Pollution
Humain
Environnement
Economique

In a factory manufacturing meat-based dishes, wastewater overflowed onto the site’s internal roadway during the day. The stormwater containment basin’s valve was closed as soon as the overflow was detected. The water contained in the basin had a volume of 20 to 25 m³, consisting mainly of water for washing vegetables and for cooling pasta and rice.

The incident was attributed to the decrease in the flow rate on one of the lifting pumps on the tank used to pretreat the wastewater from the manufacturing workshops. While the pump was still in operation, the emergency pump did not trip on. This generated an increase in the load on the upstream wastewater network from the plant, which then resulted in the overflow. The decrease in the flow rate was due to partial obstruction of the lift pump by a large piece of carrot.

After closing the valve on the containment basin, the operator set the emergency pump to manual override to stop the flow of water, removed the carrot from the main pump, and then restarted it.

The following actions were programmed:

  • a reminder of the good practices to be followed in the workshops (keeping screens and sewer baskets in place, pick up waste off the floor);
  • welded bars added to wastewater pipes not yet equipped;
  • increased sensitivity of the alarm in place;
  • addition of a second pump failure alarm at the lift station;
  • modification of the emergency procedure in the event of the accidental discharge of wastewater into the stormwater basin, ensuring immediate pumping.

Analyses were carried out by an approved company prior to pre-treatment. The results provided a month later (on 2/09) indicated that 2 values were exceeded, COD (128 mg/l) and oils/fats (24 mg/l).

A second incident took place a few days later: on 8/09, after a day of high heat and heavy rain, the basin contained 1,300 m³, including 20 to 25 m³ of washing water from the previous incident. In light of the analysis results, the dilution and additional purification treatment operation through the hydrocarbon separator sludge trap, the operator decided to reopen the overflow valve. On 12/09, an agent from ONEMA (The French National Agency for Biodiversity) came to the company to inform the operator that dead fish had been found in the Touch River.