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Re: metal finishing question

Phosphating and chromating are two very general
categories of conversion coating.  Within each
there are operating conditions and applications
that are better and worse for achieving a goal of
zero (water) discharge.  My first stop would be to
evaluate the process solutions for their tolerance
to return of rinsate, as well as the inevitable
build-up of contaminants from dissolution of parts
being processed, like aluminum and iron.  Then I
would assure that all incoming sources of
contaminants, like cleaners, acids and tap water
have been controlled.  Once the solutions are
optimized in this way (and it may require
switching solutions) they can start some very
simple, low-cost things like rinsing over heated
process solutions or making the first rinse a
still rinse (probably phosphate; maybe not for

The big problem will be that while it may be
possible to make the needed adjustments to keep
rinse water out of the sewer, eventually these
process solutions will require disposal.  Many
small shops just "trickle" them slowly to the
sewer, with a hose running nearbly for dilution.
If this is indeed the "waste management method" at
the shop you are describing, you are back where
you started.  If, however, they are already used

to drumming and shipping concentrated processs
solutions for off-site waste management,  you have
at least theoretically helped the POTW (Karl
DeWahl's analysis duly noted).  I seriously doubt
whether all these machinations are really worth
the effort, though.  These solutions are not very
expensive compared to the hassle and expense of
rejects caused by a questionable process solution,
and most operators can easily subvert this set-up
in the interest of running things the way they see
fit.  I have heard of one jurisdiction going so
far as to seal drains to assure zero water
discharge, though.

----- Original Message -----
From: Catherine Dickerson <cdickerson@pprc.org>
To: 'p2tech' <p2tech@great-lakes.net>
Sent: Monday, January 31, 2000 4:00 PM
Subject: metal finishing question

> Hi folks,
> I have a question about P2 options for a metal
finishing process, and thought I might be able to
get some help from other p2ers out there.  A small
metal finishing business is process wastewater to
the city's wastewater system.  The metal finisher
is the only discharge the city gets that makes
them subject to national pretreatment standards.
Both the city and the company would like to avoid
being subject to those standards, and is looking
for a (cost effective) P2 solution.  Some of the
> The company discharges industrial process
wastewater to the city as a way to dispose of
rinsate from normal business operations.  The
coating processes are small operations: a worker
lowers a basket of parts into a coating tank using
an overhead wench on a sliding track, then raises
the basket, moves it to a rinse tank, lowers it
into the rinse, raises it, then moves it to the
final rinse tank.  For both lines (phosphorous and
chromate conversion coating processes - no
electroplating involved) there is a continuous
rinse discharge from the rinse tanks.  There are
four rinse tanks, two for each line.  If both
lines and all rinse tanks are in operation at the
same time, then the discharge to the city is about
10 gallons per minute; or about two-and-a-half
gallons per minute per tank.  That is the maximum
amount of flow from industrial processes that
would be expected to be discharged to the city.
> Has anyone else out there dealt with such a
situation?  Is there a feasible cost-effective
approach?  One gentleman we've spoken with has
said the capital costs of implementing a
closed-loop system make the payback period
prohibitively long.  Any thoughts/leads (as
always) are appreciated.
> cmd
> ~~~~~~~~~~~~~~~~~~~~~~
> Catherine M. Dickerson
> Technical Lead
> Pacific Northwest Pollution Prevention Resource
> 1326 Fifth Avenue, Suite 650
> Seattle, WA 98101
> Phone:  206-223-1151
> Fax:  206-223-1165
> email:  cdickerson@pprc.org
> Check out our website:  http://www.pprc.org
> ~~~~~~~~~~~~~~~~~~~~~~~