CONTRAFAST reactor chamber mixes water with previously settled solids to promote flocculation and solids contacting. Chemical addition is also introduced.
WesTech Engineering Inc. CONTRAFAST reactor chamber mixes water with previously settled solids to promote flocculation and solids contacting. Chemical addition is also introduced.

In wake of the water crisis in Flint, Mich., a dozen communities in Flint’s Genesee County are now receiving potable water from one of the newest water treatment facilities. The facility services more than 200,000 customers and receives water from Lake Huron via the newly-built $274 million Karegnondi Water Authority (KWA) pipeline. The pipeline is capable of delivering 125 million gallons per day (MGD) of raw water. The plant can treat about 30 MGD.

Genesee County officials are making rigorous efforts to ensure its water meets state and EPA requirements. Safety testing took place for four months at the treatment plant and multiple locations along the distribution system. The county completed its lead and copper testing in 2017. They also measured parameters such as temperature, pH, hardness, chlorine, fluoride, aluminum, zinc and sulfates, among others. The tests established a baseline for future water testing.

Conventional treatment was chosen as the best system to deliver the highest quality water. Traveling 67 miles, the raw water reaches a 150 million gallon holding pond where it can settle before it is screened and released into the plant.

CONTRAFAST High-Rate Sludge Thickening Clarifier

Genesee County began testing a clarifying technology called CONTRAFAST, developed by WesTech Engineering Inc., at one of the City of Saginaw’s 90-million-gallon reservoir cells. The CONTRAFAST pilot was designed to assess the effectiveness of the entire plant treatment process. A filtration pilot column was included as part of the testing to determine filterability of the CONTRAFAST unit effluent. Testing gauged pH levels, turbidity, and other factors.

“The clarifier utilizes a combination of internal and external solids recirculation, and tube-settling clarification,” said WesTech Process Engineer, Jeff Easton. “It is capable of running at four times the rate typically used for conventional clarifiers, and produces sludge with as much as 10% solids by weight, eliminating the need for a gravity thickener.”

The entire process takes place in a single basin; greatly reducing the plant's carbon-footprint.

Here’s how the CONTRAFAST clarifier works:

  1. Raw water is combined with recirculated sludge and treatment chemicals in a center draft tube.
  2. A variable-speed impeller mixes the flow at high G-values, accelerating flocculation and densifying the solids.
  3. Water and densified solids are recirculated within the reactor chamber.
  4. A high velocity upflow port prevents settling in the reactor and transfers the water to the settling chamber.
  5. A baffle directs the water to a more quiescent settling area where the solids settle out.
  6. Tube or plate settlers remove residual solids.
  7. Effluent launders collect clarified water.
  8. Dense sludge settles to the basin floor where it is continually scraped and further thickened.
  9. Thickened solids are recirculated to the draft tube to seed future floc and densify sludge.
  10. Periodic blowdown removes solids from the process as needed.

Once the CONTRAFAST units clarify the water, it passes through two CenTROL gravity filters in a cluster arrangement. Each CenTROL unit includes four gravity filter cells arranged around a centrally located influent distributor box and backwash waste control column. An operating platform on top of the distributor box allows convenient visual inspection of four filter cells from this central location. Inlet weirs within the distributors evenly divide flow between all online filter cells without the use of electro-mechanical flow control systems. Hydraulic flow control through the filter system eliminates potential flow surging providing a consistent high-quality effluent.

CenTROL Gravity Filter
WesTech Engineering, Inc. CenTROL Gravity Filter

Use of a downstream effluent weir system allows the filter system to generate the required backwash supply without the need for additional storage or pumping systems. Backwash of the filter incorporates WesTech’s MULTIWASH Filtration Process. It uses sustained simultaneous air-water backwashing to return the filter media to like-new condition after each backwash, while minimizing backwash waste generation.Specially-designed baffles, situated around the wash troughs, prevent media loss during the backwash process.

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