Drinking Water Disinfection by Solar Energy in Rural Areas Dr. Souad N. Abdul Majeed & Dr. Awatif Alsaqqar
The goal of this study is to design and to operate a treatment water system based on utilization solar energy as a disinfecting agent & testing its efficiency.
Experimental Work: Pilot Plant: The proposed pilot treatment unit makes use of the solar energy to disinfect water by the thermal effects of the sunlight spectrum. The unit consists of the following parts as shown in Fig.(1):
1- Raw Water Tank: Galvanized steel tank with dimensions (0.5x0.5x0.5) m.
Front View Fig. (1): The Pilot Plant. 1 = Raw Water Tank. 2 = Thermal Storage Tank. 3 = Solar Collector. 4=3-Way Thermal Valve. 5 = Stand 6 = Piping. All Dimensions in (mm). 4 5 6 3 6 3 7 2 1 1530 500 500 1150 1640 870 720 870 Right Side View
<ul><li>2- Heating Unit: </li></ul><ul><li>Consists of two solar collectors of an area (0.75 x 1.8) m each, to convert solar energy into useful heat. </li></ul><ul><li>3-way thermal valve to control the flow of water by the effect of its temperature. </li></ul><ul><li>Thermal storage tank: galvanized steel tank with dimensions (0.5x0.5x0.5) m , which is isolated from the outside by a 50mm fiberglass. This tank is used to complete the closed water circulation from the solar collectors. </li></ul>
Front View 6 3 7 2 1 870 720 870 3 Fig. (1): The Pilot Plant. 1=Raw Water Tank. 2=Thermal Storage Tank. 3=Solar Collector. 4=3-Way Thermal Valve. 5 = Stand 6 = Piping. All Dimensions in (mm).
Fig. (1): The Pilot Plant. 1=Raw Water Tank. 2=Thermal Storage Tank. 3=Solar Collector. 4=3-Way Thermal Valve. 5 = Stand 6 = Piping. All Dimensions in (mm). 4 5 6 1530 500 500 1150 1640 Right Side View
Fig. ( 1 ): Pilot Plant Source: - 1- Raw water tank Heating Unit. Thermal storage tank. Solar collector. 3 Way thermal valve. Collector Tank. Sampling Valves. 4 6 5 2 3 6 1 Heating unit Source
Fig. ( 3-1 ) : Flow diagram of the disinfection unit Source: - 1- Raw water tank 10- Stand – by tank Heating Unit. 2-Thermal storage tank 3-Solar collector 4- 3 Way thermal valve UV – exposure unit 5-1mm Galvanized plate 6-Quartz tube 7-Glass tube 8-Plastic tube 9-Sampling valves 10 6 7 8 6 7 8 4 9 9 5 2 3 9 1 UV Exposure unit Heating unit Source 10
Source: - 1- Raw water tank 10- Stand – by tank Heating Unit. 2-Thermal storage tank 3-Solar collector 4- 3 Way thermal valve UV – exposure unit 5-1mm Galvanized plate 6-Quartz tube 7-Glass tube 8-Plastic tube 9-Sampling valves
Solar collector Parallel connection : Valve 1 and 2 open Valve 3 and 4 closed Series connection : Valve 1 and 2 closed Valve 3 and 4 open Fig. ( 3-4 ) : Solar collector connection pattern Solar collector 1 44 321 2 Thermal storage tank
Fig. (3-3): Cross Section in the Absorber Plate. 75 mm 3 mm O 20 mm
Front View Fig. (3-1): The Pilot Plant. 1 = Raw Water Tank. 2 = Thermal Storage Tank. 3 = Solar Collector. 4 = 3-Way Thermal Valve. 5 = U.V. Exposure Unit. 6 = Piping. 7 = Stand. All Dimensions in (mm). 4 7 6 3 6 3 5 7 2 1 1530 500 500 1150 1640 400 870 720 870 Right Side View
3-UV-Exposure Unit: Consists of three different tube materials that are selected to study the best performance that can be obtained from this unit. Each tube 1.5 m in length, 16mm +-1 inner diameter, & 1mm wall thickness. The selected materials as specified to be the best in transmitting short wave radiation are glass , quartz , and plastic .
2-The natural thermosyphon process takes place as soon as the absorber plate is heated by the sun radiation. Operation of the Unit: 1- The unit was filled with raw water at the early hours of the working day.
3-The warm water flows up the risers through the top header and to the top level of the thermal storage tank through the thermal valve.
4-Cold water flows down from the bottom of the thermal storage tank to the bottom header and then warms up along its flow inside the risers . 5-The thermal valve was set to open at different water temperatures.
Sampling: 1- To specify the physical quality of the raw and treated water. 2- To specify the chemical quality of the raw and treated water. 3- To specify the bacteriological quality of the raw and treated water.
<ul><li>Laboratory Work: </li></ul><ul><li>To evaluate the efficiency of the disinfection process, the following bacteriological tests were performed: </li></ul><ul><li>Total Bacterial Count (TBC); measured as CFU/ml </li></ul><ul><li>Coliform and Fecal Coliform, measured as MPN/100ml </li></ul><ul><li>Streptococcus and Fecal Streptococcus, measured as MPN/100ml </li></ul><ul><li>These tests were performed according to the procedures as in APHA 1981. </li></ul>
<ul><li>The water production process from the system was affected by: </li></ul><ul><li>Climatic Conditions. </li></ul><ul><li>a- ambient temperature </li></ul><ul><li>b- wind speed and direction </li></ul><ul><li>c- sky cloudiness </li></ul>Quantity of the Treated Water:
2- Type of the solar collectors connection arrangements.
<ul><li>1- Chemical and Physical characteristics: </li></ul><ul><ul><li>The water treatment process used in the study, (heating and exposure to sunlight) did not change the chemical properties of water. </li></ul></ul>Quality of the Treated Water:
Quality of the Treated Water: 2- Bacteriological Water Quality: The disinfection process was improved after exposing the heated effluent (from the heating unit) to direct sunlight. As shown from tables (2,3, &4), there is a clear reduction in bacterial counts after exposing the water to direct sunlight for different exposure times.
Conclusions: Water production from the system: 1- Seasonal variation was observed to meet drinking water demand. The daily production varied from 260L in summer to about 50L in winter. The collected water may provide 10-20 persons with enough drinking water. As the WHO 1995 assumed 2 l/c/d drinking water is required. This assumption may be increased to 5 l/d for each Iraqi citizen especially in summer.
2- Climatic conditions affected the performance of the unit. Heat losses from the absorber system were affected by the blowing winds mainly those blowing from the south. As the system faces the south higher heat losses occurred from the glass cover. A reduction of about 24% in the water production in such conditions was observed. Also water production decreased 48% was measured on cloudy days that were about 50% overcast., as clouds absorb and reflect solar radiation.
3- The series connection of the solar collectors improved the unit performance in cold weather. The production increased about 22% to 31% with such arrangement.
Water quality: … .Conclusions: 1- The treatment process used in this study did not change the chemical water quality. So the water source to be used in this kind of water treatment should be specified as a good source.
2- High bacterial reductions were observed when heating the water up to (70, 60 and 55)ºC. The total bacterial counts, Coliform and Streptococcus measurements confirmed with the drinking water specifications at the heating temperature of 70ºC. More treatment was needed when heating temperatures of (60 and 55) ºC were used.
3- Exposure of the preheated water by solar radiation up to 60 and 55ºC to direct sunlight improved its biological quality. For water at 60ºC a minimum fluenece of 7.3Wh/m² was needed for Streptococcus and total bacterial reductions. At the 55ºC heating temperature Coliform required 10Wh/m² and 16Wh/m² for Streptococcus and total bacterial inactivation.
4-The materials used in the exposure unit influenced the inactivation rates for the different microorganisms measured. High rate values were observed in the quarts tube.