Ultra Filteration

Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane. This separation process is used in industry and research for purifying and concentrating macromolecular (10^3 - 10^6 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from reverse osmosis, microfiltration or nanofiltration, except in terms of the size of the molecules it retains.
Industries such as chemical and pharmaceutical processing, food and beverage processing, and waste water treatment, employ UF in order to recycle flow or add value to later products. UF's main attraction is its ability to purify, separate, and concentrate target macromolecules in continuous systems. UF does this by pressurizing the solution flow, which is tangential to the surface of the supported membrane (cross-flow filtration). The solvent and other dissolved components that pass through the membrane are known as permeate. The components that do not pass through are known as retentate. Depending on the Molecular Weight Cut Off (MWCO) of the membrane used, macromolecules may be purified, separated, or concentrated in either fraction. Currently, the study of UF processing occurs mainly in laboratory setups because it is very prone to membrane fouling caused by increased solute concentration at the membrane surface (either by macromolecular adsorption to internal pore structure of membrane, or aggregation of protein deposit on surface of membrane), which leads to concentration polarization (CP). CP is the major culprit in decreasing permeate flux.

UF is a low pressure (5 - 150 psig) process for separating larger size solutes from aqueous solutions by means of a semi-permeable membrane.

Retains oils, particulate matter, bacteria and suspended solids large macromolecules and proteins

  • Passes most surfactants, water, acid and alkaline compounds
  • Pore sizes ranging from 0.005 – 0.1 micron; 1K – 500K MWCO
  • Permeate is clear (non-turbid) solution void of suspended solids

    Most KMS UF products for industrial applications are designed for crossflow separation, where a feed stream is introduced into the membrane element under pressure and passed over the membrane surface in a controlled flow path. A portion of the feed passes through the membrane and is called permeate. The rejected materials are flushed away in a stream called the concentrate. Crossflow membrane filtration uses a high cross flow rate to enhance permeate passage and reduce membrane fouling.
      Examples of UF Applications
    Application Permeate Concentrate (Retentate) Benefits of UF
    Potable Water Potable water free of suspended solids, turbidity, bacteria and large viruses Water, particulate solids Certified for 4-log removal of bacteria, giardia, cryptosporidium and viruses from drinking water.
    Turbidity < 0.1 NTU
    Oily Wastewater Oil free (< 50 mg/L) water Water, suspended solids, insoluble metal hydroxides, etc Consistent permeate water quality even when feed composition subject to upsets.  Highly concentrated oil emulsion for waste disposal.
    Electrocoat Paint Water, dissolved salts and solvents Water, paint resins and pigments Allows the recovery of valuable paint resins and pigments.
    Milk Lactose and salts solution Protein concentrate Protein concentration at lower energy cost than evaporation.
    Whey Lactose and salts solution Whey Protein Concentrate (WPC) Protein concentration at lower energy cost than evaporation.
    Apple juice clarification Low turbidity, clear juice Juice, suspended solids, pulp, colloidal haze particles. Removes suspended solids and turbidity while allowing the passage of juice, sugar and taste.
    Reuse of municipal wastewater Water free of suspended solids, bacteria & viruses

    Turbidity < 0.1 NTU
    Water, particulate solids Polishes biologically treated municipal effluent for discharge, reuse, or feed to reverse osmosis
    Industrial MBR, e.g. malting industry Water Containing*:

    Suspended solids < 0.1 mg/liter
    BOD 2-3 mg/liter
    COD 100-200 mg/liter
    Ntotal 1/2 mg/liter
    Malting wastewater, activated sludge Meets stringent effluent discharge requirements, eliminates solids, reduces wastewater discharge fees, and requires less space than conventional wastewater treatment
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