Ronald Halim

Extraction of oil from microalgae for biodiesel production: a review.

The rapid increase of CO(2) concentration in the atmosphere combined with depleted supplies of fossil fuels has led to an increased commercial interest in renewable fuels. Due to their high biomass productivity, rapid lipid accumulation, and ability to survive in saline water, microalgae have been identified as promising feedstocks for industrial-scale production of carbon-neutral biodiesel. This study examines the principles involved in lipid extraction from microalgal cells, a crucial downstream processing step in the production of microalgal biodiesel. We analyze the different technological options currently available for laboratory-scale microalgal lipid extraction, with a primary focus on the prospect of organic solvent and supercritical fluid extraction. The study also provides an assessment of recent breakthroughs in this rapidly developing field and reports on the suitability of microalgal lipid compositions for biodiesel conversion.

Oil extraction from microalgae for biodiesel production

This study examines the performance of supercritical carbon dioxide (SCCO(2)) extraction and hexane extraction of lipids from marine Chlorococcum sp. for lab-scale biodiesel production. Even though the strain of Chlorococcum sp. used in this study had a low maximum lipid yield (7.1 wt% to dry biomass), the extracted lipid displayed a suitable fatty acid profile for biodiesel [C18:1 (∼63 wt%), C16:0 (∼19 wt%), C18:2 (∼4 wt%), C16:1 (∼4 wt%), and C18:0 (∼3 wt%)]. For SCCO(2) extraction, decreasing temperature and increasing pressure resulted in increased lipid yields. The mass transfer coefficient (k) for lipid extraction under supercritical conditions was found to increase with fluid dielectric constant as well as fluid density. For hexane extraction, continuous operation with a Soxhlet apparatus and inclusion of isopropanol as a co-solvent enhanced lipid yields. Hexane extraction from either dried microalgal powder or wet microalgal paste obtained comparable lipid yields.

Chlorophyll Extraction from Microalgae: A Review on the Process Engineering Aspects

Chlorophyll is an essential compound in many everyday products. It is used not only as an additive in pharmaceutical and cosmetic products but also as a natural food colouring agent. Additionally, it has antioxidant and antimutagenic properties. This review discusses the process engineering of chlorophyll extraction from microalgae. Different chlorophyll extraction methods and chlorophyll purification techniques are evaluated. Our preliminary analysis suggests supercritical fluid extraction to be superior to organic solvent extraction. When compared to spectroscopic technique, high performance liquid chromatography was shown to be more accurate and sensitive for chlorophyll analysis. Finally, through capture and wastewater treatment, microalgae cultivation process was shown to have strong potential for mitigation of environmental impacts.

Mechanical cell disruption for lipid extraction from microalgal biomass

Cell disruption is an integral part of the downstream operation required to produce biodiesel from microalgae. This study investigated the use of ultrasonication and high-pressure homogenization (HPH) as cell disruption methods for two microalgal species, Tetraselmis suecica (TS) and Chlorococcum sp. (C sp.). The kinetics of cell disruption followed a first-order model (0.65<R(2)<1.00). Disruption rate constant for ultrasonication was directly proportional to power level and followed a parabolic relationship with initial cell concentration, while that for HPH was directly proportional to operating pressure and inversely proportional to initial cell concentration. Mean disruption rate constant for HPH was approximately seven times that for ultrasonication. Mean disruption rate constant for TS cells was roughly 20% higher than that for C sp. cells. Subjecting TS culture to cell disruption prior to lipid extraction resulted in 5-8-fold increase in lipid yield and 3-5-fold increase in triglyceride yield.

Bioprocess Engineering Aspects of Biodiesel and Bioethanol Production from Microalgae

Rapid increase of atmospheric carbon dioxide together with depleted supplies of fossil fuel has led to an increased commercial interest in renewable fuels. Due to their high biomass productivity, rapid lipid accumulation and high carbohydrate storage capacity, microalgae are viewed as promising feedstocks for carbon-neutral biofuels. This chapter discusses process engineering steps for the production of biodiesel and bioethanol from microalgal biomass (harvesting, dewatering, pre-treatment, lipid extraction, lipid transmethylation, anaerobic fermentation). The suitability of microalgal lipid compositions for biodiesel conversion and the feasibility of using microalgae as raw materials for bioethanol production will also be evaluated. Specific to biodiesel production, the chapter provides an updated discussion on two of the most commonly used technologies for microalgal lipid extraction (organic solvent extraction and supercritical fluid extraction) and evaluates the effects of biomass pre-treatment on lipid extraction kinetics.

Conversion and recovery of saponifiable lipids from microalgae using a nonpolar solvent via lipase-assisted extraction

A single-step method for transesterifying and recovering lipids in concentrated slurries (ca 20% w/w solids) of ruptured microalgae is presented. A soluble Rhizomucor miehei lipase (RML) was used to directly transesterify the lipids in the marine microalgae Nannochloropsis salina. This allowed both triglycerides (TAG) and polar saponifiable lipids to be recovered as fatty acid methyl esters (FAME) using a nonpolar solvent (hexane). Up to 90 wt% of the total saponifiable lipids (SL) were converted to FAME within 24 h, approximately 75% of which was recovered in the hexane by centrifugation. Two pathways for the conversion and recovery of polar lipids were identified. The water in the slurry buffered against potential lipase inhibition by methanol, but necessitated a high methanol dose for maximal FAME conversion. Nonetheless the method enables the recovery of polar lipids as FAME while avoiding the need for both drying of the biomass and a downstream transesterification step.

Nile Red Staining for Oil Determination in Microalgal Cells: A New Insight through Statistical Modelling

In the wake of global warming and rapid fossil fuel depletion, microalgae emerge as promising feedstocks for sustainable biofuel production. Nile red staining acts as a rapid diagnostic tool to measure the amount of biodiesel-convertible lipid that the cells accumulate. There is a need for the development of a more uniform staining procedure. In its first phase, this study examined the dependence of microalgal Nile red fluorescence (Tetraselmis suecica) in terms of its most pertinent staining variables. A quadratic surface model that successfully described the Nile red fluorescence intensity as a composite function of its variables was generated (). Cell concentration was shown to have a significant effect on the fluorescence intensity. Up to a certain threshold, fluorescence intensity was shown to increase with Nile red dye concentration. In its second phase, the study reviewed findings from previous Nile red studies to elucidate some of the fundamental mechanism underlying the diffusion of Nile red dye molecules into the microalgal cells and their subsequent interaction with intracellular lipids. Through the review process, we were able to develop a simple framework that provided a set of guidelines for the standardization of the Nile red staining procedure across different microalgal species.

Bioprocess Development for Chlorophyll Extraction from Microalgae

Chlorophyll, a green pigment found abundantly in plants, algae, and cyanobacteria, plays a critical role in sustaining life on earth and has found many applications in pharmaceutical, food, as well as cosmetic industries. Because of their high intracellular chlorophyll accumulations (up to 10% of cell dry weight), green microalgae are recognized as promising alternative chlorophyll sources. Successful co-production of a high value product such as chlorophyll in a microalgal bio-refinery is desirable as it will alleviate the overall cost of producing microalgal biodiesel. This chapter evaluates the bioprocess engineering required to recover and to purify chlorophyll molecules from microalgae. The use of organic solvents and supercritical fluids to extract microalgal chlorophyll on a commercial scale is examined. The use of chromatographic techniques to purify the recovered chlorophylls is also reviewed. Finally, the chapter ends by presenting a case study which investigates the use of organic solvents (acetone and methanol) to extract chlorophyll from Tetraselmis suecica on a laboratory scale.