Colour removal and the effect of reactive dyes on acid producing anaerobic microorganisms

The cultures from a sucrose-fed anaerobic acid reactor were dosed with 0, 60, 100, 200, 400, 800 and 1,500 mg/L, of a mixture of three Procion reactive dyes, Red MX-8B, Red MX-5B and Orange MX-2R, in order to study the colour removal and the toxic effect of the dyes on anaerobic acidification of sucrose. Sucrose undergoes a possible extracellular transformation into intermediate substances before being taken up by the acidogens for volatile fatty acid (VFA) synthesis. The rate and the extent of this uptake is unaffected by the presence of dyes. The dyes, however, reduced the rate of synthesis of VFA, and considerably diminished the VFA production potential of sucrose. The acidification stopped, likely due to an inhibition caused by VFA accumulation. As a result, only 50–60% of the soluble organic carbon was utilised for VFA synthesis. The removal of colour by the unacclimated anaerobic acidogenic biomass takes place by adsorption. However, Freundlich's adsorption constants did not suggest a favourable adsorption.