Iron & Manganese Removal

[semo]

Just curious; but, has anyone had any dealings good or bad with using membrane technology to filter iron/manganese from potable water applications?

I've done many plants using conventional methods (aeration/sedimentation/filtration, oxidation/greensand, etc.); but, have only seen membrane technology for this process as illustrated by a couple membrane providers.

The iron/manganese after oxidation forms a floc that is light and sticky. It seems to me that this will have a detrimental affect on the membrane, causing it to foul early.

 

[aussiemike]

I know of at least one RO plant here in Australia that was rendered virtually useless by the presence of iron and manganese in the borewater feed.

The feedwater was delivered to a break tank upstream of the RO unit - heavily aerating it in the process - and presumably increasing the fouling tendency.

Minimising aeration upstream of the plant would seem to be a good idea.

A plant incorporating direct bore feed (without the break tank) to the pre-filtration will soon be commissioned about 100km from the plant previously mentioned. I'll tell you how well it works in a couple of months.

Cheers
Aussie Mike

 

[matty77]

Aussie Mike,
Out of interest, do you know what levels of iron and manganese were present in the bore water? Did they follow the aeration step with media or other types of filtration?
We are currently building RO units for desalinaiton of saline bore water for farms etc and are interested in any war stories as well as lessons learned.

Thanks

Matty 77

 

[semo]

Thank you AussieMike. That is kind of what I feel would happen. I've seen some systems that promote aeration, sedimentation, and then filtration with membranes and I don't see how that can work without problems. It also makes the treatment cost just as high or higher than the same system with standard media filtration.

I also think that the direct bore method would depend upon the water characteristics and the pretreatment chemicals. If the iron/manganese is oxidized in any way, there could be problems. Using low pH membranes I think would be a requirement to slow the oxidation process.

Let me know how that system turns out.

Thanks,

Semo

 

[sbush]

When you use the term "membrane technology", it encompasses a lot of technologies that are centered around various membrane-based components. Aussiemike refers to one, reverse osmosis. I too am not aware of any reverse osmosis systems that work well in the presence of iron and manganese. However, there are several others that do.

Hollow-fiber and tubular ultrafiltration systems work well when configured for high velocity-tangential flow. This is typically referred to as a "feed and bleed" operation. The high shear velocity keeps the metal oxides from plugging the boundry layer at the membrane surface. This results in substantially higher flux rates over single-pass configurations. These polysulfone membranes are then cleaned periodically with a mild acid solution, in order to restore flux. My experiences are based on the Romicon hollow-fiber membranes manufactured by Rohm & Haas. They are no longer available from Rohm & Haas, but I believe that Koch (Wilmington, DE) purchased the rights to make them.

Another method, involves using dynamically-formed membranes on a tubular ceramic substrate. As with the above, this method is typically set up using the feed and bleed configuration for high velocity tangential flow. In my personal experience, we were primarily removing boron from a nuclear reactor cooling water system, however, iron and manganese were present and easily removed by the process. As with all dynamically-formed membrane processes, the flux rate is re-established by dissolving the old membrane and then forming a new one.

About five to ten years ago, Smith & Loveless had purchased a technology from overseas (Denmark, I think). It is a membrane technology that they were promoting for reverse osmosis pretreatment to remove iron, manganese and to reduce silt. They also recommended it for municipal drinking water, particularly iron and manganese. As I recall, it was based on hollow-fibers and it appeared to be single-pass configured. It had a quirky name (not Zee-Weed, but something like that). It used to appear in trade magazines, but I haven't seen it lately.

And finally, electro-dialysis reversal is another membrane technology that is proven to work well on very high iron and manganese bearing waters. I don't have any direct experience with this technology, but I have read numerous testimonials to it's success with a wide range of typical membrane foulants, including iron and manganese. There are a number of communities in Texas that have extremely high TDS coupled with iron and manganese and, after failing miserably with reverse osmosis, electro-dialysis reversal was the only method that worked.

For obvious reasons, if you are just trying to remove iron and manganese from water, the conventional filtration-based or sedimentation-based methods are the least expensive ways to go. But, if you need to remove other contaminants that can only be removed by membrane, as well as iron and manganese, then the membrane approach can be worth the cost.



S. Bush

http://www.water-eg.com

 

[sbush]

Here is a link to an article from Water & Waste Digest concerning electrodialysis reversal systems used in municipal water treatment plants. The article specifically mentions a plant in Albuquerque, NM where EDR is being used to reduce iron and manganese, as well as hardness and TDS.

http://www.wwdmag.com/wwd/index.cfm...5925220/fuseaction/showArticle/articleID/3692

S. Bush

http://www.water-eg.com

 

[semo]

Thanks SBush. Sorry I wasn't back sooner; but, been a busy summer lately.

I'm assuming that with any of these membrane technologies, the iron must stay in solution (no oxidation) for treatment.

I'm well versed in conventional iron/manganese treatment methods; but, have been curious as to any membrane capabilities.

 

[sbush]

Both, soluble and insoluble. Sorry, I can't remember the concentrations.

S. Bush

http://www.water-eg.com

 

[brennanpe]

Here's the link to the Koch Membrane Systems website regarding:

http://www.kochmembrane.com/mww_purification.html#inorganic