Evaluation and optimization of a stand-alone solar driven membrane filtration system for surface water treatment

Abstract

South Africa is classified as a water-stressed country and is faced with widespread water scarcity. Water scarcity is worse in rural areas of the country where a third of the population still reside. This is due to low levels of development with no water treatment systems or piping networks and most of rural areas lack access to electricity thereby hindering the installation of conventional water treatment facilities. Membrane technology presents an opportunity to bring water treatment facilities to these areas due to its compact nature, consistent water quality production and ease of maintenance. Among membrane systems, ultrafiltration uses comparably low pressures hence making it energy efficient. Solar energy has been proven to be effective in providing energy to drive membrane filtration systems and its utility in South Africa is very viable due to the abundance of solar insolence. South Africa receives an average of 2500 hours of sunshine per year and with solar radiation reaching up to 6,5kWh/m2 on some days, thereby making the use of solar energy highly favourable. In this research, water production by a solar hydraulic pump was optimized. A nanofluid was developed to improve the thermal conductivity of the working fluid for the pump and a custom-made ultrafiltration membrane was adopted for use in the membrane filtration unit. Heat transfer mechanisms within the system were investigated and the membrane filtration performances on real surface water samples collected from a lake and a stream were also determined. The nanoparticles and membranes were characterized using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FTIR) spectroscopy, Zeta-potential, drop-shape analysis, dynamic light scattering, and stability tests. Laboratory-scale application of the system was then done together with real-world studies. The optimum conditions were established to be a nanofluid composition of 0,1 %w/w CuO working fluid operated within the temperature range of 25oC – 50oC and at a pH of 6. This significantly improved the net water production of the developed prototype by 13,35 % as well as the efficiency of the prototype by 21,3%.