Sustainable microalgal biomass production in food industry wastewater for low-cost biorefinery products: a review.

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.

Production of microalgae with high lipid content and their potential as sources of nutraceuticals.

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.

Statistical optimization and formulation of microalga cultivation medium for improved omega 3 fatty acid production.

Microalgae are considered a rich source of high-value metabolites with an array of nutraceutical and pharmaceutical applications. Different strategies have been developed for cultivating microalgae at large-scale photobioreactors but high cost and low productivity are the major hurdles. Optimizing the composition of media for the cultivation of microalgae to induce biomass production and high-value metabolite accumulation has been considered as an important factor for sustainable product development. In this study, the effect of plant growth regulators together with basal microalgal cultivation medium on biomass, total lipid, and EPA production was studied using the Plackett-Burman model and Response surface methodology. The traditional one-factor-at-a-time optimization approach is laborious, time-consuming, and requires more experiments which makes the process and analysis more difficult. The Designed PB model was found to be significant for biomass (396 mg/L), lipid (254 mg/L), and EPA (5.6%) production with a P value < 0.05. The major objective of this study is to formulate a medium for EPA production without compromising the growth properties. Further, we had formulated a new media using RSM to achieve the goal and the significant variables selected were NaNO3, NaH2PO4, and IAA and was found to be significant with 16.72% EPA production with a biomass production of 893 mg/L with a P value < 0.05. The formulated medium can be used in large-scale cultivation systems which can enhance biomass production as well as the omega 3 fatty acid production in marine microalgae Nannochloropsis oceanica. Supplementary Information: The online version contains supplementary material available at 10.1007/s43393-021-00069-1.

Role of microbes in bioaccumulation of heavy metals in municipal solid waste: Impacts on plant and human being.

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.

Mass cultivation and harvesting of microalgal biomass: Current trends and future perspectives.

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.

Enhancement of lipid accumulation in microalga Desmodesmus sp. VV2: Response Surface Methodology and Artificial Neural Network modeling for biodiesel production.

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 NaNO3 starvation, CaCl2 depletion, and supplementation of magnesium oxide nanoparticles (MgO). Among different stress conditions, 57.6% lipid content was achieved from RSM optimized media. Owing to this, RSM results were also validated by the Artificial Neural Network (ANN) with 11 training algorithms and it is found that RSM was more significant. In addition, the saturated fatty acid (SFA) content was noticeably increased in RSM optimized media (95.8%) while compared with control. Further, the highest total FAME content 97.21% was also achieved in cells grown in RSM optimized media. Biodiesel quality parameters were analyzed and found that they are in accordance with international standards. Thus, this study suggesting that the fatty acid profile of Desmodesmus sp. VV2 attained under optimized media conditions would be suitable for biodiesel production for future energy demand.

Design and applications of photobioreactors- a review.

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.

Role of microbial community and metal-binding proteins in phytoremediation of heavy metals from industrial wastewater.

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.

Biocatalytic remediation of industrial pollutants for environmental sustainability: Research needs and opportunities.

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.

Stress hormones mediated lipid accumulation and modulation of specific fatty acids in Nannochloropsis oceanica CASA CC201.

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.

Selective enrichment of Eicosapentaenoic acid (20:5n-3) in N. oceanica CASA CC201 by natural auxin supplementation.

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%).