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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 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]

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]

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] • 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]

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]

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]

Microalgae culturing in municipal wastewater treatment plants (WWTP) can be a solution to lower the effluent's nitrogen and phosphorus concentrations to comply with the new legislative limits. Microalgae can also promote a circular approach to WWTP by recycling material streams and reducing the energetic consumption of the treatment process. This study aims to perform a techno-economic assessment of the integration of microalgae culture (Chlorella vulgaris) as tertiary treatment at a WWTP in northern Portugal. This evaluation took into account information collected from the specific WWTP under study as well as relevant literature for each stage of the process. The major system flows: (i) a 7377 m3 d−1 treated water flow (ii) the treatment of 107,736 kg d −1 of sludge; (iii) a biosolids soil amendment production of 7580 kg d−1; and (iv) 10,874 kW h d−1 energy for self-consumption. In this work, the integration of microalgae in WWTP achieved yearly gross earnings of approximately 619,100 €. • Efficient nutrient removal: Microalgae lower nitrogen and phosphorus in wastewater. • Circular approach: Microalgae recycle materials, reduce energy consumption in WWTP. • Resource recovery: 7580 kg d−1 of fertilizers produced from microalgae cultivation. • Economic viability: Microalgae integration yields yearly earnings of 619,100 €. [ABSTRACT FROM AUTHOR]

Due to the low electrical power generation in liquid cultures of photosynthetic microalgae, a solid medium culture is demanded for the efficient design of biophotovoltaic (BPV) cells. In particular, the conductivity of the culture medium and the contact of microalgae with an electrode are crucial in harvesting electrons in BPV cells. Here, an ion-crosslinked carboxymethylated cellulose nanofiber (CM-CNF)/alginate is proposed as a living hydrogel for the green power generation of Chlorella vulgaris embedded in the hydrogel. The hydrogel crosslinked with Ca2+ and Fe3+ ions showed more efficient BPV properties than the hydrogel crosslinked with only Ca2+ due to the increase of conductivity. The efficient transport of electrons generated by C. vulgaris improves the power generation of BPV cells. Moreover, the fluid channels imprinted in the living hydrogel maintain the viability of C. vulgaris even under the ambient environment by preventing the solid medium from being dried out. [ABSTRACT FROM AUTHOR]