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How to eliminate Sulfates from waste water effluents
3

How to eliminate Sulfates from waste water effluents

How to eliminate Sulfates from waste water effluents

(OP)
I would like to know which are the most used methods o technologies to eliminate or reduce sulfates contents from industrial waste water to comply with municipal regulations.

Main quantities of sulfates come from neutralizing basin of demin water plant and cooling water tower blow down.

RE: How to eliminate Sulfates from waste water effluents

What are the concentrations? Interesting that you have a discharge limit for sulfates to a municipal wastewater treatment plant. Unless they are really high concentrations. The most likely treatment is membrane technology, reverse osmosis or ultrafiltration depending on the characteristics of the influent and effluent.

RE: How to eliminate Sulfates from waste water effluents

(OP)
In fact the municipal regulation is related to the discharge to the sea. We have a limit of 100 mg/lt.-

In general, individual effluents have the following concentrations:

Neutralization basin from demin water plant:  4900 mg/lt discontinuous.
NH3 system cooling water blowdown 825 mg/lt continuous
Urea system cooling water blowdown: 675 mg/lt continuous

Final effluent: 550 mg/lt

I don't think reverse osmosis should work in this case. What about rejection water (approx. 25 % of influent water) ??

RE: How to eliminate Sulfates from waste water effluents

You can combine wastestreams into one outfall, but you can't use dilution as a treatment method. Why don't you think membranes would work here? I'll look into some other processes, but they would most likely require energy input.

RE: How to eliminate Sulfates from waste water effluents

Evaporation to dryness and disposal of mineral to landfill?
Reverse osmosis, etc, would help to preconcentrate the stream for subsequent and expensive evaporation to slurry and drying to paste for handling as solid.
?
Sounds like some pretty strick environmental regulations.  Strange cause operating cooling towers at lower cycles of concentration (higher blowdown rate) and other such methods may reduce your concentration, but this is essentially dilution, where additional phosphates etc will just go to environment...
Perhaps regenerating demin train with HCl instead of H2SO4 would help, although likely increaseing regen costs and certainly the chloride content of its waste stream would result...
Maybe your sulphuric acid feed to cooling towers can be reduced by operating with an alkaline cooling water treatment program (such as Betz' AEC program, etc), if you aren't already ... that would reduce sulphate somewhat, depending upon how much is in your make-up water top begin with.
Maybe there are other upstream things that you can do, such as reducing cooling load through plant heat integration, increasing % condensate returns at boilers (reducing demin make=up need), switching to air cooled exchangers (expensive?).
Good luck.

RE: How to eliminate Sulfates from waste water effluents

Don't over complicate the issue here - you can break most of the sulfates with rapid/vigourous aeration, especially in combination with electrolytic treatment - this will release the sulfur as gas to the air. Whether you would need to air scrub is another questions. However, rapid aeration will not eliminate the ammonia, but break it to Nitrate (NO3) - the nitrate would also be oxidized/reduced by exposure to the electrolytic field - producing nitric oxide, hydroxyl ion, water, and some hydrogen gas.

Dave/Aquatic Technologies

RE: How to eliminate Sulfates from waste water effluents

Muggle, where are you coming from?
What do you accomplish by aerating sulfate .. it is already fully oxidized.
If you went to the expense of electrolyzing sulfates to make sulfur, then what?
Ammonia does not appear to be the issue, it's just that its an ammonia plant.
Is your main thrust here to advertise?
Good luck

RE: How to eliminate Sulfates from waste water effluents

Sulfates in water are turned to sulphur gas, which if not released almost immediately, will recombine into sulfate or other sulphur compounds. As to ammonia, just looked like you would be required to eliminate the ammonia prior to any discharge, just as with the sulfates - you spoke of "wastewater" not ammonia product being produced.

Since there are numerous electrolytic companies to choose from, why would I advertise for a competitor. Just trying to give "alternatives" as their are many technologies to reduce pollutants (sulfate or otherwise) then R/O or membranes. But no one on this site seems to be following AOT and other "new" technologies. Don't you guys follow the DOD and various other governmental testing reports?

RE: How to eliminate Sulfates from waste water effluents

Magnesium hydroxide is used in municipal waste treatment plants to remove sulfates from the sewage.  It should also help in your case.  

Mike Bensema
www.dutchmenservices.com

RE: How to eliminate Sulfates from waste water effluents

Sulphur gas? Using Magnesium hydroxide to remove sulphates?
Electrolysis of aqueous sulphate to elemental sulphur?

Aerating sulphate solutions will not volatilise the sulphate, as sulphur or as sulphide. These are the products of reduction, not oxidation.

Magnesium hydroxide is used to prevent volatilisation of hydrogen sulphide, not sulphate.

Electrolysis of aqueous sulphate occurs in car batteries. It does not yield sulphur.

Ammonia is stripped by rapid aeration, not oxidised. Stripping to atmosphere of ammonia, sulphur oxides, or even sulphur is not an acceptable waste treatment process.

RE: How to eliminate Sulfates from waste water effluents

Oh, by the way, you could also consider calcium sulphate precipitation by lime addition at the concentrations you have here. much cheaper than membranes or IX.

RE: How to eliminate Sulfates from waste water effluents

This seems all very odd to me.
Why bother with complicated sulfate removal schemes, do a simple substitution and the problem will vanish:
Switch your acid from sulfuric to hydrochloric.  
Then no sulfates are generated, and since you discharge (either directly or through a POTW) to the ocean, you probably have no problem with chlorides in the effluent.

RE: How to eliminate Sulfates from waste water effluents

I had assumed this was undesirable due to equipment not being designed to withstand chloride.

RE: How to eliminate Sulfates from waste water effluents

It looks to me that the (bulk of the) sulfates come from adding sulfuric acid to a neutralization basin, so downstream of any equipment.
"Main quantities of sulfates come from neutralizing basin of demin water plant and cooling water tower blow down."

RE: How to eliminate Sulfates from waste water effluents

I'd assumed they are from regen. of the demin bed. If That's not the case, I'm with you.

RE: How to eliminate Sulfates from waste water effluents

waterexpert,
I think sulfuric acid is used for regenerating cation beds (& neutralizing NaOH from anion regen.) because it's the cheapest acid. Our IX beds are FRP & PVC plumbing, so I don't see any equipment problem using HCl at 5 or 10%.
What's your view on that?

Although, to be sure, I'd check w. resin mfr.

RE: How to eliminate Sulfates from waste water effluents

Can't see any problem with the plastics, but there may be some austenitic stainless in the system in question which won't be too keen on chloride.

As you say, the resin producer will have an opinion too.

RE: How to eliminate Sulfates from waste water effluents

True, I wouldn't want SS to remain in any HCl continuously.
There's probably an SS mixer in the neutralization tank (and I've replaced a few setscrews on those cuz originals were a lower,magnetic SS grade). But, I neutralize lots of acids & let T rise to 140 F, too.

But, regeneration temperatures are ~ambient, so as long as use PVC pumps & valves in general, I think the principle is valid.

Anybody know any technical reason to not regen. cation bed w. HCl (5 or 10%)?  

RE: How to eliminate Sulfates from waste water effluents

HCl is not recommended for use in  high capacity,high purity cation beds. HCl has a tendency to break the molecular links of the resin particles. So over a period of time the life of the resin bed gets reduced.

Hope this helps.

RE: How to eliminate Sulfates from waste water effluents

Interesting. I happen to have a system where 5% HCl is specified for the strong cation resin regen., and 4% NaOH for the anion.  The resins have considerably exceeded their 3-year warranteed lifetimes.

However, as noted, check with the resin mfr. of your particular resin.

RE: How to eliminate Sulfates from waste water effluents

So on balance, it is worth a little initial investigation to see whether it will be simpler and quicker to change acids, or add one of the simpler sulphate removal techniques.

I'd probably favour lime precipitation and removal by gravity settlement if sulphate removal is needed. Other removal techniques can be considered if space is limited. It's fairly simple to design, and likely to be reliable and cheap to run. It will be far cheaper to build and run than evaporation or membranes.   

Seán
www.expertise-limited.co.uk

RE: How to eliminate Sulfates from waste water effluents

22854,
Any update?
Does your cation resin mfr. permit use of HCl 5% for regen?

RE: How to eliminate Sulfates from waste water effluents

(OP)
Thanks to all for this ample discussion.

We studied the option to use HCL to regenerate IX resins but it is not a good option from the economical point of view and have also to change materials and increase storage capacities three times.

The use of RO means that we will still have sulfates (even more concentrated) in the rejected water, so how can we dispose the rejected water?.

We are still thinking in the best solution.

RE: How to eliminate Sulfates from waste water effluents

We are back to where we started...
Same problem .. its just concentrated .. perhaps making evaporation to calcium sulphates, etc, more economical .. not necessarily economical .. just more economical as its more concentrated in the RO reject stream ...
(aside: I dont think that lime softening will remove sulfates ... it just removes Ca as CaCO3 ...  you may need to add soda-ash .. and SO4 will leave as soluble Na2SO4)

Anyhow, think we answered your questions.  when you do your analyses, you may find that repalcing H2SO4 with HCl is the cheapest and most effective option... it wont be "free"..
It will be interesting to see the outcome.  Good luck

RE: How to eliminate Sulfates from waste water effluents

I'm not quite sure what you are trying to say, Deltacascade,
but I beleive your submission may contain a factual error.

Adding lime to a concentrated sulphate solution will precipitate calcium as sulphate, not as the carbonate. I understand that there are high sulphate levels here, rather than high carbonate levels. It will additionally precipitate any carbonates present, but I cant see what the problem is with that. CaSO4 has very low solubility in water. That is why its production from sulphates by lime is used for desulphurisation of flue gases at power stations.

As I said before, lime will precipitate an easily thickened calcium sulphate sludge from concentrated sulphate solutions. This is the process used in flue gas desulphurisation, and therefore thoroughly tried and tested.

The relative economics of this compared with evaporation are likely to be good for all but the most concentrated solutions. Heat is effectively free at power stations, but they still use lime precipitation to remove sulphate from flue gas scrubbings.

RE: How to eliminate Sulfates from waste water effluents

Yes, agree, and thank you. I am thinking lime-softening of surface waters.  And, yeah, we need a waste water analysis ... cant be more than about 2-8max% H2SO4? what with it being demin plant regenerant waste, and thats if it isnt mixed with backwash or (fast, slow or preservice) rinse waters.

One thing for sure, this has been an interestin debate amonst us observers.  The calcs for CaSO4 precipitation oughta be interesting.

Best wishes, 22854.  Please do let us know how it turns out  

Cheers

RE: How to eliminate Sulfates from waste water effluents

DeltaCascade,

You answer on Nov 30 was the only one that made sense in these threads.

22854,

One additional thought you might try is eliminate the IX system.  If you go with an RO/CDI system, you will reduce the amount of chemicals that you are using to produce the product water. IX systems typically use 2x molar concentrations in order to regenerate.  So an RO/CDI will have less total ions in the wastewater.

Also, the permitting agency is basically telling you that they want zero discharge.  To go zero discharge, you will need to obtain a brine concentrator, which is an evaporator.  A brine concentrator recycles about 95+% of distillate that will be the source of your DI water. This is expensive, but is a workable zero discharge system.

RE: How to eliminate Sulfates from waste water effluents

In response to the question 22854 posed in the last post....chemical ppt folled by downstream RO is the answer here. Keep your hardness down prior to RO. Next, concentrate up to say 6% brine strength and ppt that AS WELL using chemical ppt. Recycle the effluent back up front.

Net affect, you are constantly removeing the SO4 as CaSO4-2H2O using simple chemical ppt while...at the same time, producing a pretty nice, clean water that should be down around 20-30mmho.

We need some simple flowcharting functionality on these threads, I am dying to map this out! HAHA

Later,

Bob

RE: How to eliminate Sulfates from waste water effluents

Thanks, bimr, i needed that  
One other option to consider may be adding use of weak acid cation (WAC) resins with the strong acid cation resins that we assume are being used.. WACs are more than twice as efficient in use of sulphuric acid regenerant when calcium is in bicarbonate form ("temporary hardness")... and will reduce acid use, but we can't tell if it may be enough without further problem definition.
Cheers, all!//

RE: How to eliminate Sulfates from waste water effluents

RG Cook,

Chemical precipitation is not used for this application because of the high solubility of calcium sulfate (+2000 mg/l).  What can you do with a waste stream with 2,000 mg/l sulfates?  Nothing except evaporation, which could you have done without the precipitation step.

RO is also problematic when used on waste streams with high dissolved solids levels.

DeltaCascade has mapped this out for you.  If we want to flowchart this thread, just erase everything but his answers.

RE: How to eliminate Sulfates from waste water effluents

bimr,

I understand your point; however, the solubility of CaSO4-2H2O (not SO42-) is about 2,000-2,200 mg/L. Also, RO can be applied to concentrate streams like this in a zero-liquid discharge application. You seem to have missed the implication that Ca must be removed prior to RO or, as you say, it will not be very effective concentrating, because it will likely salt out. Yeah...ok... Remove the Ca hardness using NaCO3, essentially dropping the Ca as CaCO3 up front using NaOH, to elevate pH. This leaves you with a Na2SO4 salt going to RO that is effectively concentrated very will up to about 6% by weight. In a ZLD facility I was involved in, it is true that we evaporate in a forced circulation crystallizer to drop the salt. However, if one was to recycle the concentrated NaSO4 solution and ppt with lime, it is something that, in my opinion, should at least be explored. It may be conceivable to get creative and at least minimize the load on the downstream crystallizer.

Don't be so quick to dismiss ideas. That is the point of the thread. And with all due respect, you seem to have missed the chemistry.

RE: How to eliminate Sulfates from waste water effluents

FAQ164-544 covers this area.

RE: How to eliminate Sulfates from waste water effluents

RGCook,

What am I missing?  I agree that RO has been used at some zld facilities.  My point was that the use of RO for zld has been problematic.  It is not just the salts that you have to worry about.  You have to be concerned with organics, suspended matter, barium, pH, chlorine, etc.  With enough pretreatment, RO can be made to work in almost any application, but it not necessarily economical.  If I had a choice between an RO unit or a brine concentrator, I would go to a brine concentrator.  Most of the successful zld facilities use evaporators.

Again, I agree with you that you can knock down the calcium, thereby minimizing the potential scaling of calcium sulfate.  But, how are you going to do that? For high levels of calcium (greater than 300 mg/l) there is nothing that is economical.  The relative cost of removing calcium noncarbonate hardness with precipitation is 5 times the cost of removing bicarbonate hardness.  The relative cost of removing sulfates with lime or soda ash is probably worse.

22854 wanted to know which are the most used methods or technologies to eliminate or reduce sulfates contents from industrial waste water to comply with municipal regulations.  I don't see that he was looking for someone to be creative.

RE: How to eliminate Sulfates from waste water effluents

It will be removed by wet air oxidation..if u want any info please go to google.com

RE: How to eliminate Sulfates from waste water effluents

nareshiitr: Glad to see that you know about google.com. Maybe you can use it to improve your posts.

In this thread, we have calcium sulfate salts which 22854 would like to remove from wastewater.

I would agree that sulfides can be oxidized to sulfates. But generally, no significant quantity of sulfides are present present in wastewater. Unless you are a tannery.



RE: How to eliminate Sulfates from waste water effluents

Sulfates' elimination is indeed a difficult problem to solve.

It is strange that a limitation of 100 ppm of sulfates in water going to the sea has been imposed since the average content of sea water is near 900 ppm S as Ca, Mg and K sulphates. This is probably the result of a waiver on the content of other contaminants.

Anyway, when speaking of precipitating sulfates I recall that analytical chemists actually use Ba salts to measure-gravimetrically- sulfates in body fluids by weighing the precipitated BaSO4. Its solubility product Ksp=10-10, resulting in a solubility of less than 30 ppm at 25-30oC. Could this fact be used in 22854's case without becoming too "creative" as bimr implies? BTW, it is CaSO3 that has a very low solubility in water (less than 60 ppm at ambient temperatures).

Ba salts are toxic, therefore their addition, if at all, should be done with utmost care in a manner that their presence is less than stoichiometric, and, even better, a cation exchange resin should be used, after the separation of BaSO4 has taken place, to ensure no Ba ions escape with the effluent. This salt should precipitate quite easily having a density of 4.5 times that of water. Because of its low solubility BaSO4 can be "safely" used to X-ray the digestive tracts of humans.

Would a lab trial be practical? I wonder.


RE: How to eliminate Sulfates from waste water effluents

Re sulfate limit: this may be due to sulfate attack of concrete.

Re Barium toxicity: Barium is actually pretty non-toxic, see MSDS at https://fscimage.fishersci.com/msds/02510.htm
An isotope is used for medical imaging.  

Presume that barium is little used for sulfate precipitation due to cost and because using BaCl2 or Ba(NO3)2 would just substitute chloride or nitrate ions.

RE: How to eliminate Sulfates from waste water effluents


To kenvlach, the website you mention refers to Ba sulfate (barite) which I already said is non toxic because it precipitates, and it is widely used in medicine as an X-ray contrast medium, as a filler in paints, plastics, rubber, the ceramic industry, and in drilling muds.

Barium metal and most barium compounds, with the exception of barium sulfate, are extremely poisonous, regardless of price. See, for example,

http://www.jtbaker.com/msds/englishhtml/b0372.htm
http://physchem.ox.ac.uk/MSDS/BA/barium_chloride_anhydrous.html

RE: How to eliminate Sulfates from waste water effluents

(OP)
Dear Friends,

Thank you all for your help and assesment. Regarding the limits of 100 ppm of sulfates going to the sea, by the time I asked my first question we sent a reclamation to the authorities to study and reestablish new limits for this and other parameteres of contaminants in the effluent waters going to the sea. Last week we have received a still non-official notification from the government that is changing the requested parameters. Specifically for sulfates they are changing from 100 ppm to Not Specified. This means that no controls will be done on this until a new limit is stablished.

RE: How to eliminate Sulfates from waste water effluents

Dear all

There appear to be two threads on the same topic. Have a look at thread Thread164-47948. It has some alternative technologies.

Greetings,

Jacco

RE: How to eliminate Sulfates from waste water effluents

it has been realy nice going through all the postings. I am new to this website. I am working in a Env Engg company in india. we are recently a successful bidder for treating this type of wastewater in IOCL, india. Where the Consultants are going for wet air oxidation. But i think this is very expensive for highly concentrated wastewater.

Please let me know your views.

India

RE: How to eliminate Sulfates from waste water effluents

Dear Nareshiitr

I am not sure that I understand your posting, but are you saying that you can remova sulfate from water through wet air oxidation? That would be worth a price or two, or I am totally misunderstand your posting.
Could you please specify what kind of technology you have been succesful with and what wet air oxidation has to do with sulfate removal.

Jacco

RE: How to eliminate Sulfates from waste water effluents

Nareshiitr is confused between sulphate and sulphide.  Sulphide does react with oxygen under relatively mild conditions to produce sulphate and sulphur.  The balance between sulphate and sulphur products is pH dependent.  Hydrogen peroxide at room temperature is another option for sulphide, if you want to trade operating cost for capital cost.

Sulphate is rarely regulated in discharge permits in my experience, so the fact that the original poster's regulatory authority had sulphate on its list and then removed it is not surprising.  It doesn't represent much of a toxicological issue.  Usually it's covered under the catch-all of total dissolved solids (TDS).

RE: How to eliminate Sulfates from waste water effluents

I have heard that zeolithes even sodium alumino silicates can be used as way to reduce sulfates in waste waters.
Has anyone heard about that?

RE: How to eliminate Sulfates from waste water effluents

Yes, this is well-known, but I  think organic resins are more efficient. The sulfate anion can be removed with a Cl-type anion exchanger:

  SO42- + ACl2 --> ASO4 + 2 Cl-

RE: How to eliminate Sulfates from waste water effluents

Then when you regenerate the resin where does the sulphate go?
Looks like this topic is pretty well beat up.
Keep smilin  

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