Biostimulation strategies to enhance manganese removal in drinking water biofilters

In the North of Europe, drinking water treatment is commonly based in aeration and biofiltration of groundwater. Biofilters are defined as submerged, granular filters in which the individual grains have developed a natural coating of both inorganics and biofilms capable of treating water to national drinking water criteria. The period during which virgin filter media matures into a fully functional biofilter is designated as the start-up period. The duration of a start-up for efficient manganese removal varies from weeks to more than a year.

The aim of this study was to investigate biostimulation strategies to enhance manganese removal during start-up of biofilters for treatment of groundwater. The investigation focused on the effect that different biostimulation strategies have on the onset of manganese removal, and on the bacterial communities formed in the early stages of the biofilter.

Two major biostimulation strategies were investigated: biostimulation using different filter media (e.g. quartz, calcium carbonate, polystyrene, manganese oxide), and biostimulation using chemical and biological amendments (e.g., addition of macronutrients, trace metals, matured medium, backwash sludge, and isolated manganese oxidizing bacteria). The onset and extent of manganese oxidation was determined spectrophotometrically, and the bacterial communities were characterized using DAPI staining, qPCR, 16S rRNA pyrosequencing, and enrichments of manganese oxidizing bacterial consortia.

The investigation suggested that when inoculating different filter media with an identical water source, the bacterial community formed during the start-up period is strongly influenced by the filter media type. Hence, management of bacterial communities may be possible by selecting specific filter media to enhance growth and activity of specific bacteria. Biostimulation of virgin media to enhance initial manganese removal using different amendments strategies is possible especially in the early stages of filter development whereas autocatalytic processes appear to become dominant with time. The complex interactions between biological and chemical oxidation processes should be considered when optimizing biofilters for efficient removal of manganese from drinking water.