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Siltbuster helps treat drained reservoir water

Siltbuster has supplied a system to deal with more than 250,000m³ of water drained from Wentwood Reservoir in Wales to allow maintenance and repair works to be completed on a control tower.

Morgan Sindall was appointed by Welsh Water to upgrade and replace the Victorian tower’s 18th Century valves and bring it up to current working standards. To do this Morgan Sindall’s workers needed to access the base of the tower, and mechanically remove and lift out redundant fittings, but with the tower situated in the middle of the reservoir, this work could only be done when the 42-acre reservoir is drained.

With the reservoir’s dedicated permanent downstream water treatment house no longer operational, Morgan Sindall asked Siltbuster to supply a temporary solution to treat the waters so that they could be discharged directly to the natural environment.

Siltbuster devised a multistage system to treat the peak reservoir discharge of up to 600m³/hr. This involved eight HB50E lamella clarifiers, four MT30 mixing tanks and two chemical dosing containers. Due to the slow settling characteristics of the solids suspended in the water, an automated chemical dosing system aggregated any solids in the water and makes them settle more quickly. Dosing the feed waters with both a coagulant and flocculant, via digital magnetic flowmeters, and using highly accurate peristaltic dosing pumps prior to clarification, the treated water quality is consistently within specification, with the Total Suspended Solids (TSS) never exceeding 60mg/l.  

As part of the system design, Siltbuster installed a turbidity sensor on the plant’s inlet, which is connected to the chemical dosing pumps. This ensures that pre-treatment chemicals are only introduced when required, conserving chemical supplies and minimising consumable costs.

Further sensors installed at the outlet point and linked to the Siltbuster equipment also ensure that if the treated water quality decreases, actuated valves will automatically isolate the feed preventing any sediment rich waters from escaping to the environment. A GSM module will also send text messages alerting users that the system has auto-shutdown, whilst a visual alarm beacon will alert staff onsite.   

As the reservoir’s levels drop and the treated water is discharged safely to the surrounding environment, the sediment and solids are captured within each of the lamella clarifiers’ hoppers. A duty and standby sludge pump allows each settlement unit to be remotely emptied. The slurry is then held and stored within a 30m³ agitated tank, whilst a vacuum tank periodically empties and disposes of the sludge offsite.     

All the chemical dosing, monitoring and data logging equipment is housed within purpose built 20ft containers to prevent unauthorised access, vandalism and containment of the bulk chemical supply. These chemical dosing containers are complete with a triple IBC spill stand and a cut-out self-bunded floor, so in the event there is a breach or spill, the chemical solution is contained.  

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