Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semi permeable membrane. Suspended solids and solutes of high molecular are retained, while water and low molecular weight solutes pass through the membrane.
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Ultrafiltration is not fundamentally different from microfiltration, Nano-filtration or gas separation, except in terms of the size of the molecules it retains. Ultrafiltration is applied in cross- flow or dead-end mode and separation in ultrafiltration undergoes polarization. It is equally used in an advanced treatment of waste-water to get high quality end products like water that can be reused or recovered.
Fig.: Ultrafiltration Process
Many of the Crystal Quest water coolers use the ultrafiltration water purification process. Ultrafiltration (UF) is an important purification technology used for the production of high-purity water in the biochemical, food and beverage, and biopharmaceutical industries.
When strategically combined with other purification technologies in a complete water system, UF is ideal for the removal of colloids, proteins, bacteria, pyrogens, and other organic molecules.
Basic Principles and Process of Ultra filtration Principles
Ultrafiltration is a pressure-driven purification process in which water and low molecular weight substances permeate a membrane while particles, colloids, and macromolecules are retained.
The primary removal mechanism is size exclusion, although the electrical charge and surface chemistry of the particles or membrane may affect the purification efficiency. Ultrafiltration pore ratings range from approximately 1,000 to 500,000 daltons, thereby making UF more permeable than Nano filtration (200 – 1.000 daltons).
UF membranes are composed of a polymer, such as polysulfone or polyamide that is usually extruded into flat sheets or hollow fibers or cut into disks as required by the specific application.
A small disk of UF membrane may be subject to rapid fouling and produce a low flow rate for many processes.
As a result, UF membranes are typically arranged in a configuration which maximizes surface area and reduces fouling by using a tangential flow design to reduce solute accumulation at the membrane surface.
Tangential flow UF devices may be spiral-wound cartridges containing several square feet of membrane wrapped onto a central core tube or hollow-fiber cartridges containing dozens of thin UF membrane fibers.
Fig.: Principles of Ultrafiltration
Ultrafiltration systems eliminate the need for clarifiers and multimedia filters for waste streams to meet critical discharge criteria or to be further processed by waste-water recovery systems for water recovery.
Efficient ultrafiltration systems utilize membranes which can be submerged, back-flushable, air scoured, spiral wound UF/MF membrane that offers superior performance for the clarification of waste-water and process water.