 | Sourcebook of Alternative Technologies for Freshwater Augmentation in some Asian Countries (UNEP-IETC, 1998) |
 |  | Part B - Technology profiles |
| | 1. Water conservation technologies |
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1.2 Evaporation reduction
Technical Description
Evaporative losses can be controlled using various technologies. For example, the use of mono molecular organic surface films has been shown to be an efficient technology for reducing such losses. The mono molecular film is applied to an open surface water storage area and allowed to over the water surface. Typical mono molecular films are comprised of long-chain fatty alcohols such as cetyl alcohol (hexadecanol) and stearyl alcohol (octadecanol). These chemical not only suppress evaporation but also prevent mosquito breeding in the water. The use of stearyl alcohol in doses of up to 70 g/cm2 can reduce evaporative losses by up to 55% of the loss due to evaporation from a free water surface. However, the economics and extent of use of this technology are yet to be explored and established.
Extent of Use
Use of surface films to reduce evaporative losses is principally in arid and semi-arid regions.
Operation and Maintenance
The operation and maintenance requirements of this technology are negligible. Maintenance is required only for the rafts and boats, which may be locally constructed, used during the application of the evaporation retardants. No specialized skill is required.
Level of Involvement
The implementation of this technology is generally carried out by government departments, primarily the public health engineering and water supply departments. In India, it is now being promoted by various state government agencies and local authorities. Generally, control of evaporation is focused at the government level having prime responsibility for water resources management.
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Water Evaporation Retardants In India, the use of Water Evaporation Retardants (WER) is being investigated as a water conservation measure in surface waters. Control of evaporative losses is being effected using Ceto-Stearyl alcohol, a blend of saturated fatty alcohols, previously imported at high cost and not readily available in India. India's first fatty alcohol plant was commissioned in 1981 at Jalgaon, Maharashtra, by Aegis Chemical Industries L-td,, using an exclusive technology based on an high pressure hydrogenation technology developed in collaboration with Haldor Topsoe, Denmark. The plant is one of the few in the world and the only one in India, producing alcohols to international specifications. In 1983, Aegis successfully developed an effective water evaporation retardant, Acilol TA 1618 WER, an emulsion based on fatty alcohols manufactured from natural vegetable oils. Acilol TA 16118 WER was developed in the laboratory after extensive research aimed at identifying a product compatible with the climatic conditions of the country. Field trials were conducted in March 1984 with the help of Gujarat Engineering Research Institute. These trials confirmed the effectiveness of Acilol TA 1618 WER. A dispensing technique for applying Acilol TA 1618 WER to water
surfaces, consisting of barrel tanks with a drip feed arrangement mounted on
"Floating Rafts" anchored at different points on the lakes or reservoirs, was
also developed to suit Indian conditions. The first major project using this
technique to conserve water was undertaken by the Public Health Engineering
Department (PHED), Jaipur, at Ramgarh Lake in April, 1985. About 50
mg/m2/d of the chemical is required arid can result in a savings of
about 30% of the daily loss of water due to evaporation. |
Costs
No cost data were available as this technology remains largely experimental.
Effectiveness of the Technology
Of the various substances capable of forming mono molecular layers on a water surface, fatty alcohols in their pure form have been found to be most suitable and effective in retarding evaporation with no side effects (AIT, 1982). Savings from the prevention of water loss due to evaporation have been reported to be as high as 0.70 million cubic metres of water (equivalent to one month's water supply for Jaipur City, India) using Cetyl and Stearyl Alcohol as an evaporation retardant.
Suitability
The technology is most suitable in small surface water storages where there are no strong winds to disrupt the retardant layer.
Advantages
Use of evaporation control techniques requires a small capital investment. Locally constructed rafts can be used in its application, and skilled labour is not required, except for operation of motorized boats. Fatty alcohols present no hazards in handling, and are non-inflammable, non-toxic, and non-irritating. There are no known harmful effects, making this technology safe for application on drinking water lakes and reservoirs. There are also no known ecological ramifications, as the alcohols contain straight chain carbon compounds which are biodegradable and permeable to oxygen.
Disadvantages
The fatty alcohols used as WERs are not readily available and are costly. Historically, fatty alcohols were produced only by sperm whales or by sodium reduction of animal oils and fats. It was only after the development of high pressure hydrogenation process that good quality fatty alcohols are now commercially available. However, this is a very advanced technology, and requires trained and skilled staff to operate.
Cultural Acceptability
There are no known problems with cultural acceptability.
Further Development of the Technology
More research is necessary in the area of stabilising the chemical film in the face of high wind velocities. Properties such as rate of spreading, specific resistance to evaporation and surface viscosity are required to be measured in evaluating the efficiency of the retardant.
Information Sources
Contacts
Asian Institute of Technology,
Water Engineering
and Management Program,
Post Office Box 2754, Bangkok, Thailand.
Tel. 00
662 516 0110,
Fax: 00 662 516 2126,
E-mail: [email protected].
Bibliography
A.C. Desai, T.K. lyer, and V.M. Tople 1990. Use of Water Evaporation Retardants for Water Conservation, Journal of Indian Water Works Association, April-June, 193-194.
Asian Institute of Technology (AIT) 1982. Evaporation Control Using Monomolecular Organic Surface Films. AIT Research Report No. 1982-2, Division of Water Resources Engineering, AIT, Bangkok.
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