Black Oxide Plating Wastewater Treatment

[BlaineW]

Not sure if this is the best spot to put this topic in, but here it goes anyway.

I'm looking for some advice on Alkaline waste water treatment.

The current setup gets ph balanced and discharged into the city sewer system, however, we are moving plant locations in a month and the new site does not have sewer access.

This leaves me with the choice of 1) trucking it away at high costs, 2) somehow recycling the water for reuse to lower gallon usage, 3) possibly evaporate water and dispose of sludge.

Has anyone had any experience in doing something like this, and any advice on the best way to go or any other options or companies who do this thing in New England?

Thanks,

Blaine

 

[plasgears]

It would behoove you to consider the professional path to solution of this nasty problem. (Get consultation.) The process steps could include:
- neutralization;
- settling of the byproducts;
- packaging and documented disposal of byproducts;
- dilution of the stream;
- filtering and evaporation of the remainder.

See film starring Travolta re polution, damages and legal claims in Woburn, MASS.

 

[DedalusEnviro]

I assume you are talking about real black oxide - that which is done in a very hot bath comprised of sodium hydroxide and sodium nitrite. "Cold blacks" have an entirely different chemistry.

Your best recycling option, I think, would be ion exchange. RO is another option, but rinse water like this contains significant particulate matter that might foul the membranes.

Treatment for release is more problematic. In areas without sewers, discharge to dry wells or leach fields is heavily regulated. The nitrite ion in the rinse would likely exceed permit limitations. The best way I could think of around this is pH adjustment followed by biological denitrification. Running such a process is not a trivial matter.

By the way, using spent black oxide baths as a neutralizer for waste acids is something that might occur to somebody as a cost saver. Watch out! I tried to do this once, and got copious evolution of nitrogen dioxide, a very nasty toxic gas.

Good luck!

Cheers!
Dave Wichern

http://www.dedalusenviro.com

 

[BlaineW]

Thank you for the replies....yes I am referring to a hot black process.

Regarding ie or ro, will either actually get rid of the alkaline? I was under the impression that they are really just other means of filtering, but that if the alkaline is in a true solution of water those processes would only remove the particulates. Maybe I was mistaken, could anyone elaborate on this?

Essentially I want to reduce my wastewater to a point where I only have to dispose of a small amount of sludge by reusing the water instead of having to haul gallons and gallons of water away.

 

[DedalusEnviro]

Both ion exchange and reverse osmosis are specifically geared to remove dissolved matter. Both will also remove particulate matter, but that will foul both types of water treatment systems. It should be filtered out upstream of them.

Can you just put the rinse water back in the bath? This process operates really hot, I imagine you have to add make up water on a daily basis.

Here's what I would do: use a non-flowing rinse right after the process tank. Never dump it - maintain the concentration at a high, but stable level by using it as make up water for the process tank. Make it up, in turn, out of the flowing rinse.

Follow this with a flowing rinse that you recirculate through an ion exchange system. When you have to regenerate the resin bottles, you can either haul the spent regen, or evaporate it. Do that, you'll likely wind up with (I do not know the size of your operation) at most, a couple of barrels a year of crap to haul away. If you have enough spent acid to make the evaporator feed roughly neutral, the residue might not even be hazardous.

If this has been helpful to you, please visit my site and let me know what you think.

http://www.dedalusenviro.com

Cheers!
Dave Wichern

 

[kenvlach]

BlaineW,
You really need to provide more information for a proper answer.
What volume of material is currently being processed?
Are enough parts processed to warm the rinsewater following black oxide?
What is the entire process. I.e., maybe soak cleaner (what type?), rinse, hydrochloric acid, rinse, black oxide, rinse, water-displacing oil?
What are current volumes of rinsewaters being used?
Any fume scrubbers included in the system?
Is a dilute chromic acid dip included as per MIL-HDBK-205A PHOSPHATIZING AND BLACK OXIDE COATING OF FERROUS METALS?

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=53933

I partially agree with Dave. Have a drag-out rinse following the black oxide, used to replenish the black oxide solution. Also mentioned here:

http://www.nmfrc.org/wwarchive/Mar02c.cfm

I would add, use DI water to avoid accumulating hard water salts in the solution.
Also, use a black oxide solution containing a surfactant to reduce drag-out (a surfactant included in the black oxide chemistry by the mfr., not a D-I-Y kind).

But, ion exchange (IX) is perhaps not the proper treatment.
The biggest volumes to treat will be rinsewater (some of the better proprietary black oxide solutions can go years w/o dumping; only sludge removal). Most dissolved solids from combining/neutralizing the rinses is simply salt (NaCl & some nitrate a bit of nitrite). A possible treatment is filter, reverse osmosis (probably with pH adjust to slightly acidic), with permeate being recycled to the rinse tanks, and the reject water going to a vacuum evaporator. (An atmospheric evaporator may build up lots of carbonate due to high sodium content).

An article on vacuum evaporation:
'Coming into Compliance Using Vacuum Distillation
Tubing manufacturer employs vacuum distillation to clean up its cleaning and pickling line... '

http://www.pfonline.com/articles/129505.html

Also, do you have a chemist or trained technician to handle the wastewater treatment? IX, with cation & anion beds requiring acid & alkaline regeneration, takes some knowledge (although you can substitute money and get highly automated systems). Depending upon the volumes involved, may require significant time:

http://www.nmfrc.org/bluebook/sec652.htm

I have seen several expensive WWT systems screwed up because of untrained operators.

Some more reading:
'Approaching Zero Discharge in Surface Finishing
A capsule report…' [nothing specific on black oxide, though] -- U.S. EPA, EPA/625/R-99/008

http://www.pfonline.com/articles/web040201.html

'Cleaner Helps Bottom Line
Environmentally safe cleaner does not require maintenance shutdown, periodic dumping' [A bio-cleaner]

http://www.pfonline.com/articles/049806.html

Also, consider Birchwood-Casey's TRU TEMP® Low Temperature [200-205° F] Black Oxide Process. More dilute, so less drag-out. Also, uses an oxalic acid prep. instead of the usual hydrochloric acid, so less fumes [although slower than hydrochloric, but the subsequent blackening may be faster]

http://www.birchwoodcasey.com/downloads/safety.html

 

[DedalusEnviro]

Ken mentions a very important point that I missed - using DI water for make up of the bath.

He also proposes an excellent, but very capital intensive solution to your problem. It is probably the best way to go, if you want an "idiot proof" set up.

Ion exchange has an important advantage: the worst that can happen is that the resin gets fouled, and the deionization resins need to be replaced. An expensive mistake, but not a catastrophic one. I'd also suggest something fairly simple, and manually operated. Don't let the salesman get carried away and sell you something with more computing power than the lunar module.

And, it is true that you need a skilled, attentive operator to run it. I believe that an intelligent worker with a high school diploma could be trained to do it. It is true that good workers are not easy to find, but they are around.

Pick somebody who works on his own automobile.

Dave Wichern

http://www.dedalusenviro.com

Science is a business of empiricism.

 

[BlaineW]

Thank you again for all your replies. I'd like to ask a few more questions if you can help me, and I'll try to answer your questions Ken.

Hard to say what volume of material we go through, but currently we use 1700 gallons of water a day to keep a "clean" rinse tank. My first priority is lowering this usage by reusing the water.

What gain is there in warming the rinsewater?

Process goes alkaline cleaner, rinse, black oxide, rinse...acid and oil are no longer used.

Not sure exactly what a fume scrubber is, but there is a vacuum vent over the black oxide tank.

After the black oxide, it gets rinsewater dipped, but no acid dip.

So far, I think the biggest step I can take is feeding the rinsewater back into the tank, I think my question now is IX or RO, and in either case I need an evaporator so I don't have to haul water. I may have some issue with expertise on the system, currently it is a fairly untrained job and we have no chemical people here.

The DI water is intriguing, but is that something I would have to buy or can I just use filtered city water? I would have to look at the payoff.

Thanks again for everyones help.

 

[kenvlach]

Most commercial black oxide plants have a fume scrubber to remove hydrochloric acid fumes from above the pretreatment tank; which it seems you don't need since no rusty parts. Any need to strip and rework?

Using DI water for the drag-out rinse is common where the rinse is recycled into the process solution. Avoids buildup of hard water constituents such as Ca, Mg, Fe, silica, etc. in the process solution. Heating the tank, which occurs naturally from processing hot parts, and using DI water aids the dissolution of dragged-out salts on the parts, as does agitation (maybe add a filter pump discharging through a few eductors. Heating also cause evaporation, concentrating the solution so can add more to the process tank w/o excessively diluting it. The EPA considers this part of 'best available control technology' (BACT) for metal finishers.

A big question: how much water is added daily to the black oxide tank in your current operations? Knowing this, then by combination of spray rinsing and countercurrent flow rinses can reduce the rinsewater flow to this level.

Spray rinsing with DI water (can be done above the black oxide tank if restricted to a fine mist) is perhaps the simplest and most cost-effective means for reducing drag-out and WWT. Considered BACT. Can follow with a separate spray rinse tank, maybe reducing drag-out such that any flowing rinse doesn't need treatment. Using several counterflowing rinses greatly reduces the necessary flows to achieve a clean final rinse, making it feasible to use DI rinsewater for solution replenishment. This, plus perhaps increasing evaporating from the black oxide solution by leaving it constantly heated (a frequent practise due to dangers of reheating a crusted-over tank) could obliviate the need for on-site WWT.

I doubt whether IX is useful for lowering pH by removing NaOH. Maybe Dave is concerned with removal of cations (metals). IX won't remove nitrates and nitrite anions at high pH (as NaOH solution is used to regenerate anion IX cylinders), so neutralization is a necessary first step. Having both anion & cation beds, their regeneration solution tanks, plus a neutralization and precipitation system and assorted plumbing and sensors seems rather more complex and expensive than an RO system IMHO. As to completely 'idiot-proofing' a WWT system, not possible.

 

[DedalusEnviro]

The problem Ken mentions can be avoided by using a two column system, with the cationic resin first. H+ goes in as Na+ comes out, and the pH goes down before the water hits the anionic resin column. Most systems on the market now are single column, mixed bed systems, they're more efficient. But dual column set ups are out there too. And the engineering is simpler.

1700 gallons a day, with a single rinse? Do as Ken suggests; put in a couple of counterflowed rinses, and DI spray rinse over the process tank. This, along with drag-out return, should allow you to cut that rinse water flow in half.

I must confess that I am not very familiar with RO systems. My general impression was that they weren't very forgiving with regard to fouling, and that the membranes were easily fouled and expensive to replace. It is certainly true that they are less labor intensive to run than IX. A skilled operator would be required to run an ion exchange system, but I don't think you need an actual chemist. About RO, I do not know.

With RO, you will have retentate (the water with all the dirty stuff in it that doesn't pass the membrane) and with ion exchange, you will have spent regenerants. Either will have to be evaporated. The thing to find out is how much volume reduction you will get from each, because it takes a lot of energy to evaporate water. I'd suggest you make this decision based on data obtained with water from the same kind of process that you are running, or bench testing of the actual process water.





Dave Wichern

http://www.dedalusenviro.com

Science is a business of empiricism.

 

[kenvlach]

I thought IX for pH control was considered wasteful due to high acid regeneration & neutralization requirements. Also, Na+ is one of the least adsorbed cations, so especially bad if have a hard water supply. May also require HCl for regen. (instead of cheaper sulfuric) to avoid clogging the resin beds with sodium sulfite.

With 2 countercurrent rinses + spray rinsing, probably can reduce water usage by more than 10x. If you design a system with very low water usage, then economical to use DI water, which will give better rinsing plus avoid removing the hard water components at the end. These cations & anions would get removed by either IX or RO anyway, so eliminate at the start where it improves the process rather than the end where the disposal cost is higher.

For DI water supply of rinsewater & makeup water: use RO first, with a very small RO unit (e.g., 1 gpm) running ~continuously to maintain a storage tank of RO water. Then DI water is created on demand by pumping RO water through a single mixed bed IX.

For RO treatment of WWT, use the broad pH range membrane (not cellulose acetate, which is cheaper but more vulnerable) and have the vendor do trials of your actual wastewater.

http://www.pfonline.com/articles/089907.html