Membrane fouling polymeric coagulants

Unlike PA membranes, polyether urea (PEU) membranes are neutral to shghdy positive. PEU (and CA) membranes, unhke aromatic PA membranes, have a smooth surface and are, therefore, less prone to fouling [23], For RO feed water such as surface and municipal water, which are treated with cationic polymeric coagulants, PEU membranes, not negatively charged PA membranes, are used to minimise fouhng. 

Cationic polymeric coagulants have a natural affinity for the negatively-charged polyamide composite membranes, leading to irreversible fouling... 

The breakdown of organic material, such as plants, in the soil, produces a mixture of complex macromolecules called hmnic acids. These complex molecules have polymeric phenolic structures with the ability to chelate metals especially iron. It is recommended that humic acids be removed from process water before filtration by complexation (i.e., floc-culation/coagulation see Section 12.4.1). Humic acids give surface water a yellowish to brownish color and often cause fouling problems in membrane filtration [31,49]. The fouling tendency of humic acids appears to be due to their ability to bind to multivalent salts. Nystrom et al. [31], for example. 

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