AWWA WQTC60569

The goal of this paper was to establish a fundamental understanding of manganese (Mn) indistribution systems with particular emphasis on the utilization of Mn by indigenous bacteria anda strain of manganese oxidizing bacteria (MOB), Leptothrix discophora. Mn causes discolorationof drinking water and will deposit on household fixtures, clothes, and boiled food. Consequently,utilities with chronic Mn episodes will strive for concentrations below the current secondarymaximum concentration level (SMCL) of 0.05 mg/L. Studies have identified Mn occurrence byfull scale evaluation, but little information is available to utilities for mitigating Mn. Althoughwell documented, MOB's role in Mn accumulation in the distribution system is poorlyunderstood. Two annular reactor (AR) trains containing polycarbonate (PC) coupons and twocontaining cast iron (CI) coupons are used to model distribution systems. Each train has twoARs in series with retention times of 2 and 6-h, respectively. Influent Mn concentrations were0.02 or 0.05 mg/L. In one trial no microbial spike was provided to determine background Mnoxidation from Cl₂ and potential biological oxidation from indigenous MOB. The chlorineresidual from the first AR was 1.0 mg/L. Results from this study revealed that biologicaloxidation by indigenous MOB in the heterotrophic bacteria was minimal. Oxidation by residualchlorine was the dominant factor in Mn accumulation in both polycarbonate and cast iron ARtrains, for both low (0.02 mg/L) and high (0.05 mg/L) dose of Mn. During the Leptothrixdiscophora trial there was once again little biological oxidation by heterotrophic bacteria.However, when the Leptothrix discophora were introduced into the system they resulted insignificant accumulation in all ARs. After chlorination in this trial the dominant oxidant becamethe chlorine residual, where a residual was present. As in a full-scale distribution system, bothtrials predominately had chemical oxidation occur in the first ARs where a residual of chlorinewas present. Where there was little to no residual in the second ARs microbial oxidation stilldominated. The findings from this research project should help utilities develop bettermitigation strategies for manganese occurrence in the distribution system. Includes 27 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

12

File Size:

1 file , 350 KB