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Utilization of harmful algal blooms (HABs) for the cultivation of oleaginous microorganisms can provide dual benefits of mitigating the toxicity from the aquatic reservoirs and generation of copious media for biodiesel production. In the present investigation, microwave-assisted dilute alkali-freeze pretreatment was optimized to develop a low-cost growth medium from HAB dried biomass. The electron micrographs along with the elemental analysis confirmed the efficient breakage of HABs after the microwave-assisted hydrolysis treatment as compared with the acid hydrolysis. Moreover, the sugar analysis revealed ~ 46% higher carbohydrate content in microwave-assisted hydrolysate as compared with acid hydrolysate. The microwave-assisted hydrolysate and conventional dilute acid hydrolysate were then used to cultivate microalga (Chlorella minutissima) and yeast (Trichosporon cutaneum) for biomass and lipid accumulation and compared to artificial media. Microalga showed ~ 1.3- and 2-fold higher dry cell weight (DCW) and lipid content, respectively, while the yeast growth increased by ~ 27% with lipid content of 30%. The fatty acid profiles and biodiesel properties were also amenable to the international biodiesel standards. Hence, the present study provides a proof-of-concept of utilizing HAB hydrolysate for culturing oleaginous microorganisms for potential biodiesel production.

The present study investigates the hydrothermal liquefaction (HTL) of harmful green macroalgal blooms at a temperature of 270 °C with, and without a catalyst with a holding time of 45 min. The effect of different catalysts on the HTL product yield was also studied. Two separation methods were used for recovering the biocrude oil yield from the solid phase. On comparision with other catalyst, Na2CO3 was found to produce higher yiled of bio-oil. The total bio-oil yield was 20.10% with Na2CO3, 18.74% with TiO2, 17.37% with CaO, and 14.6% without a catalyst. The aqueous phase was analyzed for TOC, COD, TN, and TP to determine the nutrient enrichment of water phase for microalgae cultivation. Growth of four microalgae strains viz., Chlorella Minutissima, Chlorella sorokiniana UUIND6, Chlorella singularis UUIND5 and Scenedesmus abundans in the aqueous phase were studied, and compared with a standard growth medium. The results indicate that harmful macroalgal blooms are a suitable feedstock for HTL, and its aqueous phase offers a promising nutrient source for microalgae.

Microalgae biotechnology has made it possible to derive secondary bioactive metabolites from microalgae strains that have opened up their entire potential to uncover a wide range of novel metabolic capabilities and turn these into bio-products for the development of sustainable bio-refineries. Nuclear Magnetic Resonance Technology (NMR) has been one of the most successful and functional research technology over the past two decades to analyse the composition, structure and functionality of distinct metabolites in the different microalgae strains. This technology offers qualitative as well as quantitative knowledge about the endogenous metabolites and lipids of low molecular mass to offer a good picture of the physiological state of biological samples in metabolomics and lipidomics studies. Henceforth, this review is aimed at introducing the metabolomics and lipidomics studies into the field of NMR technology and also highlights the protocols for the isolation and metabolic measurements of metabolites from microalgae that should be redirected to resource recovery and value-added products with a systematic and holistic approach for scalability or sustainability.

The hydrothermal liquefaction of municipal sludge was investigated under isothermal conditions (255 °C, 45 min) with TiO2 as a catalyst. In this study, we used two separation methods (an organic solvent-assisted extraction method and the Soxhlet extraction method) for the production of bio-crude oil. The maximum yield of bio-crude oil was 20.7 wt. % reported with the Soxhlet extraction method. The aqueous phase was examined for TN, TP, COD, and TOC to determine the suitability of this phase for microalgae cultivation. Four strains of oleaginous microalgae were cultivated in the aqueous phase. The results show that the growth of microalgae in the aqueous phase was lower compared to the control medium; this may be due to the high COD value. Microalgae and yeast co-cultivation increases biomass and lipid productivity using nutrients in the aqueous phase.

Ageratum conyzoides, an herb found throughout the year, is generally considered as a weed: it causes reduction in soil productivity and leads to health hazards for cattle and humans. However, its biomass can easily represent a cost‐effective source, which can be used for lignocellulosic biofuel production. The conversion of lignocellulosic biomass to ethanol has drawn much attention in recent times due to abundance of biomass. In the present study, the cellulose and hemicellulose biomass of the leaf and stem of A. conyzoides was converted to sugars using acid hydrolysis.146.01 ± 02 mg/g of fermentable sugar was obtained from A. conyzoides. The maximum ethanol concentration 11.89 g/L was obtained after 7 days. Scanning electron microscopy was used to characterize the surface morphology after acid hydrolysis of biomass. In the current study, the residues of acid hydrolysis and fermented wastewater was used for biogas production through anaerobic digestion. The yield of biogas from the residues of acid hydrolysis and fermented wastewater was 204 L kg−1VS. The results obtained indicate that A. conyzoides may be considered as a promising feedstock for bioethanol and biogas production.

Thermochemical transformation of microalgae biomass into graphitic bio-chars entices as proficient bio-adsorbents for heavy metal contaminants. This study explores the synergistic impact of Chlorella sorokiniana on biomass generation and wastewater remediation in high rate algae pond (HRAP). Biomass produced was applied for hydrothermal carbonization-co-liquefaction (HTCL). The structural and morphological characteristics of HTCL products (i.e. bio-chars and bio-oils) have been systematically studied by XRD, Raman, FTIR, elemental analyzer, SEM, BET, and 1H NMR spectroscopy. The crystallite size of the graphite 2H indexing planes was to be 4.65 nm and 14.07 nm in the bio-chars of oiled biomass (MB-OB) and de-oiled biomass (MB-DOB), respectively. The increase in the ID/IG ratio of MB-DOB indicated the highly disordered graphitic structure due to the appearance of carbonyl, hydroxyl, and epoxy functionalities in the line of high C/N and low C/H ratio. Also, the multiple heavy metals remediation of MB-DOB revealed better efficiency as ~100% in 720 min. The kinetics analysis shows the correlation coefficient of pseudo-second-order is well fitted compared to the pseudo-first-order. The Langmuir adsorption model signifies the adsorption of heavy metal ions in a monolayer adsorption manner. The study proposes the microalgae bio-char potential for multiple heavy metals remediation alongside bio-oils.

The effect of UV light on growth, biomass, lipid accumulation and biodiesel properties of microalgae was studied. A Microalgae strain Chlorella sorokiniana UUIND6 was cultivated for 14 days as unde...

The present study describes an integrated method that can be used to sequentially extract five economically important fractions viz., essential oil, organic acids, resin, cellulose, and residual carbon from biomass of pine needles. It is a simple but very effective approach which can give consistent yields from the residual biomass with every successive extraction step. For example, aqueous extracts 0.2 ± 0.5 ml/g, essential oil 0.03 ± 0.1 ml/g, resin 64.125 ± 0.2 mg/g, and 302.20 ± 04 mg/g of sugar and 1 ± 0.3 g of residual carbon. Sugars were further fermented under optimized conditions for the production of ethanol (18.2 ± 0.4 g/l). These yields were compared to direct processing of the individual components. Residual carbon obtained after hydrolysis was used for the preparation of activated carbon. This combined ethanol production and chemical extraction approach may provide a compelling model for a biorefinery and increasing commercial viability.

In this study, an integrated biomass conversion concept of producing liquid biofuels from fresh water macroalgal biomass was investigated. The algal biomass was collected from the Song river, Dehradun, Uttarakhand, India and processed under laboratory. 0.650 g dry wt m−2of algal biomass was harvested from the freshwater river. The collected algal biomass contained mainly 2 macroalgae species. Lipid extraction was done by soxhlet extraction method using chloroform: methanol (2:1) as solvent. 18.6% of lipid was obtained from macroalgae biomass. Blends of algae biodiesel with, butanol and diesel fuel (A5B25D70 and A10B30D60) were prepared by Inline blending method on a volume basis. Oil extracted algal biomass was further hydrolyzed for release of fermentable sugar. The theoretical yield of conversion of fermentable sugars to bioethanol was estimated and found to be 61.0%.

Pyrene (polycyclic aromatic hydrocarbon), an anthropogenic organic pollutant prevalent in various ecological units, receives more attention for bioremediation and energy transformation using microalgae. In this study, we have used pyrene pollutant (50–500 ppm) to evaluate the half-maximal inhibitory concentrations (IC50) of Chlorella sorokiniana and the impact on metabolites as well as the induction of lipid biosynthesis to produce renewable biodiesel. Pyrene concentration at 230 ppm (IC50) caused half-maximum inhibition for the 96 h incubation. The harvest in the stationary stage (day 16) for C. sorokiniana revealed a biomass generation of 449 ± 7 mg L−1 and 444 ± 8 mg L−1 dcw in the control medium and pyrene IC50 medium, respectively. An insignificant decline in biomass generation (1.2%) was observed due to the stress effect of the pyrene IC50 medium on metabolic biosynthesis. Although contrary to biomass generation, IC50 of pyrene assisted to induce lipid biosynthesis in C. sorokiniana. The improvement in lipid biosynthesis was observed as ~24% higher in pyrene IC50 compared to the control medium. The chemical composition of the microalgae biomass, metabolites, and lipids was examined using FTIR spectra. The extracted lipid was transesterified to produce biodiesel via methanolic-H2SO4 catalysis. The renewable biodiesel obtained was evaluated using FTIR and 1H NMR spectra. The transformation efficiency of the lipid of C. sorokiniana in biodiesel was calculated as ~81%. This research offers the incentive in lipid biosynthesis in microalgae cells using pyrene for the production of renewable and sustainable ecological biofuels along with bioremediation of pyrene.

Microalgae have been the subject of recent research as a sustainable feedstock for the large-scale production of metabolites for commercial purposes. This study presents a green bio-remediation approach towards heavy metal contaminations and biomass production for biofuels in microalgae metabolomics and lipidomics approaches. Two novel microalgae, Chlorosarcinopsis bastropiensis and Polyedriopsis spinulosa, were isolated during the study and subjected to Pb(II) and Cd(II) pollutants. The isolated microalgae strains have shown a varied behavior towards cell growth, pigment accumulation, and lipids profiles during the impact of short-term (96 h) and long-term (14 d) heavy metal tolerance. Cell viability and IC50 value (397.75 mg/L for C. bastropiensis and 490.16 mg/L for P. spinulosa) have indicated higher tolerance towards Pb(II) in both microalgae. FTIR analysis of microalgal biomass has revealed insignificant differences during long and short-term heavy metal toxicity, clearly indicating the bio-tolerance for Pb(II) and Cd(II) in both microalgae. Principal component analysis has revealed the expression of metabolites (such as glycine, proline, valine, isoleucine, linoleic acid, glucose, sucrose, etc.) under heavy metal stress. 1H NMR analysis has demonstrated the prominent expression of metabolites under heavy metal stress. ICP-MS-based studies do not reflect the correlation between cellular tolerance and bioaccumulation of each heavy metal by both microalgae. Lipidomics based on 1H NMR has revealed an increase in unsaturated fatty acids under the impact of heavy metals. Therefore, this study offers a sustainable bioremediation technique for heavy metal contaminants and biomass production with significant enhancement of metabolites and lipid components for biofuels and/-or other commercial applications.

Microalgae have emerged as a potential alternative for the production of many useful compounds like protein, carbohydrate and lipid. Lipid-rich microalgae are important and rich source for alternative energy production. In order to commercially utilize microalgae for energy production, the lipid productivity should be enhanced. Keeping in view the above-mentioned potentials of microalgae, in the present study, we have attempted to display the role of chemical stimulants and light in the growth and lipid production of the microalgae Chlorella singularis (UUIND5). During the present investigations, effect of varying photoperiods and different types of lights and chemical stimulants, viz. CaCl2 and kinetin on growth rate and lipid production, was studied. The maximum growth rate recorded was 166 ± 0.3 mg/L/d, when 0.80 g/l CaCl2 and 0.5 mg/l kinetin were added to Bold’s basal medium. C. singularis was then cultivated in this medium for 14 days under sunlight +LED (10-h sunlight + 14-h LED light) at photoperiod 24-h light/0-h dark. The maximum lipid yield 30.2% of dry wt. was obtained under sunlight +LED. Further, the gas chromatography analysis also showed the presence of fatty acid methyl esters (FAME). FAMEs profile was analyzed according to ASTM D6751 specification. Thus, it was concluded that sunlight +LED at 24-h light/0-h dark (100 μmol photons m−2 s−1) photoperiod with CaCl2 and kinetin is an effective strategy to boost lipid productivity in C. singularis (UUIND5).

Green oleaginous microalgae are good candidates for the integration of heavy metal bioremediation with the generation of biofuels. To be effective, this requires a comprehensive understanding and optimization of the metal concentration that generates maximum growth along with a high yield of lipids from microalgae cells. This work follows the aforementioned strategy and involves the use of oleaginous microalgae Chlorella sorokiniana for lead mitigation and biodiesel production. The short-term effects (IC50 value at 96 h of culture) and the long-term effects (pigments and biomass) of the exposure of lead (Pb) to the growth and biochemical compositions (pigments, proteins, carbohydrates, and lipids) of microalgae have been also determined. Chlorella sorokiniana has a high half-maximal inhibitory concentration (IC50 value and higher metal bio-concentration factor (BCF) for Pb (II), which represents that this strain can be considered as a lead (Pb) hyperbioaccumulator. FTIR analysis revealed a reduction in proteins and carbohydrates under the influence of Pb while an increase in lipids has been recorded. The lipid profile based on 1H NMR and GC–MS has been followed for the quality analysis of the biodiesel produced that indicated altered lipid profiles under stress by Pb and elevated levels of SFA and MUFA.

In this study, hydropyrolysis was carried out using sodium carbonate to convert the green algal bloom into bio-oil, biochar, aqueous solution, and gases. The effect of supercritical conditions (400, 450, 500 °C) on the product yield, bio-oil composition, and structure, and functionalities of the biochar was determined. The high yield of biochar and bio-oil was reported at 400 °C. A significant reduction in bio-oil and increment in hydrocarbon content was reported on the elevation of temperature from 450 °C to 500 °C. After that, kinetic and isotherm analysis was investigated simultaneously to remove four heavy metals viz. Cu(II), Ni(II), Co(II), and Cd(II) from the mixture solution. Results show that kinetics data follow a pseudo-second-order kinetics model and adsorption isotherm is in better agreement with the Langmuir model, not with the Freundlich model. The maximum adsorption capacity was found 10.90, 5.74, 5.80, and 16.28 mg/g with the biochar prepared at 500 °C for Cu(II), Ni(II), Co(II), and Cd(II) metals, respectively. The current investigation provided a promising way for the utilization of freshwater algal bloom biomass for renewable products and simultaneously heavy metal removal from the water.

Heavy metal pollution is one of the major environmental concerns worldwide. Toxic heavy metals when untreated get accumulated in environment and can pose severe threats to living organisms. It is well known that metals play a major role either directly or indirectly in different metabolic processes of bacteria. This allows bacterial cells to grow even in the presence of some toxic heavy metals. Microbial biotechnology has thus emerged as an effective and eco friendly solution in recent years for bioremediation of heavy metals. Therefore, this review is focused on summarising bacterial adaptation mechanisms for various heavy metals. It also shares some applications of have metal tolerant bacteria in bioremediation. Bacteria have evolved a number of processes for heavy metal tolerance viz., transportation across cell membrane, accumulation on cell wall, intra as well as extracellular entrapment, formation of complexes and redox reactions which form the basis of different bioremediation strategies. The genetic determinants for most of these resistances are located on plasmids however some may be chromosomal as well. Bacterial cells can uptake heavy by both ATP dependent and ATP independent processes. Bacterial cell wall also plays a very important role in accumulating heavy metals by bacterial cells. Gram-positive bacteria accumulate much higher concentrations of heavy metals on their cell walls than that of metals gram -ve bacteria. The role of bacterial metallothioneins (MTs) in heavy metal has also been reported. Thus, heavy metal tolerant bacteria are important for bioremediation of heavy metal pollutants from areas containing high concentrations of particular heavy metals.

The global energy demand is increasing at an exponential rate, and available petroleum sources are rapidly decreasing. In this context, microalgae regained attention for biodiesel production due to its high growth rate and high lipid content. One of the major obstacles for large-scale production of biodiesel from microalgae is extracting intracellular lipids which are present inside the cell wall and membrane. Therefore, there is a substantial necessity to develop a cost-effective, safe, environment-friendly, and efficient extraction method of microalgae lipids. In downstream processing, algal cell disruption and lipid extraction techniques are important for biodiesel production due to high energy consumption and high costs involved. Several techniques for lipids extraction from microalgae have been reported by various researchers. This chapter provides an overview on latest advancements that have been made on the different cell disruption methods including mechanical, chemical, and biological cell disruption methods and different lipid extraction methods including conventional extraction lipid methods, green solvent-based extraction methods, and solvent-free extraction methods.

Aromatic compounds are widely distributed in nature. Free phenols are frequently liberated as metabolic intermediates during the degradation of plant materials. In recent years the natural supply of phenolic substances has been greatly increased due to the release of industrial byproducts into the environment. Phenolic compounds are hazardous pollutants that are toxic at relatively low concentration. Effluents from petrochemical, textile and coal industries contain phenolic compounds in very high concentration; therefore there is a necessity to remove phenolic compounds from the environment. Microorganisms capable of degrading phenol are common and include both aerobes and anaerobes. The use of microbial catalysts in the biodegradation of organic compounds has advanced significantly during the past three decades. The efficiency of biodegradation of organic compounds is influenced by the type of the organic pollutant, the nature of the organism, the enzyme involved, the mechanism of degradation and the nature of the influencing factors.

Organophosphorus compounds exhibit a wide range of toxicity to mammals. In this study the effect of malathion on the growth and biochemical parameters of microalgae was evaluated. Three microalgae (Micractinium pusillum UUIND2, Chlorella singulari UUIND5 and Chlorella sorokiniana UUIND6) were used in this study. Among the three algal strains tested, Chlorella sorokiniana UUIND6 was able to tolerate 100 ppm of malathion. The photosynthetic pigments, the protein, carbohydrate and lipid contents of microalgal cells were also analyzed. About 90% degradation was recorded in 25 ppm, 50 ppm and 70% was recorded in 100 ppm of malathion by Chlorella sorokiniana. A mechanism of degradation of malathion by Chlorella sorokiniana is proposed in this study. Activity of carboxylesterase was increased in algal cells cultivated in malathion containing medium which confirmed that malathion degraded into phosphate. Increased amount of Malondialdehye (MDA) indicate the development of free radicals under the stress of malathion which substantialy increase de novo TAG biosynthesis, while increased level of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) suggested their association in scavenging of free radical.

The declining reserves of fossil fuels and fossil fuel-related environmental issues, especially greenhouse gas (carbon dioxide, methane) emissions, have posed a great threat and challenge to the sustainability of the world economy, the global environment, and hence the quality of life of human beings. Biomass pyrolysis could help reduce both the world’s dependence on oil and CO2 production. These bio-oils have the potential to cut CO2 emission because they are made up of plants that use CO2 for growth. There is a need to integrate process operation and reactor design to improve the effectiveness of different processes used for biomass to produce multiple products using a combination of technologies.

Fuels derived from biomass are essential in order to overcome the excessive dependence on petroleum. They also minimize the emissions of greenhouse gases. Pretreatment in biofuel production is a very important step. Pretreatment is not only costly in its own right but also has a pervasive impact on the cost of virtually all other processing operations. The present study investigates the effect of bacterial amylase pretreatment on ethanol production from different kinds of starch-based solid waste (SBSW). For this purpose four amylase-producing bacterial isolates were obtained from samples collected from municipal waste dumping sites. The isolated bacteria were then used for the pretreatment of SBSW for ethanol production. After bacterial amylase pretreatment, 13% yield of ethanol was obtained.

A number of different pretreatments involving biological, chemical, physical, and thermal approaches have been investigated over the years to reduce the cost of biofuel production. This study investigates the effect of bacterial amylase pretreatment on bioethanol production from different kinds of starch-based solid waste. We have isolated one strain (Xenorhabdus japonica) of amylase-producing bacteria from municipal waste dumping site's soil. Maximum ethanol yield was obtained after bacterial amylase pretreatment from wheat bread and rice (132 g/L), while the minimum was obtained from potato (99 g/L). Bacterial amylase pretreatment shows the best results as compared to the acid pretreatment.

The influence of glyphosate herbicide stress was investigated in the freshwater green microalgae Chlorella sorokiniana for metabolic growth and lipid induction. Glyphosate herbicide concentration at 30.10 ppm (IC50) elicited half-maximal inhibition during 96 h of incubation. After 24 days of harvest, C. sorokiniana produced 442.18 ± 9.1 mg/L and 427.73 ± 5.0 mg/L dcw of biomass in the control media and glyphosate IC50, respectively. A nominal reduction in biomass production was observed (~ 3.26%) due to stress in metabolic biosynthesis in glyphosate IC50 media. However, in contrast to biomass production, glyphosate IC50 stress aided in the induction of lipid biosynthesis in microalgae cells. The improvement in lipid synthesis was found to be ~17% higher in glyphosate IC50 compared to control. The chemical construction of the biomass, metabolites, and lipids of C. sorokiniana was analyzed via FTIR spectroscopy. The lipids extracted from C. sorokiniana were used for methanolic-H2SO4 catalyzed transesterification for the production of biodiesel. The synthesized biodiesel was analyzed by FTIR and 1H NMR. The conversion efficiency of microalgae lipids into biodiesel was estimated at ~77%. This study insights the use of glyphosate in lipid induction in microalgae to produce renewable and sustainable biofuels for the clean environment.

A low-cost small-scale high-rate algal pond (HRAP) was constructed to investigate the synergistic potential of a novel oleaginous microalga, Chlorella sorokiniana for phyco-mitigation, and biodiesel production using raw urban wastewater. An enhanced nutrient removal (97%), total organic carbon (74%), alkalinity (70%) and hardness (75%) from the wastewater was obtained. The microalga dominated in the HRAP as ~90% increase in the dissolved oxygen with high biomass (1.13 g/L) was noted. The microalga biomass showed sufficient lipid content (~31% of dry cell weight) as compared to control (Bold’s Basal media). The total lipid profiling of the microalga cultivated in wastewater showed augmentation in the levels of both storage and neutral lipids with good quality fatty acids composition. Moreover, the sucker fishes grew healthy in the treated wastewater with an increase in body weight.

Graphical abstract, Highlights • Lipids yield increased by osmotic shock cell disruption method. • High percentage of hexadecanoic acid (52–68%) was obtained by soxhlet extraction. • Impurities of chlorophyll and protein were also detected in the extracted lipids. • Only one type of FAME, hexadecanoic acid methyl ester was obtained by Triton X-100. • 23.3 wt% of crude oil was produced by HTL of algal biomass with TiO2 at 300 °C., Cell disruption and lipid extraction methods for macroalgae are not well reported. Therefore, we compared various lipid extraction methods and extraction efficiency of various solvents to improve lipid yields from Oedogonium fresh water macroalgae. Lipid extraction was done by 2 methods viz., modified Bligh and Dyer method and soxhlet extraction using either single solvents or mixtures. In soxhlet extraction method five solvents were used (1) Hexane commonly used solvent for lipid extractions, (2) chloroform: methanol (2:1), (3) Chloroform: hexane (1:1), (4) Chloroform: hexane (1:2), (5) Dichloromethane + methanol (2:1). To improve lipid extraction yields, various cell disruption methods were also compared during the present study. Impurities of chlorophyll and protein were also detected in the extracted lipids. Hydrothermal liquefaction of algal biomass with TiO2 was also conducted at 300 °C. HTL was more effective by which 23.3 wt% of bio-crude oil was obtained.