United Utilities Invests in Disc Filtration to Meet Phosphate Limits

United Utilities has invested in innovative DynaDisc disc filtration technology from Hydro International (UK) to improve phosphates removal at its Congleton and Saddleworth wastewater treatment works and meet Urban Wastewater Directive water quality targets.

The DynaDisc installations have been successfully completed at both plants in a project to supplement secondary trickling filter beds treatment. Nomenca Ltd, the specialist Mechanical, Electrical, Instrumentation, Control and Automation (MEICA) contractor, also installed new dosing systems and integrated the new equipment with existing instrumentation systems as part of United Utilities’ AMP5 investment programme.

Both DynaDisc units are capable of treating 100% of the final effluent flow, but will normally operate at 50% duty with standby to ensure continuous service. The DynaDisc mechanical disc filtration system from Hydro International offers high efficiency microscreen filtration which can be precisely tailored to wastewater composition, flow and discharge requirements. As part of the filtration process the removed solids and backwash are returned through the site systems for treatment.

“We were asked by United Utilities to look at a range of options for improving phosphates removal at the two sites,” reports Phil Algawi, Project Manager for Nomenca. “One of the criteria, apart from meeting the set limits, was to expand the range of technologies that United Utilities was using so as to have a more diverse range of solutions.

“Before recommending the Hydro solution to United Utilities, we examined the operation of a DynaDisc at an established site elsewhere in the country and were very impressed with its operation.  Hydro worked with us very professionally to achieve an installation that met the specifications of a compact site and satisfied the requirements of United Utilities.

“We found DynaDisc easy to install, connect to the existing site systems and commission. Following the installation we conducted a successful fourteen day trial,” he added.

United Utilities has invested in the new technology as part of its £3.5bn capital programme between 2010 and 2015. The water company was required to meet new phosphorous consent limits based on the Urban Wastewater Directive. For Congleton WWT in Cheshire, with discharge to the River Dane, a new phosphorous consent of 2 mg/l (annual average) is accompanied by aluminium consent of 1mg/l.  The process improvement package also includes a polyaluminium dosing plant and the DynaDisc units.

For Saddleworth WwTW in Greater Manchester, with discharge to the River Tame, a new phosphorous consent of 2mg/l (annual average) is allied to an iron consent of 2mg/l total iron. Here, ferric sulphate and sodium hydroxide dosing plant packages are teamed with the DynaDisc. 

The maximum instant peak design flow at Saddleworth is 266 l/s, the duty design flow ranges from dry weather at 5.77 ml/d, through an average flow of 9.28 ml/d and a full treatment flow of 19.9 ml/d. At Congleton maximum instant peak design flow is 272 l/s, the range is dry weather 4.9 ml/d, average 6.8 ml/d and full flow 20.4 ml/d. 

Saddleworth and Congleton are both long-established wastewater treatment works for domestic waste and Congleton also has significant retail waste input.

Phil Algawi concludes: “Nomenca provides turnkey design, build, operation and maintenance solutions to water utilities companies across the UK, many through framework agreements and we were more than satisfied with the support provided by Hydro. Hydro worked very diligently to satisfy all parties.”

DynaDisc is an advanced technology that comprises modular disc-shaped screen cassettes covered with fine woven filter media to specified pore sizes, suspended on a rotatable shaft within a drum. Key benefits include a very compact footprint, low head requirements, high suspended particle removal.