Screening of different species of Scenedesmus isolated from Egyptian freshwater habitats for biodiesel production

A biphasic photobioreactor system for consecutive extraction of lipids and carotenoids from pre-hydrolysed microalgae and evaluation of its biodiesel potential

A green extraction method is developed using partially hydrolysed microalgal cells grown in biocompatible solvent for simultaneous cultivation and extraction of bioproducts from a highly efficient permeabilized microalgal cell with enhanced biomass and lipid content for potential use in biodiesel production. Incomplete digestion of cell wall was achieved by regulating the incubation time of the enzymatic pretreatment of the microalgal cells. 15.77% increase in lipid content was seen when untreated cells were cultured with biocompatible solvent, while cultivation of these enzymatically pretreated cells with biocompatible solvent, the lipid content increased by 53.33% and 22% higher carotenoid content was observed as compared to conventional extraction. The total fatty acids obtained after 1st and 2nd extractions in untreated samples were 67.82%, while those in enzymatically partially digested samples were 91.94%. The untreated and partially enzymatically predigested strain showed suitable properties for quality biodiesel production as per international recommendations. The cost benefit analysis of the overall process showed the use of biocompatible solvent coupled to enzymatically predigested biomass was a favorable option as compared to conventional extraction.

Sustainable Feedstocks and Challenges in Biodiesel Production: An Advanced Bibliometric Analysis

Biodiesel can be produced from vegetable oils, animal fats, frying oils, and from microorganism-synthesized oils. These sources render biodiesel an easily biodegradable fuel. The aim of this work was to perform an advanced bibliometric analysis of primary studies relating to biodiesel production worldwide by identifying the key countries and regions that have shown a strong engagement in this area, and by understanding the dynamics of their collaboration and research outputs. Additionally, an assessment of the main primary feedstocks employed in this research was carried out, along with an analysis of the current and future trends that are expected to define new paths and methodologies to be used in the manufacture of biodegradable and renewable fuels. A total of 4586 academic outputs were selected, including peer-reviewed research articles, conference papers, and literature reviews related to biodiesel production, in the time period spanning from 2010 to 2021. Articles that focused on feedstocks for the production of biodiesel were also included, with a search that returned 330 papers. Lastly, 60 articles relating to biodiesel production via sewage were specifically included to allow for an analysis of this source as a promising feedstock in the future of the biofuel market. Via the geocoding and the document analyses performed, we concluded that China, Malaysia, and India are the largest writers of articles in this area, revealing a great interest in biofuels in Asia. Additionally, it was noted that environmental concerns have caused authors to conduct research on feedstocks that can address the sustainability challenges in the production of biodiesel.

Usage of Moringa oleifera residual seeds promotes efficient flocculation of Tetradesmus dimorphus biomass

Bio-flocculation is a sustainable low-cost harvesting technique for microalgae biomass production; however, it is generally less efficient than chemical flocculants. This study aims to investigate the efficiency of Moringa oleifera seeds as a bio-flocculant for harvesting Tetradesmus dimorphus biomass. Four extracts from integral and residual (seeds without lipids) biomass of M. oleifera seeds using salt or aqueous solutions were used at four concentrations (100, 200, 300, and 400 ppm). Flocculation efficiency (FE) increased as the pH decreased. The addition of the extracts reduced the pH of the cultures, dispensing pH adjustment after dosing the flocculating agent. Salt extracts exhibited higher flocculation efficiency than aqueous extracts. The highest flocculation efficiency (~ 98%) was obtained using a salt extract of residual biomass of seeds in any concentration varying from 100 to 400 ppm. The predicted values obtained from a data modeling using response surface methodology approached the real values (r 2 = 0.9382), resulting in an adequate optimization of the flocculant concentration of ~ 335 ppm and pH 5.6 for a predicted FE of ~ 106%. The findings of the present study confirmed that the salt extract from residual biomass of M. oleifera seeds is an effective bio-flocculant for T. dimorphus biomass harvesting.

A Review of Microalgae- and Cyanobacteria-Based Biodegradation of Organic Pollutants

This review proposes a new bioremediation method based on the diverse functionalities of algae. A greenway for cleansing wastewater is more ecologically friendly and environmentally sustainable than prior methods with other bacteria. New bioremediation technology employing algae and cyanobacteria for the removal of a wide range of organic contaminants is reasonable and has great potential. The prevalence of organic contaminants in aquatic habitats may endanger the health and well-being of several marine creatures. Agriculture, industry, and household trash are just a few of the human-caused sources of organic pollutants that contaminate waterways around the world. Before wastewater can be released into waterways, it must be cleaned. Algae-based wastewater treatment systems are becoming increasingly popular because of their environmental sustainability and lack of secondary pollutants. According to the kind of pollutant, the physicochemical properties of wastewater, and the algal species, algae and cyanobacteria can absorb and accumulate a wide spectrum of organic pollutants at different rates. In addition, phytoremediation is a cost-effective alternative to conventional treatments for degrading organic contaminants. Phycoremediationally produced algal biomass may also be an important part of the bioenergy value chain. This article focuses on microalgae and cyanobacteria species, which may remove many organic contaminants from water systems.

A comprehensive review on carbon source effect of microalgae lipid accumulation for biofuel production

Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO₂-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.

Valorization of lipidic food waste for enhanced biodiesel recovery through two-step conversion: A novel microalgae-integrated approach

The present study designed an innovative route for two-step biodiesel recovery from lipidic food waste followed by microalgae cultivation. Optimization of oil conversion showed the highest fatty acid methyl esters (FAMEs) recovery of 92.6% (lipid basis). Microalgal lipid accumulation enhanced by the increased lipid-free waste hydrolysate ratio in the medium, where the maximum lipid content of 26.2 dw% was recorded using 50% hydrolysate. Application of 30% hydrolysate ratio resulted in the maximum recorded lipid productivity, which was 99.4% higher than that of the control and insignificant with 40% hydrolysate. Waste oil-derived FAMEs showed 69.0% higher saturated fatty acids (SFAs) proportion than that of algal lipids. In contrast, the highest polyunsaturated fatty acids (PUFAs) proportion (48.8% of total fatty acids) was recorded in microalgal lipids. The study concluded that mixing microalgal lipids with waste oil (1:1, w/w) provides a desirable practical route for enhanced biodiesel production complying with the international standards.

Combined effect of salinity and pH on lipid content and fatty acid composition of Tisochrysis lutea

The haptophyte microalga Tisochrysis lutea was heterotrophically grown in F2 medium with different combinations of pH and salinity. Growth, oil content and fatty acids (FAs) profile were determined under each set of conditions. The salinity was adjusted using NaCl at concentrations of 0.4, 0.6, 0.8, or 1.0 M, while pH was adjusted at 7, 8, or 9, and heterotrophic growth was performed using organic carbon in the form of sugar cane industry waste (CM). Fatty acid methyl esters (FAMEs) were identified by gas chromatography. The results showed that pH of 8.0 was the optimal for dry weight and oil production, regardless of the salinity level. At pH 8.0, growth at a salinity of 0.4 M NaCl was optimal for biomass accumulation (1.185 g L^-1). Under these conditions, the maximum growth rate was 0.055 g L^-1 d^-1, with a doubling time of 17.5 h and a degree of multiplication of 2.198. Oil content was maximal (34.87%) when the salinity was 0.4 M and the pH was 9.0. The ratio of saturated to unsaturated FAs was affected by the pH value and salinity, in that unsaturated FAs increased to 58.09% of the total FAs, considerably greater than the value of 40.59% obtained for the control (0.4 M NaCl and pH 8.0).

Effects of different nitrogen sources and light paths of flat plate photobioreactors on the growth and lipid accumulation of Chlorella sp. GN1 outdoors

To assess the potential of Chlorella sp. GN1 for producing biodiesel raw materials in flat plate photobioreactors (FPPs) outdoors, we optimized the nitrogen sources and concentrations for the growth of the algae. The effects of different light paths of FPPs on the growth, lipid accumulation, and fatty acids of Chlorella sp. GN1 were also studied. As the light path of the FPPs was reduced, the alga could accumulate lipids rapidly, achieving high lipid content and lipid productivity outdoors. The highest lipid content obtained was 53.5%, when the light path was 5 cm. In addition, the lipid productivity was 66.7 mg L^-1 day^-1. The main fatty acids were C16/C18, accounting more than 90% of the total fatty acids. Results showed that Chlorella sp. GN1 had the ability to accumulate large quantities of lipids in FPPs outdoors and was a promising microalgal species for biofuel production.

Evaluation of Infrared Radiation Combined with Hot Air Convection for Energy-Efficient Drying of Biomass

Cost-effective biomass drying is a key challenge for energy recovery from biomass by direct combustion, gasification, and pyrolysis. The aim of the present study was to optimize the process of biomass drying using hot air convection (HA), infrared (IR), and combined drying systems (IR-HA). The specific energy consumption (SEC) decreased significantly by increasing the drying temperature using convective drying, but higher air velocities increased the SEC. Similarly, increasing air velocity in the infrared dryer resulted in a significant increase in SEC. The lowest SEC was recorded at 7.8 MJ/kg at an air velocity of 0.5 m/s and an IR intensity of 0.30 W/cm2, while a maximum SEC (20.7 MJ/kg) was observed at 1.0 m/s and 0.15 W/cm2. However, a significant reduction in the SEC was noticed in the combined drying system. A minimum SEC of 3.8 MJ/kg was recorded using the combined infrared-hot air convection (IR-HA) drying system, which was 91.7% and 51.7% lower than convective and IR dryers, respectively. The present study suggested a combination of IR and hot air convection at 60 °C, 0.3 W/cm2 and 0.5 m/s as optimum conditions for efficient drying of biomass with a high water content.