Archive for the ‘Water’ Category
Water Technology – 3. Reverse Osmosis
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Since distillation is considered energy intensive, reverse osmosis as a process was developed and found to be more economical as it works at low temperatures but higher pressures. “Reverse osmosis is highly effective in removing several impurities from water such as total dissolved solids (TDS), turbidity, asbestos, lead and other toxic heavy metals, radium, and many dissolved organics. The process will also remove chlorinated pesticides and most heavier-weight volatile organic compounds”.
http://www.freedrinkingwater.com/water-education/quality-water-filtration-method.htm
The basic principle is difficult to explain but let me give it a try. Suppose we have two chambers separated by a membrane. On one side we have salt water and on the other side fresh drinking water. We know over a period of time the fresh water will move into the salt water and thus try to reduce the concentration on that side. This is what is called osmosis. Reverse osmosis means we want to squeeze the salt and make the fresh water go back (reverse). So essentially we need a suitable membrane (technical name semi-permeable membrane) that can withstand very high pressure and only allows water to flow to the fresh water side. If my explanation is not satisfactory see http://science.howstuffworks.com/reverse-osmosis.htm
This technology was used at the village level by many civil society organisations including the Byrraju Foundation, Nandi Foundation and many others to provide potable water to rural communities. Providing safe drinking water is seen as a good entry point for many social entrepreneurs in the villages of rural India.
Water Technology – 2 Distillation
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The most perfect way to treat and purify water is through distillation. In this process water is boiled and converted to its vapour phase. When this happens all dissolved ions and other particles get left behind. The vapour is taken to a cool surface and it condenses back as liquid droplets. Distillation happens to be one of the most energy intensive techniques for treating and purifying water but it is also the best.
The energy intensive nature of this process is due to the physical properties of water. If we take I gram of water (1gm =1 ml) it will take 1 calorie of energy to raise its temperature by 1 degree centigrade. So typically it takes 70 calories to take the temperature of water from 30 degrees centigrade to 100 degrees centigrade. However when we want the water to change phase from liquid to vapour each gram of water requires 550 calories of energy. This is a very large amount of energy that is again released by the vapour when it condenses back to liquid.
Engineers have designed systems that capture the energy when the liquid condenses and use that energy to evaporate more water. This is called multiple effect distillation. Countries in the Middle East typically combine their electricity power plants with Multiple Effect Distillation plants to desalinate sea water to meet their drinking water needs. See http://people.uwec.edu/piercech/desalination/MED.htm
http://www.h2ome.net/en/tag/multiple-effect-distillation-med/
Many inventors play with building multiple effect distillation units with solar power as the thermal input. So far these have remained as laboratory prototypes and have not shown technical or commercial viability. It remains a challenge.
Managing Rainwater
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Kerala and Tamil Nadu have opposite priorities when it comes to rain. Kerala (3000mm) receives almost 3 times the annual rainfall of Tamil Nadu (1000mm). In Kerala civil engineering designs concentrate on quickly draining the rainfall to the nearest river without eroding the land. Tamil Nadu civil engineering designs have strived to tap the rain in many different ways and prevent its run off to the sea.
The boundary between houses in the heavy rainfall areas of Kerala consisted of deep channels that would flood during the rains and connect to other channels that eventually led to the rivers. Tamil Nadu built dykes on the surface that would have spill overs and channels leading to recharge structures like tanks. All across Tamil Nadu these man made structures arrest the flow of water and allow people in that region to use the water as a common facility. A very dramatic image of these structures can be seen at http://wikimapia.org/#lat=10.0188914&lon=79.0706635&z=11&l=0&m=t
Harvesting rain water and storing can be done in many different ways and the wikipedia entry on these describes the techniques very well.
(http://en.wikipedia.org/wiki/Rainwater_harvesting)
Since water is so crucial for human survival and has become a serious problem in many different parts of India, there are public and private efforts to address the issue. The Tamil Nadu government was the first to mandate by law the use of water harvesting structures in buildings. Many other governments are expected to follow suit. There are some civil society efforts like the Rain Water Concepts run by Ayappa Masagi, http://www.rainwaterconcepts.co.in/, Narieta Services Private Ltd, run by Biplab K Paul in Gujarat, Sekhar Raghavan and the Rain centre in Chennai (http://www.rainwaterharvesting.org/network/raincentre.htm) and Varsha Jal run by Vijay Kedia http://www.varshajal.com/jalmitra_kedia.htm
For those interested in building water harvesting structures this is a good start (http://www.saiplatform.org/uploads/Modules/Library/SAI%20Technical%20Brief%202%20Rain%20Water%20Harvesting%20and%20Artificial%20Recharge-2.pdf)
Water Technology 1- Filteration
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There will be short pieces on water and water treatment technologies from time to time in this blog. The world is going to experience many different types of problems with respect to fresh water. The availability of fresh water is one issue. The more important one is around what the quality of the water will be like. The quality will decide what treatment needs to be done. With the rise of air pollution around the world even rain water cannot be considered safe, as small particles will form part of the rain drop.
The simplest, cheapest and oldest technology for treating water is filtration. Filtration is a process by which water flows through a membrane like cloth. It is one of the oldest water treatment technologies. It is almost always used as a first step before more complex processes are implemented. Filtration removes macro level contaminants like dust and is very versatile as very large filtration systems can be built at relatively low cost. Filtration systems need regular maintenance otherwise they can end up contaminating the water they are meant to treat. Important design consideration for a water filtration system therefore is how quickly and cheaply can the maintenance be done.
The biggest drawback for a conventional filtration system is that it cannot get rid of chemicals dissolved in the water (like salt). More recent technologies can do this too but then the cost would be higher and the quantity of water the system can treat would be limited and maintenance would be costlier. The following link gives more technical update. http://www.allaboutwater.org/filtration.html
Water Under the Ground
There have been several important regulations on ground water usage in India. The Chennai Metropolitan Area Groundwater (Regulation) Act of 1987 is one such. (see http://www.chennaimetrowater.tn.nic.in/admin/rainwater_rn.htm). The Government of India is now contemplating a cap on ground water usage and a tax to discourage its indiscriminate use for irrigation. These steps may be on the cards as the government looks to preserve this precious resource that is depleting at an alarming rate. This kind of regulation will have a direct impact on farm livelihoods and food security. Are there other mechanism that can serve the purpose is the question being raised here.
There have been many experiments, studies and enterprises that have attempted to resolve issues around ground water usage in a democratic way. Farmers in Andhra Pradesh have found interesting solutions to this issue. An interesting case study is presented in the handbook “Piloting Knowledge Swaraj: A Handbook on Indian Science and Technology,” edited by XIMB Professor Shambu Prasad. The case study can be found on pages 120 to 125 of the handbook. Click this link to access the Handbook: http://kicsforum.net/index.php?option=com_sectionex&view=category&id=16&Itemid=83.