Effect Of Nano TiO₂ Photocatalytic Preoxidation On Membrane Fouling Of Organic Matter And Ultrafiltration Process In The Secondary Effluent Of Municipal Wastewater

In the case of serious environmental pollution and shortage of water resources,people are getting more and more attention to the problem of waste water, among them,the regeneration and utilization of the secondary water is particularly emphasized. This paper takes the secondary effluent of municipal wastewater as the research object, the influence factors and the oxidation efficiency of organic compounds in the secondary effluent were investigated by nano TiO₂ photocatalysis, meanwhile, the kinetic analysis was carried out on the photocatalytic oxidation reaction of the secondary water, In the end, the membrane fouling of the secondary effluent ultrafiltration process was studied,in order to provide reference and basis for the regeneration of two grade water in the future and control of membrane fouling. The conclusions of this paper are as follows:（1）According to the removal rate of TOC and UV254 in water, It is concluded that the optimal photocatalytic oxidation conditions for the two stage effluent are Nano titanium dioxide dosage of 300mg/L and aeration rate of 1 L/min.（2）The photocatalytic reaction is a pseudo first order reaction, and the reaction kinetic equation is obtained. Photocatalytic degradation of secondary effluent organic matter in varying degrees, one of the fastest reaction rate of UV254, K value is8.81×10^-3min^-1, shorter half-life, show that secondary water containing pi bond unsaturated substances after photocatalytic, than the other substances faster degradation.（3）The molecular weight distribution of organic matter in the secondary effluent was greatly influenced by photocatalysis. With the increase of photocatalytic time, the proportion of less than 3kda small organic molecules by 32.8% gradually increased40.3%, more than 100 kda macromolecular organic matter is by 36.1% dropped to 6.7percent, other regions account for a smaller proportion. The photocatalytic reaction of60 min, on the secondary effluent in organic molecular weight change larger,（4）In the secondary effluent, the humic substances in the effluent are continuously degraded with the increase of the photocatalytic time, and are degraded into the intermediate substances such as protein, amino acid and so on, among them, the most obvious degradation of the fluorescent substance was the photocatalytic 60 min.（5）The structure of the two stage water before and after GC-MS was detected by the contrast analysis, and the species and quantity of organic matters were obviously increased, this is mainly due to the amount of organic compounds with a new structure,which has a large amount of organic compounds with small molecular weight range.Which and there has been a marked increase in alkanes, and alcohol, ring structure and carboxylic acid compounds significantly reduced. this is mainly photocatalytic oxidation of the double bond, benzene ring structure of varying degrees of damage.（6）Different conditions in mixed liquor of the flux of membrane in varying degrees of attenuation, with the reaction when 60 min change water molecules to alleviate membrane flux attenuation degree is most obvious. The flux attenuation of 60 min mixed liquid membrane is lower than that of pure secondary effluent, it is main that the photocatalytic degradation of organic matter in the secondary effluent is a small molecule organic matter, which reduces the pollutant amount of membrane fouling caused by membrane surface. When the ultrafiltration membrane is mixed with different conditions, membrane flux recovery rate is slightly lower, and the pollution layer is easy to clean. Comprehensive discovery, photocatalytic pre oxidation of a certain time can slow down the membrane fouling in the subsequent ultrafiltration process, on the one hand, by changing the organic molecular weight of water the size and distribution of membrane pollution mitigation, on the other hand, some small organic molecules can be adsorbed on the surface of nano TiO₂ photocatalyst, in order to accumulate on the surface of the film lead to a certain increase in the amplitude of membrane flux decay,but this part of the membrane fouling is easier to eliminate and restore the.