Controlled Backmixing post gravity belt thickeners using Primary Sludge at Reading STW

Massé, A-L. – Thames Water


A stable dry solids feed to digesters is a crucial parameter to ensure a stable digestion process and optimum gas production. At Reading STW, the dry solids post primary belt thickeners usually vary between 8 and 12%DS (Dry Solids) even though the downstream systems (pasteurisation and digester feed) are unable to cope with sludge this thick as it causes blockages. Alternatively the belts can be “derated” by reducing polymer injection but this
leads to poor flocculation and solids capture rate as well as limited control. The alternative would be to dilute automatically the thick sludge with unthickened Primary Sludge after the belt to keep the Dry Solids at an optimum and controlled level. This method has been used previously on pre-THP dewatering but is now being tested on conventional sludge thickening.
The aim of this paper is to explain the logic behind the project and describe the trial and system installed at Reading STW where three different methods of calculating in real time the dilution were tested and assessed (cake pump torque, sludge dry solids and pipe pressure). Additionally, the paper will give an overview of similar equipment and processes implemented and tested at Oxford STW (pre-dewatering THP).

The Biosolids conference attracts the most authoritative global experts in the area of biosolids and organic resource handling, treatment and recycling. The programme covers both the latest innovations and updates of existing technologies. Presentations from respected industry experts and newcomers follow the development of technologies and legislation from inception to full-scale installations.

The conference regularly gathers over 200 delegates from all over Europe, many of them return every year both for the technical presentations and fantastic networking opportunities.

Regular conference themes include:

• Thickening and Dewatering
• Modelling Sludge Handling and Utilisation
• Commissioning and Operating Experiences with Thermal Hydrolysis
• Tackling Potential Odour Problems
• Operating Experiences and Potential Problems in Digester Operation
• Ensuring Optimum Energy Recovery from Biogas
• Liquor Treatment and P Removal
• Alternative Products from Sludge
• Enhancing the Value of Biosolids and Digestate
• Pathogens and Pollutants In Digestate
• Sharing Experiences

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