Up to 8m litres of waste could have been spilled in a leak of anaerobic digestate at Harper Adams University College, it has emerged.
Emergency services were called after digestate started spewing from a faulty storage tank, which is part of the college's flagship green energy system at Newport, Shropshire.
Harper Adams said two storage tanks were associated with the anaerobic digestion system - one capable of holding 5.6m litres and another with an 8m litre capacity.
The leak involved the larger tank, the college confirmed. A bund built to contain any leaks also failed, causing digestate to flow on to an adjacent field.
Harper Adams has been unable to tell Farmers Weekly whether the 8m litre tank was full when the leak occurred. It has also been unable to say how much digestate was spilled.
The cause of the incident remains unclear. The Environment Agency has suggested it was a broken valve, while other reports have described a mechanical failure within the tank itself.
The clean-up operation has seen a fleet of articulated lorries and tankers used to move the digestate from behind the bund and other areas.
Eyewitnesses have described the area around the digester as "a mess".
Environment Agency officials announced that the leak had stopped at 1pm on Thursday (21 February) - some 36 hours after it started.
"Teams are working around the clock to manage the impact of the digestate that has leaked and remove it from the site," said an agency statement.
No-one was injured, but the agency described the spillage as a "large-scale environmental incident".
Special oxyjets pump remain in action - injecting hydrogen peroxide into nearby watercourses to raise oxygen levels, enabling fish and other wildlife to survive.
The statement said the agency had not received any reports of environmental damage or fish deaths, but would continue to monitor the situation.
Swift action had stopped the flow of pollution into the Pipe Strine and the River Strine, it said.
"By using temporary dams across ditches, blocking up culverts and pumping the pollution out of channels, we were able to stop the pollution flowing in to local watercourses."
There have been local reports of pollution, but the agency said it had worked with Harper to contain the digestate within the site and prevent a serious pollution incident.
Severn Trent Water has been assisting the clean-up operation by taking some of the waste to a nearby sewage treatment works to be processed.
Haydn Knowles-Love, the water company's regional production manager, said: "The quick action of all agencies has been important to alleviate the pollution impacts."
He added: "We will continue to monitor this situation closely, and can confirm that public water supplies have not been affected".
The leak was first reported to the agency during the afternoon of Tuesday (19 February).
Shropshire Fire and Rescue Service were called to the site at 7.45pm the same evening, where they deployed 35 firefighters and officers.
Incident commander Andy Perry said: "The value of our close working relationship with the Environment Agency has proved itself once again at this incident, with both agencies working extremely well together with the occupier to bring the incident under control."
Mark Bowers from the Environment Agency said Harper Adams quickly alerted the authorities to the situation.
"Our priority is to minimise the impact to the environment and by working with our partners we have been able to achieve this in a reasonable timescale."
"We are continuing to work with them on and off site to address the leak, and contain and remove the pollution."
Harper vice-chancellor David Llewellyn said college staff and local contractors had worked tirelessly for two days to remove the digestate and minimise the environmental impact.
"We take our environmental responsibilities very seriously and are now in the process of conducting an investigation into what happened and why."
Meanwhile Biogen, the company that constructed the anaerobic digester, said it was not responsible for the faulty storage tank or failed containment bund.
The company said: "The storage tank and containment bund was supplied and installed at the AD plant by another contractor after Biogen had completed the plant build and handed it over to Harper Adams' operational team."
It added: "Although the particular storage tank is outside of Biogen's scope of supply, Biogen is making itself available to offer advice and support to Harper Adams Energy if required.
"Biogen has arrangements in place for Harper Adams Energy to process food waste on its behalf.
"As a result of this incident, we have arranged for this food waste to be treated elsewhere until such time as it can be processed by Harper Adams again.
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