How To Improve Dewatered Sludge Handling

Jon Lawson

One of the leading progressive cavity pump specialists has developed a new system to improve dewatered sludge handling, enabling long distance transfer with reduced operational costs by using a combination of PC pump technology and dense-phase conveying.

The technology has already been trialled by Thames Water at its Reading Sewage Treatment Works (STW) and is now being installed as part of the new Thames Water Riverside project, providing an energy-efficient, high-performance alternative to conventional sludge handling systems.

Smart Air Injection (SAI) Technology

Seepex has a longstanding relationship with Thames Water, having worked for many years to increase the water company’s process efficiency and reduce the energy consumption of dewatered biosolids sludge handling. As the UK’s largest water and sewage treatment company, Thames Water provides wastewater services to 15 million customers and is committed to reducing its energy consumption. Its interest in smart air injection (SAI) technology was linked to a new project at Riverside STW to handle dewatered sludge.

Following a visit by Thames Water representatives to observe SAI in action in Sweden, the company decided to measure the potential energy savings it could make by installing a trial SAI system at its Reading STW.

This site had previously used piston pumps, but as a result of process limitations and high operating costs, Thames Water switched to Seepex’s multistage PC pumps in 2014. This solution halved energy use, as well as reducing transport and maintenance costs. Four years on, it was time to see if SAI could improve things further.

Energy Savings From Smart Air Injection Technology

The SAI Reading trial set out to not only prove the technology, but also to quantify the additional energy savings that could be delivered by pumping the dewatered biosolids from the centrifuge discharge to the storage silo. An SAI trial unit, including full controls and monitoring, was installed on the multistage PC pumps for a trial period and the results were recorded. Superior energy savings

During the trial, energy use and discharge pressure measurements were taken. Using these figures, together with the volume and height of the discharge pipework, Seepex engineers could then calculate the optimum amount of air required. The trial concluded the energy saving with SAI compared to a multistage PC pump without air injection was 15%. Compared to the original piston pumps, the energy saving was an astonishing 61%.

Adding Smart Conveying Technology (SCT)

However, there were even greater savings to be made by switching to a single stage SAI pump fitted with Seepex’s smart conveying technology (SCT), instead of the multistage pumps currently in use. Air usage data from a working SAI installation using SCT pumps in Belgium, enabled the firm to produce an estimate for Thames Water, based on the trial results from Reading.

It concluded that, if SCT single stage pumps were used in place of multistage pumps, the energy saving at Reading STW would be approximately 40%. When compared to the original piston pumps, an SAI system with SCT pumps would reduce energy consumption on this application by approximately 75%.

Benefits of Smart Conveying Technology

SCT pumps deliver a range of other benefits, too: reduced investment costs; longer service intervals; lower maintenance costs; smaller pump footprint; maintain in place capability; and long-distance transfer of non-flowable products.

As a result of the successful Reading trial, Thames Water has procured several of the SAI units for its Riverside project. “We were faced with a particularly tough challenge at Riverside,” explains Paul Fountain, senior consultant – Biosolids, for Thames Water. “Replacing a problematic conveyor system with proven PC pumps was the preferred solution, but due to very tight space constraints, low access walkways and a labyrinth of pipework to work around, the traditional multi-stage pump was not going to be possible.

“We decided to purchase several single stage SCT PC pumps, coupled with SAI innovation,” continues Fountain. “This allowed us to reduce the pump length and installed motor powers, and has the added benefit of ease of maintenance.”