Pollution
Humain
Environnement
Economique

Fishermen reported that over 8○km of the River Seiche was polluted and that much of its water life was dead. The culprit was an abnormally high amount of raw lactose that had been discharged from a cheese factory’s wastewater treatment plant and depleted the river’s oxygen.

The results of a sample collected 3 days later showed that the discharges from the WWTP were over the legal limit. A total of 1.3○t of organic matter was discharged into the river, which already had been severely affected by drought. The lactose extraction workshop was shut down on 22○August.

Lactose was rerouted to the plant’s retention ponds. The plant analysed the effluent entering and leaving the WWTP over the following two weekends. A team worked from 24○August to 1○September to pull the dead fish out of the river. By 28○August, they collected 1○t of dead fish. The plant began analysing the effluent entering and leaving the WWTP seven days a week. The water in the river was diluted by accelerating discharges from the upstream pond and a specialist company reoxygenated the river on 30○August. The remediation efforts cost €250,000. On 1○September, an estimated 6○t of dead fish had been collected and the cheese plant’s discharges were back within the legal COD limit. On 4○September, the river’s oxygen level improved significantly. Four aerators continued operating and water continued to be fed in from the pond. On 8○September, tests showed that the river was back to normal.

The plant operator issued a press release on 4○September. The discharge was caused by an incident on the lactose workshop’s PLC. The incident was caused by a modification of a valve’s computer program. The impacts of this modification have not been sufficiently verified.

The operator took the following measures:

  • procedure for draining the buffer pond at the WWTP’s inlet to the containment pond in the event of pollution;
  • study into the feasibility of having the effluent entering and leaving the WWTP analysed each weekend by the site’s security firm, with the results being sent to the WWTP’s on-call staff;
  • weekly inspections of the site’s discharge point to the Seiche and measurement of upstream and downstream oxygen levels;
  • procedure for managing forecasted high loads sent to the WWTP;
  • installation of a TOC analyser to measure flows entering the WWTP and anticipate incoming loads;
  • qualification of the remote system used monitor the WWTP’s operation and alert its on-call staff;
  • qualification of the automatic changeover from the stormwater network to the containment basin in the event of chemical spills (acids and bases);
  • technical study and proposal regarding a system for continuously evaluating loads entering the WWTP instead of with the current 24-hour delay.