High frequency pulsed electrodialysis of acidic filtrate in kraft pulping.

We introduce high frequency pulsed electrodialysis (hf-pED) to process the acidic filtrate of a Kraft pulp bleaching stage, tested in a pilot trial. Compared with conventional electrodialysis, hf-pED at 2,000 Hz allows a reduction in operational cost by 12%, estimated as 0.54 USD/m3 of acidic filtrate, while simultaneously preventing membrane fouling. The proposed sectorial stream treatment is demonstrated to significantly improve the quality of the final effluent, according to mass balances, making it more suitable for irrigation applications, considering requirements of irrigation norms. Thus, we estimate a reduction of 59, 21, and 20% in the concentration of chloride, sodium, and sulfate, respectively, in the final effluent of a conventional Kraft pulping mill. This strategy is presented as a sustainable and economic solution compared with the desalinization of the whole final effluent.