Adsorption optimization of a biomass-based fly ash for treating thermomechanical pulping (TMP) pressate using definitive screening design (DSD)

Wood chips are pretreated with steam or hot water prior to refining in a thermomechanical pulping (TMP) process. Currently, the resultant effluent (i.e., TMP pressate) must be treated in the wastewater treatment facility of the mill. Biomass fly ash is also generated in pulp mills as a residue from burning wood and other biomass in boilers. Fly ash utilization is currently limited and most of it is landfilled worldwide. In this study, biomass fly ash is used as an adsorbent for removing lignocelluloses from a TMP pressate. Biomass fly ash samples were fractionated, and the results showed that their carbon content decreased, but their metal content increased, as the particle size of the fly ash decreased. The main factors impacting the chemical oxygen demand (COD) and lignin concentration of a TMP pressate via treating with biomass fly ash samples (FA1 and FA2) were determined. Model equations and optimum conditions for these reductions were developed using definitive screening design (DSD). Generally, FA1 was considered a more effective adsorbent than FA2. The maximum COD removal from a TMP pressate (91.3%) was achieved by using FA1 with a particle size of 0.43mm at a dosage of 70mg/g FA1/TMP pressate and a treatment time of 2h. The maximum lignin removal from the TMP pressate (95%) was obtained by using FA1 with a particle size of 0.11mm at a dosage of 46.5mg/g FA1/TMP pressate.