Enhanced biohydrogen production from microalgae by diesel engine hazardous emissions fixation

Abstract

Microalgae cultivation has gained increased attention from research and industry sectors in recent years, due to the wide variety of applications for the produced biomass, such as biofuels and substances of high economic value. Indirect biophotolysis biohydrogen production from microalgae has been shown recently to be limited by the amount of accumulated biomass during the growth phase. As a result, this study focused on developing a strategy to increase biohydrogen generation via biomass production increase through microalgae cultivation using exhaust gases from diesel engines. In order to achieve that objective, four simultaneous cultures were conducted to compare the growth of microalgae under pure air and emissions injection, in different flow regimes. An indigenous microalgae strain was selected to be robust under different weather conditions and was identified as Acutodesmus obliquus through rDNA sequence analysis. The results indicate an increase in biomass production of about 2.8 times for the best case of cultivation with emissions in comparison to a compressed air condition. Besides the growth analyses, the potential for treating the hazardous emissions injected into the system was investigated and the data demonstrated that the CO2 and NOx content was substantially reduced, showing that no damage to the microalgae is caused by the diesel engine emissions. Numerical simulation results for the H2 production indirect biophotolysis demonstrate that there is an optimal rhythm for maximum time averaged H2 production rate, and that the stoichiometrically limited total H2 production is augmented by a similar factor to microalgae biomass production increase.