| Treatment of industry wastewater is a concern, especially for those pollutants that can not be treated by traditional biological methods, such as endocrine disruptors, azo dyes and heavy mental. Even with low concentrations, they can bring huge environmental pollution and toxic danger. These pollutants should be dealt by the physico-chemical treatment and process, in which photocatalysis using TiO2particles and air stripping process attract extensive attention for their simple processes, low cost and no need to add any chemical reagent. However, there exists low proficiency, few studies on the equipments and other problems. In order to solve these problems, in this thesis, physico-chemical treatment and process intensification of recalcitrant pollutants of azo dye, endocine disruping chemicals, ammonia and hexavalent chromium were investigated, and the thesis could be divided into five parts of contents:I Design a new circulating ultrasound directly-intensified photocatalytic reactor to solve the problems that the nanometer photocatalyst is easily agglomerated and limited the mass transfer in the suspension slurry reaction system of photocatalysis. In this chapter an original ultrasound (US) directly intensified photocatalytic reactor was designed to find a more efficient intensification manner for the scale-up of sonophotocatalytic process. Azo dye of methyl orange (MeO) was used as model pollutant using Degussa TiO2as the photocatalyst. The sonolytic, photocatalytic and sonophotocatalytic degradation of MeO in the new reactor and the synergistic effect between sonolysis and photocatalysis were investigated. Effects of operation parameters i.e., US power. TiO2dosage, liquid circulation velocity and air flow rate on degradation efficiency were investigated and optimized. The results showed that all parameters have optimal values for the sonophotocatalytic degradation of MeO, and the optimum conditions for the new process are US power600W, TiO2dosage3g/L, liquid circulation velocity4.05×10-2m/s and air flow rate0.2L/min. Under the optimum conditions,91.52%MeO had been degraded within1h, and the combination of sonolysis and TiO2photocatalysis exhibited an obvious synergetic effect.2The suspended slurry photocatalytic systems using TiO2nanoparticles can maximize the efficiency of photon utilization, oxidation rates and reactor throughput. However, the nanophotocatalysts easily agglomerate in slurry system, reducing the efficiency of photocatalytic process. It also exist separation problem of nanophotocatalysts using in the slurry system. In order to solve the problem, a new gas-liquid-solid circulating fluidized bed photocatalytic reactor (GLSCFBPR) with internally placed multi-layered UV lamps was developed and micrometer Gd-TiO2particles was chosen as the photocatalyst to intensify the treatment process. Hazardous substance bisphenol A (BPA) was chosen as the model pollutant to investigate the performance of this new photocatalytic system. The results showed that the photocatalytic degradation efficiency of the micrometer Gd-TiO2particles was similar to that of the nanometer P-25particles at their respective optimum dosage but the former could be easily separated out by gravity. After investigating the effects of process parameters on the photocatalytic BPA degradation, the response surface method (RSM) was further used for process optimization. The interactions among process parameters, i.e. TiO2concentration, superficial gas velocity and superficial liquid velocity were discovered and a related analysis was carried out to explore the underlying mechanism. A quadratic mathematic model was established and performed satisfactorily when used for prediction. The optimum conditions for this new process were as follows:TiO2concentration4.5g/L, superficial gas velocity7.83×10-3m/s and superficial liquid velocity8.65×10-3m/s. Under the optimum conditions,91.74%MeO had been degraded within1h, and the apparent degradation rate constant is3.96×10-2min-1. The synergy between photocatalysis and sonolysis is as high as2.26.3、Water-sparged aerocyclone (WSA) is new gas-liquid mass transfer equipment developed by our research group using of supergravity field of sparged air. In order to investigate the mechanism of the jet-sparged system of the WSA and improve its mass transfer performance, jet flow pattern and interfacial area (a) of the WSA were determined by directly observed method and the chemical reaction method with CO2-NaOH solution system. Then the transition of jet flow pattern and the a were correlated. The results show that jet flow pattern is mainly affected by jet velocity and air inlet velocity. There exists steady state je;, deformed spiral jet, broken spiral jet, atomized spiral jet and total atomized spiral jet in the WSA when the jet velocity is lower than4.42ni/s. Besides, when the jet velocity is higher than6.19m/s there exists only deformed spiral jet, broken spiral jet and atomized spiral jet. The a is related to jet flow pattern, and a is higher in atomized spiral jet than in the other jets. Moreover, the value of a increases with liquid jet velocity because of the gas-liquid intense interaction in WSA.4、In order to improve its mass transfer performance and establish design principles, spray hole distribution and jet hole diameter of the WSA was optimized by means of theoretic analysis and experimental method. A new concept, critical distance of spray holes,lc, and its calculation formula were put forward. A new dimensionless number, Jc, characterizing the mass transfer performance in the liquid jet-gas cyclone coupling field, was suggested. The results showed that the WSA with square arrangement of spray holes exhibited higher mass transfer efficiency than that with triangle arrangement of spray holes in air stripping of ammonia. The distance between adjacent spray holes of the WSA had obvious effect on volumetric mass transfer coefficient, the optimal distance was about1.28lc and the perforation area was about78%of the central tube height in the WSA. The mass transfer efficiency of the WSA increased with increasing jet hole diameter under a certain liquid jet velocity in air stripping of ammonia. However, excessive jet hole diameter will consume more energy for the reeireillation of wastewater. The optimum jet hole diameter could be calculated asdh=lo/6.39, herelo is the annular with of the WSA. To predict the effects of jet hole diameter on mass transfer characteristics in WSA, empirical formula for correlating the experimental data was developed, as Jc=2.77×10-9Reg0.37ReL1.18(?)eL-1.05.These results could be used as a guide for the design of WSA with good mass transfer performance.5、The removal of hexavalent chromium (Cr(Ⅵ)) from wastewater by sulfur dioxide(SO2) reduction was conducted in the water-sparged aerocyclone (WSA) reactor, and a satisfactory result was obtained. When chromium containing wastewater of1134mg/L was treated for6min with a gas containing SO2of3582mg/m3, more than99.9%Cr (Ⅵ) was removed. Alkaline Cr (Ⅵ) containing wastewater is beneficial to the absorption of SO2, increasing the efficiency of Cr (Ⅵ) reduction. Initial concentrations of SO2and Cr(Ⅵ) have significant influence on the efficiency of Cr (Ⅵ) removal, but wastewater jet velocity has less effects. Increasing SO2concentration increased Cr (VI) removal efficiency, whereas increasing Cr (Ⅵ) concentration decreased the treatment efficiency. Compared with the SO2reduction process conducted in some traditional gas-liquid reactors like packed towers, this SO2reduction process conducted in the WSA has obvious advantages such as no need for adjusting pH of wastewater to2～3before SO2reduction, easy operation and no Cr (OH)3scale deposited in reactor. So the investigation could provide a new sulfur dioxide reduction process for Cr (Ⅵ) containing wastewater using SO2containing gas. |
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