Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/1108873
It's not easy being green With a £60 million investment aimed at producing 30 per cent more green energy from its largest sewage treatment works, Severn Trent's upgrade of its 12 anaerobic digesters has put people and pumps to the ultimate test By Chris French 12 WET NEWS MAY 2019 | wwtonline.co.uk S evern Trent is experienced in t r e a t i n g s l u d g e w i t h advanced digestion but con- verting its conventional digesters to a new thermal hydrolysis pro- cess involved a difficult transition phase requiring a specialist pump selection. Treating wastewater from a population equivalent of 2.5 mil- lion people and industry in the Birmingham area, each 5,000m3 digester at Minworth STW built up an amount of settled grit and rag, making the legacy sludge difficult to pump. Severn Trent already generates approximately 34 per cent of all the energy it uses as a business from renewables and, in seeking to reach a target of 50 per cent by 2020, it brought in the trusted ser- vices of framework partners MWH Treatment to design and construct a three-stream thermal hydrolysis p l a n t ( T H P ) u s i n g C a m b i technology. Making the AD process more efficient also provides the addi- tional benefit of sludge cake being classified as enhanced product fertiliser with potential use in the production of crops for human consumption. Severn Trent is a leader in renewable energy and the Minworth site already has combined heat and power (CHP) that can generate over 8MW con- tinuously and a gas-to-grid pro- cess that produces up to 750 m3/ hour of biomethane. Cambi's advanced THP reac- tors destroy pathogens prior to digestion. It is designed to treat 70,000 tonnes of (dry solids) sludge per year with a peak of 250 The CHP at Minworth can generate over 8MW continuously ONSITE SLUDGE TREATMENT AND ENERGY total dry solids (tds) per day. For many years at Minworth, sludge was moved from holding tanks to digesters for around 15 days' retention time, then to sec- ondary digesters, before going on to be dewatered. As MWH Treat- ment project director Richard Thomson explains, upgrading to Cambi's advanced digestion pro- cess also meant sourcing pumps that were capable of such a demanding duty point. "We knew of other treatment plants that had issues with sludge recirculation," he said, "and the head and the pipework distance were a concern in the design – not to mention the fact that the pumps would have to be capable of handling that very challenging legacy sludge without blockages or breakdowns." Part of the THP using Cambi technology