Brian Glennon

Characterizing the Metastable Zone Width and Solubility Curve Using Lasentec FBRM and PVM

A successful industrial crystallization typically requires the development of a robust process in the laboratory. Knowledge of the solubility curve and the stability of the solution in the vicinity of the equilibrium point, as indicated by the metastable zone width, is essential to the successful development, optimization, and scale-up of a crystallization process. Use of the Lasentec Focused Beam Refiectance (FBRM) system, with aqueous potash alum solutions, to determine both the metastable zone width and solubility curve is demonstrated. The measured metastable zone width data are also used to estimate the nucleation kinetics of the system. Lasentec Particle Vision and Measurement (PVM) images are also employed to validate the results. The data collected using the FBRM system compare very well with published literature values for potash alum solubility and metastable zone width in aqueous solutions.

Review of membrane aerated biofilm reactors

Membrane aerated biofilm reactors (MABRs) represent a new technology for aerobic wastewater treatment. Oxygen diffuses through a gas permeable membrane into the biofilm where oxidation of pollutants, supplied on the biofilm side of the membrane, takes place. The potential of this system for various wastewater treatment applications is reviewed in the context of recent developments in the understanding of the fundamentals of such systems. The difference between MABRs and conventional biofilm reactors is highlighted by the concept of active layers within biofilms and the importance of active layer location. This review also discusses the choice of membrane in such reactors and the development of mathematical models that describe MABR performance. All published studies on the use of MABRs are discussed under pollutant species headings: organic carbonaceous pollutant biodegradation, volatile organic pollutant removal, and nitrification/denitrification processes.

In‐line FBRM Monitoring of Particle Size in Dilute Agitated Suspensions

The use of laser light scattering technology, as applied by the Focused Beam Reflectance Measurement (FBRM) probe from Lasentec, for the in-line monitoring of particle size was investigated. In particular, the effects of probe position and orientation were studied for a dilute agitated aqueous particulate suspension of known particle size distribution in a number of vessels. In all cases, the normalised chord length distribution recorded with the FBRM system was consistent with the theoretically predicted distribution. However, the total number of counts measured was a function both of solids concentration and probe location. Optimum probe location is dependent on the ease with which the solid phase can be suspended with the available agitation system and on the associated dominant flow direction within the vessel.

Oxygen mass transfer characteristics in a membrane-aerated biofilm reactor.

Immobilization of pollutant-degrading microorganisms on oxygen-permeable membranes provides a novel method of increasing the oxidation capacity of wastewater treatment bioreactors. Oxygen mass transfer characteristics during continuous-flow steady-state experiments were investigated for biofilms supported on tubular silicone membranes. An analysis of oxygen mass transport and reaction using an established mathematical model for dual-substrate limitation supported the experimental results reported. In thick biofilms, an active layer of biomass where both carbon substrate and oxygen are available was found to exist. The location of this active layer varies depending on the ratio of the carbon substrate loading rate to the intramembrane oxygen pressure. The thickness of a carbon-substrate-starved layer was found to greatly influence the mass transport of oxygen into the active biomass layer, which was located close to, but not in contact with, the biofilm-liquid interface. The experimental results demonstrated that oxygen uptake rates as high as 20 g m-2 d-1 bar-1 can be achieved, and the model predicts that, for an optimized biofilm thickness, oxygen uptake rates of more than 30 g m-2 d-1 bar-1 should be possible. This would allow membrane-aerated biofilm reactors to operate with much greater thicknesses of active biomass than can conventional biofilm reactors as well as offering the further advantage of close to 100% oxygen conversion efficiencies for the treatment of high-strength wastewaters. In the case of dual- substrate-limited biofilms, the potential to increase the oxygen flux does not necessarily increase the substrate (acetate) removal rate.

In situ Raman spectroscopy for simultaneous monitoring of multiple process parameters in mammalian cell culture bioreactors.

In this study, the application of Raman spectroscopy to the simultaneous quantitative determination of glucose, glutamine, lactate, ammonia, glutamate, total cell density (TCD), and viable cell density (VCD) in a CHO fed‐batch process was demonstrated in situ in 3 L and 15 L bioreactors. Spectral preprocessing and partial least squares (PLS) regression were used to correlate spectral data with off‐line reference data. Separate PLS calibration models were developed for each analyte at the 3 L laboratory bioreactor scale before assessing its transferability to the same bioprocess conducted at the 15 L pilot scale. PLS calibration models were successfully developed for all analytes bar VCD and transferred to the 15 L scale.

Biofilm Development in a Membrane-Aerated Biofilm Reactor: Effect of Flow Velocity on Performance

The effect of liquid flow velocity on biofilm development in a membrane-aerated biofilm reactor was investigated both by mathematical modeling and by experiment, using Vibrio natriegens as a test organism and acetate as carbon substrate. It was shown that velocity influenced mass transfer in the diffusion boundary layer, the biomass detachment rate from the biofilm, and the maximum biofilm thickness attained. Values of the overall mass transfer coefficient of a tracer through the diffusion boundary layer, the biofilm, and the membrane were shown to be identical during different experiments at the maximum biofilm thickness. Comparison of the results with published values of this parameter in membrane attached biofilms showed a similar trend. Therefore, it was postulated that this result might indicate the mechanism that determines the maximum biofilm thickness in membrane attached biofilms. In a series of experiments, where conditions were set so that the active layer of the membrane attached biofilm was located close to the membrane biofilm interface, it was shown that the most critical effect on process performance was the effect of velocity on biofilm structure. Biofilm thickness and effective diffusivity influenced reaction and diffusion in a complex manner such that the yield of biomass on acetate was highly variable. Consideration of endogenous respiration in the mathematical model was validated by direct experimental measurements of yield coefficients. Good agreement between experimental measurements of acetate and oxygen uptake rates and their prediction by the mathematical model was achieved.

Characteristics of a Methanotrophic Culture in a Membrane-Aerated Biofilm Reactor

The membrane‐aerated biofilm reactor (MABR) shows considerable potential as a bioprocess that can exploit methanotrophic biodegradation and offers several advantages over both conventional biofilm reactors and suspended‐cell processes. This work seeks primarily to investigate the oxidation efficiency in a methanotrophic MABR. A mixed methanotrophic biofilm was immobilized on an oxygen‐permeable silicone membrane in a single tube hollow fiber configuration. Under the conditions used the maximum oxygen uptake rate reached values of 16 g/m2·d, and the rate of biofilm growth achieved was 300 μm/d. Both indicators reflect a very high metabolic rate. It was shown that the biofilm was predominantly in a dual‐substrate limitation regime but below about 250 μm was fully penetrated by both substrates. Oxygen limitation was not observed. Analysis indicated that microbial activity stratification was evident and the location of stratified layers of oxygen‐consuming components of the consortium could be manipulated via the intramembrane oxygen pressure. The results confirm that an MABR can be employed to minimize substrate diffusion limitations in thick biofilms.

Process model comparison and transferability across bioreactor scales and modes of operation for a mammalian cell bioprocess

A Monod kinetic model, logistic equation model, and statistical regression model were developed for a Chinese hamster ovary cell bioprocess operated under three different modes of operation (batch, bolus fed‐batch, and continuous fed‐batch) and grown on two different bioreactor scales (3 L bench‐top and 15 L pilot‐scale). The Monod kinetic model was developed for all modes of operation under study and predicted cell density, glucose glutamine, lactate, and ammonia concentrations well for the bioprocess. However, it was computationally demanding due to the large number of parameters necessary to produce a good model fit. The transferability of the Monod kinetic model structure and parameter set across bioreactor scales and modes of operation was investigated and a parameter sensitivity analysis performed. The experimentally determined parameters had the greatest influence on model performance. They changed with scale and mode of operation, but were easily calculated. The remaining parameters, which were fitted using a differential evolutionary algorithm, were not as crucial. Logistic equation and statistical regression models were investigated as alternatives to the Monod kinetic model. They were less computationally intensive to develop due to the absence of a large parameter set. However, modeling of the nutrient and metabolite concentrations proved to be troublesome due to the logistic equation model structure and the inability of both models to incorporate a feed. The complexity, computational load, and effort required for model development has to be balanced with the necessary level of model sophistication when choosing which model type to develop for a particular application.

Comparison of Morphological Characteristics of Streptomyces natalensis by Image Analysis and Focused Beam Reflectance Measurement

A morphological interpretation is presented for data collected during growth of a filamentous organism, using a focused beam reflectance measurement (FBRM) system. The morphology of the organism was also obtained using conventional semiautomatic image analysis to support the interpretation of the FBRM data. The model organism employed is the filamentous soil‐borne actinomycete Streptomyces natalensis, which produces the antifungal agent pimaricin. The organism was cultivated both in shake flasks and in a bench‐scale stirred tank bioreactor. It was found that FBRM could be used to track changes in the morphology of the organism throughout the course of its growth on both scales. These changes were highlighted using both the median chord length and length‐weighted mean chord length obtained from the chord length distribution measured with the FBRM probe. The ability of the FBRM probe to respond to changes in both the size and morphology of mycelial aggregates was supported by standard image analysis parameters, including equivalent diameter, convex area, and compactness.

Use of focussed beam reflectance measurement (FBRM) for monitoring changes in biomass concentration

The potential of focussed beam reflectance measurement (FBRM) as a tool to monitor changes in biomass concentration was investigated in a number of biological systems. The measurement technique was applied to two morphologically dissimilar plant cell suspension cultures, Morinda citrifolia and Centaurea calcitrapa, to a filamentous bacteria, Streptomyces natalensis, to high density cultures of Escherichia coli and to a murine Sp2/0 hybridoma suspension cell line, 3–2.19. In all cases, the biomass concentration proved to be correlated with total FBRM counts. The nature of the correlation varied between systems and was influenced by the concentration, nature, size and morphology of the particle under investigation.