As an expert in filtration, FSI uses fouling-resistant micro-filtration (MF)/Ultra-filtration (UF) filters for wastewater processes. These filters are highly hydrophilic (characterized by an affinity for water). This type of filter possesses a high surface tension value and has the ability to form "hydrogen-bonds" with water. Particles that foul in aqueous media tend to be hydrophobic, e.g. colloids, proteins, clays, and oily particles (hydrocarbons, surfactants, greases). Hydrophobic particles tend to cluster or group together because this lowers the interfacial free energy (surface tension) resulting from surface area exposure. Because of that, general tendency will favor particle attachment to any material less hydrophilic than water, including filter surfaces. To prevent fouling, the filter requires a surface chemistry that prefers binding to water over other materials, such as the HP Series and SHP Series filters provided by FSI.
Both the HP Series and SHP Series membrane filters are made of polyacrylonitrile (PAN) polymer, which are intrinsically hydrophilic. The HP Series membrane filters are in hollow fiber form. The SHP Series membrane filters are made of chemically modified polyacrylonitrile (PAN) polymer, which exhibit the most hydrophilicity available on the market, in spiral-wound form.
The figure to the right shows a hydrophilicity comparison of various membranes. The membrane hydrophilicity is quantified by measuring water-membrane-air contact angles for the various membrane types. A smaller contact angle correlates with a more hydrophilic surface and less fouling by 'free' oils and highly concentrated oily emulsions. In practice, this property results in consistent performance and reliable filtration system operation.