Pollution
Humain
Environnement
Economique

During the month of September, it was noted that the parameters at the outlet of the wastewater treatment plant (WWTP) of a sugar plant (COD, MeS, Nitrogen and BOD5) were exceeded. The WWTP only treats effluents containing organic matter (sugar cane microfibres) because the sugar factory uses only hot water for cleaning purposes; no chemicals are used.

The disruption of the biological treatment of the aeration basins was attributed to a drop in the pH between 4 and 5, whereas the pH must be maintained between 7 and 8 for optimal purification by microorganisms. This decrease was due to an excessively high influx of pollution from the start of the season and to the delay in the completion of maintenance on the WWTP. To complicate matters, the sugar season had also started early. The time between these two periods did not allow the sludge to be correctly prepared. In addition, there had been a change in the plant’s organisation, which is still poorly controlled with regard to the cleaning of gutters and occasionally generates high pollution loads, some chronic equipment leaks, a loss of power for oxygenation of one of the 4 aeration tanks and a lack of reliability on the part of the service provider in charge of sludge management.

As a result of this incident, the quantity of dewatered sludge to be managed during this period doubled.

The operator had diagnostic testing performed (leak testing of the equipment, power of the WWTP boosters, etc.) and an audit was conducted by a specialised company regarding the operation of the WWTP (validity of the analysis values, the various treatment steps, flocculent efficiency, etc.).

Following these diagnoses and audits, the following measures were implemented:

  • repair of equipment leaks and pumps under the tables;
  • reminder of the instructions concerning the management of the valves for the various pits in the plant;
  • optimisation of the screen rake and the oil separator;
  • successive passage of effluents through the 2 buffer basins before release into the aeration basins instead of distributing the effluents between these 2 basins;
  • seeding of the aeration tanks with purifying bacteria;
  • increase in the frequency of sludge extraction in the aeration tanks;
  • the service provider in charge of waste management was issued a reprimand.

The WWTP resumed normal operations on October 14th.

Other actions had been planned:

  • feedback on the operation of the WWTP by a specialised company in order to propose organisational and technical improvements;
  • implementation of a monitoring plan for sensitive equipment to reduce the pollution load sent to the WWTP during the next campaign;
  • training of technicians on the impact of releases from the plant to the WWTP and on the plant’s cleaning instructions;
  • a form for reporting malfunctions and ensuring the traceability of corrective actions was implemented;
  • improvement of internal reporting of WWTP management indicators.