Mechanism And Performance Of Photocatalytic Fiber Coupled With Microalgae To Remove Cr(Ⅵ)

IIn today’s world,rapid population growth and industrial development lead to soil destruction,groundwater,river water and other water quality pollution,which seriously threatens human health.Among various pollutants,the heavy metal Cr（Ⅵ）is highly toxic,and has the most serious and common impact on water bodies.Actively researching environmentally friendly and low-cost Cr（Ⅵ）wastewater purification technology has become a matter of concern to China’s sustainable development and the realization of"important strategic needs of“Beautiful China”.The current Cr（Ⅵ）wastewater treatment methods mainly include physical method（physical adsorption method,membrane filtration method）,chemical method（chemical precipitation method,electrochemical method）,photocatalytic method and biological method.Among them,although the physical method and chemical method are easy to operate,the equipment is easy to install and the Cr（Ⅵ）is removed completely;but they are expensive,high energy consumption,easy to produce sludge,and easy to form secondary pollution.The photocatalytic method has the advantages of low cost,low energy consumption and high efficiency in removing Cr（Ⅵ）;however,the reduced Cr（Ⅵ）cannot be further processed,and the recovery performance of Cr（Ⅵ）is poor.Biological methods are environmentally friendly in removing Cr（Ⅵ）,and can completely remove Cr（Ⅵ）in wastewater through reduction and adsorption,and can also recover Cr;however,biological methods have low removal efficiency.Therefore,it is particularly important to construct an environmentally friendly,low-cost,thorough and efficient method for Cr（Ⅵ）removal.In this paper,a photocatalytic fiber-coupled microalgae reactor is designed to couple photocatalysis and microalgae to improve the removal efficiency of Cr（Ⅵ）.The main research work is as follows:（1）In order to improve the photocatalyst activity and light utilization efficiency in the photocatalytic system,the non-metallic N-doped TiO₂photocatalyst was first prepared by wet method,and then coated on the surface of silica glass beads and silica fiber by sol-gel method.The physical and optoelectronic properties of N-TiO₂photocatalytic fibers were tested by material characterization and optoelectronic properties testing.The detection results show that the N-TiO₂photocatalyst has the characteristic of visible light response,and its absorption spectrum extends to 525 nm.The photocatalyst has excellent optoelectronic properties.During the excitation period,the charge transfer is fast,the photocurrent can reach up to 10 m A,and the photovoltage can reach up to 0.48 V,which is suitable for photocatalytic reactions.（2）In order to study the effect of the photocatalytic system and microalgae system on the removal efficiency of Cr（Ⅵ）,a photocatalytic experimental system was built by using a photocatalytic fiber,and the liquid p H,Cr（Ⅵ）concentration,photocatalyst loading and The effect of photocatalytic carrier on the efficiency of photocatalytic removal of Cr（Ⅵ）;at the same time,the BG11 medium was used to expand the culture of Chlorella,and the light-guiding nuclear pore filter was used to build a microalgae experimental system.)concentration and the amount of Chlorella algae on Cr（Ⅵ）removal efficiency.Experiments show that when p H=2,Cr（Ⅵ）concentration is 5 mg/L,photocatalyst loading is 70 mg,and the photocatalytic carrier is silica fiber,the removal rate of Cr（Ⅵ）in 3 h reaches 64.7%.When the p H of the algae solution was 2 and the initial Cr（Ⅵ）concentration was 5 mg/L,the removal rate of Cr（Ⅵ）in 3 h was 38.3%.（Ⅵ）Toxicity to microalgae quickly leads to their death.（3）In order to improve the removal performance of Cr（Ⅵ）,a photocatalytic fiber-coupled microalgae reactor was constructed.The study found that when the liquid phase temperature was 35±0.5℃and p H=2,the removal efficiency of 5mg/L Cr（Ⅵ）reached 100%within 3 h,which was higher than that of photocatalysis alone and microalgae alone under the same environmental parameters.The sum of the removal efficiencies（96%）.In addition,the removal efficiency of total chromium by the coupled system was 45.3%within 3 h,which was higher than the sum of total chromium removal by photocatalysis and microalgae alone（39%）.（4）The periodic stability performance of photocatalytic fiber-coupled microalgae system for Cr（Ⅵ）removal was experimentally studied.The experimental results show that when the liquidus temperature is 35±0.5℃,p H=2,and the Cr（Ⅵ）concentration is 5 mg/L,the photocatalysis alone can completely remove Cr（Ⅵ）in 9h,and the performance is stable;The removal efficiency of Cr（Ⅵ）in the first cycle of9 h was 61%,and the removal efficiency of Cr（Ⅵ）gradually decreased with the increase of cycle time.The coupled system completely removed Cr（Ⅵ）within 3 h,but the time for complete removal of Cr（Ⅵ）was extended to 5 h after the 4th cycle of cycling.In order to further improve the stability and efficiency of the photocatalytic fiber-coupled microalgae system for removing Cr（Ⅵ）,10 mg/L phenol was added to the 5 mg/LCr（Ⅵ）waste liquid as the carbon source for the growth of microalgae.It was found that the time for complete removal of Cr（Ⅵ）was stable at 2 h,the time for complete degradation of phenol was stable at 2.5 h,and the microalgae grew well within 8 consecutive cycles,indicating that phenol contributes to the removal of Cr（Ⅵ）by the coupled system.