Sustainable production of liquid biofuels from renewable microalgae biomass

Development of Microalgae Biodiesel: Current Status and Perspectives

Microalgae are regarded as a promising source of biodiesel. In contrast with conventional crops currently used to produce commercial biodiesel, microalgae can be cultivated on non-arable land, besides having a higher growth rate and productivity. However, microalgal biodiesel is not yet regarded as economically competitive, compared to fossil fuels and crop-based biodiesel; therefore, it is not commercially produced. This review provides an overall perspective on technologies with the potential to increase efficiency and reduce the general costs of biodiesel production from microalgae. Opportunities and challenges for large-scale production are discussed. We present the current scenario of Brazilian research in the field and show a successful case in the research and development of microalgal biodiesel in open ponds by Petrobras. This publicly held Brazilian corporation has been investing in research in this sector for over a decade.

Microalgal-based biochar in wastewater remediation: Its synthesis, characterization and applications

Microalgae are drawing attentions among researchers for their biorefinery use or value-added products. The high production rate of biomasses produced are attractive for conversion into volatile biochar. Torrefaction, pyrolysis and hydrothermal carbonization are the recommended thermochemical conversion techniques that could produce microalgal-based biochar with desirable physiochemical properties such as high surface area and pore volume, abundant surface functional groups, as well as functionality such as high adsorption capacity. The characterizations of the biochar significantly influence the mechanisms in adsorption of pollutants from wastewaters. Specific adsorption of the organic and inorganic pollutants from the effluent are reviewed to examine the adsorption capacity and efficiency of biochar derived from different microalgae species. Last but not least, future remarks over the challenges and improvements are discussed accordingly. Overall, this review would discuss the synthesis, characterization and application of the microalgal-based biochar in wastewater.

Biofuels and Their Potential in South Korea

We investigated the biofuel potential of South Korea and the implications of the introduction of biofuels for the Korean fuel market. We approximated the upper-bound biomass potential from forestry residues, livestock manure, and staple crops and calculated the amount of fuel that could be produced using these different biomass feedstocks. Our assessment suggests that biomass can be used to produce a significant portion of the fuel consumed annually in South Korea, with the most promising feedstock being forestry residues. Out of all the technologies considered, the production of cellulosic ethanol from forestry residues could potentially impact the fuel market the most. The key novelty of our study lies in that we considered a broad portfolio of biofuel technologies and carefully examined their potential economic and environmental implications for South Korea given its biomass availability (which we estimated).

Influence of photobioreactor configuration on microalgal biomass production

Biodiesel production from microalgae depends on the biomass concentration and lipid content in microalgal cells. Photobioreactors (PBRs) facilitates cultivation of microalgae and renders better process control than open systems. However, reactor configuration and consequential hydrodynamics considerably influence biomass and lipid production from microalgae. Here, four different configurations of PBRs, viz. airlift and bubble column with orifice sparger and newly designed ring sparger, were investigated. Resulting volumetric mass transfer coefficient, mixing time, and shear stress were analyzed at different air flow rates to realize their influence on biomass and lipid production from Neochloris oleoabundans UTEX 1185. Bubble column reactor with ring sparger was observed to exhibit superior performance, which was subsequently simulated using a two-phase Eulerian model to comprehend the influence of air flow rates on mixing time. The developed computational model corroborates well with the experimental findings of optimum air flow rate for maximum biomass yield in bubble column configuration.

Production and characterization of Spirulina sp. LEB 18 cultured in reused Zarrouk's medium in a raceway-type bioreactor

The objective was to evaluate the effect of reusing Zarrouk's medium on a Spirulina sp. LEB 18 culture by determining kinetic parameters, chemical composition, biofuels, and thermal characterization. Cultivation was performed in a raceway bioreactor for 7 days, the supernatant was reused for four cycles. Culturing the microalga in the reused medium resulted in a cellular yield of 2.30 g L^-1 (control) and 2.04, 1.89, 1.73, and 1.15 g L^-1 for four cycles with no influence on cell growth and productivity. Biomass with high contents of carbohydrates (58.00%, 3rd cycle), phycocyanin (2.47 mg mL^-1, 1st cycle), and saturated fatty acids (60.13%, 4th cycle) were obtained with an increase in the profiles of C16:0 (45.85%) and C18:2n6 (47.40%) in the 1st cycle. The reuse of Zarrouk's medium allowed obtaining biomass with reduced cost and differentiated characteristics, allowing the exploration of commercially important biomolecules by the completion of up to four cycles.

Cultivation of different microalgae with pentose as carbon source and the effects on the carbohydrate content

In the search for alternative carbon sources for microalgae cultivation, pentoses can be considered interesting alternatives since the most abundant global source of renewable biomass is lignocellulosic waste, which contains significant quantities of pentoses. However, the use of pentoses (C5) in the cultivation of microalgae is still not widely studied and only recently the first metabolic pathway for pentose absorption in microalgae was proposed. So, the objective of this work was to evaluate if the use of pentoses affects the growth and carbohydrates content of Chlorella minutissima, Chlorella vulgaris, Chlorella homosphaera and Dunaliella salina. The kinetic parameters, carbohydrate and protein content and the theoretical potential for ethanol production were estimated for all strains. The highest cellular concentrations (1.25 g L^-1) were obtained for D. salina with 5% of pentoses. The addition of pentoses leads to high levels of carbohydrates for C. minutissima (58.6%) cultured with 5% of pentoses, and from this biomass, it is possible to determine a theoretical production of ethanol of 38 mL per 100 g of biomass. The pentoses affect the growth and the biomass composition of the studied strains, generating biomass with potential use for bioethanol production.

Complex mathematical analysis of photobioreactor system

Modeling as a tool solves extremely difficult tasks in life sciences. Recently, schemes of culturing of microalgae have received special attention because of its unique features and possible uses in many industrial applications for renewable energy production and high value products isolation. The goal of this review is to present the use of system analysis theory applied to microalgae culturing modeling and process development. The review mainly focuses on the modeling of the key steps of autotrophic growth under the integral biorefinery concept of the microalgae biomass. The system approach follows systematically a procedure showing the difficulties by modeling of sub-systems. The development of microalgae kinetics and computational fluid dynamics (CFD) studies were analyzed in details as sub-systems in advanced design of photobioreactor (PBR). This review logically follows the trends of the modeling procedure and clarifies how this approach may save time and money during the research efforts. The result of this work is a successful development of a complex PBR mathematical analysis in the frame of the integral biorefinery concept.

Catalytic upgrading of pyrolysis vapor from rape straw in a vacuum pyrolysis system over La/HZSM-5 with hierarchical structure

Catalytic upgrading of pyrolysis vapor from rape straw was performed in a vacuum pyrolysis system over La/HZSM-5 with hierarchical structure. When 3M Na₂CO₃ was used for alkali treatment, the desilication process of HZSM-5 zeolite was highly controllable and the hierarchical porous HZSM-5(Hi-ZSM-5) zeolite was formed. After that, Hi-ZSM-5 was modified by impregnation with lanthanum ion, the acid sites of Lewis increased and the concentrations ratio of Brönsted acid and Lewis acid of the catalyst was improved. The highest hydrocarbons selectivity (49.86%), the lowest carbonyl compounds content (11.06%), and reasonable catalytic stability were obtained by the La/Hi-ZSM-5 catalyst. In addition, La/Hi-ZSM-5 further reduced the coke content of the catalyst to 11.05%, while increasing the selectivity of high value aromatic hydrocarbons. Obviously, La/Hi-ZSM-5 zeolite had high catalytic activity, and exhibited good potential and a beneficial nature for efficient preparation of high-valued bio-oil from rape straw.

Nano-Immobilized Biocatalysts for Biodiesel Production from Renewable and Sustainable Resources

The cost of biodiesel production relies on feedstock cost. Edible oil is unfavorable as a biodiesel feedstock because of its expensive price. Thus, non-edible crop oil, waste oil, and microalgae oil have been considered as alternative resources. Non-edible crop oil and waste cooking oil are more suitable for enzymatic transesterification because they include a large amount of free fatty acids. Recently, enzymes have been integrated with nanomaterials as immobilization carriers. Nanomaterials can increase biocatalytic efficiency. The development of a nano-immobilized enzyme is one of the key factors for cost-effective biodiesel production. This paper presents the technology development of nanomaterials, including nanoparticles (magnetic and non-magnetic), carbon nanotubes, and nanofibers, and their application to the nano-immobilization of biocatalysts. The current status of biodiesel production using a variety of nano-immobilized lipase is also discussed.

Non-plastidial expression of a synthetic insect geranyl pyrophosphate synthase effectively increases tobacco plant biomass

Designing effective synthetic genes of interest is a fundamental step in plant synthetic biology for biomass. Geranyl pyrophosphate (diphosphate) synthase (GPPS) catalyzes a bottleneck step toward terpenoid metabolism. We previously designed and synthesized a plant (Arabidopsis thaliana)-insect (Myzus persicae, Mp) GPPS- human influenza hemagglutinin (HA) cDNA, namely PTP-MpGPPS-HA (or PTP-sMpGPPS-HA, s: synthetic), to localize the protein in plastids and improve plant biomass. To better understand the effects of different subcellular localizations on plant performance, herein we report PTP-sMpGPPS-HA re-design to synthesize a new MpGPPS-HA cDNA, namely sMpGPPS-HA, to express a non-plastidial sMpGPPS-HA protein. The sMpGPPS-HA cDNA driven by a 2 × S 35S promoter was introduced into Nicotiana tabacum Xanthi. PTP-MpGPPS-HA and PMDC84 vector transgenic plants were also generated as positive and negative controls, respectively. Eighteen to twenty transgenic T0 lines were generated for each sMpGPPS-HA, PTP-sMpGPPS-HA, and PMDC84. Transcriptional genotyping analysis demonstrated the expression of sMpGPPS-HA in transgenic plants. Confocal microscopy analysis of transgenic progeny demonstrated the non-plastidial localization of sMpGPPS-HA. Growth of T1 transgenic and wild-type control plants showed that the expression of sMpGPPS-HA effectively increased plant height by 50-80%, leaf numbers and sizes, and dry biomass by 60-80%. Calculation of the vegetative growth rates showed that the expression of sMpGPPS-HA increased plant height each week. Moreover, sMpGPPS-HA expression promoted early flowering and reduced leaf carotenoid levels. In conclusion, non-plastidial expression of the novel sMpGPPS-HA was effective for improving tobacco growth and biomass. Our data indicate that research examining different subcellular localizations facilitates a better understanding of in planta functions of proteins encoded by synthetic cDNAs.

A general reaction network and kinetic model of the hydrothermal liquefaction of microalgae Tetraselmis sp

In this work, the hydrothermal liquefaction (HTL) of microalgal Tetraselmis sp. was conducted at various reaction temperatures (250-350°C) and reaction times (10-60min). A general reaction network and a quantitative kinetic model were proposed for the HTL of microalgae. In this reaction network, the primary decomposition of lipids, proteins, and carbohydrates generated heavy oil (HO), light oil (LO), and aqueous-phase (AP) products. Then, reversible interconversions and further decomposition of these product fractions to produce gas product were followed. The model accurately captures the trends observed in the experimental data. Analyses of the kinetic parameters (reaction rate constants and activation energies) suggested the dominant reaction pathways as well as the contribution of the biochemical compositions to the bio-oil yield. Finally, the kinetic parameters calculated from the model were utilized to explore the parameter space in order to predict the liquefaction product yields depending on the reaction time and temperature.

Pentoses and light intensity increase the growth and carbohydrate production and alter the protein profile of Chlorella minutissima

High concentrations of carbon, which is considered a necessary element, are required for microalgal growth. Therefore, the identification of alternative carbon sources available in large quantities is increasingly important. This study evaluated the effects of light variation and pentose addition on the carbohydrate content and protein profile of Chlorella minutissima grown in a raceway photobioreactor. The kinetic parameters, carbohydrate content, and protein profile of Chlorella minutissima and its theoretical potential for ethanol production were estimated. The highest cellular concentrations were obtained with a light intensity of 33.75µmol.m^-2.s^-1. Arabinose addition combined with a light intensity of 33.75µmol.m^-2.s^-1 increased the carbohydrate content by 53.8% and theoretically produced 39.1mL·100g^-1 ethanol. All of the assays showed that a lower light availability altered the protein profile. The luminous intensity affects xylose and arabinose assimilation and augments the carbohydrate content in C. minutissima, making this microalga appropriate for bioethanol production.