Abstract
Packed bed bioreactors were used to remove soluble manganese from a synthetic mine water as the final stage of an integrated bioremediation process. The synthetic mine water had undergone initial processing using a sulfidogenic bioreactor (pH 4.0–5.5) which removed all transition metals present in elevated concentrations (Cu, Ni, Zn and Co) apart from manganese. The aerobic bioreactors were packed with pebbles collected from a freshwater stream that were coated with black-colored, Mn(IV)-containing biofilms, and their capacity to remove soluble Mn (II) from the synthetic mine water was tested at varying hydraulic retention times (11–45 h) and influent liquor pH values (5.0 or 6.5). Over 99% of manganese was removed from the partly processed mine water when operated at pH 6.5 and a HRT of 45 h. Molecular techniques (clone libraries and T-RFLP analysis) were used to characterize the biofilms and identified two heterotrophic Mn-oxidizing microorganisms: the bacterium Leptothrix discophora and what appears to be a novel fungal species. The latter was isolated and characterized in vitro.
Highlights
Analysis) were used to characterize the biofilms and identified two heterotrophic Mn-oxidizing microorganisms: the bacterium Leptothrix discophora and what appears to be a novel fungal species
In phase C1, during which the influent liquor was that draining the sulfidogenic bioreactor with no pH adjustment (Table 1) and the hydraulic times (HRTs)
Manganese is often the most recalcitrant transition metal found in elevated concentrations in mine drainage waters in terms of how amenable it is to be removed by chemical means
Summary
Small pebbles (1.5–5.0 cm in diameter) covered with thin black coatings (Supplementary Figure S1) were collected from a catchment stream (pH 6.5, containing ~30 μM soluble manganese) located in the Snowdonia National Park, North Wales, UK (GPS coordinates: 53◦ 110 51.5112” N, 4◦ 70 39.7596” W), and stored in plastic bottles at 4 ◦ C until use. Mariner et al [11] have previously shown that the coatings on similar pebbles contained Mn (IV) by positive reaction with hydrogen peroxide. The pebbles were packed into 32.0 by 6.8 cm Perspex® columns to a depth of 24.5 cm (Figure 1), and partly processed synthetic mine water (~600 mL) was added, to 3.5 cm above the pebbles, giving the column bioreactor a working volume of 1.02 L.
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