Research On The Influence Of KMnO₄ On Membrane Material Performance And Process Stability In Membrane Drinking Water Process

The low-pressure membrane process with organic polymer as the core is considered to be the most promising technology for drinking water purification in the21st century.It has attracted widespread attention from researchers at home and abroad for its advantages such as good effluent water quality,high filtration efficiency,small footprint and high degree of automation.In order to enhance the removal effect of algae and organic pollutants and improve the efficient operation of subsequent coagulation and membrane filtration processes,potassium permanganate is added to the front end of the membrane filtration process as a green,economical and convenient pre-oxidant.However,the effects of potassium permanganate on membrane property and process stability in membrane water purification processes have not been systematically and thoroughly studied while controlling membrane fouling and increasing membrane flux.This paper starts with static immersion and dynamic filtration,and focuses on the effects of potassium permanganate on the physicochemical properties and filtration performance of polyvinylidene fluoride?PVDF?modified hollow fiber membranes.First,under static conditions,the surface morphology,hydrophobicity,mechanical strength,Zeta potential,functional group,a pure water flux,and membrane fouling behavior of PVDF membrane materials at the pH of 5,7,and 9 were measured by potassium permanganate?KMn O₄?,respectively;experimental results show that under different pH conditions,KMn O₄ damages the modified layer and separation layer on the surface of PVDF membrane,which results in different morphological structures,chemical components,hydrophilicity and Evolution of pollution resistance.Under acidic conditions,due to the oxidizing properties of potassium permanganate,the C-H of the PVDF membrane material was destroyed.At the same time,the hydroxyl group?-OH?was introduced to continue the oxidation to generate carbonyl groups?C=O?of aldehydes and ketones;and Under alkaline conditions,a dehydrofluorination reaction occurred on the surface of the membrane to form a carbonyl group?C=O?.Membrane fouling experiments show that changes in the physical and chemical properties of the membrane separation interface severely affect membrane fouling behavior.With the decrease of the pH of KMn O₄ solution and the increase in contact time,irreversible pollution of the membrane surface becomes more and more serious.Secondly,an on-line pre-oxidation+coagulation+ultrafiltration membrane filtration system was set up under the condition of pH 7 and room temperature.The evolution of PVDF membrane surface morphology,hydrophobicity,zeta potential,functional group,flux and membrane fouling behavior and the influence on the operation stability of membrane process were studied under the conditions of potassium permanganate concentration of 0.3,0.5 and 1.0mg/L,respectively.The results show that compared with the coagulation+ultrafiltration membrane filtration system,the addition of KMn O₄ pre-oxidant can improve the water quality of the membrane effluent and reduce membrane pollution in the early stage of operation,but the incompletely reacted KMn O₄ will damage the modified layer and separation layer on the surface of modified PVDF membrane,resulting in changes in the morphological structure,chemical composition,hydrophobicity and charge property of the membrane surface.Filtration-backwash experiments show that with the increase of the amount of potassium permanganate added,the chemical cleaning cycle of the membrane is gradually shortened,and the stability of the membrane filtration process is gradually deteriorated.This study provides data reference for the effect of potassium permanganate on the surface physicochemical properties and process stability of PVDF membranes in the pre-oxidation+membrane drinking water filtration process.