Carbon-cutting bioresources tech puts engineers in a spin

Photo caption: The Volute system installed by United Utilities

Innovative technology which replaces power-hungry centrifuges at wastewater treatment works would cut electricity consumption and carbon emissions for bioresources operations.

Early results from a 12-month trial by water company United Utilities and Evergreen Water Solutions, as part of the Department of Business Energy and Industrial Strategy’s Industrial Energy Efficiency Accelerator (BEIS IEEA), suggest power savings of up to 84% compared to a typical centrifuge.

The system, called Volute, is manufactured in the Czech Republic by Amcon Europe and distributed under licence in the UK by Evergreen Water Solutions. Volute revolves just twice a minute, compared to traditional centrifuges which can reach speeds of up to 3,500 revolutions per minute (RPM).

Photo caption: The £100 million Manchester Bioresource Centre (MBC) plant at Davyhulme opened in 2011 and treats around 91,000 tonnes of wastewater sludge from Manchester and sites in Lancashire.

Pat Horne, Bioresources Head of Strategy and Commercial Services, who is overseeing the trial at Davyhulme Wastewater Treatment Works on behalf of United Utilities, said, with another three months of the trial left to run, the results had been excellent.

“Compared to traditional de-watering processes we have seen a reduction in the power consumption of sludge de-watering from 23kWh per tonne of solids, to less than 4kWh, depending on the throughput setting. For a site the size of Davyhulme that equates to potential cost savings in the hundreds of thousands of pounds a year,” he said.

“Although the technology had been used on smaller wastewater sites in the UK before, the units had been too small to use effectively at the sort of scale we would need for a large regional processing centre like the one we have at Davyhulme.”

When the new larger unit became available, United Utilities, which is widely regarded for its investment in innovation, recognised the carbon and energy reducing potential of Volute and committed to partnering to test the technology.

The company, in collaboration with Evergreen Water Solutions, successfully applied for a grant from the BEIS IEEA, which is managed by the Carbon Trust, to support the first demonstration of Volute in an operational environment. The BEIS IEEA funds commercial scale demonstrations of novel technology with the potential to reduce energy consumption and carbon emissions to accelerate their uptake in wider UK industry. A key focus is innovations with large cross-sector energy and carbon reduction impact, using either new technologies or established technologies applied to new sectors.

Paul McKinney, Senior Manager at the Carbon Trust commented:
“The Carbon Trust is delighted to have supported Evergreen Water Solutions and United Utilities in this demonstration project through the BEIS IEEA programme. Based on the initial results the technology has the potential to have a significant impact on reducing energy consumption and the carbon impact of waste water treatment. We are looking forward to seeing further uptake of the technology within UK industry. Continued innovation is critical to ensure novel technologies like Volute are commercialised to help the UK achieve its industrial decarbonisation ambitions.“

So far, United Utilities has successfully tested the system on large volumes of raw sludge, digested sludge and centrate returns. The final part of the trial will involve using it with direct dewatering activated sludge (SAS) to produce a manageable sludge cake.

Once trials are complete, the data will be fully assessed and the whole life cost modelled, before the results are released by the Carbon Trust before the end of the year.

“This is an important part of the trial. While Volute did better than traditional centrifuges in some significant ways, it does require additional polymer in some dewatering processes,” explained Pat Horne.

“But the size and the capacity of the new units are certainly comparable to a centrifuge. The twin Volute disc screw unit we are trialling processes up to 800kg of sludge per hour, so the four unit version would be double that. A centrifuge processes around 1,400kg per hour but is bigger and very energy hungry.”

The successful demonstration of Volute is another example of United Utilities’ commitment to improving overall efficiency. It follows the installation of Nereda – another treatment process that does not require a primary step and which earlier this year won a Water Industry Award for Wastewater Innovation Project of the Year.