Desalination holds promise

This plant was built on the rooftop of Civil Engineering Department building, BUET.

Safe drinking water is essential to humans and other life forms. The coastal region of a country has to face tremendous drinking water crisis, as most of the water available is saline. In Bangladesh 19 out of 64 districts are in proximity to the Bay of Bengal. The chief difficulty in the development of appropriate water supply system for the communities in the affected area is that deep aquifers containing sweet water are not found at all possible locations in the coastal region. One of the most convenient options to ensure potable water is to make use of the abundant source of seawater and brackish water. One may think it to be insane - drinking a glass of seawater! Well, to bring down the salinity under specified limit, desalination is widely practised all over the world. Ways of desalination are many. The conventional methods of desalination of salt waters to produce fresh water such as distillation, electrolysis and reverse osmosis are intensive energy techniques. Due to increasing energy costs and declining energy sources, there is a growing interest in the use of low cost technologies.
Solar energy is free of cost and easily available. The technology involved in distillation of saline water using solar energy is relatively simple and maintenance can be carried out by semi-skilled and unskilled operators. Moreover, Rural community is settled at widely spaced intervals. A centrally operated treatment plant would become costly in terms of supply pipes etc. Therefore, a study was carried out to evaluate the viability of a small solar desalination plant for a single family residing in the coastal area of our country.

A PLANT WAS BUILT
Presently, solar still plants, for desalination purpose, are not in use in this country. Hence a plant was constructed on the rooftop of Civil Engineering Department building, BUET and plant operation was performed for the months of Nov 2011, Dec 2011, Jan 2012 and Feb 2012 to observe the variation of diurnal distillate production of such a plant. The diurnal output of the plant was found 1.198 litre per sq. meter of the basin on an average. The salinity removal of the plant was more than 92%. So the pure water obtained from the solar still can be mixed up with the feed water prior to consumption. However, the mixture should not have salt concentrations beyond the tolerable limit. Other aesthetically important water quality parameters were tested in the output water (color, turbidity) to ensure its acceptibility to the users.
As a material of construction brick was given preference because of its availibility throughout the country and low-cost. Glass satisfactorily served the need of a transparent cover material. Inlet and outlet to the basin were PVC pipes. The total cost involved to construct the plant was tk3800.00. More than 40 percent of this cost was spent for paying construction labor. In rural areas where labor is cheap compared to Dhaka city, the cost can be considerably minimised.
The plant was run during dry season. If the plant was incorporated with a rainwater harvesting system, the output would obviously be very high. The future researchers in this area can investigate on it.
Lastly, a solar desalination unit makes use of renewable energy and as a result a green solution to the water scarcity problem. Locally available and cheap materials were used to construct the solar still. Low cost and sustainibility were the key points of the study.
Summary :
Both seawater and solar energy is abundant and free in nature. Together they can ensure a great drinking water resource.
Installation of a small desalination plant is cheap. Maintenance can be carried out even by unskilled operators.
Solar desalination plant incorporates solar energy directly, no need of expensive PV cells. Use of renewable energy makes this technology eco-friendly.

The writer is a graduate in civil engineering from BUET.