Water Treatment For Printed Circuit Manufacturers ©1998
Recycling, why you're spending
more now and enjoying it less.
by Robert E. Mesick
(Published in Circuitree Magazine,
only considers normal PWB processing and examines the following
metals, Copper, Nickel, Zinc, Lead, Tin, Gold, and the problem
anions. cyanide and EDTA complexes. If you've added something
new, check it's treatability first. All of these systems can keep
you in compliance, even at 0.003 ppm, some will just cost you
more to operate or require a "patch".
days, everyone wants to recycle something. The latest and greatest
thing over the last three to four years is recycling water from
PCB plants. Millions of dollars have been spent on huge recycling
systems without much thought on whether or not this is really
worthwhile. What are the advantages and disadvantages of recycling
and what are the problems you can encounter when recycling?
keep your eye on the ball. What do YOU want: Recycling, waste
minimization, sludge reduction, low labor costs, automation, etc.?
When any one of these is pushed to extremes, something else becomes
are really only four types of cost effective treatment systems
that are available with some sub-categories. They are:
- Precipitation with gravity settling -
These conventional systems were used for years when the limits
were 5 ppm heavy metals. Additives keep these systems alive but
the cost of sulfiding and reducing agents make them very expensive
require final filter
require chelate breaker (see below)
pipe system is possible with chelate breaking additives
large floor space required
- Precipitation with membrane filtration -
These were breakthrough systems in the late 1980's when limits
went under 5 ppm and there were no addition agents to keep the
precipitation systems in compliance. Initially they were supposed
to work with the same chemistry as the precipitation systems but
used a membrane to filter continuously. It didn't work. Additives
were added to reduce the metals ions to elemental form and segregation
was required to keep the systems from fouling (no tin, photoresist,
operational cost (power costs, pump/membrane maintenance, chemical
efficient, low operator attention, automatic operation
requires reducing or sulfiding agent
floor space requirement
segregation of rinses.
to high sludge volume
- Deionization (DI)/closed loop -
When recycling became fashionable, deionization systems were adapted
to close the loop. Unfortunately, the vendors were often DI people
used to working with clean city water. Lately big DI's seem to
work but they are expensive.
Capital cost (should be, but there are quotes for 50 gpm systems
regeneration frequency - All ions are removed from the water
so these systems must be sized for total TDS. Systems are usually
regenerate once or twice per day.
carbon, ozone, uv/peroxide used to treat organics, DI's can
be an instant recycling system.
maintenance due to traditional lower cost components. High regeneration
frequency allows closer sizing of system to minimal configuration
to keep costs low.
regeneration volume. Regenerant volume for both cation and anion
resins plus water for rinsing both columns. All have metals.
batch treater required.
and rinse water metal content is too low to electrowin These
should be segregated, batch treated, and sludged.
metal is at 1-2 g/l unless a 2 or 3 stage regeneration is used.
Staging requires segregation of first portion of regenerate
for metal recovery and collection and storage of the remaining
regenerant for use in the next regeneration cycle. Staging adds
more cost and complication to the system.
Cation rinse water is added to the metal regenerant, the volume
to plate out is very high and thus, not efficient.
is generated at low to medium volume.
- Metal Recovery Ion Exchange (chelated resin) -
These systems us a chelated resin that only strips out heavy metals
(Copper, Lead, Tin, Nickel) and leaves everything else in solution.
cost (higher than basic DI, lower than membrane systems).
recovery of heavy metal. If metals are 30 ppm and total cations
including Sodium, Calcium, and Magnesium are 170, only the 30
ppm of heavy metals are removed.
maintenance due to low regeneration frequency (between twice
a week to twice a month depending on metal loading).
will strip chelated metals from rinse water, EDTA is not a major
is desirable but not an absolute requirement. Some shops run
single pipe systems or segregate only non metal bearing waste
and single pipe the rest to treatment.
low operator attention, systems are automated.
waste volume. Regeneration rinse waters are reprocessed by the
regenerant volume. Regenerant volume is 300-400 gallons for
a 75 gpm system with a concentration of 8-15 g/l of Copper in
- Fixes -
system will not meet local effluent limits, there are some patches
you can add to increase the efficiency of your system.
polishing filter -
systems sometimes "leak" precipitated metals. A polishing
filter will remove these and should get you back into compliance.
Automated filtration systems work on backpressure to initiate
backwashing. These system require 15-20 minutes of operator attention
precipitation efficiency -
and Type 2 systems operate by precipitating metal. Type 1 uses
oxide formation as the primary step and type 2 uses sulfide or
metal reduction as primary treatment. Some type 2's used to use
ferrous sulfate to break chelates and to add a lot of bulk to
control the metal but the sludge volume was huge.
chelate breaker -
are two basic types. First, reducing agents like Sodium borohydride
that turn metal ions to elemental metal.
type are sulfiding agents like dithiocarbimate and Na2S and others.
Metal sulfides have very low solubilities. These are added to
Type 1 systems to maintain compliance.
system types can be used to generate water for recycling. All
have problems that you will have to address. Each also have advantages.
You have to evaluate what waste streams you intend to put into
the "recycle mix". If you add the batch dumps, you add
a lot of dissolved solids that you have to remove. If you use
dragouts and batch treat them, you remove a lot of dissolved solids
from the "recycle mix". Labor for batch dump treatment
vs. automated treatment is another consideration.
If there is no economic advantage to recycling and it will cost
a lot more, why recycle? There is no free lunch.
Let's look at the bad reasons for recycling:
boss wants me to do it. (Have him call us)
city would like it if I did.
- I will
get my name in the paper if we recycle.
some better reasons for recycling:
costs a lot of money (you're on a desalination system).
charges are based on flow and I'm getting hit with a surcharge
that would pay off a recycling system in 18 months or less.
water quality coming in is so bad that it costs me a lot to
clean it up and what I'm sending out the back is cleaner than
what is coming in the front (like you're in Pakistan or Turkey).
city has a cement truck around the corner and is going to fill
my sewer connection because I have not been diligent in my housekeeping
and have a few hundred violations.
with recycling in general -
can use a lot of carbon to remove organics. Carbon has different
capacities for different organics and you usually have no capability
to measure what is leaking through. The result is that you haul
carbon on a time interval and hope you don't have a problem.
can destroy organics. Another layer of equipment is required which
adds to costs. Ozone (not very efficient), UV/peroxide (high cost)
and carbon (adsorption, see above) are used.
concentrates ions in a smaller volume and may result in discharge
limit violations. For example: the city's' limit is 2500 ppm for
TDS and you have been running 800 ppm. The new system increases
the TDS to 1200 ppm with the extra chemistry you will have to
add. You add a Reverse Osmosis to give you an 80% recycle rate.
This results in a discharge of 4800 ppm which the city won't like.
for recycling with each type of system -
need a very good filtration system and a reverse osmosis system
to recycle. The TDS exiting these systems is too high to feed
a DI economically. It can have the lowest total system cost. Organics
>300 molecular weight are removed by the RO. Some have tried
Ultrafiltration followed by DI but the sodium and chloride are
still very high for a DI system.
the microfiltration with an RO like type one. You should be able
to get a 75% or higher recovery rate if the system is designed
correctly. A good total water analysis of the water exiting the
microfilter is a requirement.
the microfilter are not economical. The high TDS exiting the microfiltration
due to treatment chemistry make DI systems uneconomical.
get DI water to start. Carbon filtration is needed in front to
protect anion resins from the organics and any oxidizers. These
systems are sensitive to oxidizers but carbon (lots) protects
systems should have RO water as makeup water to keep calcium and
magnesium out of regenerant. This will help if you plan to plate
metal out of the regenerant.
batches of waste that are 1-2,000 ppm. A medium DI system running
75 gpm will generate 2-3000 gallons of concentrate and DI rinse
water once or twice a day that must be processed.
systems need a RO to recycle. TDS out of the system is about ten
percent higher than the incoming TDS. The cost is higher than
a basic DI but less than Microfiltration with RO.
5 PPM - LOW
TO 0.2 PPM-HIGH
(It's just plating, really !)
are plating with junk solution. It is not consistent! It is not
a plating bath with brightners. It will plate the way the chemistry
dictates and not the way you wish it would. The purer and more
concentrated the solution, the better it will plate.
higher the concentration the better. Type 4 gives you the highest
concentration, type 3 is about 1/4 as concentrated and types 1
and 2 give you sludge. For Type 1 and 2 You can redissolve sludge
and plate the metals out. Efficiencies vary with metal concentration
and contaminants. The lower the concentration, the lower the plating
rate. The higher the levels of other metals and/or Calcium and
Magnesium, the lower the plating rate.
results vary with the solution. It won't be pretty but it will
get the metals out. You can redeposit the metals by using your
first recovery deposit as an anode for a high efficiency cathodic
deposition like the mines but it is probably not cost effective
unless you have large qualities of Copper to recover.
have to watch the connections. Like any plating bath, the connections
like to self destruct, oxidize, etc. A little maintenance with
each cycle and the systems will run carefree for a long time.
all 4 types can be used for different applications. For printed
circuit manufactures, "with no recycling", the MRIX
units are pretty much trouble free and recover Copper in a concentrated
form. Operation is also relaxed with not much worry about staying
in compliance. Surprise visits to MRIX sites usually find the
operator someplace else.
capital cost recycling", a duplex deionization system with
good segregation and much carbon is probably the best choice.
It is higher in maintenance and the operators need to be a bit
more aware. You will get bad regenerations and you don't have
much time to reinitiate a regeneration before you run out of water.
There is a lot more anxiety when you regenerate once or twice
is no object recycling systems", the low maintenance and
operation cost of a MRIX coupled with an RO is probably the best
choice. You will still need carbon filtration for organics. Microfiltration
operation has a high cost associated with it and you end up with
sludge. You still need the RO to recycle. If hauling sludge is
a desirable option, a microfiltration or gravity claification
system may be a consideration.
have a lot of different metals like a metal finishing plating
shop, a type 1 system for end-of-the-pipe treatment followed by
carbon, ultrafiltration and an RO is probably the best bet. However,
it is the most expensive option.
you have it, it is a lot to think about. Make a spread sheet for
your flows and get to work!