Scottish Water has hosted a group of councillors and local environmental stakeholders at their Ellon Waste Water Treatment Works (WWTW), to discuss the progress being made following a pollution incident during an extreme river spate in November 2022.

An extensive clean-up and recovery operation has been mounted by the publicly-owned water company after a large quantity of plastic biofilters escaped into the River Ythan when it rose to near-record levels and overwhelmed containment measures.

Scottish Water has so far committed over £315,000 to its response, with around 60 people involved from its own team and supply chain businesses in the north-east. It has also received crucial help from community-led beach cleans and from individual members of the public who have been able to pick up and dispose of biofilters.

Waste Water Operations Manager Nina Ker said: "Our two priorities since this incident occurred have been to reduce the impact on the local environment by recovering as many of the biofilters as possible; and to understand what we need to do to minimise the risk of any recurrence.

"We recognise and regret that recovery of all the biofilters is not realistically possible, but a great deal of progress has been made. Clean-up work has had to be planned carefully to minimise disturbance to sensitive habitats, especially within the nearby Forvie National Nature Reserve, and we are very grateful to NatureScot's team for their continuing support and guidance."

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The WWTW that serves Ellon was upgraded between 2019 and 2022 to ensure that it could continue to support the town's growing community. The new treatment process used a treatment technology called Integrated Fixed-film Activated Sludge (IFAS) in which biofilters suspended within aerated tanks help to provide a higher level of treatment without the need to significantly expand the footprint of the site.

Following around 6 months of initial operation, a fault occurred in November, causing the aeration lane to overtop and spill biofilters within the site. Containment measures initially functioned to protect the local environment, and the great majority of the filters were retained throughout, but safeguards were partially overwhelmed by rising floodwater when a recurrence of the fault coincided with the river level peaking over 18th and 19th November.

Nina added: "In parallel with the clean-up effort, we have confirmed that the upgraded WWTW can operate to a high standard without the need for the IFAS biofilters at this stage in Ellon's growth. We have therefore removed these from the aeration lanes and they will not be reintroduced until we are satisfied that the right measures are in place to minimise risk of recurrence, including in future extreme weather events.

"As Ellon grows in the years ahead, we expect that the operation of the IFAS element of the treatment process will be needed, but we will use the time available to ensure this can happen without unacceptable risk to the local environment."

Long term remedial measures for the site depend on the outcome of a detailed technical review which has not yet concluded. Scottish Water plans to hold a drop-in event in the local area later in the year to share its findings and provide a further update on the next steps.

In the meantime, the public water company is continuing to encourage members of the public to report any significant numbers of biofilters so that clean-up activity can be arranged.

Nina said: "The support we've had from the local community has made a huge difference to our response from the very outset, both in reporting areas in need of clean-up and assisting directly.

"As numbers of biofilters have reduced, the difficulty of locating and collecting them in a dynamic environment has increased. We are enormously grateful to everyone who has helped by collecting filters that they've found and disposing of them safely.

"While we would always encourage people to take normal hygiene precautions when carrying out beach cleans, the filters are not hazardous – and the best way to ensure they are removed from the environment is to pick them up and put them in a suitable bin."