martes, 16 de julio de 2013

Potable Water for All – More Than a Pipe Dream

by: Megan Barrett
15th July 2013

Many of us take for granted the availability of a clean glass of water. Yet even at the turn of the second millennium, approximately one billion people still did not have access to a sustainable source of potable water.[1] With water contamination and shortages most prevalent in the remote regions of developing countries (where money and technology can be limited), scientists are faced with a daunting challenge: to develop new ways of treating water to make it safe, using simple, locally sourced and inexpensive processes. Interestingly, the local environment may hold the key. Recent discoveries suggest that naturally occurring products, such as plant seeds and even tomato peel, may be used to help purify water.

Water is essential to our survival and health, with the human body being approximately 70% water. We use water in industry, to grow crops and cook; in sanitation; and for transportation purposes; yet, untreated water sources can contain many hidden threats including toxic heavy metals and dangerous pesticides. According to the World Health Organisation (WHO), approximately 80% of illness in developing countries is known to be associated with contaminated drinking water.[2]

A number of methods for treating water currently exist, mostly involving the addition of chemical substances, such as chlorine or aluminium sulphate (alum), to contaminated bodies of water. The availability, cost and knowledge to ensure the correct dosage of such substances, however, is often lacking in remote communities.[2] Consequently, some scientists are looking for more natural solutions– ones potentially more accessible to people living away from areas of development.

Figure 1: Moringa oleifera pods
The Moringa oleifera (figure 1), a variety of plant found abundantly across rural India, Africa and Cambodia has drawn considerable attention in recent history. Parul Sharma and a team from the Faculty of Science at Dayalbagh Educational Institute, Dayalbagh investigated the ability of M. oleifera seed powder to remove cadmium, a dangerous heavy metal responsible for itai-itai disease, from water sources on a laboratory scale. Cadmium was labelled with a radioactive tracer so its levels could be tracked and the M. oleifera plant seeds were crushed to form a powder. Quite surprisingly, Sharma’s group found that cadmium levels were effectively reduced by the seed powder, suggesting this species of plant may be useful in remote and developing regions of the world to help reduce contamination of the local water supplies.[3]

A second ecologically friendly method of treating water has been developed by a group of scientists from Tshwane University of Technology, South Africa. Recently, Oranso Mahlangu and colleagues tested the ‘Silver Impregnated Porous Pot (SIPP) filter’, a clay-based filtering pot, as a tool to produce safe drinking water at a household level.[4] The SIPP filter is made using certain clay types that naturally remove contaminants (e.g. toxic heavy metals) by a process known as adsorption. This is when particles in a gas, liquid or dissolved solid bind to a surface, and is not to be confused with absorption: when a gas or fluid is taken into a solid (e.g. a sponge soaking up a puddle of water).
Figure 2: Diagram illustrating the set up of Mahlangu and colleagues ‘Silver Impregnated Porous Pot (SIPP) filter’

Mahlangu’s team filtered different river sources through the SIPP filter six times, for 3 hours at a time (figure 2). They then used a method known as atomic adsorption spectrophotometry (AAS) to analyse the level of metal contaminants (such as magnesium, iron and arsenic) in the water samples before and after filtration. What they found was remarkable: the SIPP filter reduced the amounts of magnesium and iron in the water samples by more than 50% to a level below the WHO’s acceptable maximum for these heavy metals (70–100micrograms per litre and 0.2–2micrograms per litre, respectively). Arsenic levels were also reduced, though unfortunately not to within the WHO’s stated guidelines, and the effectiveness of the SIPP filter did lessen with use.[4]
Figure 3: Peeling a tomato
Nevertheless, the search for an affordable and accessible way of acquiring potable water in remote parts of the world has continued. A few months ago, Ramakrishna Mallampati and Suresh Valiyaveettil from the University of Singapore investigated a somewhat unexpected tool for water purification— the tomato peel (figure 3).[5] Remarkably, this fruit‘s “biomembrane” (or cell-covering barrier) also acts as an adsorbent to the toxic heavy metals in polluted water and removes dangerous dyes and pesticides that may have contaminated a natural water source.

Mallampati and Valiyaveettil treated their local shop-bought tomato peels by boiling them, washing them with propanol (an alcohol that removes pigment, i.e. the red colour of the tomato) and drying them. These peels were then added to different solutions containing known water contaminants and were found to effectively lower the levels of chemicals such as arsenic, alcian blue and neutral red (two dyes) and phenol which is used in pesticides. Moreover, the effectiveness of the tomato peels to help remove the water pollutants did not seem to deteriorate over time, suggesting that the easily accessible and inexpensive tomato peel may be a useful material for treating drinking water.[5]

The availability of sustainable water sources for the more isolated communities around the world; (especially in developing countries) is a serious problem facing scientists and society today. Many of the current chemical processes for treating drinking water are not obtainable or affordable for remote populations, such as those in rural India or Sub-Saharan Africa. Yet scientists have made some bio-friendly breakthroughs. The recent findings that certain heavy metals and other contaminants toxic to human health can be reduced by natural materials, such as plant seeds, clay and tomato peel, is a significant achievement in the fight to provide safe potable water for all— a battle I will definitely be thinking about the next time I turn on my tap.

  1. Rush EC. 2013. Water: neglected, unappreciated and under researched. Eur J Clin Nutr. 1-4.
  2. Yongabi K, Lewis D, Harris P. 2012. Natural materials for sustainable water pollution management. In Prof Nuray Balkis (Ed). Water Pollution. InTech.
  3. Sgarma R, Kumari P, Srivastava M, et al. 2006. Removal of cadmium from aqueous system by shelled Moringa oleifera Lam. seed powder. Bioresour Technol. 97:299-305.
  4. Mahlangu O, Mamba B, Momba M. 2012. Efficiency of Silver Impregnated Porous Pot (SIPP) filters for the production of clean potable water. Int J Environ Res Public Health. 9:3014-3029.
  5. Mallampati R, Valiyaweettil S. 2012. Application of tomato peel as an efficient adsorbent for water purification— alternative biotechnology? RSC Advances. 2:9914-9920.

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