Membrane fouling organic

Electrodialysis can be applied to the continuous-flow type of operation needed in industry. Multi-membrane stacks can be built by alternately spacing anionic- and cationic-selective membranes. Among the technical problems associated with the electrodialysis process, concentration polarization is perhaps the most serious (discussed later). Other problems in practical applications include membrane scaling by inorganics in feed solutions as well as membrane fouling by organics. 

Chlorine is the oldest and most widespread method of water disinfection. In reverse osmosis systems, chlorine may be added to feedwater for control of micro-organisms and, in addition, to prevent membrane fouling by microbiological growth. According to Vos et al. [i,2], chlorine will attack cellulose diacetate membranes at concentrations above 50 ppm. Membranes were found to show a sharp increase in salt permeability and a decrease in strength after one week of continuous exposure. Under milder conditions (10 ppm chlorine for 15 days) no detectable change in performance was observed. Spatz and Friedlander [3] have also found cellulose acetate membranes to be resistant to chlorine when exposed to 1.5 ppm for three weeks. 

Reverse osmosis can remove dissolved metals to very low levels. It can also remove a variety of pollutants such as cyanide and residual organics from refinery wastewater. However, because it is an expensive process, it would be competitive only if removal of total dissolved solids is also required. It also requires extensive pretreatment to prevent membrane fouling and deterioration [52]. The pretreatment processes may include filtration to remove suspended solids, pH adjustment, softening, and activated carbon treatment to remove organics and chlorine. A major drawback of the RO process is the handling and disposal of the reject stream, which can amount to 20-30% of the influent flow. 

Watkins and Pfromm (1999) suggested a further method based on capacitance spectroscopy in the range 102 105 Hz to identify and tracking membrane fouling with organic macromolecules, such as sulfonated lignin, in real times. 

Lindstrand, V., Sundstrom, G., and Jonsson, A.-S. 2000. Fouling of electrodialysis membranes by organic molecules. Desalination 128, 91-102. 

Subsequent individual chapters discuss membranes in organic solvent separation, gas separation and electrochemical separation. A whole chapter is focused on the fundamentals of fouling molecular separation by membranes are completed by a chapter focused on fouling, and another on energy and environmental issues. 

With the majority of MF/UF processes based on the filtration of aqueous solutions, the unavoidable presence of dissolved solutes (salts, organic macromolecules of various nature and sizes) in the feed strongly affects the membrane performances. They can be directly responsible for membrane fouling through mechanisms like... 

Membrane distillation - photocatalysis To solve the problem of membrane fouling observed in the pressure-driven membrane photoreactor, Mozia et al. [90] studied a new type of PMR in which photocatalysis was combined with a direct contact membrane distillation (DCMD). MD can be used for the preparation of ultrapure water or for the separation and concentration of organic matter, acids and salt solutions. In the M D the feed volatile components are separated by means of a porous hydrophobic membrane thanks to a vapor-pressure difference that acts as driving force and then they are condensed in cold distillate (distilled water), whereas the nonvolatile compounds were retained on the feed side. 

Membrane fouling is a result of deposition of suspended solids, organics, or microbes on the surface of the membrane, typically on the feed/concentrate side. Fouling species include ... 

Significant reduction in membrane fouling from organics and microbes... 

Puro L, Tanninen J, and Nystrom M. Analyses of organic foulants in membranes fouled by pulp and paper mill effluent using solid-liquid extraction. Desalination 2002 143 1-9. 

Lindstrand V, Sundstrdm G, and Jdnsson AS. Fouling of electrodialysis membranes by organic substances. Desalination 2000 128 91-102. 

Fig. 23. Visualization of membrane fouling by scanning electron microscopy (A) inorganic fouling dne to calcinm carbonate, calcium sulfate, silica, iron, barium and strontium sulfate (35,000x) (B) organic fonling dne to humic acid (35,000x) (C) flow channels in membrane fouled with biological growth.

Cations in conjunction with natural organics enhance membrane fouling. This effect, although being generally accepted, is not well understood. Therefore, the interactions of natural organics and cations are of particular importance. The effect of cations on natural organics solubility was discussed in section 2.5.9. 

Of particular interest in this study is the fouling of membrane processes by natural organics. Fouling depends on the characteristics of the natural organics. A detailed review of the characteristics of interest is required to highlight the factors that may influence membrane fouling. Membrane filtration... 

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