Passive Treatment of Mn-Rich Mine Water: Using Fluorescence to Observe Microbiological Activity

Conventionally, limestones have been used in passive mine water treatment systems. Limestones with the highest proportion of calcite are recommended since they have the greatest long-term alkalinity generating potential. Manganese is present in mine waters and needs to be removed in order to comply with environmental quality standards. This paper compares seven different Permian carbonate rocks, both limestone and dolomite, in their ability to promote manganese oxidation in real mine waters over an 8-h period. The substrates are characterised using thermogravimetric analysis, X-Ray diffraction and scanning electron microscopy. Fluorescence spectrophotometry is used to monitor any changes in the dissolved organic matter concentration in the water as manganese is removed. We determine that there is no statistically significant correlation between manganese removal and the proportion of calcite or between manganese removal and substrate surface roughness. Fluorescence spectrophotometry demonstrates that there is a distinct change in the observed spectra in the water during manganese removal. There is a positive and statistically significant correlation between manganese removal and the production of a tyrosine-like substance (up to ∼ 150 ppb in 8 h), which fluoresces at 270-280 nm excitation wavelength and 300-310 nm emission wavelength, suggesting that microbial activity is an important factor in promoting manganese removal within dolomite passive treatment systems. It may be possible to use fluorescence spectrophotometry to monitor for microbial activity in passive treatment systems.