| The wastewater from production of acrylic fiber contains complex, highly toxic, and poor biodegradable compounds, such as, organic nitrites, alkanes, and aromatic organic compounds. Presently, there is no fully mature technology, such as, physical/chemical-biological process, which could not achieve the desired removal efficiency by the enterprise to meet discharged standards. In the current study, a combined microbubble/ozonation-three dimensional electrodes reactor was applied for the advanced treatment of the secondary effluent from acrylic fiber manufacturing plant. The removal effectiveness, degradation kinetics and the mechanism of pollutant elimination was derived, as well as the analysis of the safety of effluent quality.Firstly, the microbubble/ozonation reactor was applied for the pretreatment of the secondary effluent from acrylic fiber manufacturing plant. The removal rates of CODcr, NH3-N, TOC and UV254 at 120 min by the microbubble/ozonation reactor were 34.7%,20.9%,31.7% and 42.1%, which increased of 24.6%,9.0%,19.6% and 34.9% respectively in comparison to those achieved by the macrobubble/ozo nation reactor. Further, the biodegradability in microbubble/ozonation reactor was improve 2.25 times higher than that in raw wastewater. Based on the analysis of acute biotoxicity and gas chromatography-mass spectrometry (GC-MS), the safety of effluent quality was enhanced in microbubble/ozonation reactor, which the removal efficiency of acute biotoxicity and the average removal efficiency of alkanes organics were 22.2% and 30.3% higher than those achieved by the macrobubble/ozonation reactor. The superior performance of microbubble/ozo nation reactor on pollutant elimination was attributed to the higher ozone gas hold, quicker ozone mass transfer coefficient, higher ozone utilization efficiency, much amounts of hydroxyl radicals and the highly concentrated negative charge on the surface of microbubbles.Secondly, the three dimensional electrodes batch reactor with introduction of activated carbon as particle micro-electrodes was used to treat the effluent of microbubble/ozonation reactor. A significantly synergistic effect was revealed among the activated carbon adsorption process and the electrochemical oxidation process during the three dimensional electrodes batch reactor. Under the optimized conditions of the batch reactor (current density of 500 A/m2, circling speed of 5 mL/min, activated carbon dosage of 50 g and chlorine concentration of 1.0 g/L), the effluent concentratons ofCODcr,NH3-N,TOC and UV254 were 76.6 mg/L,20.1 mg/L,42.5 mg/L and 0.08 Abs/cm, however, the acute biotoxicity increased at the same time. GC-MS analysis revealed that electrochemical treatment did not generate more toxic organics, and the acute biotoxicity caused primarily by the production of free chlorine (Cl2, ClO-, and HClO) has also been proved. The short-lived active chlorine has no effect on the eco-system of water body, whereas, the active chlorine has a disfection function on the treated effluent Further, the degradation of pollutants during the three dimensional electrodes batch reactor follows apseudo second-order kinetic model. The mechanism of organic pollutants in three dimensional electrode batch reactor was dominated by the indirect oxidation of electro-generated active chlorine (such as, Cl2, ClO- and HClO).In summary, a combined microbubble/ozonation-three dimensional electrodes continuous reactor process was successfully applied for the advanced treatment of the secondary effluent from acrylic fiber manufacturing plant. The effluent concentrations of CODcr and NH3-N were 50.6 mg/L and 12.6 mg/L, respectively, which satisfied with the first class of integrated wastewater discharged standards (GB 8978-1996) and the industrial standard. Therefore, the scientific basis was provided to realize the upgrade of the wastewater treatment system of enterprise. |
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