Membrane fouling treatment methods

As fouling is one of the main problems in NF membranes of textile wastewater treatment, one should be aware of the importance of fouling control methods in overcoming the limitations. Of all the practical solutions available, development of NF that is less-fouling-sensitive to dye absorption is the most sustainable one and has attracted considerable attention recently. Other possible solutions to solve fouling problems include pretreatment processes prior to NF, optimization in process conditions, and effectiveness of cleaning processes. 

Hydrophilic modification of the membrane surface is also a promising method to control membrane fouling because the surface properties of membranes dominate the membrane characteristics. Plasma treatment is a widely used and effective technique to create polar organic functional groups on the membrane surface. Membrane hydrophilicity can be drastically improved by plasma treatment using various gases such as NH3 and CO2, and plasma treated membranes show better filtration performance and antifouling characteristics compared with unmodified ones (Yu et al., 2005). 

It has been reported that the NF membrane developed by UV-photo-polymerization of sodium p-styrenesulfonate (SSS) monomers on a PSF UF membrane can be used in dye effluent treatment (Akbari et al. 2(X)2). Researchers used phase inversion method to prepare the PSF UF substrate. The photo-reactor was a cylindrical chamber, in which the membrane was placed on the wall together with a suitable concentration of SSS after washing with distilled water. A UV lamp was installed at the center of the chamber. Irradiation of the membrane was conducted for a certain period of time before it was removed from the reactor and washed with distilled water. It was postulated that the sulfonate group found in the polyelectrolyte molecules can repel the sulfonate group in dye molecules, thus reducing membrane fouling. 

Currently surface grafting is widely used by the research community to develop low-fouling composite membranes. In this method, grafted macromolecular chains are covalently bonded to the membrane surface. Surface grafting may be initiated by ultraviolet (UV)-irradiation, chemically, and by plasma or enzymatic treatment of the membrane surface. Choice of the specific graft polymerization technique depends on the chemical structure of the membrane and the desired characteristics after surface modification. 

Several cleaning methods are used to remove the densified gel layer of retained material from the membrane surface. Alkaline solutions followed by hot detergent solutions are indicated for organic polymer colloids and gelatinous materials fouling. Ferrous deposits, t3 pical in water treatments, are usually removed with a citric or hydrochloric wash. [35]. 

Patel et al (1994) employed a combined process of coagulation and MF to avoid a disinfection posttreatment. The coagulation step was used to eliminate phosphorus, arsenic, and viruses, to avoid fouling, decrease particle accumulation on the membrane surface, and improve backflush characteristics. MF pilot plant studies in constant permeate flux mode showed that turbidity, particles, and faecal coliforms could be removed, but TOC removal was unreliable. Crossflow MF showed no difference to dead-end filtration, and both methods were similar to or better than sand filtration. Results with coagulation and MF improved phosphorous and turbidity removal, but the process was not optimised. The treatment lead to a reduction of chlorine demand in the product water. 

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