Media retention screens and air grids. |
The IFAS process contains both free-floating biomass (MLSS) as well as biomass attached to a polyethylene media. The attached biomass increases the total biomass in the aeration tanks permitting more treatment in the same volume. The plastic media is retained in the aeration tanks by cylindrical screens with 5 mm slots, which allow the MLSS to pass through to the final clarifiers.
The AnoxKaldnes Hybas™ (Hybrid Activated Sludge) process was selected. Per the recommendations of AnoxKaldnes and the engineer, the demonstration train was divided into three anoxic zones, one aerobic IFAS zone approximately ½ of the total tank volume, and one swing zone. This option significantly saved the plant capitol costs and new construction was not required.
The potential for media migration due to bulk liquid velocity in the narrow plug flow tank was mitigated by installing internal recycle pump stations at both the upstream and downstream ends of the IFAS tank. By using the upstream pump station, the flow to the effluent end was reduced, preventing media migration to the IFAS stage effluent wall.
The demonstration train went on line in October of 2007 and was thoroughly studied through June of 2009.
The demonstration reactor achieved the desired effluent TN and ammonia concentrations. The owner decided to proceed with an AnoxKaldnes retrofit for all of the treatment trains. The engineer prepared a bid package to modify all nine reactors with a Kruger AnoxKaldnes Hybas process. Contractor bids were taken in April 2009. The first Hybas reactors are scheduled for startup in 2010.
Kruger's scope of supply included the 104,000 feet of AnoxKaldnes K3 type media for the nine Hybas reactors, medium bubble aeration grids, media retention screens, internal mixed liquor recycle pumps, and submersible mixers for the anoxic zone tanks.