Granulated biomass fly ash coupled with fenton process for pulp and paper wastewater treatment

The work describes the combination of granulated biomass fly ash (G_BFA) with Fenton process to enhance the removal of adsorbable organic halides (AOX) from pulp bleaching wastewater. At optimal operating conditions, wastewater's chemical and biochemical oxygen demand (COD and BOD₅, respectively) and colour were also quantified, and operating cost of treatment assessed. For the first time, raw pulp bleaching wastewater was used to granulate BFA, instead of water, reducing the water footprint of the treatment. Five wastewater treatment setups were studied: (i) conventional Fenton process; (ii) G_BFA application; (iii) simultaneous application of G_BFA and Fenton process; (iv) sequential treatment by G_BFA followed by Fenton process; (v) sequential treatment by Fenton process followed by G_BFA. The latter yielded the highest AOX removal (60-70%), whilst COD was also reduced (≈15%) and wastewater biodegradability (BOD₅/COD) was enhanced from 0.075 to a maximum of 0.134. Another positive feature of the proposed solution was that G_BFA were successfully recovered and reused without regeneration, yielding similar AOX removal compared with fresh G_BFA. The operating cost of removing 1 g of AOX from the pulp bleaching wastewater by the optimal treatment setup (60-70% removal of AOX) was 14-26% lower than the operating cost of conducting Fenton process alone (50% removal of AOX).