Ultra-pure process water membrane processes

With the advancement of membrane technologies and engineering in the integration of MF, UF, NF, and RO membrane systems, and possibly a liquid membrane system, wastewater reclamation can provide high quality water for underground water replenishment and direct household nonpotable use, and source water for ultra-pure water applications. Membrane technology provides several advantages over conventional treatment processes ... 

Two process modes, namely, dead-end and cross-flow modes, are widely used for microfiltration (14). For the dead-end mode, the entire solution is forced through the membrane. The substances to be separated are deposited on the membrane, which increases the hydraulic resistance of the deposit. The membrane needs to be renewed as soon as the filtrate flux no longer reaches the required minimum values at the maximum operation pressure. This mode is mostly used for slightly contaminated solutions, e.g., production of ultra-pure water. For the cross-flow mode, the solution flows across the membrane surface at a rate between 0.5 and 5.0 m/s, which prevents the formation of a cover layer on the membrane surface. A circulation pump produces the cross-flow velocity or the shear force needed to control the thickness of the cover layer. The system is most widely used for periodic back flushing, where part of the filtrate is forced in the opposite direction at certain intervals, and breaks up the cover layer. The normal operating pressure for this mode is 1-2 bars. 

For some industries such as pharmaceuticals, electronics, and toiletries, ultra-pure water is always demanded. Pathogens, organic substances, and inorganic substances must be effectively removed to a very low level (e.g., less than 1 ppb TOC in semiconductor fabrication manufacturing). The source water is first filtered by multimedia filters and disinfected by UV light. The water is then treated by membrane units (usually reverse osmosis) and stored. Later on, UV photolysis, ion exchange resin and micro-filters are used alternatively to produce the high pure process water. 

ULTRA FILTRATION - A process that forces water through a filtering membrane by means of pressure gradients in order to obtain ultra pure water. 

Microporous polymeric membranes are used widely for filtration and purification processes, such as filtration of wastewater, preparation of ultra-pure water, and in medical, pharmaceutical or food applications, including removal of microorganisms, dialysis and protein filtration. 

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