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Study of Modified Pvdf Uf Membrane Anti-fouling Performance

Author: LiXuHui
Tutor: YuShuiLi
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: ultrafiltration natural organic matter hydrophobicity membrane fouling adsorption
CLC: X703
Type: Master's thesis
Year: 2010
Downloads: 171
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Abstract


Membrane fouling has been one of the bottlenecks and limiting factors, which is blocking and confining the wide application of membrane technology in the water treatment. In recent years, a great many of studies indicate that hydrophobicity and molecular weight distribution （MWD） of natural organic matter （NOM） have a significant effect on membrane fouling. In this paper, the effect of characteristics of NOM on membrane fouling was investigated.NOM in surface water was isolated into strongly hydrophobic organic, weakly hydrophobic organic and hydrophilic fractions by resins. It was found that the percentages of strongly hydrophobic, weakly hydrophobic and hydrophilic fractions were 55.46%、23.62% and 23% respectively, MWD of strongly hydrophobic and weakly hydrophobic fractions was mainly 0.53 kDa, hydrophilic fractions was 3100 kDa. Filtration tests of the three organic fractions showed that, strongly hydrophobic organics show the highest fouling potential, which followed by weakly hydrophobic and hydrophilic organics, 60 minutes later, flux declines with unmodified membrane was 60.6%, 70.8% and 82.0% of the initial flux, while flux declines with modified PVDF membrane was 75.1%, 77.6% and 86.0%. DOC rejection of unmodified membrane was 15.8%, 10.5% and 5.2%, rejection of modified membrane was 28.6%, 11% and 16.3%, showing that the extent of flux decline may not be associated with the extent of organics rejected. Moreover, the removal ratio of three organic fractions using modified membrane was higher than that of using unmodified membrane, while the flux decline was lower that of unmodified membrane, indicating that the enhancement of hydrophilic property was favorable for the improvements of membrane treatment capacity and anti-fouling characteristics. Further filtration studies about model substance of NOM, Humic acid （HA）, Fulvic acid （FA）, bovine serum albumin （BSA） and polyethylene glycol （PEG） were conducted. Results showed that hydrophobicity and MWD of NOM are the main factors affecting membrane fouling, there was a negative correlation between membrane flux recovery ratio and membrane total fouling index （Ft）, also there was close relation between membrane reject ratio and hydrophilicity/hydrophobicity and MWD of organic matters. Static adsorption experiment was performed to study properties of HA adsorption onto membrane surface. The results showed that adsorption was higher at higher concentration, adsorption increases as ionic strength increases, low temperature decreases adsorption. Langmuir isotherm model fits membrane adsorption well, adsorption isothermal equation was q=18.622·0.047C/（1+0.047C）. Adsorption thermodynamics indicated that adsorption of HA on membrane was entropy increase and spontaneous process. Kinetics tests of membrane adsorption indicated that adsorption can be well describled by Intra-particle diffusion equation.Filtration of raw surface water was disscussed. Under conditions of this study, the quantitative relationship between membrane flux and dissolved organic carbon （DOC） in water was determined as J=J0t-0.0152exp（0.3735（DOC））. The removal ratio of turbidity and UV254 using modified membrane was higher than that of using unmodified membrane. Inaddition, membrane which was fouled by raw surface water was cleaned by hydraulic backwash, ethanol, hydrochloric acid and sodium hydroxide solution. Results showed that effectiveness of membrane flux recovery by hydrochloric acid （0.1%） soaking 1 h and sodium hydroxide （0.01 M） solution soaking 2 h is better.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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