How to eliminate Sulfates from waste water effluents 3

[22854]

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.

 

[vintage70]

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.

 

[22854]

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) ??

 

[vintage70]

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.

 

[DeltaCascade]

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.

 

[Muggle]

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

 

[DeltaCascade]

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

 

[Muggle]

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?

 

[ischgl99]

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

http://www.dutchmenservices.com

 

[waterexpert]

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.

 

[waterexpert]

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.

 

[kenvlach]

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.

 

[waterexpert]

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

 

[kenvlach]

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."

 

[waterexpert]

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

 

[kenvlach]

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.

 

[waterexpert]

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.

 

[kenvlach]

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%)?

 

[gkandy]

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.

 

[kenvlach]

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.