Kraft Lignin Behaviour in Diffused Aeration of Kraft Effluents Available to Purchase

Diffused aeration experiments carried out using a Kraft black liquor in batch reactors at 21±1ΩC were performed in order to characterize the relative importance of the mechanisms of chemical oxidation and condensation of lignin structures upon COD, lignin and colour removal and also to evaluate the influence of agitation intensity on these mechanisms. It was found that total COD decreased with time. This behaviour was independent of the aeration intensity and the reduction reached a value of about 18% of the initial COD after approximately 15 days. This reduction was attributed to chemical oxidation of some functional groups of the Kraft lignin contained in the substrate. However, filterable lignin (as absorbance at 272 nm) and colour (as absorbance at 465 nm) were not affected by chemical oxidation. It was also observed that agitation produced the formation of suspended solids by condensation of lignin structures. This took place during the first 2 days and provoked a reduction of filterable COD, lignin and colour which was dependent on the aeration intensity.