The Microbiological Oxidation and Removal of Manganese from Drinking Water by a Continuous Recycle Fluidized Bioreactor
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
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Report No UWRAA 124
July 1997
SYNOPSIS
This work extends the results of previous research in which a technique was developed for the immobilization of manganese-oxidizing cells of Pedomicrobium sp. ACM 3067 on magnetite particles and for their use in a continuous recycle fluidized bioreactor (CRFB) for the oxidation and removal of manganese from water.
In this previous research a laboratory model CRFB was operated for 22 weeks with removal rates of greater than 74% and up to 98% for Mn2+ concentrations in the range 0.25 to 8.5 mg/l when operated at a residence time of 21 hours.
The majority of the manganese in the effluent was residual Mn2+ with only low levels of oxidized and adsorbed manganese present.
The bulk of the oxidized manganese remained attached to the immobilized cells in the fluidized column. Under controlled conditions the optimal pH was pH 7.8-8.0 but activity sharply declined to very low levels at pH 7. As low activity at pH7 indicated a potential problem with the process for treatment of neutral surface waters, the current research investigated the effect of influents in the range of pH 6-8without pH control.
Under uncontrolled pH conditions manganese oxidation and removal was found to be unaffected as the cells maintained an optimal pH of7.9-8.0 by metabolic activity. Manganese removal was also found to be enhanced at lower dissolved oxygen conditions with the optimal level being 2-4 ppm.
Pilot plant trials operated over a period of four months confirmed the effective treatment of raw drinking water at residence times as low as 15 min. The Pedomicrobium cells appeared to remain dominant and manganese oxidation was unaffected by the presence of competing natural microorganisms in the influent water. At a residence time of 15 min soluble manganese in treated water met the 0.1 mg/l guideline level for influent soluble manganese concentrations up to 0.6 mg/l, the 0.05 mg/l guideline for influent concentrations up to 0.3 mg/l, and the 0.02 mg/l guideline for influent concentrations up to 0.1 mg/l.
The ability to remove in soluble manganese from influent water varied and apparently depended on the nature of the particulate matter. It is recommended that the microbiological process for manganese oxidation and removal be placed at the beginning of the treatment plant and be followed by a filtration step to remove particulate material, and a chlorination step for disinfection.
Further research is required to investigate manganese oxidation in waters containing high levels of ammonium, nitrite, and nitrate which may affect manganese removal rates. Further work is also required to develop a continuous process to recover and dispose of the manganese concentrate and biomass from the fluidized bed.
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