Providing Phosphorus Removal for Rural Treatment Works

Bowman, B. and Aboobakar, A. United Utilities, UK


There is an ongoing phosphorus challenge to achieve “good ecological status” in waterbodies across North West England. The size range of sites required to meet tight regulatory permits is increasing, in some cases with phosphorus targets below 0.5mg/l. In recent years, much of the focus has been on technological developments appropriate for large works, leaving a knowledge gap in how phosphorus removal can be achieved sustainably in small, rural works. For works with population equivalents under 1000, there are added complications of limited workforce, power supply and access routes. Conventional approaches of chemical or biological nutrient removal may not be appropriate for these situations and alternatives are not readily available. Utilising the concepts of a circular economy we aim to deliver low maintenance, robust, sustainable phosphorus removal for small rural works. The role of reactive media for phosphorus removal and regeneration or reutilisation routes may be critical to delivering this goal.

The Water Framework Directive (WFD) has set an objective for wastewater treatment to achieve phosphorus (P) removal for the prevention of eutrophication in waterbodies. Modelling suggests that in order to meet ‘good’ ecological status in river catchments within the United Utilities region there will be a requirement to provide P removal at a large number of small treatment facilities (<5000PE). In addition, the permit requirements are becoming tighter, in some cases below 0.5mg/l.

Conventional P removal at small treatment facilities has typically been achieved through chemical processes. These processes contribute to significant operating costs and carbon emissions as well as increased customer impact due to chemical deliveries. This leads to a disproportional cost/benefit for the intervention. Chemical P removal operates through the generation of ferric or aluminium phosphate salts; these are largely unreactive precipitates from which P recovery is not viable. In the interest of future resilience this route does not meet our strategic vision.

Developments in technology to reach total P permit conditions less than 1mg/l have exploited economies of scale and intensive processes suitable for large, urbanised treatment facilities. These have limited suitability to rural catchments where a combination of catchment and end-of-pipe solutions has been shown to be the best approach to driving overall water quality improvements. A new type of approach is needed to suit the requirements for rural catchments which could also be an enabler to the recovery of phosphorus.

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