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Apparatus and method for membrane filtration with enhanced net flux

  • US 5,958,243 A
  • Filed: 03/03/1997
  • Issued: 09/28/1999
  • Est. Priority Date: 07/11/1996
  • Status: Expired due to Term
First Claim
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1. A method of filtering a liquid at a controlled rate of flow using a membrane filtration system to provide enhanced net flux having:

  • (a) a source of liquid to be filtered;

    (b) a feed pump having a controllable speed adapted to pump liquid to be filtered from the source of liquid through a feed conduit to the system at a controlled rate;

    (c) a filtration module comprised of a nano-, micro- or ultra-filtration membrane, the module adapted to receive liquid to be filtered from the feed conduit through an inlet opening and direct the flow of the liquid to be filtered across a porous membrane mounted in the filtration module;

    (d) a permeate conduit adapted to carry liquid which has been filtered through the membrane in the filtration module out of the filtration module through a permeate outlet opening wherein said permeate conduit can be closed with a first valve;

    (e) a concentrate conduit adapted to carry unfiltered liquid out of the filtration module through a concentrate outlet opening;

    (f) a backwash conduit through which liquid enters the permeate chamber during a cleaning operation wherein said backwash conduit can be opened with a second valve;

    (g) a backwash pump for pumping backwash liquid through the backwash conduit into the permeate chamber during a cleaning operation;

    (h) a means for closing the first valve and opening the second valve when the backwash pump in running; and

    (i) backwash liquid pressure controlling means for controlling the pressure of the backwash liquid in the backwash conduit, the method comprising;

    (i) pumping liquid to be filtered through the feed conduit into the filtration module;

    (ii) withdrawing filtered liquid from the filtration module through the permeate conduit and withdrawing unfiltered liquid through the concentrate conduit;

    (iii) measuring the rate at which liquid to be filtered flows through the feed conduit to provide a measured flow rate;

    (iv) comparing the measured flow rate to a preset flow rate to determine whether the measured flow rate differs from the preset flow rate;

    (v) if the measured flow rate is different from the preset flow rate, adjusting the rate at which liquid to be filtered flows through the feed conduit until the rate at which liquid flows through the feed conduit is equal to the preset flow rate by adjusting the speed of the pump; and

    periodically backwashing said membrane by;

    (vi) closing said permeate conduit and opening said backwash conduit;

    (vii) pumping backwash liquid through said backwash conduit into said permeate chamber; and

    (viii) controlling the pressure of the backwash liquid in the backwash conduit using said backwash liquid controlling means, said backwash liquid controlling means comprising a backwash pump speed controller for adjusting the pressure of the backwash liquid by adjusting the speed of backwash pump, said speed controller controlling said backwash pump and generating pulses in the backwash liquid to dislodge foulants from said membrane to provide said enhanced net flux.

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