EVERY MOLECULE COUNTS
Rachel Edgington and Andrew Thompson
Severn Trent Water
(free)
Severn Trent Water operates over 1000 sewage works and 43 sludge treatment centres.
About 150,000 dry tonnes per annum of biosolids are produced of which about 75% is
recycled to agriculture. The majority of raw sludges are anaerobically digested. In more
recent years, combined heat and power systems have been installed with a total capacity of
30MW to maximise revenues from the digester gas produced from the mesophilic anaerobic
digesters. The company strategy of increasing income, reducing our carbon footprint and
reducing the quantity of biosolids for recycling has resulted in digester optimisation and the
assessment of sludge technologies that enhance sludge digestion to increase gas production.
Two technologies are being taken forward by the company for full scale operation. Firstly,
Sonix, a sludge disintegration technology has been installed at Minworth (Birmingham) STW.
This process is operational and undergoing its performance testing. Initial data looks
promising and is highlighting the importance of good baseline data. Secondly, after R&D work
and assessment of the alternative technologies, acid phase digestion is being designed for
Derby STW with commissioning due in early 2009.
KEY WORDS
Sewage sludge, biosolids, enhanced digestion, ultrasound, Sonix, acid phase digestion
