Strategies and advances in the pretreatment of microalgal biomass

Enhanced toxicity-free astaxanthin extraction from Haematococcus pluvialis via concurrent cell disruption and demulsification

The extraction of astaxanthin from Haematococcus pluvialis involves the utilization of petroleum-derived organic solvents or supercritical CO2, beset by safety concerns, high costs, and environmental sustainability limitations. This study, in contrast, employed a method involving the adjustment of salt concentration, propylene glycol, and vegetable oil fraction to disrupt emulsion in aqueous cell lysates for facilitating the separation of astaxanthin. Under optimized conditions, an astaxanthin-containing oil with a content of 1.88% was obtained even with the use of wet biomass, and four rounds of consecutive extraction resulted in a cumulative recovery yield of 66.41%. This process produced astaxanthin-enriched soybean oil with 9.49 times improved antioxidant capacity that satisfies a requirement for health functional application. Omitting the solvent removal and drying processes, which consume tremendous energy, can reduce the production cost by 2.98 times compared to conventional methods. Consequently, this study suggests an effective technique for producing edible oil containing H. pluvialis-derived astaxanthin.

Mechanism and kinetic model of microalgal enzymatic hydrolysis for prospective bioethanol conversion

Tetraselmis chuii is a potential microalgae that is in consideration for producing bioethanol owing to its large content of carbohydrates. The glucose production from T. chuii through an enzymatic process with cellulase and xylanase (pretreatment process) and α-amylase and glucoamylase (saccharification process) was studied. The mechanism of the enzymatic process was developed and the kinetic models were then evaluated. For the pretreatment process, enzymes with 30% concentration reacted at 30 °C for 40 min resulted in 35.9% glucose yield. For the saccharification process, the highest glucose yield of 90.03% was obtained using simultaneous α-amylase (0.0006%) and glucoamylase (0.01%) enzymes at 55 °C and for 40 min. The kinetic models fitted well with the experimental data. The model also revealed that the saccharification process performed better than the pretreatment process with a higher kinetic constant and lower activation energy. The proposed kinetic model plays an important role in implementing processes at a larger scale.

Rapid and mild fractionation of hemicellulose through recyclable mandelic acid pretreatment

The development of organic acid pretreatments from biological sources is essential to facilitate the progress of green and sustainable chemistry. In this study, the effectiveness of mandelic acid pretreatment (MAP) was analyzed for eucalyptus hemicellulose separation. 83.66% of xylose was separated under optimal conditions (temperature: 150 °C; concentration: 6.0 wt%; time: 80 min). The hemicellulose separation selectivity is higher than acetic acid pretreatment (AAP). The stable and effective separation efficiency (56.55%) is observed even after six reuses of the hydrolysate. Higher thermal stability, larger crystallinity index and optimized surface element distribution in the samples were demonstrated by MAP. Lignin condensation is effectively inhibited through MAP, as determined from the structural of different lignin. In particular, the demethoxylation of lignin by MA was found. These results open up a new way to construct a novel organic acid pretreatment for separating hemicellulose with high efficiency.

Emerging trends in the pretreatment of microalgal biomass and recovery of value-added products: A review

Microalgae are a promising source of raw material (i.e., proteins, carbohydrates, lipids, pigments, and micronutrients) for various value-added products and act as a carbon sink for atmospheric CO₂. The rigidity of the microalgal cell wall makes it difficult to extract different cellular components for its applications, including biofuel production, food and feed supplements, and pharmaceuticals. To improve the recovery of products from microalgae, pretreatment strategies such as biological, physical, chemical, and combined methods have been explored to improve whole-cell disruption and product recovery efficiency. However, the diversity and uniqueness of the microalgal cell wall make the pretreatment process more species-specific and limit its large-scale application. Therefore, advancing the currently available technologies is required from an economic, technological, and environmental perspective. Thus, this paper provides a state-of-art review of the current trends, challenges, and prospects of sustainable microalgal pretreatment technologies from a microalgae-based biorefinery concept.

Current trends in the pretreatment of microalgal biomass for efficient and enhanced bioenergy production

Biofuels from microalgal biomass is among some of the promising sustainable energy technologies that can significantly replace the dependence on fossil fuels worldwide due to potentiality to lower CO₂ emissions. Nevertheless, the extraction of biomolecules for biofuel generation is inhibited by the rigidity of the cellular structure of microalgal biomass. Various pretreatment strategies have been evaluated for their efficacy in microalgal cell wall disruption to enhance microalgal bioenergy production. However, the efficiency of the pretreatment methods depend on the particular species being treated due to the inherent variability of the composition of the cell wall. This paper reviews pretreatment strategies (mainly novel physical, chemical and physicochemical) employed in bioenergy generation from microalgal biomass, address existing constraints and provides prospects for economic and industrial-scale production. The authors have also discussed the different pretreatment methods used for biodiesel, bioethanol, and biohydrogen production.

Recent advances in lignocellulosic and algal biomass pretreatment and its biorefinery approaches for biochemicals and bioenergy conversion

As the global demand for sustainable energy increases, lignocellulosic (such as agricultural residues, forest biomass, municipal waste, and dedicated energy crops) and algal (including macroalgae and microalgae) biomass have attracted considerable attention, because of their high availability of carbohydrates. This is a potential feedstock to produce biochemical and bioenergy. Pretreatment of biomass can disrupt their complex structure, increasing conversion efficiency and product yield. Therefore, this review comprehensively discusses recent advances in different pretreatments (physical, chemical, physicochemical, and biological pretreatments) for lignocellulosic and algal biomass and their biorefining methods. Life cycle assessment (LCA) which enables the quantification of the environmental impact assessment of a biorefinery also be introduced. Biorefinery processes such as raw material acquisition, extraction, production, waste accumulation, and waste conversion are all monitored under this concept. Nevertheless, there still exist some techno-economic barriers during biorefinery and extensive research is still needed to develop cost-effective processes.

Microalgal Biomass as Feedstock for Bacterial Production of PHA: Advances and Future Prospects

The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.

Algae biorefinery: a promising approach to promote microalgae industry and waste utilization

Microalgae have a number of intriguing characteristics that make them a viable raw material aimed at usage in a variety of applications when refined using a bio-refining process. They offer unique capabilities that allow them to be used in biotechnology-related applications. As a result, this review explores how to increase the extent to which microalgae may be integrated with various additional biorefinery uses in order to improve their maintainability. In this study, the use of microalgae as potential animal feed, manure, medicinal, cosmeceutical, ecological, and other biotechnological uses is examined in its entirety. It also includes information on the boundaries, openings, and improvements of microalgae and the possibilities of increasing the range of microalgae through techno-economic analysis. According to the findings of this review, financing supported research and shifting the focus of microalgal investigations from biofuels production to biorefinery co-products can help guarantee that they remain a viable resource. Furthermore, innovation collaboration is unavoidable if one wishes to avoid the high cost of microalgae biomass handling. This review is expected to be useful in identifying the possible role of microalgae in biorefinery applications in the future.