Study On The Influence Of Ozone-PAC Adsorption On Ceramic Membrane Fouling And Water Purification Efficienc

As the standards for drinking water quality gradually improve,there is an urgent need for further upgrading and transformation of conventional water treatment processes.Ultrafiltration technology has advantages such as good effluent water quality,high degree of modularization,and high biological safety.It is highly valued in the field of water treatment.However,membrane fouling has always been an important obstacle to the promotion and application of ultrafiltration technology.The surface of the membrane is easily contaminated by organic matter,microorganisms,colloids,etc.after long-term operation,resulting in a decrease in membrane flux and an increase in membrane resistance,reducing the performance and service life of the ultrafiltration membrane.Adsorption is an effective pretreatment method to alleviate membrane fouling.Powdered activated carbon（PAC）has a large specific surface area and high porosity and is commonly used in water treatment.However,a single adsorbent often has difficulty meeting the removal requirements for different organic substances.O₃ has strong oxidation properties and can oxidize most organic substances into substances that are easily biodegradable or adsorbable,thereby improving removal efficiency.At present,most water plants use organic membranes for ultrafiltration due to their low investment cost.However,organic membranes are not resistant to oxidation and have poor chemical stability.They are difficult to combine with ozonation.Ceramic membranes can solve this problem well.This study uses O₃-PAC adsorption as a pretreatment method for ceramic membranes to explore the synergistic mechanism of O₃ and PAC,analyze the removal rules of typical organic substances by O₃-PAC,reveal the mechanism of O₃-PAC adsorption pretreatment on ceramic membrane pollution control,and conduct multi-angle analysis on ceramic membrane pollution and changes in inlet and outlet water quality.Firstly,the effects of ozonation and PAC adsorption on the properties of different organic substances were investigated.The feasibility of O₃-PAC adsorption pretreatment was evaluated through indicators such as DOC,UV₂₅₄,and SUVA,and the pathways for removing different pollutants from water were explored.Research has found that the removal rate of aromatic hydrocarbons in water by ozonation increases linearly with the amount of O₃ added.The removal effect is more significant compared to the removal of soluble organic matter,and there is no significant difference in the change of DOC for different organic matter.However,PAC adsorption had a better removal effect on humic acid and bovine serum albumin,but its removal ability for hydrophilic large molecule sodium alginate was poor.After O₃-PAC adsorption combined pretreatment,the organic matter level in the ultrafiltration effluent was significantly reduced.The DOC removal rates of humic acid,sodium alginate and bovine serum albumin in the ultrafiltration effluent were 44.2%,74.8%and 42.3%,respectively.The combined process had the most significant improvement in the removal effect of sodium alginate,and the UV₂₅₄removal rate of humic acid was also as high as 65.8%.PAC can adsorb small molecule organic substances such as oligosaccharides and bovine serum albumin that are difficult to completely oxidize by O₃,preventing them from passing through the membrane pores into the effluent,effectively controlling the problem of increased DOC in sodium alginate ultrafiltration effluent after O₃ pretreatment.The synergistic mechanism of ozonation and PAC adsorption plays an important role in reducing the concentration of organic matter level in membrane effluent and helps improve the water quality of effluent.Secondly,the study investigated the effect of O₃-PAC adsorption pretreatment on membrane fouling caused by typical organic matter in water during ultrafiltration.The study found that the degree of membrane fouling caused by different organic matter was in the order of sodium alginate>humic acid>bovine serum albumin,with sodium alginate causing the most severe membrane fouling.After O₃-PAC adsorption pretreatment,the membrane flux decline rates of humic acid,sodium alginate and bovine serum albumin were alleviated by 35.2%,55.2%and 31.0%,respectively,showing the most significant alleviation effect on membrane fouling caused by sodium alginate.This is because O₃ can oxidize and break the main carbon chain of polysaccharides,degrade polysaccharides that are difficult to be adsorbed and removed into small oligosaccharides,which can be adsorbed by PAC.The synergistic effect of O₃ and PAC effectively alleviates membrane fouling.The single ozonation did not show a control effect on the membrane fouling caused by bovine serum albumin,because bovine serum albumin has a low molecular weight and can easily pass through the ceramic membrane pores into the effluent.However,PAC’s good adsorption capacity for low molecular weight organic matter effectively solves this problem.It can be seen that the O₃-PAC adsorption pretreatment system has achieved good alleviation effects on membrane fouling caused by different organic matter,effectively solving the problem that single pretreatment is difficult to control membrane fouling caused by different types of organic matter.Finally,the effects of O₃,PAC adsorption single pretreatment and combined pretreatment on the membrane filtration characteristics and water purification efficiency of natural surface water（Langmaoshan Reservoir water）were investigated.Methods such as particle size distribution measurement,Zeta potential measurement,three-dimensional fluorescence parallel factor analysis,and scanning electron microscopy observation were used to characterize the changes in organic matter properties and membrane fouling.The study found that O₃-PAC adsorption pretreatment showed good removal effect on organic matter in natural surface water,with DOC and UV₂₅₄ removal rates reaching 30.6%and 68.4%,respectively.The reduction of UV₂₅₄ index helps to reduce the formation of disinfection by-products.O₃-PAC adsorption pretreatment showed the best removal effect on humic acid and fulvic acid fluorescent components in natural surface water,with a fluorescence intensity reduction of 88.7%.This is due to the fact that its chemical structure contains aromatic rings and unsaturated bonds that are more easily attacked by O₃ selectively,oxidizing to form saturated organic matter such as carboxylic acids.The production of carboxyl groups and the reduction of SUVA value also improve the hydrophilicity of organic matter to a certain extent.O₃-PAC adsorption pretreatment can alleviate the ultrafiltration membrane pollution of surface water,and the terminal specific flux is increased from 0.39 of raw water to 0.75.The alleviation of membrane flux decline rate can reach 59.0%,and the reversible and irreversible pollution resistance can also be reduced to different degrees.Ozonation changes the functional groups and spatial structure of organic matter,causing the carbon chain to break and re-aggregate,widening the particle size range.After O₃-PAC adsorption pretreatment,it can be seen that the proportion of small particle size organic matter in the effluent is significantly reduced.PAC has a good adsorption effect on small particle size organic matter,and the synergistic effect of the two reduces membrane fouling.After O₃-PAC adsorption pretreatment,the filter cake layer is significantly reduced,the distribution of pollutants is more uniform,the number of membrane pores after filtration is more,and the blockage of small pore diameter channels is also significantly alleviated.This study proposes a new method of using ozonation-PAC adsorption and ceramic membrane ultrafiltration to solve the problems of membrane fouling and poor organic matter removal in traditional ultrafiltration processes.This method has the potential to achieve short process water treatment.In addition,the application of ceramic membranes can achieve direct contact between the oxidant and the membrane,thereby inhibiting the growth of microorganisms on the membrane surface and having reliable ability to control microbial risks such as Giardia and Cryptosporidium.