Experimental Validation of a Solar Still with High Productivity Using Rotating Desalination Contactors

Abstract

Solar stills offer a simple and affordable way to produce potable water from saline or brackish sources, but their productivity is often low. In this experimental study on brackish water desalination, founded and originated by Dr. George Ayoub, three solar still units; one as a control unit and the other two as modified units; were constructed, where the addition of rotating contactors was investigated to boost productivity and upgrade system performance, while maintaining the simplicity and cost-effectiveness of the system. The control unit (U1) was used as a base to compare its distillate output with that of the first modified unit (U2) having rotating contactors (larger evaporation area), and that of the second modified unit (U3) having contactors and an expanded cover area (larger evaporation and condensation areas), so as to measure the enhancement in water productivity. In September 2023, U3 achieved a maximum yield of 5.25 kg/m2/day, showing a 210% improvement over the control unit, and an improvement ratio of 1.75 over the triangular drum solar still. Better performance was observed upon decreasing the water depth from 9 cm to 3 cm and the rotational speed from 0.75 rpm to 0.25 rpm. It was also observed that U3 was more productive in the warmer months (September, April, May, June, July), while U2 was more productive in the colder/rainier months (October, November, December, February, March), as a result of their geometry. Moreover, a configuration of 30 contactors spaced equally at 3 cm exhibited better results than that of 15 contactors spaced equally at 6 cm. Furthermore, installation of the motor timer reduced the cooling effect during nighttime and minimized energy consumption by 58.33%. Also, natural disinfection by sunlight reduced fecal coliform in brackish water by 100%. In addition, economic analysis demonstrated that the modified units have lower lifecycle costs, freshwater costs, and payback period than that of RO over a period of 10 years, contributing to the system’s economic feasibility.