Green approaches and separation techniques for the recovery of pigments from microalgae

Microalgae have provided great exploitation of biofuels and bioproducts production over fossil fuels and other plant-based sources owing to its high accessibility, non-competition, and renewability advantages. The production of natural carotenoids from microalgae are safer than petrochemical feedstock due to the inherent toxicity concerns for direct human consumption. However, the recalcitrant structure of microalgae cell wall restricted the direct recovery and extraction of the carotenoids accumulated inside the biomass which requires an additional pretreatment process. The current conventional technologies (e.g. bead beating, homogenizers, high pressure heating and chemicals) of biomass processing are incompetent and not feasible for the downstream processing of microalgae. This creates an opportunity of developing novel bioprocessing approaches to reduce the overall cost- and time processing and enhance the efficient production of carotenoids. This thesis presents the development of liquid biphasic- and ionic liquid technologies for the downstream processing of carotenoids such as astaxanthin and fucoxanthin from different microalgae strains. This thesis firstly introduces the application of liquid biphasic flotation system in the extraction and partitioning of astaxanthin from Haematococcus pluvialis microalgae. The optimized liquid biphasic flotation system is further employed with ultrasound- and electropermeabilization-assisted technologies for a simultaneous pretreatment and extraction of carotenoids from microalgae. These integrated technologies with liquid biphasic flotation system provide a one-step rapid processing, environmentally friendly, achieved higher yield and separation efficiency. In fact, the integrated technologies liquid biphasic flotation system was scale-up to investigate the feasibility for large scale and commercializing its usage for industrial proposes. This thesis also presented a greener and sustainable solvent using ionic liquids technology for the cell permeabilization and extraction of astaxanthin and fucoxanthin from microalgae. The green concept of the proposed ionic liquid in this research work utilized carbon dioxide as one of its reactants and they can be easily separated from the extracted bioproduct compared to conventional imidazole- and pyridinium-based ionic liquids. The characterization of the synthesized ionic liquid was comprehensively evaluated in this work. Besides, the cellular and surface morphology after treated with the ionic liquid were investigated. This work also illustrated the recyclability studies of the proposed ionic liquid for subsequent extraction. Moreover, the antioxidant properties of the extracted astaxanthin and fucoxanthin were subjected for antioxidant analysis. The research achievements in these works and future opportunities are highlighted in the last chapter of the thesis

Green approaches and separation techniques for the recovery of pigments from microalgae

Microalgae have provided great exploitation of biofuels and bioproducts production over fossil fuels and other plant-based sources owing to its high accessibility, non-competition, and renewability advantages. The production of natural carotenoids from microalgae are safer than petrochemical feedstock due to the inherent toxicity concerns for direct human consumption. However, the recalcitrant structure of microalgae cell wall restricted the direct recovery and extraction of the carotenoids accumulated inside the biomass which requires an additional pretreatment process. The current conventional technologies (e.g. bead beating, homogenizers, high pressure heating and chemicals) of biomass processing are incompetent and not feasible for the downstream processing of microalgae. This creates an opportunity of developing novel bioprocessing approaches to reduce the overall cost- and time processing and enhance the efficient production of carotenoids. This thesis presents the development of liquid biphasic- and ionic liquid technologies for the downstream processing of carotenoids such as astaxanthin and fucoxanthin from different microalgae strains. This thesis firstly introduces the application of liquid biphasic flotation system in the extraction and partitioning of astaxanthin from Haematococcus pluvialis microalgae. The optimized liquid biphasic flotation system is further employed with ultrasound- and electropermeabilization-assisted technologies for a simultaneous pretreatment and extraction of carotenoids from microalgae. These integrated technologies with liquid biphasic flotation system provide a one-step rapid processing, environmentally friendly, achieved higher yield and separation efficiency. In fact, the integrated technologies liquid biphasic flotation system was scale-up to investigate the feasibility for large scale and commercializing its usage for industrial proposes. This thesis also presented a greener and sustainable solvent using ionic liquids technology for the cell permeabilization and extraction of astaxanthin and fucoxanthin from microalgae. The green concept of the proposed ionic liquid in this research work utilized carbon dioxide as one of its reactants and they can be easily separated from the extracted bioproduct compared to conventional imidazole- and pyridinium-based ionic liquids. The characterization of the synthesized ionic liquid was comprehensively evaluated in this work. Besides, the cellular and surface morphology after treated with the ionic liquid were investigated. This work also illustrated the recyclability studies of the proposed ionic liquid for subsequent extraction. Moreover, the antioxidant properties of the extracted astaxanthin and fucoxanthin were subjected for antioxidant analysis. The research achievements in these works and future opportunities are highlighted in the last chapter of the thesis

Review on demulsification techniques for oil/water emulsion : Comparison of recyclable and irretrievable approaches

Since the establishment of the first global refinery in 1856, crude oil has remained one of the most lucrative natural resources worldwide. However, during the extraction process from reservoirs, crude oil gets contaminated with sediments, water, and other impurities. The presence of pressure, shear forces, and surface-active compounds in crude oil leads to the formation of unwanted oil/water emulsions. These emulsions can take the form of water-in-oil (W/O) emulsions, where water droplets disperse continuously in crude oil, or oil-in-water (O/W) emulsions, where crude oil droplets are suspended in water. To prevent the spread of water and inorganic salts, these emulsions need to be treated and eliminated. In existing literature, different demulsification procedures have shown varying outcomes in effectively treating oil/water emulsions. The observed discrepancies have been attributed to various factors such as temperature, salinity, pH, droplet size, and emulsifier concentrations. It is crucial to identify the most effective demulsification approach for oil/water separation while adhering to environmental regulations and minimizing costs for the petroleum sector. Therefore, this study aims to explore and review recent advancements in two popular demulsification techniques: chemical demulsification and magnetic nanoparticles-based (MNP) demulsification. The advantages and disadvantages of each technique are assessed, with the magnetic approach emerging as the most promising due to its desirable efficiency and compliance with environmental and economic concerns. The findings of this report are expected to have a significant impact on the overall process of separating oil and water, benefiting the oil and gas industry, as well as other relevant sectors in achieving the circular economy

Advanced adsorptions of non-steroidal anti-inflammatory drugs from environmental waters in improving offline and online preconcentration techniques : An analytical review

Humans and animals frequently utilize nonsteroidal anti-inflammatory drugs (NSAIDs) as analgesics for various conditions. The ubiquitous use of NSAIDs has resulted in their widespread presence in environmental waters (concentrations detected in water (Malaysia) ranging from 1.40 × 10-1 to 9.72 × 10-2 mg L−1), which may threaten human health. Consequentially, continuous vigilance and resolve are indispensable for preventing any catastrophe. Numerous preconcentration techniques have been developed in response to the rising demand for a rapid, sensitive, and robust method capable of producing a dependable result (relative recoveries (RR) > 70% and limit of detection (LOD) 0.1 ng mL−1). Methods: This review aims to summarize the advancement of pre-concentration techniques using advanced adsorptive materials in quantifying NSAIDs from water mediums. Different univariate and multivariate optimization approaches for offline and online preconcentration are discussed in detail. Significant findings: The multivariate approach is more promising compared to conventional approach for developing an offline preconcentration technique. The analytical performance of online and offline preconcentration is comparable, but online preconcentration utilizes less solvent, aligning with the Green Analytical Chemistry initiative

Effective solvents for proteins recovery from microalgae

From an industrial perspective, the exploitation of microalgae as protein source is of great economical and commercial interest due to several attractive characteristics. However, the protein extraction efficiency is limited by the multiple layers of rigid and thick cell walls that are enriched with recalcitrant structure of cellulose. Therefore, an efficient method of cell disruption is necessary to disintegrate the cell wall and promote the release of protein contents. The conventional methods for downstream processing, e.g. disruption, isolation, extraction, concentration and purification, are energy-intensive and costly because they typically compose of several operational units. To reduce the overall process cost and establish an economical feasible process for the large-scale production of microalgae derived products, a more cost-effective and ecofriendly technique in downstream processing is in critical demand. One of the main challenges for protein extraction from microalgae cells is the recalcitrant structure of microalgae cell wall. This work aims to provide a guideline on the selection of the solvent to facilitate the proteins release during the cell disruption process. The influences of various solvent types (methanol, ethanol, 1-propanol and water) were evaluated and compared based on the protein yields. It was found that water solvent released the highest protein concentration from microalgae compared to the other tested solvents

Process optimization and simulation of biodiesel synthesis from waste cooking oil through supercritical transesterification reaction without catalyst

This study reports optimization and simulation of biodiesel synthesis from waste cooking oil through supercritical transesterification reaction without the use of any catalyst. Although the catalyst enhances the reaction rate but due to the presence of water contents in waste cooking oil, the use of catalyst could cause a negative impact on the biodiesel yield. The transesterification reaction without catalyst also offers the advantage of the reduction of pretreatment cost. This study comprises of two steps; first step involves the development and validation of process simulation scheme. The second step involves the optimization using Response Surface Methodology. Face-centered central composite design of experiments is used for experimental matrix development and subsequent statistical analysis of the results. Analysis of variance is employed for optimization purpose. In addition, a sensitivity study of the process parameters including pressure, temperature, and molar ration of oil-to-methanol was conducted. The statistical analysis reveals that temperature is the most influential process parameter as compared to pressure and oil-to-methanol molar ratio. The optimization study results in the maximum biodiesel yield (94.16%) at an optimum temperature of 274.8 °C, 7.02 bar pressure, and an oil-to-methanol molar ratio of 12.43

Microwave-Absorbing Catalysts in Catalytic Reactions of Biofuel Production

Catalytic reactions in producing biofuels often face issues such as low product yield, low selectivity to preferred products and serious environmental issues which leads to the exploration of green technologies. Microwave technology is one of the green technologies that is widely applied in the field such as medical, food, signal processing or navigation, and has been reviewed for its potential in the catalytic reactions for biofuel production. With the application of microwave technology, its unique heating mechanism consists of magnetic field energy and electric field energy that enables the selective heating of materials, allowing rapid reaction and enhancement of catalytic performance of catalysts. In general, this review has discussed on the fundamentals and mechanisms of microwave technology with an in-depth discussion on the application of microwave-absorbing catalysts for biofuel production, especially in ammonia synthesis, bio-oil and 5-HMF production as well as methanation. Lastly, the challenges and future prospect of microwave-absorbing catalysts are included as well

Characterization and Preliminary Application of a Novel Lipoxygenase from Enterovibrio norvegicus

Lipoxygenases have proven to be a potential biocatalyst for various industrial applications. However, low catalytic activity, low thermostability, and narrow range of pH stability largely limit its application. Here, a lipoxygenase (LOX) gene from Enterovibrio norvegicus DSM 15893 (EnLOX) was cloned and expressed in Escherichia coli BL21 (DE3). EnLOX showed the catalytic activity of 40.34 U mg−1 at 50 °C, pH 8.0. Notably, the enzyme showed superior thermostability, and wide pH range stability. EnLOX remained above 50% of its initial activity after heat treatment below 50 °C for 6 h, and its melting point temperature reached 78.7 °C. More than 70% of its activity was maintained after incubation at pH 5.0–9.5 and 4 °C for 10 h. In addition, EnLOX exhibited high substrate specificity towards linoleic acid, and its kinetic parameters of Vmax, Km, and Kcat values were 12.42 mmol min−1 mg−1, 3.49 μmol L−1, and 16.86 s−1, respectively. LC-MS/MS analysis indicated that EnLOX can be classified as 13-LOX, due to its ability to catalyze C18 polyunsaturated fatty acid to form 13-hydroxy fatty acid. Additionally, EnLOX could improve the farinograph characteristics and rheological properties of wheat dough. These results reveal the potential applications of EnLOX in the food industry

Bioengineering strategies of microalgae biomass for biofuel production: recent advancement and insight

ABSTRACTAlgae-based biofuel developed over the past decade has become a viable substitute for petroleum-based energy sources. Due to their high lipid accumulation rates and low carbon dioxide emissions, microalgal species are considered highly valuable feedstock for biofuel generation. This review article presented the importance of biofuel and the flaws that need to be overcome to ensure algae-based biofuels are effective for future-ready bioenergy sources. Besides, several issues related to the optimization and engineering strategies to be implemented for microalgae-based biofuel derivatives and their production were evaluated. In addition, the fundamental studies on the microalgae technology, experimental cultivation, and engineering processes involved in the development are all measures that are commendably used in the pre-treatment processes. The review article also provides a comprehensive overview of the latest findings about various algae species cultivation and biomass production. It concludes with the most recent data on environmental consequences, their relevance to global efforts to create microalgae-based biomass as effective biofuels, and the most significant threats and future possibilities

Thermochemical conversion of different biomass feedstocks into hydrogen for power plant electricity generation

Most hydrogen production technologies are dependent on non-renewable resources, which are not sustainable in the long run. However, H2 can be produced in the future from renewable sources, becoming one of the cleanest energy carriers. Compared to other biomass treatment methods, the thermochemical pathways from biomass for sustainable H2 generation offers a considerable promise for its industrial use. The most studied routes are biomass gasification and reformation of the bio-oil generated by biomass pyrolysis, while some works on supercritical water gasification and bio-oil gasification are extensively developed to improve hydorgen production efficiency. This review discusses the most current developments in research on the methods of pyrolysis, gasification, steam reformation, and microwave-induced plasma for producing hydrogen from various types of biomasses, including lignocellulosic and woody biomasses. By utilizing the hydrogen produced from biomass, possibilities of creating a sustainable city were analyzed. There are many upgraded technologies to generate electricity using hydrogen produced from biomass such as gas turbines, combined cycle power plants, and fuel cells. The environmental feasibility of hydrogen usage was also evaluated, along with the status quo of hydrogen power plants in several countries. This review contributes to the large-scale implementation of hydrogen energy with in-depth discussion on the latest development.Nanyang Technological UniversityThe authors would like to thank Nanyang Technological University (Singapore) for the facilities and resources provided for the completion of this work