AWWA ACE65310

The City of Chicago, Department of Water Management owns and operates two large conventional water treatment plants. In order to optimize treatment processes at these plants without affecting full-scale operations, a pilot plant was built. The pilot plant consisted of two side-by-side treatment trains and was carefully designed to simulate Jardine Water Purification Plant operations while allowing for flexibility in source waters, additional treatment processes, chemical application points, and filter media. After successful calibration of the pilot plant to JWPP operations, research was conducted into ozonation of taste- and odor-causing compounds as well as bromate control. Because the pilot plant used sodium hypochlorite instead of chlorine gas, the coagulation pH levels in the pilot plant were slightly higher than those in full-scale operations. Both alum and sulfuric acid addition were effective at reducing the pilot plant pH to produce similar settled water turbidity levels to those in full-scale operations. Pilot plant ozonation resulted in significant removal of MIB and geosmin. At an ozone dose of 3.0 mg/L, MIB and geosmin removal occurred much faster than at a dose of 1.5 mg/L. At a contact time of 10 min. and a dose of 3.0 mg/L, ozone was found to reduce MIB and geosmin by 95.8 and 73.7%, respectively, to below 5 ng/L. At the same dose, however, bromate in the pilot plant was found to exceed the Stage 2 D/DPBR MCL of 10 µg/L. Successful bromate control strategies included reducing the ozone dose to 1.5 mg/L with a contact time of 13 minutes or less, lowering the pH to 7.3 or lower, and addition of 0.065 mg/L ammonia-nitrogen. Includes 4 references, tables, figures.