H2S and Barium removal 1

[Watro]

Having read several threads on H2S removal, I was initially bit reluctant to start a new thread. However i have several questions.

We have brackish well water source with 5.2 mg/l of H2S, 1.5 of Ba, 4.4 of St, 0.08 of Fe, TDS is 8700, pH is 7, HCO3 - 182, Ca/Mg - 432/175. What are all the options to turn this a Potable water? Main challenges are Barium and H2S. Turbidity is 0.9 NTU

We have proposal to Oxidize with Cl2 - 8ppm against 1 ppm of H2S, then filter with MMF, 12 m/hr

Followed by a Softener to get rid of Ba and Cartridge filter followed by a single pass BWRO. Any other option other than softener to deal with Ba?

Antiscalant and SBS will be injected upstream of Cartridge filter.
Any idea how much FRC is expected, after Oxidation/filtration to fix the SBS dosage. I think all Cl2 will convert to Cl

Reducing pH with Sulfuric acid will help H2S reduction by oxidation? H2S need to be close to Zero prior to RO, I believe
Any other economical solutions?

Thank you in advance

 

[ashtree]

One of the problems you may experience with the process you are proposing is that the MMF is unlikely to remove the total quantity of elemental sulfur that forms in the conversion process from H2S to sulfate. Whilst you are dosing enough chlorine to achieve full conversion to sulfate it is unlikely that you will get 100% conversion to sulfate with no elemental sulfur forming. That sulfur will foul the RO membranes and can be very difficult to clean. Likewise you will probably need about 20 mins contact time for the reaction to be completed. A little aeration may help the process along as well.

The iron in the water will also compete for the chlorine and this too will need to be filtered out.

You should plan to have a very low residual chlorine leaving the filters so that your SBS dose is kept to a minimum. However given that you may have sulfur reducing bacteria passing through the process the SBS may be a food source and you will still have problems with sulfur fouling on the RO.

A pH of 7 is okay for what you are proposing and i would be trying to reduce it by acid dosing. The range is about 6.7 to 7.3 for conversion to soluble sulfate.

I assume the bariumm is in the sulfate form? If it is this tends to be relatively insoluble and you might be lucky enough to filter some out in the MMF. You probably need to do some further analysis on that, to be certain whether or not a "softener" is the right process to remove the barium.

Turbidity might be an issue for particulate fouling on the RO but this may be reduced with the MMF. That would be something that needs to be investigated a little as well.

There are plenty of other process options that might be effective in overcoming the problems of turbidity , iron, H2S and Barium.
These would include: FeS coagulation and precipitation and filtration , greensand absorption




Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Watro]

Thank you Ash,
I missed to note that the MMF may be used with deep bed media, mixture of Anthracite, Silica, Alumina, Magnetite, etc which is commercially termed as Super flux media, which has exceptional filtration efficiency with higher flux (almost double the regular flux) across the MMF. There are few references of Seawater Pre-treatment plant operating with this media and meeting the SDI. I believe the converted Ferric salts would too be filtered with MMF.

Is this an ideal pH range 6.7 to 7.3? The reports from different wells indicate 6.8 - 7.
Yes, Ba in Sulfate form, kindly clarify what is further analysis mean to decide on Softener.

Regards
Niss

 

[ashtree]

Where i have said :" A pH of 7 is okay for what you are proposing and i would be trying to reduce it by acid dosing." I meant to say i would not be doing acid dosing.
Yes 6.7 to 7.3 is about the optimal pH range. You should get this tested on site not sent off to a remote lab just to be certain.
The MMF will have to remove elemental sulfur, precipitated iron, and turbidity. The Super flux unit may be be suitable but some elemental sulfur will probably get through.

What i mean by the Barium comment is that you need to make sure that it is not already in particulate form which might filter out in which case you might not need a softener. If its not in particulate form than a Strong acid cationic exchange softener might be an option for you.


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Oxidizing with chlorine is generally not economical. However, it will be dependent on the capacity of your system which has not been stated.

Using the water softener will help to reduce the fouling.

Is there any local assistance available that may provide some real experience on this application?

 

[Watro]

@ashtree, it is not established that the Ba is associated with particulate, in order to avoid risk we have SAC resins in the proposed Softener

@bimr, the system capacity is around 5 m3/hr of permeate and Cl2 will be dosed on a flow rate of 8.3 m3/hr. Its not that big system, i believe Chlorination will be cheaper compared to Aeration or H2S removal in a tower with acidification

we dont have any local assistance, we rely on the exp of the OEMs

Thanks

 

[Watro]

Please advise the removal efficiency of H2S by oxidation and filtration. We will have a chlorination break tank with 20 min contact time after chlorination prior to Super flux MM filtration.

Further any idea about the size of Elemental sulfur that would form? The Super flux media will have an efficiency of removal up to 0.2 micron (laboratory scale work consistently removes 99.97% solids down to 0.2 micron in size), however some Nano particulate Sulfur is expected to be <0.2 micron. In such case some oxidized elemental sulfur will form a coating on RO Membrane surface, i believe. I am not sure if that could be remove able with CIP or lead to irreversible fouling. Please share if you have any thoughts on this. In such case CF would be with 0.1 or 0.5 micron as least available

In worst case, acidify the feed water <5 - 5.5 pH and feed in anaerobic condition and oxidize it downstream RO? Will this help. But any contact with air will lead to formation of Sulfur. I am not sure the effect of H2S on SAC resin surface, when passed with low pH

Any other ways to reduce Ba to bring down to Saturation levels with Antisclant, other than Softening.

A preliminary schematic is attached

 

[ashtree]

It is difficult to completely oxidise H2S with chlorine at concentrations above 3mg/l so it is likely that you will get some elemental sulfur in your filters and passing through to the RO.
Sulfur fouling on RO membranes is difficult to remove and is often irreversible. You should not be reliant on the cartridge filters to remove the sulfur either. Cartridge filters are usually installed to provide protection for the RO in case of an upstream failure and not for routine particle removal. Despite having an MMF ahead of the cartridges i would expect that 0.1 micron cartridges will foul quite quickly and will require a lot replacements. The norm would be to have a minimum of about 1 micron.

You could as you propose lower the pH and airstrip the H2S however given the alkalinity a reasonable amount of acid will be required.
Stripping off the H2S will also strip off CO2. Caustic and soda ash or perhaps lime will be required to raise the pH and add alkalinity to prevent corrosion.

If you operate at a lower recovery than the concentration of Barium may be within the capability of the antiscalant to prevent scaling.





Regards
Ashtree
"Any water can be made potable if you filter it through enough money"