Advanced oxidation of bleached eucalypt kraft pulp mill effluent.

In this study a poorly biodegradable (BOD/COD = 0.3) industrial alkaline ECF bleaching filtrate was treated using different advanced oxidation processes to evaluate their use in combined chemical-biological treatment aimed at increasing recalcitrant COD removal and improving final effluent quality. Oxidative treatments included ozonation combined with hydrogen peroxide (2, 5, 10, 20 mmol L(-1) O3/0.7, 2, 5, 10 mmol L(-1) H2O2) and photocatalysis with hydrogen peroxide (UV/2, 4 and 8 mmolL(-1) H2O2) and with TiO2 (UV/TiO2/0.7 and 4 mmol L(-1) H2O2). The O3/H2O2 process increased effluent biodegradability by up to 68% as a result of increasing BOD and decreasing COD. Increasing the O3 dose had a greater effect on biodegradability improvement and lignin and colour removal efficiencies than increasing the H2O2 dose. A combined oxidant dose of 5 mmol L(-1) O3 and 2 mmol L(-1) H2O2 resulted in 75% lignin removal, 40% colour removal and 6% carbohydrate loss without mineralizing the organic carbon. The photocatalytic processes led to a decrease in effluent biodegradability through combined decrease in BOD and increase in COD and did not result in efficient lignin or colour removal. Photocatalytic oxidation was apparently inhibited by the high chloride and COD levels in the alkaline filtrate, and may be more efficient in recalcitrant COD removal if performed after biological.

Combined chemical biological treatment of bleached eucalypt kraft pulp mill effluent.

Effectiveness of ozonation before and after biological treatment for removal of recalcitrant organic matter in bleached kraft pulp effluents was compared. Two industrial ECF bleached eucalypt kraft pulp effluents (E1 and E2) were pretreated with 100 mg O3/L. Raw and pretreated effluents were treated biologically in bench-scale sequencing batch reactors, under constant conditions. Following biological treatment, effluents were post-treated with 100 and 200 mg O3/L. Effluent pretreatment increased effluent biodegradability by 10% in E1 and 24% in E2. Combined O3-biological treated led to small but significant increases in COD, BOD and lignin removal over biological treatment alone, but pretreatment had no significant effect on effluent colour and carbohydrate removal. Ozone pretreatment did not affect biological activity during treatment of effluent E1 but resulted in a 38% lower specific oxygen uptake rate in effluent E2. At an equivalent dose of 100 mg/L, pre-ozonation produced better quality effluent than post-ozonation, especially with regard to COD and colour. Likewise, when an equivalent dose of 200 mg/L was applied, splitting the dose equally between pre- and post-treatments was more efficient than applying the entire dose in the post-treatment. The potential for combined chemical-biological treatment to improve effluent quality has been confirmed in this study.