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I am having problems with floating sludge in my clarifier. Instead of a clarifier I have a desolved air flotation system. The system is as follows:
If anyone can help I would really be greatful.
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Perhaps air is entering somehow - maybe via the gravity pipe to the final chamber, dissolved carbon dioxide from neutralization, or air itself adhering to the flocculated metals (or even from the flocculant, which I would not guess is continually stirred, but made in batches).
An old fashioned solution might be to sprinkle lime (calcium oxide) over the liquid in the clarifier. As lime is insoluble in neutral or basic solution, it provides a high surface area for gas collection and allows the floc to settle. It is then removed through the press.
Best of luck,
Condor
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Your problem may be where you add the DTC and what it is reacting with. DTC is a reducing agent and if you have a metal oxide in solution, it reduces to the metal and oxygen. You may have a lot of oxygen in solution that is causing the problem. If this is an old installation and a new problem, you may want to look upstream to see what processes have changed recently.
DTC should be added late in the clarification stage, as a secondary step to polish the waste stream. I you add it early, you loose the advantage of hydroxide precipitation. DTC should be added last as a polishing step to take out any residual metal. It's a very expensive way to precipitate metal.
I think our newsletter number 4 or 5 talked about DTC use.
Bob Mesick
Remco Engineering
Water and Wastewater Treatment Systems
http://remco.com/home.htm
HYPERLINK mailto:Remcobob@remco.com Remcobob@remco.com
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To get a heavier sludge with a greater copper removal try using Ferric Chloride as the metal for the electron transfer. If your stream is typically less than 100 ppm of copper coming in, Ferric Chloride (conc needed determined by jar tests) and lime above pH of 8 can yield final water copper concentrations less than 100 ppb. If the pH is kept above 12.5, a softening effect will take place and Calcium Chloride and Magnesium compounds will precipitate out and the copper will resolubilize. Chelating agents in you waste stream will complex your metals and are difficult to break the bonds to get the copper out of solution. There are some commercially available polymers that attach these chelates and then allow the Ferric compounds to work.
This type of treatment is typical of water treatment for large scale power plants which have very low discharge permits.
Dave Creager
Industrial Chemist
We treat with lime but first acidify to pH 2.5 with waste acid solutions to crack the metal ions, then add lime to pH 8.5 before pumping to a flocc dosing tank which sits on top of the clarifier. Flocc should be added just before settling otherwise it will be broken down and won't do the job. We consistently achieve a copper level of better than 2.5 ppm although this may not be acceptable where you are. All developer and stripper dumps are treated separately and by pass the main effluent treatment.
As someone else pointed out, lime only partially dissolves and is mostly in a slurry form which considerably aids settling. It will also attach to any surplus flocc and prevent carry over. It is a pain to use because it needs constant circulation and mixing to keep it in suspension but it does the job better than Caustic and is cheaper. We have a final band filter for removing any organic material and avoid dumping developer and stripper solutions into the effluent stream as these can contain complexing chemistry as well as a lot of organic material.
Hope this is of some help. Small scale lab simulation of your treament process can sometimes help but it is difficult to reproduce the full treatment process especially with a varaible waste stream.
Good luck
Paul Gould
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Maybe in reply to: BOYDA225@aol.com: "Floating waste water treatment sludge"
BOYDA225: Your problem is either chemical or physical. Here are my thoughts on both possibilities, although my experience with similar wastestreams/treatment schemes suggest that the physical is the greater possibility.
Chemical: You could have strong oxidizers coming into the wastestream that are wreaking havoc on the organics present, with resultant gassing and floatation. I know of one guy who traced his floating problem to nitric acid wastes that he was metering into the system. What do you do with your spent solder strip? As a short term fix for a problem like this you could add/meter in a sodium metabisulfite solution. This seems to work no matter what the cause of the microbubbles (which I assume you can see on your sludge). I notice you got a few responses telling you ways to weight down your sludge. You should consider recirculating sludge from the bottom of your clarifier (if you have any down there-ha ha) if you are not already doing so. Use a Wilden M-2 to pump it back to your DTC-addition tank at a slow continuous rate. There are many benefits to this.
Physical: Any pump involved in your wastetreatment system could be physically entraining air in the water. Although it is difficult to track down the source, almost all of our floating problems were the direct result of a perforated diaphragm in a Wilden pump or a bad seal on a centrifugal pump. If you have a suspect just switch it out with a spare and see if the problem lessens or goes away. Additionally any loose fitting or hose on the suction side of a good pump cïuld be dragging in air. As mentioned above, the sodium metabisulfite feed will temporarily fix this problem too. I have very rarely seen excess polymer causing a severe floating problem, although this is often talked about.
I hope this helps you; if you want to give me a call feel free.
Keith Perrin
Lead
Wastetreatment Operator
Printed
Circuit Corporation
617-935-9570x300
I forwarded your sludge issue to one of my fellow engineers.
Here is his reply.
Dave Sullivan
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Subject: Re[2]: Floating waste water treatment sludge
Author: pmcarter at po5
Date: 1/8/97 5:16 PM
Mr. Gould:
I'd lean towards one of the possibilities mentioned by Mr. Creager. Aqueous photoresist-containing stripper and developer solutions and their rinses, when combined with the pH reduction step, can make a low solubility, gummy, floating mass. In areas where the option exists, I've always tried to pre-treat those resist waste streams separately. Depending on the nature of your permit, availability of separate tankage, and the contents of the resist rinses, it may not be necessary to go through the metal-removal portions of your treatment scheme with the resist-bearing streams. Marc Carter, ex-resist person