Research On The Degradation Of Refractory Organic Pollutants Wastewater By Advanced Oxidation Technologies (AOTs)

Advanced oxidation technologies (AOTs) are effective technologies and have good prospect of development application for the treatment of refractory organic wastewaters. In present study, the degradation of several azo dyes such as Orange G, Brilliant red X-3B and Acid Black 1-containing wastewater, and p-Nitroaniline-containing wastewater by immobilized nanometer-sized TiO₂ photocatalytic oxidation technique or Fenton oxidation processes were investigated. The operational parameters and the degradation characteristics of pollutants in each process were studied in detail. The degradation kinetics of p-Nitroaniline by Fenton oxidation process was analyzed. The results obtained in this study could provide some important theory guides for the treatment of refractory organic wastewaters. All the experimental results were demonstrated as follows:1. The degradation of azo dyes using nanometer-sized TiO₂ immobilized on activated carbon photocatalyst (TiO₂/AC). In this study, TiO₂/AC photocatalyst was prepared by sol-gel-dip-calcine method. The crystallographic mode of immobilized TiO₂ was full of anatase, the mean particle size was 7^-10 nm, and the loading amount of TiO₂ was 10 wt. %. The photocatalytic degradation of azo dyes Orange G and Brilliant red X-3B by TiO₂/AC were investigated. In the optimal conditions of [TiO₂/AC] = 12 g L^-1, [H₂O₂] = 2 ml L^-1, pH = 2.0, [Orange G] = 25 mg L^-1 and [Brilliant red X-3B] = 50 mg L^-1, the degradation efficiencies of Orange G and Brilliant red X-3B were achieved 99.71% and 97.12% within 60 min reaction; the removal efficiencies of TOC were achieved 81.54% and 81.99% after 180 min reaction, respectively. The recovery rate of TiO₂/AC photocatalyst was more than 95% and the photocatalytic degradation efficiencis of orange G was achieved 95.93% by calcination regenerated TiO₂/AC especially. The disadvantages of nano-sized TiO₂ powder, such as easy losting with effluent, difficult separation and callback after reaction, were all effectively overcome.2. The degradation of azo dye using low concentration iron of Fenton process facilitated by ultrasonic irradiation. In this study, a combination of ultrasonic irradiation with low concentration iron (< 3 mg/L) of Fenton process (US/Fenton) has been investigated to treat azo dye acid black 1 (AB1) containing wastewater. The results showed that the oxidation power of low concentration iron of Fenton could be significantly enhanced by ultrasonic irradiation. The pH value has a great effect on the degradation of AB1 by US/Fenton and the optimum pH value was 3.0. Increasing the dosages of H₂O₂ and Fe²⁺ has enhanced the degradation efficiency efficiently, but the immoderate enhancement of H₂O₂ also inhibited the reaction. Under the optimum conditions, 98.83% of degradation efficiency was achieved within 30 min reaction by US/Fenton. The effect of various anion follows in the following decreasing order: SO32ˉ> CH3COOˉ> Clˉ> CO₃^2- > HCO₃^- > SO₄^2- > NO₃^-. The results show that it was easier to destruct the azo linkage (–N═N–) group than the aromatic rings of AB1 by the US/Fenton process.3. The degradation of p-Nitroaniline (PNA) containing wastewater using low concentration iron of Fenton facilitated by solar irradiation. In this study, low concentration iron of Fenton and solar photo-Fenton oxidation processes were employed to treatment PNA wastewater. In the optimal conditions: [H₂O₂] = 10 mM, [Fe²⁺] = 0.05 mM, pH = 3.0, temperature = 20°C, [PNA] = 0.072-0.217 mM, 98% degradation efficiency of PNA was achieved within 30min reaction by solar photo-Fenton oxidation process, but 93% degradation efficiency of PNA was achieved within 60 min reaction by Fenton oxidation process. The results showed that the conjugatedÏ€systems of the aromatic ring in PNA molecules were effectively destructed. 4. Kinetics study on the degradation of PNA by Fenton oxidation process. The results showed that thedegradation of PNA fits the pseudo-first-order kinetic model well. The kinetic rate constants, kap, for PNA degradation was: 1) achieved to maximum only at pH value of 3.0; 2) increased with the increase of H₂O₂ and Fe²⁺ dosages, however, much higher levels of H₂O₂ also inhibited the reaction kinetics; 3) decreased with the increase of initial PNA concentration; 4) remarkably increased with the raising of temperature. The derived activation energy for PNA degradation by Fenton oxidation is 53.96 kJ mol^-1.