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
 ----------
From: Paul Gould
To: [log in to unmask]
Subject: Re: Floating waste water treatment sludge
Date: Tuesday, January 07, 1997 3:25PM

In message <[log in to unmask]>,
[log in to unmask] writes
>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:
>- Continuous treatment system about (80 gpm) treating all printed circuit
>board chemical manufacturing waste.
>- First step: the waste floes to a lift station where it is pumped into the
>first treatment tank.
>-The first tank: The pH adjusted to 8.0 with caustic,
>sodiumdimethyldithiocarbamate (DTC) is added to an ORP of around 0 mv.  Then
>it flows by gravity to the second tank.
>- The second tank: Polyaluminium chloride, and an anionic polyelectrolyte is
>added.  The treated solution then flows by gravity into the clarifier.
>
>I have tried different concentrations of anionic flocculent, it doesn't seem
>to be a floccluent overdose.

If you have organic matter in the waste stream such as resist developers
or strippers then this may be the stuff which is floating. Check the
incoming stream. Otherwise it is flocc which has nothing to attach to. A
small amount of flocc goes a very long way.

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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