Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/730827
18 | OCTOBER 2016 | WWT | www.wwtonline.co.uk Project focus: catchment permitting of upgrading individual sites to meet phosphorus standards under the Water Framework Directive were going to be prohibitive," says Matt Wheeldon, Director of Assets and Compliance at Wessex Water. "We both recognised that given the number of sites involved and the cost of improving each of them, there was a risk that nothing was going to happen. The EA made it clear to us that they were open to innovative approaches. "With this in mind, we went away and came up with an approach that would look at the total tonnage of phosphorus entering the watercourse. This, a•er all, is the overall outcome we are all concerned with, whatever the individual output of any capex or opex solution we pursue." Since 2000 Wessex Water has installed chemical dosing with ferric sulphate – a typical capex solution – to deal with phosphorus at the larger sewage treatment works in the catchment, but this is a relatively expensive option both in terms of upfront cost and ongoing running costs. Rather than investing heavily, and uneconomically, at a large number of further sites the company of the assets in that catchment and thinking about how we might regulate that. "If you say that you will take a certain load out of the environment on phosphorus across all those assets, but you can do it in a more flexible manner, it gives you a much better basis for looking at innovation and it will be more cost effective." Catchment permit design Once the concept had been established and included in Wessex's business plan, much detailed work has followed to establish which treatment sites made the most difference to P levels in the watercourse and should therefore be included in the permit. The eventual list of 24 includes the treatment sites where there is most scope for improvement and those which are most influential, because of their size and position in the catchment. Each has been assigned a 'stretch target' - an ambitious target for phosphorus load reduction expressed in tonnes per year – which Wessex will aim to hit but will not suffer a penalty if they do not. More important in compliance terms is the wanted to pursue a mixed approach using more opex solutions, such as optimising or improving the dosing processes it already has. While there are gains to be made from these solutions they have a less certain outcome than capex investment in new processes, hence the need for a less rigid, risk-sharing permitting regime. The idea of setting Wessex a catchment-wide target for reducing phosphorus was one to which the Environment Agency was very much receptive, explains the EA's Deputy Director of Water Quality Paul Hickey. "We have been actively encouraging the concept of catchment permitting and flexible regulation for some time," says Hickey. "Achieving environmental standards obviously involves a cost both in terms of building assets and the operating costs associated with them, and we were thinking about how we might flex our regulatory approaches to maintain the same safeguards to the environment in a more cost effective manner. So on the back of some of that previous thinking, between Wessex and ourselves we came up with this concept of looking at all A map of the Bristol Avon catchment showing stretch targets for P reduction at treatment works (Source: Wessex Water)