Title: Fouling behavior and foulant characteristics of reverse osmosis membranes for treated secondary effluent reclamation
Journal: Journal of Membrane Science
Authors: Yan Zhaoa, Lianfa Songb, Say Leong Onga
Corresponding author: Say Leong Ong
Institute:
a Division of Environmental Science & Engineering, National University of Singapore, 10 Kent Ridge Crescent, 119260 Singapore, Singapore
b Department of Civil and Environmental Engineering, Texas Tech University, 10th and Akron, Lubbock, TX 79409, USA
The original and creativity of paper: In this paper, fouling behaviors (i.e. the rate and extent of flux decline and fouling reversibility) of a laboratory-scale RO system fed with ultrafiltration (UF) prefiltered secondary effluent were studied at two operationally important permeate recovery levels. The associated fouling mechanisms were delineated with the aid of microscopic analysis of the fouling layer characteristics (i.e. composition, morphology and the fouled membrane surface properties). There was a remarkable correlation between the different fouling behaviors observed and the characteristics of fouling layers developed.
Summary:
In this study intended to provide a better understanding of the fouling phenomenon occurring during membrane process. Fouling mechanism and factors affecting fouling were investigated systematically. Results will be summarized following;
1. Fouling behavior with increasing permeate recovery
a. Fig.1 shows flux decline curve versus permeate recovery at two different initial fluxes of 1.0 x 10-5 m/s and 2.0 x 10-5 m/s. Result showed that more flux decline was observed at a higher initial flux due to a higher permeate drag and stronger concentration polarization which promoted foulant transport and deposition on the membrane surface.
b.
Fig 1. Permeate flux as a function of recovery in concentration mode fouling experiments fed with UF prefiltered secondary effluent. pH was not adjusted for the pHambient run; pH was kept at 5.0±0.5 for the pH 5.0 run. Operating conditions: applied pressure 300 psi for initial flux of 2.0×10?5 m/s and 160 psi for initial flux of 1.0×10?5 m/s, cross-flow velocity = 0.1 m/s, temperature = 24±1 ?C.
c. A turning point of higher initial flux experiment was observed at a permeate recovery of 50% beyond as well as it showed greatly increased after the turning point. In contrast, a turning point of lower initial flux occurred at a relatively higher recovery of 60%. This is because of the precipitation of sparingly soluble salts when their saturation degree has exceeded the solubility limit associated with this high recovery.
2. Fouling layer characteristics
a. Fouling layer as dry condition was quantified using FTIR spectra. Fig. 2(a) , the clean membrane showed the typical pattern of TPC-PA membranes with polysulfone support layers .
b. It can be observed that the vibrational spectrum of the PA membrane became more obscured upon fouling at increasing permeate recoveries.
c. When the ease of striping was considered, the spectral patterns of the fouled membrane could be fully restored to its virgin state at a permeate recovery of 55%. Whereas at a higher permeate recovery of 70%, the restoration of spectral patterns after physical striping was minimal.
d. To differentiate the absorbance bands of potential foulants from membrane substrate in certain wavelength regions, FTIR spectrum of the physically stripped fouling later was also recorded as showed in Fig. 2(b).
e. For both recoveries, a distinctive peak was exhibited at 1040 cm-1, which is often found associated with carbonyl bonds of carbohydrates.
f. Absorption bonds were also detected at 1652 cm-1 and 1558 cm-1 relating to amide I and amide II group of protein and/or amino sugars.
Fig 2. FTIR spectra of (a) new membrane, membrane fouled at initial flux of 2.0×10?5 m/s and after physically stripped, (b) physically stripped fouling layer.
3. Fouling potential with increasing recovery
a. Fig.3 showed that the organic fouling potential of feed water with increasing recovery was characterized aster inhibition of scaling was attained through pH adjustment.
b. At permeate recovery of 50%, feed water concentration corresponded a factor of 2. Whereas, at permeate recovery of 75%, feed water concentration corresponded a factor of 4 which point out that the fouling potential increased to 10 times of the original value.
a. This significant increased in organic fouling potential could be attributed to increases in both organic and inorganic concentrations along with increasing recovery. According to this situation, the organic-organic and organic-membrane electrostatic interactions would reduce.
Fig.3. Incremental resistance as a function of permeates volume. Operating conditions: applied pressure 160 psi for initial flux of 1.0×10?5 m/s, cross-flow velocity = 0.1 m/s, temperature = 24±1 ?C, pH= 5.0±0.5.
Application & further study: The data and methodology are possible to apply to observe the effect of permeate recovery to fouling mechanisms of seawater RO fouling. And also this paper showed the better way to understand fouling development which can be applied to desalination fouling investigation.
By Monruedee Moonkhum
Email: moon@gist.ac.kr
Journal: Journal of Membrane Science
Authors: Yan Zhaoa, Lianfa Songb, Say Leong Onga
Corresponding author: Say Leong Ong
Institute:
a Division of Environmental Science & Engineering, National University of Singapore, 10 Kent Ridge Crescent, 119260 Singapore, Singapore
b Department of Civil and Environmental Engineering, Texas Tech University, 10th and Akron, Lubbock, TX 79409, USA
The original and creativity of paper: In this paper, fouling behaviors (i.e. the rate and extent of flux decline and fouling reversibility) of a laboratory-scale RO system fed with ultrafiltration (UF) prefiltered secondary effluent were studied at two operationally important permeate recovery levels. The associated fouling mechanisms were delineated with the aid of microscopic analysis of the fouling layer characteristics (i.e. composition, morphology and the fouled membrane surface properties). There was a remarkable correlation between the different fouling behaviors observed and the characteristics of fouling layers developed.
Summary:
In this study intended to provide a better understanding of the fouling phenomenon occurring during membrane process. Fouling mechanism and factors affecting fouling were investigated systematically. Results will be summarized following;
1. Fouling behavior with increasing permeate recovery
a. Fig.1 shows flux decline curve versus permeate recovery at two different initial fluxes of 1.0 x 10-5 m/s and 2.0 x 10-5 m/s. Result showed that more flux decline was observed at a higher initial flux due to a higher permeate drag and stronger concentration polarization which promoted foulant transport and deposition on the membrane surface.
b.
Fig 1. Permeate flux as a function of recovery in concentration mode fouling experiments fed with UF prefiltered secondary effluent. pH was not adjusted for the pHambient run; pH was kept at 5.0±0.5 for the pH 5.0 run. Operating conditions: applied pressure 300 psi for initial flux of 2.0×10?5 m/s and 160 psi for initial flux of 1.0×10?5 m/s, cross-flow velocity = 0.1 m/s, temperature = 24±1 ?C.
c. A turning point of higher initial flux experiment was observed at a permeate recovery of 50% beyond as well as it showed greatly increased after the turning point. In contrast, a turning point of lower initial flux occurred at a relatively higher recovery of 60%. This is because of the precipitation of sparingly soluble salts when their saturation degree has exceeded the solubility limit associated with this high recovery.
2. Fouling layer characteristics
a. Fouling layer as dry condition was quantified using FTIR spectra. Fig. 2(a) , the clean membrane showed the typical pattern of TPC-PA membranes with polysulfone support layers .
b. It can be observed that the vibrational spectrum of the PA membrane became more obscured upon fouling at increasing permeate recoveries.
c. When the ease of striping was considered, the spectral patterns of the fouled membrane could be fully restored to its virgin state at a permeate recovery of 55%. Whereas at a higher permeate recovery of 70%, the restoration of spectral patterns after physical striping was minimal.
d. To differentiate the absorbance bands of potential foulants from membrane substrate in certain wavelength regions, FTIR spectrum of the physically stripped fouling later was also recorded as showed in Fig. 2(b).
e. For both recoveries, a distinctive peak was exhibited at 1040 cm-1, which is often found associated with carbonyl bonds of carbohydrates.
f. Absorption bonds were also detected at 1652 cm-1 and 1558 cm-1 relating to amide I and amide II group of protein and/or amino sugars.
Fig 2. FTIR spectra of (a) new membrane, membrane fouled at initial flux of 2.0×10?5 m/s and after physically stripped, (b) physically stripped fouling layer.
3. Fouling potential with increasing recovery
a. Fig.3 showed that the organic fouling potential of feed water with increasing recovery was characterized aster inhibition of scaling was attained through pH adjustment.
b. At permeate recovery of 50%, feed water concentration corresponded a factor of 2. Whereas, at permeate recovery of 75%, feed water concentration corresponded a factor of 4 which point out that the fouling potential increased to 10 times of the original value.
a. This significant increased in organic fouling potential could be attributed to increases in both organic and inorganic concentrations along with increasing recovery. According to this situation, the organic-organic and organic-membrane electrostatic interactions would reduce.
Fig.3. Incremental resistance as a function of permeates volume. Operating conditions: applied pressure 160 psi for initial flux of 1.0×10?5 m/s, cross-flow velocity = 0.1 m/s, temperature = 24±1 ?C, pH= 5.0±0.5.
Application & further study: The data and methodology are possible to apply to observe the effect of permeate recovery to fouling mechanisms of seawater RO fouling. And also this paper showed the better way to understand fouling development which can be applied to desalination fouling investigation.
By Monruedee Moonkhum
Email: moon@gist.ac.kr