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The numerous challenges attributed to fossil fuels and the transformation of food crops for energy production necessitate the search for better energy options. Algae valorization via liquefaction under hydrothermal conditions is one of the re-ignited areas of interest for liquid fuels production. Their cultivation and processing feasibilities could infer good benefits for future energy sustainability. The paper explored the role of catalytic systems, especially the heterogeneous catalysts during the liquefaction process. Solid catalysts such as supported metals, zeolites and silica-alumina are so far given preference as catalytic materials for improving bio-oil and associated hydrocarbon fuels yields. The paper therefore analyzed critical literature on the process catalysis and simultaneously discussed new directions for further investigations. [ABSTRACT FROM AUTHOR]

This literature review discusses several aspects of biodiesel production from microalgae. This paper elucidates the optimal bioenvironmental conditions for microalgae cultivation, process design of algal biodiesel production, physicochemical properties of lipids extracted from microalgae and the properties of the produced biodiesel fuel, and the transesterification process. On the other hand, this paper illustrates the designs of up-to-date full-scale and lab-scale photobioreactors (PBRs). Furthermore, this paper argues different bioengineering aspects of biodiesel production from microalgae. Eventually, the measurements, calculations, design parameters, Life Cycle Analysis (LCA) of the production process are discussed. [ABSTRACT FROM AUTHOR]

Despite a substantial literature using life cycle assessment (LCA) approach, the extent to which second and third generation biofuels are more sustainable than the first generation remains a subject of debate. Although the existence of limitations due to LCA variability and uncertainty, this paper intends to determine global tendencies based on a statistic and critical interpretation of previously published study results, reviewing 61 recent papers addressing an environmental evaluation of microalgae biofuels. Such information is compared to the same impact indicators for fossil fuels and for ethanol and biodiesel from terrestrial crops in Europe and Brazil. For each case, the system boundaries and the methodological choices were precisely described. The sustainability potential of all biofuels was evaluated by the Global Warming Potential (GWP), the Energy Ratio (ER) and the Land Use (LU), allowing a broad estimation of the biofuels’ contribution to climate change mitigation, their net energy efficiency and their competiveness with food production chain. The results highlight that algae-derived biodiesel is, by far, the most efficient alternative in terms of land use compared to other biofuels, avoiding competition with food crops. Some biodiesel pathways can also satisfactorily perform in terms of greenhouse gases emissions reduction, but some others can be even worst than fossil diesel. Nevertheless, in terms of energy efficiency, algae biofuels cannot compete with other biofuels or fossil fuels. They present very low performances, even demanding more energy for its production then the energy they can deliver. Moreover, no pathway can be conclusively selected as preferable between the two main technologies available for microalgae biodiesel due to high uncertainties. However, open raceway pounds technology seems to be preferable as it looks less GHG intensive, requiring lower energy input and land use. Energetic and GWP performances can be improved if production pathways are carefully chosen and optimized. [ABSTRACT FROM AUTHOR]

Biofuels derived from algae can have lower impact on the environment and the food supply than biofuels produced from crops. The strain selection, cultivation method, culture conditions and the chemical composition strongly influences the production costs but also the engine's performance and the exhaust gas emissions. The scope of this paper is to make a critical review about the impact of the use of biofuels produced from (micro) algae to power diesel engines. There is a huge disparity in the amount of papers published for algae culture, oil extraction, and biodiesel production compared to reporting performance on diesel engines. This paper presents an analysis of the papers published in this specific field. Generally, a reduction of torque and power output is reported. A wide range of blends up to B50 but also pure biodiesel has been tested. The blend showing results closest to diesel fuel appears to be B20. Several pollutants can be reduced if biofuels from different strains are used but an increase in NOx is generally reported, associated to higher temperatures in the combustion chamber. The use of emulsions instead of blends or neat biodiesel reveals a promising alternative with important reductions of CO 2 and NOx. However, the few reports for engine tests present some contradictions, or are lacking important information about the experiments. The assessment of biodiesel produced from algae or microalgae is a field hardly explored and until today some reference papers contain contradictory results or non-well studied behaviors as this survey demonstrates. [ABSTRACT FROM AUTHOR]

Algae is recognized as a potentially valuable source of biofuels and biochemicals; however, a major limitation to commercialization is in the high cost of harvesting, de-watering, and downstream processing of dilute algae biomass when it is grown planktonically. Growing algae as a biofilm offers potential advantages for biomass processing because biofilms are immobilized and orders of magnitude more concentrated. For these reasons there has been an emerging interest in algae biofilm biofuel research over the past several years. Additionally, there has been a considerable amount of work on understanding algae biofilms in nature, and on using algae biofilms for tertiary wastewater treatment. This review paper draws from all of this literature to describe algae biofilm composition, and their growth responses to the key environmental factors affecting growth and internal lipid concentrations; the emphasis being on optimizing biomass and lipid productivity. Additionally, the paper summarizes key things known about planktonic algae growth and bacterial biofilm growth in order to make inferences about the potential growth of algae biofilms. The paper identifies many key knowledge gaps in the potential for producing biomass and lipids from algae biofilm growth systems. [ABSTRACT FROM AUTHOR]

The supply of nutrients is a great issue to a sustainable scale-up of microalgal biofuels production, as these photosynthetic microorganisms require large amounts of N, P and other micronutrients to grow, which turns into high fertilizers demand. Additionally, recovery and reuse of nutrients (particularly N & P) are a must to reduce the non-point pollution emanating from their release into water or air during the downstream processing steps to biofuels or bioproducts. In the recent years, strong research efforts have been paid for developing nutrient recovery and recycling techniques, in order to reduce the net amount of fertilizers required. One possibility is exploiting nutrients from waste streams, such as wastewaters, while others focus on the recovery of N and P from the non-fuel fraction of the produced microalgal biomass, which is then recycled to the cultivation system, in a closed-loop perspective. In both cases, the presence of possible contaminants as well as nutrients bioavailability can impact the biomass productivity compared to standard synthetic media. Although the nutrients recovery and reuse has been in the forefront for a few years, there are no review publications available yet. In this paper, state-of-the art studies on nutrients recovery and recycling methods in microalgae processing from the last decade are reviewed. The study focuses on the different N and P recovery methods and yields, as well as on their subsequent use in algal cultivation and impact on algae productivity. Possible bioproducts exploitation is considered, and perspectives of closed-loop material balances on a large-scale are eventually provided. [ABSTRACT FROM AUTHOR]

An algal feedstock or biomass may contain a very high oil fraction, and thus could be used for the production of advanced biofuels via different conversion processes. Its major advantage apart from its large oil fraction is the ability to convert almost all the energy from the feedstock into different varieties of useful products. In the research to displace fossil fuels, algae feedstock has emerged as a suitable candidate not only because of its renewable and sustainable features but also for its economic credibility based on the potential to match up with the global demand for transportation fuels. Cultivating this feedstock is very easy and could be developed with little or even no supervision, with the aid of wastewater not suitable for human consumption while absorbing CO 2 from the atmosphere. The overall potential for algae applications generally shows that this feedstock is still an untapped resource, and it could be of huge commercial benefits to the global economy at large because algae exist in millions compared to terrestrial plants. Algae applications are evident for everyday consumption via foods products, non-foods products, fuel, and energy. Biofuels derived from algae have no impact on the environment and the food supply unlike biofuels produced from crops. However, any cultivation method employed could control the operating cost and the technicalities involved, which will also influence the production rate and strain. The scope of this paper is to review the current status of algae as a potential feedstock with diverse benefit for the resolution of the global energy demand, and environmental pollution control of GHG. [ABSTRACT FROM AUTHOR]

In the effect of robust industrialization and rapid augmentation of a number of fleets, there has been a huge rise in the fossil fuel consumption. Tremendous increase in global warming threatens the ecological balance of the earth. Based on the recent sorts of hardship about the fuel, researchers are profoundly pondered over the field of renewability, environmentally friendly and economically doable. In recent decades biodiesel fuel becomes the center of attraction among researchers since it is renewable, bio degradable, non-noxious, eco-friendly and sustainable. This review paper highlights and reviews the properties of prosperous variety of the biodiesel fuels derived from non-edible feedstocks which are termed as third generation biodiesel and its effects on the performance and emissions of the diesel engines. It was observed that the physicochemical properties of the biodiesel differ based on the types of feedstocks and also have a considerable effect on the potential performance of engine and dynamic characteristics of emission level. Also, the usage of biodiesel commonly leads to a reduction in noxious pollutants like carbon monoxide, unburnt hydrocarbon and particulate matter with an obvious increase in fuel consumption and NOx emission. This review provides a prospective strategy for the researchers for enhancing the engine performance and emission characteristics by using the third generation biofuels and its blends with the productive marvelous outcomes. [ABSTRACT FROM AUTHOR]

Climate change is one of the main threats of the modern society. This phenomenon is associated with the increase of the greenhouse gases (GHGs, mainly carbon dioxide – CO 2 ) emissions due to anthropogenic activities. Main causes are the burning of fossil fuels and land use change (deforestation). Climate change impacts are associated with risks to basic needs (health, food security and clean water) as well as risks to development (jobs, economic growth and the cost of living). Taking into account this phenomenon, several countries participated in the last United Nations Climate Change Conference in Paris (21st Conference of the Parties – COP21) and agreed to reduce their GHG emissions to limit the rise in global temperature to less than 2 °C. Main commitments and actions are focused in energy efficiency, renewable energy deployment and forest protection (increasing the CO 2 natural sinks). In this context, biofuels (from non-edible feedstocks) have the potential to replace fossil based fuels in the transport sector, being a carbon-neutral fuel. In particular, algae–based biofuel can play a dual role in this scenario: as photosynthetic organisms, algae can capture CO 2 from industrial emissions or from atmosphere and the resulting biomass can be used to produce a wide range of materials including biofuels. Therefore, this paper reviews the research advances of algae cultures with focus on the applications (CO 2 capture and bioenergy production) related to the targets of COP21 agreement. Main recent advances in algal research studies and projects are also presented. [ABSTRACT FROM AUTHOR]

Life cycle analysis (LCA) of algal biodiesel production process can provide a quantitative measure for its sustainability. In this paper, the published LCA studies of algae biodiesel processes are reviewed, demonstrating there are few comprehensive studies covering the complete process; therefore, outcomes can be inconclusive. The variability in algae type, reactor type and conditions, and other factors will impact LCA outcomes. However, the lack of a systematic framework for LCAs applied to the algae biodiesel process is also a factor in the variable LCA outcomes. Factors such as system boundaries, temporal units, choice of allocation, land use, and biogenic carbon source have to be redefined; and other variables such as infrastructure construction, systematic maintenance, transportation, and waste management need to be considered in the LCA strategy. Critically, the economic burden associated with both upstream and downstream processes should also be included in the LCA approach. Future studies could focus on process design, optimization, and intensification. This review paper offers a comprehensive and critical literature review of the LCA and sustainability assessment for the entire algal biodiesel process, which can benefit relevant future studies. Image 1 • Several LCA studies of algae biodiesel processes are studied comprehensively. • A majority of algae biodiesel LCA studies in the literature do not cover the entire process. • Possible sources for inconclusive impact results among different LCA studies are addressed. • Effective guidelines for systematic LCA study of algae biodiesel production are provided. • Future perspectives and potential areas for research are highlighted. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are bioelectrochemical devices that allow the harvesting of electricity generated during anaerobic respiration of selected bacterial species. This technology shows promise in both wastewater treatment and sustainable bioenergy conversion applications. Bacterial respiration occurs in the anaerobic anode compartment of the MFC, and is electrochemically coupled with electron acceptors in the MFC's aerobic cathode compartment. This paper summarizes the published results of bacterio-algal MFCs. The use of microalgae in MFCs has gained interest primarily due to algae's ability to photosynthesize atmospheric CO 2 , producing both biomass and oxygen and thereby facilitating the cathodic reaction. These phototrophic microorganisms can serve as biocatholytes in MFCs because the oxygen produced is an electron acceptor for the electrons harvested from the anode compartment. The bacterio-algal MFC can provide multiple benefits including 1) power generation, 2) wastewater treatment, 3) algal biomass cultivation and pigment production, 4) carbon dioxide assimilation, and 5) oxygen production. This review article summarizes not only successful published results of bacterio-algal fuel cells but also highlights critical operational parameters and their effect on power generation and output efficiency. [ABSTRACT FROM AUTHOR]

Fuel security, economics and climate change issues are creating a requirement for alternative renewable fuels. Bioethanol produced by algal biomass is becoming increasingly popular all over the world due to the sustainability of feed stock and environmentally friendly nature. This review paper describes the bioethanol production technology from algae using various cultivation, harvesting, extraction and commercialization techniques and its environmental perspectives. The economic sustainability of algae-derived bioethanol biofuel depends on the cost of production that could be minimized by producing valuable secondary by-products, which is the aim of current algal biofuel research. Future technologies with sufficient potential for maximum extraction capacity and minimal downstream processing using low cost feedstock will address the cost-effectiveness of renewable bioethanol biofuel. [ABSTRACT FROM AUTHOR]

Algae are considered to be the most viable feedstock for alternative aviation fuel production. The alternative (nonpetroleum) fuel from biomass could be produced as “drop-in” fuels with no effects on flight safety and would be interchangeable with current fuels in performance and handling. Accordingly, alternative fuels blended with petroleum fuels should meet jet fuel׳s requirements as laid out in the specifications (ASTM D7566). The current jet fuel specifications have implicitly limited jet fuel hydrocarbons with carbon numbers owing to the meeting of suitable physical properties. Accordingly, the carbon distribution of lipids in algae influences the aviation fuel yield and the use of biorefining pathway. This paper investigates the carbon distributions of lipids in different types of algae and characteristics of jet fuels derived from algae have also been discussed by four pathways including Fischer–Tropsch (FT) jet fuel process, hydrotreated renewable jet fuel process, pyrolysis-hydrotreated renewable jet fuel process and hydrothermal liquefaction-hydrotreated renewable jet fuel process. Moreover, carbon distributions of microalgae lipids in 103 species from 10 phyla have been concluded in order to obtain the more potential candidates for sustainable resources of bio-kerosene. The carbon distribution of a typical FT jet fuel can be modeled by the Anderson–Schultz–Flory distribution, which content can be produced to be similar to that kerosene by optimizing the FT process. The hydrotreated renewable jet fuel contains a complex carbon distribution between C 7 and C 18 due to the hydrotreating reactions applied, including hydrodeoxygenation, hydrocarbonylation, and decarboxylation. Pyrolysis biocrude is similar to hydrothermal liquefaction biocrude as regards carbon distribution. In pyrolysis-hydrotreated renewable jet fuel process, higher pyrolysis temperature and catalyst seem to be helpful to production of C 8 –C 16 compounds in biofuels. In hydrothermal liquefaction-hydrotreated renewable jet fuel process, the carbon distribution of jet fuel is similar to that of pyrolysis-derived jet fuel and it lead to higher bio-kerosene product. [ABSTRACT FROM AUTHOR]

The modern world is highly dependent on energy. Biodiesel is recognized as a green and alternative renewable diesel fuel, and Brazil is the world׳s third largest producer of biodiesel, which in this country is mainly produced from soybeans. As the demand for biodiesel is increasing due to the increasing use of transportation fuel, it is advisable to look for other sources that would not need a vast cropland. Recently, microalgae have emerged as a source than can play the dual role of bioremediation of wastewater and generation of biomass for biodiesel production. This paper focuses on the feasibility of utilizing wastewater to cultivate algae for the production of biodiesel in Brazil. By using only domestic wastewater from 40% of Brazilian municipalities, the production of biodiesel would increase by 21.4%. Moreover, the use of wastewater treatment becomes an economically attractive alternative as the revenue from selling biodiesel overcomes the production costs by at least 10%. As a result, Brazil could easily increase its current biodiesel production and simultaneously amazingly improve its index of sanitation. [ABSTRACT FROM AUTHOR]

Hydrogen is considered as an ideal alternative to fossil fuels due to its high energy density by mass and clean combustion product. Using anaerobic bacteria to ferment biomass and produce renewable hydrogen is receiving increased attention. Aquatic algal biomass, which can be sourced from natural algal bloom or mass cultivation, is considered as a promising substrate for hydrogen fermentation. This paper reviews the recent developments in fermentative hydrogen production from algal biomass, with the main focus on hydrogen production potential and its current technological state. The stoichiometric hydrogen yields of algal biomass in dark fermentation are predicted based on the theoretical contents of monosaccharides from carbohydrates and glycerol from lipids in biomass. Hydrogen yields of algal biomass by dark fermentation can be improved by using efficient pretreatments at optimized biomass carbon/nitrogen ratios with domesticated hydrogen-producing bacteria as the inoculum. The effluent of dark fermentation, which is rich in volatile fatty acids, should be used for the production of biofuels and biochemicals to further improve the energy efficiency and economic feasibility of hydrogen fermentation. [ABSTRACT FROM AUTHOR]

Many authorities have reached the conclusion that using fossil fuels, as the main source of energy to satisfy the increasing global energy demand, is ultimately unsustainable. This is because of depleting resources, and also because, if this approach is followed, emissions of carbon dioxide would continue to build up. Consequently, research on biofuel, that is fuel made from biomass, derived from materials that were recently living, has attracted attention. In this context, the generation of biofuels from algae shows promise for the following reasons. The algae can be grown quickly, all the materials produced are non-toxic and biodegradable, and during this growth there is an opportunity to cause greenhouse gas fixation. Also, since growing algae does not need arable land, it can be grown without competing with food or feed crops, the fuel derived from it being a “third generation” biofuel. This paper describes different types of algae (microalgae and seaweeds), and presents different technologies employed in making biofuels (biogas and biodiesel) from them. [ABSTRACT FROM AUTHOR]

The study found that promising algae biofuels R&D breakthroughs (hydrothermal liquefaction technology, high-frequency magnetic impulse cavitation reactors, etc.) and industry milestones (technologies of hydrorefining and catalytic selective oxidation among others), in order to move forward, require for implementation of new synergies and further innovations needed to improve economical production of advanced biofuels that are not applicable today. It seems that already viable state-of-the-art findings must be re-examined extensively in all of the different aspects in order to hasten the commercialisation of algal biofuels production in sustainable biorefineries. The same could be said about the feedstock selection for algal biomass production and its cultivation. It is the first step to successful large-scale algae cultivation in new regions of the world. Based on the above mentioned we identified fourteen promising algae species that can successfully grow in various regions of Russia under local climatic conditions. Samples collected during expedition were analysed at Lomonosov Moscow State University. Providing predetermined alternate periods of light and darkness and for temperature control of the different mediums to improve photosynthetic responses we investigated two different microalgal production systems: open ponds of the volume V =500 l and closed bioreactors of the volume V =1.0 l. Later on, a review on interdisciplinary synergies between biology and technology to open up new avenues of R&D in the field of algae-for-transport was carried out by leading universities of Lithuania, Russia, and Ukraine. In summary, we found that it is already possible to reduce the price of the 3rd and 4th generation biodiesel fuel from algae by applying the synergistic approaches to sustainable energy production highlighted in this paper, and probably some other ones as well. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction (HTL) has recently received increasing attention due to its advantages in rapid reaction, using wet feedstocks with no lipid-content restriction. These characteristics make HTL especially suitable for conversion of algae into biocrude oil. This paper aims to provide a state-of-the-art review of HTL technologies from a perspective of algal biorefinery. In this review, we first summarize the updated researches and technologies of algae HTL. Specially, an "Environmental-Enhancing Energy" (E2E) paradigm based on algal biorefinery has been proposed and discussed. Second, the principles and crucial factors for algae HTL are discussed with focus on (1) algae species and characteristics including lipids, proteins and carbohydrates; (2) the operational parameters including total solids, holding temperature, retention time and catalysts; and (3) the critical principles of HTL reaction and the role of deoxygenation and denitrogenation. In addition, potential applications of HTL are discussed. Prospective and challenges of HTL for algal biorefinery are finally addressed including feedstock preparation, scale-up of algae HTL, and process integration. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction of algal biomass is growing as a promising technology for the production of liquid biofuels in the renewable energy sector. The potential of this technology under varied process conditions has been extensively demonstrated worldwide. Recent developments have revealed that the feedstock quality and extraction solvents have a considerable effect on the biocrude quality and yield. Algal lipids and proteins contribute significantly to biocrude formation, while carbohydrates contribute mainly to the production of gaseous products. However, the challenges associated with high N/C and O/C ratios in biocrude derived from proteinaceous biomass need to be addressed. Recently, co-liquefaction of carbonaceous biomass with different biochemical compositions has proven promising in biocrude upgradation. The most contemporary research also revealed that solvents as a co-solvent and/or extraction agent have the most significant effect on biocrude quality and yield in the HTL mixture. These solvents could also intensely influence the properties and distribution of energy-dense compounds in the biocrude. The present paper extensively reviews the effect of feedstock composition on HTL biocrude formation and its characteristics based on the information collected from more than 150 scientific resources published between 2010 and 2021. Furthermore, the role of solvents as reaction medium and extraction agent on biocrude yield and composition has been critically reviewed. Future perspectives and challenges in the use of approaches for improving biocrude formation are also discussed. [Display omitted] • Biochemical composition and extraction solvents influence algal biocrude yield and quality. • The use of solvents could play imperative role as co-solvent and extraction agent for enhancing biocrude yield and quality. • Much attention needed to improve the N/C & O/C ratio of algal crude to match fossil crude standards. • Feedstock characteristics and extraction solvents influence the distribution of compounds in the biocrude. • The exploration of appropriate extraction solvents is still in the early-stage and needs developments. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, algae-based fuels have received a growing interest of the industry sector and the US Government as a sustainable and renewable energy source. Algae constitute a unique feedstock as they contain high levels of both lipids and sugars and, thus, can be used for both biodiesel and ethanol production successively, in a two-stage process. In addition, the production of algae-based fuels shows a low environmental footprint and high energy efficiency. Algae can produce between 10 and 100 times more oil per acre as compared with traditional oil crops (e.g., oil palm) and can also grow 20–30 times faster than food crops. The production of algae does not compete with traditional crops for fresh water, high quality soil or fertilizers and, if cultivated off-shore, algae production does not require land resources at all. Furthermore, algae-based fuel is carbon-neutral, as algae assimilate similar amounts of CO2 for its growth as is released upon fuel combustion. From the policy perspective, algae-based fuels can provide a buffer for mitigating the food/feed vs. fuel problem in the long-term. The paper analyzes and discusses very recent developments in the algae R&D from the economic, environmental and policy perspective. It presents ways for solving the economic impediments as well as prospects for the commercialization of the algae technology in the near future. It covers multiple scientific and industry-related research and experimental studies to provide a comprehensive picture of the trends and patterns in the field. [Copyright &y& Elsevier]

Abstract: Microalgal species are recently in the spotlight for biofuels production like biodiesel, bioethanol and biohydrogen. Algae are also used as a biofertiliser, source of nutrient and for controlling pollution. Algae being a photosynthetic organism are produced in the photo bioreactors. Hence the design and development of photobioreactors for maximum production of algae is very important. Apart from maximum production, other factors such as design, cost effectiveness of the bioreactor, purity of the algae produced, user friendly, low maintenance and space convenience need to be optimized. The bioreactors which are used for the purpose of growing algae are bubble column photobioreactor, airlift photo bioreactor, flat panel bioreactor, horizontal tubular photobioreactor, stirred tank photobioreactor etc. These bioreactors have their own advantages and disadvantages. Work is on for developing hybrid type of bioreactors which may overcome the limitations of the developed photobioreactors. This paper covers the salient features, limitations of developed photobioreactors and recent developments in the field of photobioreactors. [Copyright &y& Elsevier]

Abstract: This paper critically discusses the scope, potential and implementation of biomass conversion to energy in Indian scenario. The feasibility as well as suitability of the various categories of biomass to energy in India has been discussed. Brief descriptions of potential conversion routes have been included, with their possible and existing scope of implementation in Indian context. As far as possible, the most recent statistical data have been reported from the available sources. The figures reported have been updated as on March 2009, in most of the cases. The discussion reveals that a large potential exists for the biomass feed-stocks from the various kinds of waste biomass. The gasification as well as anaerobic digestion processes seem to be most attractive in Indian scenario. [Copyright &y& Elsevier]

The current energy demands continuously lead us to the quest of developing alternative energy sources to compete with the depleting fossil fuel reserves. In the recent years algae have garnered attention as third generation biofuel. However, low biomass concentration and metabolite accumulation results in low biofuel yield, thereby limiting its application. The present study reviews three possible approaches for enhancing biofuel production from algae: biochemical engineering, genetic engineering and application of omics/metabolic flux. Biochemical engineering depends on changing different physiological conditions such as increasing cultivation temperature or applying nitrogen stress to route the carbon flux towards metabolite accumulation. Genetic engineering exploits the knowledge of the major molecules for metabolite accumulation to create recombinant microalgal strains, which overexpresses specific enzymes or blocks certain pathways to improve metabolism of targeted biomolecules. Omics and flux analysis helps to mathematically analyze these manipulations and interpret different possible responses in silico , based on which experiments can be conducted in-vivo. Currently biochemical engineering is the most recognized technique for metabolite improvement in algae. However, these approaches have inhibitions which can be reduced by genetic engineering, metabolic flux or omics strategies. It was analyzed that integration of these approaches may help us to overcome the current limitations of algal biofuel production. The present paper discusses the merits, success rates and constraints of each of these approaches. The article explicitly discusses how combining these engineering techniques may help us to enhance the starch/carbohydrate and the lipid content in algae for establishing it as a promising energy feedstock for the future. • Algal metabolites are differentially dependent on the concentration of macronutrients. • Transgenic and cisgenic microalgae aide in improving biofuel production. • Enrichment of biofuel production by combining in silico and in vivo techniques. • Enhancement of algal biofuel production by implementing omics and metabolic flux analysis. [ABSTRACT FROM AUTHOR]

Microalgae based microbial fuel cells are efficient systems to remove nitrogen, phosphorous and CO 2 from wastewater, to produce bioelectricity and value-added products from microalgal biomass. Microalgae can be used in MFCs as algae assisted cathode systems, microbial carbon capture cells or sediment microbial fuel cells as well as photosynthetic microalgae microbial fuel cell. These MFCs are shown efficient for CO 2 capture with a low risk of carbon emission, N and P removal via symbiotic interactions of microalgae-bacteria consortia in wastewater treatment along with power generation. The oxygen production by microalgae during the light period reduces the need for external oxygen supply for cathodic reactions, which is advantageous for reducing the aeration cost, as otherwise power needs to be supplied for mechanical aeration. Utilization of algal biomass harvested from the cathodic compartment requires a pretreatment in a biorefinery concept. This still remains a major drawback, but current advances towards the choice of a biofilm on the cathode allow for further recovery of value-added products from algal biomass. Alternatively, the algal biomass can be utilized as the sole feedstock in the anodic compartment. This paper reviews the application of algae based microbial fuel cells for bioelectricity production, mainly focusing on the use of algae in the cathodic compartment, microalgae in the anodic compartment and the main interactions between the compartments affecting the bioelectricity production. Image 1 • Photosynthetic aeration by microalgae can replace conventional aeration in MFCs. • PAMFCs are well-suited for electricity production without mechanical aeration. • Use of microalgae in MFCs improves nitrogen, phosphorous and CO 2 removal rates. • Microalgae can be effectively used as a substrate for the anodic compartment. [ABSTRACT FROM AUTHOR]