Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/538666
14 WET NEWS JULY 2015 T he benefits of thermal hydrolysis in sludge digestion – improved biogas yield, reduced sludge volumes for disposal and higher digester loadings – are well known and, when Thames Water needed to upgrade its Oxford Sewage Treatment Works, it selected a Veolia Biothelys plant as part of a £22M project that also included refurbishment of the existing anaerobic digestion plant and new sludge storage and handling facilities. The modified Oxford works treats 25,000 tonnes of dry solids per year, primary and secondary sludge from the Oxford works plus sludge from outlying treatment works. The thermal hydrolysis process heats sludge to 165°C at 7barg using 12bar steam and retains it at this condition for 20-30 minutes. Treated sludge is fed to the Installing a Biothelys plant on a space restricted site is no mean feat. But with contractors and subcontractors vying for the same space, one scheme became a logistical challenge. Tim Humphreys explains. The challenge: Construction site safety INSIGHT HeaLTH & safeTY existing downstream anaerobic digesters at a dry solids concen- tration of 10-12% – about twice that of untreated sludge, almost doubling the digester throughput. Restricted site Installing the Biothelys plant with its six reactors, each 1.6m diameter and 8.5m height, and two 2.5m diameter hydrolysed sludge buffer tanks, on what was always going to be a restricted site presented something of a logistical challenge for the principal contractor, AECOM-Kier (AKT). It was further complicated by the number of other subcontractors involved in the project, all wanting to work in the same area. As more and more of the site became occupied with plant and equipment, access for con- struction became progressively more difficult, creating both programme and health and safety challenges. Project planning made exten- sive use of building information modelling (BIM). AKT had previ- ously used BIM and was con- vinced of its advantages, but it can only be applied if all the information is available. Routine procedure This meant laser scanning the existing assets into AKT's building information model. Veolia had already developed a detailed 3D model of the Biothelys plant, a routine procedure on all its projects to ensure optimised layout and good access. "Importing our Biothelys 3D model into AKT's BIM not only helped to keep construction on programme, but also had a pos- itive impact on the health and safety record for the project," says Veolia's health and safety manager, Lyndsey Wicks.