Challenge

Northumbrian Water was to cease using the existing belt presses (which were old and requiring increased maintenance) to dewater sludge at its 52-acre Bran Sands sewage treatment works and construct two new dewatering facilities to dewater the sludge using centrifuge technology - one to treat raw sludge and the other to treat sludge that has been treated by the Advanced Digestion (AD) process.

Further objectives of the project were to:

  • increase efficiency of the sludge and effluent treatment process
  • reduce energy consumption and the associated carbon emissions

Solution

MSE Hiller supplied four Decapress model DP76–402 VAHY centrifuges  to the site, as well as a complete spare rotating assembly via JN Bentleys, the contractor commissioned by NWL to design, construct, install and commission the new raw and digested sludge dewatering process units at Bran Sands STW near Redcar.

Two of the centrifuges are used to pre-thicken sludge prior to the THP plant providing a controlled discharge of cake at 18% dry solids at flow rates of up to 100m3/hr each. The HMR5000 control system and accurate hydraulic scroll drive enables the machine to counter for variances in feed dry solids and continuously optimises machine performance.

Post THP the digested sludge is dewatered at flow rates of 35-70m3/hr using two of the Hiller DP76-402VAHY centrifuges to a cake of >30% dry solids prior to disposal off site as a Class A bio solid with no detectable pathogens and as a valuable agricultural fertiliser.

Hiller discharged digested cake at 30-35% dry solids.

Outcome

The project used the CAMBI thermal hydrolysis process (THP), using heat and pressure to break down cell walls increasing enzyme hydrolysis and therefore digestion rates. This leads to a 50% reduction in the volume of sludge produced and a significant increase in biogas quantity.

The new plant generates some 4.7 MWe from biogas which is used to power the treatment process. Reliance on natural gas has been reduced to less than 1/10th of its former figures, aiding the path to become a self-sufficient plant.