The Water Framework Directive sets out an ambition to achieve ‘good ecological’ status across all rivers in England and Wales by 2027. A healthy river can provide us with a host of benefits, and clean water is only part of it. The river catchment land itself provides us with flood management, produce from agriculture, biodiversity and scenery to keep us fit in body and mind.
Currently only a small number achieve this target with phosphorus concentrations being the predominant reason for a river being of moderate or poor status. The presence of phosphorus can lead to eutrophication and algal blooms which impact on fish and wildlife by depleting oxygen levels within the river. So where does phosphorus come from? It’s found in soaps and detergents, fertilisers as well as human and animal waste. Depending on the river catchment the proportion of phosphorus from each source will vary: in rural catchments the amount of phosphorus from non-water industry sources can be ignificant.
Prior to the current water industry investment period (AMP6) phosphorus permits were driven by the Urban Wastewater Treatment Directive which focusses on large sites in urban environments. Under this directive sites with a population equivalent of less than 10,000 would not have a phosphorus permit. The Water Framework Directive has led to an increased focus on phosphorus in rural catchments and has resulted in an increasing number of small wastewater treatment works with phosphorus permits.
Modelling of river water quality can predict permits less than 0.1mg/l total P at very small works in order to achieve ‘good’ status in the watercourse. Is this an achievable standard to meet? Recent industry wide studies into achievable levels of phosphorus removal at wastewater treatment works have set a standard of 0.25mg/l total phosphorus as the lowest technically achievable limit.
However, the technologies used to meet this standard have been developed to take advantage of economies of scale and are therefore focused on larger, urbanised wastewater treatment facilities. Once scaled down to small works with a population equivalent of less than 1000 these technologies cease to deliver a cost benefit. So how can we improve river quality in these rural catchments?
The conventional approach to phosphate management
Conventional approaches of removing phosphorus from wastewater have focused on interventions at a wastewater treatment works that have followed either a biological or chemical removal route. These approaches involve major civil engineering and are either energy- or chemical-intensive processes. Biological phosphorus removal is not practically achievable at small rural treatment works leaving chemical treatment as the viable method of removal.
Chemical phosphorus removal involves the additional of metal salt coagulants to crude sewage, metal ions form a phosphorus precipitate which is then removed through settlement in primary treatment. The action of coagulant addition consumes alkalinity present in wastewater, which is of particular concern in areas of soft water such as Cumbria.
The introduction of chemicals to small, rural works also has implications on the number of vehicle movements needed for chemical deliveries; this can also lead to concerns around access routes which may not currently be suitable for frequent deliveries. The addition of chemicals to a site leads to extra requirements in terms of water supply for safety showers and increased frequency of site team visits.
Is this really the best way to tackle the problem, especially in a rural area? Are we over-engineering the solution – using a sledgehammer to crack a nut? Are we building expensive assets and leaving a legacy of big future operational costs for our customers?
How can looking at this differently provide greater benefits?
United Utilities has created a case study around the River Petteril in Cumbria to understand the issues to be faced in rural catchments and to develop an alternative approach to provide improved river quality. Based on partnership working, it will deliver more effective interventions and reduce the burden of investment costs on customers.
The River Petteril begins at Motherby near Penrith and flows north through farmland and rural communities until it joins the River Eden in Carlisle. There are 10 wastewater treatment works along its course, 10 combined sewer overflows and 12 wastewater pumping stations. There are also more than 100 farms, numerous private septic tanks and one motorway service station.
According to the Environment Agency the majority of phosphorus in the River Petteril is from non- water industry assets. So it became clear that a non-traditional approach was required to achieve tangible benefits in river water quality. We wanted to see how innovative treatment solutions and catchment solutions might provide a better option in the round. To improve our understanding of the River Petteril we have carried out catchment sampling and modelling to determine where effective interventions could be made.
We have been trialling innovative treatment methods at one of the wastewater treatment facilities in the Petteril catchment. This involves the use of reactive media to provide sustainable phosphorus reduction without chemical dosing or significant levels of energy consumption. The media captures phosphorus in a slow release bioavailable form opening up opportunities to recycle this to land as an alternative to conventional fertiliser. The results have been encouraging and show that the required level of phosphorus reduction can be achieved by this treatment process without the need for chemical addition.
Interventions focussed solely at the wastewater treatment works will address these point source discharges, however this has been found to be the source of less than a third of the phosphorus entering the River Petteril. Interventions are also needed that will reduce other sources of phosphorus within the catchment.
This is where we have built on best practice and case studies from other parts of our region. Since 2005 we have been leading on a range of catchment-based projects all aimed at keeping livestock out of watercourses, reducing nutrient addition from run-off and helping maintain improvements to the local bathing waters.
Through the Petteril project, working with partners like the Environment Agency, the Eden Rivers Trust and Carlisle City Council we’re getting the buy-in to bring all these ideas together into one approach with multiple benefits.
And what does this mean for our customers? The original cost of installing and operating traditional phosphate removal technology at all of our assets along the Petteril would have missed the majority of the problem. The cost of the integrated catchment management strategy comes in at a significantly lower cost and will address phosphorus throughout the catchment, there may also be additional benefits by slowing the flow of floodwater and reducing risk to water supply boreholes. This is the start of a three year pilot scheme, but it shows how working in partnership can bring exponential improvements.
DEFRA’s current 25 year plan sets out “to be the first generation to leave the environment in a better state than we found it.” Part of its approach, “Pioneer”, brings different agencies together to tackle environmental challenges in a new way, to get the best possible outcomes for the least cost.
We’re going to be sharing what we learn from the Petteril project with Pioneer, to help shape the UK’s environmental policy for years to come.