The Effect Of Inorganic Particles On The Organic Pollution Of Ultrafiltration Membrane During Water Purification

Ultrafiltration has been used in drinking water treatment increasingly as a new water treatment technology because of its high efficiency and safety.However,membrane fouling is the most important obstacle for its application.The actual composition of polluted water is complex.Inorganic particles and dissolved organic matters always coexist,and their interactions have a synergetic effect on the ultrafiltration membrane fouling.An in-depth investigation onthe membrane fouling behavior in the case of the co-existence of inorganic particles and organic matter is of great significance for the control of membrane fouling.In this study,humic acid(HA)was used as the surrogate of dissolved organic matters(DOM),while,Al2O3,zeolite,and SiO2 particles were selected as the inorganic particles.The effect of particle properties on membrane fouling in the filtration system containing both inorganic particles and DOM was comprehensively investigated.Firstly,the adsorption behavior of the inorganic particles to HA were investigated when the inorganic particles were used as adsorbents.Then,the membrane fouling experiments were carried out contain the single foulant and the organic-inorganic foulant coexisted to study the effect of inorganic particles on the fouling of ultrafiltration membrane caused by HA.The adsorption capacity of inorganic particles to HA is Al2O3>zeolite>SiO2.Moreover,the adsorption of inorganic particles on HA was selective.The adsorption rate of 128?m Al2O3 to>30KDaHA was more faster,the adsorption equilibrium reached at 380min and it can be fitted with pseudo-first-order kinetic model.The thermodynamic adsorption was satisfied with the Langmuir model with the maximum adsorption capacity of 19.96mg/g.The adsorption rate of 189?m zeolite to<30KDa HA is more faster and the adsorption equilibrium time is 180 min.The adsorption process can be fitted with pseudo-first-order kinetic model.The thermodynamic adsorption can be fitted with the Langmuir model with the maximum adsorption capacity of 5.24 mg/g.SiO2 was confirmed has no adsorption capacity to HA.Consideration the influence of particle size to HA adsorption,the smaller of particle size,the more adsorption sites was exposed,the faster the adsorption rate and the more of adsorption capacity.The maximum adsorption capacity of 7?m Al2O3 particles to>30KDa HA was 28.75 mg/g;the maximum adsorption capacity of 5?m zeolite particles to<30KDaHA was 9.48 mg/g.Filtering the inorganic particles by themselves did not result in any significant fouling,as evidence by the low permeability decline and high hydraulic reversibility(>94%).However,HA filtration can cause relatively serious membrane fouling with the flux decline of>30KDa HA was 43%and the water flux recovery was 53%.In the presence of inorganic particles coexisting with HA,the synergistic fouling of inorganic particles with HA occurred markedly,and the degree of membrane fouling was SiO2>zeolite>Al2O3.This shows that there is interaction between inorganic particles and HA.Moreover,the membrane fouling caused by the coexistence of inorganic particles with>30kDa HA is more severe than<30kDa HA.The distribution of membrane resistance and the SEM graphs show that Al2O3 and zeolite particles have a control effect on membrane irreversible fouling.The presence of SiO2 caused more severe irreversible fouling.Membrane fouling model analysis showed that the cake layer filtration in the inorganic-organic hybrid filtration system became the main mechanism of the membrane fouling,which contribute to serious fouling membrane.Analysis of the electricity properties of the membrane surface,the Zeta potential of mixed filtration membrane after back-washing is large than new membrane but small than HA fouling membrane.It indicated that exist of inorganic particles could reduce HA on the membrane.According to XDLVO theory,?GmlfTOT between inorganicparticles with HA is smaller than HA with membrane,so HA can be more easily combined with inorganic particles to form organic-inorganic composite particles.Moreover,the value of ?GmlfAB of HA with Al2O3 is the smallest,zeolite is second,SiO2 is the largest,so HA is easily to combine with Al2O3 to form organic-inorganic composite particles and deposited on the membrane surface,while the exclusion of HA with SiO2 could increase the chance of HA contact with the membrane,resulting in more severe irreversible fouling.Experiment proves that the size of inorganic particles is also the key factor that affects the membrane fouling.When the size of inorganic particle is small,cake layer more dense,and membrane fouling is more serious.However,compared with big size of inorganic particles,small size of inorganic particles have more better control effect on irreversible fouling.