Outdoor Cultivations Research Articles

Pilot-scale microalgae cultivation and wastewater treatment using high-rate ponds: a meta-analysis

Microalgae cultivation in wastewater has been widely researched under laboratory conditions as per its potential to couple treatment with biomass production. Currently, only a limited number of published articles consider outdoor and long-term microalgae-bacteria cultivations in real wastewater environmental systems. The scope of this work is to describe microalgal cultivation steps towards high-rate algal pond (HRAP) scalability and identify key parameters that play a major role for biomass productivity under outdoor conditions and long-term cultivations. Reviewed pilot-scale HRAP literature is analysed using multivariate analysis to highlight key productivity parameters within environmental and operational factors. Wastewater treatment analysis indicated that HRAP can effectively remove 90% of NH4+, 70% of COD, and 50% of PO43−. Mean reference values of 210 W m−2 for irradiation, 18 °C for temperature, pH of 8.2, and HRT of 7.7 are derived from pilot-scale cultivations. Microalgae biomass productivity at a large scale is governed by solar radiation and NH4+ concentration, which are more important than retention time variations within investigated studies. Hence, selecting the correct type of location and a minimum of 70 mg L−1 of NH4+ in wastewater will have the greatest effect in microalgae productivity. A high nutrient wastewater content increases final biomass concentrations but not necessarily biomass productivity. Pilot-scale growth rates (~ 0.54 day−1) are half those observed in lab experiments, indicating a scaling-up bottleneck. Microalgae cultivation in wastewater enables a circular bioeconomy framework by unlocking microalgal biomass for the delivery of an array of products.Graphical

Yield and Composition of the Essential Oil of Clinopodium nepeta subsp. spruneri as Affected by Harvest Season and Cultivation Method, i.e., Outdoor, Greenhouse and In Vitro Culture.

Clinopodium nepeta subsp. spruneri is an aromatic herb with a mint-oregano flavor, used in Mediterranean regions in traditional medicine. The aerial parts of the plant are rich in essential oil that has antioxidant, antimicrobial and anti-inflammatory properties as well as insecticidal activity. The aim of our work was to determine the yield and composition of the essential oil of the plant, in relation to the harvest season and cultivation method, i.e., outdoor, greenhouse and in vitro culture, using gas chromatography-mass spectrometry (GC-MS) as an analytical tool. Essential oil yield fluctuated similarly in outdoor and greenhouse plants during the year (0.9-2.6%), with higher percentages (2.1-2.6%) in the hottest periods June-October (flowering stage) and April (vegetative stage), and was similar to the yield in in vitro plants (1.7%). More compounds were identified in the oil of outdoor and greenhouse plants (35) compared to that of in vitro plants (21), while the main compounds were the same, i.e., pulegone (13.0-32.0%, highest in February-April, 15.0% in vitro), piperitenone oxide (3.8-31.8%, lowest in February, 34.2% in vitro), piperitone epoxide (4.6-16.4%, highest in February, 15.5% in vitro), D-limonene (2.1-8.8%, lowest in February, 10.0% in vitro), isomenthone (2.3-23.0%, highest in February, 4.6% in vitro), germacrene D (1.9-6.5% highest in December-April, 2.9% in vitro) and dicyclogermacrene (2.1-5.3%, highest in December-April, 5.2% in vitro). Therefore, greenhouse and in vitro cultures were equally efficient in yielding essential oil and its constituents as outdoor cultivation, while in outdoor and greenhouse cultivations, the harvest season, mainly due to the prevailing ambient temperatures, affected the essential oil yield and its percentage composition.

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.

The effect of LEDs on Galdieria sulphuraria cultivation at indoor and outdoor condition.

Conventional methods for recovering heavy metals from industrial waste stream often involve significant energy consumption and chemical use. Hence, using microalga as a biosorbent material can be a low-cost and eco-friendly solution. Galdieria sulphuraria is a red microalga which is known to be capable of recovering heavy metals. This algal species is resistant to extreme temperatures and acidic environment. It is also well-established that light emitting diodes (LED) is effective at promoting algal growth. Our research objectives were to study the effects of LED lightings (red, blue, green, and white) on the growth of G. sulphuraria and to compare the growth in indoor and outdoor cultivations. In this work, the culture medium was the modified 2x Allen’s with pH 2.5. To promote the rapid growth of G. sulphuraria, the culture medium was supplemented with 2% CO2. Algal growth was determined by measuring the optical density at 750nm (OD750) using UV-vis spectrophotometer. Results have shown that in indoor cultivation, the growth rate of G. sulphuraria was highest under red light (μ= 0.06 day−1) and lowest under blue light (μ= 0.02 day−1). For outdoor cultivation, algal growth rate increased by 2 to 6-fold higher compared to that in indoor cultivation. Algal cultivation in outdoors was best with white light (OD = 2.46 ± 0.09; μ = 0.13 day−1). Although the use of LEDs enhanced algal growth, we found it did not make a significant difference statistically when compared to the set without LEDs. This may be attributed to the Malaysia’s environment (photoperiods, temperatures, etc.). This paper will serve as a foundation for future research on cultivating G. sulphuraria indoors and outdoors using various LED lights.

Obtaining Bioproducts from the Studies of Signals and Interactions between Microalgae and Bacteria.

The applications of microalgae biomass have been widely studied worldwide. The classical processes used in outdoor cultivations of microalgae, in closed or open photobioreactors, occur in the presence of bacteria. Understanding how communication between cells occurs through quorum sensing and evaluating co-cultures allows the production of microalgae and cyanobacteria to be positively impacted by bacteria, in order to guarantee safety and profitability in the production process. In addition, the definition of the effects that occur during an interaction, promotes insights to improve the production of biomolecules, and to develop innovative products. This review presents the interactions between microalgae and bacteria, including compounds exchanges and communication, and addresses the development of new pharmaceutical, cosmetic and food bioproducts from microalgae based on these evaluations, such as prebiotics, vegan skincare products, antimicrobial compounds, and culture media with animal free protein for producing vaccines and other biopharmaceutical products. The use of microalgae as raw biomass or in biotechnological platforms is in line with the fulfillment of the 2030 Agenda related to the Sustainable Development Goals (SDGs).

Rapidly Improving High Light and High Temperature Tolerances of Cyanobacterial Cell Factories Through the Convenient Introduction of an AtpA-C252F Mutation.

Photosynthetic biomanufacturing is a promising route for green production of biofuels and biochemicals utilizing carbon dioxide and solar energy. Cyanobacteria are important microbial platforms for constructing photosynthetic cell factories. Toward scaled outdoor cultivations in the future, high light and high temperature tolerances of cyanobacterial chassis strains and cell factories would be determinant properties to be optimized. We proposed a convenient strategy for rapidly improving high light and high temperature tolerances of an important cyanobacterial chassis Synechococcus elongatus PCC 7942 and the derived cell factories. Through introduction and isolation of an AtpA-C252F mutation, PCC 7942 mutants with improved high light and high temperature tolerances could be obtained in only 4 days with an antibiotics-free mode. Adopting this strategy, cellular robustness and sucrose synthesizing capacities of a PCC 7942 cell factory were successfully improved.

Hericium: A review of the cultivation, health-enhancing applications, economic importance, industrial, and pharmaceutical applications

Hericium is a genus of edible mushroom with proven medicinal efficacy. The mycelium and basidiomata contain many nutrients and bioactive compounds with therapeutic uses. Recent and emerging evidence has shown that Hericium is helpful to various diseases with medicinal properties, such as anti oxidant, anti cancer, anti diabetic, anti hyperglycemic, hypolipidemic properties, anti inflammatory, anti microbial, anti viral, and hepatoprotective. Over the past decade, many studies have been done on Hericium cultivation to produce enough basidiomata for culinary and medical purposes, due to its rarity in natural habitat. The purpose of this review is to provide the cultivation methods including indoor outdoor cultivations and submerged culture methods, health enhancing applications, economic importance, and industrial applications of Hericium mushroom.

Effects of different light regimes on Dunaliella salina growth and β-carotene accumulation

Outdoor cultivations of microalgae for commercial scale production usually rely on natural sunlight following ‘Sine’ regime, but most lab scale studies adopt ‘Block’ or ‘Continuous’ regimes, leading to poor prediction of outdoor cultivation results. To fill this gap on β-carotene production by Dunaliella salina, the effects of light regimes (‘Block’, ‘Sine’, ‘Continuous’) on cell growth and β-carotene accumulation in D. salina were investigated in this study. The results showed significant difference between these regimes. When receiving the same amount of illumination, ‘Sine’ mode inferred 10–55% higher biomass yield and 31–58% higher β-carotene yield than those under the ‘Block’ mode. The biomass concentration, as well as protein and total fatty acid (TFA) content, has no significant difference between different light regimes, but the starch content in the ‘Continuous’ light regime was higher than that of ‘Sine’ and ‘Block’ regime. β-carotene accumulation under ‘Continuous in summer’ and ‘Simulated diurnal irradiance in summer’ regimes were correlated with increase (C18:1, C18:2) and decrease (C16:4, C18:3) of specific fatty acids (FAs) contents, rather than TFA content. Meanwhile, it was found that β-carotene accumulation was correlated with periodical Fv/Fm fluctuations under different light regimes, and indicate that exposure to periodical strong light is more favorable for β-carotene accumulation, rather than continuous light. These results indicated the significance of using ‘Sine’ light regime since it not only provided better predictions on outdoor production, but also helpful for increase biomass and β-carotene productivities.

Semi-continuous removal of nutrients and biomass production from domestic wastewater in raceway reactors using Chlorella variabilis TH03-bacteria consortia

Abstract Production of algae biomass from wastewaters have been considered as an economical strategy for feasible commercialization of microalgae industry. Technically, large scale cultivation of microalgae in wastewaters should be conducted in semi-continuous and/or continuous modes, in which stable health of algal cultures of previous generations for the use of later generations needs to be ensured. In this regards, this study has investigated stability of growth and pollutant removal capability of Chlorella variabilis TH03-bacteria consortia using domestic wastewater as the sole of nutrient source in raceway ponds. Experiments were performed in semi-continuous mode with the aim of recovering valuable nutrients including carbon, nitrogen and phosphorous from the waste stream to algal biomass. Data revealed that prior domestication of C. variabilis TH03 in unsterilized domestic wastewaters established seed cultures of C. variabilis TH03–bacteria consortia, which enabled to grow effectively in new wastewaters under highly variable conditions. Moreover, once nutrient levels dropped below those required by the national technical regulation on domestic wastewater QCVN 14 : 2008/BTNMT, the replacement of 80% volume of the algal–bacteria culture with new wastewater media was recommended to ensure both culture stability as well as high pollutant treatment capacity of the raceway systems. Under the optimal replacement, biomass concentration and areal biomass productivity of 1.67–1.85 g/L and 11.1–15.3 g/m2 day, respectively, were steadily achieved over 148 days of the outdoor cultivations. Removal efficiencies of nutrients in the form of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorous (TP) removed by the C. variabilis TH03-bacteria consortia in the reactor systems were determined as 64.7–90.7, 85.1–96.8 and 99.7%–100%, respectively. The obtained results are useful for further optimization including design and manage C. variabilis TH03-bacteria consortia based continuous processes in larger scales for the production of high volume and low price biomass, helping to obtain returns from treatment of the waste stream, which is currently considered as a major source of water pollution in Vietnam.

Biomass and pigment production for Arthrospira platensis via semi-continuous cultivation in photobioreactors: Temperature effects.

This study describes the response of Arthrospira platensis to a variety of temperature conditions as reflected in variations of photosynthetic parameters, pigmentation, and biomass productivity in indoor photobioreactor (PBR) cultivations. These experiments are designed to better understand the impact of temperature, seasonal variations, and acclimation effects on outdoor biomass production. The irradiance level and temperature range (20-39°C) are chosen to enable modeling of semi-continuous operation of large-scale outdoor PBR deployments. Overall, the cultivations are quite stable with some pigment-related instabilities after prolonged high-temperature exposure. Changes in productivity with temperature, as reflected in measured photosynthetic parameters, are immediate and mainly attributable to the temperature dependence of the photosaturation parameter, a secondary factor being variation in pigment content on a longer time scale corresponding to turnover of the culture population. Though pigment changes are not accompanied by significant changes in productivity, prolonged exposure at 35°C and above yields a clear degradation in performance. Productivities in a semi-continuous operation are quantitatively reproduced with a productivity model incorporating photosynthetic parameters measured herein. This study confirms the importance of temperature for biomass and pigment production in Arthrospira cultivations and provides a basis for risk assessments related to temperature mitigation for large-scale outdoor cultivations.

A Library of Tunable, Portable, and Inducer-Free Promoters Derived from Cyanobacteria.

Cyanobacteria are emerging as hosts for various biotechnological applications. The ability to engineer these photosynthetic prokaryotes greatly depends on the availability of well-characterized promoters. Inducer-free promoters of a range of activities may be desirable for the eventual large-scale, outdoor cultivations. Further, several native promoters of cyanobacteria are repressed by high carbon dioxide or light, and it would be of interest to alter this property. We started with PrbcL and PcpcB, the well-characterized native promoters of the model cyanobacterium Synechococcus elongatus PCC 7942, found upstream of the two abundantly expressed genes, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase, and phycocyanin β-1 subunit, respectively. The library of 48 promoters created via error-prone PCR of these 300-bp-long native promoters showed 2 orders of magnitude dynamic range with activities that were both lower and higher than those of the wild-type promoters. A few mutants of the PrbcL showed greater strength than PcpcB, which is widely considered a superstrong promoter. A number of mutant promoters did not show repression by high CO2 or light, typically found for PrbcL and PcpcB, respectively. Further, the wild-type and mutant promoters showed comparable activities in the fast-growing and stress-tolerant strains S. elongatus PCC 11801 and PCC 11802, suggesting that the library can be used in different cyanobacteria. Interestingly, the majority of the promoters showed strong expression in E. coli, thus adding to the repertoire of inducer-free promoters for this heterotrophic workhorse. Our results have implications in the metabolic engineering of cyanobacteria and E. coli.

Spirulina sp. LEB 18 cultivation in a raceway-type bioreactor using wastewater from desalination process: Production of carbohydrate-rich biomass

This study aimed to evaluate the biomass production of Spirulina sp. LEB 18 cultivated in wastewater from the desalination process. The outdoor cultivations (210 L) were performed using as culture medium 100% wastewater supplemented with 25% of Zarrouk constituents (Tcs). In parallel, it was performed a control assay using 100% Zarrouk constituents. The biomass production in Tcs assay (1.14 g L-1) was only 9% lower than the control assay (1.25 g L-1). The Tcs assay showed a higher content of carbohydrates (52.29%), lipids (12.79%) and ash (2.69%) compared to the control assay (47.91; 7.59 and 1.29%, respectively). The biomass from the control and Tcs assays had mostly monounsaturated fatty acids C15:1 and C18:2n6t. The Spirulina sp. LEB 18 could use efficiently the nutrients from the wastewater, showing high removal efficiency of NO3– (96.99%), PO4 (83.11%) and Z (96.43%). At the same time, high added value biomolecules were produced for different purposes.

A Novel Cyanobacterium Synechococcus elongatus PCC 11802 has Distinct Genomic and Metabolomic Characteristics Compared to its Neighbor PCC 11801

Cyanobacteria, a group of photosynthetic prokaryotes, are attractive hosts for biotechnological applications. It is envisaged that future biorefineries will deploy engineered cyanobacteria for the conversion of carbon dioxide to useful chemicals via light-driven, endergonic reactions. Fast-growing, genetically amenable, and stress-tolerant cyanobacteria are desirable as chassis for such applications. The recently reported strains such as Synechococcus elongatus UTEX 2973 and PCC 11801 hold promise, but additional strains may be needed for the ongoing efforts of metabolic engineering. Here, we report a novel, fast-growing, and naturally transformable cyanobacterium, S. elongatus PCC 11802, that shares 97% genome identity with its closest neighbor S. elongatus PCC 11801. The new isolate has a doubling time of 2.8 h at 1% CO2, 1000 µmole photons.m−2.s−1 and grows faster under high CO2 and temperature compared to PCC 11801 thus making it an attractive host for outdoor cultivations and eventual applications in the biorefinery. Furthermore, S. elongatus PCC 11802 shows higher levels of key intermediate metabolites suggesting that this strain might be better suited for achieving high metabolic flux in engineered pathways. Importantly, metabolite profiles suggest that the key enzymes of the Calvin cycle are not repressed under elevated CO2 in the new isolate, unlike its closest neighbor.

Development of a monitoring tool based on fluorescence and climatic data for pigments profile estimation in Dunaliella salina

When growing microalgae for biorefinery processes, a high product yield is desired. For that reason, monitoring the concentration of the desired products during growth and products induction procedure is of great interest. 2D Fluorescence spectroscopy is a fingerprinting technique, used in situ and at real time, with a high potential for online monitoring of biological systems. In this work, Dunaliella salina pigment content was monitored using fluorescence data coupled with chemometric tools. Climatic parameters were also used as input variables due to their impact on the pigments profile in outdoor cultivations. Predictive models were developed for chlorophyll content (a, b, and total) with variance captured between 50 and 90%, and R2 varying between 0.6 and 0.9 for both training and validation data sets. Total carotenoids models captured 70 to 80% of variance, and R2 between 0.7 and 0.9, for training and validation. Models for specific carotenoids (zeaxanthin, α-carotene, all-trans-β-carotene, and 9-cis-β-carotene) captured variance between 60 and 90%, with validation and training R2 between 0.6 and 0.9. With this methodology, it was possible to calibrate a monitoring tool for pigments quantification, as a bulk and as individual compounds, proving that 2D fluorescence spectroscopy and climatic data combined with chemometric tools can be used to assess simultaneously and at real time different pigments in D. salina biomass production.

Physical and biological fixation of CO2 with polymeric nanofibers in outdoor cultivations of Chlorella fusca LEB 111

The objective of this study was to cultivate Chlorella fusca LEB 111 with nanofibers indoors and outdoors to verify the effect on CO2 biofixation and macromolecule production. The microalgae were cultured with 10% (w v−1) polyacrylonitrile (PAN)/dimethylformamide (DMF) nanofibers containing 4% (w v−1) iron oxide nanoparticles (NPsFe2O3), which were added to the cultivations at concentrations of 0, 0.1, 0.3 and 0.5 g L−1. The CO2 biofixation was higher in outdoor assays (270.6 and 310.9 mg L−1 d−1) than in indoor assays (124.6 and 131 mg L−1 d−1) with 0.1 and 0.3 g L−1 nanofibers, respectively. The outdoor assays with 0.3 g L−1 nanofibers had 10.9% greater lipid production than the assays without nanofibers. Thus, this first study of outdoor cultivations with nanofibers as physical adsorbents of CO2 showed the effect of nanostructures in maximizing gas biofixation and producing biomolecules that can be used to obtain bioproducts.

Cooling coil led to the collapse of N-replete Haematococcus pluvialis cultures by releasing lethal levels of Cu2+

Photobioreactors for outdoor microalgal cultivation should be equipped with temperature control devices to avoid overheating. However, it is still not clear whether the cooling devices would release poisonous levels of Cu2+ that could affect the growth of microalga. In this study, the half maximal inhibitory concentration (IC50) of Cu2+ was determined by studying the effects of Cu2+ concentrations on the growth and photosynthesis of Haematococcus. Then, the Cu2+ release dynamics were studied by soaking copper cooling coils in water for different times. The results indicated that the IC50 of Cu2+ for Haematococcus was approximately 20 μM (16.9 μM) and, above this level, the growth and photosynthesis were obviously inhibited before astaxanthin production. Meanwhile, after being soaked in water for only 10 h, the copper cooling coil released 40 μM Cu2+, which was 100% higher than the IC50 and high enough to impose severe heavy metal stress on cells. These results indicated that Haematococcus was sensitive to Cu2+. Devices made with copper or copper-containing materials could release lethal levels of Cu2+ if exposed to a liquid environment and brought into direct contact with microalgal cells. This research sheds some light on the design and operation of cooling systems for outdoor large-scale microalgal cultivations.

Cultivation of oleaginous microalga Scenedesmus obliquus coupled with wastewater treatment for enhanced biomass and lipid production

Coupling microalgae cultivation with wastewater treatment is a promising strategy to purify the waste streams and harvest the enhanced biomass production. In this study, an oleaginous alga Scenedesmus obliquus that was isolated from the dairy wastewater was examined for its bioremediation of municipal wastewater. Water samples, including raw and treated ones, were collected from three wastewater treatment plants at different scales. Under indoor conditions, S. obliquus showed strong nutrient removal efficiency, with nitrogen and phosphorus removal rates being over 99%. The alga grew faster in the raw wastewater (specific growth rates: 0.37−0.45 d−1), whereas more lipids accumulated in the treated wastewater (31.45–35.74%of dry weight). The raw wastewater-based culture was subsequently enlarged by using panel photo-bioreactors (PBRs) in semi-continuous mode. Such outdoor cultivations were conducted twice in different seasons, reflecting the impacts of environmental fluctuation. Results showed that under the natural condition, the hydraulic retention time (HRT)-based culture was significantly impacted by the changeable temperatures and illumination; instead, replacing the medium (i.e. raw wastewater) following biomass concentration rather than HRT made the culture system more stable. An average biomass productivity of 0.22 g L−1 d−1 was obtained, regardless of the changing environmental conditions. These findings may advance the knowledge of employing S. obliquus for raw wastewater treatment at the industrial scale.

Cultivation of Ascochloris sp. ADW007-enriched microalga in raw dairy wastewater for enhanced biomass and lipid productivity

A potential microalgal strain was isolated from dairy industrial effluent contaminated water and genetically identified as a close relative of Ascochloris sp. The current study demonstrates growth, biomass and lipid productivity of Ascochloris sp. ADW007 and simultaneous bioremediation of raw dairy waste water (RDW). Indoor microalgal cultivation studies were conducted in controlled conditions of light and temperature, while outdoor pilot-scale experiments were performed in errant conditions using semi-cylindrical barrel shaped open troughs. The rate of biomass productivity of ADW007 was improved with RDW as growth nutrient in indoor bench-scale (0.102 ± 0.003 g/L/d) and outdoor pilot-scale cultivations (0.207 ± 0.003 g/L/d) when compared with the algal growth in synthetic BG 11 medium (0.086 ± 0.004 g/L/d) and TAP medium (0.099 ± 0.003 g/L/d), respectively. Similarly, in outdoor conditions, the lipid content reached maximum to 34.98 ± 0.21% with volumetric and areal lipid productivities of 0.072 ± 0.001 g/L/d and 9.63 ± 0.08 g/m2/d, respectively. With this, the estimated annual algal oil production is nearly 20,495 ± 1953 gallons/acre/yr, if cultivated throughout the year. C18:0/C18:1 were the predominant fatty acids in lipid which indicates a great potential of ADW007 for biodiesel production and simultaneous bioremediation processes using RDW. Post-harvesting process includes hollow fiber filtration followed by activated carbon treatment and resulted in 95.1, 79.7 and 98.1% reduction in chemical oxygen demand, nitrate and total phosphate, respectively.

Empirical operating strategy to reduce the light-specific energy consumption of a flat-panel airlift photobioreactor with intrinsic static mixers cultivating Thermosynechococcus elongatus BP-1

During photoautotrophic cultivations using optimized synthetic media, light is the limiting “substrate” of high-density cultures, especially throughout outdoor cultivations prohibiting adjustment of photon-flux density (PFD). Convective mass transfer (turbulence) is the method of choice to cope with that limiting effect. Then again, turbulence comes at costs through the energy required for its generation. In this context and based on laboratory data generated with Thermosynechococcus elongatus BP-1, an empiric operating strategy for flat-panel airlift photobioreactors with intrinsic static mixers is suggested. Repeated cultivations were performed from sub- to supra-saturating PFD (180 to 780μmolm−2s−1) at aeration rates ranging from 0.11 to 0.83vvm assessing the cultures' productivities along the courses of biomass concentrations. The results indicate that, owing to the culture-flow directing mixers, there is a strong interrelation between the effects of PFD, biomass concentration and aeration rate (thus energy input) applied. Hereby, the positive impact of directed turbulence on the cultures' performance with respect to productivity and yield was greatest at high biomass concentration (>5gDWL−1) and PFDs with effects becoming less dominant while the latter two were reduced. Based on the quantitative findings and utilizing the easily monitored parameters PFD and biomass concentration, a computational model may be defined automatically controlling the easily adjustable parameter aeration rate. Without a negative influence on cultures' performance, this will allow for both, increase of culture performance at times of intense light and high biomass concentration as well as reduction of operational expenditures (OPEX) at times of dim light or low biomass concentration. Compared to the standard, continuous aeration regime, this may lead to a reduction of energy required for the generation of turbulence of 37%, especially when considering outdoor cultivations in temperate climate zones.

Rescuing ethanol photosynthetic production of cyanobacteria in non-sterilized outdoor cultivations with a bicarbonate-based pH-rising strategy

BackgroundEthanol photosynthetic production based on cyanobacteria cell factories utilizing CO2 and solar energy provides an attractive solution for sustainable production of green fuels. However, the scaling up processes of cyanobacteria cell factories were usually threatened or even devastated by biocontaminations, which restricted biomass or products accumulations of cyanobacteria cells. Thus it is of great significance to develop reliable biocontamination-controlling strategies for promoting ethanol photosynthetic production in large scales.ResultsThe scaling up process of a previously developed Synechocystis strain Syn-HZ24 for ethanol synthesis was severely inhibited and devastated by a specific contaminant, Pannonibacter phragmitetus, which overcame the growths of cyanobacteria cells and completely consumed the ethanol accumulation in the cultivation systems. Physiological analysis revealed that growths and ethanol-consuming activities of the contaminant were sensitive to alkaline conditions, while ethanol-synthesizing cyanobacteria strain Syn-HZ24 could tolerate alkaline pH conditions as high as 11.0, indicating that pH-increasing strategy might be a feasible approach for rescuing ethanol photosynthetic production in outdoor cultivation systems. Thus, we designed and evaluated a Bicarbonate-based Integrated Carbon Capture System (BICCS) derived pH-rising strategy to rescue the ethanol photosynthetic production in non-sterilized conditions. In lab scale artificially simulated systems, pH values of BG11 culture medium were maintained around 11.0 by 180 mM NaHCO3 and air steam, under which the infection of Pannonibacter phragmitetus was significantly restricted, recovering ethanol production of Syn-HZ24 by about 80%. As for outdoor cultivations, ethanol photosynthetic production of Syn-HZ24 was also successfully rescued by the BICCS-derived pH-rising strategy, obtaining a final ethanol concentration of 0.9 g/L after 10 days cultivation.ConclusionsIn this work, a novel product-consuming biocontamination pattern in cyanobacteria cultivations, causing devastated ethanol photosynthetic production, was identified and characterized. Physiological analysis of the essential ethanol-consuming contaminant directed the design and application of a pH-rising strategy, which effectively and selectively controlled the contamination and rescued ethanol photosynthetic production. Our work demonstrated the importance of reliable contamination control systems and strategies for large scale outdoor cultivations of cyanobacteria, and provided an inspiring paradigm for targeting effective solutions.