Factors Affecting Degradation and Decolourisation of an Azo Dye, Methyl Red, in Fixed Film Bioreactors

The effects of texture, aeration, inorganic (PO₄-P and NO₃-N) and organic (milk whey) nutrients are reported here on degradation and decolourisation of methyl red. The effects have been quantified by comparing UV-visible spectra of untreated and treated 100ppm of the dye in two types of fixed film bioreactors that differed in composition of their solid matrix (one containing gravel only, gravel bed; while the other has gravel + coarse river sand, mixed bed). Methyl red degradation was better in gravel bed reactors in comparison to mixed bed reactors. Aeration improved its degradation in both the types of reactors. Nutrients favoured reduction in bandwidth of spectra in near UV region (hence degradation of benzenoid compounds) in outflows from gravel (non-aerated and aerated) and mixed bed (aerated) bioreactors, while an opposite trend was noted for their OD values in far UV and visible region responsible for the colour. Mixed bed (non-aerated) bioreactor was, however, the exception, where inorganic nutrients, especially NO₃-N improved reduction of bandwidth as well as OD values in the spectra of outflows.