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October 1997

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Subject:
From:
Paul Gould <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Wed, 29 Oct 1997 18:52:45 +0000
Content-Type:
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Marie Holmgard wrote:-
>Hi
>i work at PCB shop in New Zealand and i am looking at waste treatment
>options and water savings for the whole factory.
>
Hi Marie,

We are currently looking at installing an ion exchange recycling plant
and the payback period looks like being 3 years on water savings. You
still need to treat the regenerant chemicals which have a high metal
content. There is also the question of waste chemistry such as tin-lead
strippers, copper cleaners, micro-etches, and waste acids which also
have to be separately treated.

We have a simple settling plant at the moment which keeps our effluent
within 4ppm, which is quite generous by todays standards. Acidifying the
stream with waste acids, then neutralising with lime to pH 9, then
adding flocculating agent and passing through a settling tank give us a
good clear effluent stream. This has to be a large plant to cope with
the volume and we have to have a regular tanker collection to take away
the sludge which is around 99% lime and water.

If I had my time again I would go for ion exchange and recycling all
rinse waters, with a smaller treatment plant for the concentrated
chemistry and regenerants from the ion exchange.

You can treat some concentrated copper cleaners which are complexing by
passing through selective ion exchange to remove metals only and then
neutralise and discharge to drain. This is very cheap. Small ion
exchange units can also be fitted to rinses containing metals so they
can be discharged without treatment.

Your idea of recycling cooling water is good and, as you say, you do
need a water cooler in the summer as we found.

Your approach will depend on your water costs as recycling is expensive.
As Rudy Sedlak has pointed out, you can't put everything in one stream
but have to keep certain waste streams from getting into the recycling
plant.

Also, you can cut down contamination from the worst processes such as
the etchants, by using anti-pollution units which rinse boards in clean
replenisher solution. By re-using as much water as possible in
counterflow rinses, and using water savers to switch off rinses when no
panels are going through, a lot of water can be saved and the reduced
volume is easier to treat whichever option you choose.

To conclude, you will need some form of treamtment of the non-recyclable
waste which can be by precipitation and settling. The size of the plant
will depend on whether you go for this as an intermediate solution, or
implement recycling at the same time in a comprehensive package.

Good luck with your plans.
--
Paul Gould
[log in to unmask]
Isle of Wight,UK

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