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Severn Trent Services Ltd


Products and turnkey systems design and implementation capability in water analysers/monitors, disinfection equipment using chlorine, electrolytic and U.V. technologies, chemical dosing skids, hazardous gas safety shut-down systems, water audit/metering, waste-water and industrial effluent filtration systems


Mr Alex Lloyd
Arley Drive Birch Coppice Business Park
B78 1SA

Storm Water Success for TETRA SAF

Severn Trent Services has developed a new process for treating storm water at sewage works. The system, which employs the company's proven TETRA® SAF (submerged aerated filter), enables a sewage works to cope with storm flows and comply with new discharge standards.

(AquaTech 2004 - Stand 02.209 - Hall 2)

New regulations mean that all sewage works must now protect water courses from storm water discharge. Until this time such discharge may have received little or no treatment. Now all sewage effluent discharged at these locations must be treated to the same regulatory standard regardless of the flow to the sewage treatment works.

Conventional treatment of storm overflow at sewage works can include retention in storage tanks, settlement and screening. These basic levels of treatment will not now meet the improved treatment performance level during periods when storm overflow occurs at the sewage works.

The TETRA SAF has been used successfully for over 10 years for wastewater treatment with many plants in operation providing secondary and tertiary treatment of sewage effluent. The TETRA SAF is a biological fixed film process in which the biomass grows on a mineral support medium, the process is designed to carry out biological oxidation only and suspended solids removal may be unnecessary - as with many tertiary ammonia removal applications - or is accomplished by a subsequent filtration, settlement or constructed wetland stage.

Recently installed SAF plants have shown that the SAF process, when used for tertiary and secondary ammonia removal, is extremely robust to large changes in feed ammonia concentrations. Severn Trent Services have conducted trials work on its SAF process to evaluate how the process performance was affected by shock biological, hydraulic and suspended solids loads on to the plant. The outcome of the work showed that the TETRA SAF process is a very viable treatment method for bypass storm flows around sewage works.

The storm bypass treatment flowsheet developed by Severn Trent Services includes a tertiary SAF plant to treat secondary effluent to a high standard. It also uses the same SAF plant to treat directly the sewage storm flow that would normally discharge to the receiving water course so removing BOD and ammonia to meet the more stringent discharge standards for sewage storm overflows.

For further information please email Severn Trent Services Ltd

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