Photocatalytic Oxidation And Enhancement Technologies For Atrazine Wastewater Treatment

In the global pesticide market,herbicide is leading the growth.Atrazine is one of herbicides with large amounts of production,use and export.Due to its bio-accumulativity and persistenty in the environment,it can cause nagatvie impact on the human health and ecological environments,which has gained growing concerns.During pesticide production,the generated wastewater contains high level of salts and organic pollutants and the treatment efficiency and biodegradability are relatively low which has been a key technical challenge.The advanced oxidation process has been recognized as one of the most promising treatment technologies.Although it has been widely studied and applied in many areas,the past efforts mainly focuses on photochemical oxidation,catalytic wet-air Oxidation,ozonation,and Fenton oxidation.There still lacks in-depth studies on its hybrid treatment of industrial wastewater,especially agrochemical wastewater with high organic contents and high salinity,consequently leading to limited application in practice.Therefore,this thesis research targeted high salinity atrazine wastewater and focused on the advanced oxidation process(e.g.,photocatalytic oxidation)and its enhanced integrated methods(e.g.,modified catalytic oxidation and ultrasonication).Through the design and employment of bench and pilot scale experiment,the reaction kinetics and optimal treatment conditions were also studied.The research consists of three parts:Firstly,given the relatively weak oxidative capacity by using ozonation alone,UV/O3 and UV/O3/US were integrated and applied for atrazine wastewater treatment.It was found that the oxidative capacity of ozone was significantly enhanced under UV irradation,and the degradation rates of COD and ammonia nitrogen in the UV/O3 system were increased from 4%to 56%and from 25%to 65%,respectively.In particular,the degradation rates increased in proportion to the UV intensity in the range of 7w to 14w but showed an inversely proportional relationship in the range of 21 w to 28w even leading to increase of COD concentration in some cases.The phenomena were also observed in the UV/O3/US system along with some unfavorable effects of ultrasonication on atrazine wastewater treatment.The degradation mechanism of the two reaction systems and the reasons of the phenomena were discussed and provided a solid base for the further enhancement studies.Secondly,in order to further improve degradation efficiency,activated carbon and photocatalyst was integrated and applied for the photo-ozonation of the high salinity atrazine wastewater.The influence of three key factors,AC-catalyst dosage,UV intensity and aeration intensity,were quantified and optimized.The results showed that the removal efficiency was the best,when the AC-catalyst dosage=40g/L,the UV intensity=14w,the aeration intensity=800L/h,with the rates of 70.9%and 87.7%respectively for COD and ammonia nitrogen respectively.The Langmuir-Hinshelwood(LH)model was used to describe the UV/O3/AC system and the apparent rate constant and the function relationships of the three factors were further discussed.The results indicated that the degradation rate followed the first-order kinetics and the function relations at different factor levels fitted well with the apparent first order rate constants.Langmuir isotherm could accurately describe the adsorption equilibrium of atrazine wastewater on the AC-catalyst with the equation as:1/q=0.0758+87.96×1/p.In addition,it was observed that the TiO2 catalyzed photo-ozonation(UV/O3/TiO2)system could improve the utilization efficiency of UVC light by about 50%,which would be useful to improve the photon utilization and reduce processing cost.Finally,the response surface method was employed to optimize photocatalytic oxidation of atrazine wastewater integrated with ultrasoniccation in the pilot-scale experiments by Central Composite Design(CCD).The effects of three key factors,UV intensity,O3 and US intensity,as well as their interactions were examined.When the reaction constant k of COD degradation was used as the response value,the quadratic regression equation was obtained.Among the three factors,the UV intensity and O3 were signifincant;When the atrazine degradation rate was used as the response value,the optimal degradation conditions were achieved:UV intensity=35w,O3=lOg/L,and US intensity=1500w,leading to the maximum atrazine degradation rate of 96.85%.The experimental and modeling data matched with each other well,which approved the application potential of the developed model for related atrazine wastewater treatment research and industrial practice.What's more,the crystallized salt with high purity and pure white,which in line with national secondary standards of chlor-alkali salt.