Research On Degradation And Conversion Performance Of Tetracycline Wastewater Based On Photobiocatalysis

With the rapid development of the pharmaceutical industry,humans and animals consume more and more antibiotics.So far,a variety of antibiotic drugs have been used,such as tetracycline,erythromycin,quinolone and penicillin.Antibiotics protect humans and animals from bacterial infections,saving many lives.However,most antibiotics will be excreted in urine and feces.In addition to causing serious water pollution,the persistence and non-degradability of antibiotics will also bring some serious environmental problems,such as the emergence of super bacteria and drug resistance.Tetracycline is one of the most widely used and typical antibiotics.However,the current methods for treating tetracycline pollution still have some disadvantages,such as low degradation efficiency,incomplete degradation and difficult to realize resource transformation in wastewater treatment.In order to achieve efficient degradation and conversion of tetracycline wastewater,this paper is based on the novel intimate coupling of photocatalysis and biodegradation（ICPB）technology,the following three research works were mainly carried out in this paper:（1）In order to improve the photocatalytic activity and the efficiency of degrading tetracycline wastewater,new photocatalysts and photocatalytic hollow fibers were prepared.Firstly,the Ge O₂/Zn-HPW/TiO₂photocatalyst was prepared by two-step impregnation method,and the Ge O₂/Zn-HPW/TiO₂photocatalytic sol was configured with ethylene glycol as dispersant,and its electrochemical performance was tested.Secondly,a photocatalytic fiber based on Ge O₂/Zn-HPW/TiO₂material was prepared by using the sol coated on the surface of hollow quartz fiber by the lifting method,and the optical properties of the photocatalytic fiber were investigated.Finally,an experimental system for photocatalytic degradation of tetracycline wastewater was established to screen the optimal physical conditions（such as the temperature of the substrate concentrate and initial p H,etc.）for photocatalytic fiber degradation of tetracycline wastewater,and investigate the performance of photocatalytic fiber degradation of tetracycline wastewater.The experimental research shows that:Tetracycline wastewater has a concentration of 100 mg/L,a flow rate of 5 ml/min,a temperature of 35℃,and a p H=7.0,the degradation rate of tetracycline wastewater by Ge O₂/Zn-HPW/TiO₂photocatalytic fiber is 98.79%and the chemical oxygen demand（COD）degradation rate is 47.8%within 10 hours.（2）In order to investigate the performance of a single biofilm to degrade and transform tetracycline wastewater,a fiber-optic microalgal biofilm reactor was designed.The reactor is divided into two layers by a light-guiding nuclear pore filter membrane.The upper layer is a microalgal biofilm area,and the lower layer is a light-emitting hollow optical fiber（the optical fiber is only used to provide light energy for microalgal growth）.An experimental system for the degradation of tetracycline wastewater with fiber optic microalgae biofilm reactor was established.The experimental research shows that the degradation and transformation efficiency of tetracycline in a single biofilm system is low,which is attributed to the great effect of tetracycline on single biofilm.Within 10 h,the degradation rate of tetracycline was only 11.66%and COD remained at92.27%,respectively.After 45 days of operation,the degradation performance of tetracycline was further decreased,and the biomass and lipid content of microalgal biofilm in the reactor were only 167.18%and 12.11%higher than that of the initial biofilm,respectively.（3）In order to achieve high efficiency of tetracycline wastewater degradation and resource conversion efficiency（microalgal biomass production）,hollow fiber was replaced with Ge O₂/Zn-HPW/TiO₂coated hollow fiber on the basis of fiber microalgal biofilm reactor（realize the photocatalytic degradation of tetracycline and provide light energy for microalgal growth at the same time）.The photocatalytic microalgae close coupling reactor（ICPB）was constructed.The degradation and conversion performance of tetracycline wastewater by biofilm（B）,photocatalysis（P）and photocatalytic-biofilm direct coupling（ICPB）systems were compared and studied.Experimental research shows that compared with the system B and the system P,the ICPB system has obvious advantages in the degradation and conversion performance of tetracycline wastewater.Under the same conditions,ICPB system can completely degrade 100 mg/L tetracycline wastewater within 6 h,which takes 4 h less than P system.Chemical oxygen demand（COD）can be completely removed within 10 h.The ICPB system can degrade tetracycline wastewater for a long time（120 d）and multiple cycles with stable performance.In the ICPB reactor,the biomass of biofilm in the reactor increased to17.25 mg/d,and the lipid content of microalgae reached 28.34%,which was 1.75 times higher than the initial lipid content.In addition,Rhizobium,Salinarimonas and Coelastrella sp.were enriched in the biofilm,which promoted the growth of microalgae and biomass production,and realized the effective conversion and recycling of wastewater resources.