| Dye wastewater is characterized with high colority and complex compositions, which is hard to be degraded. Dye wastewater has been a considerable source of environmental contamination, and severely restricted the development of China's textile industry. In this dissertation, reactive brilliant red X-3B dyestuff was used as research object. Sulfate radical produced by zero valent iron (ZVI) activated sulfite was utilized for the degradation of X-3B. Furthermore, the enhancement of ultrasonic and simulated sunlight on sulfite activation were investigated in this study. The mechanism and treatment efficiency of Fe(III)/sulfite/persulfate system were also studied in the dissertation. Based on the results of the experiments, steel slag was used as an alternative to metal ions to activate sulfite and persulfate individually under the simulated sunlight. A comparative study for the degradation of X-3B and actual dye wastewater by different process was presented in this section. This study is motivated by "using waste for waste treatment", and devoting to develop a practical method for dye wastewater treatment. The main contents and results consist of:(1) Zero valent iron was used to activate sulfite to degrade X-3B at near-neutral pH. The effects of dosage, pH, dissolved oxygen and halide ions on X-3B degradation were examined in batch experiments. Further study on the mechanism of ZVI/sulfite system was discussed in the dissertation. The results showed that 77.4% degradation of X-3B was achieved by ZVI/sulfite system, and the optimal dosage was 0.5:1.0 (molar ratio). The highest concentration of HSO3- produced at the pH values of 4-6, leading to the optimal performance of the system. Dissolved oxygen (DO) in the solution had great impact on the treatment of X-3B. Dissolved oxygen could react with SO3- to generate SO5-, which was the necessary reactant for SO4- production. The negative impacts of halide ions were showed with different strengthen following the sequence of I-> Br-> Cl-. A kinetic model based on steady state hypothesis was developed to testify the inhibition effect of halogen ions on the ZVI/sulfite system. Quenching tests by adding inhibitors confirmed the main reactive oxygen specie was the sulfate radical (74.5%), HO· and SO5- accounted for as much as 15.3% and 10.2% individually in the experiments.(2) Enhancement methods by ultrasonic and simulated sunlight on the ZVI/sulfite system was studied respectively in this section. The impacts of dosage, pH, temperature and dissolved oxygen on X-3B degradation were investigated in a comparative study. Moreover, the identification of Radicals and TOC removal by each enhanced method was presented in the study. The ultrasonic showed greater enhancement than simulated sunlight at the pH value above 5, while an opposite effect observed at the pH value below 4. Increasing the temperature had a positive impact on both enhancement methods, and the activation energy of ultrasonic (106.04kJ mol-1) was higher than the latter (90.23kJ mol-1). Both ultrasonic and simulated sunlight increased the ratio contributed by hydroxyl radical and TOC removal.(3) Fe(?)/sulfite/persulfate system was developed to degrade dye wastewater. The effects of mole ratio, initial pH, dissolved oxygen were investigated in this section, and the degradation of actual dye wastewater by this system was also studied. The results showed that the optimal dosage ratio of 0.1:1:2 in Fe(?)/sulfite/persulfate system. The steady-state concentration of SO4- was tended to similar as the reaction proceed when the initial pH ranged from 3 to 6, leading to similar degradation of X-3B in this range. Based on the study of cycling reuse, two reaction ways were revealed in this system:1) In the role of O2, SO4-and HO· were generated through the serials reaction of Fe(?) with sulfite.2) FeSO3+ was decomposed to Fe(?) in the reaction, which could activate persulfate and produce SO4·- and HO·.(4)With the enhancement of simulated sunlight, steel slag was used to activate sulfite and persulfate respectively in this section. The Removal efficiency of X-3B and actual dye wastewater by two system was presented in a comparative study. The results showed that similar performance of X-3B degradation by slag/sulfite system(78.2%) and slag/persulfate system(79.4%) under the simulated sunlight condition. However, a passivation coating formed during the process of slag/persulfate, which restricted the reuse of slag and produce a great amount of sludge. Correspondingly, iron absorbed on the slag surface during the treatment of slag/sulfite system, which effectively avoided the loss of iron and passive coating, leading to an efficient reuse of slag. Compared with the slag/persulfate system, slag/sulfite system enhanced by simulated sunlight showed a better performance for decoloration and COD removal and made the real dye wastewater more available for biodegradation in the sequence batch experiment. Therefore, it is obviously that simulated sunlight/slag/sulfite system was more favored than simulated sunlight/slag/persulfate system to treat actual dye wastewater. |
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