Continuous Resin Process Removes DOCs

July 15, 2002 -- The Water Corporation of Western Australia is building the world's first large scale MIEX® plant at the Wanneroo groundwater treatment plant.

Two years of pilot testing have shown that this ion exchange process effectively removed dissolved organic carbon (DOC), a precursor of disinfection by-products (DBPs).

The pilot trials and laboratory results indicate that the MIEX® Process, and alum coagulation, or other chemical coagulation, complement each other, regardless of process order. For the raw water at the Wanneroo facility, the MIEX process favored the lower molecular weight fraction of DOC, while alum coagulation removed the larger molecular weight DOC components.

Enhanced coagulation alone could not match the reductions in DOC, non-sulfide reduced sulfur (NSRS) and Trihalomethane formation potential (THMFP) that MIEX treatment, together with enhanced coagulation, achieved. The graph compares the reductions in THMFP and NSRS achieved with MIEX treatment alone, enhanced coagulation alone, and MIEX treatment combined with alum coagulation.

The new process differs from conventional ion exchange technology in that the ion exchange step occurs continuously, while the regeneration step is performed in a batch operation. This allows steady state conditions to be maintained in the ion exchange area of the process.

The MIEX resin particles are smaller than conventional ion exchange resins. Following contact with the raw water, a magnetic component within the resin matrix allows the particles to form larger agglomerates that settle out faster.

MIEX® treatment combined with enhanced coagulation reduced dissolved organic carbon (DOC), non-sulfide reduced sulfur (NSRS) and Trihalomethane formation potential (THMFP) to levels lower than coagulation alone.

The resin and raw water mix in the two 105,670 gal. concrete contactors and require only a minimal contact time of 10 minutes, even at full flow rate. Plant operators can adjust the resin concentration in the contactors to suit raw water quality and plant flow.

The resin and raw water mixture flows from the contactors to six concrete hopper-bottomed settlers. The gentle flow conditions allow the magnetic forces of attraction between the resin particles to form agglomerates, which settle out.

The MIEX treated water rejoins the existing conventional treatment flow upstream of the plant clarifiers. The resin slurry either returns back to the first contactor, or is diverted for regeneration using 12% brine solution.

Black and Veatch, Australia, is the contractor for the new resin plant, which is being retrofitted at the Wanneroo groundwater treatment plant. The full-scale MIEX train will have a capacity of 30 MGD.