A New Technique of Solar Bioremediation

Disinfection with solar energy has been in practice for centuries. This article uses this old technology and builds on some of its unique features in order to develop an effective method of bioremediation. Recently, a strain of thermophilic bacteria was isolated from the environment of the United Arab Emirates. These bacteria show extraordinary resistance to heat and have their maximum growth rate around 80°C. They are found to be extremely efficient in remediating petroleum contaminants in the presence of high salinity water (simulated seawater). This article investigates the potential of using these facultative bacteria in a bioreactor in conjunction with solar irradiation. The bioreactor, recently developed at the UAE University, uses air flow through a transverse perforated pipe in order to create effective mixing, leading to optimum growth environment for bacteria. Solar energy is used in two ways. UV radiation from the sun destroys most pathogens and creates an environment that offers little competition for the thermophilic bacteria that cannot be destroyed with the UV. Also, the second advantage of the solar energy is the increase in temperature of the reactor water to a level that is more suitable for growth of the thermophilic bacteria. Heat also decreases the viscosity and interfacial tension of the petroleum contaminant, leading to the profuse emulsification. Emulsification makes more bacteria available to the petroleum contaminant and enhances bioremediation. Detailed pictorial visualization performed with a computer image analyzer showed the extinction of bacteria other than the useful thermophilic bacteria and helped measure their growth. Finally, mathematical models are developed for determining the degradation rate in the presence of solar exposure. Corrections are made to accommodate both the effects of temperature, salinity, and solar intensity. To the best of the knowledge of the authors, this coupling has not been done before. Predictive runs are conducted to observe the role of various governing parameters prevalent in environmental applications of solar disinfection systems.