Tuesday, June 15, 2010

Veolia Filters Aid Effluent Wastewater Treatment

Glen Water has selected Hydrotech Discfilter technology from Veolia for a project that is providing final effluent wastewater treatment and a sludge disposal solution in compliance with EU Directives. The Hydrotech Discfilter is considered to be a flexible technology that uses a series of segmented discs to support a woven media (polyester or stainless steel). The Hydrotech Discfilter was selected for use on the Omega scheme due to its modular design and compact layout. Under normal operating conditions the Hydrotech Discfilter will remain stationary.

The influent enters the inside of the unit via a central drum, which houses a series of paired filter elements that remove particulate solids from the influent. As the water passes through the woven filter, solids are captured on the inner face of the element. Accumulation of these captured solids reduces the hydraulic throughput, which results in an increase in head loss over unit. At a predetermined influent level, the unit automatically initiates a backwash, which flushes away the captured solids from the inner face of the filter, resulting in clean elements media being presented to the influent.

The Hydrotech Discfilter uses the filtered water produced by the process for backwashing. The benefit of this system is that power consumption is reduced by only backwashing to meet on-site demands. The dirty backwash water produced by the Hydrotech Discfilter process is collected by a trough located within the unit. Backwash water is discharged under gravity for onsite disposal or blending to the head of the works. The backwash water volume produced by the Hydrotech Discfilter is typically between one per cent and three per cent of the maximum design flow. Filtration is continuous throughout the backwash cycle and once the cycle is completed, the Discfilter stops rotating.

For the Northern Ireland Water Omega project, the Hydrotech Discfilter has been applied in both its tank and frame using both the 1700 and 2200 versions. The tanked version has been designed to be a stand-alone model that can be adapted to any site where a suitable base is available. This Hydrotech Discfilter is housed inside a stainless-steel tank for direct installation at site. The frame version has been designed for installation inside a concrete chamber and has the flexibility to be adapted for use inside an existing sand filter structure. The Hydrotech Discfilters are providing tertiary treatment at four sewage treatment works in Northern Ireland: Armagh, Richhill, Ballyrickard and North Down Ards.

Armagh has been designed to serve a population equivalent of 21,000. The scheme uses two HSF 2212-2F filters, capable of meeting the projected 2030 design horizon of 50,000PE. Richhill, which currently receives about 1,300m3/day of mainly domestic wastewater, has been designed for a 2030 loading of 5,000PE; this duty is met by two HSF 1706/5-2F filters. Ballyrickard receives wastewater from a 50,000PE catchment and discharges treated effluent into Strangford Lough via Newtown Burn; consequently the Northern Ireland Environment Agency has imposed a more stringent consent on this discharge. Here, the duty is met by three HSF 2214-2F filters, each rated for 50 per cent of the flow.

The North Down Ards works is a new facility that will rationalise the existing wastewater treatment systems in the surrounding catchments. It treats combined domestic and industrial wastewater from a 110,000PE to meet the requirements of the Urban Wastewater Treatment Directive. After sequence batch reactors, tertiary treatment uses four tank-mounted HSF 2220-IF filters prior to UV treatment. The Hydrotech Discfilter has proved a cost-effective and reliable solution for tertiary treatment applications. The compact design means a small footprint compared with other technologies such as sand filters and the low wash-water consumption gives it a clear hydraulic advantage.

Standard modular designs in four ranges can individually treat up to 400 litres/s (any flow rate can be treated by applying further Hydrotech Discfilter units to suit on site conditions). The units are available in a choice of materials: ABS plastic or stainless steel for the discs and 304, 316 or Duplex stainless steel for frames and tanks. The woven media can be supplied to suit any application with a range between 10 and 500 micron. The Hydrotech Discfilter is considered to have a low head loss, low power consumption and minimal maintenance requirements.

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