Anglian Water invests in sewage treatment technology

Ely, UK – Anglian Water is investing £1million in technology to optimise screenings and dewatering efficiency at ten sewage treatment works, supporting its targets for enhanced sludge treatment capacity and renewable energy generation.

A total of 22 SludgeScreen units, from Hydro International, are being installed at works across the east of England to ensure effective and efficient screening procedures to protect equipment and help optimise sludge output.

The investment brings the total number of units installed by Hydro throughout the region to 75.

According to Anglian Water’s special projects technical manager, Steve Riches, the new units provide high performance screening and dewatering.

“The equipment protects downstream equipment such as pumps, heat exchangers and anaerobic digesters from difficult inclusions such as rag which evade mechanical screening,” he said. “Our experience has shown that investment in these units completely outweighs the costs of unforeseen blockages, maintenance and downtime, which could affect biogas production efficiency.”

The SludgeScreen installations will be delivered to nearly all the Anglian Water sites as ‘packaged units, notes Chris Day, operations director for Hydro Wastewater in the UK.

“The units will be platform-mounted with control panels fitted and complete,” said Day. “This greatly reduces the time required to install [them] on site. As a result, they can be commissioned and brought into operation very quickly to support Anglian Water’s project timescales.”

Anglian Water is upgrading its sludge treatment operations to support its ‘special projects biosolids’ programme under its AMP5 capital investment plans. It aims to process at least 80% of its sludge output by advanced anaerobic digestion by the end of 2015.

Optimising biogas production efficiency is essential to help meet targets to generate around 87GWh of electricity annually. Anglian Water is making significant progress towards its target of energy self-sufficiency through a programme of building combined heat and power plants, aiming for a total installed capacity of 20MW.

The new SludgeScreen units are being installed at main and satellite sewage treatment works across the Anglian Water region at sites from Lincolnshire to Suffolk and Essex, in separate contracts delivered by Black and Veatch and GTM - a JV between Imtech Process and Galliford Try.

According to Hydro, its design enable screenings to be dewatered to 25% thickness, thus enhancing the efficiency of sludge production, reducing carbon footprint implications of transporting sludge in tankers to Anglian Water’s Sewage Treatment Centres (STCs).

In each unit, sludge to be treated is first pumped into the screening zone and flows through a perforated screen. Solid matter larger than the screen perforations is retained inside the screen basket and transported via Archimedean screw to the pressing zone where it is compacted into a plug under gradually increasing compression.

Any superfluous liquid that is released flows through the perforated pressing zone screen and is recycled back to the screened sludge outlet for further treatment. Difficult inclusions like rag, which have not been removed by mechanical screening, are separated from the sludge and the screening plug is broken up and discharged into a skip for disposal.

At the STCs, dewatered sludge and heavy sludge cakes produced at some works are blended with locally produced liquid sludge to around 8% solids suitable for digestion. After undergoing high temperature retreatment to kill pathogens, the sludge is fed to the advanced aerobic digesters. Using a very efficient process, biogas is generated and stored and the remaining solids constitute an effective soil conditioner, which is sent to agriculture.