The goal of this paper was to establish a fundamental understanding of manganese (Mn) in
distribution systems with particular emphasis on the utilization of Mn by indigenous bacteria and
a strain of manganese oxidizing bacteria (MOB), Leptothrix discophora. Mn causes discoloration
of 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 secondary
maximum concentration level (SMCL) of 0.05 mg/L. Studies have identified Mn occurrence by
full scale evaluation, but little information is available to utilities for mitigating Mn. Although
well documented, MOB's role in Mn accumulation in the distribution system is poorly
understood. Two annular reactor (AR) trains containing polycarbonate (PC) coupons and two
containing cast iron (CI) coupons are used to model distribution systems. Each train has two
ARs in series with retention times of 2 and 6-h, respectively. Influent Mn concentrations were
0.02 or 0.05 mg/L. In one trial no microbial spike was provided to determine background Mn
oxidation from Cl<sub>2</sub> and potential biological oxidation from indigenous MOB. The chlorine
residual from the first AR was 1.0 mg/L. Results from this study revealed that biological
oxidation by indigenous MOB in the heterotrophic bacteria was minimal. Oxidation by residual
chlorine was the dominant factor in Mn accumulation in both polycarbonate and cast iron AR
trains, for both low (0.02 mg/L) and high (0.05 mg/L) dose of Mn. During the Leptothrix
discophora trial there was once again little biological oxidation by heterotrophic bacteria.
However, when the Leptothrix discophora were introduced into the system they resulted in
significant accumulation in all ARs. After chlorination in this trial the dominant oxidant became
the chlorine residual, where a residual was present. As in a full-scale distribution system, both
trials predominately had chemical oxidation occur in the first ARs where a residual of chlorine
was present. Where there was little to no residual in the second ARs microbial oxidation still
dominated. The findings from this research project should help utilities develop better
mitigation strategies for manganese occurrence in the distribution system. Includes 27 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/15/2004 |
