innovative process control automation and operational experience gained from managing pilot trials for a 12 month period within a research and development program.”

Working closely with the Water Company and their contractors has enabled WPL to engineer a solution that not only meets the needs of the Water Company, but also incorporates new technology that will also be available to other Water Companies in the UK with similar requirements.

WPL have provided the works with two steel above ground tanks to provide aerobic/anoxic treatment of influent wastewater from existing mineral filters at the works. WPL was appointed to design and supply a solution that would meet tighter effluent standards than those the existing plant produced; namely to reduce nitrate levels. Submerged Aerated Filters (SAFs) were designed by WPL to meet effluent discharge standards (95%ile) of ammoniacal nitrogen at 5.0 mg/l and total inorganic nitrogen at 35mg/l (annual average).

THE PROCESS

The wastewater flows through the existing plant’s inlet works, primary treatment chamber and trickling filters. Once the biologically treated effluent leaves the secondary trickling filters, it enters one of two Anoxic N-SAF HiPAFs via a flow-splitting chamber. Each Anoxic N-SAF HiPAF comprises five cells: the first three of which have been assigned as aerobic and the remaining two as anoxic. The aerobic sections are assigned for the process function of nitrification and are therefore continually aerated for carbonaceous and nitrifying degrading of the sewage.

Flow will then continue into the anoxic sections, where it is continuously forced to change direction across the profile of the tank. This allows for maximum contact with the submerged media, prevents excessive sedimentation of particulate solids and facilitates mixing without turbulence that would entrain air. Short and infrequent periods of scouring prevent anaerobic conditions to occur on the high voidage media, however the addition of this air introduced during scouring makes negligible difference to the levels of dissolved oxygen.

Although the plant has been designed with the first three cells being aerobic and the last two as anoxic, there is flexibility in the design to increase the amount of aerobic cells to four or five and subsequently decrease the number of anoxic cells to one or zero.

As the N-SAFs had to sit within the existing plant in place of the sedimentation tanks, it was necessary to size the tanks adhering to a small footprint, which was easily achievable with WPL’s above ground NSAF solutions.

The above ground tanks allow for full access from top level to all parts of the unit for maintenance and long-term reliability is ensured due to the complete absence of any mechanical or electrical components within the hostile environment in the treatment tanks.

WPL not only designs, manufactures and commissions its wastewater treatment solutions, but also provides maintenance as well, offering a comprehensive package if required.

For more information visit www.wpl.co.uk.

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