Chemical and Bioprocess Engineering Research Collection

Chemically resistant parts for flow chemistry, with integrated mixing elements have been produced using the 3D printing process of fused filament fabrication, from poly(etheretherketone). Poly(etheretherketone) has greater chemical resistance than common fused filament fabrication materials such as acrylonitrile butadiene styrene, polypropylene, or even high-performance plastics like poly(etherimide), in addition to having superior thermal resistance and excellent mechanical strength. Printed reactors were demonstrated to be suitable for liquid–liquid extraction and flow chemistry and to be capable of withstanding pressures of at least 30 bar allowing superheated solvents to be used. Burst tests in simple geometries of 20 minute duration have indicated that increased operating pressures of up to 60 bar could be accommodated in future reactor designs. The ability to use fused filament fabrication for these reactors allows highly customisable, cost effective flow reactors and equipment to be fabricated on relatively inexpensive benchtop scale printers. X-ray microcomputed tomography was utilised to non-invasively image and verify the internal structure of the prints to ensure fidelity in reactor fabrication. This non-invasive method of equipment validation shows potential in helping to demonstrate regulatory compliance for bespoke additively manufactured components, for example in continuous pharmaceutical manufacturing where the methods and printer used in this work should be sufficient to produce, (continuous) manufacturing scale equipment.

The accurate ab initio modeling of prototypical and well-representative photoactive interfaces for candidate dye-sensitized solar cells (DSCs) is a perennial problem in physical chemistry. To this end, the use of ab initio density functional theory-based molecular dynamics (AIMD) has been studied here to investigate the effect the choice of functional has on a system mimicking the essential workings of a DSC: the energetic properties of a [bmim]+[NTf2]- room-temperature ionic liquid (RTIL) solvating an N719-sensitizing dye adsorbed onto an anatase-titania (101) surface were scrutinized. In so doing, we glean important insights into how using an RTIL as electrolytic hole acceptor alters and modulates the dynamical properties of the widely used N719 dye. A fully crossed study has been carried out comparing the Becke-Lee-Yang-Parr (BLYP) and Perdew-Burke-Ernzerhof (PBE) functionals, both unsolvated and solvated by the RTIL, both with and without Grimme D3 dispersion corrections. Also, vibrational spectra for the photoactive interface in the DSC configuration were calculated by means of Fourier-transforming atomic mass-weighted velocity autocorrelation functions. The ab initio vibrational spectra were compared to high-quality experimental data and against each other; the effects of various methodological choices on the vibrational spectra were also studied, with PBE generally performing best in producing spectra, which matched the experimental frequency modes typically expected.

The photoactivity of carbon-incorporated titanium dioxide (TiO2) has been widely reported. This study involves a novel approach to the incorporation of carbon into TiO2 through the use of microwave plasma processing. The process involved thermally treating printed TiO2 nanoparticle coatings in a microwave-induced argon-oxygen plasma containing low concentrations of methane. The resulting deposited carbon layer was characterized using XRD, XPS, Raman, UV–vis, ellipsometry, and optical profilometry. It was found that the methane gas was dissociated in the microwave plasma into its carbon species, which were then deposited as a nm-thick layer onto the TiO2 coatings, most likely in the form of graphite. The photovoltaic performances of both the TiO2 and the carbon-incorporated TiO2 were assessed through J-V and IPCE measurements of the N719-sensitized solar cells using the titania as their photoanodes. Up to a 72% improvement in the maximum power density (Pd-max) was observed for the carbon-incorporated TiO2 samples as compared to the TiO2, onto which no carbon was added. This improvement was found to be mainly associated with an increase in the short-circuit current density (Jsc), but independent from the open-circuit voltage (Voc), the filter factor (FF), and the level of dye adsorption. Possible contributory factors to the improved performance of the carbon-incorporated TiO2 were the enhanced electron conductivity and electron lifetime, both of which were elucidated through electrochemical impedance spectroscopy (EIS). When the surface layer was examined using XPS, the optimal carbon content on the TiO2 coating surface was found to be 8.4%, beyond which there was a reduction in the DSSC efficiency.

Hematite nanorod arrays were activated through proper control of annealing conditions. The 100-fold improvement in photocurrent was correlated with increased absorption and Sn doping from the tin oxide coated glass substrate. The low onset potential is attributed to a reduction in surface defects, while the morphology is credited for promoting tin diffusion and facilitating electron transport.

The amelioration of biofouling in industrial processing equipment is critical for performance and reliability. While conventional biocides are effective in biofouling control, they are potentially hazardous to the environment and in some cases corrosive to materials. Enzymatic approaches have been shown to be effective and can overcome the disadvantages of traditional biocides, however they are typically uneconomic for routine biofouling control. The aim of this study was to design a robust and reusable enzyme-functionalized nano-bead system having biofilm dispersion properties. This work describes the biochemical covalent functionalization of silica-based nanobeads (hereafter referred to as Si-NanoB) with Proteinase K (PK). Results showed that PK-functionalized Si-NanoB are effective in dispersing both protein-based model biofilms and structurally altering Pseudomonas fluorescens biofilms, with significant decreases in surface coverage and thickness of 30.1% and 38.85%, respectively, while increasing surface roughness by 19 % following 24 h treatments on bacterial biofilms. This study shows that enzyme-functionalized nanobeads may potentially be an environmentally friendly and cost effective alternative to pure enzyme and chemical treatments.

In this study the use of microwave plasma sintering of nickel oxide (NiOx) particles for use as p-type photoelectrode coatings in dye-sensitized solar cells (DSSCs) is investigated. NiOx was chosen as the photocathode for this application due to its stability, wide band gap and p-type nature. For high light conversion efficiency DSSCs require a mesoporous structure exhibiting a high surface area. This can be achieved by sintering particles of NiOx onto a conductive substrate. In this study the use of both 2.45 GHz microwave plasma and conventional furnace sintering were compared for the sintering of the NiOx particles. Coatings 1 to 2.5 μm thick were obtained from the sintered particles (mean particle size of 50 nm) on 3 mm thick fluorine-doped tin oxide (FTO) coated glass substrates. Both the furnace and microwave plasma sintering treatments were carried out at ~ 450 °C over a 5 minute period. Dye sensitization was carried out using Erythrosin B and the UV-vis absorption spectra of the NiOx coatings were compared. A 44% increase in the level of dye adsorption was obtained for the microwave plasma sintered samples as compared to that obtained through furnace treatments. While the photovoltaic performance of the DSSC fabricated using the microwave plasma treated NiOx coatings exhibited a tenfold increase in the conversion efficiency in comparison to the furnace treated samples. This enhanced performance was associated with the difference in the mesoporous structure of the sintered NiOx coatings.

The emergent realisation of Industry 4.0 principles across biomanufacturing, through recent endeavours, will markedly enhance the development and manufacture of modern therapeutics. Through implementation of digital process models, a greater understanding of the intricate relationship between product quality attributes and manufacturing process performance may be established. While contributing towards accelerated process development, representative process models enable advanced optimisation of process parameters, thus having a tangible impact on the assurance of product quality and manufacturing robustness. Hybrid approaches, which couple mechanistic interpretability with statistical data-fitting, are posed to broaden the value and utility of digital models. To augment the advancement in modelling techniques and high-throughput technology, there is a growing requirement for automated approaches towards data processing and model assembly. In this study, a novel strategy is proposed, which leverages saturation and sigmoidal relationships, along with an underlying material balance framework, for the automated assembly of hybrid dynamic models of cell growth. The proposed hybrid model is compared against an equivalent mechanistic model based on Monod expressions. While both models achieve a reasonable fit against experimental data, the hybrid model demonstrates superior predictive performance. Development of automated hybrid models, as demonstrated in this study, may greatly accelerate process digitalisation across biopharmaceutical manufacture.

The influence of permeate flux on bacterial adhesion to NF and RO membranes was examined using two model Pseudomonas species, namely Pseudomonas fluorescens and Pseudomonas putida. To better understand the initial biofouling profile during NF/RO processes, deposition experiments were conducted in cross flow under permeate flux varying from 0.5 up to 120 L/(h m2), using six NF and RO membranes each having different surface properties. All experiments were performed at a Reynolds number of 579. Complementary adhesion experiments were performed using Pseudomonas cells grown to early-, mid- and late-exponential growth phases to evaluate the effect of bacterial cell surface properties during cell adhesion under permeate flux conditions. Results from this study show that initial bacterial adhesion is strongly dependent on the permeate flux conditions, where increased adhesion was obtained with increased permeate flux, until a maximum of 40% coverage was reached. Membrane surface properties or bacterial growth stages was further found to have little impact on bacterial adhesion to NF and RO membrane surfaces under the conditions tested. These results emphasise the importance of conducting adhesion and biofouling experiments under realistic permeate flux conditions, and raises questions about the efficacy of the methods for the evaluation of antifouling membranes in which bacterial adhesion is commonly assessed under zero-flux or low flux conditions, unrepresentative of full-scale NF/RO processes.

The electronic properties and photocatalytic activity of X (N, C) / transition metal (TM=Ta, Hf, Fe) – codoped anatase TiO2 have been investigated using density functional theory. It was found that only the (N, Ta)-codoping case narrows the band gap significantly by about 0.48 eV, driven by the continuum-like p-d hybridized states above the top of valence band and d states at the bottom of conduction band. The calculated energy results suggest that codoping of Ta with N can increase the N concentration in N-doped TiO2 based on energy results.

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.

It is now generally accepted that biofouling is inevitable in pressure-driven membrane processes for water purification. A large number of published articles describe the development of novel membranes in an effort to address biofouling in such systems. It is reasonable to assume that such membranes, even those with antimicrobial properties, when applied in industrial-scale systems will experience some degree of biofouling. In such a scenario, an understanding of the fate of planktonic cells, such as those entering with the feed water, has important implications with respect to contact killing particularly for membranes with antimicrobial properties. This study thus sought to investigate the fate of planktonic cells in a model nanofiltration biofouling system. Here, the interaction between auto-fluorescent Pseudomonas putida planktonic cells and 7-day-old Pseudomonas fluorescens resident biofilms was studied under permeate flux conditions in a nanofiltration cross flow system. We demonstrate that biofilm cell recruitment during nanofiltration is affected by distinctive biofilm structural parameters such as biofilm depth.

Aims:  The purpose of this study was to develop a system that would allow biofilms to be cultivated under strictly defined conditions in terms of dissolved oxygen, fluid shear and to assess whether the method was suitable for the detection of respiratory activity stratification in biofilm samples. Methods:  The system is a modified version a commercially available laboratory biofilm reactor and incorporates a number of features such as the provision of defined levels of dissolved oxygen, constant average shear, enhanced gas–liquid mass transfer, aseptic operation and the ability to remove biofilm for ex situ analysis during or after continuous cultivation. Conclusions:  The system was shown to be effective for the characterization of the effects of dissolved oxygen on a pure culture of Staphylococcus epidermidis. The versatility of the system offers the potential for cultivating pure culture biofilm in defined, controlled conditions and facilitates a range of analyses that can be performed ex situ. Significance and Impact of the Study:  The ability to provide strict regulation of environmental conditions and enhanced transfer of oxygen to the biofilm during cultivation are important, first because oxygen is known to regulate biofilm development in several micro-organisms and second because many conventional biofilm cultivation systems may not provide adequate oxygen supply to the biofilm.

The purpose of this study was to investigate the feasibility of cultivating the biotechnologically important bacterium Streptomyces griseus in single-species and mixed- species biofilms using a Tubular Biofilm Reactor (TBR). Streptomyces griseus biofilm development was found to be cyclical, starting with the initial adhesion and subsequent development of a visible biofilm after 24 hours growth, followed by the complete detachment of the biofilm as a single mass, and ending with the re-colonization of the tube. Fluorescence microscopy revealed that the filamentous structure of the biofilm was lost upon treatment with protease, but not DNase or metaperiodate, indicating that the extracellular polymeric substance is predominantly protein. When the biofilm was cultivated in conjunction with Bacillus amyloliquefaciens, no detachment was observed after 96 h, although once subjected to flow detachment occurred. Electron microscopy confirmed the presence of both bacteria in the biofilm and revealed a network of fimbriae-like structures that were much less apparent in single-species biofilm, and are likely to increase mechanical stability when developing in a TBR. This study presents the very first attempt in engineering Streptomyces griseus biofilms for continuous bioprocess applications.

Recently, the surface of the wings of the Psaltoda claripennis cicada species has been shown to possess bactericidal properties and it has been suggested that the nanostructure present on the wings was responsible for the bacterial death. We have studied the surface-based nanostructure and bactericidal activity of the wings of three different cicadas (Megapomponia intermedia, Ayuthia spectabile and Cryptotympana aguila) in order to correlate the relationship between the observed surface topographical features and their bactericidal properties. Atomic force microscopy and scanning electron microscopy performed in this study revealed that the tested wing species contained a highly uniform, nanopillar structure on the surface. The bactericidal properties of the cicada wings were investigated by assessing the viability of autofluorescent Pseudomonas fluorescens cells following static adhesion assays and targeted dead/live fluorescence staining through direct microscopic counting methods. These experiments revealed a 20-25% bacterial surface coverage on all tested wing species; however, significant bactericidal properties were observed in the M. intermedia and C. aguila species as revealed by the high dead:live cell ratio on their surfaces. The combined results suggest a strong correlation between the bactericidal properties of the wings and the scale of the nanotopography present on the different wing surfaces.

The membrane-aerated biofilm reactor (MABR) is a technology that can deliver oxygen at high rates and transfer efficiencies. This paper provides a comparative cost analysis of the MABR compared to the activated sludge process. Membrane cost and electricity cost were found to be the critical parameters determining the relative feasibility of the conventional process to the membrane based process. The general downward trend in the market price of membranes and the steady increase in energy costs in recent years may prove to be a strong driver for the further development of this technology.

We evaluate the minimum energy configuration (MM) and binding free energy (QM/MM and QM) of CO2 to Rubisco, of fundamental importance to the carboxylation step of the reaction. Two structural motifs have been used to achieve this goal, one of which starts from the initial X-ray Protein Data Bank structure of Rubisco's active centre (671 atoms), and the other is a simplified, smaller model (77 atoms) which has been used most successfully, thus far, for study. The small model is subjected to quantum chemical density functional theory (DFT) studies, both in vacuo and using implicit solvation. The effects of the protein environment are also included by means of a hybrid quantum mechanical/molecular mechanical (QM/MM) approach, using PM6/AMBER and B3LYP/AMBER schemes. Finally, linear-scaling DFT methods have also been applied to evaluate energetic features of the large motif, and the result obtained for the binding free energy of the CO2 underlines the importance of the accurate modelling of the surrounding protein milieu using a full DFT description.

In the context of biofilm development, detachment is of practical importance when placed in a biofilm management perspective. The objective of the present study was to examine biofilm structure and biofilm detachment under controlled conditions for two distinct microorganisms grown under constant shear conditions. Detached biofilm biomass was regularly collected and analysed over the course of 72 h biofilm growth by Pseudomonas putida and Pseudomonas fluorescens cells, and biofilm structural development assessed using confocal microscopy. The two Pseudomonas spp., which had very similar specific growth rates in planktonic culture, presented notably different characteristics in terms of biofilm morphology but their detachment behaviours over time were very similar. These findings underline the intrinsic complexity of the detachment phenomenon.

Comparisons between the physiological properties of Pseudomonas fluorescens biofilm cells grown in a tubular biofilm reactor and planktonic cells grown in a chemostat were performed. Fluoroacetate was the sole carbon source for all experiments. The performance of cells was assessed using cell cycle kinetics and by determining specific fluoroacetate utilization rates. Cell cycle kinetics were studied by flow cytometry in conjunction with the fluorescent stain propidium iodide. Determination of the DNA content of planktonic and biofilm cultures showed little difference between the two modes of growth. Cultures with comparable specific glycolate utilization rates had similar percentages of cells in the B phase of the cell cycle, indicating similar growth rates. Specific fluoroacetate utilization rates showed the performance of planktonic cells to be superior to that of biofilm cells, with more fluoroacetate utilized per cell at similar specific fluoroacetate loading rates. A consequence of this decreased biofilm performance was the accumulation of glycolate in the effluent of biofilm cultures. This accumulation of glycolate was not observed in the effluent of planktonic cultures. Spatial stratification of oxygen within the biofilm was identified as a possible explanation for the overflow metabolism of glycolate and the decreased performance of the biofilm cells.

A low-cost, modular, robust, and easily customisable continuous liquid-liquid phase separator has been developed that uses a tubular membrane and annular channels to allow high fluidic throughputs while maintaining rapid, surface wetting dominated, phase separation. The system is constructed from standard fluidic tube fittings and allows leak tight connections to be made without the need for adhesives, or O-rings. The units tested in this work have been shown to operate at flow rates of 0.1 – 300 mL/min, with equivalent residence times from 80 to 4 seconds, demonstrating the simplicity of scale-up with these units. Further scale-up to litre per minute scales of operation for single units and tens of litres/minute through limited numbering up should allow these low cost concentric annular tubular membrane separators to be used at continuous production scales for pharmaceutical applications for many solvent systems. In principle this approach may be sufficiently scalable to be utilized in-line, in batch pharmaceutical manufacturing also, through further scale-up and numbering up of units. Several solvent systems with varying interfacial tensions have been investigated, and the critical process parameters affecting successful separation have been identified. An additively manufactured diaphragm based back pressure regulator was also developed and printed in PEEK, allowing highly accurate, adjustable, and chemically compatible pressure control to be accessed at low cost.

Crystalline titanium dioxide (TiO2) coatings have been widely used in photo-electrochemical solar cell applications. In this study, TiO2 and carbon-doped TiO2 coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO2. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45 GHz microwave-induced nitrogen plasma where they were heated to approximately 550°C. It was observed that for treatment times as short as 1 minute, the 0.25-µm thick coatings were converted into the anatase crystalline phase of TiO2. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO2 with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO2 exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings’ surface morphology and band gap energy, both of which influence the coatings’ photoabsorption efficiency.