WET News

16 WET NEWS DECEMBER 2014 The inlet works at Yorkshire Water's Cudworth WwTW had to be upgraded to meet the daily FFT. ASP was rejected because of cost. The challenge: Upsizing to meet demand S ituated in the Barnsley area, Yorkshire Water's Cudworth Wastewater Treatment Works (WwTW) serves a growing population of around 12,000 people. The existing inlet works was undersized for the 5.4Ml/ day full flow to treatment (FFT) required and the asset life of the works had expired, result- ing in the carry forward of sol- ids / grit and screenings. Ultimately this would affect the way the process operated, causing an increased risk of consent failure. Therefore, to meet future Environment Agency (EA) con- sent compliance measures related to the Water Frame- work Directive (WFD) and Freshwater Fish Directive INSIGHT SLUDGE TREATMENT & DISPOSAL (FFD) the works needed to reduce the ammonia and Bio- chemical Oxygen Demand (BOD) limits produced by this site. The treatment plant had to meet the new 95% tile consent for discharge to the River Dearne of 10mg/l total BOD; 3mg/l ammoniacal nitrogen; and 55mg/l total suspended solids. Other economic and envi- ronmental factors to be addressed included future population growth and a more cost-effective process to help reduce the operational expenditure of this site were also included in the brief. An initial solution based on a conventional treatment pro- cess using an Activated Sludge Plant (ASP) followed by sand filtration was proposed. How- ever, Turner & Townsend and joint venture Morgan Sindall Grontmij (MGJV), the contrac- tor on the project, challenged this standard approach. This option was estimated to cost about £9.7M and have high operating costs. Sludge storage was also an issue. The ASP process would have produced a greater quan- tity of sludge than humus sludge production in conjunc- tion with biological filter beds. As a result, MGJV sought alternative treatment process options as well as more inno- vative solutions that would also integrate the site's exist- ing assets. Having opted not to use an ASP, adopting a MBBR and DiscFilter offered capital efficiencies. A solution: MBBR innovation for conventional processing M GJV proposed the instal- lation of a packaged in- let works, comprising a Moving Bed Biofilm reactor (MBBR) and DiscFilter system as tertiary treatment, along with a new approach to design manage- ment. This had a single detailed design acceptance (DDA) encom- passing all the works rather than individual DDAs. All of which were a first for Yorkshire Water. The MBBR is a fixed film pro- cess. However, unlike the major- ity of fixed film systems, in this application the media can move freely within the aeration reac- tor. This combines the high bio- mass concentration achievable with fixed film processes with the small footprint of a conven- tional activated sludge process. The MBBR plant consists of two parallel streams each with two reaction compartments in series. To ensure complete nitrifica- tion, each compartment is charged with 44m 3 of Veolia's AnoxKaldnes Type K5 carrier ele- ments, which have a protected surface area for biofilm growth of 800m 2 /m 3 . The design allows one com- partment to be taken off-line for maintenance by pumping the media into the corresponding compartment in the other stream. The media only occupies 30% of the aeration tank volume, enabling it to circulate freely, and this is aided by the aeration system which consists of a floor mounted fine bubble diffuser grid supplied by variable speed blowers controlling the dissolved oxygen concentration to 5mg/l. Final solids removal is pro- vided by two 100% duty HSF 2208/7-1F Veolia's HydrotechTM Discfilters. The self-cleaning disc filter consisting of a series of hol- low segmented discs supporting a 10μm woven polyester screen and mounted on a central sha¦. Influent liquor enters along the centre line of the unit and is distributed radially on the inside of the discs. The flow passes through the mesh leaving sus- pended solids retained on the inner face of the filter elements. Filtered water is collected in the chamber around the disc filter and an outlet weir, which is part of the structure. This maintains the filtered water level so that the discs are approximately 65% submerged. The innovative solution used has had a positive impact upon the environment, reducing the carbon footprint through provid- ing more environmentally friendly assets, which will also provide a considerably reduced opex for the site by utilising bio- logical treatment in preference to the ASP process. n THE CONCEPT • Veolia's AnoxKaldnes Type K5 MBBR technology was installed along with the Hydrotech DiscFilter • The technology eliminated the need for deep excavation and inter-stage pumping • The footprint over the overall treatment process units was minimised • Sludge handling require- ments were reduced • Much of the existing process was retained with additional tertiary polishing NEED TO KNOW 1 A conventional treatment process using an Activated Sludge Plant (ASP) was estimated to cost £9.7M and have high operating costs. 2 Sludge storage also had to be taken into consideration. 3 The solution had to have a positive impact on the environment, and integrate into the site's existing assets THE VERDICT • Embedded carbon has reduced by 25% compared with the ASP • Capital efficiencies amounted to £2.6M and out-performance savings came to £900K • Reduced ammonia and BOD limits to achieve an average reading of 0.5

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