Effects of alkalinity and co-substrate on the performance of an upflow anaerobic sludge blanket (UASB) reactor through decolorization of Congo Red azo dye

The effect of substrate (glucose) concentrations and alkalinitiy (NaHCO3) on the decolorization of a synthetic wastewater containing Congo Red (CR) azo dye was performed in an upflow anaerobic sludge blanket (UASB). Color removal efficiencies approaching 100% were obtained at glucose-COD concentrations varying between 0 and 3000 mg/l. The methane production rate and total aromatic amine (TAA) removal efficiencies were found to be 120 ml per day and 43%, respectively, while the color was completely removed during glucose-COD free operation of the UASB reactor. The complete decolorization of CR dye under co-substrate free operation could be attributed to TAA metabolism which may provide the electrons required for the cleavage of azo bond in CR dye exist in the UASB reactor. No significant differences in pH levels (6.6–7.4), methane production rates (2000–2700 ml/day) and COD removal efficiencies (82–90%) were obtained for NAHCO3 concentrations ranging between 550 and 3000 mg/l. However, decolorization efficiency remained at 100% with decreasing NaHCO3 concentrations as low as 250 mg/l in the feed. An alkalinity/COD ratio of 0.163 in the feed was suggested for simultaneous optimum COD and color removal.