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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]

Graphical abstract Highlights • A perforated inverted arc trough internals was proposed to promote CO 2 bio-fixation. • Gas–liquid contact time was prolonged from 0.448 s to 256 s by the PIAT internals. • Dissolved CO 2 concentration in microalgae culture of PIAT-PBR increased by 26.0%. • 20.9% and 26.2% increase in biomass productivity and CO 2 fixation rate were obtained. • The maximum CO 2 fixation rate by Chlorella vulgaris reached to 36.6 mg L−1 h−1. Abstract Flat-plate photobioreactor (PBR) with perforated inverted arc trough (PIAT) internals was proposed to promote CO 2 bio-fixation by microalgae. The PIAT internals can enhance CO 2 transfer from gas to culture medium by prolonging CO 2 gas–liquid contact time and generate periodic aeration in the suspension upper side the PIAT providing suspension mixing. Experimental results showed gas–liquid contact time was prolonged from 0.448 s to 256 s and the CO 2 partial pressure inside the PIAT internals was about 15.5 kPa during microalgae cultivation. Consequently, the dissolved CO 2 concentration in the microalgae suspension of the proposed PBR was increased by 26.0% compared to that in the PBR without PIAT internals when 15% CO 2 (v/v) was aerated at a rate of 15 mL min−1. The elevated CO 2 transfer contributed to a 20.9% increment in biomass concentration (3.35 g L−1) and a 26.2% increment in CO 2 fixation rate (36.6 mg L−1 h−1). [ABSTRACT FROM AUTHOR]

The present study aimed at: (1) determining the effect of sulfur addition on biomass growth and (2) assessing the effect of sulfur, phosphorus and nitrogen limitation on lipid accumulation by C. vulgaris SAG 211-11b. The sulfur cellular content was more than two-fold higher under nitrogen and phosphorus limitation (0.52% and 0.54% w w −1 , respectively) compared to sulfur requirements (0.20% w w −1 ) under sulfur limiting conditions. The nitrogen needs are significantly lower (2.81–3.35% w w −1 ) when compared to other microalgae and become 23% lower under nitrogen or phosphorus limitation. The microalga exhibited substrate inhibition above 30 g L −1 initial glucose concentration. Sulfur limitation had the most significant effect on lipid accumulation, resulting in maximum total lipid content of 53.43 ± 3.93% g g DW −1 . In addition to enhancing lipid productivity, adopting the optimal nutrient limitation strategy can result in cost savings by avoiding unnecessary nutrient additions and eliminate the environmental burden due to wasted resources. [ABSTRACT FROM AUTHOR]

Harvesting involves nearly thirty percent of total production cost of microalgae that needs to be done efficiently. Utilizing inexpensive and highly available biopolymer-based flocculants can be a solution for reducing the harvest costs. Herein, flocculation process of Chlorella vulgaris microalgae using cationic starch nanoparticles (CSNPs) was evaluated and optimized through the response surface methodology (RSM). pH, microalgae and CSNPs concentrations were considered as the main independent variables. Under the optimum conditions of microalgae concentration 0.75 g dry weight/L, CSNPs concentration 7.1 mg dry weight/L and pH 11.8, the maximum flocculation efficiency (90%) achieved. Twenty percent increase in flocculation efficiency observed with the use of CSNPs instead of the non-particulate starch which can be due to the more electrostatic interactions between the cationic nanoparticles and the microalgae. Therefore, the synthesized CSNPs can be employed as a convenient and economical flocculants for efficient harvest of Chlorella vulgaris microalgae at large scale. [ABSTRACT FROM AUTHOR]

To improve microalgae biomass utilization efficiency during biofuel production process, medium-low temperature hydrothermal hydrolysis pretreatment was adopted in this study. The pretreatment kinetic characteristics of concentrated wet microalgae Chlorella vulgaris biomass (50 g/L) under medium-low temperature hydrolysis (100°C-200°C) were experimentally investigated. The hydrothermal hydrolysis kinetics describing the coupled effects of temperature, initial pressure and retention time then were proposed using response surface methodology (RSM). The maximum carbohydrate yield reached 327.3 mg/g dried biomass under initial pressure of 4 MPa at reaction temperature of 150°C for 120 min. The maximum protein yield (321.5 mg/g dried biomass) was obtained under initial pressure of 4 MPa at reaction temperature of 200°C for 60 min. Based on the hydrothermal hydrolysis kinetic models, it was confirmed that temperature was the most important factor affecting both carbohydrate and protein release during hydrothermal hydrolysis process. Hydrothermal initial pressure and retention time were significant to carbohydrate release, but not to protein release. While, lipid was mainly distributed in microalgae residual and almost did not exist in supernatant (about 8.03 mg/g). And with assistance of mixed hexane and methanol (the ratio of hexane to methanol was 7:3), 67.69% of microalgae lipid was extracted out from hydrothermal hydrolysed microalgae residual (123.3 mg/g dried biomass). [ABSTRACT FROM AUTHOR]

In this study, five microalgae strains were cultured for their ability to survive in biogas slurry, remove nitrogen resources and accumulate carbohydrates. It was proved that five microalgae strains adapted in biogas slurry well without ammonia inhibition. Among them, Chlorella vulgaris ESP-6 showed the best performance on carbohydrate accumulation, giving the highest carbohydrate content of 61.5% in biogas slurry and the highest ammonia removal efficiency and rate of 96.3% and 91.7 mg/L/d respectively in biogas slurry with phosphorus and magnesium added. Additionally, the absence of phosphorus and magnesium that can be adverse for biomass accumulation resulted in earlier timing of carbohydrate accumulation and magnesium was firstly recognized and proved as the influence factor for carbohydrate accumulation. Microalgae that cultured in biogas slurry accumulated more carbohydrate in cell, making biogas slurry more suitable medium for the improvement of carbohydrate content, thus can be regarded as a new strategy to accumulate carbohydrate. [ABSTRACT FROM AUTHOR]

To improve light penetrability and biomass production in batch cultivation, a cultivation mode that periodically pre-harvesting partial microalgae cells from suspension with culture medium recycling was proposed. By daily pre-harvesting 30% microalgae cells from the suspension, the average light intensity in the photobioreactor (PBR) was enhanced by 27.05–122.06%, resulting in a 46.48% increase in total biomass production than that cultivated in batch cultivation without pre-harvesting under an incident light intensity of 160 μmol m −2 s −1 . Compared with the semi-continuous cultivation with 30% microalgae suspension daily replaced with equivalent volume of fresh medium, nutrients and water input was reduced by 60% in the proposed cultivation mode but with slightly decrease (12.82%) in biomass production. No additional nutrient was replenished when culture medium recycling. Furthermore, higher pre-harvesting ratios (40%, 60%) and lower pre-harvesting frequencies (every 2, 2.5 days) were not advantageous for the pre-harvesting cultivation mode. [ABSTRACT FROM AUTHOR]

Microalgae currently receive growing attention as promising candidates for future bio-economy concepts. However, the reliable maintenance of production strains remains challenging. The well-established serial subculturing techniques suffer from low long-time stability and high effort and are therefore stepwise being replaced by cryopreservation. Currently, available protocols are often deduced from cell culture technology and are rather complex. This study aimed to investigate if less complex approaches can be applied. We introduce an easy-to-use cryopreservation protocol based on the model organism Chlorella vulgaris. To overcome error-prone viability estimation by plating techniques, an alternative method using growth pattern analysis was developed. As revealed by growth pattern analysis, the preservation of stationary phase cells proved superior to the commonly applied concept of freezing cells from the growing phase. Controlled-rate cooling using simple devices resulted in reproducibly high post-thawing viabilities in the range of 63 ± 2%. Moreover, the presented protocol highlights the potential of simplifying microalgal cryo-preservation procedures, thereby reducing the required labor and material need to a minimum. Apart from the viability analysis of the cryopreserved microalga C. vulgaris, this approach seems to have the potential to be applied for other algae species and microorganisms, as well. [ABSTRACT FROM AUTHOR]

Microalgae have been used as energy resources in recent decades to mitigate the global energy crisis. As the demand for pure microalgae strains for commercial use increases, designing an effective photobioreactor (PBR) for mass cultivation is important. Chlorella vulgaris, a local freshwater microalga, was used to study the algal biomass cultivation and lipid production using various PBR configurations (bubbling, air-lift, porous air-lift). The results show that a bubbling column design is a better choice for the cultivation of Chlorella vulgaris than an air-lift one. The highest biomass concentration in the bubbling PBR was 0.78 g/L while the air-lift PBR had a value of 0.09 g/L. Key operating parameters, including draft-tube length and bubbling flowrate, were then optimized based on biomass production and lipid yield. The highest lipid content was in the porous air-lift PBR and the air-lift PBR with shorter draft tube (35 cm) was also better than a longer one (50 cm) for algal cultivation, but the microalgae attachment on the inner tube of PBR always occurred. The highest biomass concentration could be produced under the highest gas flowrate of 2.7 L/min, whereas the lowest dry cell mass was under the lowest gas flowrate of 0.2 L/min. [ABSTRACT FROM AUTHOR]

This study investigated the microalgae biomass production and nutrients removal efficiency from treated sewage by newly developed membrane photobioreactor in which Chlorella vulgaris was cultured in batch flow mode. Its performance was compared with conventional photobioreactor. The results show that the volumetric microalgae productivity was 39.93 and 10.36 mg L-1 d-1 in membrane photobioreactor and conventional photobioreactor, respectively. The nutrients removal rate in membrane photobioreactor was 4.13 mg N L-1 d-1 and 0.43 mg P L-1 d-1, which was obviously higher than that in conventional photobioreactor (0.59 mg N L-1 d-1 and 0.08 mg P L-1 d-1). The better performance of membrane photobioreactor was due to the submerged membrane module in the reactor which acted as a solid-liquid separator and thereby enabled the reactor to operate with higher supply flow rate of cultivation medium. Moreover, in the outflow stage of the membrane photobioreactor, the microalgae culture liquor in the reactor could be further concentrated. [ABSTRACT FROM AUTHOR]

Improvements in lipid productivity would enhance the economic feasibility of microalgal biodiesel. In order to optimise lipid productivity, both the growth rate and lipid content of algal cells must be maximised. The lipid content of many microalgae can be enhanced through nitrogen limitation, but at the expense of biomass productivity. This suggests that a two-stage nitrogen supply strategy might improve lipid productivity. Two different nitrogen supply strategies were investigated for their effect on lipid productivity in Chlorella vulgaris. The first was an initial nitrogen-replete stage, designed to optimise biomass productivity, followed by nitrogen limitation to enhance lipid content (two-stage batch) and the second was an initial nitrogen-limited stage, designed to maximise lipid content, followed by addition of nitrogen to enhance biomass concentration (fed-batch). Volumetric lipid yield in nitrogen-limited two-stage batch and fed-batch was compared with that achieved in nitrogen-replete and nitrogen-limited batch culture. In a previous work, maximum lipid productivity in batch culture was found at an intermediate level of nitrogen limitation (starting nitrate concentration of 170 mg L). Overall lipid productivity was not improved by using fed-batch or two-stage culture strategies, although these strategies showed higher volumetric lipid concentrations than nitrogen-replete batch culture. The dilution of cultures prior to nitrogen deprivation led to increased lipid accumulation, indicating that the availability of light influenced the rate of lipid accumulation. However, dilution did not lead to increased lipid productivity due to the resulting lower biomass concentration. [ABSTRACT FROM AUTHOR]

Abstract: Biohydrogen is usually produced via dark fermentation, which generates CO2 emissions and produces soluble metabolites (e.g., volatile fatty acids) with high chemical oxygen demand (COD) as the by-products, which require further treatments. In this study, mixotrophic culture of an isolated microalga (Chlorella vulgaris ESP6) was utilized to simultaneously consume CO2 and COD by-products from dark fermentation, converting them to valuable microalgae biomass. Light intensity and food to microorganism (F/M) ratio were adjusted to 150 μmol m−2 s−1 and F/M ratio, 4.5, respectively, to improve the efficiency of assimilating the soluble metabolites. The mixotrophic microalgae culture could reduce the CO2 content of dark fermentation effluent from 34% to 5% with nearly 100% consumption of soluble metabolites (mainly butyrate and acetate) in 9 days. The obtained microalgal biomass was hydrolyzed with 1.5% HCl and subsequently used as the substrate for bioH2 production with Clostridium butyricum CGS5, giving a cumulative H2 production of 1276 ml/L, a H2 production rate of 240 ml/L/h, and a H2 yield of 0.94 mol/mol sugar. [Copyright &y& Elsevier]

Background: Lack of accounting for proton uptake and secretion has confounded interpretation of the stoichiometry of photosynthetic growth of algae. This is also problematic for achieving growth of microalgae to high cell concentrations which is necessary to improve productivity and the economic feasibility of commercial-scale chemical production systems. Since microalgae are capable of consuming both nitrate and ammonium, this represents an opportunity to balance culture pH based on a nitrogen feeding strategy that does not utilize gas-phase CO2 buffering. Stoichiometry suggests that approximately 36 weight%N-NH4+ (balance nitrogen as NO3- ) would minimize the protonimbalance and permit high-density photoautotrophic growth as it does in higher plant tissue culture. However, algalmedia almost exclusively utilize nitrate, and ammonium is often viewed as 'toxic' to algae. Results: The microalgae Chlorella vulgaris and Chlamydomonas reinhardtii exclusively utilize ammonium when bothammonium and nitrate are provided during growth on excess CO2. The resulting proton imbalance from preferential ammonium utilization causes the pH to drop too low to sustain further growth when ammonium was only 9% of the total nitrogen (0.027 gN-NH4+/L). However, providing smaller amounts of ammonium sequentially in the presence of nitrate maintained the pH of a Chlorella vulgaris culture for improved growth on 0.3 gN/L to 5 gDW/L under 5% CO2 gas-phase supplementation. Bioreactor pH dynamics are shown to be predictable based on simple nitrogen assimilation as long as there is sufficient CO2 availability. Conclusions: This work provides both a media formulation and a feeding strategy with a focus on nitrogen metabolism and regulation to support high-density algal culture without buffering. The instability in culture pH that isobserved in microalgal cultures in the absence of buffers can be overcome through alternating utilization ofammonium and nitrate. Despite the highly regulated array of nitrogen transporters, providing a nitrogen source with abalanced degree of reduction minimizes pH fluctuations. Understanding and accommodating the behavior of nitrogen utilization in microalgae is key to avoiding 'culture crash' and reliance on gas phase CO2 buffering, which becomes both ineffective and cost-prohibitive for commercial-scale algal culture. [ABSTRACT FROM AUTHOR]

Abstract: Reusing supernatant of microalgae culture medium can have inhibitory or toxic effects on the biomass production because of the release of organic metabolites by cells in the culture medium during their growth. This work investigated the impact of Chlorella vulgaris medium recycling on culture productivity, cells quality and accumulation of excreted metabolites in the culture medium. No significant impact on the C. vulgaris growth was observed after 63days of recycling, the productivity remained stable at around 0.55kgm−3 day−1. Organic matters accumulated in supernatant were identified as biopolymers (BP) poor in nitrogen and with a size above 40kDa (probably polysaccharides), and small organic molecules (SOM) richer in nitrogen with a molecular size ranging from 1 to 3kDa. The concentration of biopolymers in the supernatant increased till to a maximum and then decreased, possibly consumed by bacteria, whereas small organic compounds accumulated in the medium. [Copyright &y& Elsevier]

Abstract: When microalgae culture medium is recycled, ions (e.g. Na+, K+, Ca2+) that were not assimilated by the microalgae accumulate in the medium. Therefore, a growth medium (HAMGM) was developed that included ions that were more easily assimilated by Chlorella vulgaris, such as ammonium one (NH4 +). Recycling performance was studied by carrying out 8-week continuous cultivation of C. vulgaris with recycled HAMGM medium. No loss of biomass productivity was observed compared to culture in a conventional medium, and accumulation of ions over time was negligible. [Copyright &y& Elsevier]

Abstract: While current approaches have limitations for efficient and cost-effective microalgal biofuel production, new processes, which are financially economic, environmentally sustainable, and ecologically stable, are needed. Typically, microalgae cells are small and grow individually. Harvest of these cells is technically difficult and it contributes to 20–30% of the total cost of biomass production. A new process of pelletized cell cultivation is described in this study to co-culture a filamentous fungal species with microalgae so that microalgae cells can be co-pelletized into fungal pellets for easier harvest. This new process can be applied to microalgae cultures in both autotrophic and heterotrophic conditions to allow microalgae cells attach to each other. The cell pellets, due to their large size, can be harvested through sieve, much easier than individual cells. This method has the potential to significantly decrease the processing cost for generating microagal biofuel or other products. [Copyright &y& Elsevier]

Abstract: The potential application of Chlorella vulgaris UMACC 001 for bioremediation of textile wastewater (TW) was investigated using four batches of cultures in high rate algae ponds (HRAP) containing textile dye (Supranol Red 3BW) or TW. The biomass attained ranged from 0.17 to 2.26mg chlorophyll a/L while colour removal ranged from 41.8% to 50.0%. There was also reduction of NH4–N (44.4–45.1%), PO4–P (33.1–33.3%) and COD (38.3–62.3%) in the TW. Supplementation of the TW with nutrients of Bold’s Basal Medium (BBM) increased biomass production but did not improve colour removal or reduction of pollutants. The mechanism of colour removal by C. vulgaris is biosorption, in accordance with both the Langmuir and Freundlich models. The HRAP using C. vulgaris offers a good system for the polishing of TW before final discharge. [Copyright &y& Elsevier]