Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe UV-induced colour generation of pulp and paper mill eﬄuents as a proxy of ligno-cellulosic bioreﬁnery wastewater Galuh Yuliani a, ⁎ , Alan L. Chaﬀee b , Gil Garnier c, ⁎ a Chemistry Department, Universitas Pendidikan Indonesia, Dr. Setiabudi 229, Bandung, Indonesia b School of Chemistry, Clayton Campus, Monash University, VIC, 3800, Australia c Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical Engineering, Clayton Campus, Monash University, VIC, 3800, Australia ARTICLE INFO Keywords: UV irradiation Lignin compounds Colour generation Forest bioreﬁnery 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 ef- ﬂuent. 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. 1. Introduction The transformation of ligno-cellulosic biomass into a combination of biofuels, green chemicals and materials is currently very topical [1–5]. Accordingly, a consideration of the expected aqueous discharge asso- ciated with integrated forest bioreﬁnery process strategies is crucial. The bioreﬁnery concept highlights sustainability, climate change miti- gation and low carbon footprint, and hence the development of water treatment systems that are equally environmentally friendly is corre- spondingly important. The utilization of ligno-cellulosic biomass in both bioenergy and biomaterial production is commonly conducted via an initial biomass pretreament to overcome the recalcitrance of the lignin-hemicellulose matrix so as to solubilize and degrade it, providing access for sub- sequent processing [6–8]. The strategies typically include steam ex- plosion, dilute acid and organosolv pretreatment, usually performed under elevated temperature and strong shear (pressure or mechanical). Amongst these, acid-catalyzed or auto-catalyzed processes are be- coming dominant pretreatment strategies for the bioreﬁnery. One problem regarding wastewater streams that have originated from wood/lignocellulosic processing is the persistent colour of the treated eﬄuent [9–12]. Additionally, there is a concern regarding fur- ther yellowing of the treated wastewater that may occur and intensify beyond the point of discharge, even after prolonged time periods. This study aimed to investigate the mechanism of UV-induced colour gen- eration associated with wastewater from the acidic (bisulphite) pulping process, considered in the context of prospective integrated forest bioreﬁneries. Components of bioreﬁnery eﬄuents that are believed responsible for the colour include residual cellulose, hemicelluloses, lignin, pulping process chemicals and microorganism from the wastewater stream. Oxidative reactions of these components may result in coloured de- gradation products, usually containing carbonyl (C]O) groups and carbon-carbon double bonds (C]C) [10,13,14]. Among those, lignin residues have often been linked to eﬄuent colour development [15,16]; however, evidence is scarce, and even more scarce concerning the governing mechanisms. Successful methods for colour removal from pulp and paper mill eﬄuents [17–24] have been reported. These include physicochemical treatment, biological treatment and integrated treatments which com- bine two or more processes [25–27]. Physicochemical treatments, such as coagulation [18,23], electrocoagulation [17,28,29], and adsorption [19,24] can remove up to 90% of colour from the eﬄuents. Biological treatment with algae can successfully remove 84% of the colour from a pulp and paper industry eﬄuent [30]. Combining coagulation-ﬂoccu- lation with heterogeneous photocatalysis (a UV/TiO 2 /H 2 O 2 process) https://doi.org/10.1016/j.jwpe.2019.100781 Received 29 November 2018; Received in revised form 11 February 2019; Accepted 25 February 2019 ⁎ Corresponding authors. E-mail addresses: galuh@upi.edu (G. Yuliani), gil.garnier@monash.edu (G. Garnier). Journal of Water Process Engineering 29 (2019) 100781 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. T