Fly ash based adsorbent for treating bleaching effluent of kraft pulping process

Abstract

Abstract The bleaching operation of a kraft pulping process generates a large amount of effluents with high organic loads. The affinity of biomass-based fly ash as a low-cost adsorbent for reducing lignin concentration, chemical oxygen demand (COD) and turbidity of the bleaching effluents prior to a biological treatment process was studied in this work. The results showed that the optimized conditions for obtaining the maximum removals of lignin (81.6%) and COD (67.9%) were the fly ash dosage of 6 wt% in the effluent and the treatment time of 30 min and temperature of 30 °C. The results also showed that the settling rate of the fly ash in fly ash/effluent suspension systems increased as fly ash dosage increased. Charge neutralization played a key role at a low fly ash dosage (less than 2 wt%) for removing lignocellulosic flocs smaller than 10 µm, while complexion of small flocs to larger ones (with the size of 30–500 µm) occurred at the higher fly ash dosage in the effluent. Coagulation and adsorption were the main phenomena for the removals of COD, lignin and turbidity at a higher fly ash dosage and a prolonged treatment time.