The Clari-DAF system significantly increased the plant’s capacity without a physical addition to the building. The dissolved air floatation was installed as two, parallel trains in the former sedimentation basin.
The engineers modeled the five conceptual alternatives to achieve a maximum daily water production of 81 ML/d during peak demand periods. The models would all be capable of an ultimate demand of 111 ML/d through Year 2025. After assessing how to consistently produce the desired volume and water quality, the best option for meeting peak demands was increased supplemental reliance on Penticton Creek. This offered the highest benefit-to-cost ratio and lowest life cycle operating costs within the plant’s existing 60 ML/d design capacity and ultimate annual production of 7900 ML.
DAF System
The team decided to go with a dissolved air flotation (DAF) system that could overcome the creek’s raw water shortcomings. The upgrade provide an impressive 75 percent capacity increase.
The system was installed within the existing single sedimentation basin that is now two parallel high-rate DAF basins. This major component fit within the existing physical footprint and with minimal environmental impacts during construction activity. The plant has increased the effective clarification capacity from 30 to an estimated 115 ML/d without requiring construction of larger basins.
The Leopold Clari-DAF® system supplied by ITT Water & Wastewater provides the utility with the flexibility to treat both the creek and lake water at any time of year to the desired water quality levels and meet peak demands without adding new clarification capacity for the immediate future. The plant continues to operate with the existing six, single-media anthracite 4.5 x 10 x 1.8-meter filters. The lake and creek raw water now can be used exclusively or alternated to compensate for seasonal changes in water quality, plant demand and to fully benefit from different costs.
In the Clari-DAF system, the Okanagan Lake raw water produces very light floc, which allows increased clarification flow with the flotation technology. Using a dual source for raw water also uses gravity flow for creek draws instead of incurring the energy costs to lift the Lake Okanagan water from an elevation of 341 meters to 461.5 meters.
Unlike traditional sedimentation basins that settle out particulates for discharge from the bottom, a DAF system receives flocculated raw water, separates and then carries the particulate matter to the surface. Countless micro-sized air bubbles injected through diffusers at the bottom of the contactor perform this task by mixing with the coagulated solids that rise to create a bed of floc across the surface where it is skimmed off mechanically. Meanwhile, the clarified water is removed from the bottom of the basin by laterals and advances to the filtration stage.
The latest DAF technology can clarify raw water at loading rates three to four times higher than a conventional design. The Penticton plant project represents the largest DAF retrofit and largest high-rate facility in Canada and supports sustained filter loadings of double the previous rate. This should prove sufficient until 2023, verified by pilot testing and subsequent full-scale challenge tests of the filters.