Introduction to Fouled Membranes

The observation of the fouled membranes by SEM showed that fouling was hardly observed on the side contacting with seawater, but severe bacterial biofilms were observed on the side contacting with wastewater.

IOS provides high diffusive and osmotic permeability, high rejection, low power consumption, and high mass transfer via the manipulation of convection, advection and diffusion, low concentration polarization gradients, low reverse salt flux, and effective restoration of performance after cleaning fouled membranes.

Moreover, the lower APAM–CO free energies for the mixed interface likely represented a more unstable thermodynamic system of the irreversible fouling layer and promoted the flux recovery of fouled membranes after chemical cleaning.

Then, a flat and homogeneous cake layer was developed with time in all the fouled membranes regardless of the cake layer thickness.

However, the presence of silica limits the RO efficiency due to its high scaling potential and the difficulty of cleaning the fouled membranes.

Moreover, ZnPc-embedded PES composite membranes were irradiated with appropriate wavelengths of light in the presence of oxygen to generate reactive oxygen species to clean fouled membranes’ surface.

Through the analyses of fouled membranes under two operating modes, the mechanism of membrane fouling mitigation was revealed as follows: A low water flux was applied in stage 1 which slowed down the interaction between foulants and membrane surface, especially reduced the deposition of proteins on the membrane surface and formed a thin and loose fouling layer.

The fouled membranes were further characterized to gain more understanding of the fouling layer properties and flux decline mechanisms.

Both the hydrophilicity of membrane and structure of target analytes had important effects on the diffusion coefficients through biofouled membranes.

Fouled membranes present higher rejection of hydrophobic neutral compounds and the concentration polarization reduces rejection.

Cleaning-in-place (CIP) is a representative fouling management process from which the filtration performances of fouled membranes can be recovered.

Meanwhile, membrane fouling was investigated through a comparison between virgin and fouled membranes.

The characterization of fouled membranes (i.

The gel layer formation model fit well for the modified ceramic membrane during HA filtration, which explained the decrease in the selected pharmaceutical retention by the HA-fouled membranes, while pore blocking governed the HA fouling for the pristine membranes, causing an increase in the pharmaceutical retention by the fouled membranes.

The fouled membranes were sparged with 1 L/min of air scouring for ∼1 to ∼2 hrs to remove the deposited colloids and impurities on the surface of the membrane.

Fouled membranes were effectively renewed by physical means, such as water flushing and sonication, or a short period of chemical backwashing with NaOH, HCl or oxidizing agents.

The calcium sulfate scalant deposition patterns on the fouled membranes were visualized by utilizing alizarin red S (ARS) staining, which was applied herein for the first time in characterizing membrane fouling.

This led to formation of a thinner cake layer on fouled membranes compared to membranes fouled with untreated raw water.

The major foulants and scalants were also identified by analysing filtrate samples and fouled membranes.

However, an analysis of the fouled membranes revealed that the PN/PS ratio of the cake layer EPS was significantly reduced in the presence of the biocarriers.

Fouled membranes were treated with a cathodic potential for 30 min, the fouling and antifouling processes were monitored with scanning electron microscopy (SEM), and contact angle and electrochemical methods were used.

The bacterial diversity on fouled membranes has been studied, especially to identify bacteria with specialized functions and to develop targeted approaches against these microbes.

This was helpful for understanding the mechanism of membrane fouling at different operational temperatures and the role of EPS, and also of significance for the design of cleaning strategies for fouled membranes after long-term operation.

In this study, an alkaline condition (∼pH 12), produced by microalgae in the light without supplemental aeration was applied for in-situ cleaning of fouled membranes.

CFD simulations explored the development of fouling over time and the CFD results were compared with scanned images of fouled membranes.

The fouled membranes were then further analyzed to verify the major causes of inorganic fouling through SEM and XPS.

Furthermore, the fouled membranes were characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy.

The fouled membranes were cleaned chemically every 3-5 d, and the membrane permeability could almost be completely recovered using chemical backwash for only 10 min with a diluted acidic, alkaline, chlorine or H2O2 solution.

The results for using the ultrasound for cleaning the fouled membranes showed that in the long distances, a large number of cavitation bubbles collapses before they reach to the membrane and in short distance, due to higher energy density, the produced acoustic and turbulence stream are increased and the membrane may be damaged.

Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the fouled membranes.

Biofouling microorganisms from the Sphingomondaceae family, which have been isolated from the fouled membranes obtained from the full-scale studies, were then physiologically characterized.

FTIR and zeta potential analyses of the fouled membranes indicated that all the tested surfactants were identically effective in removing the foulants from the membrane surface, but their cleaning efficiencies differed.

The effect of ultrasonic waves on regeneration of fouled membranes by heavy metals was investigated.

The solvent with a low concentration for zein was used as the cleaning agent to clean the fouled membranes, and the modified PVDF membrane could exhibit a very high water flux recovery ratio (＞95%) with the enhanced fouling release ability.

Attempts to clean the fouled membranes for both processes by rinsing with an NaOH solution at pH > 11 were partially effective at restoring water flux but unable to completely remove the silica scale layer.

Fourier transform infrared spectra of the fouled membranes showed that aromatic CC group and polysaccharides group in dEfOM were largely reduced after the oxidation pre-treatments, resulting in the improved membrane flux sustaining.

Moreover, application of the ultrasound in ex-situ form for cleaning the fouled membranes and pretreatment of wastewater prior to the MBR system is discussed.

The influences of pore size on the changes in membrane flux and flux recovery were investigated, followed by a SEM analysis of the fouled membranes.

Biofouling evaluation methods of fouled membranes and collected biofoulants from the treatment processes are counterproductive when biofouling prevention is warranted.