Retro-Fit - Conversion of a Failed Media Filter to a Suspended Growth Aeration System case study


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This particular project involved the conversion of a failed media filter to a suspended growth aeration system. The project was managed by Mr. Hal Lewis, P. Eng. of Stantec Consulting Limited.

Sani Tech Communal Systems was awarded the contract to design and construct the repair. Sani Tech retained the services of Mr. Robin Smith, P. Eng., of Robin Smith Engineering to provide the process design brief to be submitted to the Ministry of the Environment. Once the approval was granted, Sani Tech proceeded with the retrofit.

The existing tank consisted of a single tank approximately 30 metres in length, 3 metres wide and 2.5 metres deep. The tank had been poured in place and had a 300 mm thick roof. At one end, the filter media had rested in a raised section above the roof of the tank. This particular area was re-used for the foundation of the new control building. Inside this building now are the blowers and controls for all pumps in the system.

The Sani Tech supplied system utilized a Sani Tech Model SB26M nitrification / denitrification single sludge process based on the four-stage Bardenpho process. This process was selected as it uses the wastewater carbon to carry-out pre-denitrification thus minimizing the requirement for a carbon addition such as methanol to affect denitrification. Also, the primary denitrification stage, in advance of the nitrification stage, provides 50 percent of the alkalinity requirement for nitrification. Together with the source alkalinity present in the wastewater, the denitrification alkalinity will provide sufficient alkalinity to maintain a buffer and not inhibit complete nitrification either from alkalinity reduction or changes in pH.

The System componets were generally as follows:

  • Primary settling/grit removal
  • Primary flow equalization and raw sewage pumping
  • Biological single sludge carbon oxidation, nitrification / denitrification process. A four-stage Bardenpho process will utilize wastewater carbon to accomplish denitrification
  • Secondary clarification
  • Sludge storage facilities
  • Associated aeration, pumping, chemical storage and feed equipment

The new tank walls were poured into the existing tank. The forms were lowered through openings cored in the existing tank roof. These 600 mm openings were subsequently used as access openings for the new system.
A new clarifier tank was added for final clarification before being pumped to the leaching beds. Monitoring to date has shown BOD as low as undetectable. As the system approaches maturity, all results are anticipated to be excellent.

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