Biofilm model development and process analysis of anaerobic bio-digestion of azo dyes

Ceramic-supported graphene oxide membrane bioreactors have already shown their potential for the anaerobic decolorization of wastewater containing azo dyes. The primary goal of this investigation was to develop a mathematical model that would be able to describe the steady-state behavior of this biodegradation process. The developed model was calibrated and validated using independent experimental data sets with various dye structure, feed concentration, hydraulic retention time (HRT), and support materials on which the biofilm was grown. The calibrated and validated model was used to analyze the intrinsic mechanism of the process and the main finding was that hydrolysis is the rate limiting step. Hydrolysis rate constant is decreased with increasing the complexity of the dye structure. Support materials with high electron transfer capacity increased the biofilm activity, therefore, increased the hydrolysis rate constant. Acetate concentration, used as an external carbon source, improved the dye removal efficiency. However, acetate to dye ratio did not have a direct relation to dye removal efficiency. Higher hydraulic retention time (HRT) increased the contact time between dye molecules and biofilm and enhanced the dye removal efficiency, too. However, it is essential to impose the right balance between HRT and external carbon sources to make the process feasible.