Abstract
BackgroundAn economical strategy for producing microalgae as biofuel feedstock is driven by the freshwater and nutrients input. In this study, seawater was applied to limnetic algal cultivation and the behavior of algae in seawater media was observed including growth, lipid synthesis, and ultrastructure. To make seawater cater algae, a kind of wastewater, anaerobically digested effluent from kitchen waste (ADE-KW), was used as nutrient sources.ResultsPure seawater cannot support the growth demand of freshwater microalga, due to high salinity and lack of nutrients. However, it is the conditions triggered the algae to synthesize lipids of 60%, double of lipid content in standard medium BG11. Introducing 3 or 5% ADE-KW (volume percentage) into seawater made algal growth reach the level attained in BG11, while lipid content compared favourably with the level (60%) in pure seawater. This method achieved the goal of fast growth and lipid accumulation simultaneously with the highest lipid productivity (19 mg/L day) at the exponential stage, while BG11 obtained 10.55 mg/L day at the stationary stage as the highest lipid productivity, almost half of that in seawater media. Moreover, the condition for highest lipid productivity enlarged algal cells compared to BG11. Under the condition for highest lipid productivity, Chlorella sorokiniana SDEC-18 had enlarged cells and increased settling efficiency compared to BG11, which facilitated harvest in an energy saving way.ConclusionsThe results suggested that combining seawater with ADE-KW to cultivate microalgae had a double function: nutrients and water for algal growth, and high salinity for stimulating lipid accumulation. If this technology was operated in practice, freshwater and non-waste nutrient consumption would be completely obviated.
Highlights
An economical strategy for producing microalgae as biofuel feedstock is driven by the freshwater and nutrients input
Seawater is mainly used for diluting wastewater for marine algae cultivation, while, artificial seawater was the primary choice for trials to stimulate lipid accumulation and avoid bio-invasion from other freshwater microorganisms
Focusing on the cost of freshwater and nutrient chemicals and energy of harvest in algae production process, the main aims in our study included: (1) understanding the behavior of limnetic microalgae in a medium consisting of 100% seawater, (2) exploring the feasibility of using anaerobically digested effluent from kitchen waste (ADE-KW) as nutrient source for algae cultured in seawater, (3) establishing a cultivation system in the absence of freshwater, and (4) find a simple and economical way to stimulate lipid accumulation in freshwater microalgae
Summary
Pure seawater cannot support the growth demand of freshwater microalga, due to high salinity and lack of nutrients. Introducing 3 or 5% ADE-KW (volume percentage) into seawater made algal growth reach the level attained in BG11, while lipid content compared favourably with the level (60%) in pure seawater. This method achieved the goal of fast growth and lipid accumulation simultaneously with the highest lipid productivity (19 mg/L day) at the exponential stage, while BG11 obtained 10.55 mg/L day at the stationary stage as the highest lipid productivity, almost half of that in seawater media. Under the condition for highest lipid productivity, Chlorella sorokiniana SDEC-18 had enlarged cells and increased settling efficiency compared to BG11, which facilitated harvest in an energy saving way
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