Abstract
Microalgae are emerging as one of the most promising long-term sustainable sources of renewable energy. Studies were conducted on two freshwater Chlorophytes, Chlorella vulgaris and Scenedesmus obliquus to evaluate heterotrophic growth rate and biomass productivity in filter-sterilized defined medium (BG 11) and municipal wastewater, both with varying concentrations of nitrogen (N). For each isolate, cultures were separately incubated in triplicate at room temperature with constant agitation on a shaker at 150 rpm for 9 days. In 0.25 mg N/L BG11 medium, the growth rate and biomass productivity of C. vulgaris were 0.28 day-1 and 3.5 g·L-1, respectively. In wastewater, the same amount of N addition resulted in a higher growth rate 0.44 day-1 and associated biomass productivity of 4.96 g·L-1. Increasing N levels to 0.5 mg N/L in BG11 caused an increase in growth rate (0.37 day-1) and biomass productivity (4.28 g·L-1), while the increase in N in wastewater caused growth to decline to 0.32 day-1 with decreased biomass productivity of 2.19 g·L-1. A further increase in N to 1.0 mg N/L in BG11 caused an increase in the growth rate (0.43 day-1) and a decrease in biomass productivity (3.64 g·L-1), while in wastewater, growth rate and productivity of C. vulgaris were 0.32 day-1 and 2.31 g·L-1, respectively. Overall, C. vulgaris grew faster and produced greater biomass than S. obliquus under comparable conditions. Based on high growth rate and biomass productivity of C. vulgaris, it could be a potential candidate for further consideration for simultaneous wastewater treatment and biofuel production.
Highlights
The current trend in energy sectors shows a constant dependence on fossil fuel as a transportation energy source
The overall goal of these investigations is to couple microalgal biomass production to wastewater treatment and to convert biomass produced in the process to precursors of biodiesel
We focused our attention on finding the levels of nitrogen at which growth and biomass productivities of C. vulgaris and S. obliquuscould be optimized in the wastewater
Summary
The current trend in energy sectors shows a constant dependence on fossil fuel as a transportation energy source. Recent reports have suggested that global oil and gas reserves would be exhausted in 41 and 63 years respectively [1]. The constant rise in the price of fossil fuels is a serious threat for countries with limited resources [1] and the continuing dependence on fossil fuels as a major source of energy is recognized to be unsustainable [2]. Exploitation and use of fossil fuel have been suggested as the major driving force behind environmental degradation and associated global climate change [3]. The plethora of oil spill over the last five years serve as reminders of the dangers associated with fossil fuel exploitation and use. The environmental, economic and societal impacts of such spills last for decades [7]
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