Manganese removal from potable water using anthracite : effect of pH, chlorine, colloidal MnOx and humate

Matanitobua, Vitukawalu Peceli. (2002). Manganese removal from potable water using anthracite : effect of pH, chlorine, colloidal MnOx and humate MPhil Thesis, School of Molecular and Microbial Sciences, The University of Queensland.

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Author Matanitobua, Vitukawalu Peceli.
Thesis Title Manganese removal from potable water using anthracite : effect of pH, chlorine, colloidal MnOx and humate
School, Centre or Institute School of Molecular and Microbial Sciences
Institution The University of Queensland
Publication date 2002
Thesis type MPhil Thesis
Supervisor A/Prof Barry Chiswell
Total pages 117
Language eng
Subjects 03 Chemical Sciences
090410 Water Treatment Processes
Formatted abstract

The aim of the work, supported by Gold Coast Water, was to attempt to understand why large input concentrations of chlorine to the media in the Water Purification Plant filters were required to initiate manganese removal on the fihers using the modified manganese greensand technique of manganese removal. Was the chlorine "cleaning" the media to facilitate manganese adsorption or was it oxidising adsorbed manganese to create a greensand effect? If the former, why was there no increase in dissolved organic carbon in the filtered water following intense chlorination, and if the latter, why did the procedure take so long to produce a greensand effect? A further aim of the work was to see if chlorine could be reduced or even deleted while still achieving manganese removal.

Treatment of the media with base produced a media, which successfully (particularly in the case of lime) removed manganese. However, the process required a pH > 8 which was unacceptable in a WPP.

It was found that if the media was clean, unoxidised manganese(II) would adsorb surprisingly well at pH ~ 5. At pH ~ 7, the media showed a much more limited ability to adsorb manganese(II); still with little oxidation taking place.

The role of calcium in facilitating manganese deposition (calcium is invariably found in pipeline manganese deposits) suggested that it may be an essential ingredient in successful manganese removal. This was found not to be the case; the use of both calcium and sodium based buffers were approximately equally successful in manganese adsorption.

It was found that if the cleaned media was treated with chlorine at pH ~ 5 either before or during manganese(II) addition, the percentage adsorption of manganese(II) decreased; no oxidation of the manganese took place at this pH.

The effect of chlorination upon manganese(II) adsorption at neutral pH was the reverse of the results achieved at pH ~ 5. Whereas at pH ~ 7 little manganese(II) removal occurred when chlorine was not used, the presence of chlorine on the filters markedly enhanced both manganese(II) removal and MnOx production on the media.

The work has shown that colloidal MnOx will not adsorb to the filter media at neutral pH regardless of whether chlorine is present or not, or whether manganese(II) is present. Indeed addition of manganese(II) to the filter media together with colloidal MnOx demonstrated that the manganese(II) preferred to adsorb to the MnOx and to pass through the filter. The presence of colloidal MnOx at approximately the same concentration as manganese(II) is a major inhibitor of manganese(II) adsorption on the filter media, and thus of its removal in a WPP.

Experiments in which clean media were pre-coated with organic material (humate) indicated that this material increased the ability of the media to adsorb manganese(II) at neutral pH. In the absence of humate, adsorption was as efficient as that shown by the media at pH ~ 5, and appreciably better than when the media had not been pre-coated. The extent of humate pre-coating appears to be unimportant in terms of the work done so far.

When the media was pre-coated with manganese(II) at pH ~ 5, and pH adjusted to neutral in the presence of chlorine (which should oxidise the manganese(II) in the media), the addition of humate together with either further manganese(II) or colloidal MnOx, yielded little adsorption of manganese(II) and none of colloidal MnOx. At this stage it is suggested that chlorination of media, which does not adsorb manganese(II) successfully, until it does so adsorb, is connected with a "cleaning" process of the media, i.e. the chlorine oxidises/chlorinates and solubilizes media deposits.

Results from preliminary X-ray Photoelectron Spectroscopy studies of manganese(II) adsorption and oxidation on the media are reported; Mn(III) oxide was obtained.

Keyword Water Treatment Plants
Water -- Purification -- Chlorination

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Wed, 27 Jul 2011, 16:55:47 EST by Mr Kevin Liang on behalf of The University of Queensland Library