الفهرس 
Introduction
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Abstract
The effect of the bed characteristics on solar disinfection (SODIS) has been investigated experimentally. A series of experiments were conducted to SODIS to investigate the effect of bed type, bed color, and bed thickness, using bench-scale glass basins 175 L, (50 x 70 x 50 Cm) containing 87.5 L synthetic wastewater and inoculated with E-coli at a starting population of 106 CFU/ml and with a BOD less than 25 mg/l. Each basin was lined with different type of lining or with the same lining having different characteristics.
The study was developed in three stages, in order to clarify the effect of bed characteristics on SODIS. In the first stage, these lining were thin (5 cm) of clay soil, sand, gravel, cement base, and aluminium foil. In the second stage, the experiment on clay soil, sand, and gravel has been repeated for different lining thickness of 5, 10, 15, 20, and 25 cm. In the third stage, the experiments on cement base lining were repeated after changing the lining colour (white, gray, and black). In all runs, the initial depth of wastewater was kept constant of 25 cm above the lining surface. The basins were exposed to sunlight and subsequent samples were collected on the hour. The samples were analyzed for E-coli populations. Experiments were conducted during daylight between May and August 2012.
The results obtained confirm that the rate of inactivation varies according to the type of the bed lining. The aluminium foil was the most efficient lining as it adds to solar disinfection by acting as an explicit reflector to the solar radiation without hosing any microbial bio-film inside it. Aluminium foil and white colour cement beds achieve nearly complete disinfection before eight days and no viable E-coli organisms were detected after that time. Insignificant disinfection was observed with gravel and clay soil lining where re-growth of E-coli was traced. The thickness of clay and gravel layers affects the inactivation rate. The increase in the residual cells in the gravel bed is due to the voids and the large surface area of particles that leads to a pronounced microbial bio-film which lead to more released cells into the basin.
The bed color has a significant effect on pathogen removal efficiency. The variation in bed color was able to change the temperature and the radiation intensity inside each basin. This variation of temperature and the radiation intensity in each basin resulted to corresponding variation of pathogen removal efficiency.
This study demonstrated that maturation ponds with smooth bed surface and bright colors increase solar disinfection by acting as an explicit reflector to the solar radiation producing a final effluent suitable for agricultural irrigation. This implies that applying this technique in field can results in upgrading the existing WSPs system by increasing its capacity or its removal efficiency, reduces maintenance cost and can be maintained by low skilled personnel, have lower energy requirements and are perceived as a natural treatment system as well as minimizing the capital cost and surface area of maturation ponds for the new facilities to be designed.
Solar disinfection will be a promising way for improving waste water characteristics in developing countries with low-cost and clean energy reliable resource.