Outdoor Raceway Ponds Research Articles

A plant-wide modelling framework to describe microalgae growth on liquid digestate in agro-zootechnical biomethane plants

Microalgae cultivation on liquid digestate from the anaerobic co-digestion of agricultural feedstocks is an interesting option for digestate nutrient removal and resource recovery coupled to biomass generation. Both the reactors considered in such a biorefinery system involve complex bioprocesses. Although different pilot-scale systems coupling anaerobic digestion and algae-based bioremediation processes have been described, no previous attempts to model the entire system are available to date. In this work, a plant-wide model, named ADAB (anaerobic digestion algae-bacteria), is presented, coupling two well-established models for anaerobic digestion (IWA – ADM1) and algae-based bioremediation processes (ALBA). The models were modified with necessary equations and extensions to develop a dedicated model interface. Phosphorous dynamics were integrated, including activity corrections and precipitation processes. The ALBA model was also integrated with thermal modelling to simulate outdoor raceway ponds and greenhouse-covered systems. Solid/liquid separation units for digestate pre-treatment were also included. The prediction consistency of the adopted physicochemical sub-model (PCM) was verified with results from both reference literature and Visual MINTEQ. The reduced complexity of the PCM limits the model field of application, but it results in better computational performance and seems to be particularly suitable to simulate agro-zootechnical digesters. A scenario analysis including different co-digester design and operating conditions was carried out to assess the impacts on microalgae cultivation. It highlighted the importance of a proper biorefinery design and yet a noteworthy robustness of the system performance. The use of the ADAB model can facilitate a more realistic assessment of the technical, environmental, and economic feasibility of full-scale microalgal biorefineries based on digestate.

Poly-β-hydroxybutyrate production by Synechocystis MT_a24 in a raceway pond using urban wastewater.

Poly-β-hydroxybutyrate (PHB) is a potential source of biodegradable plastics that are environmentally friendly due to their complete degradation to water and carbon dioxide. This study aimed to investigate PHB production in the cyanobacterium Synechocystis sp. PCC6714 MT_a24 in an outdoor bioreactor using urban wastewater as a sole nutrient source. The culture was grown in a thin-layer raceway pond with a working volume of 100 L, reaching a biomass density of up to 3.5g L-1 of cell dry weight (CDW). The maximum PHB content was found under nutrient-limiting conditions in the late stationary phase, reaching 23.7 ± 2.2% PHB per CDW. These data are one of the highest reported for photosynthetic production of PHB by cyanobacteria, moreover using urban wastewater in pilot-scale cultivation which multiplies the potential of sustainable cultivation approaches. Contamination by grazers (Poterioochromonas malhamensis) was managed by culturing Synechocystis in a highly alkaline environment (pH about 10.5) which did not significantly affect the culture growth. Furthermore, the strain MT_a24 showed significant wastewater nutrient remediation removing about 72% of nitrogen and 67% of phosphorus. These trials demonstrate that the photosynthetic production of PHB by Synechocystis sp. PCC6714 MT_a24 in the outdoor thin-layer bioreactor using urban wastewater and ambient carbon dioxide. It shows a promising approach for the cost-effective and sustainable production of biodegradable carbon-negative plastics. KEY POINTS: • High PHB production by cyanobacteria in outdoor raceway pond • Urban wastewater used as a sole source of nutrients for phototrophic growth • Potential for cost-effective and sustainable production of biodegradable plastics.

Cultivation of Chlorella sorokiniana in indoor and outdoor raceway ponds under glyphosate stress for bioproduct production

Cultivation of Chlorella sorokiniana in indoor and outdoor raceway ponds under glyphosate stress for bioproduct production

Predicting microalgal biomass yield in outdoor raceway pond cultivation with the empirical modeling approach

Microalgae offer economic prospects in the industrial growth of bioenergetics. Although microalgae cultivation in open raceway ponds is manageable and cost-effective, dynamic environmental parameters can disrupt their growth cycles. Hence, models were developed to predict and optimize large-scale outdoor microalgal production, but many attempts failed to reproduce the predictive ability. This study aims to develop a prediction model for biomass yield in open raceway ponds by integrating two multivariate methods, viz. principal component analysis (PCA) and partial least squares (PLS) regression. The model was developed based on the cultural and environmental findings for cultivating a freshwater chlorophycean microalga Chlorella minutissima in open raceway ponds for two consecutive years. Results obtained from PCA revealed a strong correlation between solar intensity and temperature parameters, accounting for 91% of the variability in the resultant biomass yield. Consequently, PLS regression predictors for model fitting were solar intensity, temperature, relative humidity, and dissolved oxygen concentration. Findings from PLS model demonstrated predicted R2 value of 0.91. Further, the model was validated using the experimental data for the outdoor conditions from available literature and showed significant prediction efficiency up to 97%, with mean absolute errors in the range of 3–21%. Thus, the developed model has the potential to predict the microalgal biomass yield in outdoor raceway ponds accurately.

Outdoor culture of Halamphora coffeaeformis in the semi-arid Pampa of Argentina: A comprehensive analysis of triacylglycerol production for biodiesel

The feasibility of microalgal triacylglycerol (TAG) production for biodiesel remains constrained by high production costs under outdoor conditions. The aim of this study was to evaluate the capacity of an Argentinian strain of the diatom Halamphora coffeaeformis grown in outdoor raceway ponds to produce TAG suitable for biodiesel. The strain was cultured in seawater enriched with a biofertilizer during summer and spring in the semi-arid Pampa of Argentina. The following variables were analysed: 1) growth rate; 2) TAG accumulation; 3) lipid content and quality; 4) dissolved nutrient and physicochemical properties; and 5) climatic conditions. Intracellular TAG accumulation was evaluated with fluorometry by Nile Red. The growth rate and biomass productivity of the species were similar in the two seasons, with approximate values of 1.35 div. day−1 and 61.25 kg.ha−1.day−1, respectively. Total lipid content increased about 4-fold with respect to inocula in the 2 cultures, reaching up to 44.7 % ash free dry weight (AFDW) in summer and 36.4 % AFDW in spring. However, lipid accumulation differed between seasons: neutral lipid accumulation began at 8 days of cultivation in summer and at 19 days in spring. Salinity was the main stressor that accelerated the TAG accumulation in the species, the nutrient levels did not reach limiting values. In spring, precipitation decreased salinity levels, reducing stress and delaying the onset of TAG accumulation. The biodiesel properties inferred from the fatty acid profile of the species meet international standards and their quality ensures good performance in cold climates. Furthermore, the reported lipid productivity of the species (~25.6 kg.ha−1.day−1) is higher than that of the soybean oil used commercially for biodiesel. Based on the results obtained, H. coffeaeformis has potential for exploitation as a renewable source of TAG for biodiesel production in arid and semi-arid environments with access to brackish or marine water.

DISCOVR strain pipeline screening – Part I: Maximum specific growth rate as a function of temperature and salinity for 38 candidate microalgae for biofuels production

To identify high productivity strains for microalgal biofuels generation, the maximum specific growth rate of 38 strains was measured as a function of salinity (i.e., 5, 15, and 35 PSU) and temperature (i.e., at 8 temperatures along a linear gradient from ca. 5 to 45 °C) to determine the most suitable growth medium salinity and best growing season, respectively, for outdoor raceway pond cultivation. The following strains were evaluated: Agmenellum quadruplicatum UTEX 2268, Anabaena sp. ATCC 33081, Arthrospira fusiformis UTEX 2721, Arthrospira platensis UTEX 3086, Chlorella vulgaris NREL 4-C12, Chlorella autotrophica CCMP 243, Chlorella sorokiniana DOE1044, Chlorella sorokiniana DOE 1116, Chlorella sorokiniana DOE 1412 (UTEXB3016), Chlorella vulgaris LRB AZ-1201, Chlorococcum littorale UTEX 117, Chlorococcum sp. UTEX-B P7, Chloromonas reticulata CCALA 870, Coelastrella sp. DOE 0202, Cyanobacterium sp. AB1, Micractinium reisseri NREL 14-F2, Microchloropsis gaditana CCMP1894, Microchloropsis salina CCMP 1776, Monoraphidium sp. MONOR1, Monoraphidium minutum 26B-AM, Nannochloropsis oceanica CCAP 849/10, Oscillatoria cf. priestleyi CCMEE 5020.1-1, Picochlorum celeri TG2-WT-CSM/EMRE, Picochlorum oklahomensis CCMP 2329, Picochlorum renovo NREL 39-A8, Picochlorum soloecismus DOE 101, Porphyridium cruentum CCMP 675, Scenedesmus acutus LRB-AP-0401, Scenedesmus obliquus DOE 0152.z, Scenedesmus obliquus UTEX393,Scenedesmus rubescens NREL 46B-D3, Scenedesmus sp. IITRIND2, Stichococcus minor CCMP 819, Stichococcus minutus CCALA 727, Synechococcus elongatus UTEX2973.1, Tetraselmis striata LANL 1001, Tisochrysis lutea CCMP 1324, and Tribonema minus UTEXB3156. For each strain, the identity and the presence of bacterial cohorts was determined using 18S and 16S rDNA sequencing, respectively. The maximum specific growth rate versus temperature data were also used to determine the activation energies (Arrhenius equation) for most strains. For all strains, the measured salinity and temperature tolerance data were compared to those reported in the literature. The fastest growing strains were down-selected for subsequent biomass productivity measurements in climate-simulation photobioreactors, as reported in the next paper in the issue.

DISCOVR strain screening pipeline – Part III: Strain evaluation in outdoor raceway ponds

In our previous studies, as described in the corresponding Part I and II manuscripts in this Special issue, we selected 12 promising microalgae strains from 38 strains for high biomass productivity based on their salinity preferences, temperature profiles, and biomass growth under simulated outdoor conditions. The 12 strains include 6 cold season strains (Micractium reisseri NREL14-F2, Monoraphidium minutum 26B-AM, Monoraphidium sp. MONOR1, Chlorella vulgaris LRB-AZ-1201, Tetraselmis striata LANL1001, Phaeodactylum tricornutum UTEX646) and 6 warm seasons strains (Scenedesmus obliquus DOE0152.z, Scenedesmus obliquus UTEX393, Chlorella sorokiniana DOE1116, Picochlorum renovo NREL39-A8, Picochlorum celeri TG2-WT-CSM/EMRE, Porphyridium cruentum CCMP7765). Because the preceding screening efforts were completed in indoor systems, this study focuses on quantitatively assessing these strains in outdoor raceway ponds to further eliminate those perform poorly under outdoor conditions. The trials presented in this study, categorized as either cold or warm season experiments based on water temperature, were carried out between February and June in 2018, 2019 and 2020. For each season, a benchmark strain, M. minutum 26B-AM for the cold season and S. obliquus UTEX393 for the warm season, was grown side-by-side with the new strains to provide a baseline for comparing strains cultivated under different weather conditions. The results showed that the cold season benchmark, M. minutum 26B-AM, remained the most productive cold season strain, but two new strains, P. triconutum UTEX646 and T. striata LANL1001, demonstrated robust growth in the presence of weather changes and biological contaminants. For the warm season trials, P. celeri TG2-WT-CSM/EMRE and P. cruentum CCMP675 were 39 % and 11 % more productive than the benchmark with substantially improved culture stability. Biomass compositional analyses of the strains showed that the carbohydrate, lipid (measured as fatty acid methyl esters) and protein account for 5.2–20.6 %, 7.2–11.9 %, and 21.7–53 %, of the ash-free dry matter, respectively.

Year-round sustainable biomass production potential of Nannochloris sp. in outdoor raceway pond enabled through strategic photobiological screening.

Microalgae cultivation utilizes the energy of sunlight to reduce carbon dioxide (CO2) for producing renewable energy feedstock. The commercial success of the biological fixation of carbon in a consistent manner depends upon the availability of a robust microalgae strain. In the present work, we report the identification of a novel marine Nannochloris sp. through multiparametric photosynthetic evaluation. Detailed photobiological analysis of this strain has revealed a smaller functional antenna, faster relaxation kinetics of non-photochemical quenching, and a high photosynthetic rate with increasing light and temperatures. Furthermore, laboratory scale growth assessment demonstrated a broad range halotolerance of 10-70 parts per thousand (PPT) and high-temperature tolerance up to 45°C. Such traits led to the translation of biomass productivity potential from the laboratory scale (0.2-3.0 L) to the outdoor 50,000 L raceway pond scale (500-m2) without any pond crashes. The current investigation revealed outdoor single-day peak areal biomass productivity of 43gm-2 d-1 in summer with an annual (March 2019-February 2020) average productivity of 20gm-2 d-1 in seawater. From a sustainability perspective, this is the first report of successful round-the-year (> 347days) multi-season (summer, monsoon, and winter) outdoor cultivation of Nannochlorissp. in broad seawater salinity (1-57 PPT), wide temperature ranges (15-40°C), and in fluctuating light conditions. Concurrently, outdoor cultivation of this strain demonstrated conducive fatty acid distribution, including increased unsaturated fatty acids in winter. This inherent characteristic might play a role in protecting photosynthesis machinery at low temperatures and inhigh light stress. Altogether, our marine Nannochloris sp. showed tremendous potential for commercial scale cultivation to produce biofuels, food ingredients, and asustainable source for vegetarian protein.

Oxygen stress mitigation for microalgal biomass productivity improvement in outdoor raceway ponds

Dissolved oxygen (DO) concentrations at supersaturated levels are commonly observed in microalgae cultures due to photosynthesis. Unlike cultivation in closed photobioreactors, the impact of excessive oxygen and the mitigation methods in open systems such as raceway ponds have hardly been studied. In this study, photosynthetic rates of Monoraphidium minutum 26B-AM and Scenedesmus obliquus UTEX393, two of the top DISCOVR strains for outdoor raceway cultivation, were compared at different DO levels. Increasing DO from 0 to 30 mg L−1 caused a 36.6 % and 26.1 % reduction in photosynthetic rate for M. minutum 26B-AM and S. obliquus UTEX393, respectively. To improve the outdoor pond biomass productivity of each strain, three oxygen stress mitigation methods were tested. The first method raised the dissolved bicarbonate concentration by an order of magnitude to favor bicarbonate transport into the cell, increasing the CO2:O2 ratio near RuBisCO, thus reducing photorespiration. Although this method increased the observed photosynthesis rate of M. minutum 26B-AM by 26 % and S. obliquus UTEX393 by 13 % in laboratory testing, it failed to improve biomass productivity under outdoor pond conditions for both strains. The second method added sodium sulfite as an oxygen scavenger to chemically lower the DO concentration in the culture. Chemical reduction of dissolved molecular oxygen did not significantly improve the biomass productivity of M. minutum 26B-AM; however, a 10 % improvement in biomass productivity for S. obliquus UTEX393 was observed. The final method sparged cultures with air to strip oxygen out of the liquid medium. This did not improve the biomass productivity of M. minutum 26B-AM, likely due to unfavorable weather conditions during cold season cultivation; however, an improvement of 36 % in biomass productivity was achieved for S. obliquus UTEX393 during the warm season cultivation. Of the three tested methods, air-sparging was the most effective and practical for improving outdoor biomass production.

Long term outdoor microalgal phycoremediation of anaerobically digested abattoir effluent

Sufficient and reliable long-term field data on the growth, productivity and nutrient removal rates of microalgal based wastewater treatment system is essential to validate its overall techno-economic feasibility. Here, we investigated the semi-continuous microalgal cultivation of Scenedesmus sp. in anaerobically digested abattoir effluent (ADAE) for 13 months in outdoor raceway ponds operated at 20 cm depth. This study was initiated with three different cultures consisting of 1) monocultures of Chlorella sp., 2) Scenedesmus sp., and 3) an equal mixed concentration of both microalgae species. However, after 15 weeks, Scenedesmus sp. was found to be the most dominant microalgae species in all the different cultures, even completely taking over the Chlorella sp. monoculture. Over the course of summer and early autumn, the average weekly biomass productivity of Scenedesmus sp. cultures was 12.5 ± 0.6 g m−2 d−1 which was 16% and 30% higher than productivities recorded in spring and winter, respectively. All available ammoniacal nitrogen (NH3–N) was found to be exhausted during each growth period with an average 33.6% nitrogen assimilation rate. The average rate of phosphate and COD (chemical oxygen demand) removals were 85.2% and 37.5% throughout the cultivation period. No significant differences were found in carbohydrate, lipid and protein content of Scenedesmus sp. during different seasons of the year. Over 53% increase in biomass productivity can be achieved if CO2 is added to control culture pH at pH 6.5. Here, we successfully demonstrated reliability of continuous long-term cultivation of microalgae in ADAE for simultaneous wastewater treatment and algal biomass production.

Temperature regulation schemes for improving biomass productivity and nutrient removal rate in outdoor raceway ponds

This study investigated the possibility of enhancing the biomass productivity and nutrient removal of microalgae grown in raceway ponds through temperature regulation. Scenedesmus sp. grown in anaerobically digested abattoir effluent (ADAE) was cultivated outdoor in eight raceway ponds. Seven ponds were subjected to different temperature regulation schemes (from 15 °C to 25 °C) and varying control windows (from 24 h to daytime-only). From the results of this study, an approximate 60 % increase in biomass productivity was observed for ponds operated at a minimum temperature of 15 °C coupled with a 24 h (T15P24) and 12.5 h (T15P12.5) control period in relation to the uncontrolled temperature pond (UTP). Generally, Scenedesmus ponds operated at 15 °C used 60 % less energy for heating, were more efficient in nutrient removal, and showed significantly higher biomass productivities with respect to the uncontrolled/higher temperature regulated ponds. In other words, significant productivity improvements were observed for the systems with lower energy demands.

A novel external reflecting raceway pond design for improved biomass productivity

Outdoor raceway ponds for microalgae cultivation suffer from low biomass productivity due in part to the low photosynthetic photon flux received by the microalgae culture in the mornings and evenings and during the winter months at middle and high latitudes. This study explores the use of external mirrors to reflect additional sunlight onto the culture and increase the incident solar flux at critical times of the day and year. Four designs cultivating Chlorella vulgaris were considered: a raceway pond without mirrors (Configuration A), a pond oriented along the north/south axis with dual east/west mirrors (Configuration B), a pond oriented along the east/west axis with a single north mirror (Configuration C), and a solar tracking rotating pond with a single mirror (Configuration D). The biomass productivity was predicted by coupling the simulated radiative field within the culture to a microalgae growth kinetics model accounting for photolimitation and biomass loss due to respiration. Two different locations were considered, namely Los Angeles, CA, USA and Saint-Nazaire, France. The use of mirrors was predicted to increase the daily culture-area-based and volumetric biomass productivity at both locations and all months of the year. Configuration D yielded the highest biomass productivity year-round. Configuration B had a higher biomass productivity than Configuration C in the summer months and vice versa in the winter months. Overall, Configuration C was considered to be the simplest and most cost-effective method to increase raceway productivity. Indeed, this configuration improved the raceway pond volumetric and culture-area-based biomass productivity by as much as 73% in the winter months compared to Configuration A. Additionally, the impact of operational parameters (initial biomass concentration and culture depth) and design parameters (pond length-to-width ratio and mirror height) were assessed to provide practical recommendations for maximizing biomass productivity.

A novel approach to build algal consortia for sustainable biomass production

In the last decade, microalgae have reemerged as a feedstock for biofuels and a diverse suite of bioproducts. Yet, considerable challenges must be overcome before algal biofuels and bioproducts become technoeconomically viable. At present, single algal strains selected for particular phenotypic traits, such as maximum specific growth rate or lipid content, are commonly scaled for cultivation in open, outdoor raceway ponds. Although this monoculture approach may maximize the production of end products, monocultures are particularly susceptible to crashes associated with environmental variability. An approach that has been proposed to generate more productive and stable microalgal crops is the use of eco-engineered communities, or consortia. However, attempts to construct productive consortia have not been consistently successful. We argue that failures stem from the lack of an eco-engineering approach to design species combinations. Here, we used an in silico method to build consortia before testing their performance against monocultures in the laboratory. Focusing on consortia of Nannochloropsis and Microchloropsis, we measured growth of strains along gradients of light and temperature, as well as in response to a salinity shift. With these data, we used a functional dispersion approach to generate over 8000 consortia combinations. We then tested the 50 most functionally diverse consortia in a laboratory experiment and found that consortia overwhelmingly outperformed monocultures. A positive net biodiversity effect and overyielding was found in the majority of consortia combinations. To our knowledge, this is the first application of an in silico approach to design functionally diverse consortia before laboratory and field testing. Our results highlight the importance of employing a functional diversity approach for consortia design.

Biodiversity and disease risk in an algal biofuel system: An experimental test in outdoor ponds using a before-after-control-impact (BACI) design.

For outdoor cultivation of algal feedstocks to become a commercially viable and sustainable option for biofuel production, algal cultivation must maintain high yields and temporal stability in environmentally variable outdoor ponds. One of the main challenges is mitigating disease outbreaks that leads to culture crashes. Drawing on predictions from the ‘dilution effect’ hypothesis, in which increased biodiversity is thought to reduce disease risk in a community, a teste of whether algal polycultures would reduce disease risk and improve feedstock production efficiencies compared to monocultures was performed. While the positive benefits of biodiversity on disease risk have been demonstrated in various systems, to the best of our knowledge this is the first test in an algal biofuel system. Here, the results a before-after-control-impact (BACI) experimental design to compare mean monoculture (control) and polyculture (impact) yield, stability, and productivity before and after fungal infection when grown in 400-L outdoor raceway ponds are presented. It has been found that polycultures did not experience a reduction in disease risk compared to monocultures or differ in production efficiencies throughout the course of the 43-day experiment. These results show that polyculture feedstocks can maintain similar levels of productivity, stability, and disease resistance to that of a monoculture. Determining whether these results are generalizable or represent one case study requires additional outdoor experiments using a larger variety of host and pathogen species.

Effects of LED lighting on Nannochloropsis oceanica grown in outdoor raceway ponds

Growth in most microalgal mass cultivation systems is light-limited, particularly in raceway ponds (RWP) where the light path is higher. Artificial lighting can be a promising solution to diminishing dark zones and enhance microalgal productivity. Therefore, our goal was to prevent the cell shift from photosynthesis to a respiration-only stage by resorting to LED illumination. Nannochloropsis oceanica cultures were accordingly grown outdoors in a preliminary small-scaleexperiment, followed by pilot-scale trials. In the former, three 3.0-m2 RWP were set up under three distinct conditions: 1) without LEDs (control); 2) LEDs turned on during the night; and 3) LEDs turned on for 24 h. In the pilot-scale trial, one of two 28.9-m2 pilot-scale RWPs was coupled to the best LED setup – determined in the small-scale preliminary experiment – using the same light intensity (normal mode) and half of the intensity (economy mode), with the second RWP serving as a control. In the preliminary experiment, the use of LEDs for 24 h was deemed as not helpful during daytime, before the culture reached ≈0.5 g DW L−1 – when dark zones appeared during the day due to sunlight attenuation in the 0.1 m-deep cultures. Overall, use of LEDs increased biomass growth chiefly by increasing nighttime productivities – materialized in higher chlorophyll, protein, and carbohydrate productivities in LED-lit cultures. A higher impact of LED lighting was observed under lower sunlight irradiances. A preliminary economic analysis indicates that use of LEDs in RWPs outdoors should be considered for high-value metabolites only.

PRODUKSI LIPID ISOLAT BARU MIKROALGA LAUT Skeletonema sp. HASIL KULTUR MASSAL DI OUTDOOR SEBAGAI BAHAN BAKU BIODIESEL

Skeletonema sp. is a type of marine microalgae widely studied for its potentials a raw material for biodiesel due to fast growth, high lipid content and resistant to environmental changes. The aim of this study was to determine specific growth rate, biomass production, lipid content and lipid produksivity of a newly isolated marine microalga Skeletonema sp. mass cultivated in 1 m 2 outdoor raceway pond. This study was conducted from June - December 2019 in the hatchery of Unit PelaksanaTeknis Daerah (UPTD) Purirono Kendari. The alga species was cultivated in a 1m2 raceway pond in outdoors for a month. The alga was cultured using f/2 medium under semi-continuous mode with harvesting every 4 days. Sampling for cell counting was done every two days whereas sampling for biomass and lipid was conducted prior to harvesting (every 4 days). The results showed that the Skeletonema sp. can grow well in a 1 m 2 outdoor raceway pond with an average specific growth rate of 0.30 d-1, biomass yield of 0.62 g/L, biomass productivity of 0.222 g/L, lipid yield of0.28 g/L from biomass dry weight, lipid content of 44.81%, and lipid productivity of 0.092 g/L/h. This study showed that the Skeletonema sp. has the potential to be developed as a raw material for biodiesel due to its high growth rate, biomass and lipid productivity when mass cultured in outdoors.

Biodiversity risk assessment of genetically modified Chaetoceros gracilis for outdoor cultivation.

A genetically modified (GM) strain of the diatom Chaetoceros gracilis expressing the phosphite dehydrogenase gene (ptxD), which is a useful gene both for the biological containment and the avoidance of microbial contamination, was characterized to estimate the risk against the biodiversity by laboratory experiments. GM strain could grow in the medium containing phosphite as a sole source of phosphorus, while its general characteristics such as growth, salt tolerance, heat and dehydration resistance in the normal phosphate-containing medium were equivalent to those of wild type (WT) strain. The increase in potential toxicity of GM strain against plant, crustacean, fish and mammal was also disproved. The dispersal ability of WT strain cultured in an outdoor raceway pond was investigated for 28 days by detecting the psb31 gene in vessels, settled at variable distances (between 5 and 60 m) from the pond. The diatom was detected only in one vessel placed 5 m apart. To estimate the influence on the environment, WT and GM strains were inoculated into freshwater, seawater and soil. The influence on the microbiome in those samples was assessed by 16S rRNA gene amplicon sequencing, in addition to the analysis of the survivability of those strains in the freshwater and the seawater. The results indicated that the effect to the microbiome and the survivability were comparable between WT and GM strains. All results showed that the introduction of the ptxD gene into the diatom had a low risk on biodiversity.

Growth and Biochemical Composition Characteristics of Arthrospira platensis Induced by Simultaneous Nitrogen Deficiency and Seawater-Supplemented Medium in an Outdoor Raceway Pond in Winter.

Arthrospira platensis, a well-known cyanobacterium, is widely applied not only in human and animal nutrition but also in cosmetics for its high amounts of active products. The biochemical composition plays a key role in the application performance of the Arthrospira biomass. The present study aimed to evaluate the growth and biochemical composition characteristics of A. platensis, cultured with a nitrogen-free and seawater-supplemented medium in an outdoor raceway pond in winter. The results showed that the biomass yield could achieve 222.42 g m−2, and the carbohydrate content increased by 247% at the end of the culture period (26 d), compared with that of the starter culture. The daily and annual areal productivities were 3.96 g m−2 d−1 and 14.44 ton ha−1 yr−1 for biomass and 2.88 g m−2 d−1 and 10.53 ton ha−1 yr−1 for carbohydrates, respectively. On the contrary, a profound reduction was observed in protein, lipid, and pigment contents. Glucose, the main monosaccharide in the A. platensis biomass, increased from 77.81% to 93.75% of total monosaccharides. Based on these results, large-scale production of carbohydrate-rich A. platensis biomass was achieved via a low-cost culture, involving simultaneous nitrogen deficiency and supplementary seawater in winter.

Feasibility of Utilizing Wastewaters for Large-Scale Microalgal Cultivation and Biofuel Productions Using Hydrothermal Liquefaction Technique: A Comprehensive Review.

The two major bottlenecks faced during microalgal biofuel production are, (a) higher medium cost for algal cultivation, and (b) cost-intensive and time consuming oil extraction techniques. In an effort to address these issues in the large scale set-ups, this comprehensive review article has been systematically designed and drafted to critically analyze the recent scientific reports that demonstrate the feasibility of microalgae cultivation using wastewaters in outdoor raceway ponds in the first part of the manuscript. The second part describes the possibility of bio-crude oil production directly from wet algal biomass, bypassing the energy intensive and time consuming processes like dewatering, drying and solvents utilization for biodiesel production. It is already known that microalgal drying can alone account for ∼30% of the total production costs of algal biomass to biodiesel. Therefore, this article focuses on bio-crude oil production using the hydrothermal liquefaction (HTL) process that converts the wet microalgal biomass directly to bio-crude in a rapid time period. The main product of the process, i.e., bio-crude oil comprises of C16-C20 hydrocarbons with a reported yield of 50–65 (wt%). Besides elucidating the unique advantages of the HTL technique for the large scale biomass processing, this review article also highlights the major challenges of HTL process such as update, and purification of HTL derived bio-crude oil with special emphasis on deoxygenation, and denitrogenation problems. This state of art review article is a pragmatic analysis of several published reports related to algal crude-oil production using HTL technique and a guide towards a new approach through collaboration of industrial wastewater bioremediation with rapid one-step bio-crude oil production from chlorophycean microalgae.

Development of a microwave‐assisted solvent extraction process for the extraction of high‐value carotenoids from Chlorella biomass

AbstractThe commercial production of carotenoids as bioactive commodities from microalgae has been severely limited due to the nature of the microalgal outer cell matrix. Microwave technology offers a rapid method for obtaining larger amounts of these biochemical compounds. The process facilitates cell‐wall rupture, releasing the inner cell components. Chlorella biomass, raised in an outdoor raceway pond, is used for downstream extraction of carotenoids by following the microwave‐assisted solvent extraction (MAE) approach. The response surface modeling (RSM) strategy was employed to optimize the two independent parameters, power and extraction time, with a two‐level central composite design (CCD). Acetone, hexane, methanol, hexane : acetone (1:1), hexane : ethanol (7:3) were used as solvents of choice. Acetone gave a total carotenoid yield of 0.061 ± 0.003 mg gm−1 under optimum microwave power and time; 130 W and 1.69 min. The optimized yield from hexane was 0.00173 ± 0.005 mg gm−1 with an exposure time of 1 min to 100 W. The total carotenoid yield of the methanol‐based extraction batch was 0.0371 ± 0.004 mg gm−1 with 157 W and 1 min of extraction time. The solvent mixtures of hexane : acetone gave 0.0398 ± 0.002 mg gm−1 (185 W for 1.7 min) and hexane : ethanol gave 0.0383 ± 0.004 mg gm−1 (195 W, 1.6 min), respectively. The results indicate a satisfactory outcome to the process. They also show microwave‐based extraction to be a fast, economic, reproducible, and repeatable method in comparison with the conventional strategies used for recovering the sensitive natural pigments. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd