Study On Organic Wastewater Treatment By Fenton Reagent And TiO₂-CS Photocatalysis

The issue of environmental pollution is currently more and more serious, so that the environmental cleaning and environmental remediation is an urgent task. Among various techniques for purifying environment, advanced oxidation processes (AOPs) are paid greater attention as new environment-purifying technique. AOPs have high efficiency, have no pollution after treatment, so it is a prospective technique for treating toxic contaminations in water. The key of the AOPs technology is to produce hydroxyl radical( · OH). According to the conditions of oxidants and catalytical, AOPs can be dvided into Fenton reagent and like-Fenton reagent, ozone and combined ozone oxidation, photocatalytic degradation. The method of Fenton reagent and photocatalytic degradation are choosed to discuss in this paper.Firstly, monocrotophos and wastewater from algin production are selected to be the target object degradated by Fenton reagent.For monocrotophos, the five important factors, pH value, dosage of H₂O₂, Fe ²⁺ concentration, temperature and reaction time are designed by orthogonal experiments or single experiments. The result from orthogonal experiments show that the order of the five factors was: dosage of H₂O₂>tempreture>reaction time> pH value>Fe²⁺ concentration. The COD removed is 78.8%. The result from single experiments indicate that the optimal conditions are as following: 2.0ml H₂O₂, 70℃, 0.50mmol/l Fe²⁺, pH=3. After 10 hours, the organics in the solution are completely minerized to inorganics, and the COD removed is 100%. The kinetics of this reaction is first order kinetics. Moreover, we investigate the catalysis of four transition metal ions Cu²⁺, Mn²⁺,Co²⁺ and Zn²⁺ on the Fenton reaction. The results indicate that the degradation efficiency has been great improved when the concentration of the metal ions achieve certain value. The reason is that transition metal ions are helpful to decompose H₂O₂ and produce more hydroxyl radical. Among these four transitionmetal ions, Cu2+ has the highest catalysis efficiency. Finally, the result of GC-MS shows that monocrotophos can not be determined after 30min.For wastewater algin from production, we firstly carry out orthogonal experiments to discuss the influence of five facor on the decomposition of Fenton reagent. And the result is Fe + concentration >reaction time>tempreture>pH value >dosage of H2O2. Single experiments show that the optimal conditions are: 0.5ml H2O2, 40°C, 4.0mmol/l Fe2+, pH=3. After 60 min, Fenton reaction balanced. Finally, the COD removal ration is 62.9% and the COD value of the solution is 67mg/l after degradation.Secondly, we study photocatalyzed 2,4-dichlorophenol by TiO2-CS prepared as catalyst. The dosage of TiO2-CS, original pH value, dissolved oxygen, concentration of 2,4-dichlorophenol and irridation time are studyed.The dosage of TiO2-CS has vital effect on the removal of 2,4-dichlorophenol. In the light system without TiO2-CS, the maximal remaval rate is 80.4%. The optimal dosage of T1O2-CS is 0.1 g/1, the maximal removal rate is 95.4%. With same dosage of TiO2 powder and T1O2-CS, the removal rate of TiO2-CS in 30min is higher than TiO2 powder by 14%, literature1"91 by 36.6%.The original pH has an important effect on the removal rate, absorbance and pH value changes during the oxidation. In the system of pH=12.5, the removal rate is the highest, 94.8% in 30minutes. With different original pH value, the color of the solution are getting deeper quickly, and slowly lighter after get to the deepest. If the original pH value is too low or too high, the pH value of the solution during the oxidation has little change because of buffer ability of the solution. In the weak acid or weak alkaline system, the pH decrease rapidly to 3 in the first 30 minutes, and then become stable, because organic acids are formed during the photocatalytic reaction.Dissolved oxygen in the solution plays an important role on the photocatalytic oxidation confirmed by three control experiments. The result indicats that oxygen mainly affects the absorbance of the solution. With enough oxygen, absorbance of the solution lower rapidly after 30min, or it will not lower at all untill the oxygen isintroduced.During the oxidation, the concentration of chlorine ion has a linear relation with the reaction time, so its kinetics is zero order kinetics. The velocity constants of three solutions (25 mg/1, 50 mg/1, 100mg/l)are 0.4987, 0.9496, 1.7674 min"1, respectively.