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Wednesday, September 14, 2005

Arsenic Remediation

After spending some time on the internet looking at what has been done with respect to arsenic remediation in drinking water, I can safely say that a lot of time and money has been spent to solve a purvasive problem that afflicts a great many people with only some success. Countries afflicted by this problem include Bangladesh, India, Mexico, Chile, and Mongolia. Currently, Bangladesh and India have recieved the lion's share of attention due to the severity of the problem in those areas.
Remediation systems have ranged from simple iron/sand filtration units at the household level to larger RO systems for villages. The only phytoremediation system that I read about utilized brake fern to uptake arsenic through its root system. It appeared useful for removing arsenic from soil (which would reduce the amount of arsenic in groundwater due to leaching). I haven't run across any reports that water hyacinth is being used in a real world application to remove arsenic. Some of the pitfalls that have plagued current remediation systems revolve around a good understanding of the groundwater chemistry before bring the system on-line. High concentrations of ferrous iron and mangenese will clog up systems when aerated. It has been noted that high phosphate concentrations also shorten the lifespan of some systems. I think it would be very prudent to have a good understanding of the groundwater chemistry before we tried to install a real-world system. Hach methods (using a spectrophotometer) can provide results in the field at a reasonable cost for iron, mangenese, and phosphates. The Hach method for arsenic would not be very useful in the field due to the complexity of the analysis and the hazardous waste disposal of reagents.
I have emailed Dr. Haris, whose paper has prompted all this activity at CWB, to gather additional information about his research that was not presented in the paper. He has not responded yet, but I think his answers will be very helpful to constructing a viable remediation system. I would propose that we think small (we would need to define that in terms of gallons of water treated or people served) at first to work out the kinks before trying our hand at a larger
system. I would also propose that the system be operated via renewable energy sources. I have some thoughts on what a "first draft" system could look like, but I have to go now. I appreciate any feedback. Thanks
Brian

16 comments:

  1. Along the lines of renewable power for this system... I was also thinking that since Treadle Pumps (see Sci. Amer. Sept. 2005, p84-91) are so popular in many of these same areas, that it would be clever to devise a Treadle Pump powered remediation system. These pumps are cheap $25, human powered, and widely used for small villages and farms. Obviously, remediation systems that require electricity will need a solar or wind-up power supply. Just a thought.

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  2. When you mention powered by renewable energy sources, do you have suggestions which would work well in the countries you mentioned?

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  3. ooops- Shawn beat me to the punch... I was thinking of human power too.

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  4. I have not heard of a Treadle Pump. Thanks for the reference I'm going to check it out. I was thinking solar would work, but I will check statistics regarding sunny days in these countries (they have got to be better than Vermont!!) All the pumps and switches in a system would be 12VDC, cutting out the need for an inverter.The number of panels and batteries would be dependant on the size of the system. My initial thought was to place two 55-gallon drums full of hyacinth root in series with a 12VDC well pump. The effluent from the second drum would be pumped into a large storage container for use as potable water. It might also be wise to put a sediment filter and/or a cartridge filter in line before the first drum to eliminate materials that would clog up the drums (silts, fines, iron, manganese,etc..). The pumps would be interlocked to allow the influent water appropriate residence time in the drums before being pumped out to the storage container and a high level switch on the storage tank to prevent an overflow. This is just a rough sketch, so please let me know if this is in alignment with your ideas/goals. Thanks
    Brian

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  6. Here is more info about treadle pumps. The online version of the Sci. Amer. article pointed out that in Bangladesh alone ca. 1.5 million farmers have purchased treadle pumps. This site has all the details. Apparently these pumps can pump to a max. height of 7m, but work best around 3 meters. This should be plenty for a simple sorbent tank system. I am still going over the Haris paper with a fine tooth comb.

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  7. Shawn,
    Thanks for the info. Do you have a more detailed Haris paper than the one in C&E News? I'm going to send you the email I sent to Dr. Haris. Perhaps the paper you have can answer some of the questions.
    Thanks
    Brian

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  8. I think parts of Canada and likely the U.S. as well are also afflicted with this problem. Even some of the Gulf Islands, not far from urban areas like Victoria or Seattle, rely on well water, I understand, which is some locations contains arsenic. The reason I mention this is because pilot projects to remediate these problems might be worth starting off here, to minimize travel costs. Plenty of students nearby, too. Then bring proven solutions to the countries mentioned.

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  9. Heather,
    I concur with your idea of developing a pilot study closer to home before we try to go halfway around the world. I'm sure we'd want to modify our approach after conducting a pilot study and it would be less costly to do it in our backyard. Thanks
    Brian

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  10. I went to Home Depot this weekend and found an RO system for a private home (11 gal/day) from GE "Smart Water" for $150. They report 99% arsenic reduction. Filters reportedly last for 600 gallons. http://www.geappliances.com/smartwater/model_fs.htm?PXRQ15F
    if you want to take a look.
    Any system we develop should target this price/gallon and level of purity. Otherwise we would be better off just buying it off the shelf.

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  12. I think the cost for the RO system is $0.25/gallon. I went on the website Mark listed and the system seems very straight-forward. However, the arsenic reduction claims don't specifiy the initial concentration in the water supply. If the filter is capable of removing 99% at 50 ug/l arsenic, will it be capable of removing 99% at 200 ug/l for the same length of time? The info I've scoured on the web suggests that RO systems do work, but have larger waste streams than other technologies. However, we would need to address the waste issue in any system CWB designed as well.
    Prior to setting up our solar PV array, my wife and I hauled water from the brook behind our house for drinking, cooking, showering, toilet flushing, etc... I think we used about 15 gallons during a normal day (maybe more on weekends). I suspect that is high compared to rural developing areas which wouldn't necessarily have showers or toilets to contend with but it could be a starting point for design purposes. The small system I proposed previously would supply considerably more than that on a 24 hour basis (assuming ample water in the well). I am working up a cost sheet for materials that I will put in an excel spreadsheet and email to the people on the Arsenic Team. Thanks
    Brian

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  13. The more I look around, the more I find other groups doing similar things to what we are thinking about doing. Shawn's link above leads to IWMI. A quick internet search on treadle pumps found another group, Appropriate Technology International, who are introducing the pumps. The Water Relief Network I posted about, plus their links to other groups. It is overwhelming. I'm worried that we are "reinventing" the wheel, and everybody else is already driving around in cars. What do you all think about this?

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  14. This is nice brainstorming for the arsenic problem. We had the issue come up briefly on UsefulChem.

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  15. Here's a link to the brake fern arsenic remediation article: http://www.sciencedaily.com/releases/2001/02/010201071544.htm
    ScienceDaily: Research Shows That A Fern Soaks Up Deadly Arsenic From Soil.

    Bego

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  16. Sezer ÖZGENÇ (Chemist / Student)Sunday, September 9, 2007 at 9:32:00 AM PDT

    I think parts of Canada and likely the U.S. as well are also afflicted with this problem. Even some of the Gulf Islands, not far from urban areas like Victoria or Seattle, rely on well water, I understand, which is some locations contains arsenic.The reason I mention this is because of the pilot projects to remediate these problems might be worth starting off here, to minimize travel costs. Plenty of students nearby, too. Then bring proven solutions to the countries mentioned.

    Sezer ÖZGENÇ
    Celal Bayar University,Turkey
    Chemist(Student)

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