Effect of variability on the treatment of textile dyeing wastewater by activated sludge

Using a pilot scale continuous system with activated sludge, the effect of the variability of non-pretreated synthetic textile wastewater containing reactive dyes on the pollution bio-removal and on the characteristics of activated sludge (sludge volume index, floc size and shape, filamentous bacteria abundance) has been monitored. Off-line batch respirometry tests have been used in parallel to assess the toxic effects of some of the reactive dyes. Experiments were run by increasing the concentration of a single dye (Run 1) and by feeding with a non-repetitive (Run 2) or a repetitive (Run 3) sequence of dyes. In all runs dyes were added to a synthetic wastewater of constant composition. Although the biomass was significantly upset by some of the dyes, it was able to cope up with the variations of their chemistry and remained active throughout the experiments and could contribute to COD removal. The dyes were partially adsorbed but not degraded by the micro-organisms.