Control of Fouling

Despite long use, the meaning of the word fouling remains nebulous. In this book, fouling is considered to relate to the presence of solid materials, without respect to origin and nature, that are insoluble in the process streams of interest. These materials cause operating difficulties by deposition onto surfaces of equipment contacted by the process streams, either in zones where the insolubles are formed 

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Acrolein enters the environment as a result of normal metabolic processes incomplete combustion of coal, wood, plastics, tobacco, and oil fuels and industrial emissions. Acrolein has been detected in smog, foods, and water. It is used extensively in chemical manufacture, for control of fouling organisms, and as an herbicide to control submerged weeds in irrigation canals. 

Control of fouling because of corrosion is possible by the employment of additives. For corrosion to occur, all the elements of the electrochemical circuit must be complete, so that an imposed electrical barrier in the circuit prevents the movement of ions and electrons, which is fundamental to the fouling mechanism. A thin layer of metal oxide can act as such a barrier, provided that the layer is continuous. The protective layer is itself a product of limited corrosion, its presence inhibiting further attack. 

Even when fouling occurs, steps may be taken to compensate for or control its effect on system performance. Control of fouling is central to providing an efficient TFF system and an economical... 

Control of fouling should be attempted first before any cleaning method is attempted. The fouling control procedure should be preceded by (1) verification of the existence of fouling, (2) identification of the feature that dominates the foulant accumulation, and (3) characterization of the deposit. 

Common additives used in the control of fouling in aqueous systems are given in Table 14.2. 

A. Milne, M. E. Callow, R. Pitchers Control of Fouling by Non-Biocidal Systems," in Evans Hoagland (eds.) Algal Biofouling, Elsevier, Amsterdam 1986, pp. 145-158. 

Copper Powder. At high loading (70 percent), copper powder has been recommended for control of fouling in marine paints. 

All these examples clearly indicate that not only is the membrane performance important in microfiltration but particularly the chemical and thermal resistance of the materials used. Furthermore, the control of fouling is extremely important as well and this is discussed further in chapter VIL... 

Avoid deposit risks (control of fouling is therefore an important parameter). 

Although it is safe to say that NF nowadays can be implemented without problems in many known applications, it is expected that the evolution in NF wUl continue. Some of the expected progresses include modeling of rejection in aqueous solutions, understanding of the performance in organic solvents, prediction and control of fouling, membranes with controlled pore size, possibly in hoUow-fiber configmation, development of hydrophobic ceramic NF membranes, and the optimization of hybrid processes with NF. 

Kilduff, J.E., Mattaraj, S., Pieracci, J.P., and Belfort, G. 2000. Photochemical modification of poly(ether sulfone) and sulfonated poly (sulfone) nanofiltration membranes for control of fouling by natural organic matter. Desalination 132, 133-142. 

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