Pulse Feeding Research Articles

Production of rhamnolipids by integrated foam adsorption in a bioreactor system

Biosurfactants offer environmental as well as health benefits over traditionally used chemical surfactants and heterologous production from engineered microorganisms has been demonstrated, offering containable as well as scalable production of these alternative chemicals. Low product titers and cost intensive downstream processing are the main hurdles for economical biosurfactant production at industrial scales. Increased biosurfactant concentrations are found in the liquid fraction of the foam formed during fermentation of producing microbes. Adsorption of biosurfactants from foam fractions in cultivations may offer a simple concentration and purification method which could enable their cost-effective production. Here, foam adsorption was applied as an in situ method for separation of the rhamnolipid biosurfactants during fermentation of Pseudomonas putida EM383. An integrated process was designed to capture the produced rhamnolipids on hydrophobic adsorbent in packed bed units while minimizing the impact of adsorption on the productivity of the system by recirculating cell-containing collapsed foam flow-through back into the reactor vessel. A stable rhamnolipid production by P. putida EM383 on glucose was performed coupled to this adsorption strategy for 82 h, after which no remaining rhamnolipids were found in the cultivation broth and 15.5 g of rhamnolipids could be eluted from the adsorbent. Rhamnolipid yield from glucose feed was 0.05 g g−1, when up to 2 g L−1 glucose pulse feeding was applied. After solvent evaporation, a product purity of 96% was obtained. The results indicate that the integrated adsorption method can be efficient for simultaneous production and recovery of rhamnolipid biosurfactants from microbial fermentations.

Rational approach to improve ansamitocin P‐3 production by integrating pathway engineering and substrate feeding in Actinosynnema pretiosum

Ansamitocin P-3 (AP-3) produced by Actinosynnema pretiosum is an important antitumor agent for cancer treatment, but its market supply suffers from a low production titer. The role of AP-3 unusual glycolate unit supply on its biosynthesis was investigated in this work by overexpressing the responsible gene cluster asm13-17 in A. pretiosum (WT). As a result, the accumulation of AP-3 and its intermediate glyceryl-S-ACP in the asm13-17-overexpressed strain (Oasm13-17) versus WT was enhanced by 1.94 and 1.49-fold, respectively. To provide a higher supply of another precursor 3-amino-5-hydroxybenzoic acid, asmUdpg was also overexpressed in Oasm13-17 (Oasm13-17:asmUdpg), and an improved AP-3 titer of 680.5 mg/L was achieved in shake flasks. To further enhance the AP-3 titer, a rational fed-batch strategy was developed in bioreactor fermentation of Oasm13-17:asmUdpg; and by pulse feeding 15 g/L fructose and 1.64 g/L isobutanol at 60, 96, and 120 hr, the AP-3 production level reached 757.7 mg/L, which is much higher than ever reported in bioreactors. This work demonstrated that a rational approach combining precursor pathway engineering with substrate feeding was very effective in enhancing the AP-3 titer, and this enabling methodology would be helpful to industrial production of this eye-catching drug.

Anaerobic digestion of municipal sewage under psychrophilic conditions

Abstract The anaerobic digestion of municipal sewage was studied at psychrophilic temperatures (19 °C and 17 °C) in three up-flow anaerobic sludge bed reactors (UASB). A pulsed feeding system was operated for 430 d, during which different hydraulic retention time (HRT) (6, 8, 10, 12, 14, 18, 24 and 36 h) were tested. Granulation of the sludge was observed under the pulsed feeding strategy and a 6 h HRT. Low hydrolysis rates were obtained at HRTs lower than 10 h, as a result of an increased solids accumulation inside the reactor. An HRT of 14 h was identified as the most suitable HRT under the studied temperatures (19 °C and 17 °C), with methane yields of 136 and 117 mL CH4/g of removed chemical oxygen demand (CODremoved), respectively.

Numerical Simulation of Thermal Processes in Welding with Pulsed Electrode Wire Feeding

The use of computational methods allows us to significantly shorten the time required for researches and save welding and other consumables. In addition, the computational methods used in studies make it possible to demonstrate the obtained results with a high degree of accuracy. Computational methods are based on computer-aided mathematical modeling of welding processes. Mathematical modeling is applied specifically to develop models adequately describing various welding processes or interrelation between those processes. The article describes the model that demonstrates the distribution of temperature fields in butt joints during the arc welding with pulsed electrode wire feeding.

A review on oxygen storage capacity of CeO2-based materials: Influence factors, measurement techniques, and applications in reactions related to catalytic automotive emissions control

CeO2 is widely used as a catalyst support component due to its redox property of oxygen storage and release. This unique feature, which is usually referred to as “oxygen storage capacity” (OSC), can be quantitatively evaluated by different methods and techniques. Since the oxygen release benefits oxidation reactions, catalytic activity can be correlated with OSC. The measured amount of OSC can be influenced by a number of factors, such as the nature of the reducing agent, the conditions of reducing gas flow and operation temperature, the aging, the composition, and physical and geometric properties of CeO2-based materials, and the type of analytical technique used. Therefore, these influencing factors include, but are not limited to, the use of H2 or CO as reducing agent, continuous or pulsed feed of reducing agent, the presence of other elements in the CeO2 structure, particle size and surface area, supported catalyst components and aging, etc. This review paper focuses on the measurement of OSC, the effect of influencing factors, and the role of OSC in the typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions. Furthermore, this review addresses the reactions in which the catalytic activity can be correlated with OSC.

A pilot-scale bioprocess to produce amphidinols from the marine microalga Amphidinium carterae: Isolation of a novel analogue

Marine dinoflagellate microalgae belonging to the genus Amphidinium are a key source of an interesting group of polyketide metabolites with potent bioactivities, wide-ranging functional diversity and stereochemical complexity, but low natural availabilities. The feasibility of a microalgae dinoflagellate-based sustainable bioprocess for producing amphidinols (APDNs) by photoautotrophic culture of Amphidinium carterae in a pilot-scale LED-illuminated bubble column photobioreactor (PBR) was therefore investigated. A fed-batch culture mode with pulse feeding strategy provided a growth pattern strongly limited by the availability of phosphate content in the culture medium that stimulated the production of cellular APDNs. Since A. carterae was found to be much more shear-sensitive than other shear-tolerant non-dinoflagellate microalgae, the culture height and air flow rate were established to ensure the absence of damaging levels of hydrodynamic stress. The biomass capacity yielded by the PBR at the end of the culture (0.540 g d.w. L−1 equivalent to 1.70 × 106 cell mL−1) corresponded to that estimated stoichiometrically from the experimentally determined biomass P-molar formula (C329 O126 H732 N69 S3 P1) and the total phosphorus and nitrogen balances. The downstream processing section was initially conceived to recover APDNs excreted by cells into the supernatant. A dry APDN-enriched extract concentration of 49 mg per liter of supernatant was obtained. This purification process led to partitioning of the extract into several fractions and sub-fractions thereof. Only two sub-fractions were studied, yielding thereof highly pure (>95% pure) luteophanol D and lingshuiol A, and a new, roughly purified (>80% pure) APDN, namely amphidinol 20. The percentages of luteophanol D, lingshuiol A and amphidinol 20 by dry weight of the APDN-enriched extract obtained were 1%, 0.39% and 0.31%, respectively, thus representing a concentration in the culture supernatant of 490, 191 and 152 μg L−1, respectively.

An Experimental Study of Thermal Characteristics of Minimally Invasive Cryoprobes in Different Cooling Modes

The use of special software for planning and monitoring cryosurgical operations is one of the main ways to improve the efficiency of cryosurgery. To develop such software, it is necessary to have detailed data on the temperature characteristics of cryoprobes. In this work, time dependences of temperature distributions along the working parts of cryoprobes have been experimentally obtained for two types of minimally invasive cryoprobes in different operation modes (continuous coolant feeding with 100% cooling capacity; pulsed feeding with 20, 40, 60, 80% cooling capacity). The obtained results can be used in computer modeling of multi-probe cryosurgical operations with the use of serially produced cryoprobes and for evaluating the efficiency of the cryoprobes being developed.

The Dynamics of Dry Chemical Powder Particles Towards the Fire Source During Their Pulse Feeding into the Combustion Zone

The Dynamics of Dry Chemical Powder Particles Towards the Fire Source During Their Pulse Feeding into the Combustion Zone

Orthogonal based ANN and multiGA for optimization on WEDM of Ti–48Al intermetallic alloys

As surveyed, many efforts have been made to model the performances of electrical discharge machining (EDM) using artificial neural network (ANN). However, the selections of the network parameters were mostly prepared in a random manner, resulting to unnecessary trials. Thus, orthogonal array (Taguchi) is employed in the procedure of network function and network architecture assortment to avoid excessive random trial experimentations. This proposed orthogonal based ANN modelling is employed on WEDM of Ti–48Al intermetallic alloys. Meanwhile modified multi objective genetic algorithm (multiGA) is used as the optimization technique. Material removal rate (MRR), surface roughness (Ra), cutting speed (Vc) and width of kerf (Dk) are the machining performances considered in this study. Five machining parameters observed from the previous researches are chosen as significant factors to the machining performances in this study, which are pulse on time, pulse off time, peak current, feed rate and servo voltage. Experimental studies are carried out to verify the machining performances suggested by this approach. Feed forward back propagation neural network (FFNN) is found to be the best network type on the selected dataset. Two hidden layer 5–6–6–4 FFNN showed the most precise and generalized network architecture with very good prediction accuracy. The proposed approach, OrthoANN, reduced ANN experimentation time by a large scale and produced viable results for machining optimization when integrated with multiGA.

Targeted poly(3-hydroxybutyrate-co-3-hydroxyvalerate) bioplastic production from carbon dioxide

A microbial production process was developed to convert CO2 and valeric acid into tailored poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) bioplastics. The aim was to understand microbial PHBV production in mixotrophic conditions and to control the monomer distribution in the polymer. Continuous sparging of CO2 with pulse and pH-stat feeding of valeric acid were evaluated to produce PHBV copolyesters with predefined properties. The desired random monomer distribution was obtained by limiting the valeric acid concentration (below 1 gL-1). 1H-NMR, 13C-NMR and chromatographic analysis of the PHBV copolymer confirmed both the monomer distribution and the 3-hydroxyvalerate (3HV) fraction in the produced PHBV. A physical-based model was developed for mixotrophic PHBV production, which was calibrated and validated with independent experimental datasets. To produce PHBV with a predefined 3HV fraction, an operating diagram was constructed. This tool was able to predict the 3HV fraction with a very good accuracy (2% deviation).

Cocurrent and countercurrent extraction based on a novel three-dimensional vortex microextractor

A single-stage cocurrent arrangement was described based on a three-dimensional (3-D) vortex microextractor using the vortex effect, and the 3-D microextractor was further modified to establish a countercurrent arrangement without any interstage pumps or check valves. The 3-D vortex microextractor mainly composed of an inlet channel, two circular chambers, a slender cylindrical connection channel, and an outlet channel. In both cocurrent and countercurrent operations, the flow pattern and extraction performance were investigated and analyzed. In the cocurrent arrangement, the hydraulics experiment results demonstrated that the 3-D vortex microextractor could passively and effectively produce droplets even at high fluxes of the dispersed phase. The extraction experiment results confirmed that the vortex effect of the 3-D microextractor could enhance the shear force and facilitate the production of droplets, consequently enhancing the extraction efficiency. Furthermore, it was experimentally proved that the countercurrent arrangement could be realized relying on the modified 3-D microextractor and alternatively pulsed feeding of both phases.

Assimilation efficiency of sediment-bound PCBs ingested by fish impacted by strong sorption.

Uptake of polychlorinated biphenyls (PCBs) by fish is controlled by the bioavailability of ingested PCBs in the gut and the freely dissolved concentration in the water moving across the gills. The prediction of bioaccumulation in fish relies on models that account for these exposure routes; however, these models typically do not account for incidental ingestion of sediment by fish, which is not well studied. The literature values for the PCB assimilation efficiency in the gut have been reported for compounds in food matrices and not associated with sediment particles. It is also unclear how mitigation strategies that alter PCB bioavailability in sediments affect predictions made by the bioaccumulation models when sediment ingestion is involved. To test the bioavailability of PCBs from treated and untreated sediments, dietary assimilation efficiencies were measured for 16 PCB congeners in mummichogs (Fundulus heteroclitus) that were fed 4 experimental diets. Diets consisted of PCB-spiked earthworms, spiked untreated sediment mixed with earthworms, spiked activated carbon-treated sediment mixed with earthworms, and spiked activated carbon mixed with earthworms. Assimilation efficiencies were determined by calculating the ratio of PCB mass in the fish tissue to the PCB mass in the food after a pulse feeding experiment. Assimilation efficiencies of PCBs associated with earthworm diet were similar to the values reported in the literature. Fish that were fed the PCB-spiked untreated sediment and activated carbon particles exhibited the highest and lowest assimilation efficiencies, respectively, over a wide KOW range. Assimilation efficiencies of sediment-bound PCBs were significantly reduced (31-93% reduction for different congeners) after amendment with activated carbon. The present study indicates that assimilation of PCBs can be reduced by sorption to black carbon. Environ Toxicol Chem 2017;36:3480-3488. © 2017 SETAC.

Fed-Batch Strategies for Production of PHA Using a Native Isolate of Halomonas venusta KT832796 Strain.

In this study, polyhydroxyalkanoates (PHA) accumulation by Halomonas venusta KT832796, a moderate halophilic bacteria isolated from marine source was studied. Both nutritional requirements and process parameters for submerged cultivation of the organism in bioreactor have been standardized. From the shake flask studies, glucose and ammonium citrate as carbon and nitrogen source produced maximum PHA at a ratio 20 with 3.52g/L of dry cell weight and 70.56% of PHA content. However, ammonium sulfate as the nitrogen source was found to be more suitable for fed-batch cultivation. Several feeding strategies including pH-based fed-batch and variants of pulse feeding were studied to improve the PHA levels. pH-based feeding, although improved PHA level to 26g/L, most of the carbon flux was diverted towards biomass formation; hence, the percent PHA was only 39.15% of the dry cell weight. Maximum PHA of 33.4g/L, which corresponded to 88.12% of the dry cell, was obtained from high concentration single pulse method. There was a net 8.65-fold increase in PHA using this feeding strategy when compared to batch studies. According to our knowledge, this is the highest amount of PHA reported for a Halomonas venusta strain.

DNA-SIP based genome-centric metagenomics identifies key long-chain fatty acid-degrading populations in anaerobic digesters with different feeding frequencies

Fats, oils and greases (FOG) are energy-dense wastes that can be added to anaerobic digesters to substantially increase biomethane recovery via their conversion through long-chain fatty acids (LCFAs). However, a better understanding of the ecophysiology of syntrophic LCFA-degrading microbial communities in anaerobic digesters is needed to develop operating strategies that mitigate inhibitory LCFA accumulation from FOG. In this research, DNA stable isotope probing (SIP) was coupled with metagenomic sequencing for a genome-centric comparison of oleate (C18:1)-degrading populations in two anaerobic codigesters operated with either a pulse feeding or continuous-feeding strategy. The pulse-fed codigester microcosms converted oleate into methane at over 20% higher rates than the continuous-fed codigester microcosms. Differential coverage binning was demonstrated for the first time to recover population genome bins (GBs) from DNA-SIP metagenomes. About 70% of the 13C-enriched GBs were taxonomically assigned to the Syntrophomonas genus, thus substantiating the importance of Syntrophomonas species to LCFA degradation in anaerobic digesters. Phylogenetic comparisons of 13C-enriched GBs showed that phylogenetically distinct Syntrophomonas GBs were unique to each codigester. Overall, these results suggest that syntrophic populations in anaerobic digesters can have different adaptive capacities, and that selection for divergent populations may be achieved by adjusting reactor operating conditions to maximize biomethane recovery.

Propionic acid production from corn stover hydrolysate by Propionibacterium acidipropionici

BackgroundThe production of value-added chemicals alongside biofuels from lignocellulosic hydrolysates is critical for developing economically viable biorefineries. Here, the production of propionic acid (PA), a potential building block for C3-based chemicals, from corn stover hydrolysate is investigated using the native PA-producing bacterium Propionibacterium acidipropionici.ResultsA wide range of culture conditions and process parameters were examined and experimentally optimized to maximize titer, rate, and yield of PA. The effect of gas sparging during fermentation was first examined, and N2 was found to exhibit improved performance over CO2. Subsequently, the effects of different hydrolysate concentrations, nitrogen sources, and neutralization agents were investigated. One of the best combinations found during batch experiments used yeast extract (YE) as the primary nitrogen source and NH4OH for pH control. This combination enabled PA titers of 30.8 g/L with a productivity of 0.40 g/L h from 76.8 g/L biomass sugars, while successfully minimizing lactic acid production. Due to the economic significance of downstream separations, increasing titers using fed-batch fermentation was examined by changing both feeding media and strategy. Continuous feeding of hydrolysate was found to be superior to pulsed feeding and combined with high YE concentrations increased PA titers to 62.7 g/L and improved the simultaneous utilization of different biomass sugars. Additionally, applying high YE supplementation maintains the lactic acid concentration below 4 g/L for the duration of the fermentation. Finally, with the aim of increasing productivity, high cell density fed-batch fermentations were conducted. PA titers increased to 64.7 g/L with a productivity of 2.35 g/L h for the batch stage and 0.77 g/L h for the overall process.ConclusionThese results highlight the importance of media and fermentation strategy to improve PA production. Overall, this work demonstrates the feasibility of producing PA from corn stover hydrolysate.

Microstructural morphology and evolution of austenite stainless steel deposited using pulsed laser and wire

A deposition process based on pulsed laser processing and wire feeding was employed in this study to fabricate high-performance components. The microstructural morphology and evolution of SUS304 austenite stainless steel were examined in detail. The thin wall and ladder block samples, considered as two representative structures of metal additive manufacturing, were deposited. It was found that the microstructure is homogeneous in all the deposited samples. For the thin wall, columnar grains, which are normal to the substrate with a growth tendency to the surface and scanning direction, dominate the deposition. Columnar grains along the cooling gradient and equiaxed grains are both observed in the surface. These different grain morphologies result in different microhardness values, and the microhardness in pulsed laser deposition is universally higher than that in a 304 cold rolling metal substrate. For the ladder block, columnar grains are observed along various directions. Further, it is found that the variation in the shape of the molten pools is an essential reason for the evolution of the microstructures with the addition of the deposited layers. It not only change the nucleation condition and cooling directions near the boundaries in the molten pools, but also leads to a recrystallization along the new cooling directions in the heat-affected zone.

Study of metal transfer control in underwater wet FCAW using pulsed wire feed method

A metal transfer control method based on pulsed wire feed technology is adopted to ameliorate the underwater flux-cored arc wet welding quality. The stability of the welding process is improved with appropriate pulse parameters. The influences of pulse parameters on the metal transfer process are clarified using an X-ray transmission method. Pulse frequency has more of an effect on weld appearance and welding stability than pulse duty factor. Thirty to forty hertz is an appropriate frequency bound for a stable metal transfer process. The repelled metal transfer percentage decreases with increasing droplet growth speed. The inertia force shortens the metal transfer period and prompts droplet transfer into the pool. When the pulse frequency is less than 40 Hz, the base speed time is long enough for the inertia force to act on the droplet. But if the pulse frequency is below 20 Hz, the peak wire feed speed will be sustained for a long time, and the short-circuit frequency increases from 1 to 2.5 Hz; as a result, the welding stability and the welding appearance deteriorate. For the wire employed in this study, better welding stability is obtained at 30 Hz, while the pulse duty factor is 2.

Note: Novel trigger pulse feed method for mega-volt gas switch.

It is difficult to feed the trigger pulse into an electrically triggered mega-volt switch, and the present note presents a novel trigger pulse feed method. The trigger pulse is introduced via a damping resistor, which is mounted between the inner and outer cylindrical electrodes of the pulse transmission line. The mega-volt pulse is damped because the voltage is resistively divided by the resistor and trigger cable arrangement. Both the complex breakdown processes of the switch and its insulation issues are experimentally studied. The function and the beneficial effects of the damping resistor, installed together with an additional inductor, are discussed. Finally, the parameters of these two damping components are set to 500 Ω and 2 μH values for which the switch has been demonstrated to work successfully at over 2.3 MV.

Beet molasses-based feeding strategy enhances recombinant thermostable glucose isomerase production by Escherichia coli BL21 (DE3).

The aim of this work was to develop an effective fed-batch feeding strategy to enhance recombinant glucose isomerase (r-GI) production by recombinant Escherichia coli BL21 (DE3) pLysS on an industrially relevant feedstock without the application of an exogenous inducer. Following the batch operation (0 < t < 7H), the effects of pulse and/or continuous feeding of hydrolyzed beet molasses were investigated under five different feeding strategies. The two most promising strategies with respect to r-GI activity were (i) PM-0.05, designed with one pulse feed (t = 7H) followed by a continuous feed and (ii) 2PMF -0.05, designed with two consecutive pulse feeds (t = 7 and 10H) followed by a continuous feed. The continuous feeding of molasses for both fermentation strategies employed the same precalculated feeding rate, μo = 0.05H-1 . The maximum r-GI activities exhibited by PM-0.05 and 2PMF -0.05 were 29,050 and 30,642U dm-3 , respectively. On the one hand, compared to PM-0.05 r-GI activity reached its maximum within a shorter cultivation time (∆tmax = 2H) at 2PMF -0.05, which could be preferable in terms of manufacturing costs and possible risks; on the other hand, PM-0.05 is a simpler fermentation regime compared to 2PMF -0.05 with respect to manipulations that should be considered in large-scale production.

The effects of light, darkness and intermittent feeding on the growth and survival of reared Atlantic bonito and Atlantic bluefin tuna larvae

In larval culture, long light photoperiod regimes are used to maximize ingestion rates by increasing the accessibility to prey and therefore enhancing larval growth. Intermittent feeding could provide a viable alternative to the commonly used continuous feeding regimes that aim to improve larval growth and survival. In this study, we investigate the effect of alternating light/darkness regimes with intermittent feeding on the growth and survival of piscivorous larvae of two Scombrid species: Atlantic bonito, Sarda sarda (Bloch, 1793) and Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758). First we tested if the manipulation of a light regime generated intermittent feeding by analyzing the larval stomach content. Then, we conducted two laboratory experiments to identify the best alternating light regime that maximized larval growth and survival by comparing the results to those obtained using continuous light regimes. The manipulation of light was optimized to provide intermittent feeding opportunities for the larvae, since we discovered a clear interruption of feeding in darkness. An increase in specific ingestion throughout the day was observed in all experiments, reaching a maximum peak late in the day. Bluefin tuna larval growth rates were similar despite different alternating conditions whereas the bonito larvae grew best when provided with light at three hour intervals. In both species, growth under alternating light conditions was similar to the 15 hours continuous light treatment. No differences between the alternating and the continuous light treatments were observed in terms of their survival. Our results suggest that alternating light/feeding periods may have a beneficial effect on ingestion rates; possibly because feeding is less satiation-limited, metabolic costs are lower; or food digestion is more efficient under these conditions. Changes in the light regime, that result in pulse feeding, can thus be an optimal strategy to increase growth at no apparent survival cost in bonito or bluefin tuna larval cultures.