Project Name: Oxidation Ditch Upgrade to OPTAER Wastewater Treatment Lagoons
Location: Hecla/Grindstone Provincial Park, Manitoba (Canada)
Project Type: Municipal Wastewater Treatment
Completion Date: June 2007
The Hecla/Grindstone Provincial Park, located on an island in Lake Winnipeg. The wastewater treatment facility was constructed in 1972. The original design was for operation as an oxidation ditch. Desludging requirements, liner reconstruction, phosphorus removal, and the failure of an existing baffle wall prompted a second system upgrade in 2007 (first was in 1998). Because the facility serves a provincial park, flow into the system is highly variable with peak flows during the summer.
The system was operating above its design flow and as a result, upgrades required an increase in capacity.
The "donut" shaped oxidation pond was divided into four distinct zones using floating impermeable flow diversion baffles. The baffles created separate treatment zones while minimizing short circuiting. This effectively maximized hydraulic retention time of the system.
To increase biological reaction kinetics, thus increase treatment, a complete mix fine bubble aeration system was installed in the first cell. The second and third cells were converted to aerated partial mix for further BOD5 removal. The fourth cell would provide final polishing and solids settling. The OPTAER™ fine bubble diffusers operate efficiently at a wide range of design flows, which not only allows for future expansion but allows for blower turndown during off-peak winter months.
The OPTAER® fine bubble diffusers were suspended below floating HDPE laterals, accessible from the water surface by boat for system maintenance without dewatering. A lateral self-tensioning system was implemented to allow for lateral expansion and contraction.
Phosphorus removal was achieved by adding alum in a mixing chamber between cells 3 and 4. The resulting floc would settle in cell 4. In order to minimize algae in the system effluent, a cover composed of 100 mm hollow HDPE balls was installed on the settling cell 4. The cover blocks sunlight to prevent algae growth. Effluent from the settling cell was disinfected prior to direct discharge to Lake Winnipeg.
Approximately nine months of effluent data were collected after system commissioning as seen in the graph above. The system consistently produced effluent of the expected quality (< 20/20 mg/L BOD5/TSS) except on one occasion (May 27, 2008) when the TSS value was at 28 mg/L. Effluent BOD5/TSS are typically less than 7.5 mg/L at off-peak season. TP from the treatment facility was below the 1 mg/L limit during the entire test period. The ball cover in the polishing/settling pond is quite effective in eliminating algae as is evident from the TSS leaving the system. This system demonstrates the excellent effluent quality that can be obtained from a well designed aerated pond.