Free Chlorine Disinfection of Membrane Bioreactor Permeate: Disinfection Efficacies, Disinfection Byproducts, And Selected Microcontaminants
The membrane bioreactor (MBR) process is typically designed and operated to produce a fully nitrified, high quality permeate that makes it possible to use free chlorine for disinfection. California Water Recycling Criteria (Title 22) require all chlorine disinfection processes to meet a minimum CT value of 450 mg Cl2-min/L. This prescriptive process may be substituted by an alternative disinfection process that, when combined with filtration, has been demonstrated to achieve 5-log inactivation or removal of F-specific bacteriophage MS2 (MS2) or poliovirus. In this study, bench-scale and pilot-scale experiments were conducted, under normal and simulated membrane failure conditions, to determine the CT value required to meet 5-log virus inactivation when using free chlorine for disinfection of MBR permeate. The results from the study show that free chlorine is very effective for inactivation of MS2 and poliovirus at CT values that are significantly lower than 450 mg Cl2-min/L. A minimum 5-log MS2 and poliovirus inactivation was consistently achieved in bench-scale experiments at CT values > 10 mg Cl2-min/L. In pilotscale experiments, 5-log MS2 inactivation was consistently achieved at CT values > 40 mg Cl2-min/L. This study demonstrated that free chlorine disinfection did not lead to the formation of the disinfection byproduct N-nitrosodimethylamine, and produced levels of trihalomethanes and haloacetic acids that were well below drinking water standards. Several microcontaminants (carbamazepine, diclofenac, flame retardants, gemfibrozil, primidone, and triclosan) were detected in the MBR permeate prior to chlorination. Concentrations of diclofenac, gemfibrozil, triclosan, and total estrogenic activity were reduced by free chlorine, while carbamazepine, primidone, and flame retardants were not affected under the conditions tested.
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Document Type: Research Article
Publication date: 2009-01-01
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