Abstract
Successful long-term bioremediation of mining-influenced water using complex organic matter and naturally-occurring microorganisms in sub-surface flow constructed wetlands requires a balance between easily and more slowly degrading material. This can be achieved by combining different types of organic materials. To provide guidance on what mixture combinations to use, information is needed on how the ratio of labile to recalcitrant components affects the degradation rate and the types of microbial populations supported. To investigate this, different ratios of wood and hay were used in up-flow column bioreactors treating selenium- and sulphate-containing synthetic mine-influenced water. The degradation rates of crude fibre components appeared to be similar regardless of the relative amounts of wood and hay. However, the nature of the degradation products might have differed in that those produced in the hay-rich bioreactors were more biodegradable and supported high sulphate-reduction rates. Microorganisms in the sulphate-reducing and cellulose-degrading inocula persisted in the bioreactors indicating that bio-augmentation was effective. There was a shift in microbial community composition over time suggesting that different microbial groups were involved in decomposition of more recalcitrant material. When dissolved organic carbon (DOC) was over-supplied, the relative abundance of sulphate-reducers was low even through high sulphate-reduction rates were achieved. As DOC diminished, sulphate-reducers become more prevalent and their relative abundance correlated with sulphate concentrations rather than sulphate-reduction rate.
Highlights
Mine-influenced water (MIW) contains constituents, such as selenium and sulphate, at levels that are potentially toxic to aquatic life [1,2,3] and needs to be treated before discharging to the receiving environment
Organic materials used in biochemical reactors (BCRs) such as pine and spruce wood contain 67%–73% weight holocellulose [16]
The goal of this study was to measure the changes in organic material characteristics of mixtures of wood-chips, hay and cow manure over time in BCRs running for up to 450 days, and to see if particular changes in the organic material correlated with deviations from successful treatment
Summary
Mine-influenced water (MIW) contains constituents, such as selenium and sulphate, at levels that are potentially toxic to aquatic life [1,2,3] and needs to be treated before discharging to the receiving environment. Water 2016, 8, 124 sources such as fermentation products acetate, propionate, lactate, butyrate, alcohols, hydrogen and amines to fuel the microorganisms important for successful treatment [12,13,14,15]. Organic materials used in BCRs such as pine and spruce wood contain 67%–73% weight holocellulose [16]. These are more effective when combined with a digestible (labile) livestock feed such as grass hay containing 13%–54%
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