Ultrasonication aided in-situ transesterification of microbial lipids to biodiesel

Revealing the link between evolution of electron transfer capacity of humic acid and key enzyme activities during anaerobic digestion

Humic acid (HA) is an important active compound formed during anaerobic digestion process, with a complex structure and dynamic electron transfer capacity (ETC). However, the mechanisms by which these macromolecular organic compounds dynamically interact with the microbial anaerobic digestion process at different operating temperatures are still unclear. In this study, the link between the evolution of the ETC of HAs and the microbial community under mesophilic and thermophilic conditions was investigated. The results showed an increasing trend in the ETC of HAs in both mesophilic (671-1479 μmol gHA^-1) and thermophilic (774-1506 μmol gHA^-1) anaerobic digestion (AD) until day 25. The ETC was positively correlated with the bacterial community of hydrolytic and acidogenic phases, but negatively correlated with the archaeal community of the methanogenic phase. Furthermore, the relationship between ETC and key enzyme activity was explored using a co-occurrence network analysis. HAs revealed a high potential to promote key enzyme activities during hydrolysis (amylase and protease) and acidification (acetate kinase, butyrate kinase, and phosphotransacetylase) while inhibiting the key enzyme activity in the methanogenic phase during the anaerobic digestion process. Moreover, HAs formed under thermophilic conditions had a greater influence on key enzyme activities than those formed under mesophilic conditions. This study advances our understanding of the mechanisms underlying the influence of HAs on anaerobic digestion performance.

Comparison of Ex-Situ and In-Situ Transesterification for the Production of Microbial Biodiesel

Microbial biodiesel is converted from microbial lipids via transesterification process. Most microbial biodiesel studies are focusing on the use of microalgal lipids as feedstock. Apart from using microalgae for lipid biosynthesis, lipids can also be extracted from other oleaginous microorganisms like fungi and yeast. However, there are gaps in the studies of lipid production from filamentous fungi, especially in-situ transesterification process. The aim of this project is to compare in-situ with the ex-situ transesterification of fungal biomass from Aspergillus oryzae. In ex-situ transesterification, two methods of lipid extraction, the Soxhlet extraction and the Bligh and Dyer extraction, were performed. For in-situ transesterification, two methods using different catalysts were investigated. Base-catalyzed in-situ transesterification of fungal biomass resulted on the highest Fatty Acid Methyl Esters (FAME) yield. The base-catalyzed in-situ transesterification was further optimized via Central Composite Design (CCD) of Response Surface Methodology (RSM). The parameters investigated were the catalyst loading, methanol to biomass ratio and reaction time. The optimization showed that the highest FAME yield was at 25.1% (w/w) with 10 minutes reaction time, 5% catalyst and 360:1 of the ratio of the methanol to biomass. Based on Analysis of Variance (ANOVA), the model was found to be significant according to the value of “Prob >F” of 0.0028. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Surfactant-assisted in situ transesterification of wet Rhodotorula glutinis biomass

In situ transesterification of oleaginous microbes with short chain alcohol has been developed as a renewable process for the production of biodiesel. Dry biomass is often a requisite for the process to avoid the adverse effect of water on the productivity. As a consequence, large amount of energy consumption is required for prior biomass drying. In this study, the wet biomass of Rhodotorula glutinis, an oleaginous yeast, was used directly in in situ transesterification without biomass drying. The reaction conditions were optimized for the production of fatty acid methyl esters (FAME) and the effects of adding different surfactants were also studied. The highest FAME yield of 110% was achieved with a methanol loading of 1:100 at 90°C for 8 h as catalyzed by 0.36 M H₂SO₄, and the FAME content was 97%, which meets the 96.5% specified in both European biodiesel standards and Taiwanese biodiesel standards. The addition of 50 mM 3-(N,N-dimethylmyristylammonio)propanesulfonate (3-DMAPS, a zwitterionic surfactant) improved the FAME yield from 69% to 83%, which was obtained with a low methanol loading of 1:10 at 90°C for 10 h. Hence, the production of FAME with wet biomass under optimized reaction conditions was as effective as that with the dry form. This clearly indicates that using wet R. glutinis as the feedstock is feasible for the production of biodiesel by in situ transesterification.

Production of Biodiesel from Castor Oil: A Review

An attractive alternative to the use of fossil fuels is biodiesel, which can be obtained from a variety of feedstock through different transesterification systems such as ultrasound, microwave, biological, chemical, among others. The efficient and cost-effective biodiesel production depends on several parameters such as free fatty acid content in the feedstock, transesterification reaction efficiency, alcohol:oil ratio, catalysts type, and several parameters during the production process. However, biodiesel production from vegetable oils is under development, causing the final price of biodiesel to be higher than diesel derived from petroleum. An alternative to decrease the production costs will be the use of economical feedstocks and simple production processes. Castor oil is an excellent raw material in terms of price and quality, but especially this non-edible vegetable oil does not have any issues or compromise food security. Recently, the use of castor oil has attracted attention for producing and optimizing biodiesel production, due to high content of ricinoleic fatty acid and the possibility to esterify with only methanol, which assures low production costs. Additionally, biodiesel from castor oil has different advantages over conventional diesel. Some of them are biodegradable, non-toxic, renewable, they can be used alone, low greenhouse gas emission, among others. This review discusses and analyzes different transesterification processes, technologies, as well as different technical aspects during biodiesel production using castor oil as a feedstock.

Application of Simultaneous Oil Extraction and Transesterification in Biodiesel Fuel Synthesis: A Review

Increasing concentrations of greenhouse gases in the atmosphere are leading to increased production and use of biofuels. The industrial development of biodiesel production and the use of biodiesel in the EU transport sector have been ongoing for almost two decades. Compared to mineral diesel production, the process of producing biodiesel is quite complex and expensive, and the search for new raw materials and advanced technologies is needed to maintain production value and expand the industrial production of biodiesel. The purpose of this article is to review the application possibilities of one of the new technologies—simultaneous extraction of oil from oily feedstock and transesterification (in situ)—and to evaluate the effectiveness of the abovementioned process under various conditions.

Turbo thin film continuous flow production of biodiesel from fungal biomass

Direct biodiesel production from wet fungal biomass may significantly reduce production costs, but there is a lack of fast and cost-effective processing technology. A novel thin film continuous flow process has been applied to study the effects of its operational parameters on fatty acid (FA) extraction and FA to fatty acid methyl ester (FAME) conversion efficiencies. Single factor experiments evaluated the effects of catalyst concentration and water content of biomass, while factorial experimental designs determined the interactions between catalyst concentration and biomass to methanol ratio, flow rate, and rotational speed. Direct transesterification (DT) of wet Mucor plumbeus biomass at ambient temperature and pressure achieved a FA to FAME conversion efficiency of >90% using 3 wt/v % NaOH concentration, if the water content was ≤50% (w/w). In comparison to existing DT methods, this continuous flow processing technology has an estimated 90-94% reduction in energy consumption, showing promise for up-scaling.

Biodiesels from microbial oils: Opportunity and challenges

Although biodiesel has been extensively explored as an important renewable energy source, the raw materials-associated cost poses a serious challenge on its large-scale commercial production. The first and second generations of biodiesel are mainly produced from usable raw materials, e.g. edible oils, crops etc. Such a situation inevitably imposes higher demands on land and water usage, which in turn compromise future food and water supply. Obviously, there is an urgent need to explore alternative feedstock, e.g. microbial oils which can be produced by many types of microorganisms including microalgae, fungi and bacteria with the advantages of small footprint, high lipid content and efficient uptake of carbon dioxide. Therefore, this review offers a comprehensive picture of microbial oil-based technology for biodiesel production. The perspectives and directions forward are also outlined for future biodiesel production and commercialization.

Detergent assisted ultrasonication aided in situ transesterification for biodiesel production from oleaginous yeast wet biomass

In situ transesterification of oleaginous yeast wet biomass for fatty acid methyl esters (FAMEs) production using acid catalyst, methanol with or without N-Lauroyl sarcosine (N-LS) treatment was performed. The maximum FAMEs yield obtained with or without N-LS treatment in 24h reaction time was 96.1±1.9 and 71±1.4% w/w, respectively. The N-LS treatment of biomass followed by with or without ultrasonication revealed maximum FAMEs yield of 94.3±1.9% and 82.9±1.8% w/w using methanol to lipid molar ratio 360:1 and catalyst concentration 360mM (64μL H₂SO₄/g lipid) within 5 and 25min reaction time, respectively. The FAMEs composition obtained in in situ transesterification was similar to that obtained with conventional two step lipid extraction and transesterification process. Biodiesel fuel properties (density, kinematic viscosity, cetane number and total glycerol) were in accordance with international standard (ASTM D6751), which suggests the suitability of biodiesel as a fuel.

In-situ pyrogenic production of biodiesel from swine fat

In-situ production of fatty acid methyl esters from swine fat via thermally induced pseudo-catalytic transesterification on silica was investigated in this study. Instead of methanol, dimethyl carbonate (DMC) was used as acyl acceptor to achieve environmental benefits and economic viability. Thermo-gravimetric analysis of swine fat reveals that swine fat contains 19.57wt.% of water and impurities. Moreover, the fatty acid profiles obtained under various conditions (extracted swine oil+methanol+NaOH, extracted swine oil+DMC+pseudo-catalytic, and swine fat+DMC+pseudo-catalytic) were compared. These profiles were identical, showing that the introduced in-situ transesterification is technically feasible. This also suggests that in-situ pseudo-catalytic transesterification has a high tolerance against impurities. This study also shows that FAME yield via in-situ pseudo-catalytic transesterification of swine fat reached up to 97.2% at 380°C. Therefore, in-situ pseudo-catalytic transesterification can be applicable to biodiesel production of other oil-bearing biomass feedstocks.

Ultrasonic intensification as a tool for enhanced microbial biofuel yields

Ultrasonication has recently received attention as a novel bioprocessing tool for process intensification in many areas of downstream processing. Ultrasonic intensification (periodic ultrasonic treatment during the fermentation process) can result in a more effective homogenization of biomass and faster energy and mass transfer to biomass over short time periods which can result in enhanced microbial growth. Ultrasonic intensification can allow the rapid selective extraction of specific biomass components and can enhance product yields which can be of economic benefit. This review focuses on the role of ultrasonication in the extraction and yield enhancement of compounds from various microbial sources, specifically algal and cyanobacterial biomass with a focus on the production of biofuels. The operating principles associated with the process of ultrasonication and the influence of various operating conditions including ultrasonic frequency, power intensity, ultrasonic duration, reactor designs and kinetics applied for ultrasonic intensification are also described.

Microbial lipid-based lignocellulosic biorefinery: feasibility and challenges

Although single-cell oil (SCO) has been studied for decades, lipid production from lignocellulosic biomass has received substantial attention only in recent years as biofuel research moves toward producing drop-in fuels. This review gives an overview of the feasibility and challenges that exist in realizing microbial lipid production from lignocellulosic biomass in a biorefinery. The aspects covered here include biorefinery technologies, the microbial oil market, oleaginous microbes, lipid accumulation metabolism, strain development, process configurations, lignocellulosic lipid production, technical hurdles, lipid recovery, and technoeconomics. The lignocellulosic SCO-based biorefinery will be feasible only if a combination of low- and high-value lipids are coproduced, while lignin and protein are upgraded to high-value products.