Multi-Vortex distributor : effect on 2-D fluidized bed reactor performance

The influence of the distributor configuration on the mass transfer and bubble sizes in a 2-D FBR was studied for two types of distributor configurations: A novel multi-vortex (MV) distributor with tuyéres directed vertically and horizontally at different heights. A standard perforated plate distributor (baseline). The ozone decomposition reaction over FCC catalyst was used as an indirect meas-ure of the interphase mass transfer in the bed. The ranged between 0.1 m/s and 0.35 m/s, with air as a fluidizing medium at ambient conditions. The MV distributor displayed a significant improvement in the conversion cies (χmeasured / χPFR). For all velocities an improvement of between 0% and 30% was measured (average improvement of 14.7%). At Uo ≤ 0.2 m/s the improvement distributed evenly about the mean improvement, with a minimum improvement of 10%. The Uc for the respective distributors were determined using absolute pressure fluctuations (baseline distributor) and visual observations (MV distributor) and it was found that the Uc for the MV distributor was lower than that for the baseline: Uc Baceline = 0.30 m/s. Uc MV distributor = 0.25 m/s. The decrease in Uc indicated that the MV distributor induces faster onset of turbulent behaviour in the FBR which negates interphase mass transfer limitations in the FBR. The bubble sizes were measured visually and compared to a pressure signal decomposition technique. The bubble size growth for the MV distributor was estimated at .14 times that of the baseline. Two models were compared to the experimental results, the Kunii-Levenspiel three-phase model and the Thompson generalized bubble-turbulent model. The fitting parameters showed that the mass transfer for the MV distributor is significantly larger than that of the baseline. In addition the MV distributor decreased the axial dispersion in the FBR as Uo → Uoo, which improved the reactor performance to that of an ideal PFR. This phenomenon was observed at Uo > 0.33 m/s.Dissertation (MEng)--University of Pretoria, 2011.Chemical Engineeringunrestricte

Microbial lead(II) precipitation : the influence of growth substrate

The objective of the study was to explore the influence of various growth substrates on the removal of aqueous lead from solution. The fermentation media tested consisted of glucose- and xylose-supplemented LB-broth, with and without CaCO3 as pH buffer. In addition, combinations of the various constituents of LB-broth, i.e. yeast extract, tryptone, and NaCl, were tested. Results from the sugar-supplement runs showed that significant removal of lead, without observable precipitation, was measured both with and without pH buffering (75–90% in 48–72 hours). Significant gas build-up in all runs, and a drop in pH in the unbufferred runs, indicate an anaerobic digestion mechanism with either internal or external sequestration of lead. The LB-broth constituent experiments indicate that even though the commercial growth medium LB-broth exhibited the best performance in terms of lead(II) removal (89%), yeast extract-NaCl complex medium performed nearly as well (80%). Results show that substituting the tryptone with corn steep liquor provided minimal gains in lead removal performance, compared to the yeast extract-NaCl medium. The aqueous lead removed by the yeast extract-only medium was limited to 56% in 144 hours. Dark grey precipitates and pH values greater than 5 indicate that the lead(II) were reduced to elemental lead. The observations also suggest that the growth factors in the LB broth, required by the consortium, can be largely replaced by the yeast extract-NaCl medium.The National Research Foundation of South Africa for the grant, Unique Grant No. 106938.http://www.aidic.it/cetam2018Chemical Engineerin

The influence of shear on the metabolite yield of Lactobacillus rhamnosus biofilms

Please read abstract in the article.http://www.elsevier.com/locate/nbthb201

Succinic acid production by Actinobacillus succinogenes in chemostat and biofilm cultures

Previously published results from a novel, homogeneously distributed shear, tubular fermenter used to study continuous chemostat (high shear) and biofilm (low shear) fermentations (Brink and Nicol, 2014a), were compared to results obtained in the same reactor at intermediate shear conditions as well as batch (biofilm) fermentations of Actinobacillus succinogenes. It was found that the steady-state volumetric production rates increased by nearly an order of magnitude (1.8 g.L−1.h−1 vs 15–17 g.L−1.h−1) as the shear was reduced from the chemostat (1.83 m.s−1) to the lower shear biofilm conditions. The biofilm results indicated similar volumetric production rates for the different shear conditions, while the measured extracellular polymeric substances (EPS) in the biofilm exhibited a significant shear dependence; EPS fractions of 0.50 ± 0.05 g.g−1 vs. 0.16 ± 0.02 g.g−1 for the low and intermediate shear conditions respectively. The cell-based biofilm production rates were shown to be dependent on shear conditions at succinic acid titres less than the growth-maintenance boundary (10 g.L−1), with a reduction in cellular production rate associated with an increase in shear. Under maintenance conditions the cell-based production rates appeared independent of the shear conditions in the fermenter, with the cell-based production rates decreasing with increasing succinic acid titres. The industrial implications are that for succinic acid titres in excess of 10 g.L-1, the same mass of biomass under intermediate shear conditions should exhibit a greater volumetric production rate due to the higher fraction of cells as opposed to EPS. The initial values for the batch cell-based succinic acid production rates corresponded to the steady-state values for biofilms grown under the same continuous conditions. However, during transient operation the production rates exceeded the steady-state values; a lag in the product inhibition response was observed. The transient production rates eventually ceased at succinic acid titres in excess of approximately 60–72 g.L−1; a residual glucose concentration of 20 g.L-1 was measured at the highest succinic acid titre (72 g.L-1), indicating product related inhibition as opposed to substrate depletion. The transient results indicate that a larger average cellbased production rate can be obtained during transient operation when compared to the steady fermentation conditions due to a lag in the succinic acid inhibition during transient operation.http://www.aidic.it/cetam2017Chemical Engineerin

Succinic acid production with Actinobacillus succinogenes : rate and yield analysis of chemostat and biofilm cultures

BACKGROUND: Succinic acid is well established as bio-based platform chemical with production quantities expecting to increase exponentially within the next decade. Actinobacillus succinogenes is by far the most studied wild organism for producing succinic acid and is known for high yield and titre during production on various sugars in batch culture. At low shear conditions continuous fermentation with A. succinogenes results in biofilm formation. In this study, a novel shear controlled fermenter was developed that enabled: 1) chemostat operation where self-immobilisation was opposed by high shear rates and, 2) in-situ removal of biofilm by increasing shear rates and subsequent analysis thereof. RESULTS: The volumetric productivity of the biofilm fermentations were an order of magnitude more than the chemostat runs. In addition the biofilm runs obtained substantially higher yields. Succinic acid to acetic acid ratios for chemostat runs were 1.28±0.2 g.g-1, while the ratios for biofilm runs started at 2.4 g.g-1 and increased up to 3.3 g.g-1 as glucose consumption increased. This corresponded to an overall yield on glucose of 0.48±0.05 g.g-1 for chemostat runs, while the yields varied between 0.63 g.g-1 and 0.74 g.g-1 for biofilm runs. Specific growth rates (μ) were shown to be severely inhibited by the formation of organic acids, with μ only 12% of μmax at a succinic acid titre of 7 g.L-1. Maintenance production of succinic acid was shown to be dominant for the biofilm runs with cell based production rates (extracellular polymeric substance removed) decreasing as SA titre increases. CONCLUSIONS: The novel fermenter allowed for an in-depth bioreaction analysis of A. succinogenes. Biofilm cells achieve higher SA yields than suspended cells and allow for operation at higher succinic acid titre. Both growth and maintenance rates were shown to drastically decrease with succinic acid titre. The A. succinogenes biofilm process has vast potential, where self-induced high cell densities result in higher succinic acid productivity and yield.http://www.microbialcellfactories.com/am201

Applications and immobilization strategies of the copper-centred laccase enzyme : a review

DATA AVAILABILITY STATEMENT: No data was used for the research described in the article.Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.The National Research Foundation (NRF) of South Africa.https://www.cell.com/heliyonChemical Engineerin

The effect of glucose and nitrogen supplementation on cell metabolic activity and the reduction of selenite to elemental selenium by Pseudomonas stutzeri NT-I

Selenite (Se(IV)) readily bio-accumulates as compared to elemental selenium (Se(0)) which is considered to be biologically inert and relatively less toxic, therefore its microbial reduction from selenium laden waters is imperative. This study investigated the effect of glucose (carbon source), NH4Cl (nitrogen source) and the metabolic activity on the reduction of 2 mM Se(IV) by Pseudomonas stutzeri NT-I in order to establish the mechanism employed the bacterium. The experiments were performed aerobically under previously determined optimum conditions. Four batches were compared. These were A) glucose (10 g.L-1) and ammonium chloride (1.604 g.L−1), B) glucose only (10 g.L-1), C) no added glucose or nitrogen, and D) 1 M of the metabolic inhibitor, sodium azide (NaN3). The highest average biomass-based selenite reduction rate of 0.1061 mmol.(g.h) −1 was in the presence of glucose and nitrogen as compared to 0.0638 mmol.(g.h)−1 in the presence of glucose alone. The reduction rate decreased in the batches which did not have either of the nutrients. The lowest average biomass-based reduction rate of 0.026 mmol.(g.h)-1 was measured for the batch which had the NaN3. The overall Se(IV) removal followed a similar trend to the one observed with reduction rate, with highest reduction of 90.83 % recorded in the first batch and the lowest of 35.68 % being in the presence of NaN3.http://www.aidic.it/cetam2020Chemical Engineerin

Microbial Pb(II)-precipitation : the influence of oxygen on Pb(II)-removal from aqueous environment and the resulting precipitate identity

The study aimed to quantify the lead(II) bio-precipitation effectiveness, and the produced precipitate identities, of industrial consortia under aerobic and anaerobic batch conditions. The consortia were obtained from an automotive battery recycling plant and an operational lead mine in South Africa. The experiments were performed in the complex growth medium Luria–Bertani broth containing 80 ppm lead(II). The precipitation and corresponding removal of lead(II) were successfully achieved for both aerobic (yellow/brown precipitate) and anaerobic (dark grey/black precipitate) conditions. The removal of lead(II) followed similar trends for both aeration conditions, with the majority of lead(II) removed within the initial 48 h, followed by a marked decline in removal rate for the remainder of the experiments. The final lead(II) removal ranged between 78.11 ± 4.02% and 88.76 ± 3.98% recorded after 144 h. The precipitates were analysed using XPS which indicated the presence of exclusively PbO and elemental lead in the aerobic precipitates, while PbO, PbS, and elemental lead were present in the anaerobic precipitates. The results indicated an oxidation–reduction mechanism with lead(II) as an electron acceptor in both aerobic and anaerobic conditions, while a sulphide-liberation catabolism of sulphur-containing amino acids was evident exclusively in the anaerobic runs. This study provides the first report of bacterial bio-reduction in aqueous lead(II) to elemental lead through a dissimilatory lead reduction mechanism. It further provides support for the application of bioremediation for the removal and recovery of lead from industrial waste streams through the application of bacterial biocatalysts for direct elemental lead recovery.The National Research Foundation of South Africa for the Grant, Unique Grant No. 106938.https://link.springer.com/journal/137622020-08-16hj2019Chemical Engineerin

Lead biosorption characterisation of Aspergillus piperis

In this study, the Pb(II) adsorption capabilities of the heavy metal tolerant strain of fungus, Aspergillus piperis, were studied. This study involved finding optimal growth conditions using a plating technique, and optimal adsorption conditions using submerged fermentation and fractional factorial experimental design. The adsorption behaviour was then elucidated using isotherm and kinetic models, of which the one surface Langmuir isotherm provided the best fit, with a maximum predicted adsorption capacity of 275.82 mg g−1. The kinetic models suggested that internal mass transfer is the driving force behind the reaction rate. After adsorption, biomass surface characterisation was undertaken using FESEM, EDS, and ATR-FTIR to explain observations. The system was characterised by a cation exchange mechanism with strong carboxyl and organophosphorus group interactions. This study demonstrates that due to the ease of propagation and high adsorption capacity, this locally sourced fungal strain is an ideal adsorbent for industrial Pb(II) bioremediation.Data Availability Statement: The data presented in this study are openly available in the University of Pretoria Research Data Repository at doi:10.25403/UPresearchdata.17086016.The National Research Foundation of South Africa.https://www.mdpi.com/journal/sustainabilityChemical Engineerin

Identifying energy extraction optimisation strategies of Actinobacillus succinogenes

A. succinogenes is well known for utilising various catabolic pathways. A multitude of batch fermentation studies confirm flux shifts in the catabolism as time proceeds. It has also been shown that continuous cultures exhibit flux variation as a function of dilution rate. This indicates a direct influence of the external environment on the proteome of the organism. In this work, ATP production efficiency was explored to evaluate the extent of bio-available energy on the production behaviour of A. succinogenes. It was found that the microbe successively utilised its most-to-least efficient energy extraction pathways, providing evidence of an energy optimisation survival strategy. Moreover, data from this study suggest a pyruvate overflow mechanism as a means to throttle acetic and formic acid production, indicating a scenario in which the external concentration of these acids play a role in the energy extraction capabilities of the organism. Data also indicates a fleeting regime where A. succinogenes utilises an oxidised environment to its advantage for ATP production. Here it is postulated that the energy gain and excretion cost of catabolites coupled to the changing environment is a likely mechanism responsible for the proteome alteration and its ensuing carbon flux variation. This offers valuable insights into the microbe’s metabolic logic gates, providing a foundation to understand how to exploit the system.http://www.mdpi.com/journal/catalystsam2022Chemical Engineerin