Volumetric Productivity Research Articles

Yield and production cost of Chlorella sp. culture in a Fibonacci-type photobioreactor

In this research work, the performance of a Fibonacci-type photobioreactor scaled to 2500L to produce Chlorella sp. .is presented. The results show that this photobioreactor design kept the Chlorella culture at its optimal temperature, pH and dissolved oxygen levels. Despite the fact of being a closed reactor, the temperature was kept below 30 °C while the dissolved oxygen was maintained below 200 % Sat. under outdoor conditions at which the mean daily solar radiation ranged from 139 to 450 µE/m2s. Under these conditions, a maximum specific growth rate of 0.31 day−1, a biomass concentration of 1.9 g/L, and volumetric biomass productivity of 0.37 g/L day were achieved. The Fibonacci-type tubular photobioreactor presented here offers substantial advances compared to classic tubular photobioreactors, as it has proven to be flexible in its geometric design and it can adapt its parameters to the photosynthetic needs of the microalgae to ensure maximum efficiency, thus making it an alternative to conventional tubular systems. In addition, it is feasible to consider industrial production, since its costs have been estimated as 27.4 €/kg, at an annual production scale of 37 tons.

Development of mL-scale pseudo-perfusion methodologies for high-throughput early phase development studies

Small-scale devices enable rapid development and optimization, and while many exist for fed-batch cultures, there are few comparable devices for high cell density perfusion cultures. To address this gap, pseudo-perfusion methodologies were developed in microwell plates at mL-scale capable of achieving many of the specific characteristics of perfusion culture, including high cell density, cell retention and increased productivity. Pseudo-perfusion was achieved via sedimentation or centrifugation of 24 microwell plates prior to media exchange 1–2 times daily, generating separation efficiencies higher than 90%. Media exchanges commenced on day 3 and achieved perfusion rates of 0.5–1.8 vessel volumes per day (VVD). Pseudo-perfusion methodologies resulted in maximum viable cell densities (VCDs) of up to 42 × 106 cells mL-1, 4.2-fold greater than fed-batch cultures. Volumetric productivities increased by 1.9-fold, generating industrially relevant productivities. Similar performance was observed between sedimentation and centrifugation methodologies, with minor deviations attributed to elongated manipulation times and lower packed cell density prior to separation when sedimentation was used. The microwell plate (MWP) experiments were validated at the 5 L scale and showed comparability in metabolite and growth profiles. The work presents the development of a robust tool for high-throughput development studies which is sensitive to changes in media composition and exchange rate, which could be reliably used for initial screening of high cell density perfusion cultures.

Continuous protein refolding and purification by two-stage periodic counter-current chromatography

Matrix-assisted refolding (MAR) has been used as an alternative to conventional dilution-based refolding to improve recovery and reduce specific buffer consumption. Size exclusion chromatography (SEC) has been extensively used for MAR because of its ability to load and refold proteins at high concentrations. However, the SEC-based batch MAR processes have the disadvantages of requiring longer columns for better separation and product dilution due to a high column-to-sample volume ratio. In this work, a modified operational scheme is developed for continuous MAR of L-asparaginase inclusion bodies (IBs) using SEC-based periodic counter-current chromatography (PCC). The volumetric productivity of the modified SEC-PCC process is 6.8-fold higher than the batch SEC process. In addition, the specific buffer consumption decreased by 5-fold compared to the batch process. However, the specific activity of the refolded protein (110–130 IU/mg) was less due to the presence of impurities and additives in the refolding buffer. To address this challenge, a 2-stage process was developed for continuous refolding and purification of IBs using different matrices in sequential PCCs. The performance of the 2-stage process is compared with literature reports on single-stage IMAC-PCC and conventional pulse dilution processes for refolding L-asparaginase IBs. The 2-stage process resulted in a refolded protein with enhanced specific activity (175–190 IU/mg) and a high recovery of 84%. The specific buffer consumption (6.2 mL/mg) was lower than the pulse dilution process and comparable to the single-stage IMAC-PCC. A seamless integration of the two stages would considerably increase the throughput without compromising other parameters. High recovery, throughput, and increased operational flexibility make the 2-stage process an attractive option for protein refolding.

Research on the Ignition Process and Flame Stabilization of a Combination of Step and Strut: Experimental and Numerical Study

A combined application of step and strut was put forward to achieve reliable ignition and flame stabilization. In this work, the ignition process and temperature distribution have been tested, and a new reduction approach applied to jet fuel oxidation mechanism was developed to present a flow map via tracking C and H reaction paths, then the minor and major reactions were verified according to relative occurrence probabilities. With the half decrease of mechanism size, bias occurred and was controlled within 1.8%. This reduction method had such characteristics as universality, intuition, and quantification, due to its inherent simplification theory. This simulation of ignition process was always consistent with experimental results, which depicted kernel generation, flamelet breakup and flame propagation. Also, the influence of inlet temperature on outlet temperature and component distribution was performed, the biases of experimental and numerical results were within 5%. Chemical characteristics of Kerosene/air premixed combustible had changed and side reactions occurred to jet fuel above 900 K, which led to a converse effect on flame spreading. The side reactions aggravated the increasing coproducts of CO and CH4, which caused the decrease of volumetric heat production.

Large-scale micro-aerobic digestion studies at municipal water resource recovery facilities for process-integrated biogas desulfurization

Biogas generated from anaerobic digestion processes typically requires gas conditioning including hydrogen sulfide removal before it is used on-site to generate electricity and heat or before upgrading to biomethane for gas pipeline distribution or vehicle fuel. Experiments of process-integrated micro-aeration in three different large-scale sludge digesters (effective volume 2450 m3, 3250 m3 and 3300 m3) were undertaken at municipal wastewater treatment plants and compared with large-scale applications reported in literature. This work discusses critical process parameters, advantages, and potential limitations of micro-aerobic digestion in comparison with other commonly used biogas desulfurization methods. It shows that high H2S reduction in the biogas can be obtained and that the H2S reduction is dependent not only on the air injection rate and location, but also on the digestion activity identified by the volumetric biogas production. Reliability testing of typical micro-aerobic upset scenarios and long-term micro-aerobic digester operation as part of this study provided deeper insights in the MA process that could also provide valuable input to what operational, maintenance and safety measures should be considered when applying micro-aeration in large-scale digesters. The large-scale micro-aerobic digestion trials demonstrated that the hydrogen sulfide concentration in the biogas can be controlled using minimal plant upgrades, contributing to the sustainability and economic efficiency of the energy recovery process of waste sludge digestion at water resource recovery facilities.

Multi-criteria analysis of cell-recycle based continuous lactic acid production process

ABSTRACT This study focuses on the optimization of the cell-recycle based continuous lactic acid (LA) fermentation production process with the estimation of improved kinetic parameters. The non-dominated sorting genetic algorithm II (NSGA-II) is used considering seven variables and five imposed constraints for multi-objective optimization (MOO) study. Three objectives namely LA productivity, substrate conversion, and yield are formed for the maximization purpose. Three different cases are constructed by using a combination of two bi-objectives and one tri-objective optimization problem, and the modified differential evolution (MDE) algorithm is used to individually optimize each case. Pareto ranking is carried out for MOO, and the best optimal solution is determined using the technique for order preference by similarity to the ideal solution (TOPSIS) method. The highest value of volumetric productivity of LA (184.363 kg/m3.h) is reported in case-4a. The highest yield (1.176) is reported in case-2, while the highest substrate conversion (0.963) is reported in case-1.

Protease from Bacillus subtilis ZMS-2: Evaluation of production dynamics through Response Surface Methodology and application in leather tannery

Proteolytic enzymes are the most versatile and commercially viable group of enzymes comprising over 65% share in the global enzyme market amongst which alkaline proteases have extensive applications in detergent and leather industry. Current study was designed to assess the potential of an alkaline serine protease from Bacillus subtilis ZMS-2 as a bating agent in leather processing. Initially, the production parameters were investigated through Response Surface Methodology (RSM) using Plackett-Burman Design, which identified substrate, agitation speed and incubation temperature as the most significant factors. The optimal levels of these factors were determined through the Box-Behnken experimental analysis as 0.436% substrate concentration, 36.5 °C incubation temperature and 56 rpm agitation speed. The statistical optimization experiments increased the volumetric production of enzyme by 3.94 times (2246 U mL−1) than the initial titer (571 U mL−1). The enzyme was partially purified and characterized as metal ions and detergent compatible serine protease having optimum activity at pH 8 and 60 °C. During the pilot-scale application as a bating agent, the enzyme (340 U mL−1) successfully removed the hair roots and other unwanted proteins from goat skins as observed during scudding and confirmed through Scanning Electron Microscopy. The processed skins displayed enhanced porosity, thumb impression, smoothness and pliability. These findings provide a strong basis for the use of this protease as an efficient and eco-friendly alternative for bating of animal skins in leather tanneries.

Fermentation of Sweet Sorghum (Sorghum bicolor L. Moench) Using Immobilized Yeast (Saccharomyces cerevisiae) Entrapped in Calcium Alginate Beads

As the population grows, there is a need to address the continuous depletion of non-renewable energy sources and their negative effects on the environment. This led to a substantial assessment of possible innovations and raw materials to increase the volumetric productivity of alternative fuels to supply the energy needed worldwide. In addition to its environment-friendly properties, a biofuel derived from plant-based sources is also a sustainable material. For high ethanol production from plant-based biofuel, several techniques have been developed, including cell or enzyme immobilization. The key purposes of utilizing immobilized cells or enzymes are to improve bioreactor yield with upgraded enzyme establishment and to increase enzyme utilization. The fermentation of sweet sorghum extract to produce ethanol was conducted in this study, and it was found that the optimum sodium alginate concentration for immobilizing yeast is 3% w/v. It was also found that the free yeast has a shorter optimum fermentation period which is four days (96 h), in comparison with the immobilized yeast, which is five days (120 h). The immobilized yeast has a higher ethanol concentration produced and percent conversion compared to the free yeast. The immobilized yeast entrapped in calcium alginate beads permitted ten five-day (120 h) reuse cycles which are still in stable final ethanol concentration and percent conversion. Due to a lack of experimental support in the necessary condition (optimum level of the number of fermentation days and the concentration of sodium alginate) for the optimal ethanol yield from the extract of sweet sorghum, this study was conducted. This study also tried to address the global demand for ethanol by specifying the optimum conditions necessary for efficient fermentation, specifically for ethanol production using an extract from sweet sorghum. Furthermore, this experimental work serves as a basis for further investigations concerning ethanol production from Agri-based materials, such as sweet sorghum.

Optimization of co-culture condition with respect to aeration and glucose to xylose ratio for bioethanol production

ABSTRACT The present study was designed to find a suitable microaerobic condition and ratio of glucose and xylose for maximum ethanol production using co-culture of Saccharomyces cerevisiae and Pichia stipitis. The maximum ethanol concentration and yield were achieved at 0.05 vvm aeration rate and 2:1 glucose/xylose ratio. The co-culture resulted in maximum ethanol concentration, ethanol yield, and volumetric productivity of 12.33 ± 0.10 g/L, 0.43 g/g, and 0.26 g/L/h, respectively. While, the monoculture of P. stipitis resulted in 8.96 ± 0.13 g/L, 0.36 g/g, and 0.19 g/L/h respectively. The fermentation carried out in microaerobic mode delivered 10.68% and 10.56% more ethanol concentration and ethanol yield respectively from glucose compared to the combination of anaerobic and microaerobic mode. Also, the glucose uptake rate increased to 0.83 g/L/h, which corresponds to an improvement of 50.16%, suggesting that the lower microaerophilic condition not only supports P. stipitis metabolism but also does S. cerevisiae to convert glucose faster in a co-culture system. Hence, co-culture cultivation in microaerobic mode would be a better condition to achieve maximum ethanol and productivity.

Membrane-based continuous fermentation with cell recycling for propionic acid production from glycerol by Acidipropionibacterium acidipropionici

BackgroundMicrobial production of propionic acid (PA) from renewable resources is limited by the slow growth of the producer bacteria and product-mediated inhibition. The present study evaluates high cell density continuous PA fermentation from glycerol (Gly) using Acidipropionibacterium acidipropionici DSM 4900 in a membrane-based cell recycling system. A ceramic tubular membrane filter of 0.22 μm pore size was used as the filtering device for cell recycling. The continuous fermentations were run sequentially at dilution rates of 0.05 and 0.025 1/h using varying glycerol concentrations and two different yeast extract concentrations.ResultsPA volumetric productivity of 0.98 g/L.h with a product yield of 0.38 gPA/gGly was obtained with 51.40 g/L glycerol at a yeast extract concentration of 10 g/L. Increasing the glycerol and yeast extract concentrations to 64.50 g/L and 20 g/L, respectively, increased in PA productivity, product yield, and concentration to 1.82 g/L.h, 0.79 gPA/gGly, and 38.37 g/L, respectively. However, lowering the dilution rate to 0.025 1/h reduced the production efficiency. The cell density increased from 5.80 to 91.83 gCDW/L throughout the operation, which lasted for a period of 5 months. A tolerant variant of A. acidipropoinici exhibiting growth at a PA concentration of 20 g/L was isolated at the end of the experiment.ConclusionsApplying the current approach for PA fermentation can overcome several limitations for process industrialization.

From start-up to maximum loading: An approach for methane production in upflow anaerobic sludge blanket reactor fed with the liquid fraction of fruit and vegetable waste

This investigation provides a reproducible approach for determining the limits of an upflow anaerobic sludge blanket (UASB) reactor designed for the methanization of the liquid fraction of fruit and vegetable waste (FVWL). Two identical mesophilic UASB reactors were operated for 240 days with a three-day fixed hydraulic retention time and an organic load rate (OLR) increased from 1.8 to 10 gCOD L−1 d−1. Because of the previous estimation of flocculent-inoculum methanogenic activity, it was possible to design a safe OLR for the quick start-up of both UASB reactors. The operational variables obtained from the operation of the UASB reactors did not show statistical differences, ensuring the experiment's reproducibility. As a result, the reactors achieved methane yield close to 0.250 LCH4 gCOD−1 up to the OLR of 7.7 gCOD L−1 d−1. Furthermore, the maximum volumetric methane production rate of 2.0 LCH4 L−1 d−1 was discovered for the OLR ranges between 7.7 and 10 gCOD L−1 d−1. The possible overload at OLR of 10 gCOD L−1 d−1 resulted in a significant reduction of methane production in both UASB reactors. Based on the methanogenic activity of the UASB reactors sludge, a maximum loading capacity of approximately 8 gCOD L−1 d−1 was estimated.

Metabolic Engineering for Efficient Ketocarotenoid Accumulation in the Green Microalga Chlamydomonas reinhardtii.

Astaxanthin is a valuable ketocarotenoid with various pharmaceutical and nutraceutical applications. Green microalgae harbor natural capacities for pigment accumulation due to their 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Recently, a redesigned ß-carotene ketolase (BKT) was found to enable ketocarotenoid accumulation in the model microalga Chlamydomonas reinhardtii, and transformants exhibited reduced photoinhibition under high-light. Here, a systematic screening by synthetic transgene design of carotenoid pathway enzymes and overexpression from the nuclear genome identified phytoene synthase (PSY/crtB) as a bottleneck for carotenoid accumulation in C. reinhardtii. Increased ß-carotene hydroxylase (CHYB) activity was found to be essential for engineered astaxanthin accumulation. A combined BKT, crtB, and CHYB expression strategy resulted in a volumetric astaxanthin production of 9.5 ± 0.3 mg L-1 (4.5 ± 0.1 mg g-1 CDW) in mixotrophic and 23.5 mg L-1 (1.09 mg L-1 h-1) in high cell density conditions, a 4-fold increase compared to previous reports in C. reinhardtii. This work presents a systematic investigation of bottlenecks in astaxanthin accumulation in C. reinhardtii and the phototrophic green cell factory design for competitive use in industrial biotechnology.

Process intensification strategies towardcell culture-based high-yield production of a fusogenic oncolytic virus.

We present a proof-of-concept study for production of a recombinant vesicular stomatitis virus (rVSV)-based fusogenic oncolytic virus (OV), rVSV-Newcastle disease virus(NDV), at high cell densities (HCD). Based on comprehensive experiments in 1 L stirred tank reactors (STRs) in batch mode, first optimization studies at HCD were carried out in semi-perfusion in small-scale cultivations using shake flasks. Further, a perfusion process was established using an acoustic settler for cell retention. Growth, production yields, and process-related impurities were evaluated for three candidate cell lines (AGE1.CR, BHK-21, HEK293SF)infected at densities ranging from 15 to 30 × 106 cells/mL. The acoustic settler allowed continuous harvesting of rVSV-NDV with high cell retention efficiencies (above 97%) and infectious virus titers (up to 2.4 × 109 TCID50 /mL), more than 4-100 times higher than for optimized batch processes. No decrease in cell-specific virus yield (CSVY) was observed at HCD, regardless of the cell substrate. Taking into account the accumulated number of virions both from the harvest and bioreactor, a 15-30 fold increased volumetric virus productivity for AGE1.CRand HEK293SF was obtained compared to batch processes performed at the same scale. In contrast to all previous findings, formation of syncytia was observed at HCD for the suspension cells BHK 21 and HEK293SF. Oncolytic potency was not affected compared to production in batch mode. Overall, our study describes promising options for the establishment of perfusion processes for efficient large-scale manufacturing of fusogenic rVSV-NDV at HCD for all three candidate cell lines.

Comprehensive metabolomics reveals correlation between sophorolipid biosynthesis and autophagy

Sophorolipids are biobased and biodegradable glycolipid surface-active agents contributing to the shift from petroleum to biobased surfactants, associated with clear environmental benefits. However, their production cost is currently too high to allow commercialisation. Therefore, a continuous sophorolipid production process was evaluated, i.e., a retentostat with an external filtration unit. Despite an initial increase in volumetric productivity, productivity eventually declined to almost 0 g L−1 h−1. Following comprehensive metabolomics on supernatant obtained from a standardised retentostat, we hypothesised exhaustion of the N-starvation-induced autophagy as the main mechanism responsible for the decline in bolaform sophorolipid productivity. Thirty-six metabolites that correlate with RNA/protein autophagy and high sophorolipid productivity were putatively identified. In conclusion, our results unveil a plausible cause of this bola sophorolipid productivity decline in an industrially relevant bioreactor set-up, which may thus impact majorly on future yeast biosurfactant regulation studies and the finetuning of bola sophorolipid production processes.

Immobilization techniques improve volumetric hydrogen productivity of Caldicellulosiruptor species in a modified continuous stirred tank reactor

BackgroundCo-cultures and cell immobilization have been used for retaining biomass in a bioreactor, with the aim to improve the volumetric hydrogen productivity (QH2). Caldicellulosiruptor kronotskyensis is a strong cellulolytic species that possesses tāpirin proteins for attaching on lignocellulosic materials. C. owensensis has its reputation as a biofilm former. It was investigated whether continuous co-cultures of these two species with different types of carriers can improve the QH2.ResultsQH2 up to 30 ± 0.2 mmol L−1 h−1 was obtained during pure culture of C. kronotskyensis with combined acrylic fibres and chitosan. In addition, the yield of hydrogen was 2.95 ± 0.1 mol H2 mol−1 sugars at a dilution rate (D) of 0.3 h−1. However, the second-best QH2 26.4 ± 1.9 mmol L−1 h−1 and 25.4 ± 0.6 mmol L−1 h−1 were obtained with a co-culture of C. kronotskyensis and C. owensensis with acrylic fibres only and a pure culture of C. kronotskyensis with acrylic fibres, respectively. Interestingly, the population dynamics revealed that C. kronotskyensis was the dominant species in the biofilm fraction, whereas C. owensensis was the dominant species in the planktonic phase. The highest amount of c-di-GMP (260 ± 27.3 µM at a D of 0.2 h−1) were found with the co-culture of C. kronotskyensis and C. owensensis without a carrier. This could be due to Caldicellulosiruptor producing c-di-GMP as a second messenger for regulation of the biofilms under the high dilution rate (D) to prevent washout.ConclusionsThe cell immobilization strategy using a combination of carriers exhibited a promising approach to enhance the QH2. The QH2 obtained during the continuous culture of C. kronotskyensis with combined acrylic fibres and chitosan gave the highest QH2 among the pure culture and mixed cultures of Caldicellulosiruptor in the current study. Moreover, it was the highest QH2 among all cultures of Caldicellulosiruptor species studied so far.

De novo tryptophanase-based indole production by metabolically engineered Corynebacterium glutamicum

Indole has an increasing interest in the flavor and fragrance industry. It is used in dairy products, tea drinks, and fine fragrances due to its distinct floral odor typical of jasmine blossoms. The current production of indole based on isolation from coal tar is non-sustainable and its isolation from plants is often unprofitable due to low yields. To offer an alternative to the conventional production, biosynthesis of indole has been studied recently. A glucose-based indole production was achieved by employing the Corynebacterium glutamicum tryptophan synthase α-subunit (TrpA) or indole-3-glycerol phosphate lyase (IGL) from wheat Triticum aestivum in a genetically-engineered C. glutamicum strain. In addition, a highly efficient bioconversion process using C. glutamicum heterologously expressing tryptophanase gene (tnaA) from Providencia rettgeri as a biocatalyst was developed. In this work, de novo indole production from glucose was enabled by expressing the P. rettgeri tnaA in a tryptophan-producing C. glutamicum strain. By metabolic engineering of a C. glutamicum shikimate accumulating base strain, tryptophan production of 2.14 ± 0.02 g L-1 was achieved. Introduction of the tryptophanase form P. rettgeri enabled indole production, but to low titers, which could be improved by sequestering indole into the water-immiscible solvent tributyrin during fermentation and a titer of 1.38 ± 0.04 g L-1 was achieved. The process was accelerated by decoupling growth from production increasing the volumetric productivity about 4-fold to 0.08 g L-1 h-1.Key points• Efficient de novo indole production via tryptophanases from glucose• Increased indole titers by product sequestration and improved precursor supply• Decoupling growth from production accelerated indole production

Culture depth effect on Scenedesmus sp. growth, photo-physiology and nutrient removal rate in anaerobically digested abattoir effluent

Here, we evaluated the effect of culture depth on the growth and nutrient removal rate of Scenedesmus sp. grown in anaerobically digested abattoir effluent (ADAE) and cultivated semi-continuously in raceway ponds at depths of 14 cm, 17 cm, 20 cm, and 23 cm during Austral winter and summer. Culture medium pH was kept constant at pH 6.5 for all treatments throughout the experimental period using a pH–stat system. Algal cultures grown in summer had 2.3- 2.7 times higher biomass productivity than the same grown in winter. In both seasons, maximum volumetric productivity of this alga was achieved at 14 cm depth (14 cm depth⩾ 17 cm depth⩾ 20 cm depth⩾ 23 cm depth). However, areal biomass productivity of culture grown at 23 cm depth was 12% and 29% higher than that of culture grown at 14 cm depth in winter and summer, respectively. In addition, nitrogen, phosphorus and COD areal removal rates were significantly higher in cultures operated at 23 cm among all treatments in both seasons. The effective quantum yield (Fq'/Fm') in summer was 23 cm depth = 20 cm depth > 17 cm depth = 14 cm depth while it followed 14 cm depth⩾ 17 cm depth⩾ 20 cm depth⩾ 23 cm depth in winter, indicating significance of operational conditions on algal photosynthesis. The outcome of this study shows that, irrespective of the season, operating the culture in higher depths significantly increased areal biomass productivity as well as areal nutrient removal rates when treating ADAE.

Developing a single-stage continuous process strategy for vitamin B12 production with Propionibacterium freudenreichii

BackgroundVitamin B12 is a widely used compound in the feed and food, healthcare and medical industries that can only be produced by fermentation because of the complexity of its chemical synthesis. Besides, the use of Generally Recognized as Safe (GRAS) and Qualified Presumption of Safety (QPS) microorganisms, like Propionibacterium freudenreichii, especially non-GMO wild-type producers, are becoming an interesting alternative in markets where many final consumers have high health and ecological awareness. In this study, the production of vitamin B12 using the Propionibacterium freudenreichii NBRC 12391 wild-type strain was characterized and optimized in shake flasks before assessing several scale-up strategies.ResultsInitial results established that: (i) agitation during the early stages of the culture had an inhibitory effect on the volumetric production, (ii) 5,6-dimethylbenzimidazole (DMBI) addition was necessary for vitamin B12 production, and (iii) kinetics of vitamin B12 accumulation were dependent on the induction time when DMBI was added. When scaling up in a bioreactor, both batch and fed-batch bioprocesses proved unsuitable for obtaining high volumetric productivities mainly due to carbon source limitation and propionic acid inhibition, respectively. To overcome these drawbacks, an anaerobic single-phase continuous bioprocess strategy was developed. This culture strategy was maintained stable during more than 5 residence times in two independent cultures, resulting in 5.7-fold increase in terms of volumetric productivity compared to other scale-up strategies.ConclusionOverall, compared to previously reported strategies aimed to reduce propionic acid inhibition, a less complex anaerobic single-phase continuous and more scalable bioprocess was achieved.

High cell density culture of Neochloris oleoabundans in novel horizontal thin-layer algal reactor: Effects of localized aeration, nitrate concentration and mixing frequency

A horizontal thin-layer algal reactor was designed, constructed and tested for high cell density culture of an oil-rich green alga, Neochloris oleoabundans, at a thickness of 6 mm. A hollow fiber membrane sparger was used for localized aeration with CO2-enriched air, which allowed control of culture pH at a narrow range of pH 7.0–7.5. The optimal nitrate concentration under the investigated conditions was 345 mg-N/L with a cell density of ∼6.6 × 108 cells/mL and biomass concentration of ∼8 g/L. The volumetric and areal biomass productivities were 1.81 g/L/day and 10.85 g m− 2/day, respectively, and the maximum volumetric and areal productivities 3.57 g/L/day and 21.42 g m− 2/day, respectively. Intermittent mixing at a frequency of once every two hours (five min mixing each time) produced a cell growth profile similar to that of continuous mixing. Such intermittent mixing resulted in 98.38 % saving on mixing energy and 33.9 % reduction in water evaporation. It was observed that metabolic stress such as high pH and high nitrate concentration could inhibit cell division while causing cell size to enlarge abnormally. The results indicate that it is technically feasible to have high cell density culture of photoautotrophic microalgae with intermittent mixing and no culture circulation, opening the door towards the development of open algal farming systems of low capital, operational, and maintenance costs.

Influence of jet velocity and heat recuperation on the flame stabilization in a non-premixed mesoscale combustor: An exergetic approach

An experimental and numerical model to determine the exergy balance based on flow availability and availability transfer in the process of liquefied petroleum gas (LPG)/air combustion in mesoscale gas turbine combustor is developed to elucidate the second law efficiency and total thermodynamic irreversibility. In terms of developing an energy and exergy-efficient combustor design, the present work highlights the influence of vortex shedding and recirculation in the volumetric entropy production and the exergy efficiency. It is performed in a heat recuperative high-intensity LPG-fueled mesoscale combustor for mini-gas turbine applications. The combustor is operated at different thermal inputs ranging from 0.2 to 1.0 kW under range of equivalence ratios of ϕ = 0.4–1.23. The Favre-averaged governing equations are solved by using finite volume-based approach. The standard k–ε turbulence model with modified empirical constant, Cɛ1=1.6, is considered to model the turbulence quantities. The volumetric reaction-based eddy-dissipation concept model and a reduced skeletal model (50 species and 373 reactions) are used for turbulence–chemistry interaction. The design methodology, total volumetric entropy generation, destructive exergy due to thermodynamic irreversibility, exergy efficiency, flow recirculation, and mixing characteristics (reacting and non-reacting) are reported. The entropy generation rate due to thermal conduction is approximately 50% of the total entropy generation, while its contribution percentage due to chemical reaction is the smallest. The exergy efficiency reaches its peak with ηII = 79.41% at 1.0 kW under fuel-rich condition, while its minimum value of 41.49% is obtained at 0.2 kW under fuel-lean (ϕ = 0.8) condition.