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Sizing considerations for gravel beds treating acid mine drainage by sulfate reduction

An important consideration in the use of sulfate-reducing bacteria (SRB) for treatment of acid mine drainage (AMD) is that SRB require a physical support such as a gravel bed to become established. A quantitative method of describing the relationship between SRB activity and the physical parameters of the bed was investigated in a series of column reactors, as such information would be useful in the sizing of AMD treatment systems using SRB. This was accomplished by the use of ratios comprised of the amount of fresh AMD entering the system (V c ) and of physical parameters of the bed, namely the total surface area (tSA) of the gravel in the bed, the interfacial or superficial surface area (sSA) of the bed, and the void volume (V v ). Two numbers, D (= V c /V v * sSA/tSA) and F (= V v /V c * sSA/tSA), were used in the analysis of the sulfate removal data obtained in column reactors. The sulfate removal data can be expressed either as the proportion of sulfate removed or the rate of sulfate removal. A relationship existed between the proportion of sulfate removed data and number D but not with F, while a relationship existed between the rate of sulfate removed data and number F, but not with D. This difference was due to the arrangement of the parameters in the numbers which reflected fundamental relationships between the physical environment and SRB activity. The relationships observed were that sulfate removal was optimal for D values between 0.0075 and 0.015, and that the rate of sulfate removal decreased as F-values increased.