Pretreatment of algal biomass using fungal crude enzymes

Extremely chaotolerant and kosmotolerant Aspergillus atacamensis - a metabolically versatile fungus suitable for recalcitrant biosolid treatment

Obligate halophily is extremely rare in fungi. Nevertheless, Aspergillus atacamensis (strain EXF-6660), isolated from a salt water-exposed cave in the Coastal Range hills of the hyperarid Atacama Desert in Chile, is an obligate halophile, with a broad optimum range from 1.5 to 3.4 M of NaCl. When we tested its ability to grow at varied concentrations of both kosmotropic (NaCl, KCl, and sorbitol) and chaotropic (MgCl2, LiCl, CaCl2, and glycerol) solutes, stereoscopy and laser scanning microscopy revealed the formation of phialides and conidia. A. atacamensis EXF-6660 grew up to saturating levels of NaCl and at 2.0 M concentration of the chaotropic salt MgCl2. Our findings confirmed that A. atacamensis is an obligate halophile that can grow at substantially higher MgCl2 concentrations than 1.26 M, previously considered as the maximum limit supporting prokaryotic life. To assess the fungus' metabolic versatility, we used the phenotype microarray technology Biolog FF MicroPlates. In the presence of 2.0 M NaCl concentration, strain EXF-6660 metabolism was highly versatile. A vast repertoire of organic molecules (~95% of the substrates present in Biolog FF MicroPlates) was metabolized when supplied as sole carbon sources, including numerous polycyclic aromatic hydrocarbons, benzene derivatives, dyes, and several carbohydrates. Finally, the biotechnological potential of A. atacamensis for xenobiotic degradation and biosolid treatment was investigated. Interestingly, it could remove biphenyls, diphenyl ethers, different pharmaceuticals, phenols, and polyaromatic hydrocarbons. Our combined findings show that A. atacamensis EXF-6660 is a highly chaotolerant, kosmotolerant, and xerotolerant fungus, potentially useful for xenobiotic and biosolid treatments.

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.

Solid-state fermentation-based enzyme-assisted extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp

Enzymatic treatment of microalgal biomass is a promising approach for extraction of microalgal lipid, but high cost of commercially sourcing enzyme is a major drawback in industrial implementation. Present study involves extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp. biomass using low cost cellulolytic enzymes produced from Trichoderma reesei in a solid-state fermentation bioreactor. Maximum total fatty acid recovery of 369.4 ± 4.6 mg/g dry weight (total fatty acid yield of 77%) was achieved in 12 h from the enzymatically treated microalgal cells, of which the eicosapentaenoic acid content was 11%. Sugar release of 1.70 ± 0.05 g/L was obtained post enzymatic treatment at 50 °C. The enzyme was reused thrice for cell wall disruption without compromising on total fatty acid yield. Additionally, high protein content of 47% in the defatted biomass could be explored as a potential aquafeed, thus enhancing the overall economics and sustainability of the process.

Sustainable production of biohydrogen from algae biomass: Critical review on pretreatment methods, mechanism and challenges

The production of chemicals and energy from sustainable biomass with an important objective decreasing carbon impressions has recently become one of the key areas of attention. Algae biomass have been recognized and researched as a potential renewable biomass of biohydrogen production attributed to their limited multiplying time, fast growing qualities and ability of lipid accumulation. This review additionally envelops various key perspectives such as composition and properties of algae biomass and pretreatment strategies such as physical, chemical and biological methods adopted for the algae biomass. This review is mainly focused on pretreatment strategies which have been developed to enhance biohydrogen production. The present review deals with methods and mechanism, enzymes involved and factors influencing on biohydrogen production which help to grasp various bottlenecks, challenges and constraints. Finally, the significant progressions and economical perspective on improving biohydrogen yield because of the expansion of co-substrates and the current trends are examined.

Enzymatic cell disruption followed by application of imposed potential for enhanced lipid extraction from wet algal biomass employing photosynthetic microbial fuel cell

Solvent-free algal cell lysis using fungal enzyme for enhanced lipid recovery diminishes per unit production cost of algal biodiesel. In this investigation, a triple chamber photosynthetic microbial fuel cell (PMFC) was fabricated, where positive potential was imposed in the extraction chamber to draw the negatively charged lipid ions from the cathodic chamber. Under optimum imposed potential of + 3.0 V (vs standard hydrogen electrode) and with 3.5% (v/v) dosage of fungal enzyme in to the algal consortium of cathodic chamber, a maximum of 79.0% of lipid was recovered. Additionally, enzyme-assisted de-oiled algal biomass was applied in the anodic chamber to function as substrate and mediator for exo-electrogens, and the maximum power density of 10.0 W/m³ with 82.4% removal of chemical oxygen demand was achieved while treating synthetic wastewater. Therefore, this cost-effective exploration demonstrated successful bioelectricity production and concomitant wastewater treatment with solvent-free direct lipid recovery from wet algal biomass through PMFC.

Enzymatic pretreatment of algal biomass has different optimal conditions for biogas and bioethanol routes

Enzymatic pretreatment is emerging as an efficient tool for the extraction of biofuel precursors from algal biomass. However, yardsticks for end-use directed selection of optimal pretreatment conditions are not yet identified. The present study, for the first time, reveals different optimal conditions for algal biomass solubilization and sugar release. Algal biomass pretreatment optimization was carried out using the Taguchi method. Crude enzyme from Aspergillus fischeri was found effective for pretreatment of Chlorella pyrenoidosa. Maximum sugar yield (190 mg g^-1 biomass) from algal biomass was observed at a substrate concentration of 4 g L^-1, with a 5% enzyme load at temperature 60°C, pH 5.5, and shaking speed of 80 rpm. In contrast, maximum sCOD (1350 mg g^-1 biomass) was obtained at 2 g L^-1 substrate concentration with enzyme load of 20% v/v, at 60°C, pH 4, and shaking speed of 100 rpm. Hence, the first set of conditions would be more beneficial for bioethanol production. Whereas another set of conditions would improve the biofuel production that requires maximum solubilization of algal biomass, such as fermentative methane production. Overall, the present observations established that process conditions required for enzymatic pretreatment of algal biomass should be selected according to the desired biofuel type.

Strategies and advances in the pretreatment of microalgal biomass

Modification of structural components, especially the cell wall, through adequate pretreatment strategies is critical to the bioconversion efficiency of algal biomass to biorefinery products. Over the years, several physical, physicochemical, chemical and green pretreatment methods have been developed to achieve maximum productivity of desirable by-products to sustain a circular bioeconomy. The effectiveness of the pretreatment methods is however, species specific due to diversity in the innate nature of the microalgal cell wall. This review provides a comprehensive overview of the most notable and promising pretreatment strategies for several microalgae species. Methods including the application of stress, ultrasound, electromagnetic fields, pressure, heat as well as chemical solvents (ionic liquids, supercritical fluids, deep eutectic solvents etc.) have been detailed and analyzed. Enzyme and hydrolytic microorganism based green pretreatment methods have also been reviewed. Metabolic engineering of microorganisms for product specificity and lower inhibitors can be a future breakthrough in microalgal pretreatment.

A review of biochemical and thermochemical energy conversion routes of wastewater grown algal biomass

Microalgae are recognized as a potential source of biomass for obtaining bioenergy. However, the lack of studies towards economic viability and environmental sustainability of the entire production chain limits its large-scale application. The use of wastewaters economizes natural resources used for algal biomass cultivation. However, desirable biomass characteristics for a good fuel may be impaired when wastewaters are used, namely low lipid content and high ash and protein contents. Thus, the choice of wastewaters with more favorable characteristics may be one way of obtaining a more balanced macromolecular composition of the algal biomass and therefore, a more suitable feedstock for the desired energetic route. The exploration of biorefinery concept and the use of wastewaters as culture medium are considered as the main strategic tools in the search of this viability. Considering the economics of overall process, direct utilization of wet biomass using hydrothermal liquefaction or hydrothermal carbonization and anaerobic digestion is recommended. Among the explored routes, anaerobic digestion is the most studied process. However, some main challenges remain as little explored, such as a low energy pretreatment and suitable and large-scale reactors for algal biomass digestion. On the other hand, thermochemical conversion routes offer better valorization of the algal biomass but have higher costs. A biorefinery combining anaerobic digestion, hydrothermal carbonization and hydrothermal liquefaction processes would provide the maximum possible output from the biomass depending on its characteristics. Therefore, the choice must be made in an integrated way, aiming at optimizing the quality of the final product to be obtained. Life cycle assessment studies are critical for scaling up of any algal biomass valorization technique for sustainability. Although there are limitations, suitable integrations of these processes would enable to make an economically feasible process which require further study.

Deoiled algal biomass derived renewable sugars for bioethanol and biopolymer production in biorefinery framework

The present study is designed to evaluate the potential of deoiled algal biomass (DAB) residue as an alternative resource for the production of bioethanol and biopolymers in a biorefinery approach. Hybrid pretreatment method resulted in higher sugar solubilization (0.590 g/g DAB) than the corresponding individual physicochemical (0.481 g/g DAB) and enzymatic methods (0.484 g/g DAB). Subsequent utilization of sugars from hybrid pretreatment for bioethanol using Saccharomyces cerevisiaeresulted in maximum bioethanol production at pH 5.5 (0.145 ± 0.008 g/g DAB) followed by pH 5.0 (0.122 ± 0.004 g/g DAB) and pH 6.0 (0.102 ± 0.002 g/g DAB). The experiments for biopolymer (PHB: polyhydroxybutyrate) production resulted in 0.43 ± 0.20 g PHB/g DCW. Extracted polymer on NMR and FT-IR analysis showed the presence of PHB. Exploration of DAB as an alternative renewable resource for multiple biobased products supports sustainability and also enables entirety use of DAB by addressing the DAB-residue allied disposal issues.

Nanoparticle induced biological disintegration: A new phase separated pretreatment strategy on microalgal biomass for profitable biomethane recovery

This study involves the application of new phase separated biological pretreatment (PSBP) strategy on microalgal biomass using the nickel nanoparticle induced cellulase secreting bacterial disintegration. Particularly, interest was focussed on cell wall weakening (CWW) of microalgae biomass besides the cell disintegration (CD) and release of organics. During CWW, protein, carbohydrate, cellulose, hemicellulose and DNA were used as evaluation indexes. Similarly, during CD, soluble chemical oxygen demand was used as evaluation index to assess the disintegration effect. A higher CWW was achieved at nickel nanoparticle (Np) dosage of 0.004 g/g SS. During CD, a clear demarcation in biomass solubilisation was achieved by PSBP (36%) than the sole biological pretreatment -BP (24%). The biomethanogenesis test results showed that enhanced methane production of 411 mL/g COD was achieved by PSBP than BP. Energy analysis showed that a higher net energy production of 6.467 GJ/d was achieved by PSBP.

Potential role of N-acetyl glucosamine in Aspergillus fumigatus-assisted Chlorella pyrenoidosa harvesting

BACKGROUND

Algal harvesting is a major cost which increases biofuel production cost. Algal biofuels are widely studied as third-generation biofuel. However, they are yet not viable because of its high production cost which is majorly contributed by energy-intensive biomass harvesting techniques. Biological harvesting method like fungal-assisted harvesting of microalgae is highly efficient but poses a challenge due to its slow kinetics and poorly understood mechanism.

RESULTS

In this study, we investigate Aspergillus fumigatus-Chlorella pyrenoidosa attachment resulting in a harvesting efficiency of 90% within 4 h. To pinpoint the role of extracellular metabolite, several experiments were performed by eliminating the C. pyrenoidosa or A. fumigatus spent medium from the C. pyrenoidosa-A. fumigatus mixture. In the absence of A. fumigatus spent medium, the harvesting efficiency dropped to 20% compared to > 90% in the control, which was regained after addition of A. fumigatus spent medium. Different treatments of A. fumigatus spent medium showed drop in harvesting efficiency after periodate treatment (≤ 20%) and methanol-chloroform extraction (≤ 20%), indicating the role of sugar-like moiety. HR-LC-MS (high-resolution liquid chromatography-mass spectrometry) results confirmed the presence of N-acetyl-d-glucosamine (GlcNAc) and glucose in the spent medium. When GlcNAc was used as a replacement of A. fumigatus spent medium for harvesting studies, the harvesting process was significantly faster (p < 0.05) till 4 h compared to that with glucose. Further experiments indicated that metabolically active A. fumigatus produced GlcNAc from glucose. Concanavalin A staining and FTIR (Fourier transform infrared spectroscopy) analysis of A. fumigatus spent medium- as well as GlcNAc-incubated C. pyrenoidosa cells suggested the presence of GlcNAc on its cell surface indicated by dark red dots and GlcNAc-specific peaks, while no such characteristic dots or peaks were observed in normal C. pyrenoidosa cells. HR-TEM (High-resolution Transmission electron microscopy) showed the formation of serrated edges on the C. pyrenoidosa cell surface after treatment with A. fumigatus spent medium or GlcNAc, while Atomic force microscopy (AFM) showed an increase in roughness of the C. pyrenoidosa cells surface upon incubation with A. fumigatus spent medium.

CONCLUSIONS

Results strongly suggest that GlcNAc present in A. fumigatus spent medium induces surface changes in C. pyrenoidosa cells that mediate the attachment to A. fumigatus hyphae. Thus, this study provides a better understanding of the A. fumigatus-assisted C. pyrenoidosa harvesting process.

Improved methane yield from wastewater grown algal biomass

Methane production from the algal biomass cultivated in a laboratory scale continuous photobioreactor (PBR) using sewage was evaluated in the present work. During the preliminary experiments, algal biomass reached up to 1.69 ± 0.35 g L^-1 in 12 days' growth period. Besides, 65 to 100% removal in concentrations of total dissolved phosphorus (TDP), nitrate nitrogen (NO₃-N), total ammoniacal nitrogen (TAN) and soluble chemical oxygen demand (sCOD) was also recorded. The sCOD removal in the reactor was 100%, whereas removal of TDP, NO₃-N and TAN were up to 75, 40 and 92%, respectively. Upon anaerobic digestion, the fresh algal biomass showed methane yield of 180 mL g^-1 VS_fed. Further, algal biomass was stored under natural conditions in open containers (aerobic conditions) in darkness at room temperature (27-30 °C) for 72 h. Interestingly, >48% COD solubilization from algal biomass was observed during storage. Pretreatment through natural storage was further confirmed with qualitative observations including scanning electron and fluorescence microscopic analysis. Moreover, higher methane yield (284.38 mL g^-1 VS_fed) was observed from the samples stored for 60 h. Thus, natural storage for a designated period may be recommended as a prerequisite stage in the process of methane production from wastewater-grown algal biomass.

The effect of the algal microbiome on industrial production of microalgae

Microbes are ubiquitously distributed, and they are also present in algae production systems. The algal microbiome is a pivotal part of the alga holobiont and has a key role in modulating algal populations in nature. However, there is a lack of knowledge on the role of bacteria in artificial systems ranging from laboratory flasks to industrial ponds. Coexisting microorganisms, and predominantly bacteria, are often regarded as contaminants in algal research, but recent studies manifested that many algal symbionts not only promote algal growth but also offer advantages in downstream processing. Because of the high expectations for microalgae in a bio‐based economy, better understanding of benefits and risks of algal–microbial associations is important for the algae industry. Reducing production cost may be through applying specific bacteria to enhance algae growth at large scale as well as through preventing the growth of a broad spectrum of algal pathogens. In this review, we highlight the latest studies of algae–microbial interactions and their underlying mechanisms, discuss advantages of large‐scale algal–bacterial cocultivation and extend such knowledge to a broad range of biotechnological applications.

Biological disintegration of microalgae for biomethane recovery-prediction of biodegradability and computation of energy balance

The present study investigates the synergistic effect of combined bacterial disintegration on mixed microalgal biomass for energy efficient biomethane generation. The rate of microalgal biomass lysis, enhanced biodegradability, and methane generation were used as indices to assess efficiency of the disintegration. A maximal dissolvable organics release and algal biomass lysis rate of about 1100, 950 and 800mg/L and 26, 23 and 18% was achieved in PA+C (protease, amylase+cellulase secreting bacteria), C (cellulase alone) and PA (protease, amylase) microalgal disintegration. During anaerobic fermentation, a greater production of volatile fatty acids (1000mg/L) was noted in PA+C bacterial disintegration of microalgal biomass. PA+C bacterial disintegration improve the amenability of microalgal biomass to biomethanation process with higher biodegradability of about 0.27gCOD/gCOD, respectively. The energy balance analysis of this combined bacterial disintegration of microalgal biomass provides surplus positive net energy (1.14GJ/d) by compensating the input energy requirements.

Improving biogas production from microalgae by enzymatic pretreatment

In this study, enzymatic pretreatment of microalgal biomass was investigated under different conditions and evaluated using biochemical methane potential (BMP) tests. Cellulase, glucohydrolase and an enzyme mix composed of cellulase, glucohydrolase and xylanase were selected based on the microalgae cell wall composition (cellulose, hemicellulose, pectin and glycoprotein). All of them increased organic matter solubilisation, obtaining high values already after 6h of pretreatment with an enzyme dose of 1% for cellulase and the enzyme mix. BMP tests with pretreated microalgae showed a methane yield increase of 8 and 15% for cellulase and the enzyme mix, respectively. Prospective research should evaluate enzymatic pretreatments in continuous anaerobic reactors so as to estimate the energy balance and economic cost of the process.

Enhanced methane production from algal biomass through short duration enzymatic pretreatment and codigestion with carbon rich waste

Novel two fold approach comprising short duration fungal crude enzyme pretreatment of algal biomass followed by codigestion with cattle dung resulting in enhanced methane yield is disclosed.