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Plastic consumption has increased globally, and environmental issues associated with it have only gotten more severe; as a result, the search for environmentally friendly alternatives has intensified. Polyhydroxyalkanoates (PHA), as biopolymers produced by microalgae, might be an excellent option; however, large-scale production is a relevant barrier that hinders their application. Recently, innovative materials such as carbon dots (CDs) have been explored to enhance PHA production sustainably. This study added green synthesized multi-doped CDs to Scenedesmus sp. microalgae cultures to improve PHA production. Prickly pear was selected as the carbon precursor for the hydrothermally synthesized CDs doped with nitrogen, phosphorous, and nitrogen–phosphorous elements. CDs were characterized by different techniques, such as FTIR, SEM, ζ potential, UV–Vis, and XRD. They exhibited a semi-crystalline structure with high concentrations of carboxylic groups on their surface and other elements, such as copper and phosphorus. A medium without nitrogen and phosphorous was used as a control to compare CDs-enriched mediums. Cultures regarding biomass growth, carbohydrates, lipids, proteins, and PHA content were analyzed. The obtained results demonstrated that CDs-enriched cultures produced higher content of biomass and PHA; CDs-enriched cultures presented an increase of 26.9% in PHA concentration and an increase of 32% in terms of cell growth compared to the standard cultures. [ABSTRACT FROM AUTHOR]

Microalgae-based biodiesel production has gained momentum over petroleum-based fuels due to its carbon neutrality and environment friendly properties. However, issues like high cost of cultivation and usage of inorganic fertilizers possess hindrance towards its commercial production and warrant new approaches of its eco-friendly cultivation techniques. In the present study, effect of hydrochar derived from hydrothermal carbonization (HTCb) of banana pseudostem as a supplement was investigated on the growth performance of microalgae, Graesiella emersonii MN877773, for biodiesel production. The study revealed that hydrochar supplementation (250 ppm) to the 10 days old microalgae culture improved (p < 0.05) biomass productivity (2 times higher; 0.018 g/L/day). There was also 27% increase (p < 0.05) in lipid content (16%) and improved lipid productivity (i.e. 0.003 g/L/day) noticed due to the reduction of culture solution pH from highly alkaline to slightly alkaline through hydrochar addition. Fatty acid profiling revealed presence of more amount of methyl palmitate (56% higher) with the high saturated/unsaturated fatty acid ratio (1.3). The vehicular properties of the biodiesel produced from the hydrochar treated microalgae were also found in compliance with the national and international standards with the high heating value of 40.2 MJ/kg. Microalgae grown in hydrochar-supplemented treatment also settled at the bottom within 1 h of resting period with the flocculation efficiency of 50%. This leads to the reduction (62%) in energy expenditure (5.5 kWh/g) and cost (0.4 US$/g) required for harvesting the microalgae. The present study accentuates that hydrochar supplementation at certain dosage to the pre-grown microalgae stimulates more production of quality lipids in the test microalgae with possibility to thrust sustainable biodiesel production. [ABSTRACT FROM AUTHOR]

Currently, the whole world is facing hunger due to the increase in the global population and the rising level of food consumption. Unfortunately, the impact of environmental, climate, and political issues on agriculture has resulted in limited global food resources. Thus, it is important to develop new food sources that are environmentally friendly and not subject to climate or space limitations. Microalgae represent a potential source of nutrients and bioactive components for a wide range of high-value products. Advances in cultivation and genetic engineering techniques provide prospective approaches to widen their application for food. However, there are currently problems in the microalgae food industry in terms of assessing nutritional value, selecting processes for microalgae culture, obtaining suitable commercial strains of microalgae, etc. Additionally, the limitations of real data of market opportunities for microalgae make it difficult to assess their actual potential and to develop a better industrial chain. This review addresses the current status of the microalgae food industry, the process of commercializing microalgae food and breeding methods. Current research progress in addressing the limitations of microalgae industrialization and future prospects for developing microalgae food products are discussed. [ABSTRACT FROM AUTHOR]

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented. [ABSTRACT FROM AUTHOR]

Green algae are well known for their plant growth-promoting role, but the biofertilization potential of some industrial algae waste has yet to be tested. Industrial algae production facilities are increasing rapidly yearly, but most growing liquids are unused and remain as waste. Here we examined the effects of various microalgae byproducts as tea plant growth biostimulants. The roles of cell-free supernatant (CFS), sonicated microalgae biomass and living cells of the freshwater alga Chlorella vulgaris in promoting tea plant growth were investigated through real field applications. All three algae by-products of the same culture were applied to the tea plants three times either from aerial parts or from the soil. After 40 days of incubation, it was determined that all microalgae waste, even CFS, significantly improved the vegetative growth of the treated tea plants. CFS were also able to improve chlorophyll accumulation, node length, leaf length, and leaf width by 23%-26%, 62%-69%, 5%-36%, and 23%-54%, respectively. Notably, the sonicated microalgae effluents were able to improve the node growth by 123%. To our knowledge, this is the first study revealing the significant biofertilization potential of C. vulgaris CFS for shoot growth of tea plants. The obtained results highlight the agricultural potentials of both microalgae culture broths and degreased microalgae wastes as sustainable and environmentally-friendly biofertilizers for Camellia sinensis organic farming. [ABSTRACT FROM AUTHOR]

Aerial microalgae are resistant to nutrient and drought stresses and can survive even in harsh environments lacking water and nutrients. In this study, the adaptation mechanisms of microalgae to water stress by culturing aerial microalgae in a water-deprived environment were elucidated, and their biomass and lipid productivity were evaluated. Biofilms of the aerial microalga Coccomyxa subellipsoidea KGU-D001 (C. subellipsoidea) or the freshwater microalga Chlorella vulgaris (Chl. vulgaris) growing on silicon sheets were cultured under the same water stress conditions. C. subellipsoidea could maintain its photosynthetic activity at least for 14 days, while Chl. vulgaris drastically decreased its photosynthetic activity during the first 7 days. The cell wall carbohydrate content of C. subellipsoidea increased during the first 7 days more than Chl. vulgaris. The fatty acids content in C. subellipsoidea increased 3.0-fold during the first 7 days and 1.7-fold from day 7 to day 14 of culture. In Chl. vulgaris, the fatty acid content increased by 2.2 times during the first 7 days and then remained constant from days 7 to 14 of culture. Fatty acid productivities were 17.3 and 14.2 mg/g/d in C. subellipsoidea and Chl. vulgaris, respectively. These findings suggest that the rapid formation of a thicker cell wall contributes to cellular acclimation to water stress conditions and the accumulation of lipids in C. subellipsoidea. [ABSTRACT FROM AUTHOR]

Microalgae have been reported to be excellent producers of bioactive molecules. Lutein is a pigment reported to have various beneficial effects for humans, and especially for eye well-being. In the current review, we summarize various methods that have been developed to optimize its extraction and bioactivities reported for human health. Several protective effects have been reported for lutein, including antioxidant, anticancer, anti-inflammatory, and cardioprotective activity. This review also reports attempts to increase lutein production by microalgae by changing culturing parameters or by using pilot-scale systems. Genetic engineering lutein production is also discussed. Considering the increasing aging of the worldwide population will create an increased need for lutein, a viable economic and eco-sustainable method to produce lutein is needed to face this market demand. [ABSTRACT FROM AUTHOR]

This work is focused on investigating the nutrient compositions, growth, and fatty acid composition of Chlorella vulgaris, Euglena gracilis, Pavlova lutheri, and Diacronema vlkanium, which are natural diets of bivalve, crustaceans, live prey such as rotifer, copepods, daphnia and feed ingredients in aquaculture nutrition. Microalgae culture was performed in a live feed laboratory under controlled physical and chemical conditions. The initial concentration of microalgae species was adjusted as 2×106 cells/mL and growth performance was calculated by Neubauer Hemocytometer daily. The maximum growth performance was detected in Diacronema vlkanium culture with 1.78×107 cells/mL. In the case of proximate composition, the highest dry matter content was found in Pavlova lutheri (6.21%). Freshwater microalgae species Chlorella vulgaris (50.5%) and Euglena gracilis (42.5%) had high crude protein compared to Pavlova lutheri and Diacronema vlkanium. Fatty acid compositions of microalgae were also determined. The highest EPA (C20:5n-3) content was found in Pavlova lutheri (6.85%) whereas arachidonic acid (C20:4n-6) and docosahexaenoic acid (C22:6n-3) contents were only found with a level of (3.32%) and (1.79%) in Euglena gracilis, respectively. Microalgal culture should have high biomass in a short time of culture and in this study, E.gracilis and P.lutheri showed high growth and essential nutrients gain in laboratory scale production and this result could be applied in larger volume photobioreactor. [ABSTRACT FROM AUTHOR]

The microalga Haematococcus lacustris has a complex life cycle and a slow growth rate, hampering its mass cultivation. Culture of microalgae with organic carbon sources can increase the growth rate. Few studies have evaluated the effects of organic carbon sources on H. lacustris. We compared the vegetative and inductive stages of H. lacustris under autotrophic and mixotrophic conditions using four organic carbon sources: sodium acetate, glycerol, sodium gluconate, and ribose, each at various concentrations (0.325, 0.65, 1.3, and 2.6 g/L). The cell density was increased by 1.3 g/L of glycerol in the vegetative stage. The rapid transition to the inductive stage under nitrogen-depletion conditions caused by 1.3 or 2.6 g/L sodium acetate promoted the accumulation of astaxanthin. The production of astaxanthin by H. lacustris in mass culture using organic carbon sources could increase profitability. [ABSTRACT FROM AUTHOR]

Mixing of the algal culture medium in a photobioreactor (PBR) is a crucial factor to enhance microalgae cultivation and production, since it ensures microalgae cells can homogeneously access nutrients and light radiation. Hydrodynamic conditions in an industrially applicable PBR cannot be tested in laboratory cultivation systems since the scale-up methodology is not specified; hence requiring complex tests at a demonstrative scale or the application of mathematical models. In this study, a three-dimensional numerical model of the hydrodynamic conditions in a hybrid horizontal tubular PBR was developed to investigate the mixing of the culture medium under various operating conditions, in order to optimize biomass production in this type of system. The PBR consists of two open tanks connected through sixteen polyethylene transparent tubes, at a demonstrative scale (total volume 11.7 m3). Microalgae cells movement inside the tubes was simulated. Cell trajectory prediction allows to simulate the intensity of mixing of the culture medium. Subsequent coupling with the biokinetic BIO_ALGAE model allows to monitor the influence of hydrodynamic conditions on the distribution of light in the culture medium and the yield of microalgae. The simulations were experimentally validated. The more intense mixing of the culture medium caused by increasing flow rate (Re = 23,700–46,200) allows more frequent exposure of the microalgae cells to the light source, which according to the results obtained can increase the microalgal yield by 14% in the summer cultivation period and by 151% in the winter period. [Display omitted] [ABSTRACT FROM AUTHOR]

This study examined the potential for green microalgae to produce lipid that could be used for biodiesel production from wastewater substrate. Green microalgae has the potential to be used in the production of biodiesel because it accumulates 5.3211 g of lipid in 39.2246 g of centrifuged and oven-dried algae biomass, accounting for 13.57% of its dry cellular weight. This was obtained with wastewater substrate under open-culture growth conditions. The wastewater substrate contained phosphate, nitrate, nitrite, ammonia, and sulfate at relatively optimal concentrations for culturing algae. The algae assimilated 95% of these nutrients on average for growth until the stationary phase was reached in 13 days. The most rapid cell doubling time observed was 192 h, and the maximum biomass production rate observed was 0.00057 mg/mg/day, reaching a peak algae weight fraction of 0.00926 mg/mg in 13 days. This study also examined and presented the scale-up of growing green microalgae in an open raceway culture system for obtaining maximum lipid yield from a wastewater substrate. The cost-benefit analysis of designing and building such a system was also presented in this study. The open raceway system described and modeled in this study measured 8 m * 3 m * 0.6 m and had a capacity of 10,000 liters, yielding 0.45 kg of biocrude lipid for each cycle of green microalgae culture harvested. [ABSTRACT FROM AUTHOR]

In this study, Dunaliella salina and Porphyridium cruentum biomass were encapsulated by using a spray-dryer (SD) and combined D-optimal method. The independent variables were SD inlet temperature (170–190 °C), maltodextrin (25–75%, w/w, in dm), and microalgae biomass (25–75%, w/w, in dm). Prior to spray drying, P. cruentum and D. salina were cultivated in a pilot scale tubular photobioreactor and than harvested using a conical plate centrifuge. Significant models were determined for the effects of independent variables on total carotenoids, chlorophyll-a, crude protein, moisture contents and encapsulation yield (EY), water activity, average particle size, wettability, hygroscopicity, L* and C* properties for both microalgae species (p <.05). Due to the low EY (11.1–33.1%), we recommend encapsulation and drying of P. cruentum biomass with alternative methods to SD. The extracellular, as well as the cell wall and storage polysaccharides released into the culture medium of these microalgae are possible reasons for the low EY. [ABSTRACT FROM AUTHOR]

In this work, a model for the characterization of microalgae cultures based on artificial neural networks has been developed. The characterization of microalgae cultures is essential to guarantee the quality of the biomass, and the objective of this work is to achieve a simple and fast method to address this issue. Data acquisition was performed using FlowCam , a device capable of capturing images of the cells detected in a culture sample, which are used as inputs by the model. The model can distinguish between 6 different genera of microalgae, having been trained with several species of each genus. It was further complemented with a classification threshold to discard unwanted objects while improving the overall accuracy of the model. The model achieved an accuracy of up to 97.27% when classifying a culture. The results demonstrate the effectiveness of the Deep Learning models for the characterization of microalgae cultures, it being a useful tool for the monitoring of microalgae cultures in large-scale production facilities while providing accurate characterization over a wide range of genera. [Display omitted] • Classification of six microalgae genera based on artificial neural networks. • Models trained with several species from each genus. • Models based on cell images enhanced with classification thresholds. [ABSTRACT FROM AUTHOR]

The potentiality of microalgae–bacteria consortia applied in a circular economy is acknowledged and explored; however, the commercialization of biofuel from microbial technology remains complex and controversial regarding the practicability of the technology. This review provides a concise and comprehensive analysis of various extraction techniques of the microalgae-bacteria consortium, algae cultivation methods, and biofuel production processes. The conversion processes are critically reviewed along with the challenges faced to lay the foundation of in-depth microalgae–bacteria biotechnology. The yield of biohydrogen produced and the lipid content of the obtained biomass can be greatly improved through the cultivation of a microalgae–bacteria consortium compared to the pure culture of microalgae. The consumption of nutrients in wastewater by the microalgae–bacteria consortium protects the environment as the effluent returned to nature is of minimum toxicity. The symbiotic relationship between microalgae and bacteria has enhanced the lipid productivity of biomass in previous studies. In contrast to other recent reviews, the linkage of the circular economy with the microalgae–bacteria consortium was critically reviewed and discussed. Uncertainties under culturing conditions and techno-economics are the concerns and factors that impede the development of microalgae–bacteria consortia in energy commercialization. [ABSTRACT FROM AUTHOR]

Microalgae are excellent sources of biomass containing several important compounds for human and animal nutrition—proteins, lipids, polysaccharides, pigments and antioxidants as well as bioactive secondary metabolites. In addition, they have a great biotechnological potential for nutraceuticals, and pharmaceuticals as well as for CO2 sequestration, wastewater treatment, and potentially also biofuel and biopolymer production. In this review, the industrial production of the most frequently used microalgae genera—Arthrospira, Chlorella, Dunaliella, Haematococcus, Nannochloropsis, Phaeodactylum, Porphyridium and several other species is discussed as concerns the applicability of the most widely used large-scale systems, solar bioreactors (SBRs)—open ponds, raceways, cascades, sleeves, columns, flat panels, tubular systems and others. Microalgae culturing is a complex process in which bioreactor operating parameters and physiological variables closely interact. The requirements of the biological system—microalgae culture are crucial to select the suitable type of SBR. When designing a cultivation process, the phototrophic production of microalgae biomass, it is necessary to employ SBRs that are adequately designed, built and operated to satisfy the physiological requirements of the selected microalgae species, considering also local climate. Moreover, scaling up microalgae cultures for commercial production requires qualified staff working out a suitable cultivation regime. Key points: • Large-scale solar bioreactors designed for microalgae culturing. • Most frequently used microalgae genera for commercial production. • Scale-up requires suitable cultivation conditions and well-elaborated protocols. [ABSTRACT FROM AUTHOR]

Automation of the lighting system for phototrophiccultures in photobioreactors is a process of automation and control of lighting inside. Photosynthetic microorganisms, in order to develop and grow, require a species-specific type of visible light radiation. The automation of the lighting system was based on the industrial PLC Modicon TM221C24T controller according to the submitted and received patent No. 242154. The system was integrated with a quantum sensor, which allows for setting the colour of light and controlling the intensity and exposure time based on protocols set by the operator. The data obtained from the PAR photosynthetically active radiation sensor make it possible to adjust the distribution of light to the actual needs of the culture's radiant energy. The unit also allows for remote control of multiculture farms. It allows you to simulate sunrise and sunset using the astronomical clock function set for a given species of microalgae. Ultimately, the work was undertaken on the implementation and use of a system for measuring the light spectrum at each point of the bioreactor using a fibre-optic immersion probe. [ABSTRACT FROM AUTHOR]

The use of microalgae in biotechnological studies is increasing day by day because of their ability to produce and store secondary metabolites under extreme conditions. When the culture conditions such as light, nutrients, pH, and temperature are modified, the synthesis and storage amount of these secondary metabolites change. In this study, the effects of different nitrogen and phosphorus concentrations on the morphological changes, growth, biochemical composition, total phenolic content, and antioxidant activity of Desmodesmus multivariabilis were investigated. The study results show that changing of the nitrogen and phosphorus concentration in the microalgae culture medium is an effective strategy for changing growth, biochemical composition, total phenolic content, and antioxidant activity parameters of microalgae. All culture conditions should be detected, depending on the substance desired to be obtained from microalga and its biotechnological application. Therefore, this study is substantial as it is the first study on this concept with D. multivariabilis, and for obtaining economically important bioactive compounds of this species, this paper will play a key role. [ABSTRACT FROM AUTHOR]

Sloshing is the movement of fluid in a partially filled vessel subjected to external motions. Although sloshing causes intense forces and instability to floating structures, the internal motion of liquid caused by external forces might be useful for devices that require mixing. For offshore floating photobioreactors, sloshing induced by external ocean wave forces are desirable, as the movement of liquid is able to bring about mixing and mass transfer for the nutrients and gas in the microalgae culture. The objective of this study is to investigate the correlation between the regular wave-induced sloshing of different motions (surge, heave, and pitch) on the mixing behaviour of the novel offshore floating photobioreactor designed to utilize the ocean surface waves for the effects of mixing. To determine the residence time distribution (RTD) of the stagnant volume of the photobioreactor, dissolved solids were injected into the system. The concentration of dissolved solids was measured using a total dissolve solid (TDS) sensor. The mixing caused by sloshing motion had the highest intensity during pitching motion. A homogenous solution was formed just after 65.9 s for the filling ratio of 30 %, with the rotation angle of 8 degrees and frequency of 0.21 Hz. Thus, wave-induced sloshing is able to generate intense mixing to the medium during pitching motion but still has non-ideal behaviours, such as bypass and dead zones during horizontal and vertical motion. [Display omitted] • Proposed novel floating photobioreactor to utilize the ocean surface waves for mixing. • Study on effects of surge, heave, and pitch on the mixing behavior of floating photobioreactor. • Mixing induced by sloshing is maximum with pitching motion. [ABSTRACT FROM AUTHOR]

Microalgae remove nitrogen and phosphorus from water for their growth and biomass production, wich has several biotechnological applications. This study evaluated the growth, NO3 −, NO2 −, NH4+, urea, PO43− and total nitrogen removal capacity, as well as the biomass production and the CO2 fixation of two new microalgae isolates, Chlorella sp. and Quadrigula sp., from the coast of Chiapas, México. Chlorella sp. had a higher specific growth rate (0.74/day) and a shorter doubling time (0.92 days) than Quadrigula sp. Removal per unit volume (mg/L) of NO3−, NH4+ and total nitrogen by Chlorella sp. was higher (26.88%, 10.58% and 16.63%, respectively) than removal by Quadrigula sp. On the other hand, daily removal (mg/L/d) of NO3−; NH4+; NO2−; urea and total nitrogen by Chlorella sp. was also higher (88%, 33%, 89%,15% and 50%, respectively) than daily removal by Quadrigula sp. The biomass productivity (mg/L/d) and the CO2 fixation rate (mg/L/d) were similar among both microalgae. The results of this study suggest that Chlorella sp. and Quadrigula sp. have potential for nutrient removal, biomass production and CO2 fixation. [ABSTRACT FROM AUTHOR]

In airlift systems, the difference in gas holdup (εg) between the riser and the downcomer creates the driving force for liquid circulation. This feature can be an interesting approach to using an airlift pump instead of the conventional paddlewheels for simultaneous mixing between phases and supply of air to microalgae in the biomass culture ponds. Before any biomass cultivation, the hydrodynamic behavior of the system must be recognized. Therefore, cold model hydrodynamic characteristics in the air–water system of a novel oval airlift open pond (AOP) are presented by studying gas holdup and riser liquid velocity (Ulr) at different ratios of baffle clearances from the top and bottom (ht/hb) in the AOP. The gas holdup is one of the key parameters to describe the performance of airlift systems, so the effect of riser superficial gas velocity (Ugr), riser liquid velocity, and ht/hb ratios on gas holdup are investigated in this research. The results of this study indicate that superficial gas velocity, riser liquid velocity, and ht/hb ratio have a pronounced effect on the gas holdup. Moreover, due to the lack of gas holdup correlations in the AOP system, new empirical correlations have been developed to predict total gas holdup, riser gas holdup (εgr), and downcomer gas holdup (εgd) with satisfactory accuracy. [ABSTRACT FROM AUTHOR]

Microalgae-based carbon sequestration is emerging as a green and sustainable way to achieve negative carbon while recycling CO2 into biomass used for the production of bioenergy and value-added products. However, its successful implementation is still to be realized due to the low solubility of CO2 and ion accumulation with the addition of bicarbonate in the culture medium. In this study, we proposed, developed and verified a novel system integrating electrolysis and ionic membranes (EIMs) that enables the artificial recycling of CO2 utilization and alleviation of metal cation stress in microalgae cultivation. HCO3− was selected to transfer from the cathode chamber to the culture pond with sodium bicarbonate as the catholyte, while Na+ cations were blocked with the anionic membrane in EIMs, accompanied by a gradually decreasing pH value, which facilitates microalgae growth. The reliability and universality of EIMs was further verified with both a cation-tolerant marine strain, Dunaliella salina HTBS, and cation-sensitive freshwater strains, Chlamydomonas and Chlorella. In particular, the cell densities of cation-sensitive strains in EIMs were much higher than those in the NaHCO3 group in both 800 mL- and 150 L-scale applications, demonstrating their great potential. Moreover, the intracellular metabolites were not affected when microalgae were cultured in EIMs, implying their feasibility for commercial cultivation. Therefore, we established robust EIMs that facilitate both the efficient utilization of CO2 and commercial application, which will shed light on the development of green technology for microalgae-based carbon sequestration in the future. [ABSTRACT FROM AUTHOR]

Co-cultivation and effective downstream processing of microalgae and oleaginous yeast are potential strategies to enhance lipid yield. The findings of this work suggest that each cultivable partner should be screened and optimized for the best mutualistic co-cultures. In this case, T. pullulans was found to be the most effective yeast culture with microalgae S. obliquus, C. sorokiniana, and C. protothecoides along with additional cell disruption techniques. Co-cultures of C.protothecoides and T.pullulans had the highest relative lipid yield (RLY) of 68.71%, 59.32%, 55.33%, 53.19%, and 47.3% with sonication, microwave, osmotic shock, freeze-drying, and autoclave, respectively. Sonication was concluded as the best disruption technique with five out of nine co-cultures showing significant lipid enhancement. Even though T. pullulans was the best yeast partner with disruption techniques, co-culture of Y. lipolytica and S.obliquus (RLY 37.11%) produced lipids which was significantly higher than that of their respective monocultures (S. obliquus RLY 23.96%, Y. lipolytica RLY 4.96%) without any disruption process. R. glutinis and Y. lipolytica produced significantly enhanced lipid yield with C.sorokiniana and S. obliquus with sonication (RLY 51.44%) and osmotic shock (RLY 57.70%), respectively. FAME analysis reported that the co-cultures produced higher percentage of total FAME nearly 100% in the case of C. sorokiniana and R. glutinis with high content of saturated fatty acids (SFAs). The presence of biofuel precursors like palmitic acid, linoleic acid, oleic acid, and heptadecanoic acid, confirms their suitability for biofuel production. [ABSTRACT FROM AUTHOR]

Biochemical profile of five marine microalgae Isochrysis galbana, Chaetoceros calcitrans, Tetraselmis suecica, Nannochloropsis oculata and Aphanocapsa sp. was studied to understand the changes of the biochemical profile under different culture conditions, i.e. Conway and f/2 media at 20 and 30ppt salinities (‰). The microalgae culture was undertaken in the indoor facility with 24±1° C temperature, PH 8.7±1, 24-hour illumination. Biochemical constituents of five algal species showed variations, the highest protein (26.86%) was recorded in C. calcitrans in f/2 medium at 30‰, lipid (32.00%) in N. oculata in Conway medium at 30‰, carbohydrate (32.06%) in T. suecica in Conway medium at 30‰ and ash (54.71%) in C. calcitrans in f/2 medium at 30‰. Among macro minerals, a high concentration of sodium (1.05g/100g) was recorded in C. calcitrans in Conway medium-20‰, potassium (4.12g/100g) in C. calcitrans in f/2 medium-30‰, calcium (1.57g/100g) in C. calcitrans in Conway medium-20‰, phosphorus (8.53g/100g) in C. calcitrans in Conway medium-20‰, magnesium (4.10g/100g) in N. oculata in f/2 medium-20‰. Among micro minerals, a high concentration of iron (1.44g/100g) was recorded in C. calcitrans in f/2 medium-30‰, zinc(0.95g/100g) in I. galbana in Conway medium20‰, manganese(0.02g/100g) in N. oculata in Conway medium-30‰, copper(0.04g/100g) in Aphanocapsa sp. in Conway medium-30‰. Among fatty acids, C16:0 become the dominant saturated fatty acid (SFA) found in I. galbana, C16:1 become the dominant monounsaturated fatty acid (MUFA) found in N. oculate and C18:2 become the dominant polyunsaturated fatty acid (PUFA) found in I. galbana cultured in Conway medium-20‰. The biochemical composition of five microalgae indicated that these are potential food sources for humans, cattle and aquaculture industries. [ABSTRACT FROM AUTHOR]

Microalgae play an important economic role as aquaculture feed. This study aimed to create an automated algae cultivation system with variable light intensity for the culture of Chlorella ellipsoidea strain TISTR 8260. The automated cabinet could work continuously for at least 30 days, with the growth rates of microalgae in culture systems with light intensities of 1000 Lux, 3000 Lux, and 5000 Lux peaking on day 14, whereas the fluorescent control showed peak microalgae growth on day 6. On day 30, the biomass harvested from microalgae grown in 1000 Lux, 3000 Lux, 5000 Lux, and fluorescent control was 0.1935 ± 0.151 mg/L, 0.1996 ± 0.220 mg/L, 0.2041 ± 0.159 mg/L, and 0.0674 ± 0.191 mg/L, respectively, which was not significantly different between the groups but significantly higher than the control (P-value = 0.05, DF = 3, F(3,36) = 7). The automated algae cabinet with a light intensity of 5000 Lux and a rotation speed of 150 r.p.m produced the maximum biomass, which was three times that produced by a fluorescent light source. [ABSTRACT FROM AUTHOR]

Simple Summary: Overusing synthetic pesticides has resulted in environmental problems and human health risks while contributing to pesticide-resistant pests. Microalgae, being natural producers of highly diverse bioactive compounds, represent a promising alternative to replace synthetic pesticides as a more environmentally friendly and safe alternative. In this study, we screened biomass extracts from 10 green microalgae from the Chlorophyta phylum to identify molecules with potential pesticide activities. All tested strains exhibited herbicidal, nematocidal, or algicidal activities. Metabolomics analysis of six strains showed the presence of fatty acids, isoquinoline alkaloids, and aldehydes, which may be responsible for the observed pesticide activities. Our study highlights the algicidal, herbicidal, and nematocidal activities of biomass extracts derived from green microalgae and the metabolites and metabolic pathways potentially involved in producing the bioactive molecules. Our study supports the potential of microalgae for developing more effective and eco-friendlier biopesticides for sustainable agriculture. The excessive use of synthetic pesticides has caused environmental problems and human health risks and increased the development of resistance in several organisms. Allelochemicals, secondary metabolites produced as part of the defense mechanisms in plants and microorganisms, are an attractive alternative to replace synthetic pesticides to remediate these problems. Microalgae are natural producers of a wide range of allelochemicals. Thus, they provide new opportunities to identify secondary metabolites with pesticide activities and an alternative approach to discover new modes of action and circumvent resistance. We screened 10 green microalgae strains belonging to the Chlorophyta phylum for their potential to inhibit the growth of photosynthetic and nonphotosynthetic organisms. Bioassays were established to assess microalgae extracts' effectiveness in controlling the growth of Chlorella sorokiniana, Arabidopsis thaliana, Amaranthus palmeri, and the model nematode Caenorhabditis elegans. All tested strains exhibited herbicidal, nematocidal, or algicidal activities. Importantly, methanol extracts of a Chlamydomonas strain effectively controlled the germination and growth of a glyphosate-resistant A. palmeri biotype. Likewise, some microalgae extracts effectively killed C. elegans L1 larvae. Comprehensive metabolic profiling using LC-MS of extracts with pesticide activities showed that the metabolite composition of Chlamydomonas, Chlorella, and Chloroidium extracts is diverse. Molecules such as fatty acids, isoquinoline alkaloids, aldehydes, and cinnamic acids were more abundant, suggesting their participation in the pesticide activities. [ABSTRACT FROM AUTHOR]

Microalgae are a promising source of renewable fuels and value‐added chemicals but are hampered by the high cost of cultivation. Sparging CO2 in water bodies can increase the yield and reduce the cost. This work studies the feasibility of synergistically integrating a biogas digester with a microalgae cultivation system. Raw biogas is sparged through the microalgal culture to increase the microalgae yield while also purifying biogas for further use. At laboratory scale, Chlorella vulgaris was cultivated in a 1‐L batch, and biogas was sparged for 3 h per day. For a demonstration‐scale 4000‐L raceway pond, a special contacting device was used to supply biogas to the microalgal culture. On the laboratory scale, C. vulgaris concentration increased by 30 % when sparged with biogas. Moreover, the protein and lipid contents were higher than in an air‐sparged control batch. The cultivation cost of microalgae decreased by 20 %. [ABSTRACT FROM AUTHOR]

The influence of confinement and rheological properties of the liquid phase on the gas holdup and flow regimes in a 2 mm gap bubble column intended as an intensified photobioreactor at high cell concentration is investigated. The results indicate that at a given superficial gas velocity (UGsup), the gas holdup is higher with viscous or non‐Newtonian (nN) fluids than in water and also in a thin‐gap column than in an unconfined one. This behavior increases when confinement ratio increases. Regime transitions occur at lower UGsup for nN fluids compared to water and for a thin‐gap column compared to classical columns. This information constitutes a first step toward the identification of optimal operating conditions for efficient operation of microalgae culture. [ABSTRACT FROM AUTHOR]

Microalgae culture is an interesting step in wastewater treatment since it provides a tertiary biotreatment while also producing potentially valuable biomass that may be used for a variety of applications. Microalgae cultures, with their ability to utilize inorganic nitrogen and phosphate for growth, provide an elegant solution to tertiary and quaternary treatments. Scenedesmus quadricauda culture was employed with three different doses, 2g/l, 1g/l, and 0.2g/l, to investigate the impacts of microalgae in wastewater. Standard procedures were used to measure samples for physicochemical parameters such as pH, EC, PO4, NO3, NO2, NH4 and BOD5 every third day for 21 days. Results showed that a higher dose of 2g.l-1 was the most effective for removing the highest rate of nutrients. It was confirmed by significant differences (p≤0.05) between all doses. Ammonium pass had the highest removal percentage of 97%, followed by NO3 with 95.7%, and BOD5 with a range of 90.3 to 93.5 %. Decreases in nutrients were accompanied by a rise in chlorophyll content, with the greatest biomass of 1.52 mg. l-1 on the 17th day of the experiment. The purpose of this paper is to provide an overview of the methods that microalgae use to bioremediate organic contaminants in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Microalgae-mediated industrial flue gas biofixation has been widely discussed as a clean alternative for greenhouse gas mitigation. Through photosynthetic processes, microalgae can fix carbon dioxide (CO 2) and other compounds and can also be exploited to obtain high value-added products in a circular economy. One of the major limitations of this bioprocess is the high concentrations of CO 2 , sulfur oxides (SOx), and nitrogen oxides (NOx) in flue gases, according to the origin of the fuel, that can inhibit photosynthesis and reduce the process efficiency. To overcome these limitations, researchers have recently developed new technologies and enhanced process configurations, thereby increased productivity and CO 2 removal rates. Overall, CO 2 biofixation rates from flue gases by microalgae ranged from 72 mg L−1 d −1 to over 435 mg L−1 d−1, which were directly influenced by different factors, mainly the microalgae species and photobioreactor. Additionally, mixotrophic culture have shown potential in improving microalgae productivity. Progress in developing new reactor configurations, with pilot-scale implementations was observed, resulting in an increase in patents related to the subject and in the implementation of companies using combustion gases in microalgae culture. Advancements in microalgae-based green technologies for environmental impact mitigation have led to more efficient biotechnological processes and opened large-scale possibilities. [Display omitted] • Microalgae exhibits potential for flue gas biofixation with byproducts recovery. • Flue gas can increase microalgal biomass yield on a larger scale. • Hybrid systems have been explored to improve process performance. • Reactors connnected in series promise efficient flue gas CO 2 biofixation. • Obtaining multiple products from microalgae reduces risks and increase profit margin. [ABSTRACT FROM AUTHOR]

The increasing global population has led to a significant accumulation of food waste. It is important to focus on reducing food waste instead of disposal methods like landfilling and incineration, which have severe environmental impacts. Upcycling food waste has emerged as an effective strategy for repurposing discarded food into higher-value products. However, concerns about food safety and public acceptance of products directly produced from food waste persist. Consequently, there is growing interest in utilizing food waste rich in moisture and biodegradable organic compounds as a potential medium for cultivating microalgae. This review article examines the utilization of food waste as a culture medium for microalgae cultivation and the methods for treating food waste to enhance its nutrient content. Additionally, it discusses the influence of nutrients such as carbon, nitrogen, and phosphorus on microalgae growth and external factors such as pH and light intensity. The article also addresses the innovation of the food supply chain from environmental, social, and economic perspective, along with food safety and public acceptability concerns. Furthermore, it explores the legislative issues surrounding products derived from food waste and the end use of microalgae biomass produced from food waste. Overall, this review provides insight into the potential of microalgae cultivation using food waste, serving as a platform towards the realization of a circular bioeconomy. [ABSTRACT FROM AUTHOR]

Shrimp production facilities produce large quantities of wastewater, which consists of organic and inorganic pollutants. High concentrations of these pollutants in shrimp wastewater cause serious environmental problems and, therefore, a method of treating this wastewater is an important research topic. This study investigated the impact of algae and indigenous bacteria on treating shrimp wastewater. A total of four different microalgae cultures, including Chlorococcum minutus, Porphyridum cruentum, Chlorella vulgaris and Chlorella reinhardtii along with two cyanobacterial cultures, Microcystis aeruginosa and Fishcherella muscicola were used with indigenous bacterial cultures to treat shrimp wastewater. The highest soluble chemical oxygen demand (sCOD) removal rate (95%) was observed in the samples that were incubated using F. muscicola. Total dissolved nitrogen was degraded >90% in the C. vulgaris, M. aeruginosa, and C. reinhardtii seeded samples. Dissolved organic nitrogen removal was significantly higher for C. vulgaris (93%) as compared to other treatments. Similarly, phosphate degradation was very successful for all the algae-bacteria consortium (>99%). Moreover, the degradation kinetics were calculated, and the lowest half-life (t 1/2) for sCOD (5 days) was recorded for the samples seeded with M. aeruginosa. Similarly, treatment with F. muscicola and C. reinhardtii showed the lowest t 1/2 of NH 3 –N (2.9 days) and phosphate (2.7 days) values. Overall, the results from this study suggest that the symbiotic relationship between indigenous bacteria and algae significantly enhanced the process of shrimp wastewater treatment within 21 days of incubation. The outcome of this study supports resource recovery in the aquaculture sector and could be beneficial to treat a large-scale shrimp facility's wastewater worldwide. [Display omitted] • Shrimp wastewater contains high levels of nitrogen and phosphate. • Algae-bacteria consortium is a feasible solution for a sustainable environment. • TDN and DON decreased (>90%) in the presence of algae-bacteria consortium. • Symbiotic relationship between algae and bacteria increased treatment performance. • Nutrients in wastewater are converted to biomass during the treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microalgae have great potential to capture CO 2 and produce high-value bioproducts. • The photosynthetic efficiency of microalgae is difficult to be greatly improved. • The concept and application of artificial photosynthesis were summarized. • Acetate produced by artificial photosynthesis is ideal organic source for algae. • Artificial photosynthesis combined with heterotrophic algae has bright prospects. Recently, microalgae had received extensive attention for carbon capture and utilization. But its overall efficiency still could not reach a satisfactory degree. Artificial photosynthesis showed better efficiency in the conversion of carbon dioxide. However, artificial photosynthesis could generally only produce C1-C3 organic matters at present. Some studies showed that heterotrophic microalgae can efficiently synthesize high value organic matters by using simple organic matter such as acetate. Therefore, the combination of artificial photosynthesis with heterotrophic microalgae culture showed great potential for efficient carbon capture and high-value organic matter production. This article systematically analyzed the characteristics and challenges of carbon dioxide conversion by microalgae and artificial photosynthesis. On this basis, the coupling mode and development trend of artificial photosynthesis combined with microalgae culture were discussed. In summary, the combination of artificial photosynthesis and microalgae culture has great potential in the field of carbon capture and utilization, and deserves further study. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Chlorella sp. CN6 with high macular pigment (MP) production was isolated. • A four-stage continuous microalgal culture module was established for MP production. • MP concentration of CN6 through white light and blue LED irradiation was 8.16 g/L. • MP productivity in the continuous culture module was 7.28 mg/L/day for 10 days. • The MP recovery and purity were > 80 % and > 90 %, with a lutein: zeaxanthin of 4–5:1. This study established and investigated continuous macular pigment (MP) production with a lutein (L):zeaxanthin (Z) ratio of 4–5:1 by an MP-rich Chlorella sp. CN6 mutant strain in a continuous microalgal culture module. Chlorella sp. CN6 was cultured in a four-stage module for 10 days. The microalgal culture volume increased to 200 L in the first stage (6 days). Biomass productivity increased to 0.931 g/L/day with continuous indoor white light irradiation during the second stage (3 days). MP content effectively increased to 8.29 mg/g upon continuous, indoor white light and blue light-emitting diode irradiation in the third stage (1 day), and the microalgal biomass and MP concentrations were 8.88 g/L and 73.6 mg/L in the fourth stage, respectively. Using a two-step MP extraction process, 80 % of the MP was recovered with a high purity of 93 %, and its L:Z ratio was 4–5:1. [ABSTRACT FROM AUTHOR]

[Display omitted] • A modelling visualised flow field changes in a photobioreactor was established. • Utilised 24 baffles to enhance hydrodynamic effects on an increase in cell numbers. • Achieved high growth rates for C.vulgaris in PBRM at airflow rates of 45−50L/h. • Observed composition variations in cells with CO 2 concentrations ranging from 5−20% • Introduced newly proposed PBRM featuring ordered vortex pairs that benefit cultures. Microalgae play a crucial role as bioresources, yet the culture systems of photobioreactors (PBR) encounter challenges. Many engineered PBRs tend to incorporate internals build-ups, serving photoautotroph production, and requiring substantial microalgal biomass. This study quantified the baffle effects on airlift flat plate PBRs based on the performance of Chlorella vulgaris. The impacts of baffle configurations, air velocity, and CO 2 contents, three dominant parameters, on microalgae culture were investigated using culture experiments, numerical simulations, and flow visualisation techniques. The results demonstrate that multiple baffle design strategies enhance microalgae growth and production. On the 11th cultivation day, airflow rates of 6, 45, or 90 L/h produced 1.5, 3.0, or 1.9 times the biomass weight and 1.76 × 107 cell numbers/mL in PBR M with 24 baffles, compared to 1.44 × 107 cell numbers/mL in PBR C without baffles. Furthermore, it revealed an intensification in the generation potential of biocomponents with C–H, C = O, and C–O–C functional groups at a 45−50 L/h airflow rate and CO 2 (20 %) aerated PBR M. Additionally, it presented the first visualisation explanation of the baffle-guided vortex flow pair symmetry PBR M. This study demonstrated enhancements by modelling newly proposed PBRs with baffles and high-valued bioproducts harvesting through the combination of culture parameters. [ABSTRACT FROM AUTHOR]

• Culturing microalgae by fermentation liquid with additional inorganic carbon sources. • Acetic acid was proved to be a more advantageous carbon source than glucose. • The highest lipid yield 1228.62 mg/L was obtained at OC/IC = 3:1 with acetic acid. • The highest polyunsaturated fatty acids content (74.6%) was obtained without NaHCO 3. • Inorganic carbon sources increased microalgal cell sizes and reduced cell mortality. The cultivation of microalgae using acidogenic fermentation liquid shows great potential due to the ample presence of volatile fatty acids (VFAs) as organic carbon (OC) sources. However, the availability of inorganic carbon (IC) sources in the fermentation liquid might be insufficient to support microalgal photosynthesis, thereby limiting the application of this approach. This study aimed to address this limitation by introducing NaHCO 3 as additional inorganic carbon sources into the fermentation liquid. The effects of different VFAs and organic carbon to inorganic carbon ratios (OC/IC) on the growth kinetics, biochemical composition synthesis, and physiological characteristics of microalgae were investigated. Results showed that C. pyrenoidosa cultivated in acetic acid with an OC:IC ratio of 3:1 exhibited the highest values for the specific growth rate (0.245 d−1) and maximum biomass productivity (0.254 g·L−1·d−1). Furthermore, acetic acid was more beneficial than other VFAs in promoting microalgal photosynthesis and contributing to lipid accumulation. The highest lipid content of C. pyrenoidosa (39.9 %) was obtained with acetic acid at the OC/IC ratio of 3:1, and the highest percentage of polyunsaturated fatty acids (74.6 %) was obtained with acetic acid in the 100 % OC group. The flow cytometry results indicated that at OC/IC ratio of 3:1, the proportion of normal cells in different organic acids groups higher than other OC/IC ratios. Acetic acid was beneficial for maintaining normal cell morphology, and IC sources could increase microalgal cell sizes and reduce cell mortality. This study deepens the understanding of microalgae cultivation using fermentation liquid and provides theoretical insights for the application of this approach. [ABSTRACT FROM AUTHOR]

Microalgae demonstrate significant potential as a source of liquid-based biofuels. However, increasing biomass productivity in existing cultivation systems is a critical prerequisite for their successful integration into large-scale operations. Thus, the current work aimed to accelerate the growth of C. vulgaris via exogenous supplementation of biostimulant derived from onion peel waste. Under the optimal growth conditions, which entailed a biostimulant dosage of 37.5% v/v, a pH of 3, an air flow rate of 0.4 L/min, and a 2% v/v inoculum harvested during the mid-log phase, yielded a maximum biomass concentration of 1.865 g/L. Under the arbitrarily optimized parameters, a comparable growth pattern was evident in the upscaled cultivation of C. vulgaris , underscoring the potential commercial viability of the biostimulant. The biostimulant, characterized through gas chromatography-mass spectrometry (GC-MS) analysis, revealed a composition rich in polyphenolic and organo-sulphur compounds, notably including allyl trisulfide (28.13%), methyl allyl trisulfide (23.04%), and allyl disulfide (20.78%), showcasing potent antioxidant properties. Additionally, microalgae treated with the biostimulant consistently retained their lipid content at 18.44% without any significant reduction. Furthermore, a significant rise in saturated fatty acid (SFA) content was observed, with C16:0 and C18:1 dominating both bench-scale (44.08% and 14.01%) and upscaled (51.12% and 13.07%) microalgae cultures, in contrast to the control group where C18:2 was prevalent. Consequently, SFA contents reached 54.35% and 65.43% in bench-scale and upscaled samples respectively, compared to 33.73% in the control culture. These compositional characteristics align well with the requirements for producing high-quality crude biodiesel. [Display omitted] • Biostimulant supplementation triggered high microalgal biomass up to 1.865 g/L. • Possibility for culture scale-up without decline in growth performance. • Characterizations verified presence of polyphenolic and organo-sulphur elements. • Acquired fatty acid profile satisfied higher diesel standards. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimization of microalgae culture through a two-stage cultivation strategy. • Biomass accumulation was enhanced by 23.62% under optimal conditions. • Optimal dual stress enhanced lipid and SFA content by 128.38% and 56.30%. • Microalgae recycling efficiency increased under dual stress environments. In this study, a two-stage culture strategy was refined to concurrently enhance the growth and lipid accumulation of Tetradesmus obliquus. The results unveiled that, during the initial stage, the optimal conditions for biomass accumulation were achieved with 0.02 mg·L−1 Cu2+ concentration and red light. Under these conditions, biomass accumulation reached 0.628 g·L−1, marking a substantial 23.62 % increase compared to the control group. In the second stage, the optimal conditions for lipid accumulation were identified as 0.5 mg·L−1 Cu2+ concentration and red light, achieving 64.25 mg·g−1·d−1 and marking a 128.38 % increase over the control. Furthermore, the fatty acid analysis results revealed an 18.85 % increase in the saturated fatty acid content, indicating enhanced combustion performance of microalgae cultivated under the dual stress of red light and 0.5 mg·L−1 Cu2+. This study offers insights into the potential application of Tetradesmus obliquus in biofuel production. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the feasibility of microalgal biomass production and nutrient removal from recirculating aquaculture systems (RAS) water (RASW) with low phosphate concentration. For this purpose, Nannochloropsis oculata, Pavlova gyrans, Tetraselmis suecica, Phaeodactylum tricornutum , and their consortium were cultivated in RASW and RASW supplemented with vitamins (+V). Among them, N. oculata showed the maximum biomass production of 0.4 g/L in RASW. Vitamins supplementation significantly increased the growth of T. suecica from 0.16 g/L in RASW to 0.33 g/L in RASW + V. Additionally, T. suecica showed the highest nitrate (NO 3 –N) removal efficiency of 80.88 ± 2.08 % in RASW and 83.82 ± 2.08 % in RASW + V. Accordingly, T. suecica was selected for scaling up study of microalgal cultivation in RASW and RASW supplemented with nitrate (RASW + N) in 4-L airlift photobioreactors. Nitrate supplementation enhanced the growth of T. suecica up to 2.2-fold (day 15). The fatty acid nutritional indices in T. suecica cultivated in RASW and RASW + N showed optimal polyunsaturated fatty acids (PUFAs)/saturated fatty acid (SFAs), omega-6 fatty acid (n-6)/omega-3 fatty acid (n-3), indices of atherogenicity (IA), and thrombogenicity (IT)). Overall, the findings of this study revealed that despite low phosphate concentration, marine microalgae can grow in RASW and relatively reduce the concentration of nitrate. Furthermore, the microalgal biomass cultivated in RASW consisting of pigments and optimal fatty acid nutritional profile can be used as fish feed, thus contributing to a circular bioeconomy. [Display omitted] • Nutrient removal in low phosphate RAS water was studied. • Biomass production of T. suecica was almost double after vitamin supplementation. • T. suecica, removed 83.82 and 80.88% of NO 3 –N in RASW + V and RASW, respectively. • PUFAs were detected in P. gyrans, P. tricornutum , N. oculata and T. suecica. • T. suecica cultivated in RASW has optimal nutritional fatty acid indices. [ABSTRACT FROM AUTHOR]

Large amounts of produced water are extracted by the Oil and Gas energy sector since the industrial revolution. This available water, often salty, can be used to dilute liquid digestate from the anaerobic digestion process, a promising source of nutrients for microalgae cultivation. The study investigates the growth of halotolerant microalgae and their associated bacteria in column photobioreactors (PBRs) and open raceway pond (RWP), to treat industrial wastewaters while producing biomass for energy valorisation. Microalgae were cultured in mixtures of saline artificial produced water (7–44 %v/v), liquid digestate (5 %v/v using PBRs, 29–63 %v/v using RWP) and seawater. Nannochloropsis oceanica and Tetraselmis suecica strains were firstly cultivated in 70 L PBRs in indoor conditions for 3 months and later in 1.1 m3 RWP operated in outdoor conditions for 5 months in spring-summer period. In PBRs, average productivity was 9.0 ± 4.2 gVSS·m−2·d−1 (102–153 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 61.8, 31.6 and 97.2 %, respectively. In RWP, strong changes in the microalgae populations were observed. Productivity was 6.7 ± 5.2 gVSS·m−2·d−1 (30 ± 23 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 48.4, 44.4 and 88.1 %, respectively. In parallel with the production of microalgae, a nitrifying microbial population grew in the RWP despite the high salinity (70 g L−1). Over these periods of several months, microalgae production was maintained using a culture medium containing high salt concentration, metals and harmful aromatic compounds. [Display omitted] • Halotolerant microalgae were cultivated in column photobioreactors and raceway pond. • Similar areal productivities (7-9 gVSS·m−2·d−1) were obtained using both systems. • Up to 62% COD, 32% nitrogen and 98% phosphorous removed using column photobioreactors. • Up to 48% COD, 44% nitrogen and 88% phosphorous removed using raceway pond. • High nitrification was observed despite the high salinity of the culture medium. [ABSTRACT FROM AUTHOR]

Bioenergy generation from microalgae can significantly contribute to climate mitigation and renewable energy production. In this regard, several multi-criteria decision-making method were employed to prioritize appropriate microalgae culture system for bioenergy production. Entropy weight, Criteria Importance Through Intercriteria Correlation (CRITIC) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) were the employed MCDA method. Fourteen microalgae culture systems were selected as a case study, which contain teen monoculture and four dual-culture. Initially, through ans in-depth review of the literature and expert views, four categories total eight indicators were selected as the evaluation indices of the study, namely 1) Proliferation: Half growth cycle and Max growth rate,2) Biomass output: Bio-crude yield and Lipid yield, 3) Nutrient utilization: residual concentration of total Nitrogen and total Phosphorus, and, 4) Stability: coefficient of variation of Bio-crude yield and Lipid yield. The result indicated that " Pediastrum sp. & Micractinium sp." was identified as the most bioenergy potential microalgae culture system, and the evaluation results of entropy weight method and CRITIC method are similar. It is pertinent to note that 1)the entropy weight method exhibits lower sample size requirements, 2) the critic method excels when dealing with larger sample sizes, and 3) the TOPSIS method necessitates the incorporation of appropriate weighting methods to ensure credible results. In the application stage, the key indicators related to cost can be further included in the evaluation indices. • Multi-Criteria Decision Analysis (MCDA) methodologies adopted to evaluate fourteen microalgae culture systems. • An MCDA for the bioenergy production of microalgae cultures with four categories total eight indicators was created. • Entropy weight, CRITIC and TOPSIS calculation methods were analyzed and compared. • Pediastrum sp. & Micractinium sp. were identified as the most bioenergy potential microalgae culture system. [ABSTRACT FROM AUTHOR]

In this study, the growth characteristics of microalgae cultured with different carbon sources were analyzed, and the flocculation characteristics under the influence of carbon sources were evaluated using three typical flocculants. The results showed that the organic carbon sources could significantly increase the content of extracellular proteins in microalgae. Specifically, the extracellular protein concentrations of microalgae cultured with pure BG-11, ethanol, sodium acetate and glucose were 18.2 29.2, 97.3, and 34.7 mg/g, respectively. During the flocculation process, microalgae cultured with sodium acetate exhibited a weak response to the flocculant because of excessive extracellular proteins inhibited flocculation. In addition, the flocculation efficiency was also less than 50.0% cultured with sodium acetate in all pH test ranges when alum and chitosan were used as flocculants. It could be inferred that the flocculant initially happened to charge neutralization with the negatively charged proteins in the solution and then bridged the charges with the microalgae. These findings provide insights into the effects of different carbon sources on microalgal flocculation, promising organic integration of microalgae wastewater treatment and harvesting. [Display omitted] • Three typical flocculants were utilized to assess the flocculation of microalgae. • An additional carbon source can enhance the production of EPS in microalgae. • EEMs-PARAFAC was utilized to analyze the composition of EPS. • CH 3 COONa inhibited flocculation of microalgae due to excess extracellular protein. • Ethanol has been identified as a promising carbon source for flocculation. [ABSTRACT FROM AUTHOR]

Microalgae are one of the promising unicellular species for biosynthesis of functional natural products, such as omega-3 long-chain polyunsaturated fatty acids, carotenoids, proteins, and vitamins. As they readily grow on organic and nitrogenous substrates, they have vast phycoremediation potential for different industrial wastewater and side-streams. The side-streams from dairy industry have the enormous potential of valorization as they have high carbon and nutrient load, which could serve as growth media for microalgal cultivation. This review addresses the most recent examples of valorization of several types of dairy side-streams using microalgae. The aim is to provide better understanding of the issues and challenges of valorizing the industrial dairy side-streams as substrates for value added microalgal biomass production with focus on nutrient, particularly lactose utilization by using different microalgae species, mostly from Chlorella , Scenedesmus , and Spirulina genera. So far, mixotrophic and heterotrophic microalgae cultivation has been tested in various genuine and model dairy side-streams, wherein mixotrophic cultivation exhibited better biomass productivity. Moreover, this review identifies microalgae cultures capable of nutrient utilization and lactose assimilation, providing valuable guidance for future research in phycoremediation of dairy side-streams for value-added food production. Further investigations on different microalgal species for lactose utilization and β-galactosidase activity in model media are required to enable efficient valorization of lactose in the side-streams. • Dairy side-streams are feedstock for algal biomass production for functional food. • Mixotrophic cultivation of microalgae is a low-cost biomass production strategy. • Selection of lactose utilizing microalgae species is crucial. [ABSTRACT FROM AUTHOR]

In this study, Haematococcus pluvialis and Coelastrella saipanensis were evaluated for heterotrophic nutrition potential in dairy waste medium by blocking the PSII using DCMU. The study was done by four sets of experiments. In the first set, in the different concentrations DCMU-treatments, 20μL showed pronounced effect in H. pluvialis and C. saipanensis as 89 % and 83% decrease in cells (>30 and > 250 cells/mL) compared to control (536 ± 12.35 × 104 and 1167 ± 15.35 × 104 cells/mL, respectively). Damage to the PS II by DCMU interrupted the growth, which in turn produced a significant drop in the number of cells. In the second round of experiment, growth of algae in various dairy waste concentrations suggest that dairy wastewater (DWW) provides enough nutrients to produce 35.71 % and 64.74 % more cells in H. pluvialis and C. saipanensis, respectively compared to the control. In the third set, high DCMU concentration was added to microalgae cultures in DWW to assess the heterotrophic nutrition potential. Growth in cell number 34.4 ± 19 and 617.46 ± 60.44 cells/mL was recorded in H. pluvialis and C. saipanensis when grown control medium whereas addition of DCMU reduced the cell number to 1.53 ± 0.75 and 55.13 ± 0.75 cells/mL on 15th day, respectively. This shows cells in cultures treated with DCMU reveal that algae can sustain their metabolic activity by utilizing the nutrients of dairy waste inhibiting photosystem. Fourth round of experiments found that microalgae could resume their growth and productivity by adapting to heterotrophic nutritional behaviour when DCMU given in mild dose at different time interval. This study conclude as C. saipanensis grows more readily by absorbing dairy waste nutrients than H. pluvialis. Therefore, C. saipanensis is an excellent choice for wastewater treatment through sustainable environmentally benign process after scale-up investigation. These results provide useful information to advance to molecular study for measuring microalgae's capability for bioremediation application. [Display omitted] • Dairy waste nutrients are an efficient substrate for the growth of H. pluvialis and C. saipanensis. • These algae can thrive in the waste medium by utilizing the available nutrients by disabling phtosystem II using DCMU. • DCMU can be used to measure the microalgae capability of adaptation to heterotrophic nutrients. • In light of this, both algae, C. saipanensis in particular, is a good candidate for wastewater cleanup. [ABSTRACT FROM AUTHOR]

• Waste activated sludge extracts can be effectively used to produce algal lipids. • Temperature significantly affected the growth and lipid synthesis of microalgae. • The highest lipid content of 59.13 % was obtained at temperature of 10 °C. • Multi-omics revealed the mechanism of temperature in algal lipid synthesis. • Several genes for lipogenesis, antioxidants, and autophagy were upregulated. Waste activated sludge (WAS) as one of the major pollutants with a significant annual production, has garnered significant attention regarding its treatment and utilization. If improperly discharged, it not only caused environmental pollution but also led to the wastage of valuable resources. In this study, the microalgae growth and lipid accumulation using waste activated sludge extracts (WASE) under different temperature conditions were investigated. The highest lipid content (59.13%) and lipid productivity (80.41 mg L−1 d−1) were obtained at cultivation temperatures of 10 and 25 °C, respectively. It was found that microalgae can effectively utilize TN/TP/NH 4 +-N and other nutrients of WASE. The highest utilization rates of TP, TN and NH 4 +-N were achieved at a cultivation temperature of 10 °C, reaching 84.97, 77.49 and 92.32%, respectively. The algal fatty acids had carbon chains predominantly ranging from C14 to C18, making them suitable for biodiesel production. Additionally, a comprehensive analysis of transcriptomics and metabolomics revealed up-regulation of genes associated with triglyceride assembly, the antioxidant system of algal cells, and cellular autophagy, as well as the accumulation of metabolites related to the tricarboxylic acid (TCA) cycle and lipids. This study offers novel insights into the microscopic mechanisms of microalgae culture using WASE and approaches for the resource utilization of sludge. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the effect of external agricultural phytohormones (mixed phytohormones) addition (1.0, 5.0, 10.0, and 20.0 mg L−1) on the growth performance, lipid productivity, and sedimentation efficiency of Chlorella pyrenoidosa cultivated in saline wastewater was investigated. Among the different concentrations evaluated, the highest biomass (1.00 g L−1) and lipid productivity (11.11 mg L−1 d−1) of microalgae were obtained at 10.0 mg L−1 agricultural phytohormones addition. Moreover, exogenous agricultural phytohormones also improved the sedimentation performance of C. pyrenoidosa , which was conducive to the harvest of microalgae resources, and the improvement of sedimentation performance was positively correlated with the amount of agricultural phytohormones used. The promotion of extracellular polymeric substances synthesis by phytohormones in microalgal cells could be considered as the reason for its promotion of microalgal sedimentation. Transcriptome analysis revealed that the addition of phytohormones upregulated the expression of genes related to the mitogen-activated protein kinase (MAPK)-mediated phytohormone signaling pathway and lipid synthesis, thereby improving salinity tolerance and lipid production in C. pyrenoidosa. Overall, agricultural phytohormones provide an effective and inexpensive strategy for increasing the lipid productivity and sedimentation efficiency of microalgae cultured in saline wastewater. [Display omitted] • Agricultural phytohormone promote efficient and inexpensive culture of microalgae. • Agricultural phytohormone of 10 mg L−1 resulted in the highest lipid productivity. • Agricultural phytohormone effectively improved the sedimentation of microalgae. • The mechanism of phytohormone promoting microalgae sedimentation is related to EPS. • Hormones upregulate the genes related to lipid synthesis and antioxidant stress. [ABSTRACT FROM AUTHOR]

Microalgae are photosynthetic microorganisms playing a pivotal role in primary production in aquatic ecosystems, sustaining the entry of carbon in the biosphere. Microalgae have also been recognized as sustainable source of biomass to complement crops. For this objective they are cultivated in photobioreactors or ponds at high cell density to maximize biomass productivity and lower the cost of downstream processes. Photosynthesis depends on light availability, that is often not constant over time. In nature, sunlight fluctuates over diurnal cycles and weather conditions. In high-density microalgae cultures of photobioreactors outdoors, on top of natural variations, microalgae are subjected to further complexity in light exposure. Because of the high-density cells experience self-shading effects that heavily limit light availability in most of the mass culture volume. This limitation strongly affects biomass productivity of industrial microalgae cultivation plants with important implications on economic feasibility. Understanding how photosynthesis responds to cell density is informative to assess functionality in the inhomogeneous light environment of industrial photobioreactors. In this work we exploited a high-sensitivity Clark electrode to measure microalgae photosynthesis and compare cultures with different densities, using Nannochloropsis as model organism. We observed that cell density has a substantial impact on photosynthetic activity, and demonstrated the reduction of the cell's light-absorption capacity by genetic modification is a valuable strategy to increase photosynthetic functionality on a chlorophyll-basis of dense microalgae cultures. • Microalgae biomass is a promising alternative to crops. • The impact of cultivation at scale on photosynthesis is still under-investigated. • The Photosynthesis-Irradiance (PI) relationship is informative. • High-sensitivity oxygen measurements for PI investigation was validated. • The effect of cell density on PI was studied in Nannochloropsis pale mutants. [ABSTRACT FROM AUTHOR]