At 4:30 p.m., 20 t of sludge from organic products from a poultry processing plant were released into the GRANDE SAULDRE River. The facility operator initiated the site’s internal contingency plan, and the ditch involved was stripped to clean out the affected area. The release had resulted in equipment damage estimated at 0.10 M€.

The operator established several causes for the release:

• breakdown in the degreaser resulting in an accumulation of greasy foam in the basins. This grease caused an imbalance within the treatment plant, strongly reducing the decantation of sludge in the clarifiers;
• failure of the transfer gear motor at the gravity table outlet, which led to an increase in the amount of sludge in the aeration basins;
• a problem with the water supply used to clean the gravity table’s cloth element, reducing its overall efficiency;
• an overflow of the sludge silo owing to the incorrect opening of the valve;
• a failure of the scraper designed to remove excess grease from the clarifiers.

Several pieces of equipment were affected following the repeated power line disturbance that became increasingly pronounced the previous week owing to the works.

The operator undertook the following actions following the event:

• skimming of the grease layer on the basins;
• renovating the press to extract the sludge;
• ordering and replacing the faulty part on the outlet sampler;
• re-commissioning of the degreaser’s bubbling system;
• investigate to optimise the water supply for the operation of the gravity table;
• chlorine supply for shock chlorination to treat filamentous bacteria;
• develop a grease collection system to relieve the strain on the basins;
• raise the sludge extraction operations on the aeration tanks;
• complete diagnosis of the plant’s operation.