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In water treatment, the bulk solution, concentration polarization, permeate flux and membrane properties are some of the parameters that can be influenced
Fouling is one of the most vexing problems in water-treatment systems that use membranes to remove suspended and dissolved particles. The deposition and accumulation of these substances on membrane surfaces inevitably lead to loss of performance for the membrane [1], While there are several strategies for reducing fouling, the right solution varies with the process and type of fouling.
Increasingly specified for process water and wastewater treatment, membranes provide better removal efficiencies than conventional filters because they have smaller pore sizes. Also, membranes have fewer consequences for the environment because they eliminate or significantly reduce the need for coagulants and flocculants, as well as the handling and auxiliary equipment required for traditional chemical-treatment methods.
Fouling can dramatically reduce the efficiency and economic benefits of a membrane process. The type of fouling and how strongly it appears depends on several parameters:
* nature of solutes and solvents
* membrane process
* pore-size distribution
* membrane surface characteristics and material of construction
* hydrodynamics of the membrane module
* process conditions
The most common fouling types are shown in Table 1.
Fouling can dramatically reduce the economic benefits of a membrane process, especially during the filtration of wastewater, when the filtered water is in economic competition with fresh water sources. Certain economic aspects have to be taken into account and a systematic analysis of the various options has to be considered. As illustrated in Figure 1, there are several basic tools, or parameters, that can be influenced to reduce fouling:
* bulk properties
* membrane properties
* concentration polarization
* permeate flux
Influence of the bulk solution
Parameters that can be used to influence the fouling behavior of a bulk solution are primarily pH, temperature and particle size. An example is the scaling of calcium sulfate. Operation at low pH and the addition of scaling inhibitors, which prevent scaling by changing the solubility of the salts, can significantly reduce the precipitation of calcium sulfate on the membrane.
Proteins are a special group of macromolecules. Variations in temperature, ionic strength, concentration and pH can influence the tendency of membranes to foul. If protein denaturation occurs,...