Research On Degradation Of Fulvic Acid In Leachate By Advanced Oxidation Processes

Leachate is a kind of refractory organic wastewater and will cause serious environmental problems when discharged without efficient treatment and is difficult to degrade by the conventional biological combined processes.Many researches suggest that the main refractory organics in leachate are water-soluble humus,which are mainly composed of humic acid(HA)and fulvic acid(FA).Advanced Oxidation Processes(AOPs)which are based on the production of free radicals with strong activity(such as hydroxylradical·OH)are irreplaceable in water treatment.It was found that the macromolecular refractory organics could be degraded to non-toxic small molecule products by these free radicals.There are many kinds of AOPs,however,ozone oxidation process,TiO2 photocatalytic oxidation process and BiVO4 photocatalytic oxidation process have triggered lots of concentration due to their unique advantages.Ozone oxidation process contains two kinds of mechanism of action:the direct reaction and the indirect reaction,it is quick and without secondary pollution;for TiO2 photocatalytic oxidation process,electron transition occured when the TiO2 photocatalyst absorb ultraviolet energy and it will lead to free radical chain reactions to produce free radicals with high activity(mainly·OH)to degrade organics,it is mild;for BiVO4 photocatalytic oxidation process,BiVO4 has a lower band gap,it could degrade organics under visible lights,the BiVO4 photocatalyst is of high photocatalytic activity and no toxicity.In this paper,ozone oxidation process,TiO2 photocatalytic oxidation process and BiVO4 photocatalytic oxidation process were used to degrade FA,the influencing factors and the efficiency ratio EDR were explored to find the the best experimental conditions to provide detailed and realiable reference for the treatment of leachate treatment.Using ozone oxidation process to degrade FA,the solution was of 40 L with a concentration of 250 mg·L-1,and the removal rate of COD,UV254 and CN were used to evaluate the effects of the degradation of FA,the effects of ozone concentration,reaction time and initial solution pH value on the degradation of FA were studied to find the best experimental conditions,the efficiency ratio EDR was also analysed.And the results showed the maximum renoval rates of COD,UV254 and CN respectively reached 36.58%,76.56%,95.66%under the best experimental conditions:ozone concentration=36.7 mg·L-1,reaction time=60 min,initial solution pH value=9,EDR=2.10×10-3 Kg/KJ.Using TiO2 photocatalytic oxidation process to degrade FA,the solution was of 100 mL with a concentration of 50 mg·L-1,the removal rate of UV254 was used to evaluate the effects of the degradation of FA,the effects of TiO2 concentration,reaction time and initial solution pH value on the degradation of FA were studied to find the best experimental conditions,the efficiency ratio EDR was also analysed.And the results showed the maximum renoval rate of UV254 reached 95%under the best experimental conditions:TiO2 concentration=0.09 g,reaction time=60 min,initial solution pH value=5,EDR=2.20 × 10-5 Kg/KJ.The BiVO4 photocatalyst was synthesized via solution combustion method(SCM).The sample was characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscope(TEM)and Ultraviolet-visible spectroscopy(UV-Vis).Then,FA was degraded by BiVO4 photocatalyst,the solution was of 50 mL with a concentration of 10 mg·L-1,the removal rate of UV254 was used to evaluate the effects of the degradation of FA,the effects of BiVO4 concentration,reaction time and initial solution pH value on the degradation of FA was studied to find the best experimental conditions,the efficiency ratio EDR was also analysed.The results showed that the BiVO4 sample was of monoclinic structure with high purity,and the maximum renoval rate of UV254 reached 52%under the best experimental conditions:BiVO4 concentration=1.5 g,reaction time=80 min,initial solution pH value=6;when reaction time=60 min,EDR=4.81 × 10-7 Kg/KJ.When reaction time is 60 min,the efficiency ratio EDR of degradation of FA under ozone oxidation process is way lager than the other two advanced oxidation processes.So,in this thesis,based on the energy consumption,for the degradation of FA,the ozone oxidation process is the best experimental scheme.