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topic 43864

Reducing nickel content in wastewater effluent


A discussion started in 2007 but continuing through 2018

(2007)

Q. From history, my WWTP effluent could comply to Malaysia's limit of 1.0 mg/L for nickel. however, recently, the limit could not be met and nickel has been in the region of 1.3 - 1.8 mg/L. We are currently operating at pH 9.5 for to precipitate all heavy metals (Ni, Zn, Cu, Mn, Boron). FYI, my WWTP is servicing electroplating and paint shop wastewater. There were no changes in the process at WWTP and in the plant.

Afif
car assemblies - Kuala Lumpur, Selangor, Malaysia


Water and Waste Control for the Plating Shop
from Abe Books

or

(2007)

A. A pH of 9.5 is a bit low for Ni.

Your best bet would be to add a bit of sulfide type precipitant, such as sodium sulfide, or dimethyldithiocarbamate. This would be a lot more forgiving than 'plain vanilla' hydroxide precipitation.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


(2007)

A. Good afternoon:

You didn't mention whether the nickel present in the wastewater discharge is dissolved nickel or nickel bearing suspended solids which passed through your treatment system. I'll assume that its dissolved nickel that's causing your problems.

As a preventative measure, if you are using cyanide based solutions in your finishing operations, please make sure you are not accidentally mixing cyanide bearing wastewater and nickel bearing wastewater. Nickel-cyanide complex can be tough to waste treat.

If you don't have a problem with nickel-cyanide complex, then the sulfide or carbamate additions mentioned by David Wichern are a great idea. Just remember not to exceed the recommended dosage; use only enough to precipitate out the stubborn metals in solution. Carbamate compounds are toxic to marine wildlife.

Steve Bizub
- St Louis, Missouri


Advances in Water & Wastewater Treatment
from Abe Books

or

(2007)

A. Not only that: if you use too much, it won't work as well. This is of particular concern with DTC, because getting rid of an excess is not so easy. You wind up with this unbreakable tea colored colloid. To break it, you need to add a bunch of ferrous or alum or something. It's a real pain in the neck.

That is why I always liked sodium sulfide. Easy to get rid of excess S2-, just blow air through it, or add some hypochlorite. Unfortunately, NaS2 has some OSHA issues associated with it that make people not want to have it in the plant.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

February , 2007

A. Before deciding that DTC is preferable to sodium sulfide or simple lime precipitation, readers should see:

http://www.state.in.us/idem/your_environment/wrcac/whiteriver/complaint/complaint.pdf

. . . which describes a pollution catastrophe -- 187 tons of fish killed in the White River in Indiana due to a grossly excessive discharge of DTC from an electroplating plant. This was by far the worst pollution incident ever caused by an electroplating plant, and ironically it was not from an electroplating waste, but from a treatment chemical required to meet over-the-top discharge standards.

An interpretation which probably resonates with platers is that if you are relentlessly pressured to use incredibly powerful toxins like DTC in pursuit of that meaningless last fraction of a milligram of metal, you open the door for accidents that are a thousand times as injurious.

Not saying that I would view the White River disaster exactly that way (I don't know all the facts) -- but smarter people than me, like Dr. Leslie Lancy, who brought waste treatment of electroplating wastes to this country, struggled mightily to tell us that the old idiom "the cure is worse than the disease" most definitely applies to "split milligram" discharge standards... but his words fell on plugged ears. 187 tons of dead fish later I hope we've started listening but I doubt it :-(

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey

----
Ed. note: Sorry, but Indiana has removed that link ... but the White River pollution disaster was so significant that you'll have no problem googling it.


O&M of Surface Finishing Wastewater Treatment Systems
Clarence Roy
from Abe Books

or

(2007)

A. In addition to environmental considerations, a practical problem often occurs in lowering [Ni] using DTC or soluble sulfide: As the DTC lowers [Ni] and other metal concentrations, previously precipitated hydroxides such as Ni(OH)2 dissolve toward maintaining their equilibrium Ni, Cu, Zn, etc. solubilities. One may end up using very large amounts of DTC precipitating all metals. Hence, precipitation with DTC or soluble sulfide should only be used as a 'polishing' treatment on filter press effluent water. In which case, it's easier to do a 2-stage pH precipitation, removing most metals at pH 8.5 and residual Ni, Zn, etc. at pH 10.5.

Possibly, Ni-containing waste waters can be segregated and treated separately.

Ken Vlach
- Goleta, California
contributor of the year

Finishing.com honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.



(2007)

A. Dave: Good point about sulfide, and thanks for it. sulfide is a much stronger precipitant than hydroxide. But I've done a lot of jar testing and it's just not as effective as DTC at approaching zero concentration of metals.

Ken: I agree that we shouldn't use DTC in the first stage of a wastewater treatment system, and should reserve its use (if used at all) for segregated polishing of what's left after hydroxide precipitation. But I don't think much precipitation happens at pH 8.5; about the only thing that comes out in many shops at that pH is iron.

I think the right approach was developed by Leslie Lancy before the EPA even existed: hold the pH low or make it low; add ferric chloride or aluminum sulphate as a co-precipitant; raise the pH to 10.5; filter or clarify; reduce the pH to acceptable discharge point. If this doesn't reduce the contaminants to a low enough level to comply with the law, change the process chemistry or change the law because the treatment regimen is right :-)

The above assumes, of course, that we consider end-of-pipe treatment of mixed metals satisfactory; and that premise must be continually reexamined as times change.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


(2007)

A. Malaysia in particular has a tough go from a discharge standard, as they are usually put into categorical standards known as Malaysia a or Malaysia b, both of which exist based on WHO water standards. Usually, they do not have the luxury of a secondary or tertiary POTW, so the use of DTC is out - they don't even set limits on it (but there are limits!) Sulfide works, however you also have sulfide standards for discharge, as well as chlorine (for those of you that want to use a little hypo to destroy the sulfide). Lastly, with all this treatment, there is (or at least was) a TDS limit, so adding a raft of chemicals to treat this is probably not the panacea that it may be here.

You didn't mention what type of nickel it was - the originating bath, so the final treatment technique could be hard to find. If its chelated at all - you cannot treat it - even with Doc's method, unless you get rid of the chelator, or tie it up. Iron does that, but there are sulphate and chloride discharge standards to consider as well. lets not forget, while KL is a BIG city, its treatment works are not what they are here - and unlike people here, that depend on well or tap water to live, there are still many many people that live by the rivers there - washing, drinking, existing etc. That's why the WHO standards are there. They don't have the benefit of chlorination at every point.

I might suggest ion exchange as an alternate, depending on the origination of the nickel and the form, either on a point of use basis, or end of pipe if necessary, but controlling it POU is a heck of a lot easier and more efficient - and cost effective. It can usually easily get well below the discharge point before the stream is commingled with the effluent, and once mixed, it could be virtually undetectable in the final outfall.

tom baker
Tom Baker
   wastewater treatment specialist
Warminster, Pennsylvania



(2007)

thumbs up sign Thanks, Tom, for reminding us that the question was about a discharge situation in Malaysia, not here.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


(2007)

A. It is true that there are discharge standards for sulfide - I operated under a pretty tough one (0.5 mg/l, Santa Clara, CA) for some years. Either because I used sodium sulfide in conjunction with ferrous sulfate, because I was treating fairly small batches (2,000 - 3,000 gallons) or because the sulfide ion is so easily oxidized, I never had a problem with it. I used to batch treat, and I'd add many pounds of sodium sulfide to batches. I never had to treat for residual sulfide with hypo or peroxide or anything else. Just the O2 diffusing into the treated water through the surface took care of any excess. The treated decant...well, I wouldn't put it up against Chanel #5 in a Sweet Smelling Derby, but it didn't reek of H2S, either.

Tom is, of course, correct in saying that the best solution to the problem is POU control - don't make the problem in the first place!

That is perhaps the wisest word yet.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

(2007)

A. Dear Sirs,

I was browsing the Internet in search for information for a presentation on electroplating effluent treatment when I happened to find your discussion on nickel problems.

I was a little surprised to see that the Degussa trimercapto-s-triazine, marketed as TMT 15, was not mentioned at all. TMT 15 should solve the problem easily and without toxicity.

Best regards,

Esko Meloni
- Nummela, Uusimaa, Finland


(2007)

A. I routinely get under 1 ppm nickel but my method may not be applicable to your waste plant. I precipitate at pH 10.5 or 11 first, allow to settle, correct the pH and then discharge. I can do this because I have reduced the quantity of water used so much that I have days between discharges.

Nick Clatworthy
- Whitstable, Kent, UK


(2007)

A. As metals enter the treatment process, they are in a stable, dissolved aqueous form and are unable to form solids. The goal of metals treatment by hydroxide precipitation is then to adjust the pH (hydroxide ion concentration) of the water so that the metals will form insoluble precipitates. Once the metals precipitate and form solids, they can then easily be removed, and the water, now with low metal concentrations, can be discharged.
Metal precipitation is primarily dependent upon two factors: the concentration of the metal, and the pH of the water. Heavy metals are usually present in wastewaters in dilute quantities (1 - 100 mg/L) and at neutral or acidic pH values (< 7.0). Both of these factors are disadvantageous with regard to metals removal. However, when one adds caustic to water which contains dissolved metals, the metals react with hydroxide ions to form metal hydroxide solids:

I would try keeping the pH around 8.0 - 8.5.

Chris Willcox
- Dayton, Ohio


February 25, 2010

Q. I am making tests for removal of Nickel (doesn't react with hydroxide and sulfide) using product Bulab (Buckman) that is the base of DTC.
However when we reduced the pH the < 2 form a brown precipitate that if it is separated presents better efficiency. Which is the best pH strip for use of DTC?
Which is dosage of DTC so that the final wastewater treated is not toxic?

Tatiana Bigardi
- Jundiai, São Paulo, Brazil


July 18, 2018

Q. I have some question, currently the chemicals that I have used in wwtp are coagulant, polymer neutralide, and decomplex 200, so How is the way to reduce the nickel value?

wan muhammad
tnp - Pahang, Malaysia


July 2018

A. Hi Wan. The first step is jar testing while adhering to the basics. If you can't get proper levels in jar tests with the basic approaches, then you would need to either see how to modify the process which is generating the nickel problem or start applying more complex reductants like TMT-15 or sulphides or DTC.

What is the source of the nickel, what other processes mix with it before WWTP, and what pH do you precipitate at? What is the allowable nickel ppm in the discharge, and what is your current dissolved and filterable nickel in ppm? Thanks.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


July 19, 2018

A. Hello Mr. Muhammad,
Check the source chemical for addition of a chelating agent, which will make your treatment method more difficult. For example, the ubiquitous Reliant Nickel acetate seal has a chelator added. To perform a 'destruct' rendering it possible to separate as solids and clean dischargeable wastewater, it must be brought to pH greater than 11 to break the chelation effect. We don't have to use any polymers etc to do this, just solid sodium hydroxide added while mixing (watch your temperature!). If a smut reducing additive has been put in the bath, which contains even more chelator, an additional first step may be necessary, which is to first drop the pH to about 3.5 using Ferric Chloride (about 1 kilo per 1000L) and then Nitric acid to further reduce the pH. Then proceed bringing the pH way back up again. Not knowing what exactly you are starting with, this is just a simple example of one way to deal with a heavily chelated plating chemical.
As Ted says, you'll want to jar test before trying to full-scale the treatment process. Good luck!

rachel_mackintosh
Rachel Mackintosh
Plating Solutions Control Specialist / Industrial Metals Waste Treatment - Brattleboro, Vermont


July 22, 2018

A. Hi All

Excellent advice on the treatment of waste water but I would suggest that there is another approach.

If expensive chemicals do not enter the waste stream they do not have to be removed by even more expensive treatment.

Assuming we are discussing plating wastes, I would look first at the plant and its operation. Much can be achieved by …

Jigging with minimal solution traps (not so easy on a barrel line).

Counter-flow rinses

Adequate draining time over the tank (without drying out); Operators rarely understand the importance of this.

Fine demin spray rinse over the tank; With a little practice you can balance evaporation/dragout losses, you save chemicals ($s) and never have to top up again!

Recirculated rinses with deioniser.

It is possible in some cases to completely eliminate the need for any effluent treatment.

geoff smith
Geoff Smith
Hampshire, England



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