The pollution of a watercourse, tributary of the SEVRE NIORTAISE, was discovered by 2 fishermen not far from the outfall of the plant treating effluent from a slaughterhouse. They notified the Departmental Fishing Federation offices as well as the local fire station. The operator immediately stopped discharge to the natural environment and used the irrigation network to store the sludge in a backup silo at the nearest sewer treatment plant. The drinking water supply plant, located a few kilometres downstream and supplying water to the entire sector, interrupted its pumping into the SEVRE River. The consequences on fauna were difficult to evaluate.
The accident was caused by the development of filamentous bacteria that served to disturb the treatment plant’s sludge deposit at the level of lagoons and moreover discharged the bacteria along with effluent, at the outfall of the 3rd lagoon, into the natural environment.
The operator started chlorination treatment on 13th May at the aeration basin to eliminate bacteria and installed a mobile centrifuge in order to extract a greater volume of basin sludge. It was also planned to observe the sludge under a microscope every other week to prevent bacteria from developing and then, beginning on 19th May, to empty and spread sludge from the first 2 lagoons. Over the longer term (2008-09), it was scheduled to introduce a 2nd centrifuge or else replace the current one by another with twice the capacity, in the aim of removing at least 4 tonnes of sludge a day instead of 2 tonnes. Both the skimming tank at the plant entrance and clarifier were to be overhauled.
The drinking water purification plant had been bought in 2006 by the slaughterhouse, with the management function contracted to an outside firm. A major works programme had been completed at the beginning of 2008.