Method for treating wastewater or produced water

  • US 7,815,804 B2
  • Filed: 12/12/2006
  • Issued: 10/19/2010
  • Est. Priority Date: 12/12/2006
  • Status: Active Grant
First Claim
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1. A method for treating produced water derived from an oil recovery operation and containing contaminants including organics, silica, hardness, dissolved solids, and suspended solids, the method comprising:

  • a. removing hardness from the produced water by chemically softening the produced water in a series of reactors by;

    i. in one reactor mixing a coagulant with the produced water and destabilizing solids contained within the produced water;

    ii. in one reactor mixing lime with the produced water, and converting carbon dioxide to bicarbonate ions and neutralizing bicarbonate alkalinity to remove calcium carbonate hardness;

    iii. in one reactor mixing a caustic with the produced water to remove magnesium hardness and wherein the lime and caustic cause the pH of the produced water to be raised above 10.5;

    iv. in one reactor mixing a polymer with the produced water to facilitate separation of solids in the produced water;

    v. clarifying the produced water by separating sludge from the produced water; and

    ,vi. directing at least a portion of the sludge to at least one reactor and mixing the sludge with the produced water;

    b. after chemically softening, filtering the produced water with a multimedia filtration unit to further separate suspended solids from the produced water to produce filtered produced water and a first waste stream;

    c. recycling at least a portion of first waste stream to at least one of the reactors;

    d. after filtering the produced water with the multimedia filter, further softening the produced water by directing the produced water through an ion exchange softening unit wherein calcium and magnesium ions are displaced by sodium ions supplied by an added chemical, producing further softened produced water and a second waste stream;

    e. recycling at least a portion of the second waste stream to at least one reactor;

    f. after ion exchange softening, directing the produced water though a cartridge filtration unit to further separate contaminants from the produced water; and

    g. directing produced water at said pH from the cartridge filtration unit to at least one reverse osmosis unit and removing organics, boron, silica and dissolved solids from the produced water and producing product water.

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