Nitrogen recycling from fuel-extracted algal biomass: residuals as the sole nitrogen source for culturing Scenedesmus acutus

Efficiency of the fatty acids extracted from the microalga Parachlorella kessleri in wound-healing

Wound healing is a physiological process that results in the reconstruction and restoration of granulation tissue, followed by scar formation. We explored the impact of fatty acids in the form of oils on wound healing since they are part of membrane phospholipids and participate in the inflammatory response. This work investigated the efficiency of fatty acids extracted from microalga Parachlorella kessleri in treating excisional wounds and burns and evaluated their antioxidant activity. The rationale behind this investigation lies in the integral role fatty acids play in membrane phospholipids and their involvement in the inflammatory response. Among different nitrogen sources, glycine showed the highest biomass and lipid productivity (0.08 g L-1 d-1 and 58.37 μgml-1 day-1, respectively). Based on the percentage of polyunsaturated fatty acids that increased by 50.38 % in the Glycine culture of P. kessleri, both total antioxidant capacity and DPPH radical scavenging activity were higher in the Glycine culture than control culture. In 30 anaesthetized male mice divided into 6 groups, using either a burn or an excision, two identical paravertebral full-thickness skin lesions were created. Either oils of P. kessleri (extracted from control and glycine culture) ointments or the vehicle (placebo cream) were applied twice daily to the excisional wounds of mice, while mebo cream was used for burn wounds as well as P. kessleri oil. P. kessleri oils (control or glycine culture) showed a significant effect on the reduction of excisional wounds and burns. Histopathological analysis showed that angiogenesis, collagen fiber formation, and epidermis creation were some of the healing indicators that improved. The key elements for this healing property are omega -3 fatty acids, and both P. kessleri oils extracted from control and glycine culture have significant wound-healing effects. Oil of glycine culture of P. kessleri, however, displayed superior results in this regard.

Microalgae as tools for bio-circular-green economy: Zero-waste approaches for sustainable production and biorefineries of microalgal biomass

Microalgae are promising organisms that are rapidly gaining much attention due to their numerous advantages and applications, especially in biorefineries for various bioenergy and biochemicals. This review focuses on the microalgae contributions to Bio-Circular-Green (BCG) economy, in which zero-waste approaches for sustainable production and biorefineries of microalgal biomass are introduced and their possible integration is discussed. Firstly, overviews of wastewater upcycling and greenhouse gas capture by microalgae are given. Then, a variety of valuable products from microalgal biomass, e.g., pigments, vitamins, proteins/peptides, carbohydrates, lipids, polyunsaturated fatty acids, and exopolysaccharides, are summarized to emphasize their biorefinery potential. Techno-economic and environmental analyses have been used to evaluate sustainability of microalgal biomass production systems. Finally, key issues, future perspectives, and challenges for zero-waste microalgal biorefineries, e.g., cost-effective techniques and innovative integrations with other viable processes, are discussed. These strategies not only make microalgae-based industries commercially feasible and sustainable but also reduce environmental impacts.

Improved laccase production from Pleurotus floridanus using deoiled microalgal biomass: statistical and hybrid swarm-based neural networks modeling approach

Fungal laccases are versatile biocatalyst and occupy a prominent place in various industrial applications due to its broad substrate specificity. The simplest method to enhance the laccase production is by usage of cheap substrates in the fermentation processes incorporating modeling approaches for optimization. Integrated biorefinery concept is receiving wide popularity by making use of various products from microalgal biomass. The research aimed to identify the potential of deoiled microalgal biomass (DMB), a waste product from algal biorefinery as a nutrient supplement to enhance laccase production in Pleurotus floridanus by submerged fermentation. The maximum production was obtained in the presence of DMB as an additional nutrient supplement and copper sulfate as an inducer. The predictive capabilities of the two methodologies Response Surface Methodology (RSM) and hybrid Particle swarm optimization (PSO)-based Artificial Neural Network (ANN) were compared and validated. The results showed that ANN coupled with PSO predicted with more accuracy with an R 2 value of 0.99 than the RSM model with an R 2 value of 0.97. The optimized condition as predicted by superior model hybrid PSO-based ANN was glucose (3.51%), DMB (0.545%), pH (4.9), temperature (24.68 ℃) and CuSO4 (1.35 mM). The experimental laccase activity was 80.45 ± 0.132 U/mL which was 1.3 fold higher than unoptimized condition. This study promotes the usage of DMB as a novel supplement for the improved production of Pleurotus floridanus laccase.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03404-y.

Full utilization of marine microalgal hydrothermal liquefaction liquid products through a closed-loop route: towards enhanced bio-oil production and zero-waste approach

The present study aimed to evaluate the potential of aqueous phase after hydrothermal liquefaction of microalgae (Aq-P), enriched with seawater, as a growth medium coupled with crude bio-oil production by the halophyte Dunaliella salina. Results showed that Aq-P showed higher content of total organic carbon (TOC) and total nitrogen (10.24, and 5.11 g L-1, respectively), while seawater showed higher anions and cations content. At the 12th day of microalgae incubation, the Aq-P growth medium showed 15.9% higher dry weight than the control (f/2 medium), with enhanced lipid content by 21.2% over the control, and 5.7% significant reduction in carbohydrates. The bio-oil yields of microalgal biomass cultivated in f/2 and Aq-P were 28.74% and 29.54%, respectively. Using Aq-P enhanced the fatty acids/esters and hydrocarbons in the crude bio-oil by 12.6% and 1.7 times, respectively, comparing to f/2-derived bio-oil. However, nitrogen-containing compounds in the Aq-P-derived bio-oil reduced by 60.7% comparing to f/2 medium. Interestingly, diesel carbon-range represented the majority of the products in both f/2- and Aq-P-derived bio-oil (69.1% and 78.3%, respectively). The findings of the present study provide a new approach for development of sustainable microalgal cultivation system for crude bio-oil production through a closed-loop route using Aq-P and seawater.

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.

Biomass and Lipid Productivity by Two Algal Strains of Chlorella sorokiniana Grown in Hydrolysate of Water Hyacinth

Hydrolysate prepared from the chemical hydrolysis of water hyacinth biomass contains a high amount of solubilised carbohydrate and nutrients. This hydrolysate was utilised as a medium for the cultivation of two strains of Chlorella sorokiniana, isolated from a municipal wastewater treatment plant using two different media, i.e., BG-11 and Knop’s medium. Different light intensities, light–dark cycles, and various concentrations of external carbon sources (monosaccharides and inorganic carbon) were used to optimise the microalgal growth. For the accumulation of lipids and carbohydrates, the microalgal strains were transferred to nutrient amended medium (N-amended and P-amended). It was observed that the combined effect of glucose, inorganic carbon, and a 12:12 h light–dark cycle proved to be the optimum parameters for high biomass productivity (~200 mg/L/day). For Chlorella sorokiniana 1 (isolated from BG-11 medium), the maximum carbohydrate content (22%) was found in P-amended medium (N = 0 mg/L, P: 3 mg/L), whereas, high lipid content (17.3%) was recorded in N-amended medium (N = 5 mg/L, P = 0 mg/L). However, for Chlorella sorokiniana 2 (isolated from the Knop’s medium), both lipid (17%) and carbohydrate accumulation (12.3%) were found to be maximum in the N-amended medium. Chlorella sorokiniana 2 showed a high saturated lipid accumulation compared to other strains. Kinetic modelling of the lipid profile revealed that the production rate of fatty acids and their various constituents were species dependent under identical conditions.

Microalgal bioenergy production under zero-waste biorefinery approach: Recent advances and future perspectives

In view of the globalization and energy consumption, an economic and sustainable biorefinery model is essential to address the energy security and climate change. From this perspective, renewable biofuel production from microalgae along with a wide range of value-added co-products define its potential as a biorefinery feedstock. However, economic viability of microalgal biorefinery at its current state is not considered sustainable. Reduce, recycle, and reuse of waste derived from algal bioenergy conversion process will lead to an energy efficient and sustainable zero-waste microalgal biorefinery. This review focuses on three major aspects of zero-waste microalgal biorefinery approach; (1) recent advances on microalgal bioenergy conversion processes (chemical, biochemical and thermochemical); (2) mitigation and transformation of liquid and solid waste and (3) techno-economic analysis (TEA) and lifecycle assessment (LCA). In addition, the study also focuses on the challenges and future perspectives for an advanced microalgal biorefinery model.

Effect of lipid-free microalgal biomass and waste glycerol on growth and lipid production of Scenedesmus obliquus: Innovative waste recycling for extraordinary lipid production

In the present work, a novel approach of using growth medium with different substitutions of lipid-free algal hydrolysate (LFAH, 0, 5, 10 and 15%) and/or waste glycerol (WG, 0, 5, 10 and 20 g L^-1) for enhanced biodiesel production from Scenedesmus obliquus was studied. Combination of different concentrations of WG with 15% LFAH showed the maximum significant biomass productivity, which represented 27.4, 30.5 and 28.9% over the control at combined 5, 10 and 20 g L^-1 WG, respectively. The combinations of different LFAH with 20 g L^-1 WG showed the maximum significant lipid accumulation, where lipid productivity showed its maximum significant value of 59.66 mg L^-1 d^-1 using LFAH15-WG10. In addition, LFAH15-WG10 significantly enhanced total FAMEs yield by 21.2% over the control. Moreover, it reduced polyunsaturated fatty acids (PUFAs) ratio from 52.1% to 47.8% of total FAMEs, and increased monounsaturated fatty acids (MUFAs) ratio from 26.6% to 31.3% of total FAMEs.

Recent developments in synthetic biology and metabolic engineering in microalgae towards biofuel production

In the wake of the uprising global energy crisis, microalgae have emerged as an alternate feedstock for biofuel production. In addition, microalgae bear immense potential as bio-cell factories in terms of producing key chemicals, recombinant proteins, enzymes, lipid, hydrogen and alcohol. Abstraction of such high-value products (algal biorefinery approach) facilitates to make microalgae-based renewable energy an economically viable option. Synthetic biology is an emerging field that harmoniously blends science and engineering to help design and construct novel biological systems, with an aim to achieve rationally formulated objectives. However, resources and tools used for such nuclear manipulation, construction of synthetic gene network and genome-scale reconstruction of microalgae are limited. Herein, we present recent developments in the upcoming field of microalgae employed as a model system for synthetic biology applications and highlight the importance of genome-scale reconstruction models and kinetic models, to maximize the metabolic output by understanding the intricacies of algal growth. This review also examines the role played by microalgae as biorefineries, microalgal culture conditions and various operating parameters that need to be optimized to yield biofuel that can be economically competitive with fossil fuels.

Enhanced Extracellular Polysaccharide Production and Self-Sustainable Electricity Generation for PAMFCs by Scenedesmus sp. SB1

In this study, a freshwater microalga, Scenedesmus sp. SB1, was isolated, purified, and identified by its internal transcribed spacer region (ITS1-5.8S-ITS2). Media optimization through the Plackett-Burman Design and response surface methodology (RSM) showed a maximum exopolysaccharide (EPS) production of 48 mg/L (1.8-fold higher than that for unoptimized media). Characterization using gas chromatography-mass spectrometry, Fourier transform infrared, X-ray diffraction, and thermogravimetric analysis reveals that the EPS is a sulfated pectin polysaccharide with a crystallinity index of 15.2% and prompt thermal stability. Furthermore, the photoelectrogenic activity of Scenedesmus sp. SB1 inoculated in BG-11 and RSM-optimized BG-11 (ROBG-11) media was tested by cyclic voltammogram studies, revealing the potential of the inoculated strain in ROBG-11 toward photosynthetic algal microbial fuel cells over normal BG-11. To the best of our knowledge, functional group characterization, physical and thermal property and media optimization for EPS production by RSM and electrogenic activity studies are reported for the first time in Scenedesmus sp. SB1.

Nutrient recycle from defatted microalgae (Aurantiochytrium) with hydrothermal treatment for microalgae cultivation

Defatted heterotrophic microalgae (Aurantiochytrium limacinum SR21) was treated with high temperature water (175-350°C, 10-90min) to obtain nitrogen and phosphorous nutrients as a water soluble fraction (WS). Yields of nitrogen and phosphorous recovered in WS varied from 38 to 100% and from 57 to 99%, respectively. Maximum yields of nitrogen containing compounds in WS were proteins (43%), amino acids (12%) and ammonia (60%) at treatment temperatures of 175, 250 and 350°C, respectively. Maximum yield of phosphorous in WS was 99% at a treatment temperature of 250°C. Cultivation experiments of microalgae (A. limacinum SR21) using WS obtained at 200 and 250°C showed positive growth. Water soluble fractions from hydrothermal treatment of defatted microalgae are effective nitrogen and phosphorous nutrient sources for microalgae cultivation.

Applications of de-oiled microalgal biomass towards development of sustainable biorefinery

In view of commercialization of microalgal biofuel, the de-oiled microalgal biomass (DMB) is a surplus by-product in the biorefinery process that needs to be exploited to make the process economically attractive and feasible. This DMB, rich in carbohydrates, proteins, and minerals, can be used as feed, fertilizer, and substrate for the production of bioethanol/bio-methane. Further, thermo-chemical conversion of DMB results into fuels and industrially important chemicals. Future prospects of DMB also lie with its conversion into novel biomaterials like nanoparticles and carbon-dot which have biomedical importance. The lowest valued application of DMB is to use it for adsorption of dyes and heavy metals from industrial effluents. This study reviews how DMB can be utilized for different applications and in the generation of valuable co-products. The value addition of DMB would thereby improve the overall cost economics of the microalgal bio-refinery.

Cultivation of Scenedesmus obliquus in liquid hydrolysate from flash hydrolysis for nutrient recycling

The production of biofuels from microalgae is associated with high demands of nutrients (nitrogen and phosphorus) required for growth. Recycling nutrients from the residual biomass is essential to obtain a sustainable production. In this work, the aqueous phase obtained from flash hydrolysis of Scenedesmus sp. was used as cultivation medium for a microalga of the same genus, to assess the feasibility of this technique for nutrient recycling purposes. Batch and continuous cultivations were carried out, to determine growth performances in this substrate compared to standard media, and verify if a stable biomass production could be obtained. In continuous experiments, the effect of hydrolysate inlet concentration and of residence time were assessed to optimize nutrient supply in relation to productivity. Results obtained show that nutrient recycling is feasible by treating biomass with flash hydrolysis, and Scenedesmus is capable of recycling large amounts of recovered nutrients.

Hydrolysate of lipid extracted microalgal biomass residue: An algal growth promoter and enhancer

The present study demonstrates the utilization of the algal hydrolysate (AH) prepared from lipid extracted residual harmful bloom-forming cyanobacteria Lyngbya majuscula biomass, as a growth supplement for the cultivation of green microalgae Chlorella vulgaris. BG-11 replacements with AH in different proportions significantly affects the cell count, dry cell weight (DCW), biomass productivity (BP) and pigments concentration. Among all, 25% AH substitution in BG11 media was found to be optimum which enhanced DCW, BP and pigments content by 39.13%, 40.81% and 129.47%, respectively, compared to control. The lipid content (31.95%) was also significantly higher in the 25% AH replacement. The volumetric productivity of neutral lipids (ideal for biodiesel) and total protein content of the cells significantly increased in all AH substitutions. Thus, lipid extracted microalgal biomass residue (LMBR) hydrolysate can be a potential growth stimulating supplement for oleaginous microalgae C. vulgaris.