Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | MARCH 2016 | 23 While the industry struggles to develop tertiary technologies that can achieve low P consents, removing phosphorus through secondary treatment has its own problems, as phosphorus-rich sludge liquors can cause rock- like struvite to form in pipes and anaerobic digesters and lead to a large maintenance bill. One technology that deals with this issue is the Ostara Pearl, which forces precipitation of P in a reactor, allowing phosphorus to be recovered in bead-like prills that are then sold as a certified fertiliser called Crystal Green. It has been successfully used in one UK installation - at Thames Water's Slough WWTW - as well as several others in the US and Europe. Peter Brewer, General Manager at ACWA Services, which markets Ostara Pearl in the UK, says: "The fertiliser made by this process, Crystal Green, is a certified NPK fertiliser so it can be used in all sorts of industries, on golf courses, potato farming, wherever fertiliser's required. It's no longer a by-product from wastewater that people are trying to find a home for, but a valuable product in its own right. "We've had some good positive feedback from a number of water companies we've had discussions with; they are looking at between a two and six year payback on their investment. Environmentally, this is the right thing to do, but it also has a payback - the two don't always go hand in hand, but in this case they do." • Phosphorus recovery in action of Wessex Water. In 11 cases this is a capex solution, and in 13 cases this is an opex solution, such as amending an existing dosing regime. Solutions that can tackle other sources of phosphorus in the Avon can then be considered to bring the watercourse up to the overall standard. If successful, it's an approach that could be applied to the regulation of other substances across catchments. "As water companies, just because we provide treatment and it's what we do, doesn't mean it's always the answer," says Barden. "We have to understand why we do the treatment in the first place, and if there's a way of achieving that more efficiently and a cheaper cost." Meanwhile, the current focus of research and innovation on P removal is around tertiary technologies that can 'polish' the final effluent from a works to get phosphorus levels down from around 1.0 mg/l to as low as 0.1 mg/l. With this goal, a group of six water companies have jointly funded trials at Severn Trent's Packington Sewage Treatment Works to test the capabilities of six potential solutions. Three of these are proprietary technologies which are variations on current methods, using chemical coagulants and/or a filter or membrane. However three more novel approaches are being investigated: a physical solution using iron nano- particles, a biological treatment using immobilised algae, and reed beds/ constructed wetlands using reactive media. Cranfield University is leading on the research for these methods. While it is possible that the reed beds using reactive media will progress to full scale trials during this AMP, the other two innovations are longer-term and are expected to require several years of development. Another, totally different line of thought on phosphorus in wastewater is that it ought to be tackled at source by persuading manufacturers to put less phosphorus into products such as drinks and detergents. Whatever the solution the industry reaches, the irony is that phosphorus is potentially a valuable resource: an essential nutrient, it is one of the three main ingredients in most fertilisers. Recovering phosphorus effectively from wastewater could help ease reliance on mined phosphate rock, which is imported and of which there is a finite supply.

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