Index >> Waste Water Microbiology >>Rotating Biological Contractor or Biodisc System

Biofilms develop on the rotating biological contractors, and among the filamentous microorganisms that are found are Sphaerotilus, Beggiatoa, Nocardia and Oscillatoria. The rotation bio-contractors biofilm has two layers: outer whitish Beggiatoa filament and inner blackish Desulfovibrio (anaerobic) layer.

The inner layer is blackish due to the precipitation of iron sulphide when iron reacts with hydrogen sulphide produced by sulphate reducing Desulfovibrio species. In the anaerobic zone, fermentative microbes produce organic acids and alcohols that are used up by Desulfovibrio. Hydrogen sulphide produced by the Desulfovibrio diffuses into the outer aerobic zone where it is utilised by Beggiatoa as an electron donor. Hydrogen sulphide is oxidised by Beggiatoa and the elemental sulphur formed, gets deposited within the cells of bacteria (Beggiatoa). Thickness of microbial slime layer in all film flow processes is governed by the diffusion of nutrients through the film. When the film grows to a thickness that prevents nutrients from reaching the innermost microbes, these will die or autolyse and cause detachment of slime layer which can be easily removed by settling.