Ultrahigh recovery rate of nitrate from synthetic wastewater by Chlorella-based photo-fermentation with optimal light-emitting diode illumination: From laboratory to pilot plant

This review analyzes the current state of a specific niche of microalgae cultivation; heterotrophic growth in the dark supported by a carbon source replacing the traditional support of light energy. This unique ability of essentially photosynthetic microorganisms is shared by several species of microalgae. Where possible, heterotrophic growth overcomes major limitations of producing useful products from microalgae: dependency on light which significantly complicates the process, increase costs, and reduced production of potentially useful products. As a general role, and in most cases, heterotrophic cultivation is far cheaper, simpler to construct facilities, and easier than autotrophic cultivation to maintain on a large scale. This capacity allows expansion of useful applications from diverse species that is now very limited as a result of elevated costs of autotrophy; consequently, exploitation of microalgae is restricted to small volume of high-value products. Heterotrophic cultivation may allow large volume applications such as wastewater treatment combined, or separated, with production of biofuels. In this review, we present a general perspective of the field, describing the specific cellular metabolisms involved and the best-known examples from the literature and analyze the prospect of potential products from heterotrophic cultures. Copyright © 2010 Elsevier Ltd. All rights reserved. Show more

Although microalgae can serve as an appropriate alternative feedstock for biofuel production, the high microalgal cultivation cost has been a major obstacle for commercializing such attempts. One of the feasible solution for cost reduction is to couple microalgal biofuel production system with wastewater treatment, as microalgae are known to effectively eliminate a variety of nutrients/pollutants in wastewater, such as nitrogen/phosphate, organic carbons, VFAs, pharmaceutical compounds, textile dye compounds, and heavy metals. This review aims to critically discuss the feasibility of microalgae-based wastewater treatment, including the strategies for strain selection, the effect of wastewater types, photobioreactor design, economic feasibility assessment, and other key issues that influence the treatment performance. The potential of microalgae-bacteria consortium for treatment of industrial wastewaters is also discussed. This review provides useful information for developing an integrated wastewater treatment with microalgal biomass and biofuel production facilities and establishing efficient co-cultivation for microalgae and bacteria in such systems. Show more

Light-emitting diodes (LEDs) will become one of the world's most important light sources and their integration in microalgal production systems (photobioreactors) needs to be considered. LEDs can improve the quality and quantity of microalgal biomass when applied during specific growth phases. However, microalgae need a balanced mix of wavelengths for normal growth, and respond to light differently according to the pigments acquired or lost during their evolutionary history. This review highlights recently published results on the effect of LEDs on microalgal physiology and biochemistry and how this knowledge can be applied in selecting different LEDs with specific technical properties for regulating biomass production by microalgae belonging to diverse taxonomic groups. Show more