Arsenic contamination: points for consideration

Arsenic Contamination: Points For Consideration

Removing Arsenic from Water

Regarding arsenic contamination in the ground water of Bangladesh and its effect on health, the writer contacted several eminent experts who took time out to provide research papers and other detailed information on possible options that may help us to resolve the problem.

A number of papers are available on arsenic contamination in drinking water, especially in Western Canada where there is a problem similar to our own and in Argentina. The research team in Argentina have opted for small solar stills and community stills as well for removing arsenic. Whether or not this will be feasible here must be determined remains to be seen. Another possibility is suggested by Tom Lawand of the Brace Research Institute in Quebec, Canada, who notes that since iron filings absorb arsenic, it may be possible to develop a simple system for absorbing arsenic by passing drinking water through filtered sections containing iron filings and obviously sand, etc. to remove debris.

UV Disinfection

Should the decision be taken for reverting to the use of surface water, the problem of faecal contamination of the water bodies must be faced. Fortunately, since the Water Decade the overall emphasis of researchers changed from capital-intensive urban type water distribution and water-borne sewer systems to low-cost, locally-maintained alternative technologies. Among such proposals is a water disinfection system that uses ultraviolet light.

The Lawrence Berkeley Laboratory (LBL) in California, USA has plans to introduce a UV system in rural villages in India. The goal of the project is to design and field-test a water disinfection device for developing countries that is durable, easy to use, inexpensive and which can be constructed and maintained locally. Although it began its research in the summer of 1993, the UV disinfection project team increased its efforts in 1993, when an outbreak of cholera was reported in India, Thailand and Bangladesh (Altman, 1993). A year later, the cholera epidemic continued to be a problem in India - in the state of Bihar, and between the months of May and August 1994, approximately 2200 people died from cholera (Times of India, 1994).

The UV disinfection research effort received funding support from the United States Agency of International Development, the United States Department of Energy, the Rockefeller Foundation, the Joyce Mertz-Gilmore Foundation, and the Pew Foundation's award to project-team member, Dr. Ashok Gadgil. General Electric (US), and Philips (the Netherlands) donated UV lamps to the project for field tests. The researchers are establishing the program in India and hope to expand to other countries that need help combating water-borne pathogens such as Bangladesh and Thailand. In addition, the project has recently received an expression of USAID interest in supporting test sites in Mexico. As in Asia, cholera is a problem in Latin America, particularly in Peru.

The researchers estimate that the UV disinfection system can provide clean drinking water for approximately 5¢ per villager annually. The disinfection process is highly energy-efficient and uses approximately 40,000 times less primary energy than the standard alternative-boiling water over a cook-stove. The provision of a simple and inexpensive method for disinfecting drinking water will save the lives of many people, particularly the lives of children, who are the most susceptible to diarrhoeal diseases. Because women are primarily responsible for providing their families with water as well as bearing and caring for children, the UV disinfection system has the potential to greatly improve women's quality of life by reducing their workloads as well as the number of children they lose to water-borne diseases.

The disinfection system has proved successful in the laboratory. Although the equipment is also expected to perform well in the field, the primary challenge to introducing this technology to rural communities will be integrating the technological system into the community structure. The community management of the disinfection system should ensure access for all villagers and provide built-in incentives for maintenance and repair.

However, before contaminated water enters the UV disinfection chamber, the water must be filtered to reduce turbidity. The turbidity in surface water can be reduced by using an appropriate sand filter. In the disinfection chamber, water is disinfected by exposure to UV light. In the present design, the UV chamber is constructed from sheet metal and contains a UV lamp under a reflector. A shallow stream of water flows under the UV lamp through channels in a metal tray. Although ultraviolet disinfection may not be the best choice for water disinfection in all circumstances, it could be the most viable and preferred alternative in the present situation.

Two firms in India have taken up the manufacture of UV devices of LBL design. These units are now being field-tested in India. The UV project team originally comprised Dr. Ashok Gadgil, Dr. Art Rosenfeld, and Mr. Derek Yegian. The present team includes Dr. Gadgil, Mr. Yegian, and Ms. Catherine Lukancic. The LBL project team is now working in the laboratory to significantly lower the system cost without compromising performance. In the fiscal year of 1995, the researchers hope to receive feedback regarding the field performance of several test units at various rural locations in India. Because the UV system uses approximately 40,000 times less primary energy than the common developing-world practice of boiling water over a cook-stove, UV disinfection has other significant benefits. On a local level, the substitution of UV disinfection for the burning of biomass fuels reduces indoor and outdoor air pollution as well as pressure on the forests; globally, such a substitution reduces emissions of carbon dioxide, a greenhouse gas associated with global climate change.

An alternative to UV disinfection is solar radiation. This is a simple and effective method that can be applied to combat water-borne and water related diseases prevalent in Bangladesh. Dr. O. Odeyemi, a visiting UNU Fellow at the Brace Research Institute in Quebec, Canada has focused mainly on the design and adaptation of systems that can be used and maintained by the 1.4 billion inhabitants of rural areas of the world. One such appropriate technology is based on the findings of Acra et al (1984) of the American University of Beirut, Lebanon. They found that exposure of drinking water in a transparent container to a few hours of sunshine would rid the water of enteric bacteria. The process is so simple and it may be an immediate answer to the numerous incidence of preventable water-borne and water related diseases prevalent in the developing areas of the world and it is a virtually costless way to render contaminated water fit for human consumption.

The technique involves exposing transparent glass or plastic bottles of water obtained from nearby streams and other sources, for a period of 2 to 4 hours to full sunlight. It has been noticed that under these conditions, harmful pathogenic organisms that may be present in the water are killed, provided the initial degree of water contamination is not excessive. Recent reports from Canada say they have had great success with transparent plastic bags filled with water.

A summary of the experimental procedure of Acra et al (1984) is as follows:

One to two litres of water contained in transparent containers were deliberately contaminated with municipal sewage and exposed to direct sunlight for some hours to monitor solar kill of enteric bacteria.
Containers of various sizes, shapes, and colours were employed. These include Pyrex glass, glass and plastic bottles, locally made glass vessels with a spout commonly used for drinking water, and polyethylene bags.
Control experiments consisted of similar sewage-laden waters in containers kept in the dark and under room lighting.
Incubation period was generally from 09:00 hours to 14:00 hours, coinciding with hours of high light intensity.
Bacteriological analysis was done at zero time and then at every 15 to 30 minute intervals.
The standard plate count and membrane filter technique were employed for estimating total bacteria and coliform bacteria, respectively.

It should be noted that all the containers were kept in an upright position and left open-mouthed, but the polyethylene bags were laid flat on the floor, tightly sealed.

According to Acra et al. (1984):

99.9% of coliform bacteria were killed after 95 minutes of exposure to sunlight, but it took 630 minutes to achieve the same level of destruction under room lighting.
Under direct sunlight 99.9% kill of total bacteria was achieved in 300 minutes compared to 850 minutes under room conditions.
In complete darkness the coliform bacteria died out naturally but at a very slow rate, while the total bacterial density tended to increase especially during the first 60 minutes.

In similar exposure-to-sunlight experiments, the time taken to achieve complete destruction of other enteric bacteria were as follows:

Pseudomonas aeruginosa, 15 minutes
Salmonella flexneri, 30 minutes
S. typhi and S. enteritidis, 60 minutes
Escherichia coli, 75 minutes
S. paratyphi B, 90 minutes
Aspergillus niger, 3 hours
A. flavus, 3 hours
Candida and Geotrichum spp., 3 hours
Penicillium suspension required 6 to 8 hours of exposure.

The following factors were considered significant and relevant by Acra et al, in the solar destruction of the above organisms:

The intensity of sunlight at the time of exposure which in turn depends upon the geographic location (i.e. latitude), seasonal variations, cloud cover, the effective range of wavelengths of light, and time of day.
The kind of bacteria being exposed, the nature and composition of the medium, and the presence of nutritive elements capable of supporting the growth and multiplication of the organisms.
The type and characteristics of the containers e.g., colour, shape, size, wall thickness and transparency to sunlight.
Clarity of the water (i.e., degree of turbidity) and water volume and depth.

The tentative findings of INRESA researchers show:

Solar radiation seems to exert germicidal effects on coliform bacteria and also on total bacteria populations, with the former being more susceptible than the latter.
Bactericidal action of solar radiation may take only 3 hours on a clear sunny day or several longer hours on a cold cloudy day.
Bacteria seem to be more rapidly inactivated by solar radiation in distilled water than in stream or river water due to the presence of suspended particles in the latter. Bacteria also appear to be more susceptible to solar inactivation in autoclave-sterilized river water than in non-sterile water.
Sewage water may not be completely disinfected by solar radiation because of its high turbidity which can exert attenuating effects on the transmission of the rays of the sun, and also due to the presence of nutritive elements in the sullage, thus encouraging microbial proliferation. Therefore, sewage or any turbid water samples should be clarified e.g. by filtration through charcoal, clay or sand, prior to exposure to sunshine in order to achieve a reliable solar decontamination (Odeyemi, 1986).
Individual pure cultures of bacteria such as E. coli, S.Typhi, S.aureus and S.flexneri appear to be more readily inactivated by solar radiation than the mixed cultures of organisms.
The period of most rapid decline in bacteria population also coincides with the hours (10:00 to 13:00) of high insolation in most of the cases. Hence it is advisable to expose contaminated water samples to sunshine during the predetermined hours of high insolation which is generally between 10:00 and 14:00 hours.
It is possible to achieve a complete decontamination of a fairly clarified water without any danger of bacterial regrowth, if the disinfected water is properly stored.
An improperly disinfected water may have substantial increase in its bacterial density during overnight storage, i.e. the morning after. Therefore, in areas or periods of low solar intensity, it is advisable to expose water samples to sunshine for several hours or days prior to consumption.
It seems also that the vertical or horizontal positioning of water bottles exerts no influence on the rate of solar destruction of bacteria.
Solar radiation rather than temperature seems to play an essential role in the demise of bacteria in water samples exposed to sunshine. In fact the highest water temperature recorded throughout the period of this investigation was 38oC on 14 August, 1986 which is far below the thermal death points of most bacteria except psychrophiles. Cotis (1986) also reported that a water temperature of 39o has no effect on the bactericidal action of solar radiation. It should be noted though that the temperature of the water samples exposed to sunshine (highest 38oC) was consistently higher than the ambient air temperature (highest 28.5oC).
Though the investigation of exposure of the protozoan parasite to solar radiation was not conclusive , nevertheless it appears that the cysts of Giardia muris may be susceptible to solar inactivation. Further studies are necessary to confirm this observation.
The Swab and Count technique (see Appendix 1) appears to be a fairly accurate and reasonably suitable method of assessing solar disinfection of drinking water mainly because of its rapidity and also because of its relative sensitivity, ease of use, simplicity, time and labour saving. The method which seems to be more suitable for evaluating coliform bacteria, which incidentally are the indicators of faecal pollution of water, than for enumerating total bacteria. It should be mentioned also that the technique is recommended by Double Integral Sanitation Ltd., for detecting and identifying many contaminating micro-organisms found in the pharmaceutical, hospital, restaurant, food and dairy industries.

In conclusion, it should be mentioned that complete decontamination of water samples was not achieved in many of the cases investigated because of weak and diffuse solar radiation and low ambient temperatures during the period of the study. For instance, the only time when there were five straight days of sunshine was from 16 to 20 August, 1986. Most of the summer was characterized by considerable cloud coverage, incessant rainfall, and high humidity. Montreal, Canada, lies on latitude 45oN, an area that experiences a relatively low insolation due to frequent and extensive cloud cover which exerts diffusional and attenuating effects on the radiation (Acra et al., 1984, Odeyemi, 1986).

Fortunately however, most of the developing countries of the world lie between latitudes 35oN and 35oS, where solar radiation is very high, with some areas receiving about 3,000 sunshine hours per year (Acra et al, 1984). This type of investigation should therefore be carried out in such areas of bountiful sunshine where incidentally, most of the people expected to benefit from solar disinfection of drinking water, live. As the amount of sunshine needed should be in excess of 500 watts per sq.m. for several hours around mid-day, it is for our local scientists to determine if we have enough sunshine to support solar disinfection systems the year round.

Acknowledgements:

Otto Ruskulis of the Intermediate Technology Development Group - UK
Tricia Jackson of the Water Engineering Development Centre, Loughborough University, UK
Tom Lawand of the Brace Research Institute - Dept. of Chemical Engineering, Quebec, Canada
The UV project team originally comprised of Dr. Ashok Gadgil, Dr. Art Rosenfeld, and Mr. Derek Yegian and presently comprising Dr. Gadgil, Mr. Yegian, and Ms. Catherine Lukancic of the Lawrence Berkeley Laboratory (LBL) in California, USA from passages downloaded from the Internet.