The ultimate challenge was to add a beneficial treatment system, which would compliment the existing treatment system, provide for stable operation and at the same time be cost effective.

The customer's original wastewater treatment system was an extended aeration activated sludge process designed for 19,000 lb/d of BOD but was being overloaded at times to >30,000 lb/d during spill events in the factory. The overloading did not make operation of the existing system easy.

In addition, polymer was used to insure settling of MLSS in the clarifier and mechanical aeration devices (in addition to a fine bubble aeration system) were used to maintain a positive dissolved oxygen concentration in the basins, both of which translated into extra costs for the treatment facility.

The design

The overall design concept for this project consists of a combined biofilm and activated sludge system where the AnoxKaldnes Moving BedTM Biofilm Reactor (MBBR) system is used as a pre-treatment device ahead of the existing activated sludge system. The MBBR removes 30-40% of the plant's easily degradable organic matter and acts as a buffer when shock loads enter the treatment plant.

The MBBR process utilizes thousands of tiny, polyethylene Biofilm elements to provide a home for a vast, highly active bacteria culture. These buoyant elements are kept in constant motion throughout the entire volume of the reactor, resulting in uniform, highly effective treatment.

The MBBR system effluent flows directly, via gravity, into the two (2) parallel activated sludge basins, which consume the remaining organic matter contained within the wastewater. The first design phase of the upgrade treats an average flow of 0.800 MGD with a BOD load of 23,350 lb/day.

At this flow, BOD load and media fill fraction, the removal of soluble BOD is 35%, leaving <15,178 lb soluble BOD/day to be treated by the existing activated sludge units.

The overall treatment capacity of the MBBR can be upgraded by just adding media to the reactor and extra air to the existing aeration grid system. At the maximum fill of carrier media, the system will treat an average influent BOD load of 30,275 lb/day to an effluent soluble BOD of 16, 700 lb/day (45% removal of soluble BOD) at a flow rate of 1.037 MGD.

The activation of this plant has significantly improved the overall operation. The polymer usage in the secondary clarifiers has been completely turned off due to the improved settling rates of the MLSS in the clarifier. Return sludge pumping rates have decreased due to the increased concentration of settled MLSS in the clarifier. In addition, because of better settling rates, the surface aeration devices have been turned off since the extended aeration basins are now capable of maintaining a positive dissolved oxygen concentration (>2 mg/L). The reduction in use of all these items has resulted in a major cost savings for the customer.

58 Weybosset Street
Suite 400
Providence, RI 02903
www.anoxkaldnes.com
eProduct Number 445