Semi-continuous Culture Research Articles

An algal-bacterial symbiotic system of carbon fixation using formate as a carbon source

The commercial implementation of algal cultures for efficient capture of CO2 from fossil-derived flue gases is not a reality yet due to several major challenges, particularly low gas-liquid mass transport efficiency along with loss of productivity due to pests. This study has explored an algal-bacterial symbiotic system to utilize formate as a carbon source. The algal-bacterial assemblage, after a 400-day adaptive evolution using the formate medium, has demonstrated a new capability to assimilate both formate and CO2 to promote biomass production. The formate tolerant culture system also addresses CO2 mass transfer limitation under high light conditions. Continuous cultivation of the assemblage on formate led to a carbon capture efficiency of 90 % with a biomass concentration of 0.92 g L−1 and biomass productivity of 0.31 g L−1 day−1, and the system did not require CO2 aeration. In addition, 13C isotope tracing, proteomics, and microbial community analysis reveal a uniquely evolved community for formate utilizations and robust biomass synthesis, in which Chlorella sorokiniana is a dominant phototroph companying with highly diverse bacterial subpopulations. In the presence of formate, evidence has shown that Chlorella is able to form mutualism with formate utilizing bacteria in semi-continuous cultures, leading to a highly effective photomixotrophic metabolism. This study demonstrates a new route of using electrochemical-derived formate to support mutualistic algae-bacteria biorefinery while the formate as an alternative carbon source could repel pests for outdoor algal cultivations.

Regulation of the autochthonous microbial community in excess sludge for the bioconversion of carbon dioxide to acetate without exogenic hydrogen

The autochthonous microbial community from excess sludge was regulated for enhanced conversion of CO2 to acetate without exogenic H2. It was interesting that the acetate-fed system exhibited a surprising performance to regulate the microbial community for a high acetate yield and selectivity. As a result, some hydrogen-producing bacteria (e.g., Proteiniborus) and acetogenic bacteria with the ability of CO2 reduction were enriched by acetate feeding, 2-bromoethanesulfonate (BES) addition and CO2 stress. When the selected microbial community was applied to convert CO2, the accumulation of acetate was positively correlated to the concentration of yeast extract. Finally, the acetate yield reached up to 67.24 mM with a high product selectivity of 84 % in the presence of yeast extract (2 g/L) and sufficient CO2 in semi-continuous culture for 10 days. This work should help get new insights into the regulation of microbial community for the efficient acetate production from CO2.

Prediction of Microalgae Growth Kinetics In Semi-Continuous Culture From Batch Culture Experiments

Microalgae have recently attracted considerable interest worldwide, due to their extensive application potential in the renewable energy, biopharmaceutical, and nutraceutical industries. Microalgae are renewable, sustainable, and economical sources of biofuels, bioactive medicinal products, and food ingredients. For microalgal production, the choice of the photobioreactor, the method of cultivation used, and the harvesting regime adopted (batch, semi-continuous and continuous cultures) are very important. In this work, we examined the growth rate and productivity of a small volume (2 L) experimental culture in batch and semi-continuous mode. Several microalgae species have been investigated for their potential as value-added products, thus we have chosen two species: green microalga (

Effect of specific irradiance on productivity and pigment and protein production of Porphyridium purpureum (Rhodophyta) semi-continuous culture

Porphyridium purpureum is a promising microalga species due to the content of various valuable compounds. In this study, specific irradiance parameter, representing the amount of light energy per unit of microalgae biomass, was introduced. The growth characteristics and pigments and protein accumulation of P. purpureum culture were investigated under semi-continuous mode. Varying dilution rate and surface irradiance resulted in a specific irradiance of 0.2–6.7 W g−1. Using mathematical modeling, we determined the patterns of changes in biomass, pigments, protein content and productivity of P. purpureum culture depending on specific irradiance. The content of target compounds was maximized under the lowest level of specific irradiance (0.2–1.2 W g−1), while the highest productivity of this components was reached under 1.2–1.7 W g−1. Overall, lower irradiance levels were favorable for P. purpureum cultivation based on the energy consumption and production characteristics of this species.

Enhancement of microalgal biomass productivity through mixotrophic culture process utilizing waste soy sauce and industrial flue gas

Wastewater treatment plants are indispensable facilities, which emit a massive amount of greenhouse gases. To boost CO2 mitigation and wastewater treatment performance, mixotrophic microalgae cultivation using wastewater has recently been proposed. In this study, food industry wastewater (waste soy sauce) was applied to Chlorella sorokiniana UTEX 2714 cultivation. By using a medium with 20% (v/v) of 10-fold diluted soy sauce, the biomass and fatty acid methyl ester (FAME) productivity enhanced by 1.93 and 1.76 times, respectively. Biomass productivity increased up to 5.2 times when using medium with high soy sauce content under high-intensity light that inhibits cell growth in photoautotrophic environments. Furthermore, industrial flue gas treatment with wastewater was demonstrated by outdoor semi-continuous cultivation with 42% improved biomass production. Consequently, these results suggest that mixotrophic microalgal cultivation has great potential to address both climate change and water pollution while producing valuable products and can contribute to building a sustainable society.

Metagenomic reveals the methanogenesis metabolic mechanism of high-solids anaerobic digestion of human feces under gradient domestication

High-solids anaerobic digestion (HSAD) of low C/N ratio waste was difficult to long-term running. In this study, human feces (HF) HSAD were operated in semicontinuous culture with HRT of 20 days for 190 days under mesophilic condition (38 ± 1 °C), granular sludge as inoculum was gradient domesticated by gradually increasing total solid (TS) (8 % to 17 %). The results showed that the highest tolerated concentration of TS achieved 16 % and biogas was stopped producing at TS 17 %. Maximum methane production rates of TS and volatile solid (VS) were obtained at TS 11 %, 287.08 mL/g TS and 67.67 mL/g vS respectively. AD system was inhibited when thresholds of total volatile fatty acids and total ammonia nitrogen were exceeded 2414.68 ± 207.62 mg/L and 4361.33 ± 143.86 mg/L, respectively. It was worth noted that granular sludge as an inoculum could efficiently remove pathogens (E. coli, 99.80 % at TS 11 % and Salmonella, 88.98 % at TS 12 %). High concentrations of HF (TS 13 % to 17 %) suppressed the growth of dominant methanogens (Methanothrix soehngenii, Methanothrix sp., and Methanothrix harundinacea.) and facilitated the rapid proliferation of acidogenic bacteria (Defluviitoga tunisiensis, Methanoculleus bourgensis, and Tepidanaerobacter acetatoxydans). The absolute abundance of key methanogenesis enzyme-encoding genes (mcr, frh, and fwd) were suddenly increased significantly at TS 12 % and 13 %. The main types of methanogenesis (acetoclastic at 11 % TS, hydrogenotrophic at 12 % TS and methylotrophic at 13 % TS) would change with the variation of different TS. The above studies provide guidance for HF HSAD domestication in practical AD applications.

Development of a bench-scale photobioreactor with a novel recirculation system for continuous cultivation of microalgae

Microalgae cultivation can be used to increase the sustainability of carbon emitting processes, converting the CO2 from exhaust gases into fuels, food and chemicals. Many of the carbon emitting industries operate in a continuous manner, for periods that can span days or months, resulting in a continuous stream of gas emissions. Biogenic CO2 from industrial microbiological processes is one example, since in many cases it becomes unsustainable to stop these processes on a daily or weekly basis. To correctly sequester these emissions, microalgae systems must be operated under continuous constant conditions, requiring photobioreactors (PBRs) that can act as chemostats for long periods of time. However, in order to optimize culture parameters or study metabolic responses, bench-scale setups are necessary. Currently there is a lack of studies and design alternatives using chemostat, since most works focus on batch assays or semi-continuous cultures. Therefore, this work focused on the development of a continuous bench-scale PBR, which combines a retention vessel, a photocollector and a degasser, with an innovative recirculation system, that allows it to operate as an autotrophic chemostat, to study carbon sequestration from a biogenic CO2-rich constant air stream. To assess its applicability, the PBR was used to cultivate the green microalga Haematococcus pluvialis using as sole carbon source the CO2 produced by a coupled heterotrophic bacterial chemostat. An air stream containing ≈0.35 vol% of CO2, was fed to the system, and it was evaluated in terms of stability, carbon fixation and biomass productivity, for dilution rates ranging from 0.1 to 0.5 d−1. The PBR was able to operate under chemostat conditions for more than 100 days, producing a stable culture that generated proportional responses to the stimuli it was subjected to, attaining a maximum biomass productivity of 183 mg/L/d with a carbon fixation efficiency of ≈39% at 0.3 d−1. These results reinforce the effectiveness of the developed PBR system, making it suitable for laboratory-scale studies of continuous photoautotrophic microalgae cultivation.

Effects of concentration and frequency of CO2 supply on productivity of marine microalga Isochrysis galbana

Demand for the high fucoxanthin and docosahexaenoic acid (DHA) content found in the marine microalga Isochrysis galbana is rising annually, and it is essential to devise large-scale cultivation systems that are low in energy and cost. Continuous CO2 supply occupies a considerable portion of total electricity consumption for microalgae cultivation. While an intermittent, high-concentration CO2 supply/agitation has the potential to reduce the electricity consumption required for aeration, it may cause carbon starvation and sedimentation of cells when the supply frequency is insufficient. This study investigated the effects of concentration and frequency of CO2 supply on productivity of I. galbana. Semi-continuous cultivation was conducted under different conditions of CO2 supply (0.04 (air) to 10 % concentration and continuous or intermittent (1 min every 9 min) supply). Under continuous air supply (control), biomass productivity reached 0.18 g L−1 day−1. A continuous supply of CO2 at 5 % showed the highest biomass productivity (0.33 g L−1 day−1). Productivity was only 0.12 g L−1 day−1 with a continuous CO2 supply at 10 % concentration. It was confirmed that growth was suppressed under conditions of a continuous supply of CO2 at high concentrations. The study found that intermittent CO2 concentrations of 5 % and 10 % showed productivity of 0.29 and 0.24 g L−1 day−1, respectively. These productivities were higher than that in the control. Under conditions of continuous CO2 supply, 0.61 mg/g dry weight (DW) of a higher fucoxanthin content was achieved with air supply than was found at concentrations of 5 % and 10 % (0.18 and 0.11 mg/g DW, respectively). However, under intermittent supply conditions, the fucoxanthin reached the higher content of 0.56 mg/g DW under 5% supply. Under conditions of high CO2 concentrations, continuous supply inhibited the accumulation of fucoxanthin, while an intermittent supply promoted its accumulation.

Semi-continuous cultivation of indigenous Chlorella sorokiniana for biomass and pigment production

The characteristics of microalgae, the composition of the growth medium, cultivation parameters, and the design of photobioreactors should be considered when obtaining biomass and biologically active substances from microalgae. Continuous and semi-continuous cultivation of microalgae at optimal hydraulic retention time (HRT) is one of the most promising approaches to optimizing the accumulation of biomass and desired metabolites. The continuous nutrient supply to photobioreactors avoids nutrient limitation and maintains algal biomass productivity at its maximum level. This study reports the effect of HRT on the growth of Chlorella sorokiniana and nutrient uptake by algal cells. The maximum cell density in the photobioreactor was observed during cultivation at HRT of 5 days, while the concentration of pigments and ammonium uptake remained at a high level at HRTs of 5–2.5 days. The obtained results demonstrate that C. sorokiniana can grow efficiently under semi-continuous cultivation conditions and can be considered to produce valuable metabolites.

Isochrysis sp. cultivation in pilot-scale to concurrently produce sustainable triacylglycerols for human milk fat substitutes and fucoxanthin

Isochcrysis strains as versatile cell factories can produce varieties of high-valued bioproducts for food, nutraceuticals and pharmaceuticals. This work aimed to evaluate the ability of Isochrysis sp. to produce high-valued triacylglycerols (TAGs) for human milk fat substitutes (HMFs) and fucoxanthin by batch, fed-batch and semi-continuous cultivation modes in 50-L column photobioreactors. It was found that, Isochrysis cells by three cultivation modes had individual growth characteristics, nutrients consumption, and biochemical composition. In all cultivation modes, microalga cultivated by the semi-continuous cultivation at 10 % renewable rate achieves the highest TAGs and fucoxanthin productivities with 8.2 and 0.5 mg/(L·d), respectively. Additionally, the obtained results showed that the microalgal growth phase and the levels of nitrogen and phosphorus had distinct impacts on the deducting G value for microalgal TAGs produced by three cultivation modes. Based on the fatty acid composition and positional distribution, Isochrysis TAGs by the semi-continuous process at 10 % renewable rate had 73.0 deducting G value that were close to the ones by the batch cultivation (13th day) and fed-batch cultivation. Taken together, Isochrysis sp. was the promising marine microalga to concurrently produce sustainable high-valued TAGs for HMFs and fucoxanthin by semi-continuous cultivation in pilot-scale photobioreactors. This work provides a new marine microalgal platform to exploit Isochrysis-derived TAGs as human milk fat subsitutes for infant formulas and fucoxanthin for nutraceuticals and pharmaceuticals.

Effects of culture medium recycling in the chemical composition of Spirulina platensis biomass cultivated in semi-continuous mode

Commercial microalgae cultivations use the semi-continuous mode, but there are no reports of using this cultivation mode to produce carbohydrate-rich biomass. It was evaluated the biomass productivity and intracellular carbohydrates by Spirulina platensis in semi-continuous cultivation. Besides, the reuse of the culture media after the blend was accomplished in order to obtain nutrient-depleted cultures. In the first stage (Step 1), performed in closed Erlenmeyer’s flasks, it was verified that the blend concentration and renewal rate did not influence the intracellular concentration of carbohydrates. However, the interaction of variables influenced cell concentration and carbohydrates yields, being the best results obtained with blend concentration and renewal rate of 0.5 g/L and 60%, respectively. In Step 2, realized in 10 L open mini raceways, the cultures remained viable up to 3 cycles in semi-continuous mode, obtaining mean carbohydrate contents of 41.7% (w/w) and mean carbohydrate yield of 69.3 mg/L d using the media Zarrouk 30% and 70% renewal rate. These values were higher than those observed in experiments in closed bioreactors. Therefore, it was demonstrated that semi-continuous cultivation is viable to obtain biomass for bioethanol production, which represents a possibility of reusing nutrients from the culture medium itself for this purpose.

Outdoor Inclined Plastic Column Photobioreactor: Growth, and Biochemicals Response of Arthrospira platensis Culture on Daily Solar Irradiance in a Tropical Place.

Implementation of outdoor photobioreactors has been challenged by an extremely oversaturated daily peak of solar irradiance. This study aims to understand the role of column size and paranet shading as well as to investigate the most convenient light control in outdoor cyanobacterial culture. The photobioreactor (PBR) consisted of plastic columns with a diameter of 12.74 cm (PBRd-20) and 31.85 cm (PBRd-50) laid outdoors and inclined at 158.22° upwards against solar radiation, while paranet shading was provided at 0%, 50%, 70%, and 90% shading capacity. A semi-continuous culture of cyanobacterium Arthrospira (Spirulina) platensis was conducted for 6 weeks with weekly monitoring of the growth parameter as well as the proximate and pigments content, while the daily irradiance and culture maximum temperature were recorded. The result shows that the column diameter of 12.74 cm had a lethal risk of 44.7% and this decreased to 10.5% by widening the column diameter to 31.85 cm. This lethal risk can be eliminated by the application of a paranet at a 50% reduction level for the column diameter of 31.85 cm and a 70% reduction level for the column diameter of 12.74 cm. The highest culture productivity of 149.03 mg/(L·day) was achieved with a PBRd-20 with 50% shading treatment, but a PBRd-50 with 90% shading treatment led to an increase in the protein and phycocyanin content by 66.7% and 14.91%, respectively.

Novel effective bioprocess for optimal CO2 fixation via microalgae-based biomineralization under semi-continuous culture

In this study, the effects of microalgae-based biomineralization in a semi-continuous process (M-BSP) on biomass productivity and CO2 fixation rate were investigated. M-BSP significantly improved biomass production and CO2 fixation rate at the second stage of induction by sustaining relatively high photosynthetic rate without exposure to toxic substances (e.g., chlorellin) from aging cells using the microalgae Chlorella HS2. In conventional systems, cells do not receive irradiated light evenly, and many cells age and burst because of the long culture period. In contrast, in the M-BSP, the photosynthesis efficiency increases and biomass production is not inhibited because most of the cells can be harvested during shorter culture period. The accumulated biomass production and CO2 fixation rate of the HS2 cells cultured under M-BSP increased by 4.67- (25 ± 1.09 g/L) and 10.9-fold (30.29 ± 1.79 g/L day−1), respectively, compared to those cultured without the CaCl2 treatment.

Photoacclimation of the polar diatom Chaetoceros neogracilis at low temperature.

Polar microalgae face two major challenges: 1- growing at temperatures (-1.7 to 5°C) that limit enzyme kinetics; and 2- surviving and exploiting a wide range of irradiance. The objective of this study is to understand the adaptation of an Arctic diatom to its environment by studying its ability to acclimate to changes in light and temperature. We acclimated the polar diatom Chaetoceros neogracilis to various light levels at two different temperatures and studied its growth and photosynthetic properties using semi-continuous cultures. Rubisco content was high, to compensate for low catalytic rates, but did not change detectably with growth temperature. Contrary to what is observed in temperate species, in C. neogracilis, carbon fixation rate (20 min 14C incorporation) equaled net growth rate (μ) suggesting very low or very rapid (<20 min) re-oxidation of the newly fixed carbon. The comparison of saturation irradiances for electron transport, oxygen net production and carbon fixation revealed alternative electron pathways that could provide energy and reducing power to the cell without consuming organic carbon which is a very limiting product at low temperatures. High protein contents, low re-oxidation of newly fixed carbon and the use of electron pathways alternative to carbon fixation may be important characteristics allowing efficient growth under those extreme environmental conditions.

Development of a stable semi-continuous lipid production system of an oleaginous Chlamydomonas sp. mutant using multi-omics profiling

BackgroundMicroalgal lipid production has attracted global attention in next-generation biofuel research. Nitrogen starvation, which drastically suppresses cell growth, is a common and strong trigger for lipid accumulation in microalgae. We previously developed a mutant Chlamydomonas sp. KAC1801, which can accumulate lipids irrespective of the presence or absence of nitrates. This study aimed to develop a feasible strategy for stable and continuous lipid production through semi-continuous culture of KAC1801.ResultsKAC1801 continuously accumulated > 20% lipid throughout the subculture (five generations) when inoculated with a dry cell weight of 0.8–0.9 g L−1 and cultured in a medium containing 18.7 mM nitrate, whereas the parent strain KOR1 accumulated only 9% lipid. Under these conditions, KAC1801 continuously produced biomass and consumed nitrates. Lipid productivity of 116.9 mg L−1 day−1 was achieved by semi-continuous cultivation of KAC1801, which was 2.3-fold higher than that of KOR1 (50.5 mg L−1 day−1). Metabolome and transcriptome analyses revealed a depression in photosynthesis and activation of nitrogen assimilation in KAC1801, which are the typical phenotypes of microalgae under nitrogen starvation.ConclusionsBy optimizing nitrate supply and cell density, a one-step cultivation system for Chlamydomonas sp. KAC1801 under nitrate-replete conditions was successfully developed. KAC1801 achieved a lipid productivity comparable to previously reported levels under nitrogen-limiting conditions. In the culture system of this study, metabolome and transcriptome analyses revealed a nitrogen starvation-like response in KAC1801.

Semi-continuous cultivation strategy for improving the growth of Synechocystis sp. PCC 6803 based on the growth model of volume average light intensity

To develop a semi-continuous cultivation strategy to improve the growth of Synechocystis sp. PCC 6803, the growth model of volume average light intensity (VALI) was established based on the light attenuation curve and the cell growth rate under different light intensities. According to the growth model, the semi-continuous cultivation strategy was optimized by controlling microalgal cells under the optimal VALI closed to 115 μmol m−2 s−1 in the culture process. The accuracy of growth model prediction and the cultivation effect of semi-continuous strategy were both verified under indoor conditions. The microalgae grew well when the VALI was in the range of 109–121 μmol m−2 s−1 (the 3rd day as a semi-continuous start replacement point, one-day replacement). The maximum total biomass was 3.36 ± 0.09 g and increased by 86.67 % compared with that without the semi-continuous cultivation strategy (1.80 ± 0.07 g). Subsequently, the microalgae were cultured in different ranges of VALI to further verify the cultivation effect of the semi-continuous strategy. The results once again confirmed that the cell growth was more favorable when the VALI was controlled in the range of 109–121 μmol m−2 s−1. Finally, the semi-continuous cultivation strategy was conducted by controlling VALI under outdoor conditions. The results showed that the maximum total biomass was 289.19 % higher than that without the semi-continuous cultivation strategy. This study indicated that the semi-continuous culture strategy of controlling the VALI in an appropriate range could accelerate the growth of Synechocystis sp. PCC 6803 in outdoor culture, and provided an important experimental basis for the large-scale culture of Synechocystis sp. PCC 6803 outdoors.

Effect of Nitrogen, Phosphorous, and Light Colimitation on Amphidinol Production and Growth in the Marine Dinoflagellate Microalga Amphidinium carterae.

The marine dinoflagellate microalga Amphidinium carterae is a source of amphidinols, a fascinating group of polyketide metabolites potentially useful in drug design. However, Amphidinium carterae grows slowly and produces these toxins in tiny amounts, representing a hurdle for large-scale production. Understanding dinoflagellate growth kinetics under different photobioreactor conditions is imperative for promoting the successful implementation of a full-scale integrated bioproduct production system. This study evaluates the feasibility of growing Amphidinium carterae under different ranges of nitrogen concentration (NO3− = 882–2646 µM), phosphorus concentration (PO33− = 181–529 µM), and light intensity (Y0 = 286–573 µE m−2 s−1) to produce amphidinols. A mathematical colimitation kinetic model based on the “cell quota” concept is developed to predict both algal growth and nutrient drawdown, assuming that all three variables (nitrogen, phosphorous and light) can simultaneously colimit microalgal growth. The model was applied to the semicontinuous culture of the marine microalgae Amphidinium carterae in an indoor LED-lit raceway photobioreactor. The results show that both growth and amphidinol production strongly depend on nutrient concentrations and light intensity. Nonetheless, it was possible to increase Amphidinium carterae growth while simultaneously promoting the overproduction of amphidinols. The proposed model adequately describes Amphidinium carterae growth, nitrate and phosphate concentrations, and intracellular nitrogen and phosphorus storage, and has therefore the potential to be extended to other systems used in dinoflagellate cultivation and the production of bioproducts obtained therein.

Cultivation of Chlorella sorokiniana IPPAS C-1 in Flat-Panel Photobioreactors: From a Laboratory to a Pilot Scale.

Flat-panel photobioreactors are effective systems for microalgae cultivation. This paper presents the growth characteristics of the microalgae Chlorella sorokiniana IPPAS C-1 as a result of three-stage scale-up cultivation in a specially designed cultivation system. First, C. sorokiniana was grown aseptically in 250 mL glass vessels; then, it was diluted and inoculated into a 5-liter flat-panel horizontal photobioreactor; and, at the last stage, the culture was diluted and inoculated into a 70-liter flat-panel vertical photobioreactor. In the presented cycle, the cultured biomass increased by 326 times in 13 days (from 0.6 to 195.6 g dw), with a final biomass concentration of 2.8 g dw L−1. The modes of semi-continuous cultivation were considered. The biomass harvest and dilution of the suspension were carried out either every day or every 3–4 days. For C. sorokiniana IPPAS C-1, a conversion coefficient of optical density values to dry biomass (g L−1) was refined through a factor of 0.33. The key parameters of the photobioreactors tested in this work are discussed.

Effect of Different N:P Ratios on the Growth, Toxicity, and Toxin Profile of Gymnodinium catenatum (Dinophyceae) Strains from the Gulf of California.

The harmful microalgae Gymnodinium catenatum is a unique naked dinoflagellate that produces paralytic shellfish poisoning toxins (PSTs). This species is common along the coasts of the Mexican Pacific and is responsible for paralytic shellfish poisoning, which has resulted in notable financial losses in both fisheries and aquaculture. In the Gulf of California, G. catenatum has been related to mass mortality events in fish, shrimp, seabirds, and marine mammals. In this study, the growth, toxin profiles, and toxin content of four G. catenatum strains isolated from Bahía de La Paz (BAPAZ) and Bahía de Mazatlán (BAMAZ) were evaluated with different N:P ratios, keeping the phosphorus concentration constant. All strains were cultivated in semi-continuous cultures (200 mL, 21.0 °C, 120 µmol photon m−2s−1, and a 12:12 h light-dark cycle) with f/2 + Se medium using N:P ratios of: 4:1, 8:1, 16:1, 32:1, and 64:1. Paralytic toxins were analyzed by HPLC with fluorescence detection. Maximum cellular abundance and growth were obtained at an N:P ratio of 64:1 (3188 cells mL−1 and 0.34 div day−1) with the BAMAZ and BAPAZ strains. A total of ten saxitoxin analogs dominated by N-sulfocarbamoyl (60–90 mol%), decarbamoyl (10–20 mol%), and carbamoyl (5–10 mol%) toxins were detected. The different N:P ratios did not cause significant changes in the PST content or toxin profiles of the strains from both bays, although they did affect cell abundance.

Novel 3D-printed buoyant structures for improvement in flue gas CO2-derived microalgal biomass production by enhancing anti-biofouling on vertical polymeric photobioreactor

Novel 3D-printed buoyant structures can be applied in various environmental processes because of their considerable advantages. Microalgae cultivation in photobioreactors, directly supplemented by industrial CO2, enables environmental pollution mitigation/cleanup and sustainable energy production. However, in photobioreactor systems, biofilm formation due to gas bubbling decreases microalgal productivity. Therefore, in this study, we aimed to develop a novel 3D-printed buoyant structure to suppress biofilm formation. The 10 mm-sized spherical buoyant structure reduced the height and area of the biofilm by 58.3% and 82.5%, respectively. The structure decreased space where bubble burst occurred and controlled the bubble size, reducing the overall biomass loss by 58.7%. It did not reduce photobioreactor performance noticeably during semi-continuous cultivation, indicating the possibility of long-term applicability. In large-scale outdoor microalgae cultivation using flue gas CO2, the buoyant structure improved the cell density and biodiesel production potential without contamination. This study provides a promising strategy to contribute to biological CO2 mitigation through the utilization of flue gas CO2 for enhanced microalgal production, paving the way for energy and environmental sustainability.