Arsenic Contamination: Points For Consideration
by Sylvia Mortoza
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.
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
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
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
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
- 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.
- Otto Ruskulis of the Intermediate Technology Development Group - UK
- Tricia Jackson of the Water Engineering Development Centre, Loughborough
- Tom Lawand of the Brace Research Institute - Dept. of Chemical Engineering,
- 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.