Advanced treatment of wet-spun acrylic fiber manufacturing wastewater using three-dimensional electrochemical oxidation

A three-dimensional electrochemical oxidation （3D-EC） reactor with introduction of activated carbon （AC） as particle micro-electrodes was apphed for the advanced treatment of secondary wastewater effluent of a wet-spun acrylic fiber manufacturing plant. Under the optimized conditions （current density of 500 A/m2, circulation rate of 5 mL/min, AC dosage of 50 g, and chloride concentration of 1.0 g/L）, the average removal efficiencies of chemical oxygen demand （CODer）, NH3-N, total organic carbon （TOC）, and ultraviolet absorption at 254 nm （UV2s4） of the 3D-EC reactor were 64.5%, 60.8%, 46.4%, and 64.8%, respectively; while the corresponding effluent concentrations of CODcr, NH3-N, TOC, and UV2s4 were 76.6, 20.1, and 42.5 mg/L, and 0.08 Abs/cm, respectively. The effluent concentration of CODer was less than 100 mg/L, which showed that the treated wastewater satisfied the demand of the integrated wastewater discharge standard （GB 8978-1996）. The 3D-EC process remarkably improved the treatment efficiencies with synergistic effects for CODer, NH3-N, TOC, and UV2s4 during the stable stage of 44.5%, 38.8%, 27.2%, and 10.9%, respectively, as compared with the sum of the efficiencies of a two-dimensional electrochemical oxidation （2D-EC） reactor and an AC adsorption process, which was ascribed to the numerous micro-electrodes of AC in the 3D-EC reactor. Gas chromatography mass spectrometry （GC-MS） analysis revealed that electro- chemical treatment did not generate more toxic organics, and it was proved that the increase in acute biotoxicity was caused primarily by the production of free chlorine.

Oxidation and biotoxicity assessment of microcystin-LR using different AOPs based on UV, O3 and H2O2

Microcystin-LR attracts attention due to its high toxicity, high concentration and high frequency. The removal characteristics of UV/H2O2 and O3/H2O2 advanced oxidation processes and their individual process for MC-LR were investigated and compared in this study. Both the removal efficiencies and rates of MC-LR as well as the biotoxicity of degradation products was analyzed. Results showed that the UV/H2O2 process and O3/H2O2 were effective methods to remove MC-LR from water, and they two performed better than UV-, O3-, H2O2-alone processes under the same conditions. The effects of UV intensity, H2O2 concentration and O3 concentration on the removal perfomlance were explored. The synergistic effects between UV and H2O2, O3 and H2O2 were observed. UV dosage of 1800 mJ·cm^-2 was required to remove 90% of 100μg.L^-1 MC-LR, which amount significantly decreased to 500 mJ.cm^-2 when 1.7mg·L^-1 H2O2 was added. 0.25 mg.L^-1 O3, or 0.125 mg·L^-1 O9 with 1.7 mg·L^-1 H2O2 was needed to reach 90% removal efficiency. Furthermore, the biotoxicity results about these UV/H2O2, O3/H2O2 and O3-alone processes all present rising trends with oxidation degree of MC-LR. Biotoxicity of solution, equ valent to 0.01 mg·L^-1 Zn^2＋,ratsed to 0.05 mg.L Zn after UV/H2O2 or O3/H2O2 reaction. This phenomenon may be attributed to the aldehydes and ketones with small molecular weight generated during reaction. Advice about the selection of MC-LR removal methods in real cases was provided.