Effects of shear stress on microalgae - A review

Cultivation of microalgae requires consideration of shear stress, which is generated by operations such as mixing, circulation, aeration and pumping that are designed to facilitate mass and heat transfer as well as light distribution in cultures. Excessive shear stress can cause increased cell mortality, decreased growth rate and cell viability, or even cell lysis. This review examines the sources of shear stress in different cultivation systems, shear stress tolerance of different microalgal species and the physiological factors and environmental conditions that may affect shear sensitivity, and potential approaches to mitigate the detrimental effects of shear stress. In general, green algae have the greatest tolerance to shear stress, followed by cyanobacteria, haptophytes, red algae, and diatoms, with dinoflagellates comprising the most shear-sensitive species. The shear-sensitivity of microalgae is determined primarily by cell wall strength, cell morphology and the presence of flagella. Turbulence, eddy size, and viscosity are the most prominent parameters affecting shear stress to microalgal cells during cultivation.

Dry anaerobic digestion of organic waste: A review of operational parameters and their impact on process performance

Dry digestion is a suitable technology for treating organic wastes with varying composition such as the organic fraction of municipal solids waste. Yet, there is a need for further research to overcome some of the disadvantages associated with the high total solids content of the process. Optimisation of inoculum to substrate ratio, feedstock composition and size, liquid recirculation, bed compaction and use of bulking agents are some of the parameters that need further investigation in batch dry anaerobic digestion, to limit localised inhibition effects and avoid process instability. In addition, further attention on the relation between feedstock composition, organic loading rate and mixing regimes is required for continuous dry anaerobic digestion systems. This paper highlights all the areas where knowledge is scarce and value can be added to increase dry anaerobic digestion performance and expansion.

Nitrogen sources and cycling revealed by dual isotopes of nitrate in a complex urbanized environment

Elevated nutrient inputs have led to increased eutrophication in coastal marine ecosystems worldwide. An understanding of the relative contribution of different nutrient sources is imperative for effective water quality management. Stable isotope values of nitrate (δ¹⁵N_NO3-, δ¹⁸O_NO3-) can complement conventional water quality monitoring programs to help differentiate natural sources of NO₃^- from anthropogenic inputs and estimate the processes involved in N cycling within an ecosystem. We measured nutrient concentrations, δ¹⁵N_NO3-, and δ¹⁸O_NO3- in 76 locations along a salinity gradient from the lower end of the Pearl River Estuary, one of China's largest rivers discharging into the South China Sea, towards the open ocean. NO₃^- concentrations decreased with increasing salinity, indicative of conservative mixing of eutrophic freshwater and oligotrophic seawater. However, our data did not follow conservative mixing patterns. At salinities <20 psu, samples exhibited decreasing NO₃^-concentrations with almost unchanged NO₃^- isotope values, indicating simple dilution. At salinities >20 psu, NO₃^- concentrations decreased, while dual NO₃^- isotopes increased, suggesting mixing and/or other transformation processes. Our analysis yielded mean estimates for isotope enrichment factors (¹⁵ε = -2.02‰ and ¹⁸ε = -3.37‰), Δ(15,18) = -5.5‰ and δ¹⁵N_NO3- - δ¹⁵N_NO2- = 12.3‰. After consideration of potential alternative sources (sewage, atmospheric deposition and groundwater) we concluded that there are three plausible interpretations for deviations from conservative mixing behaviour (1) NO₃^- uptake by assimilation (2) in situ NO₃^- production (from fixation-derived nitrogen and nitrification of sewage-derived effluents) and (3) input of groundwater nitrate carrying a denitrification signal. Through this study, we propose a simple workflow that incorporates a synthesis of numerous isotope-based studies to constrain sources and behaviour of NO₃^- in urbanized marine environments.

Identifying and overcoming the effect of mass transfer limitation on decreased yield in enzymatic hydrolysis of lignocellulose at high solid concentrations

Cellulose conversion decreases significantly with increasing solid concentrations during enzymatic hydrolysis of insoluble lignocellulosic materials. Here, mass transfer limitation was identified as a significant determining factor of this decrease by studying the hydrolysis of delignified corncob residue in shake flask, the most used reaction vessel in bench scale. Two mass transfer efficiency-related factors, mixing speed and flask filling, were shown to correlate closely with cellulose conversion at solid loadings higher than 15% DM. The role of substrate characteristics in mass transfer performance was also significant, which was revealed by the saccharification of two corn stover substrates with different pretreatment methods at the same solid loading. Several approaches including premix, fed-batch operation, and particularly the use of horizontal rotating reactor were shown to be valid in facilitating cellulose conversion via improving mass transfer efficiency at solid concentrations higher than 15% DM.

Mitigating ammonia nitrogen deficiency in dairy wastewaters for algae cultivation

This study demonstrated that the limiting factor to algae growth on dairy wastewater was the ammonia nitrogen deficiency. Dairy wastewaters were mixed with a slaughterhouse wastewater that has much higher ammonia nitrogen content. The results showed the mixing wastewaters improved the nutrient profiles and biomass yield at low cost. Algae grown on mixed wastewaters contained high protein (55.98-66.91%) and oil content (19.10-20.81%) and can be exploited to produce animal feed and biofuel. Furthermore, algae grown on mixed wastewater significantly reduced nutrient contents remained in the wastewater after treatment. By mitigating limiting factor to algae growth on dairy wastewaters, the key issue of low biomass yield of algae grown on dairy wastewaters was resolved and the wastewater nutrient removal efficiency was significantly improved by this study.

Aeration and mass transfer optimization in a rectangular airlift loop photobioreactor for the production of microalgae

Effects of superficial gas velocity and top clearance on gas holdup, liquid circulation velocity, mixing time, and mass transfer coefficient are investigated in a new airlift loop photobioreactor (PBR), and empirical models for its rational control and scale-up are proposed. In addition, the impact of top clearance on hydrodynamics, especially on the gas holdup in the internal airlift loop reactor, is clarified; a novel volume expansion technique is developed to determine the low gas holdup in the PBR. Moreover, a model strain of Chlorella vulgaris is cultivated in the PBR and the volumetric power is analyzed with a classic model, and then the aeration is optimized. It shows that the designed PBR, a cost-effective reactor, is promising for the mass cultivation of microalgae.

Methods of administering oral formulations and child acceptability

INTRODUCTION

Children may be unable or unwilling to swallow medicines. In order to avoid or accommodate any such problems, parents may decide to administer medicines other than intended. The aim of this study was to investigate how parents administered four oral placebo formulations to infants and preschool children and how the applied methods correlated with child acceptability.

METHODS

Parents were asked to administer a 4 mm mini-tablet, powder, suspension and syrup to their child twice on one day and to report the child characteristics and administration details in a participant diary.

RESULTS

A 151 children were included. The tablet, syrup and suspension were mostly given on their own, whereas the powder was commonly given with food or drink. Generally, the higher the child acceptability (VAS-score) of the first administration of a specific formulation, the less frequently its method of administration was changed. A change in the method of administration of the same formulation involving (a larger quantity of) food or drink generally resulted in a higher VAS-score.

CONCLUSIONS

The joint administration of medicines with food or drink is an effective strategy to ensure swallowing. This study supports earlier findings that 4mm mini-tablets are a suitable dosage form from infant age.

Controlled dispensing and mixing of pico- to nanoliter volumes using on-demand droplet-based microfluidics

We present an integrated droplet-on-demand microfluidic platform for dispensing, mixing, incubating, extracting and analyzing by mass spectrometry pico- to nanoliter-sized droplets. All of the functional components are successfully integrated for the first time into a monolithic microdevice. Droplet generation is accomplished using computer-controlled pneumatic valves. Controlled actuation of valves for different aqueous streams enables accurate dosing and rapid mixing of reagents within droplets in either the droplet generation area or in a region of widening channel cross-section. Following incubation, which takes place as droplets travel in the oil stream, the droplet contents are extracted to an aqueous channel for subsequent ionization at an integrated nanoelectrospray emitter. Using the integrated platform, rapid enzymatic digestions of a model protein were carried out in droplets and detected on-line by nanoelectrospray ionization mass spectrometry.

Bidirectional impact of imperfect mask use on reproduction number of COVID-19: A next generation matrix approach

The use of masks as a means of reducing transmission of COVID-19 outside healthcare settings has proved controversial. Masks are thought to have two modes of effect: they prevent infection with COVID-19 in wearers; and prevent transmission by individuals with subclinical infection. We used a simple next-generation matrix approach to estimate the conditions under which masks would reduce the reproduction number of COVID-19 under a threshold of 1. Our model takes into account the possibility of assortative mixing, where mask users interact preferentially with other mask users. We make 3 key observations:

1. Masks, even with suboptimal efficacy in both prevention of acquisition and transmission of infection, could substantially decrease the reproduction number for COVID-19 if widely used.

2. Widespread masking may be sufficient to suppress epidemics where R has been brought close to 1 via other measures (e.g., distancing).

3. “Assortment” within populations (the tendency for interactions between masked individuals to be more likely than interactions between masked and unmasked individuals) would rapidly erode the impact of masks. As such, mask uptake needs to be fairly universal to have an effect.

This simple model suggests that widespread uptake of masking could be determinative in suppressing COVID-19 epidemics in regions with R(t) at or near 1.

Equipment characterization to mitigate risks during transfers of cell culture manufacturing processes

The production of monoclonal antibodies by mammalian cell culture in bioreactors up to 25,000 L is state of the art technology in the biotech industry. During the lifecycle of a product, several scale up activities and technology transfers are typically executed to enable the supply chain strategy of a global pharmaceutical company. Given the sensitivity of mammalian cells to physicochemical culture conditions, process and equipment knowledge are critical to avoid impacts on timelines, product quantity and quality. Especially, the fluid dynamics of large scale bioreactors versus small scale models need to be described, and similarity demonstrated, in light of the Quality by Design approach promoted by the FDA. This approach comprises an associated design space which is established during process characterization and validation in bench scale bioreactors. Therefore the establishment of predictive models and simulation tools for major operating conditions of stirred vessels (mixing, mass transfer, and shear force.), based on fundamental engineering principles, have experienced a renaissance in the recent years. This work illustrates the systematic characterization of a large variety of bioreactor designs deployed in a global manufacturing network ranging from small bench scale equipment to large scale production equipment (25,000 L). Several traditional methods to determine power input, mixing, mass transfer and shear force have been used to create a data base and identify differences for various impeller types and configurations in operating ranges typically applied in cell culture processes at manufacturing scale. In addition, extrapolation of different empirical models, e.g. Cooke et al. (Paper presented at the proceedings of the 2nd international conference of bioreactor fluid dynamics, Cranfield, UK, 1988), have been assessed for their validity in these operational ranges. Results for selected designs are shown and serve as examples of structured characterization to enable fast and agile process transfers, scale up and troubleshooting.

The social contact hypothesis under the assumption of endemic equilibrium: Elucidating the transmission potential of VZV in Europe

The basic reproduction number R0 and the effective reproduction number R are pivotal parameters in infectious disease epidemiology, quantifying the transmission potential of an infection in a population. We estimate both parameters from 13 pre-vaccination serological data sets on varicella zoster virus (VZV) in 12 European countries and from population-based social contact surveys under the commonly made assumptions of endemic and demographic equilibrium. The fit to the serology is evaluated using the inferred effective reproduction number R as a model eligibility criterion combined with AIC as a model selection criterion. For only 2 out of 12 countries, the common choice of a constant proportionality factor is sufficient to provide a good fit to the seroprevalence data. For the other countries, an age-specific proportionality factor provides a better fit, assuming physical contacts lasting longer than 15 min are a good proxy for potential varicella transmission events. In all countries, primary infection with VZV most often occurs in early childhood, but there is substantial variation in transmission potential with R0 ranging from 2.8 in England and Wales to 7.6 in The Netherlands. Two non-parametric methods, the maximal information coefficient (MIC) and a random forest approach, are used to explain these differences in R0 in terms of relevant country-specific characteristics. Our results suggest an association with three general factors: inequality in wealth, infant vaccination coverage and child care attendance. This illustrates the need to consider fundamental differences between European countries when formulating and parameterizing infectious disease models.

Nanofibers of resorcinol-formaldehyde for effective adsorption of As (III) ions from mimicked effluents

In the present study, the core-shell structured RF/PVA nanofibers have been developed and used for the adsorption of As³⁺ ions from the mimicked liquid effluents. Efficient-facile fabrication of the structured nanofibers (300-417 nm diameter) was accomplished using facile electrospinning technique. Chi parameter (χ = 25.56) and free energy of mixing (E_mix = 17.19 kcal/mol) calculated via molecular dynamics simulations depicted compatibility of the polymeric system resulting supermolecular core-shell nanofibers, whose adsorption results were also supported by the FE-SEM, FT-IR, and UV-VIS spectroscopy analysis. The adsorption analysis was performed using both linear and non-linear regression methods, for kinetic models and adsorption isotherms. The developed nanofibers demonstrated an adsorption capacity of 11.09 mg/g at a pH of 7, and an adsorption efficiency of 97.46% on protracted exposure, which is even adaptable at high temperatures with 93.1% reclamation. FE-SEM analysis and FT-IR spectra confirm the adsorption of As (III) ions on RF/PVA nanofibers and the presence of embedded hydrophilic oxygen sites for metal ion adsorption. The developed RF/PVA nanofibers demonstrate scalability in fabrication, low-cost, recycling, and less solid waste generation, depicting the large-scale applicability in removing arsenic ions from effluent waste. Graphical Abstract ᅟ.

Hydrodynamic performance of a single-use aerated stirred bioreactor in animal cell culture: applications of tomography, dynamic gas disengagement (DGD), and CFD

The hydrodynamics of gas-liquid two-phase flow in a single-use bioreactor were investigated in detail both experimentally and numerically. Electrical resistance tomography (ERT) and dynamic gas disengagement (DGD) combined with computational fluid dynamics (CFD) were employed to assess the effect of the volumetric gas flow rate and impeller speed on the gas-liquid flow field, local and global gas holdup values, and Sauter mean bubble diameter. From the results obtained from DGD coupled with ERT, the bubble sizes were determined. The experimental data indicated that the total gas holdup values increased with increasing both the rotational speed of impeller and volumetric gas flow rate. Moreover, the analysis of the flow field generated inside the aerated stirred bioreactor was conducted using CFD results. Overall, a more uniform distribution of the gas holdup was obtained at impeller speeds ≥ 100 rpm for volumetric gas flow rates ≥ 1.6 × 10^-5 m³/s.

Mechanics of flow and mixing at antroduodenal junction

The morphology of tissue structures composing the pyloric orifice is thought to play a role in effectively mixing aqueous gastric effluent with duodenal secretions. To understand the physical mechanisms leading to efficient digestion requires computational models that allow for analyses of the contributions of individual structural components. Thus, we have simulated 2-D channel flows through representative models of the duodenum with moving boundary capabilities in order to quantitatively assess the importance of notable features. A well-tested flow solver was used to computationally isolate and compare geometric and kinematic parameters that lead to various characteristics of fluid motion at the antroduodenal junction. Scalar variance measurement was incorporated to quantify the mixing effectiveness of each component. It was found that the asymmetric geometry of the pyloric orifice in concert with intermittent gastric outflow and luminal constriction is likely to enhance homogenization of gastric effluent with duodenal secretions.

Effects of agitation on particle-size distribution and enzymatic hydrolysis of pretreated spruce and giant reed

BACKGROUND

Mixing is an energy demanding process which has been previously shown to affect enzymatic hydrolysis. Concentrated biomass slurries are associated with high and non-Newtonian viscosities and mixing in these systems is a complex task. Poor mixing can lead to mass and/or heat transfer problems as well as inhomogeneous enzyme distribution, both of which can cause possible yield reduction. Furthermore the stirring energy dissipation may impact the particle size which in turn may affect the enzymatic hydrolysis. The objective of the current work was to specifically quantify the effects of mixing on particle-size distribution (PSD) and relate this to changes in the enzymatic hydrolysis. Two rather different materials were investigated, namely pretreated Norway spruce and giant reed.

RESULTS

Changes in glucan hydrolysis and PSD were measured as a function of agitation during enzymatic hydrolysis at fiber loadings of 7 or 13% water-insoluble solids (WIS). Enzymatic conversion of pretreated spruce was strongly affected by agitation rates at the higher WIS content. However, at low WIS content the agitation had almost no effect on hydrolysis. There was some effect of agitation on the hydrolysis of giant reed at high WIS loading, but it was smaller than that for spruce, and there was no measurable effect at low WIS loading. In the case of spruce, intense agitation clearly affected the PSD and resulted in a reduced mean particle size, whereas for giant reed the decrease in particle size was mainly driven by enzymatic action. However, the rate of enzymatic hydrolysis was not increased after size reduction by agitation.

CONCLUSIONS

The impact of agitation on the enzymatic hydrolysis clearly depends not only on feedstock but also on the solids loading. Agitation was found to affect the PSD differently for the examined pretreated materials spruce and giant reed. The fact that the reduced mean particle diameter could not explain the enhanced hydrolysis rates found for spruce at an elevated agitation suggests that mass transfer at sustained high viscosities plays an important role in determining the rate of enzymatic hydrolysis.

High throughput acoustic microfluidic mixer controls self-assembly of protein nanoparticles with tuneable sizes

HYPOTHESIS

Protein nanoparticles have attracted increased interest due to their broad applications ranging from drug delivery and vaccines to biocatalysts and biosensors. The morphology and the size of the nanoparticles play a crucial role in determining their suitability for different applications. Yet, effectively controlling the size of the nanoparticles is still a significant challenge in their manufacture. The hypothesis of this paper is that the assembly conditions and size of protein particles can be tuned via a mechanical route by simply modifying the mixing time and strength, while keeping the chemical parameters constant.

EXPERIMENTAL

We use an acoustically actuated, high throughput, ultrafast, microfluidic mixer for the assembly of protein particles with tuneable sizes. The performance of the acoustic micro-mixer is characterized via Laser Doppler Vibrometry and image processing. The assembly of protein nanoparticles is monitored by dynamic light scattering (DLS) and transmission electron microscopy (TEM).

FINDINGS

By changing actuation parameters, the turbulence and mixing in the microchannel can be precisely varied to control the initiation of protein particle assembly while the solution conditions of assembly (pH and ionic strength) are kept constant. Importantly, mixing times as low as 6 ms can be achieved for triggering protein assembly in the microfluidic channel. In comparison to the conventional batch process of assembly, the acoustic microfluidic mixer approach produces smaller particles with a more uniform size distribution, promising a new way to manufacture protein particles with controllable quality.

Study of expiratory droplet dispersion and transport using a new Eulerian modeling approach

Understanding of droplet nuclei dispersion and transport characteristics can provide more engineering strategies to control transmission of airborne diseases. Droplet dispersion in a room under the conventional well-mixed and displacement ventilation is simulated. Two droplet nuclei sizes, 0.01 and 10 μm, are selected as they represent very fine and coarse droplets. The flow field is modeled using k-ε RNG model. A new Eulerian drift-flux methodology is employed to model droplet phase. Under the conventional ventilation scheme, both fine and coarse droplets are homogeneously dispersed within approximately 50 s. Droplet nuclei exhibit distinctive dispersion behavior, particularly for low airflow microenvironment. After 270 s of droplet emission, gravitational settling influences the dispersion for 10 μm droplets, and concentration gradient can still be observed for displacement ventilation.

Major hydrogeochemical processes in an acid mine drainage affected estuary

This study provides geochemical data with the aim of identifying and quantifying the main processes occurring in an Acid Mine Drainage (AMD) affected estuary. With that purpose, water samples of the Huelva estuary were collected during a tidal half-cycle and ion-ion plots and geochemical modeling were performed to obtain a general conceptual model. Modeling results indicated that the main processes responsible for the hydrochemical evolution of the waters are: (i) the mixing of acid fluvial water with alkaline ocean water; (ii) precipitation of Fe oxyhydroxysulfates (schwertmannite) and hydroxides (ferrihydrite); (iii) precipitation of Al hydroxysulfates (jurbanite) and hydroxides (amorphous Al(OH)3); (iv) dissolution of calcite; and (v) dissolution of gypsum. All these processes, thermodynamically feasible in the light of their calculated saturation states, were quantified by mass-balance calculations and validated by reaction-path calculations. In addition, sorption processes were deduced by the non-conservative behavior of some elements (e.g., Cu and Zn).

Stress Factors in Protein Drug Product Manufacturing and Their Impact on Product Quality

Injectable protein-based medicinal products (drug products, or DPs) must be produced by using sterile manufacturing processes to ensure product safety. In DP manufacturing the protein drug substance, in a suitable final formulation, is combined with the desired primary packaging (e.g., syringe, cartridge, or vial) that guarantees product integrity and enables transportation, storage, handling and clinical administration. The protein DP is exposed to several stress conditions during each of the unit operations in DP manufacturing, some of which can be detrimental to product quality. For example, particles, aggregates and chemically-modified proteins can form during manufacturing, and excessive amounts of these undesired variants might cause an impact on potency or immunogenicity. Therefore, DP manufacturing process development should include identification of critical quality attributes (CQAs) and comprehensive risk assessment of potential protein modifications in process steps, and the relevant steps must be characterized and controlled. In this commentary article we focus on the major unit operations in protein DP manufacturing, and critically evaluate each process step for stress factors involved and their potential effects on DP CQAs. Moreover, we discuss the current industry trends for risk mitigation, process control including analytical monitoring, and recommendations for formulation and process development studies, including scaled-down runs.

Effects of Mixing on the Aggressive Behavior of Commercially Housed Pigs

In this study, we investigated the effects of mixing on the aggressive behavior of commercially housed pigs. The behavioral patterns of 36 groups of pigs (a total of 360 animals) were observed over 3 consecutive days directly after weaning (25±1.2 days of age), and 25 and 50 days later with the aid of video technology. Fight latency and total duration and frequency of fighting were significantly different among the age groups. The aggressive behaviors decreased in 75-day old pigs if compared to 25- and 50-day old animals. Moreover, dominance index (DI) was higher in 25-day old and lower in 75-day old pigs. A comparison of dominant (DI>0) and submissive (DI<0) pigs showed significant differences (p<0.05) for major aggressive behaviors in all age groups. Dominant pigs were involved in more aggressive interactions, had longer fights, and initiated more fights than submissive pigs. Post-mixing aggressive behavior was altered by previous experience of mixing. Aggressive behavior and DI are suitable methods for analyzing the effects of mixing on commercially housed growing pigs.

Microfluidic sample delivery for serial crystallography using XFELs

Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFELs) is an emerging field for structural biology. One of its major impacts lies in the ability to reveal the structure of complex proteins previously inaccessible with synchrotron-based crystallography techniques and allowing time-resolved studies from femtoseconds to seconds. The nature of this serial technique requires new approaches for crystallization, data analysis, and sample delivery. With continued advancements in microfabrication techniques, various developments have been reported in the past decade for innovative and efficient microfluidic sample delivery for crystallography experiments using XFELs. This article summarizes the recent developments in microfluidic sample delivery with liquid injection and fixed-target approaches, which allow exciting new research with XFELs. Graphical abstract.

Correlation between system performance and bacterial composition under varied mixing intensity in thermophilic anaerobic digestion of food waste

This study examines the stability and efficiency of thermophilic anaerobic digesters treating food waste under various mixing velocities (50-160 rpm). The results showed that high velocities (120 and 160 rpm) were harmful to the digestion process with 18-30% reduction in methane generation and 1.8 to 3.8 times increase in volatile fatty acids (VFA) concentrations, compared to mild mixing (50 and 80 rpm). Also, the removal rate of soluble COD dropped from 75 to 85% (at 50-80 rpm) to 20-59% (at 120-160 rpm). Similarly, interrupted mixing caused adverse impacts and led to near-failure conditions with excessive VFA accumulation (15.6 g l^-1), negative removal rate of soluble COD and low methane generation (132 ml gVS^-1). The best efficiency and stability were achieved under mild mixing (50 and 80 rpm). In particular, the 50 rpm stirring speed resulted in the highest methane generation (573 ml gVS^-1). High-throughput sequencing of 16S rRNA genes revealed that the digesters were dominated by one bacterial genus (Petrotoga; phylym Thermotogae) at all mixing velocities except at 0 rpm, where the community was dominated by one bacterial genus (Anaerobaculum; phylum Synergistetes). The Petrotoga genus seems to have played a major role in the degradation of organic matter.

Exploring nutrient and light limitation of algal production in a shallow turbid reservoir

Harmful algal blooms are increasingly recognized as a threat to the integrity of freshwater reservoirs, which serve as water supplies, wildlife habitats, and recreational attractions. While algal growth and accumulation is controlled by many environmental factors, the relative importance of these factors is unclear, particularly for turbid eutrophic systems. Here we develop and compare two models that test the relative importance of vertical mixing, light, and nutrients for explaining chlorophyll-a variability in shallow (2-3 m) embayments of a eutrophic reservoir, Jordan Lake, North Carolina. One is a multiple linear regression (statistical) model and the other is a process-based (mechanistic) model. Both models are calibrated using a 15-year data record of chlorophyll-a concentration (2003-2018) for the seasonal period of cyanobacteria dominance (June-October). The mechanistic model includes a novel representation of vertical mixing and is calibrated in a Bayesian framework, which allows for data-driven inference of important process rates. Both models show that chlorophyll-a concentration is much more responsive to nutrient variability than mixing, light, or temperature. While both models explain approximately 60% of the variability in chlorophyll-a, the mechanistic model is more robust in cross-validation and provides a more comprehensive assessment of algal drivers. Overall, these models indicate that nutrient reductions, rather than changes in mixing or background turbidity, are critical to controlling cyanobacteria in a shallow eutrophic freshwater system.

Optimisation of an in-line Raman spectroscopic method for continuous API quantification during twin-screw wet granulation and its application for process characterisation

In a previous publication, the development of an in-line Raman spectroscopic method for continuous API quantification during twin-screw wet granulation was presented. An in-line method was developed successfully and the developed method showed an acceptable prediction error. A disadvantage of the developed method was that a measurement was only possible in the dark since light influenced the Raman spectra and made a data interpretation impossible. Therefore, the measurement setup for the implementation of the Raman probe was optimised in the present study to allow a measurement in interior light and to further improve the predictive performance. With the optimised setup, two different calibration models were developed and compared. For the first calibration model, spectra were collected in the dark as before and for the second in interior light. The dark calibration model was able to predict the API content with an RMSEP of 0.31% and the light model with an RMSEP of 0.29%. Thus, both PLS models showed prediction errors in the same order. Consequently, it was possible to evaluate Raman spectra which were collected in interior light. Further, the previous prediction error of 0.60% could be clearly decreased. The optimised Raman method was applicable to evaluate the mixing efficiency of the twin-screw granulator during a split feeding process. The quality of the mixture was monitored behind different barrel sections by Raman spectroscopy and the corresponding API concentrations were predicted by the developed calibration model. For a screw length of 40 D and a screw configuration with two kneading blocks a good mixing ability was observed. For a screw length of 20 D and one kneading block the mixing efficiency was largely acceptable whereas a broad scattering of the API content was observed when no kneading blocks were used. In a second part, an experimental design was performed for each screw configuration to evaluate the influence of the barrel-fill level and screw speed on the mixing efficiency. The quality of the mixture using the entire barrel length was minimally influenced by the fill-level. For the other two positions, the screw speed influenced the quality of the mixture slightly. Thus, for an appropriate mixing, a certain barrel length and a screw configuration with two kneading blocks were necessary.

Predictions of dynamic changes in reaction rates as a consequence of incomplete mixing using pore scale reactive transport modeling on images of porous media

We present a pore scale model capable of simulating fluid/fluid reactive transport on images of porous media from first principles. We use a streamline-based particle tracking method for simulating flow and transport, while for reaction to occur, both reactants must be within a diffusive distance of each other during a time-step. We assign a probability of reaction (Pr), as a function of the reaction rate constant (kr) and the diffusion length. Firstly, we validate our model for reaction against analytical solutions for the bimolecular reaction (A+B→C) in a free fluid. Then, we simulate transport and reaction in a beadpack to validate the model through predicting the fluid/fluid reaction experimental results provided by Gramling et al. (2002). Our model accurately predicts the experimental data, as it takes into account the degree of incomplete mixing present at the sub-pore (image voxel) level, in contrast to advection-dispersion-reaction equation (ADRE) model that over-predicts pore scale mixing. Finally, we show how our model can predict dynamic changes in the reaction rate accurately accounting for the local geometry, topology and flow field at the pore scale. We demonstrate the substantial difference between the predicted early-time reaction rate in comparison to the ADRE model.