Interface model between the bioreactor and the membrane in a membrane bioreactor for wastewater treatment.

This paper proposes a structure of an integrated mathematical model of a membrane bioreactor (MBR) and describes the links between two main parts of a MBR model: the bioreactor and the membrane. In case of an immersed MBR three types of links are considered: a relationship between specific cake resistance (SCR) and extracellular polymeric substances (EPS) in the bioreactor, a relationship between air scour rate and shear stresses on the membrane surface, and a relationship between concentration of soluble microbial products (SMP) in the bioreactor and rate of pore constriction. While SMP concentration features directly in the equations of pore constriction, EPS are assumed to affect SCR which in turn has an effect on cake filtration. The relationship between EPS and SCR is described with a linear algebraic equation. Shear stresses on the membrane surface are calculated as a function of air scour rate with a one- imensional slug flow model

Modelling Complex Flows in Porous Media by Means of Upscaling Procedures

We review a series of problems arising in the field of flows through porous media and that are highly nontrivial either because of the presence of mass exchange between the fluid and the porous matrix (or other concurrent phenomena of physical or chemical nature), or because of a particularly complex structure of the medium. In all these cases there is a small parameter $\varepsilon$, representing the ratio between the microscopic and the macroscopic space scale. Our attention is focussed on a modelling technique (upscaling) which start from the governing equations written at the pore scale, introduces an expansion in power series of $\varepsilon$of all the relevant quantities and eventually leads to the formulation of the macroscopic governing equations at the various orders in $\varepsilon$ by a matching procedure, followed by suitable averaging. Two problems will be analyzed with some detail: soil erosion and the dynamics of water ultrafiltration devices. Moreover other problems will be occasionally discussed and open questions will be proposed

Development of a bio-inspired in silico-in vitro platform: towards personalised healthcare through optimisation of a bone-marrow mimicry bioreactor

Human red blood cell production, or erythropoiesis, occurs within bone marrow. Living animal and human cadaver models have demonstrated the marrow production of red blood cells is a spatially-complex process, where cells replicate, mature, and migrate between distinct niches defined by biochemical nutrient access, supportive neighboring cells, and environmental structure. Unfortunately, current research in understanding normal and abnormal human production of blood takes place in petri dishes and t-flasks as 2D liquid suspension cultures, neglecting the role of the marrow environment for blood production. The culture of blood on marrow-mimetic 3D biomaterials has been used as a laboratory model of physiological blood production, but lacks characterization. In this work, a 3D biomaterial platform is developed and to capture the in vivo blood production process and manufacture red blood cells from human umbilical cord blood. First ceramic hollow fibres were designed and tested to be incorporated and perfused in a 3D porous scaffold bioreactor to mimic marrow structure, provide a better expansion of cell numbers, a better diffusion of nutrients, and allow for the continuous, non-invasive harvest of small cells in comparison to static, unperfused biomaterials. Quantitative 3D image analysis tools were developed to spatially assess bioreactor distributions and associations of and between different cell types. Using these tools, the bioreactor distribution of red blood cell production were characterized within niches in collaboration with supportive, non-blood cell types and designed miniaturised, parallelised mini-bioreactors to further explore bioreactor capabilities. This thesis presents a hollow fibre bioreactor able to produce blood cells alongside supportive cells at 1,000-fold higher cell densities with 10-fold fewer supplemented factor than flask cultures, without serum, with one cell source, and continuously harvest enucleate red blood cell product to provide a physiologically-relevant model for cell expansion protocols.Open Acces

Methane management in sewage treatment

Poly-di-methyl-siloxane (PDMS) hollow fibre membrane modules were designed and built for the specific de-gassing of real and synthetic process liquids to understand: (i) the feasibility of operation; and (ii) classify the mass transfer characteristics to aid design at full scale. Liquid saturated with pure methane or a binary methane and carbon dioxide mixture was introduced into the shell side of the extraction unit, whilst sweep gas or vacuum was employed counter-currently as a stripping medium. From data analysis of operation in both anaerobic effluents obtained from Expanded Granular Sludge Blanket (EGSB) reactor and synthetic liquids, when operating under optimum conditions 93% of methane and 88% of carbon dioxide was recovered. The obtained data indicate that the extraction process is controlled by diffusivity of gases through the PDMS membrane and is proportional to the thickness of membrane wall. When applying vacuum to promote methane mass transfer, the process was highly sensitive to vacuum pressure; the highest de-gassing efficiency was recorded under the lowest absolute vacuum pressure. However, when vacuum was replaced by sweep gas, the process was insensitive to changes in gas velocity. When utilising PDMS membrane contactor for de-gassing of EGSB effluent, the net electrical output achieved by the EGSB increased by c. 24% and indicates that by integrating methane recovery, treatment of domestic wastewater using low temperature EGSB processes can become carbon positive. The potential of directing recovered methane to porous hollow fibre membrane absorbers and upgrading to national gas (NG) standards to use in national gas grid or as a vehicle fuel has been demonstrated

Investigating biomechanical determinants of endothelial permeability in a hollow fibre bioreactor

The effect of haemodynamic stresses on endothelial permeability to macromolecules is important to normal physiology and in the pathogenesis of atherosclerosis. I developed and applied novel methods to evaluate effects on such transport of acute or chronic exposure to flow along and across cultured endothelium. Porcine aortic endothelial cells were isolated and cultured at passage 1-3 within the porous capillaries of a FiberCell bioreactor. At confluence they were exposed to acute (4 h) or chronic (3-10 day) steady or pulsatile luminal flow (mean shear 3.75 dyne/cm2), with or without transendothelial flow (4 x 10-7 cm/s). Permeability to rhodamine-labelled albumin was assessed by fluorimetry. Confluence of monolayers was confirmed by confocal and scanning electron microscopy and by demonstrating established effects of vasoactive agents on permeability: 10 U/ml thrombin increased permeability, as did 500 μM Nω-nitro-Larginine methyl ester, compared to controls. Permeability was increased by acute pulsatile shear and decreased by chronic pulsatile shear compared to static controls. A decrease in PECAM-1 expression under chronic pulsatile flow was demonstrated by flow cytometry. Steady flow gave higher permeability than pulsatile flow. The introduction of transendothelial flow increased apparent permeability more than could be explained by the addition of the convective transport itself. Preliminary studies suggested that albumin transport may partially be an active process and demonstrated the potential for engineered fibre walls that would allow effects of cyclic strain to be investigated. In conclusion, the hollow fibre bioreactor allowed endothelial permeability to be measured with or without exposure to luminal flow and transendothelial flow over 30 days, permitting the investigation of effects of mechanical stresses. Effects of shear stress varied with duration, pulsatility and direction relative to the endothelial surface.Open Acces

The hydrodynamic characterisation of an axial-flow membrane module

Thesis (MScEng)--University of Stellenbosch, 2001.ENGLISH ABSTRACT: The hydrodynamics of a hollow fibre membrane module for the ultrafiltration of potable water were investigated. The purpose was to use a hydrodynamic model to predict the permeate flux for modules of various dimensions. Various models were considered, but most of them could not account for important effects such as macroscopic radial gradients and wet fibre expansion, found in hollow-fibre membrane modules. The Porous Medium Model was found to be a suitable model and it was used together with a finite element software package, Fastflo, to solve for the pressure distributions inside the membrane modules and predict permeate flux. The permeability of the membranes was obtained using a combination of numerical and experimental procedures and was found to be 2.3 x 10-13m. A cost analysis was performed to find the most economical module dimensions (outer diameter and length) for any required product flow rate. It was assumed that the cost of the fibres and module housing comprised the capital cost, while the operating cost consisted of the pumping energy. A capital recovery factor of 0.3 was used to convert capital costs to a yearly cost. It was found that the optimum module dimensions are an outer diameter of between 90mm and 160mm and a length of 0.6m. Finally the pressure distributions on the lumen and shell sides during both cross-flow filtration and backwash were examined. Shade plots proved useful for identifying possible areas of stagnant flow, as well as indicating where backwash is the most effective.AFRIKAANSE OPSOMMING: Die hidrodinamika binne-in 'n holvesel membraanmodule vir die ultrafiltrasie van drinkwater is ondersoek. Die doel was om 'n hidrodinamiese model te gebruik om die permeaatvloed vir modules van verskeie dimensies te voorspel. Verskillende modelle is oorweeg, maar die meeste kon nie belangrike faktore soos makroskopiese radiale drukqradiente of nat veselverlenging in ag neem nie. Die Poreuse Medium Model was die mees geskikte model en is gebruik saam met Fastf/o, 'n sagteware pakket wat gegrond is op die eindige element metode, om vergelykings vir die drukverspreiding binne-in die module op te los en permeaatvloed te voorspel. Die permeabiliteit van die membrane is verkry met behulp van numeriese en eksperimentele prosedures en 'n waarde van 2.3 x 10-13 m is bepaal. Hierna is 'n koste-analise uitgevoer om die mees ekonomiese module afmetings (Iengte en buitedeursnit) te bepaal vir 'n gegewe produk vloeitempo. Daar is aanvaar dat kapitaalkoste bestaan uit die koste van vesels en module-omhulsel, terwyl bedryfskoste bereken is deur die hoeveelheid energie benodig om die pomp aan te dryf. 'n Kapitaalherwinningsfaktor van 0.3 is gebruik om kapitaalkoste om te skakel na 'n jaarlikse koste. Die optimum module afmetings is 'n lengte van 0.6m en 'n buite-deursnit van tussen 90mm en 160mm. Laastens is die drukverspreidings tydens beide kruisvloeifiltrasie en die terugspoelproses ondersoek. Areas van stagnante vloei kan deur middel van skadu-grafieke geYdentifiseer word, terwyl dit ook moontlik is om die terugspoelproses te optimeer

A novel membrane process for autotrophic denitrification

This research focused on the novel use of hollow fiber membranes for gas delivery in biological dentrification using hydrogen-oxidizing bacteria. Autotrophic denitrification is a biological process that reduces nitrate to nitrogen gas using an inorganic carbon source. Hydrogen gas is an electron donor and nitrate is the electron acceptor in the reaction. The specific research objectives were to: develop a mixed acclimated culture of hydrogen-oxidizing bacteria; evaluate biodegradation kinetics of the acclimated culture; evaluate hydrogen transfer characteristics of hollow fiber membrane modules; and demonstrate technical feasibility of a continuous bioreactor-membrane system for denitrification. The following kinetic coefficients were obtained: µm of 0.65 d-1, Y of 0.78 mg cells/mg NO3-N, and kd of 0.04 d-1. The nitrate utilization rate was determined to be 1.0 mg NO3-N/mg biomass. The following mass transfer correlation can be used to design membrane modules for hydrogen dissolution into water: Sh = 2.68 Rede/L1.02Sc0.33 Continuous flow studies indicate that a stable biofilm can be developed in a packed bed reactor to remove nitrate using hydrogen as the electron donor. Hydrogen gas was successfully delivered to the reactor via the hollow fiber membrane gas transfer module without fouling. Dissolved hydrogen concentrations indicate that the system did not experience hydrogen limitations. Membrane gas delivery appears to be a viable technology for transferring hydrogen to water for autotrophic denitrificiation

Modelling and prediction of non-linear scale-up from an Ultra Scale-Down membrane device to process scale tangential flow filtration

Ultra scale-down (USD) tools have demonstrated the huge potential for accelerated process development by significantly reducing the material requirements and providing better solutions, as part of the Quality by Design initiative. Key benefits of using USD techniques include the relatively small quantities of feedstock and minimal capital equipment needed to generate large volumes of statistically significant process data in a short period, leading to significant time and cost savings during process development. However, the use of small scale devices such as the stirred cell filtration units have been primarily limited to preliminary testing and initial screening due to their geometric and flow dissimilarities to tangential flow filtration at scale. As a result, process development and optimisation trials are generally carried out using the smallest c commercially available TFF cassettes, the use of which are primarily limited by time and material constraints that are invariably present at the early stages of process development. Therefore, the central focus of this work was to develop a USD methodology and model to accurately predict the performance of large scale tangential flow filtration (TFF) using a USD membrane filtration device. // The commercial package COMSOL was used to carry out computational fluid dynamics (CFD) modelling and simulation of the fluid flow dynamics in Pellicon TFF cassettes with different feed screens and a USD membrane device, in order to develop average wall shear rate correlations and channel pressure drops expressed as functions of the respective hydrodynamic conditions across scales. In addition, the impact of non-TFF related factors such as the system and cassette-specific hydraulic resistances on TFF performance was characterised using semi-empirical models. Finally, a scale-up methodology and mathematical model to predict the large scale performance using USD data was developed by combining the various resistances, channel pressure drop correlations and an empirical USD-derived model that characterises the specific feed-membrane interactions. The CFD simulations were independently verified using 2D particle imaging velocimetry to compare experimental data to the CFD simulated data. // 100-fold scale-up experiments were carried out based on equivalent averaged wall shear rates (w) as the geometry-independent parameter. Permeate flux excursions were carried out to validate the USD methodology and prediction model, by comparing USD model predictions against the large scale experimental data. Different membranes, feed screens (A, C and V) and feedstock, ranging from simple proteins like Bovine Serum Albumin (BSA) to more complex, multicomponent feed such as Escherichia coli homogenate, were used. Predicted flux and transmission results were in good agreement with the large scale experimental data, showing less than 5% difference across scales, demonstrating the robustness of the non-linear scale-up model. // Following the successful validation of the scale-up methodology and prediction model, other potential applications of the USD membrane device such as the optimisation of TFF microfiltration was demonstrated using Saccharomyces cerevisae and Chlorella sorokiniana. Fed-batch concentration experiments using Saccharomyces cerevisae were done to compare the volumetric throughput limits. The USD-predicted capacity limit of 49.2 L/m2 was very similar to the experimental large scale capacity value of 52.0 L/m2, and considered fully scalable within experimental errors. Finally, fouling studies were performed using Chlorella sorokiniana and the USD device to investigate the impact of media type and growth conditions on the filtration performance. The results indicated a strong correlation between soluble fouling species, such as exopolysaccharides and carbohydrates, rather than the algal biomass. A novel, dynamic flux control methodology was developed based on empirically determined critical fluxes expressed as a function of cell concentration. The dynamic control strategy was successfully verified by performing a 50-fold concentration experiment using a hollow fibre module and the USD device. An improvement of greater than 50% in average throughput was achieved using the 3-step flux cascade compared to the traditional flux-time/capacity optimised fluxes, with no observable increase in TMP throughout. // The work presented here demonstrates the potential of ultra scale-down tools coupled with a mathematical modelling approach to establish a predictable scale-up performance, which can be used to rapidly develop and optimise tangential flow filtration processes, regardless of differences in geometry, flow configuration and system setup