Arsenic trap

Silver nanoparticles caged in aluminium can rid water of arsenic

By Indu Mathi S
Last Updated: Saturday 04 July 2015

imageDESPITE an abundance of water filters in the market, access to safe drinking water remains a challenge for India and other developing countries. According to WHO, “Every year there are 2 million diarrhoeal deaths related to unsafe water, sanitation, and hygiene. The vast majority of them are children under five.” IIT Chennai researchers have invented a cheap water filter, which they claim could be helpful in achieving the United Nati ons millennium development goal of sustainable access to safe drinking water.

The filter, described in PNAS on May 6, uses nanomaterial to remove diseasecausing microorganisms and toxic heavy metals from water. It works by constantly releasing silver ions, which are an effective disinfectant, into the water. Several silver-based anti-microbial devices have been designed in the past but have not been viable. One of the reasons being presence of organic and inorganic impurities in water that cling onto nanoparticle surface and hamper sustained release of silver, say the researchers.

To find a way around this technical constraint, the researchers formulated a cage-like nano-composite of aluminium oxyhydroxide–chitosan with silver particles embedded in it. This composite ensures sustained release of silver ions into the water in an amount significantly less than the permissible limit set by the US Environment Protection Agency (EPA). This eliminates a need for secondary filtrations to remove excess silver ions, say the researchers. Silver nanoparticles remain intact as the aluminium cage reduces their contact with chemicals that might anchor on them. “What we have is a complete purifier. This takes care of all contaminants in water—microbial, heavy metal, organics. All of this is done with advanced materials. There is no solution of this kind anywhere,” says T Pradeep, corresponding author of the study. “The device is efficient in the sense that it provides clean water as per EPA standards. It costs just 6-7 paise/litre for microbially as well as chemically safe water.”

However, Ashok Gadgil, division director and faculty senior scientist at Environmental Energy Technologies Division of Lawrence Berkeley National Laboratory in the US says, “The arsenic removal in the PNAS paper was reportedly tested in arsenic-spiked tap-water. In our experience, Indian tap water has pretty low phosphate ion concentration. However, these ions appear in high concentrations in groundwater and compete for the same sites that are intended to capture and remove arsenic.” So, the performance and affordability of the system for removing arsenic from real groundwater would be different from that with spiked tap-water, and those results are not presented in the paper.

Another issue left unexplored in the study is the fate of the arsenic-laden sludge formed after rem oving arsenic from water, adds Gadgil.

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.

  • Dear Team, Congratulations

    Dear Team,

    Congratulations for the feat!! I would request the author /associated team to put a you-tube video showing the mechanism related to this filter and how this technology is unique. I hope that would help readers like me to understand it better, appreciate it further.

    All the best!!!

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Sir, It is really an

    Dear Sir,
    It is really an important development in the field of Stand Alone Water Filter.
    However, I would like to know about its efficacy with water having high turbidity and ground water having high iron content. Is there any scope of impacts like, clogging of filter media due to turbid water and more specifically due to ferric iron content?
    Is there also the backwash facility? Moreover, what might be the life of such filter media for releasing the Silver Ion in case of raw water with different quality perspectives, like Alkalinity, Hardness, TDS etc.
    So I would be more interested for using the same in different parts of Assam to tackle water quality related issues with special emphasis on Iron content of groundwater.
    Thanking All.
    Best Regards.
    Nripendra Kumar Sarma
    Guwahati, Assam, India

    Posted by: Anonymous | 7 years ago | Reply
  • While appreciating the

    While appreciating the enthusiasm of youngsters in designing a filter to remove arsenic using nano technology, I want to place on record there were several efforts on water purification in the past which involved high technology. But nothing beats heating water. There were sari filter which was given wide publicity.

    Developed for use in Bangladesh, the cloth filter is a simple and cost-effectiveappropriate technology method for reducing the contamination of drinking water. Water collected in this way has a greatly reduced pathogen count - though it will not necessarily be perfectly safe, it is an improvement for poor people with limited options.
    The method used in Bangladesh is as follows: an old sari is folded to make four or eight layers. The folded cloth is placed over a wide-mouthed container used to collect surface water. It is usually sufficient to rinse the cloth and dry it in the sun for a couple of hours. In the monsoon seasons, it may be advisable to use a cheap disinfectant to decontaminate the material.

    The preferred cloth is used cotton sari cloth. Other types of clean, used cloth can be used with some effect, though the effectiveness will vary significantly. Used cloth is more effective than new cloth, as the repeated washing reduces the space between the fibres.
    The cloth is effective because most pathogens are attached to particles and plankton, particularly a type of zooplankton calledcopepods, within the water. By passing the water through an effective filter, most cholera bacteria and other pathogens are removed. It has been demonstrated to greatly reduce cholera infections in poor villages where disinfectants and fuel for boiling are difficult to get.
    In sub-Saharan Africa where guinea worm dracunculiasis infections are endemic, infection is prevented by use of a nylon mesh with pore size of approximately 150 ╬╝m to filter out the copepods that host the parasite.

    An old cotton sari, folded, creates a smaller effective mesh size (approximately 20-╬╝m). This should be small enough to remove all zooplankton, most phytoplankton, and thus a large proportion of the cholera in the water (99%, according to laboratory studies). However, the nylon net with the larger mesh size was found to be "almost equally effective."
    The cloth filter provides less than ideal purification on its own - usually filtering is an initial step, to be followed by further disinfection. However, where there are no other options, water professionals may consider that it is "of course, better than nothing"

    The cloth filter has been studied and reported on by Rita Colwell and Anwar Huq from the University of Maryland Biotechnology Institute, together with other researchers from the USA and Bangladesh. They report that:
    It is common practice in villages in Bangladesh to use cloth, frequently a flat, unfolded piece of an old sari, to filter home-prepared drinks.

    The researchers studied the application of this technique to drinking water, with folded cloth. They studied the pore size of the cloth, the effect of folding the cloth on the effective pore size, the ability of the cloth to remove particles and plankton, as well as the effect on rates of cholera when used in a Bangladesh village(Source: Wikipedia).

    In these methods as well as Brass Vessel method the draw back is certain bactyeria are heat sensitive. Unless thermal energy used,you canÔÇÖt get safe drinking water.

    I designed a low-cost solar disinfection gasdget which uses Solar Thermal and UV. It is cost effective and can be fabricated locally.
    Here are details:
    Safe Drinking for All through Solar Disinfection
    by Dr. Anumakonda Jagadeesh
    Every 8 seconds, a child dies from water related disease around the globe. 50% of people in developing countries suffer from one or more water-related diseases. 80% of diseases in the developing countries are caused by contaminated water. Providing safe drinking water to the people has been a major challenge for Governments in developing countries. Conventional technologies used to disinfect water are: ozonation, chlorination and artificial UV radiation. These technologies require sophisticated equipment, are capital intensive and require skilled operators .Boiling water requires about 1 kg of wood/liter of water which results in deforestation in developing countries. Also halazone or calcium hypochlorite tablets or solutions (sodium hypochlorite at 1 to 2 drops per liter) are used to disinfect drinking water. These methods are environmentally unsound or hygienically unsafe when performed by a layperson. Misuse of sodium hypochlorite solution poses a safety hazard .
    Treatment to control waterborne microbial contaminants by exposure to sunlight in clear vessels that allows the combined germicidal effects of both UV radiation and heat has been developed and put into practice .The SODIS system(Solar Disinfection of water) developed by scientists at the Swiss Federal Agency for Environmental Science and Technology(EAWAG) recommends placing PET bottles (usually discarded mineral water/beverage bottles) painted black on one side, aerating (oxygenating) the water by vigorous shaking three fourths water filled bottles and then filling them full and placing them in sunlight for 6 hours. In this method, the water is exposed to UV radiation in sunlight, primarily UV-A and it becomes heated; both effects contribute to the inactivation of water borne microbes. The use of PET bottles requires periodic replacement because of scratches and they become deformed if temperature exceeds 650C. Also dust accumulates on these bottles in the groves (provided for strength). The PET bottle mineral water manufacturers print on the label, ÔÇÿcrush the bottle after useÔÇÖ in India. Unless cleaned thoroughly everyday, PET bottles turn brown over usage rendering lesser transmission of sunlight.
    Microorganisms are heat sensitive. Table 1 lists up the required temperature to eliminate microorganisms within 1,6 or 60 minutes. It can be seen that it is not required to boil the water in order to kill 99.9% of the microorganisms. Heating up water to 50 ÔÇô 60C (122 ÔÇô 140F) for one hour has the same effect.
    The most favorable region for solar disinfection lies between latitudes 150 N/S and 35 0 N/S. These semi-arid regions are characterised by high solar radiation and limited cloud coverage and rainfall (3000 hours sunshine per year).The second most favorable region lies between the equator and latitude 15 0 N/S, the scattered radiation in this region is quite high (2500 hours sunshine per year).
    The need for a low-cost, low maintenance and effective disinfection system for providing safe drinking water is paramount, especially for the developing countries.
    Materials And Methods
    The innovative solar disinfection system has a wooden frame of length 2 ft,width 1 foot and depth 6 inches with bottom sinusoidal shaped polished stainless steel (curvature slightly larger than standard glass wine bottles, about 5 inches diameter) . On the front is fixed a glass sheet having lifting arrangement with a knob (this glass enclosure will protect the glass bottles from cooling down due to outside wind). There are screws which can be used to keep the contents airtight. On the backside a stand is fixed which will help the unit to be placed according to the latitude of the place for maximum solar insolation.
    In this method clear glass bottles (used wine bottles) are utilised instead of PET bottles as the former are easy to clean, lasts longer and are available at a low cost in India. Solar disinfection is more efficient in water containing high levels of oxygen; sunlight produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive forms of oxygen kill the microorganisms. Aeration of water is achieved by shaking the 3/4 water filled bottles for about 20 seconds before they are filled completely.
    The unit has an advantage in that the rear reflection stainless steel will pass the light through the bottles a second time, to both increase exposure and eliminate shadowing. This reflection system will increase the light intensity minimum 2 times.
    It has been widely experimented and established by earlier researchers that at temperature of 50C (122F), pathogenic microbes are inactivated. The temperatures which cause approximately a 1-log decrease in viability with 1 min are 55C (131F) for protozoan cysts; 60C (140F) for E.coli, enteric bacteria, and rotavirus; and 65C (149F)for hepatitis A virus .Negar Safapour and Robert H.Metcalf in their extensive studies reported enhancement of solar water pasteurization with reflectors and the crucial role of temperature above 50C (122F) in the elimination of pathogens.
    The unit is placed in the south direction (in India) around 10 am with inclination equal to the latitude of the place. The glass bottles are filled with water three fourths and shaken for 20 seconds to generate oxygen and then completely filled. The water filled bottles are fixed with caps and put in the groves of the solar disinfection unit. The glass door is closed and clipped airtight. Water bottles are removed from the unit at 3 pm and taken to a cool place and the disinfected water transferred to a clean vessel, covered for later usage.
    Suspended particles in the water reduce the penetration of solar radiation into the water and protect microorganisms from being irradiated. Solar disinfection requires relatively clear water with a turbidity less than 30 NTU.To remove turbidity traditional methods of putting the paste from seed of strichnos potatorum (Nirmal seeds) by rubbing the seed on a rough stone with water is used. The method is effective, turbidity settles down in half ofv an hour and the seed are available in plenty in forests in India besides being inexpensive.
    Sample Testing
    Water samples from the solar disinfection unit were tested with Most Probable Number (MPN) technique. To estimate the number of aerobic organisms present in water, Pour Plate Technique has been used.
    The test results of various water samples disinfected are presented in Table 2. In the samples from Ambattur Bore Water, Ambattur Well Water, Anna Nagar Bore Water and Kavaraipettai Bore Water, since they are highly contaminated, further dilutions were not carried out. The dilution should be done only when the MPN indicates more than 1100 organisms/100 ml. For these samples only log reductions can be calculated. As regards R.S.M.Nagar Bore Water and Thathai Manji Well Water, the percentage of reduction are 85 and 86.95, which indicates that the water is less contaminated. As MPN index shows less than 3 organisms for 100 ml, after solar disinfection of water, the samples are free from coli forms. The results of Avadi Waste Water and Perambur Waste Water show 3 log reduction (99.8%) and 4 log reduction (99.993%) respectively.
    For comparison PET and Glass bottles were placed with black background as well as in the innovative device I developed. It can be readily seen that solar disinfection of water is complete with the device compared to open.
    Eradication of coli forms from well water, bore water and waste water has been reported from test results. The results confirm that there is 4-log 10 reduction of coli forms in the waste water after solar disinfection..Maximum temperature occurs around 1 pm. Though 6 bottles were used in the system(each of 1 liter capacity),larger units with up to 100 bottles can be designed. The unit destroyed 99.99% of bacterial coli forms both in well water and waste water samples in 5 hours.
    The innovative solar disinfection system has the advantages like:
    1. The unit is portable,
    2. It is cost-effective.
    3. It can be fabricated in South India for US $20.
    4. The unit incorporates the principle of reflection to increase solar intensity and has protection from wind which results in temperature rise inside the unit,
    5. Larger units can be manufactured, Used glass bottles withstand higher temperatures and are available in plenty each for 2 US cents in South India, Since all the materials are available locally, the unit can be manufactured locally with local people.
    6. Temperatures above 30 degrees C occur in south India for more than 10 months in a year and as such this innovative solar disinfection unit will be a boon in this region.
    Dr.A.Jagadeesh Nellore(AP),India

    Posted by: Anonymous | 7 years ago | Reply
  • To Nripendra Sarma: About

    Nripendra Sarma:

    About Turbidity, the best and simple method is to rub the seed of STRICHNOS POTATORUM with water on a hard surface and put the paste in the turbid water. Turbidity settles down. The clear water is transferred to another container. This we practiced for years when we were in Nuzvid,Andhra Pradesh,India where we used to get water from a water tank called ERRA CHERUVU(Red Tank). Another method in use in Sudan is Moringa oleifera seeds. These traditional methods which stood the test of time need to be validated by Scientific Study.

    Also Tulasi leaves(Ocimum Sanctum) are known to have water purification properties.

    Dr.A.Jagadeesh Nellore(AP),India

    Posted by: Anonymous | 7 years ago | Reply
  • To Dr. A

    Dr. A Jagadeesh,

    Thanks a lot for your update. However, the facts remains, is that the Chennai IIT Team under the able Leadership of Dr. Pradeep, has developed the 'Arsenic Trap', which can take care of Microbial, Heavy Metal and Organics contaminants through this Stand Alone Water Filter. It does not require any secondary filtration also. Moreover, the unique feature of the same is reported to be the cost involvement @ 6/7 paisa per litre to facilitate microbial and chemically safe drinking water. It is really a remarkable approach / efforts.
    The only issue may perhaps be the upper limit of Arsenic contamination, which can be treated well in such 'Arsenic Trap'. Another issue might be the safe disposal of the arsenic laden sludge from it and also it's efficiency to get the better of the competition from Phosphate concentration. These issues are raised by Ashoka Gadgil also.
    I hope, all such issues and it's applicability for all kinds of water with different physico-chemical and microbial properties, will be overcome in a much result oriented approach.
    The facts referred by you with regards to the 'Cloth Filter' and SODIS Method are also quite relevant to take care of the Microbial Contamination of water. There is no doubt that they are very much effective, especially during emergencies like flood etc.
    Thanks a lot for referring the traditional methods like using 'Moringa Olifera', 'Tulshi Leaves' etc. More importantly the 'Tulshi Leaves' can very well be utilised to check the presence of Iron in Grounwater also as home based method.
    Finally, my Best Wishes to such noble endevour from Chennai IIT Team to facilitate us the 'ARSENIC TRAP' with all Success.
    Thanking you.
    Best Regards.
    Nripendra Kumar Sarma
    Guwahati, Assam, India

    Posted by: Anonymous | 7 years ago | Reply
  • To The Chennai Team of

    The Chennai Team of Experts

    I would like to know the updates / inputs with regard to the probable challenges, already mentioned in the discussion.
    I am interested to know about the results from the field level application of such 'Arsenic Trap'.
    Thanking you.

    Posted by: Anonymous | 7 years ago | Reply
  • Arsenic is a problem in the

    Arsenic is a problem in the public water system here in the states, especially in my hometown. I'd love to see this type of technology become accepted by private and governmental institutions. Our drinking water is what makes us thrive or hinders our health tremendously. This information needs to seen by the majority, as I believe there is a lot of ignorance in regard to drinking water and the affect it has on our health. I have also heard of the method of using Moringa to purify water.

    Posted by: Anonymous | 7 years ago | Reply
  • How exactly do the composites

    How exactly do the composites and nanoparticles work at removing impurities?

    Posted by: Anonymous | 6 years ago | Reply