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  • OT colour removal

    I need some help guys. I was asked to see if I could come up with a solution for a company that prints tee shirts. Its a screen printing company . They have to clean the screens with a high pressure jet. The municipality has given them a month to come up with a filtration system so that the pigments are removed to an extent before it lands up in the sewer works.They use about 1000liters of water a day. Is there a simple system to clean this water up? They were talking about a clarifier system but someone reckons if this went into a holding tank and had air blown into it to agitate it most of the pigment would settle and cleanish water would flow off and could be discharged into the drain. Apparently there are chemical additives that can be introduced that stick to the pigments that allow them to settle. Thanks.

  • #2
    If I remember correctly, they are called flocking agents. A dual filter trap/set up would probably the way to go. One in use and one being cleaned, we had the same type set up in the art wing of a school I worked in. Don't remember the name.
    Glen
    Been there, probably broke it, doing that!
    I am not a lawyer, and never played one on TV!
    All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only

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    • #3
      Might be worth trying something like the clarifier used for hot tubs. I think it is a flocking agent like PT mentioned. You add a cap full and the fine suspended particles clump together big enough to be caught with a paper filter.

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      • #4
        Flocking agents are a common product when treating Drilling mud in the oil patch. Baroid Mud Scientists are very knowledgable people for assistance with this type of problem.
        Byron Boucher
        Burnet, TX

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        • #5
          Flocculating agents (or flocking) are intended to keep particles IN suspension rather than making them clump and settle.

          Making the pigments settle out will cure one problem but create another. They will then be faced with the disposal of the concentrated pigment slurry or filter media. However it is done the aim should be to reduce the volume of contaminated waste to the absolute minimum. This will probably require the use of a high speed centrifuge.

          I would investigate ozone treatment of the waste water. Ozone is a powerful bleaching agent. Another bleaching option is hydrogen peroxide. I am sure that the pigments themselves pose no toxic risk. Printing pigments now are all vegetable based.
          Last edited by Evan; 07-28-2011, 01:11 PM.
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          • #6
            At the risk of starting another nomenclature or word use war, my dictionary says of flocculate "to form lumpy or fluffy masses". This corresponds to the use of flocculents in wine making including egg whites and bentonite if there's a haze that doesn't settle out. Mixing in a flocculent gets the tiny particles to form larger masses which will settle so clear wine can be decanted off.
            Last edited by TGTool; 07-28-2011, 05:13 PM.
            .
            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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            • #7
              TRy Alum(Aluminium Sulphate - used in drinking water systems)
              http://www.roejen.com.au/Dosing%20Al...g%20Agents.pdf
              They call it floccing agents!

              peter
              I have tools I don't know how to use!!

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              • #8
                http://www.mrwa.com/OP-Coagulation.pdf

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                • #9
                  Originally posted by plunger
                  ...They use about 1000liters of water a day.
                  You're in South Africa correct? Isn't it a bit warm there? Could you dispense into a large area, shallow tray and let the sun do its work evaporating off the water. Sweep up the residue, bag it up and dump it. Think of how they work on salt lakes.

                  Alternatively, a (series of) settlement tank(s) but you'd have to experiment with flow rate to allow enough still time for solids to drop out. If you let it into a holding tank and then discharge over 24h, that's only 0.7 litres/minute.

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                  • #10
                    At the risk of starting another nomenclature or word use war, my dictionary says of flocculate "to form lumpy or fluffy masses". This corresponds to the use of flocculents in wine making including egg whites and bentonite if there's a haze that doesn't settle out. Mixing in a flocculent gets the tiny particles to form larger masses which will settle so clear wind can be decanted off.
                    Hmm. In the preparation of medical dispersions they are used to prevent separation and settling. But, since I have looked it up on Google you are right in that they are used to promote settling when the vehicle is water. The effect depends on the neutralizing of charges on the particles so the effect will depend on the vehicle in which the material is suspended. Water carries a charge (ionic) so neutralizing the charge on the particles will permit them to come out of suspension. If the vehicle is covalent such as ethanol, then neutralizing the charge enhances dispersion.
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                    • #11
                      Is this material a DISPERSION of finely ground pigments, or a SOLUTION of soluble dye? Or, worst of all, is it a COMBINATION of the two?
                      If a) then it is really just "lumps in liquid" and some type of mechanical filtration will work. It may have to be very fine, but a cartridge filter of the type used for sediment in drinking water might work.
                      If b) then activated carbon MIGHT adsorb it, and then mechanical filtration to get the carbon out. Alternatively, strong oxidizers MAY disrupt the colour molecule enough that the colour is lost. In ascending order of potency would be potassium permanganate, chlorine, chlorine dioxide, hydrogen peroxide and finally, ozone.
                      If c) then it will take a combination of oxidation AND filtration. The price just went up, along with the complexity.
                      FIRST find out from the city, how clean is clean? They MUST have a standard to work to, or you are just about assured failure.
                      Is there any other way of cleaning the screens? For example, can an alcohol wash work? Then it is a matter of recovering the alcohol and reusing it. The residue from recovery would be a solid or semi-solid.
                      Flocculation, coagulation, sedimentation and filtration, (in sequence,) works GREAT at flows up to 1000 litres/sec, but it is not worth the effort at low flows, (below about 20 litres/min.) To try and work out a system for a batch-treatment, where the waste concentration is variable will be difficult. (That is the most charitable description!)
                      Finally, this stuff is WASTE and your shirt dyer wont have an awful lot of capital to spend.
                      Duffy, Gatineau, Quebec

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                      • #12
                        The colourants will be pigments since screen printing is done with paints. Most such paints are water based acrylic that are polymerized after application by the use of a hot press.

                        The first thing to do is to adjust the cleaning process to minimize the amount of waste water. That can probably be done by first soaking the screens in still water and then pressure wash with recirculated wash water. By using a series of settling tanks with each holding a day's worth of pressure wash water the water can be slowly moved along the series 24/7 to the main tank that is used to feed the pressure washer. The waste water then goes back to the first settling tank. Eventually tank cleaning will need to be done and the resulting sludge dealt with as non toxic paint disposal. Only a final rinse should be needed to remove the remaining residue from the screens and it should be clean enough to be flushable.

                        PS: I have done screen printing.
                        Last edited by Evan; 07-28-2011, 05:37 PM.
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                        • #13
                          Originally posted by djc
                          You're in South Africa correct? Isn't it a bit warm there? Could you dispense into a large area, shallow tray and let the sun do its work evaporating off the water. Sweep up the residue, bag it up and dump it. Think of how they work on salt lakes.

                          Alternatively, a (series of) settlement tank(s) but you'd have to experiment with flow rate to allow enough still time for solids to drop out. If you let it into a holding tank and then discharge over 24h, that's only 0.7 litres/minute.
                          i vote for this answer being the most sensible solution .

                          all the best.markj

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                          • #14
                            The main thing to do is to recirculate the water rather than just dumping it all down the drain. That will make the city a lot happier.
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                            • #15
                              The company is called toxic ink. Kind of ironic name.I will try to find out more about the type of pigments.The property is rented and the area where the cleaning is taking place is quite cramped. The business is big ,about 100 workers and have many carasol type screenprinting machines capable of 20000 shirts in a 12 hour period .On their e mail letterhead it states that they are enviromentally friendly phthalate compliant /free plastisols. I will also check to see if the meter reading is 700 liters or 7 kl.
                              With regards to is it warm here . You could fool me. Its been the coldest since 1994. The temperature for the last 2 days at lunchtime was 12 Celsius.Today was 20 Celsius so it is at least warming up. In winter it averages about 24 Celsius but in summer it gets over 30 Celsius with a high degree of humidity.The main road from durban to joburg was closed for 24 hours cause its the most snow we have had since 1994. But this is 3 hours away from me. I know this is mild for some of you and i don't know how you can work in such cold weather. I have had to wear a jersey at least 10 times this winter.

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