Decolorization of kraft bleaching effluent by advanced oxidation processes using copper (II) as electron acceptor

Area of Science:

• Environmental Chemistry
• Water Treatment Technologies
• Photocatalysis

Background:

• Kraft bleaching effluent poses significant environmental challenges due to its intense color and pollutants.
• Advanced Oxidation Processes (AOPs) offer promising solutions for treating recalcitrant organic compounds in industrial wastewater.

Purpose of the Study:

• To investigate and optimize the decoloration of Kraft bleaching effluent using two AOPs: TiO2/UV/O2 and TiO2/UV/Cu(II).
• To develop a mathematical model for evaluating the effects of variables on decoloration efficiency.
• To assess the impact of pH and catalyst concentrations on color removal and effluent quality.

Main Methods:

• Utilized multivariate analysis and experimental design (quadratic matrix of 30 experiments) to optimize TiO2 and Cu(II) concentrations and reaction times.
• Investigated the influence of pH on color removal efficiency.
• Evaluated effluent quality parameters including biodegradation, chemical oxygen demand (COD), and ecotoxicity using Daphnia magna.

Main Results:

• Achieved 94% color removal at acidic pH (3.0) using TiO2/UV/Cu(II) with Cu(II) acting as an electron acceptor.
• Observed a significant increase in effluent biodegradation from 0.3 to 0.6 under optimal conditions.
• Reported a 70% reduction in COD and a decrease in ecotoxicity, with minimal residual Cu(II) (0.05 mg/L) that was non-toxic to subsequent biological treatment stages.

Conclusions:

• Photocatalytic oxidation with TiO2/UV/Cu(II) is highly effective for decolorizing Kraft mill bleaching effluent, particularly under acidic conditions and with short reaction times.
• The presence of Cu(II) as an electron acceptor is more beneficial than oxygen for this specific AOP application.
• A quadratic polynomial model accurately represents the photocatalytic degradation efficiency of the Kraft bleach pulp effluent.