The increasing concentration of carbon dioxide (CO₂) in the atmosphere is considered to be one of the main causes of the global warming problem. Moreover, there is an international movement to reduce the emission of CO₂ by imposing different measures such as carbon tax. Biological CO₂ fixation has been extensively investigated as part of efforts to solve the global warming problem. Microalgae are fast growing systems that can consume high quantities of CO₂ to produce different types of biomass. The efficiency of microalgae is highly related to the concentration of CO₂ in the growth atmosphere and the higher the concentration of CO₂ the better is the growth and hence productivity. The present review aimed at shedding some light upon microalgal capability to sustain their viability and propagate under high CO₂ concentration

Aims: To improve solar water disinfection using a photocatalysing semi-conductor and to study the mechanisms involved in this process. Methods and Results: Cells of Escherichia coli were used as the microbiological indicator to study the possibility of improving the efficiency of solar water disinfection using titanium dioxide (TiO 2 ) as a photooxidizing semi-conductor. TiO 2 was used either as a suspended powder or in an immobilized form. Both applications improved the efficiency of solar disinfection. TiO 2 in suspension was more effective than the immobilized form, producing enhancement factors of 1AE62 and 1AE34, respectively. The concentration of TiO 2 greatly affected efficiency, with a maximum effect at 1 mg ml )1 . Higher TiO 2 concentrations reduced the efficiency. Dimethyl sulphoxide (DMSO) and cysteamine (Cys), hydroxyl radical (OH AE ) scavengers, were used to elucidate the mechanisms involved in the presence of TiO 2 . Both DMSO and Cys totally abolished the enhancing effect produced by the presence of TiO 2 . Conclusions: Sunlight has a potential water disinfecting capacity. The use of TiO 2 greatly improved this efficiency. The effect of TiO 2 was mainly concentration-dependent, giving maximum efficiency at 1 mg ml )1 . The presence of DMSO and Cys removed the TiO 2 -induced enhancement, indicating that OH AE may be involved in the process of cell killing.Significance and Impact of the Study: The efficiency of solar disinfection is limited and time-consuming and needs to be improved. The use of a semi-conductor is promising as it reduces the time of exposure and therefore increases the efficiency of solar disinfection. This would allow for the availability of good quality water, and hence would improve the quality of life.

Data revealed that sunlight is almost 6.5 times more effective than a phototherapy unit when operating at the ward geometry after taking isomerization efficiency and area of exposure into consideration. Moreover, sunlight is still more effective during the winter season, when its intensity is lower. Thus, sunlight may be considered an alternative phototherapy source for the treatment of neonatal jaundice, particularly in areas where conventional phototherapy units are unavailable.

Clothing plays an important role in attenuating sunlight, thus leading to diminished vitamin D3 production to an extent that would require dietary compensation.

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