Reduction Degradation Of Carbon Tetrachloride Wastewater By Zero-valent Iron

As a kind of widely used organic chloride, chlorinated hydrocarbon has a stable chemical property and biological toxicity and can exist steadily in the natural environment for a long time. It seriously pollutes soils and groundwater and does great harm to the ecological environment. The reductive degradation of chlorinated hydrocarbon with zero-valent iron was investigated in this paper. The study was intended to enhance the degradation rate of the carbon tetrachloride with zero-valent iron by the application of surfactant load, transition metal catalysis and ultrasonic assistance. Pilot test of real industrial wastewater polluted by chlorinated hydrocarbon was also conducted in the experiment.Chapte 1 and Chapter 2 mainly dealt with the source, properties of chlorinated hydrocarbon and its harm to environment. Various conventional processing methods of organic chloride were introduced. The current situation and existing problems of the application of reductive treatment of chlorinated hydrocarbon with zero-valent iron were summarized. The aim and significance of the present study were also put forward in the first two chapters.Experiment instrument, reagent used and the experiment and analysis methods of various processing methods were introduced in Chapter 3.The reducting treatment of chlorinated hydrocarbon with zero-valent iron was studied in Chapte 4. The results showed that 1) Zero-valent iron had a good dechlorination performance on the chlorinated hydrocarbon in water. With the dosing quantity of carbon tetrachloride being lOg/L, initial concentration being 20mg/L, and pH valueof 7.0, the degradation rate of 280min chlorinated hydrocarbon reached to 86.1%. The effect of degradation was influenced by dosing quantity, reaction temperature and pH value. The dosing quantity and reaction temperature could enhance the dechlorination reaction, while pH value. had great infuence on the degradation efficiency and acdity condition was favorable for the reaction. The degradation of carbon tetrachloride followed first order kinetics. Under the influence of zero-valent iron, carbon tetrachloride transformed into chloroform, and then chloroform became dichloromethane.2) When sulfate and Fe2+ iron compounds were adding, green rust formed, which inhibited the passivation of iron surface and was favoralbe to the reductive dechlorination. Two kinds of cationic and anionic surfactants were used respectively to load the zero-valent iron, and the results showed that the cationic surfactants (CTAB and CPB) could enhance the effect of dechlorination when the loading concentration was under critical micelle concentration, and the reaction rate constant could increase by 81% (CTA) and 130% (CPB). While the anionic surfactants were unfavorable to the reductive dechlorination with zero-valent iron.In Chapter 5, the binary bimetal Ni/Fe and Pd/Fe were used to degrade the chlorinated hydrocarbon. The influencing factors and dechlorination efficiency of chlorinated hydrocarbon were investigated and the kinetics and reaction products were analyzed. Compared with zero-valent iron, Ni/Fe and Pd/Fe had better capacity of reductive degradation of chlorinated hydrocarbon. After 90 minutes, the dechlorination efficiency of chlorinated hydrocarbon in the Ni/Fe system was 92.8% when the initial concentration was 20 mg/L. And in the Pd/Fe system, dechlorination efficiency of chlorinated hydrocarbon was 95.7% after 6 minutes. The main factors influencing the reductive dechlorination were: content of Ni and Pd, dosing quantity, reaction temperature and pH value. It was found that the increase of the content and dosing quantity of Ni and Pd was favoralbe to the degradation of chlorinated hydrocarbon. The initial concentration of chlorinated hydrocarbon had little effect on the dechlorination efficiency. Under weak acidic condition, pH value could be favorable to the degradation. The apparent activation energy of Ni/Fe and Pd/Fe were 6.12kJ/mol and 3.95kJ/mol respectively. The degradation products of chlorinated hydrocarbon by Ni/Fe were mainly chloroform and dichloromethane, and the degradation products by Pd/Fe were mainly chloroform and dichloromethane and methane.In Chapter 6, ultrasonic-assisted degradation of chlorinated hydrocarbon with zero-valent iron was studied. The main influencing factors were:ultrasonic power, dosing quantity of zero-valent iron and pH value. The results revealed that the combination of ultrasound and zero-valent iron had obvious synergistic effect. Under optimum conditions, the 36min dechlorination efficiency of chlorinated hydrocarbon reached to 91.2%. The reasons for the synergistic effect were as follows:The ultrasonic cavitation could remove the passive and active metal surface, and meanwhile it enhanced the chemical reaction and mass transfer process interface between. Due to the ultrasound, the ultrasonic/iron system could maintain a lower pH value, which was helpful to the reductive dechlorination by zero-valent iron.The pilot test of reductive treatment of chlorinated hydrocarbon with zero-valent iron in wastewater treatment was investigated in Chapter 7, with the aim of promoting the practical engineering application of the degradation of chlorinated hydrocarbon with zero-valent iron. The results revealed that the degradation of chlorinated hydrocarbon with zero-valent iron and flocculation process by carbide slag could solve the problems in the treatment of industrial wastedwater. When the fluidized reactor of iron powder was under flocculation process, the iron powder could have effective exposure to the wastewater, which avoided the iron powder hardening and blocking. When the pH value in real wastewater was between 2-2.5, under continuous influent,2kg/t iron powder was suitable. When the concentration of chlorinated hydrocarbon was between 5-25 mg/L, the reduction effluent concentration was 1-5 mg/L. When subsequent carbide slag pH value was 7-9, the flocculation could remove the chlorinated hydrocarbon in water with the effluent concentration below 1 mg/L.