Biological removal of manganese at Olofström (SW)
Manganese is present in groundwater at Olofström (Sweden)
The waterworks in Olofström (Sweden) were built in 1969-1970 and today deliver drinking water to 10,000 inhabitants in the municipality. The production is just over 3,000m3 per day, which corresponds to an annual output of 120,000 m3.
Inlet raw water comes from several sources, both groundwater and surface water. Some of the groundwater has high levels of manganese. Manganese can cause deposits in pipes and can also discolor dishes and laundry.
An existing sand filter is transformed in a Filtralite® biofilter
In 2015, therefore, a biofilter was installed with the aim of reducing the content of manganese. In a biofilter, microorganisms allow oxidation and convert dissolved manganese to different oxides, preferably Manganese dioxide (MnO2). Manganese then precipitates into solid form and is removed when backwashing of the filter.
To install this biofilter, the idea was to use an existing sand filter with some modification. Among other things, sand was replaced by Filtralite Pure NC 2.5-5, an effective carrier material for microorganisms.
Filtralite products have a high specific surface area and an internal pore structure that enables high biologic activity per volume unit.
The filter surface is 25 m2 with a filter depth of 1 meter. The filtration rate is about 2 m / hour, which results in a production over the filter of more than 1,000m3 / day. In order to create optimal conditions for the microorganisms, pH needs to be raised, from about 6 to 8. At higher pH, oxidation to Manganese dioxide is easier, which increases the efficiency of the filter. The pH increase occurs by removing dissolved carbonic acid in a gas stripper.
Backwashing is only required 2-3 times per year.
During start-up in 2015, it took about 4 months before the bacterial flora had established itself and worked optimally. No seeding was needed, the biofilter has been activated only by naturally occurring bacteria in the raw water.
The graph above illustrates how the biological process has started and Manganese removal obtained. Inlet water contains levels up to 0.3 mg / l while outlet water (after biofilter) is around 0.01 mg / l. Removal rate is usually over 90%.