UV-induced colour generation of pulp and paper mill effluents as a proxy of ligno-cellulosic biorefinery wastewater

Abstract

UV-induced colour generation of treated (clear) wastewater effluents from a modern bisulphite pulp and paper mill was investigated as a model for aqueous discharges likely to be encountered with emerging biorefinery concepts. Aqueous solutions of selected model compounds, namely lignosulfonic acid (LSA), humic acid and vanillin were exposed to UV light and the colour generation of these solutions compared to the industrial effluent. The colour generation trend of the wastewater was found to be similar to that of LSA. Analysis by HPLC, FTIR, MS and NMR showed that the colour development of the wastewater mimicked the paper yellowing mechanism, with the formation of quinones as a major route. UV-induced dimerization of vanillin solutions showed a dramatic increase in colour. Thus results suggest the UV induced polymerization of lignin compounds play a major role in colour development of lignocellulosic wastewater effluents unless the phenol precursors are removed or degraded.