RINGING IN THE CHANGES FOR ANAEROBIC DIGESTION ULTRASONIC TREATMENT OF SURPLUS ACTIVATED SLUDGE PRIOR TO ANAEROBIC DIGESTION
Richard Smith 1 & Matthew Griffiths 2,
1. Severn Trent Water Ltd, UK
2. Purac Ltd, UK
(free)
Severn Trent Water operates over 1000 sewage treatment works and 43 sludge treatment centres across the centre of England and Wales. It produces 140,000 dry tonnes per annum of treated bio-solids and approximately 60% is recycled to agriculture and land restoration projects. The company treats over 95% of its raw sludge by conventional mesophilic anaerobic digestion and in general recycles dewatered sludge cake. The changing nature of the raw sludge fed to the digestion process, proposed changes in the legislation controlling the recycling of sewage sludge to agriculture and the company’s developing power generation strategy have led Severn Trent Water to review and optimise the performance of its digesters.
As part of this review the company has carried out a full scale evaluation of Purac’s sonixTM disintegration system for surplus activated sludge (SAS) at a works in North Nottinghamshire. The programme of testwork reviewed the performance of a pair of conventional mesophilic digesters before, during and after the disintegration process was applied to the indigenous SAS fed to the digester. The trial generated encouraging results and suggested that the process could produce a significant improvement in volatile matter destruction. The paper will discuss the performance of the digestion process before and during the trial and will review impact of the disintegration process on the digester’s efficiency.
KEY WORDS Anaerobic Digestion, Disintegration, Surplus Activated Sludge, Ultrasound
