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In the current global scenario, the world is under a serious dilemma due to the increasing human population, industrialization, and urbanization. The ever-increasing need for fuels and increasing nutritional problems have made a serious concern on the demand for nutrients and renewable and eco-friendly fuel sources. Currently, the use of fossil fuels is creating ecological and economic problems. Microalgae have been considered as a promising candidate for high-value metabolites and alternative renewable energy sources. Microalgae offer several advantages such as rapid growth rate, efficient land utilization, carbon dioxide sequestration, ability to cultivate in wastewater, and most importantly, they do not participate in the food crop versus energy crop dilemma or debate. An efficient microalgal biorefinery system for the production of lipids and subsequent byproduct for nutraceutical applications could well satisfy the need. But, the current microalgal cultivation systems for the production of lipids and nutraceuticals do not offer techno-economic feasibility together with energy and environmental sustainability. This review article has its main focus on the production of lipids and nutraceuticals from microalgae, covering the current strategies used for lipid production and the major high-value metabolites from microalgae and their nutraceutical importance. This review also provides insights on the future strategies for enhanced microalgal lipid production and subsequent utilization of microalgal biomass. Graphical abstract

Microalgae are unicellular photosynthetic organisms that have been recently attracted potential interests and have applications in food, nutraceuticals, pharmaceuticals, animal feed, cosmetics, and biofertilizers industry. Microalgae are rich in a variety of high-value bioactive compounds which have potential benefits on human health and can be used for the prevention and curing of many disease conditions. But scale-up and safety issues remain a major challenge in the commercialization of microalgal products in a cost-effective manner. However, techniques have been developed to overcome these challenges and successfully selling the products derived from microalgae as food, cosmetics and pharmaceutical industries. Microalgae are rich in many nutrients and can be used for the production of functional food and nutraceuticals, safety and regulatory issues are major concerns and extensive research is still needed to make microalgae a commercial success in the future. Many practical difficulties are involved in making the microalgal food industry commercially viable. The present review focuses on the industrial applications of microalgae and the challenges faced during commercial production.

Omega-3 fatty acids containing microalgae are considered a promising feedstock for food and nutraceutical applications. To meet the commercial and nutritional demands of essential omega-3 fatty acids, different strategies are being implemented, including supplementation of plant growth regulators (PGRs). In the present study the effects of selected, PGRs, i.e., gibberellic acid (GA), and salicylic acid (SA), and malic acid (MA; TCA cycle intermediate), were studied on growth, lipid, and omega-3 fatty acid synthesis of Nannochloropsis oceanica CASA CC201. Significant increase in growth (10 ppm GA), a 1.9-fold increase in lipid production (40 ppm MA), and a 4-fold increase in EPA production by treatment with 10 ppm MA were found. To understand the mechanism behind significant changes in growth and metabolite production, we had analyzed the generation of oxidative stress, targeted metabolite, and amino acid profile of N. oceanica under PGR treatment. To elucidate the physiological role of key metabolic pathways and contribution to lipid synthesis, the targeted metabolites were selected from glycolysis, citric acid cycle, and pentose phosphate pathway. Metabolomics analysis revealed that there is a significant increase in ATP, NADPH, NADP, and NADH at cultures treated with high concentrations of selected PGRs and significant elevation of these metabolites are associated with increased lipid production.

The presence of heavy metals in municipal solid waste (MSW) is considered as prevalent global pollutants that cause serious risks to the environment and living organisms. Due to industrial and anthropogenic activities, the accumulation of heavy metals in the environmental matrices is increasing alarmingly. MSW causes several adverse environmental impacts, including greenhouse gas (GHG) emissions, river plastic accumulation, and other environmental pollution. Indigenous microorganisms (Pseudomonas, Flavobacterium, Bacillus, Nitrosomonas, etc.) with the help of new pathways and metabolic channels can offer the potential approaches for the treatment of pollutants. Microorganisms, that exhibit the ability of bioaccumulation and sequestration of metal ions in their intracellular spaces, can be utilized further for the cellular processes like enzyme signaling, catalysis, stabilizing charges on biomolecules, etc. Microbiological techniques for the treatment and remediation of heavy metals provide a new prospects for MSW management. This review provides the key insights on profiling of heavy metals in MSW, tolerance of microorganisms, and application of indigenous microorganisms in bioremediation. The literatures revealed that indigenous microbes can be exploited as potential agents for bioremediation.

Microalgae are the most attractive renewable energy sources for the production of biofuels because of their luxurious growth and lipid accumulation ability in diverse nutritional conditions. In the present study, Desmodesmus sp. VV2, an indigenous microalga, was evaluated for its biodiesel potential using Response Surface Methodology (RSM) to improve the lipid accumulation with the combination of nutrients stress NaNO

Microalgae are recognized as cell factories enriched with biochemicals suitable as feedstock for bio-energy, food, feed, pharmaceuticals, and nutraceuticals applications. The industrial application of microalgae is challenging due to hurdles associated with mass cultivation and biomass recovery. The scale-up production of microalgal biomass in freshwater is not a sustainable solution due to the projected increase of freshwater demands in the coming years. Microalgae cultivation in wastewater is encouraged in recent years for sustainable bioeconomy from biorefinery processes. Wastewater from the food industry is a less-toxic growth medium for microalgal biomass production. Traditional wastewater treatment and management processes are expensive; hence it is highly relevant to use low-cost wastewater treatment processes with revenue generation through different products. Microalgae are accepted as potential biocatalysts for the bioremediation of wastewater. Microalgae based purification of wastewater technology could be a universal alternative solution for the recovery of resources from wastewater for low-cost biomass feedstock for industry. This review highlights the importance of microalgal biomass production in food processing wastewater, their characteristics, and different microalgal cultivation methods, followed by nutrient absorption mechanisms. Towards the end of the review, different microalgae biomass harvesting processes with biorefinery products, and void gaps that tend to hinder the biomass production with future perspectives will be intended. Thus, the review could claim to be valuable for sustainable microalgae biomass production for eco-friendly bioproduct conversions.

Microalgae are unicellular photosynthetic organisms capable of producing high-value metabolites like carbohydrates, lipids, proteins, polyunsaturated fatty acids, vitamins, pigments, and other high-value metabolites. Microalgal biomass gained more interest for the production of nutraceuticals, pharmaceuticals, therapeutics, food supplements, feed, biofuel, bio-fertilizers, etc. due to its high lipid and other high-value metabolite content. Microalgal biomass has the potential to convert trapped solar energy to organic materials and potential metabolites of nutraceutical and industrial interest. They have higher efficiency to fix carbon dioxide (CO2) and subsequently convert it into biomass and compounds of potential interest. However, to make microalgae a potential industrial candidate, cost-effective cultivation systems and harvesting methods for increasing biomass yield and reducing the cost of downstream processing have become extremely urgent and important. In this review, the current development in different microalgal cultivation systems and harvesting methods has been discussed.

An increasing quantum of pollutants from various industrial sector activities represents a severe menace to environmental & ecological balance. Bioremediation is gaining flow globally due to its cost-effective and environment-friendly nature. Understanding biodegradation mechanisms is of high ecological significance. Application of microbial enzymes has been reported as sustainable approach to mitigate the pollution. Immobilized enzyme catalyzed transformations are getting accelerated attention as potential alternatives to physical and chemical methods. The attention is now also focused on developing novel protein engineering strategies and bioreactor design systems to ameliorate overall biocatalysis and waste treatment further. This paper presents and discusses the most advanced and state of the art scientific & technical developments about biocatalytic remediation of industrial pollutants. It also covers various biocatalysts and the associated sustainable technologies to remediate various pollutants from waste streams. Enzyme production and immobilization in bioreactors have also been discussed. This paper also covers challenges and future research directions in this field.

There has been increasing attention in recent years on the use of photobioreactors for various biotechnological applications, especially for the cultivation of microalgae. Photobioreactors-based production of photosynthetic microorganisms furnish several advantages as minimising toxicity and providing improved conditions. However, the designing and scaling-up of photobioreactors (PBRs) remain a challenge. Due to huge capital investment and operating cost, there is a deficiency of suitable PBRs for development of photosynthetic microorganisms on large-scale. It is, therefore, highly desirable to understand the current state-of-the-art PBRs, their advantages and limitations so as to classify different PBRs as per their most suited applications. This review provides a holistic overview of the discreet features of diverse PBR designs and their purpose in microalgae growth and biohydrogen production and also summarizes the recent development in use of hybrid PBRs to increase their working efficiency and overall economics of their operation for the production of value-added products.

The aim of this study is to analyze the effect of two plant growth regulators on selective modulation of nutraceutically important fatty acids. Exogenous application of methyl jasmonate (MeJA) promoted microalgal growth compared to control. Treatment with 10 ppm salicylic acid (SA) induced significantly higher lipid production of 475 mg/L (2.2 fold). Interestingly treatment with higher doses of MeJA promoted monounsaturated fatty acid production, particularly oleic acid (C18:1) at early stationary growth phase, while treatment with SA induces essential omega 3 fatty acid production (EPA, C20:5). This significant modification of fatty acid compositions was correlated with the oxidative stress in terms of total reactive oxygen species production and endogenous growth hormone levels. Taken together, the results indicated that treatment with stress associated plant hormones significantly increased high value metabolite accumulation specifically MUFA and PUFA production by modulating stress mechanisms and endogenous growth hormone levels.

Unchecked release of toxic heavy metals in industrial effluents and its environmental and public health implications have opened up a huge opportunity for environment biotechnological applications. Pollutants may be assimilated by the organism, disintegrated into less toxic compounds, or concentrated by adsorption onto the surface of dead biomass. Microalgae, rightly named as a “wonder organism,” are capable of accomplishing bioremediation efficiently by two mechanisms, namely, bioassimilation and biosorption. They have the capability to grow in polluted water as “algal blooms” and assimilate various pollutants. The algal biomass, after harvesting and lipid/protein extraction, could be used as an efficient biosorbent. Careful consideration of parameters such as growth conditions, cellular structure, pretreatment of biomass, etc. can result in development of a low-cost microalgae-based biomass with high bioremediation potential to neutralize and adsorb heavy metal ions. Hence, this chapter discusses the various avenues for bioremediation of toxic heavy metals using the biomass of microalgae.

Two functionally different plant growth regulators, Kinetin and GA3, were evaluated individually or in combination for its effect on growth, lipid yield, PUFAs and EPA accumulation in Nannochloropsis oceanica CASA CC201 . It was observed that the treatment with 0.215 ppm Kinetin resulted in high cell number of 521 × 10 6 cells per mL than the control (398 × 10 6 cells per mL), but GA3 had an adverse effect on cell number. Kinetin increases the specific growth rate to 0.24/day and doubling time to 2.86 days than control (4.38 days). Treatment with GA3 at a concentration of 50 ppm gives the highest cellular lipid accumulation of 61.5% DCW than the control (35.5% DCW). The combination of Kinetin and GA3 exhibited a synergistic effect on total lipid yield of 246.25 mg/L compared with control (121.5 mg/L). The addition of Kinetin increases the percentage of EPA 4 times as compared to the control.

Rapid urbanization and industrialization have resulted in the generation of huge amount of heavy metals-laden wastewater in the recent era. Industries, such as pulp paper, distillery, tannery, textile, etc. produce hazardous wastewater which is directly affecting the environment and human health if disposed off without any treatment. Wastewater treatment is an expensive and energy-intensive procedure not only because of the massive concentrations of pollutants but also because of its large volume. Microbes are immune to the toxicity of metals and play an important role in the ecosystem's resource cycle and energy flow. As the introduction of microbes in detoxifying wastewater has proved to be a boon for the society and hence the emphasis is put on biomineralization, oxidation-reduction, bioprecipitation, bioaccumulation, biosurfactant technology, bioleaching, biovolatilization, and biosorption processes with their selective advantages and disadvantages. Heavy metals can be compartmentalized by microbial strains, such as Corynebacterium glutamicum (Pb, Zn, Cd, Co, Cr), Aspergillus lentulus (Cr, Cu, and Pb), Bacillus, Microbacterium, Micrococcus, Shinella, Arthrobacter, Bacillus, and Serratia. Nanocomposites (CuFeO, FeO, Co3O4@SiO2, Fe3O4 etc) being unique in nature helped the researchers in treating wastewater efficiently. Hence, this review was aimed to address the treatment of wastewater by removing the heavy metals employing microbes in combination with magnetic nanocomposites. The effect of heavy metals on biodiversity, role of microbiota in the environment for detoxification, and appropriate markers that represent the efficiency of removal of the metals from industrial wastewater have also been explored in this review. Furthermore, the issues that need to be addressed in the future, and significant points for further research are also highlighted.

This review illustrated the role of metal-binding proteins (MBPs) and microbial interaction in assisting the phytoremediation of industrial wastewater polluted with heavy metals. MBPs are used to increase the accumulation and tolerance of metals by microorganisms via binding protein synthesis. Microbes have various protection mechanisms to heavy metals stress like compartmentalization, exclusion, complexity rendering, and the synthesis of binding proteins. MBPs include phytochelatins, metallothioneins, Cd-binding peptides (CdBPs), cysteines (gcgcpcgcg) (CP), and histidines (ghhphg)2 (HP). In comparison with other physico-chemical methods, phytoremediation is an eco-friendly and safe method for the society. The present review concentrated on the efficiency of phytoremediation strategies for the use of MBPs and microbe-assisted approaches.

The present study aims to evaluate the effect of different concentration of natural auxin, Indole-3 acetic acid (IAA) on growth, lipid yield, PUFA and EPA accumulation in Nannochloropsis oceanica CASA CC201. It was observed that the, treatment with 10ppm concentration of IAA resulted in high cell number 579.5×106cells/ml than the control (215.5×106cells/ml). Treatment with IAA at a concentration of 40ppm gives the highest cellular lipid accumulation of 60.9% DCW than the control 31.05% DCW). Lipid yield is also found to be increased by the addition of 40ppm IAA (319.5mg/L) compared with the control (121.5mg/L). EPA percentage is increased to 10.76% by the addition of 40ppm IAA compared to the control (1.87%).

Considering the rapid increase of world population and shrinking of arable land, algae could potentially serve as an alternate to supplement proteins and nutrients derived from terrestrial plants. Microalgae are rich in variety of nutritionally important compounds like proteins, pigments, carbohydrates, polyunsaturated fatty acids, dietary fibers and bioactive compounds with wide range of health benefits. Eicosapentaenoic acid and docosahexaenoic acid serve as wonder molecules by reducing the risk of cardiac diseases like arrhythmia, stroke, rheumatoid arthritis, and high blood pressure. Besides being used as nutritional source, microalgae are also widely used as natural colorant, pleasant aroma, and carrier molecules. Considering the health benefits of microalgae, World Health Organization declared Spirulina as one of the greatest superfood on the globe. This chapter presents the different nutraceuticals of micro- and macroalgae origin, its biochemical properties, and health benefits in a comprehensive manner.