Relatively long operational time is required to achieve effective manganese removal in conventional aeration-filtration groundwater treatment with virgin filter media. Ripening period depends on water quality, operational parameters, and the filter media used. This study assessed the role of filter media type, backwashing and iron loading on the time required to achieve very effective manganese removal. Filter runs were conducted with two set-ups each with six pilot filters with virgin sand or anthracite, and different types of manganese oxide coated sand/anthracite (MOCS/MOCA). Pre-treated groundwater (aeration-rapid sand filtration), either directly, or after an additional pre-treatment (ultrafiltration-UF), was used as feed water. UF pre-treatment eliminated head loss development in pilot filters and backwashing was consequently not required. Filters that received feed water without UF pre-treatment required backwashing after 14 d of continuous operation. Use of virgin sand and anthracite resulted in comparable ripening time (25 d and 14 d for feed water without and with UF pre-treatment, respectively). Use of fresh MOCS/MOCA directly taken from operational filters, eliminated the need for ripening of virgin filter media, while dried MOCS was less effective than fresh one, while the total period required to achieve highly effective manganese removal (≥95%) was not shortened.

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The aim of this study was to identify bacteria present in ripened manganese removal filters for drinking water production. The bacterial population was identified with 'next generation' DNA sequencing, and specific bacteria were quantified with quantitative polymerase chain reaction (qPCR) and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis. The 'next generation' DNA sequencing analysis showed a bacteria population shift from the iron oxidizing species Gallionella spp. in the Fe-filter to manganese and nitrite oxidizing species Pseudomonas spp. and Nitrospira spp., respectively, present in the manganese removal filter. qPCR analysis confirmed the presence of a low concentration of the wellknown Mn2-oxidizing species Ps. putida in the manganese removal filter backwash water. Bacteria of the genus Pseudomonas, isolated from backwash water from a manganese removal filter were cultured and identified with MALDI-TOF MS analysis. Amongst others, P. gessardii, P. grimontii, and P. koreensis were identified. The presence of several manganese oxidizing bacteria species in ripened filter media supports the assumption that a microbial consortium is involved in the oxidation of manganese. Understanding the mechanisms by which manganese coating of filter media commences could endorse the creation of conditions favouring Birnessite formation, and possibly help in reducing typically long ripening periods of manganese removal filters with virgin filter media.

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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. @en