Algae/Fungus/Biological Growth in Plating & Anodizing Rinse Tanks

A. There is no reason to have Bacteria in tin and acid rinse.
Not in sulfuric tin -- maybe in MSA tin.
How often do you replace the rinse?
What kind of water do you use?
DI, RO ?
Anyhow, after identifying the source and eliminating it, you must clean thoroughly the tank itself. You must clean the tank walls by scrubbing. The algae you observe is protected by a shield. This shield does not enable any Biocide to attack the algae. That is why you have to scrub physically the walls before continuing working. Again, scrub only after eliminating the source.
After this cleaning process, fill the tank with 5-10% bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon] or Hydrogen peroxide. Let it stand overnight and than rinse very well.

Once upon a time, we used formaldehyde. BUT, it turned out that it is carcinogenic.

Ask your vendor for an adequate Biocide.

A. Hi, Leslie. This subject of biological growth in plating rinse tanks harks back to a thread on this site from before the Internet even existed :-)
For a trip down nostalgia lane, see finishing.com/heardhot/goldplat.html and you'll find some answers.

Still, the small wiggly "worm-like" organisms that I've seen in rinse tanks were mosquito larvae. Throw a couple of hungry goldfish in for the weekend :-)

Regards,

A. You might clean out the tank and then try turning off the air agitation. In a draqout rinse, there should be enough formaldehyde from the bath present to prevent the biological growth, but it is possible that it is being oxidized by the air agitation. Alternatively, you could add a little formaldehyde.

A. It is very probably algae. It tended a little more towards green when I was in the East Industrial Park and it was definitely green in the panhandle of FL. We did not have the problem in the anodize tank or the first rinse tank as there was enough copper from 2xxx aluminum to kill it, but it sure loved some of the other tanks, especially the chem film strong rinse tank. I think that I would try UV lights at night. I have also read that you can buy "antibiotics" to kill it. I could not find any and am not in love with any unneeded stuff in any of the tanks. There is enough grief in metal finishing.

The rinses are highly important.
The CASCADE rinses after each step.
On the third rinse put an ion exchange resin.

P.S.: Ted, do you remember that I bought from you a great application for rinse calculations? It still works. February 2021 A. Very happy to hear that, Sara. I'm too lazy and busy to port it into a smartphone app, but maybe some partner will some day :-) Luck & Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey

A. That slimy stuff which grows in anodize rinse tanks is tough. Pump out the tanks, scrub them clean and disinfect with bleach before refilling. You may find that increasing the pH will stop or slow the growth, but once established in a shop it is very difficult to completely eradicate.

A. Are you sure its algae? I always thought copper was pretty toxic to these things. If it really is then perhaps try a little formaldehyde.

A. The problem may be starting with the incoming water that you use for rinsing, or an inadequate flow rate. You may need to chlorinate the incoming water or to treat it with use ultraviolet light to fix this problem. Most POP operations also dump and clean their rinse tanks on a weekly basis.

A. Dear Sir,
The problem may be starting with the incoming water that you use for rinsing & also clean their rinse tanks twice on a week, and also continuous start rinse tanks flow water.

A. You can try to maintain pH of solution 6.5 or lower that cannot affect your product because at this situation algae may be prevented.

A. I have faced algae problems in rinse tanks before and the solution we put into place was this:

We installed a "bulk water" tank in which was fed through a float valve (to maintain level) and stored. our main water feed was pumped through the plant @ 80 PSI, with a pressure relief valve that kept the pump from burning up. A recirculation system was installed and we continuously treated the "bulk water" tank water with UV light as well as a bubbler to slightly air agitate the bulk water tank.

The result: Algae was gone and the air agitation reduced the amount of chlorides in the city water making our chemistry last longer.

(Air Agitation will remove Chlorine)

A. Sodium hexachlorophenate sometimes marketed as Panacide is a wide spectrum biocide with little impact on higher life forms - including platers - but still use judiciously.
A more important consideration is the fact that a rinse tank with wildlife is not much of a rinse tank!

A. You might consider sodium benzoate at ppm levels.

A. We have the same problem with PAA tanks. We couldn't find a Boeing approved biocide and with the rinse tanks being on constant overflow we decided against that. We tried fitting a water treatment UV unit pumping the water through a loop and back into the rinse tank.
This seemed to slow things down but didn't cure the problem totally. It seemed to have an effect on the floating stuff but we still got growth on the tank walls which then started to float off over time. It became less predictable when the growth would become a problem and suddenly float off the sides so we took it out.
Over time we just got ourselves into a pattern of dropping the tanks about every 4-6 weeks and pressure washing them (at times we also use a dilute bleach with no surfactants).

To try and reduce the increased water usage we put in a system of putting the overflow from the rinses through a pre-treatment and back through the DI plant. There is a particulate filter, ion removal and UV treatment on that.

Note: We also have the Phosphoric electrolytic deoxidise step so we get the same issue there even though we run the particulate filters on the Phosphoric tanks almost constantly. In fact everyone I have spoken to does. It might not cure the problem but at least you know you are not missing something everyone else knows about.

A. You may want to try to contact Warren Fullen at Boeing out of St. Louis. He presented a number of biocides and results in a paper and presentation a few years ago. I contacted him on a similar issue and peracetic acid [on eBay or Amazon] was the solution. He may be able to clarify which chemicals are compliant with the specification.

Best Regards!

A. Thorough cleaning followed by disinfecting with bleach will hold the problem down.

A. Here is a good Boeing produced document on the subject. Don't use bleach because of the chloride contamination.

www.boeingsuppliers.com/environmental/Bio-contamination_Control_In_Metal_Surface_Finishing_Operations.pdf

A. Hi Chris,

Algae contamination of free running rinse tanks is a bane to us all. There is no easy solution, but if you are having particularly heavy contamination problems, start with an in-line filter to remove gross particulates and if it is really bad consider an in-line UV system to kill off organic contaminants.

A. Hi. Such growths are also a commonplace in the rinse tanks after gold plating. You might be interested in the solutions proposed on that topic, which began on the Finishing Technology Hotline BBS in 1991 before the internet existed: Topic 5358, "Fungus in gold plating rinse tank?"

Regards,