At around 6.30 a.m., in an anaerobic digestion firm, an overpressure caused uncovering of the flexible roof of one of the digesters. Biogas was released into the atmosphere. The alarm was raised by the nearby residents due to the strong rotten egg odour characteristic of the release of H2S, present in the atmosphere. A mixture of foam and materials undergoing anaerobic digestion was released. All this was contained in the leakproof retention system provided for around the digester. The site was secured and shut down. At around 1 p.m., the system was restored to operation except for the accidented digester. The latter was drained.

The operator said that it had not heard the first overpressure alarm which was sent to it during the night, at 2 a.m. A phenomenon of foaming in the digester was the cause of the overpressure. The overpressure valve was set to be actuated at 3.5mbar, but the substantial production of foam would 

probably have prevented it from operating correctly. The valve had been checked three months earlier. One week before the event, the inputs were changed and potato pulp was introduced as a supplement to the customary inputs. Foam appeared the day before the event and the height of the agitators was increased to reduce its production as stipulated by the operating procedures. The cause of this overproduction of foam is not known.

Following the event, the operator planned to lower the level of material in the tanks. The Classified Facilities Inspectorate also requested that an analysis of the digestates coming from the materials pumped in the retention area and reintroduced into the anaerobic digestion process should be performed before spreading.

Restarting of the digester was performed 6 weeks after the event and created olfactory nuisances for the nearby residents during 1 hour.

In July 2020, an exothermal activated carbon reaction occurred on this site (ARIA 56388).