عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Increasing global warming and decreasing rainfall is one of the serious concern in world. Population growth and increasing demand of water for irrigation, household and industrial purposes are annually faced with water shortages during the summer months. Lakes and reservoirs are the greatest resource of fresh water. One of the more serious problems faced by industry is the evaporation of water from this type of open storages that allows for the greatest loss of water by evaporation particulary during the harm months. In Sarcheshmeh tailing dam, for example, evaporation rate averages is about. ۲۲۵۰ mm per year while this dam is filled with water to a depth of ۵۰۰۰ mm. In this condition, approximately ۴۵% water might be lost due to evaporation. Thus, employ techniques for reducing evaporation is necessary to aiming at the conservation of water through control of evaporation from open storages supplies. In order to increase water supplies by reducing losses through evaporation have been investigated in both the theoretical aspects and practical applications in a number of countries. The most important is the application of the chemical evaporation reducing layers to surfaces of large bodies of open water such as reservoirs, lake and the like. Such application is especially important in arid and semiarid areas for the purpose of reducing evaporation rates from water surfaces. Among the surfactants tested, biodegradable fatty alcohols of low toxicity presented the highest resistance to water evaporation. In the present investigation, have verified the influence of monomolecular films of fatty alcohols including Hexadecanol and Octadecanol in reducing the evaporation of two water samples collected from tap water and the reservoir of sarcheshme tailing dam during two months. For two sample water were provided, twenty steel rectangular container with dimensions ۱۵*۳۰*۵. Six of containers were filled with ۵۰۰mli tap water and six other containers were filled with water collected from reservoirs Sarcheshme dam. For each water samples, five containers were considered with monolayers film and a container of water with no monolayer was used as the control used monomolecular films in ten containers filled with two samples water, were including pure hexadecanol (C۱۶), pure octadecanol (C۱۸) and mixtures of ۱:۹ , ۳:۷ and ۵:۵ (m:m) of C۱۶ and C۱۸ (C۱۶:C۱۸) on the surface of the samples by adding small volumes of ethanol solution (۴۰gr/L) using a sprayer. Values of cumulative evaporation were collected during a ۲۹-Day Period from ۱۷/۰۷/۲۰۱۶ to ۱۴/۰۸/۲۰۱۶. In all samples tested, at the same condition, performance of fatty alcohol on drinking water and wastewater is different. it was observed that, in samples ۱ that were been covered with a pure hexadecanol film, for container of drinking water, evaporation reduction of ۳۲.۲% was obtained, whereas for container of wastewater the same value of ۱۸.۲% was obtained. The results obtained with the C۱۶:C۱۸(۱:۹) mixture (samples ۲) showed ۳۹% saving water for drinking water and ۳۲.۲% saving water for wastewater. Mixtures of hexadecanol and octadecanol with weight ratios of ۳:۷ (samples ۳) showed the highest performance in reducing evaporation (۵۸.۴۷%, ۵۱.۷۵%) of drinking water and waste water, respectively. For the C۱۶ and C۱۸ mixtures (samples ۴), the best results obtained from drinking water and wastewater (۴۷.۵% and ۴۵.۵%) were at ۱ to ۱ proportions (C۱۶:C۱۸ (۵:۵)). The results obtained from pure octadecanol (samples ۵) were poor. This monomolecular film showed ۲۷.۱% and ۲۱% saving water in drinking water and wastewater respectively. According to the results obtained in the above, the minimum of difference between evaporation rate of drinking water and wastewater is related the mixture of C۱۶:C۱۸ (۱:۹). In presented experiments results, it was found that the water evaporation rate, for all of the tests were performed on wastewater using fatty alcohol, is higher than tests were performed on drinking water. It may be concluded that acidic condition and the organic and inorganic compounds in wastewater of sarcheshmeh tailing dam, with the effectiveness of the monomolecular film led to increase the evaporation rate. It is noticed that in mixed films, the differences in rate of evaporation losses of both drinking water and the wastewater was reduced when the proportion of octadecanol to hexadecanol was increased. It is well known that octadecanol films can reduce water evaporation better than hexadecanol films, but C۱۶:C۱۸ mixed films was reduced evaporation rate higher than pure films.