In the present study, the photodegradation of lignin was studied using TiO2/Polystyrene composite underUV-LED irradiation in a batch-recirculated photoreactor as a supplementary treatment for pulp and paperindustries. TiO2/PS composite was synthesized by the solvent-casting method and was characterized byscanning electron microscopy (SEM) and EDX analysis. The 3-level, 3-factor Box-Behnken design wasapplied to study the effects of main operating parameters and optimization of process circumstances.Besides, COD reduction efficiency, toxicity assays, and reusability were also investigated. The predictedmodel had R2and R2adjcorrelation coefficients of 0.97 and 0.99 respectively, which showed experimentalresults were very close to the predicted values. Furthermore, under the optimal conditions (reactiontime = 72.5, volumetric flow rate = 230 mL/min and lignin = 51.8 mg/L) the lignin degradation efficiencywas 93.98%. The maximum COD removal (89%) obtained by 250 mL/min volumetric flow rate and ligninconcentration of 50 mg/L after 120 min reaction time. Bioassay using D. Magna exhibited that at thebeginning of the process, the toxicity of solution increased but continuously decreasing after then to verylow values achieved within 120 min of photodegradation. In addition, the reusability tests demonstratedthat the TiO2/PS composite after 5 cycles has a good stability and photocatalytic activity.
