Study Of Effect And Mechanism Of Coupled Oxidation And Flocculation Process In Treating Dye Wastewater And Micro-polluted Raw Water

Characterization of polymeric phosphate ferric sulfate (PPFS) and its topography structure in this research were measured. In order to investigate the performance of this coagulate, Direct Dark Brown MM dye wastewater and micro-polluted raw water were considerably thought as the object of water treatment. In this experiment, many methods such as single parameter design, orthogonal design, Box-Behnken design and central composite design and response surface analysis were used in the investigation of the degradation efficiency, conditions optimization. In addition, the degradation mechanism of Direct Dark Brown MM by the ultrasonic-promoted heterogeneous Fenton-like process and PPFS/H₂O₂ coupled flocculation and oxidation process and micro-polluted raw water by PPFS/H₂O₂ coupled flocculation and oxidation process were detail analysised in various conditions. The purpose of this study was to expand the application range of combined AOPs in the field of wastewater treatment. At the same time, it would provide a new method to degrade the dye wastewater and micro-polluted raw water and the experimental results would provide a theoretical guidance in the treatment of the dye wastewater and micro-polluted raw water and the study of the mechanism of combined AOPs. The main conclusions in this research were summarized as follows:(1) Characteristics of PPFS were investigated using FTIR (fourier transform infrared spectrometer), XRD (x-ray diffraction) and SEM (scanning electron microscope) in this paper. The formed PPFS structure and morphology were stereo meshwork, which was clustered and closely to coral reef, synthesis of high charge density, bioactive polyhydroxy and mixed polynuclear complex PPFS. The results showed that charge neutralization of PPFS had not played a decisive role on the coagulation beaker test and the Zeta potential proved that PPFS was largely affected by bridging and coagulation and sedimentation. Fe-ferron complexation timed spectrophotometry showed that the amount of Fe(c) in Polymeric Phosphate Ferric Sulfate (PPFS) flocculants was the most in the three species, while the amount of Fe(a) and Fe(b) was small, that was PPFS mainly exists in the form of phosphate ferric polymer. Ultraviolet-visible spectrum showed that the change in the spectral curve of the different pH polymer ferric sulfate flocculants was corresponding to the flocculation morphology. Therefore, the coagulation mechanisms of PPFS were mainly composed of charge neutralization, adsorption bridging, coagulation and sedimentation mechanisms.(2) Ultrasonic-promoted heterogeneous Fenton-like process of Direct Dark Brown MM: the effects of initial pH of Direct Dark Brown MM dye solution, H₂O₂ concentration and dosage of Fe-Ni-Mn/Al2O3 on the degradation ratio of Direct Dark Brown MM were studied by using low frequency ultrasound. By the Box-Behnken centre-united experiment design and response surface methodology, a predictive polynomial quadratic model was set up and the optimum extraction conditions were developed, which were pH of dye wastewater 3.79, dosage of H₂O₂ 1.74 mM, dosage of Fe-Ni-Mn/Al2O3 1.65 g/L on the initial dye concentration 100.0 mg/L. 91.09 % of Direct Dark Brown MM was degraded under the optimal conditions. The experimental values agreed with the predicted values of the model equation with 1.35 % deviation. The UV-Vis spectra of Direct Dark Brown MM before and after degradation were analyzed and the following conclusions cound be drawn: Direct Dark Brown MM was not completely mineralized to CO2 and H2O by ultrasonic irradiation and Fenton reaction, instead, the chromophore in Direct Dark Brown MM molecular structure was just destroyed under the attack of radicals.(3) PPFS/H₂O₂ coupled flocculation and oxidation process of Direct Dark Brown MM: based on single factor experiments, the degradation degree of Direct Dark Brown MM were enhanced significantly under the optimum nPO₄^3-/nFe³⁺ and nOH-/nFe³⁺ molar ratio. Also, the results showed that the addition of H₂O₂ facilitated the degradation of Direct Dark Brown MM, which was caused by the generated Fenton-like process with H₂O₂ and Fe³⁺ after flocculation. The orthogonal experiment showed that the removal efficiency was largely affected by the PPFS dosage and H₂O₂ dosage. The results showed that in an acidic environment, Fenton-like mechanism played a key role. On the contrary, the flocculation mechanism would do in the alkaline environment. Therefore, the pH range would be greatly extended using PPFS/H₂O₂ coupled flocculation and oxidation process(4) PPFS/H₂O₂ coupled flocculation and oxidation process of micro-polluted raw water of UV₂₅₄, COD and TOC: based on the single factor experiments, the effect of UV₂₅₄ of micro-polluted raw water was investigated. The optimum conditions were as follows: the treatment efficiency would be improved in terms of the suitable nPO₄^3-/nFe³⁺ and nOH-/nFe³⁺. At the above determined optimum conditions, the removal efficiency would be enhanced in presence of H₂O₂. At the same time, the orthogonal experiment to treat UV₂₅₄ of micro-polluted raw water was carried out and the results showed that PPFS dosage, H₂O₂ dosage had a better effect on the removal of UV₂₅₄, COD and TOC.(5) PPFS/H₂O₂ coupled flocculation and oxidation process of micro-polluted raw water of PAEs and PAHs: a comparison was made between the testing of PAEs and PAHs. The results showed that PPFS/H₂O₂ had the same effect on the removal of DBP and DEHP with the PPFS alone and the removal efficiency were all over 90.0%. However, the removal rate of DMP and DEP compared with above materials had a lower efficiency of 70.0%-80.0%; Furthermore, the removal of phenanthrene and pyrene were almost 90.0%, that of the naphthalene and fluoranthene were 60.0% and 40.0%, respectively.