Manganese removal from groundwater: Role of biological and physico-chemical autocatalytic processes

In The Netherlands, Belgium and other European countries, manganese is removed from groundwater by aeration followed by rapid (sand) filtration. Although manganese removal from groundwater has been studied extensively, the mechanisms that control the ripening of filter media are not yet fully understood. This thesis highlights the role of the formation of a manganese oxide coating on virgin filter media. Characterization and identification of the media revealed that Birnessite was the manganese oxide responsible for effective manganese removal. This study confirmed that Birnessite formed at the beginning of the ripening process was of biological origin. As filter ripening progressed, the origin of the Birnessite became predominantly physico-chemical, although biological manganese oxidation still contributed to the overall removal of manganese. The formation of Birnessite at the start of filter media ripening was negatively influenced by a high filter back wash frequency. Molecular DNA analyses showed that Pseudomonas species are most likely involved at the start of the manganese oxide formation process.Based on the knowledge that manganese removal in conventional groundwater treatment is initiated biologically, long ripening times may be reduced by creating conditions favouring the growth of manganese oxidizing bacteria, e.g., by limiting the back wash frequency and/or intensity. Finally it was shown that the use of freshly prepared manganese oxide, containing Birnessite, can completely eliminate the need for filter media ripening. The results of this research enable the development of an innovative manganese removal process to shorten or completely eliminate long periods of ripening of virgin filter media, as well as significantly prolonging the lifetime of the filter media.