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Grit • Accumulates in channels, pipes, primary tanks, digesters • Wears out pumps, valves and other mechanical equipment • Blinds filters and membranes • Clogs aeration basins and diffusers • Disrupts biological processes • Reduces the effectiveness of energy recovery • Reduces the quality of final effluent with a risk of exceeding pollutant limits 24 | 25TH SEPTEMBER - 1ST OCTOBER 2015 | UTILITY WEEK Game changer /Technology/Innovation The nitty gritty Mathew Beech explores a technology that could bring about step changes in the life expectancy and operating costs of UK water assets by enabling a more rigorous approach to grit management. F or sewerage companies, grit is a perennial prob- lem. It clogs up their facilities, leaving them with costly and all too frequently recurring problems which suck in valuable time and materials and push up energy costs. One solution to this bugbear is a technology that has existed for some time but has gained little traction in the UK thanks to regulatory hoops, the old capex-dominated economic regulatory regime and the traditional risk- averse nature of the UK water sector when it comes to trying out new things. It has, however, gained a strong foothold in the United States where the ownership structure for waste- water assets has long incentivised a whole-life approach to investment. The technology in question is an "advanced grit man- agement system" called HeadCell. In the wake of the introduction of a totex regime in the UK water sector, its owner, Hydro International, is hopeful that it can repli- cate both its stateside success in terms of installations and the benefits it has brought in cost optimisation and efficiency. What's the problem? Grit is found in wastewater not only as a consequence of the sewage it carries, but also because it is washed into Operations & Assets The HeadCell system is a stack of hydraulically independent poly- ethylene trays contained within a concrete chamber. Sewage, which has already been through a screen- ing process, enters the system via an inlet at the top of the chamber. The feed establishes a vortex flow pattern within the chamber, which causes the grit to settle on the angled, layered trays. The grit settles out by gravity along the sloped surface of each tray and then solids are swept to the centre opening, which allows them to fall to a common collection sump. The effluent flows out of the trays, over a weir and into an efflu- ent trough. The settled solids are pumped from the grit sump and into a washing system. How it works