Manganese oxide deposits in water treatment facilities, North East Scotland.

The aim of this investigation was to examine the deposition of manganese oxides in water treatment facilities. To facilitate this work, suitable sources of manganese oxide were located in water treatment plants throughout the Grampian region of Scotland. These oxides provided an ideal and abundant media on which this work could be based. Manganese oxide deposits were characterised by examining their chemistry, structure and integrity. Factors affecting the deposition of these oxides were investigated in the laboratory and combined with a long term monitoring program of water treatment plant deposits in order to understand the nature of the deposition process. Oxide deposits were found to be mechanically robust and could not be easily removed from the sand substrate they uniformly encapsulated within sand filtration beds. The oxides were amorphous with a stoichiometry close to MnO2, with very little variance in stoichiometry found within filter beds and between treatment facilities. The mass of manganese oxide deposited grew significantly over the course of this study, with growth primarily limited by the concentration of manganese available in the filter influent water. The impact of this deposition was to lower the levels of manganese in water leaving the water treatment facilities by greater than 80%, compared to 1988 figures when these deposits were not present. Factors controlling the deposition process were studied using laboratory simulation. The mass of oxide present, the presence of chlorine and solution pH were found to have a major impact on the deposition process. Of these three factors, the presence of chlorine in solution had the most significant impact. Chlorine not only dramatically improved the manganese adsorption capacity of the oxide but also ensured that the adsorbed manganese could not be subsequently leached off. The effectiveness of manganese oxides for removal of metal ions from solution was determined in the laboratory. Adsorption/desorption profiles of the oxides with a range of aqueous metal solutions under different conditions was examined and a suitable model was developed to fit this process. Metals considered in this study included Co, Ni, Cu, Cd, Mn and Zn. The capacity of the oxides to remove metal ions from solution was controlled by the mass of oxide present and solution pH, regardless of the source of the oxide. Adsorption increased greatly at higher solution pH values, with adsorption being almost totally reversible. A Freundlich linear adsorption isotherm was found to model the adsorption process for all metals studied. Overall, the impact of manganese oxide deposition on the removal of metal ions from freshwater environments was considered. The suitability of these oxides for use as a novel water treatment media was examined and used as a working guide for potential future applications of this media in water treatment processes. By simply controlling conditions within water treatment facilities, a suitable manganese water treatment media could be formed. Continuous application of chlorine at l-2mg/L would provide a robust media that would be very difficult to remove, even during vigorous filter backwash cycles. If continuous application were not available, frequent shock doses of chlorine to the filter bed would help maintain oxide integrity. If no chlorine were present, manganese oxide deposits would be lost immediately during the next backwash cycle. Water pH would have to be maintained at a value >8 with a minimum of 2-3mg Mn/g of sand present within the sand filter bed. This high pH and mass of oxide would ensure that the oxide had the greatest potential for metal ion removal from solution. However, control of pH would be critical, as any major decrease in pH would allow any adsorbed metal ions to be immediately released into the treatment water.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

1997

Author dc:creator

• Eley, Mark John

Advisor dc:contributor.advisor

• K. Nicholson

• Manganese oxide deposits
• Water treatment facilities
• North-East Scotland
• Stoichiometry
• Chlorine
• Aqueous metal solutions
• Freundlich linear adsorption isotherm
• Sand substrate

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807373
https://doi.org/10.48526/rgu-wt-2807373

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807373