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Operations & Assets Market view Taking the P Removing phosphorus from wastewater has always been a difficult job for water companies, but it's about to get harder with tighter consents levels, say Julie Jeavons, Ian Cranshaw and Ajay Nair. R emoving phosphorus from wastewater has been an issue for UK water companies since the introduction of the Urban Wastewater Treatment Directive in 1991. This challenge grew with the introduction of the Water Framework Directive. Now the sixth asset management plan period, AMP6, heralds even tighter phosphorus consent limits, with consent values of less than 0.5 milligrams of phosphorus per litre (mgP/l) under discussion, with the added sting of tightening iron limits. It will be possible to achieve these consents, but expertise will be needed to intertwine technical solutions with other factors such as reducing operating costs, minimising carbon emissions and water footprint, increasing energy production and overall resource recovery. Twenty years ago, Australia and the US saw first-hand the environmental impact of phosphorus in receiving waters. It depleted oxygen in water, encouraging the growth and decomposition of oxygen-depleting plant life, harming other organisms (eutrophication). This in turn reduced the recreational value of water and drove the need for tighter phosphorus discharge permits. MWH was involved in the design of three plants in Sydney to meet very low phosphorus targets, treating 1.3 to 4 megalitres of wastewater per day. A range of processes were deployed at the plants, including biological phosphorus removal methods. Biological nutrient removal with chemical back-up and tertiary filtration was also deployed by MWH at Iowa Hill and Pinery in Colorado to achieve 0.5 and 0.05 mg/l phosphorus permit conditions. Biological nutrient removal has not been widely adopted in the UK. Chemical dosing is the standard method employed by most water companies here. This is partially due to the higher number of filter works, but coprecipitation in activated sludge plants or oxidation ditches is also practised. By 2015 more than 650 UK wastewater plants will have phosphorus-removing technology – the vast majority chemical dosing. AMP5 will see 360,000 to 572,000 tonnes of iron products used each year, at a chemi- cal cost of £50 million a year. This is likely to increase during AMP6 as more sites get phosphorus consents and the iron dose is increased to achieve the tighter phosphorusconsent limits. But is this sustainable? The Water Framework Directive and Ofwat's move to an put the emphasis on outcomes rather than outputs has provided water companies with an opportunity to review the total phosphorus load to a watercourse. By revisiting the cause and effect of multiple phosphate sources within a catchment it is possible to deliver improved river quality and reduce the cost and carbon footprint of the end-of-pipe solution. MWH has drawn on its experience of phosphorus trading in the US to offer a similar service to UK water clients. For example, MWH has helped a leading water company to reduce its potential AMP6 phosphorus drivers from 77 to 18 sites. Tight phosphorus consents will still be required but they will be delivered where they deliver the most benefit to the environment. The higher iron dose rates required to Iron 96 per. mov. avg (full flow treatment) Typical Commissioning profile Daily average ferric dose FFT l/s -ferric dose l/hr Consent P -FE mg/l P Time 24 | 22nd - 28th November 2013 | UTILITY WEEK