Clogging dynamics of particles and bacteria in microfluidic systems mimicking microfiltration processes

L'objectif de cette thèse est de progresser dans la compréhension du colmatage lors de la filtration de la matière molle (particules colloïdales et bactéries) et d'étudier l'efficacité et la faisabilité de séparateurs microfluidiques. Ces recherches sont réalisées avec des puces microfluidiques constituées de canaux dont la taille est du même ordre de grandeur que les objets filtrés. Ces puces, conçues pour représenter les processus ayant lieu en microfiltration frontale et tangentielles, permettent d'observer in-situ sous microscope les mécanismes de colmatage. Le système est instrumenté avec des capteurs de débit et de pression et permet ainsi une analyse croisée entre les observations et les variations de perméabilité. Les expériences ont été réalisées pour différentes conditions hydrodynamiques (débit, mode de filtration) et conditions d'interactions colloïdales (en changeant la force ionique). Les résultats mettent en évidence l'importance de la dynamique du blocage de pore par des agrégats de particules et du réentrainement de ces agrégats lorsqu'ils sont fragilisés par l'écoulement. La dynamique de ces évènements provoque des fluctuations de perméabilité. Les interactions particule-particule ou particule-paroi jouent également un rôle important sur la dynamique du colmatage. Trois scenarios sont discutés par analogie anthropomorphique : un scenario panique (0.01 mM) où les répulsions entre les particules induit un phénomène de poussée entre particules qui engendre la formation d'arches à l'entrée des canaux ; un scenario instinct de troupeau (10 mM) où l'attraction entre particules (dans un minimum DLVO secondaire) facilite le transport dans le canal et retarde le colmatage ; un scenario sacrificiel (100 mM) où l'efficacité de capture des particules par les parois est élevée mais les agrégats formés sont très fragiles et fréquemment réentraînés par l'écoulement. Cette analyse illustre l'importance des phénomènes collectifs lors du colmatage par des particules inter-agissantes. Le mécanisme de colmatage par des particules biologiques (bactéries) et notamment la création de panaches bactériens en aval des canaux sont ensuite analysés. Ces phénomènes sont étudiés pour différentes conditions de culture (ratio carbone-azote dans le substrat) afin d'examiner l'effet de la production de substances polymériques extracellulaires (EPS) sur le colmatage. Les résultats montrent que les EPS (et donc les conditions de cultures) jouent un rôle crucial sur le développement de panaches bactériens lors d'écoulement dans des constrictions. Il est montré également que la filtration d'un mélange entre des bactéries produisant peu d'EPS et des bactéries produisant d'EPS favorise la formation des panaches bactériens. Des filtrations de mélange de bactéries et de particules montrent que la présence de bactérie modifie la dynamique du blocage des canaux ; de façon surprenante l'ajout de bactérie permet de retarder le colmatage et de former des dépôts de particules plus fragiles. Des systèmes microfluidiques avec un design spécifique ont également été développés pour réaliser un fractionnement par taille de dispersions sous un écoulement tangentiel. Des résultats préliminaires ont permis d'optimiser leur fonctionnement en trouvant des conditions permettant de filtrer en évitant le blocage des canaux ; leur utilisation pour réaliser des fractionnements continus dans des puces microfluidiques peut être envisagée.The aim of the PhD is to progress in the understanding of the fouling phenomena during filtration of soft matter (colloidal particles and bacteria) and to examine the efficiency and feasibility of microfluidic separators. These studies are realized with microfluidic devices constituted of micrometric channels having the same size range as the materials being filtered. These devices, which mimic membrane dead-end and cross-flow microfiltration processes, allow in-situ and direct microscopic observations of the fouling mechanisms. The microfluidic system is equipped with flow rate and pressure measurement devices allowing a dynamic cross analysis of the observations with the variations of permeability. Experiments have been realized for different hydrodynamic conditions (flow rate, filtration mode) and for different colloidal interactions (by varying the ionic strength) in order to analyse their interplay in the clogging mechanism by soft matter (interacting particles). The results evidenced the importance of clogs formation, fragility and sweeping out dynamics during the fouling process. These dynamic events at bottlenecks induce important permeability fluctuations. The particle-particle and particle-wall interactions also play important roles on the clogging dynamics. Three different scenarios are discussed by analogy to crowd swarming: panic scenario (0.01 mM) where repulsion between particles induce pushing effects leading to the creation of robust arches at pore entrances; herding instinct scenario (10 mM) where the attraction (in secondary minima) between particles enhances the transport in pores and delays clogging; sacrifice scenario (100 mM) where the capture efficiency is high but the aggregates formed at the wall are fragile. These analyses illustrate the importance of collective behaviour exhibited by interacting particles during fouling. The fouling phenomena by biological particles (bacteria) are analysed in terms of the streamer formation conditions and mechanisms. The streamer formation phenomena are in turn analysed by playing with the cultivation conditions (the carbon to nitrogen ratio in the substrate) in order to study the effect of extracellular polymeric substances (EPS) on the process. The results show that EPS (and hence the bacterial cultivation conditions) play crucial role in streamer formation by microorganisms under flow in constrictions. Furthermore, the presence of non-EPS producing bacterial species along with EPS producing species in a mixed culture enhances the streamer formation. On the other hand, filtration of mixed particles and bacteria suspensions show that the presence of bacteria substantially modifies the clogging dynamics. Microfluidic devices with specific configurations have also been developed for fractionation in order to maximize performances of these processes. The preliminary results with these chips in cross-flow conditions show that it is possible to limit the clogging impact by working below a critical flux; their use for continuous microparticles fractionation could be then considered

Adsorption of methylene blue dye onto acid-treated tej residue: Kinetic, equilibrium and thermodynamic study

Dye-containing wastewater is a very toxic and a major threat to the deterioration of water quality and makes it unsuitable for domestic purposes. This drives low cost and eco-friendly adsorbents from environmental waste have been investigated to treat dye-containing wastewater. In the present study, tej residues (TR) have been successfully employed as a natural and non-conventional low-cost adsorbent for the removal of methylene blue (MB) dye from an aqueous solution. Optimization of maximum operating condition has been carried out by batch mode experiment and the result shows maximum removal efficiency of 82.1821 % at pH 8.0, adsorbent dosage 0.4g, initial dye concentration 20 ppm, contact time 60 min, and temperature 25°C on the acid-treated surface of tej residue. Adsorption kinetics of the adsorbent has been evaluated by pseudo-first-order, pseudo-second-order and intra-particle diffusion, and it is observed that the pseudo-first-order kinetic model is better fitted with a good correlation coefficient, and the equilibrium data fitted well with the Freundlich isotherm model. The Langmuir isotherm model estimates that the maximum adsorption capacity of the monolayer is found to be 215.053 mg/g. Thermodynamics parameters such as ΔG0, ΔH0 and ΔS0 indicate that the sorption process is feasible and exothermic

Loss to follow-up in "test and treat era" and its predictors among HIV-positive adults receiving ART in Northwest Ethiopia: Institution-based cohort study.

Background: People living with HIV/AIDS are enrolled in lifelong Anti-Retroviral Treatment (ART) irrespective of their clinical staging as well as CD4 cell count. Although this "Universal Test and Treat" strategy of ART was found to have numerous benefits, loss from follow-up and poor retention remained a long-term challenge for the achievement of ART program targets. Hence, this study is aimed at addressing the much-needed effect of the test and treat strategy on the incidence of loss to follow-up (LTFU) in Ethiopia. Method and materials: An institution-based follow-up study was conducted on 513 adults (age ≥15) who enrolled in ART at a public health institution in Bahir Dar City, Northwest Ethiopia. Data were extracted from the charts of selected patients and exported to Stata 14.2 software for analysis. Basic socio-demographic, epidemiological, and clinical characteristics were described. The Kaplan-Meier curve was used to estimate the loss to follow-up free (survival) probability of HIV-positive adults at 6, 12, 24, and 48 months of ART therapy. We fitted a multivariable Cox model to determine the statistically significant predictors of LTFU. Result: The incidence density of LTFU was 9.7 per 100 person-years of observation (95% CI: 7.9-11.9 per 100 PYO). Overall, LTFU is higher in the rapid ART initiation (24% in rapid initiated vs. 11.3% in lately initiated, AHR 2.08, P = 0.004), in males (23% males vs. 14.7% females, AHR1.96, P = 0.004), in singles (34% single vs. 11% married, with AHR1.83, P = 0.044), in non-disclosed HIV-status (33% non-disclosed 11% disclosed, AHR 2.00 p = 0.001). Patients with poor/fair ART adherence were also identified as another risk group of LTFU (37% in poor vs. 10.5% in good adherence group, AHR 4.35, P = 0.001). Conclusion: The incidence of LTFU in this universal test and treat era was high, and the highest figure was observed in the first 6 months. Immediate initiation of ART in a universal test and treat strategy shall be implemented cautiously to improve patient retention and due attention shall be given to those high-risk patients

Prevalence of depression and associated factors among pregnant women attending antenatal care in public health institutions of Awabale Woreda, East Gojjam Zone, Northwestern Ethiopia: A cross-sectional study

Background Antenatal depression is a serious health problem and has negative consequences for the mother, fetus, and the entire family. However, it is a neglected component of care especially bay health care providers for women in pregnancy. The purpose of this study was to assess the prevalence of depression and associated factors among pregnant women attending antenatal clinics in public health institutions, in the Awabale Woreda. Method An institutional-based cross-sectional study was conducted in 2018 and a stratified sampling technique was used to select the study health institutions. All seven public health institutions in Awabale District were included to select 393 mothers and the sample size was proportionally allocated based on the number of target mothers. We used EpiData version 3.1software for data entry and SPSS version 20 software for cleaning and analysis. A Bivariable logistic regression analysis was used to identify the association between each outcome variable and the factor. Again, a multivariable logistic regression analysis was employed to identify factors associated with each outcome variable, and variables with a p-value less than 0.05 were taken as significant variables. Edinburgh Postnatal Depression Scale was used to declare the presence of antenatal depression with a cut point score of 13 and above. Result This study showed that 63(17.8%) pregnant mothers had antenatal depressive symptoms. Women who were employed 85% reduced to develop antenatal depression than housewives [AOR = 0.15(0.001–0.25)]. Pregnant women who attended high school and above educational level were 18 times more likely to develop antenatal depression than women who had no formal education [AOR18.15 (2.73–120.76)]. Women who had poor husband feeling on the current pregnancy were 4.94 more likely to develop antenatal depression than women who had good partner feeling on the current pregnancy [AOR = 4.94(95%CI: 1.78–13.72)]. Women who had a history of depression were 8.2 times to develop antenatal depression than women who had no history of depression [AOR = 8.22 (95%CI: 2.87–23.57)]. Conclusion This study revealed that approximately one-fifth of pregnant women developed antenatal depression. Women’s occupational status, educational status, previous history of depression, and poor husband feeling on the current pregnancy were the significant factors of antenatal depression

Optimization of process parameters for the synthesis of geopolymer binders

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Bacteria Delay the Jamming of Particles at Microchannel Bottlenecks

Clogging of channels by complex systems such as mixtures of colloidal and biological particles is commonly encountered in different applications. In this work, we analyze and compare the clogging mechanisms and dynamics by pure and mixture suspensions of polystyrene latex particles and Escherichia coli by coupling fluorescent microscopic observation and dynamic permeability measurements in microfluidic filters. Pure particles filtration leads to arches and deposit formation in the upstream side of the microfilter while pure bacteria form streamers in the downstream zone. When mixing particle and bacteria, an unexpected phenomenon occurs: the clogging dynamics is significantly delayed. This phenomenon is related to apparent “slippery” interactions between the particles and the bacteria. These interactions limit the arches formation at the channels entrances and favour the formation of dendritic structures on the pillars between the channels. When these dendrites are eroded by the flow, fragments of the deposit are dragged towards the channels entrances. However, these bacteria/particles clusters being lubricated by the slippery interactions are deformed and stretched by the shear thus facilitating their passage through the microchannels

Predicting Trends, Seasonal Effects, and Future Yields in Cow’s Milk through Time Series Analysis

A dairy is a place that is used for handling milk and milk products. Dairy products are basically based on milk. Milk is used to prepare dairy products, such as butter, cheese, and milk powder. There is always a great demand for milk and milk products among people. This study attempted to investigate the trends in the actual yield of cow’s milk production at Andassa dairy farm. We used secondary data for the study of the daily milk production of cows at Andassa dairy farm. The specific objectives of the study were—to identify whether the milk production is time-dependent or not; to predict in which season the milk production is high or low; to examine the daily trend analysis of milk production; to fit the appropriate model; and to forecast the milk production for the future. The study was conducted based on quantitative variables. So, the dependent variable is the average daily milk, and the independent variable is the time measure at which milk production is measured each day. The study used both descriptive and inferential statistics to analyze the data that were collected from the dairy farms in the sector. This study covered a total of 179 days of milk production. The results reveal that the milk yield of cows is declining, and that milk output is time-dependent, according to the time series plot, and that the model is ARIMA

Trend, determinants, and future prospect of child marriage in the Amhara region, Ethiopia: a multivariate decomposition analysis

BackgroundChild marriage is a harmful traditional practice, which compromises children of their childhood and threatens their lives and health. In Ethiopia, 58% of women and 9% of men get married before the age of 18 years. Surprisingly, parents in the Amhara region make marriage promises of their children before they are even born, which will hinder the region from attaining the Sustainable Development Goal of ending child marriage. Thus, this study aimed to assess the trends, determinants, and future prospects of child marriage in the Amhara region of Ethiopia.MethodsA repeated cross-sectional study was conducted using four consecutive nationally representative Ethiopian demographic and health surveys (2000–2016). A logit-based multivariate decomposition analysis for a non-linear response model was fitted to identify factors that contributed to the change in child marriage over time. Statistical significance was declared at a p-value of < 0.05. The child marriage practice in the Amhara region by the year 2030 was also predicted using different forecasting features of Excel.ResultsThe trend of child marriage over the study period (2000–2016) decreased from 79.9% (76.7, 82.8) to 42.9% (39.1, 46.9), with an annual average reduction rate of 2.9%. Approximately 35.2% of the decline resulted from an increase in the proportion of women who attained secondary and above-secondary education over the two surveys. A decrease in the proportion of rural women and a change in the behavior of educated and media-exposed women also contributed significantly to the decline in child marriage. The prevalence of child marriage in the Amhara region by the year 2030 was also predicted to be 10.1% or 8.8%.ConclusionThough there has been a significant decline in child marriage in the Amhara region over the past 16 years, the proportion is still high, and the region is not going to eliminate it by 2030. Education, residence, and media exposure were all factors associated with the observed change in child marriage in this study. Therefore, additional efforts will be required if child marriage is to be eliminated by 2030, and investing more in education and media access will hasten the region's progress in this direction

Dyslipidemia and serum cystatin C levels as biomarker of diabetic nephropathy in patients with type 2 diabetes mellitus

BackgroundDiabetic nephropathy is a leading cause of end-stage renal disease. The diagnostic markers of nephropathy, including the presence of albuminuria and/or a reduced estimated glomerular filtration rate, are not clinically ideal, and most of them are raised after a significant reduction in renal function. Therefore, it is crucial to seek more sensitive and non-invasive biomarkers for the diagnosis of diabetic nephropathy.Objective of the studyThis study aimed to investigate the serum cystatin C levels and dyslipidemia for the detection of diabetic nephropathy in patients with type 2 diabetes mellitus.MethodologyA hospital-based comparative cross-sectional study was conducted from December 2021 to August 2022 in Tikur, Anbessa specialized teaching hospital with a sample size of 140 patients with type2 diabetes mellitus. Socio-demographic data was collected using a structured questionnaire, and 5 mL of blood was collected from each participant following overnight fasting for biochemical analyses.ResultsIn type 2 diabetes patients with nephropathy, we found significant lipoprotein abnormalities and an increase in serum cystatin C (P < 0.001) compared to those without nephropathy. Serum cystatin C, systolic blood pressure, fasting blood glucose, total cholesterol, triglyceride, low density lipoprotein, very low-density lipoprotein, high density lipoprotein, and duration of diabetes were identified as being significantly associated with diabetic nephropathy (P < 0.05) in multivariable logistic regression analysis. The mean values of total cholesterol levels, triglyceride levels, and high-density lipoprotein cholesterol levels were also found to be significantly higher (P < 0.05) in females as compared to male type-2 diabetic patients. The fasting blood glucose levels and lipid profiles of the participants were found to be significantly associated with serum cystatin C levels.ConclusionThe present study found significant serum cystatin C and lipoprotein abnormalities in T2DM patients with diabetic nephropathy when compared with those without diabetic nephropathy, and these lipoprotein abnormalities were significantly associated with serum cystatin C levels

Prescribing indicators at primary health care centers within the WHO African region: a systematic analysis (1995-2015)

Abstract Background Rational medicine use is essential to optimize quality of healthcare delivery and resource utilization. We aim to conduct a systematic review of changes in prescribing patterns in the WHO African region and comparison with WHO indicators in two time periods 1995–2005 and 2006–2015. Methods Systematic searches were conducted in PubMed, Scopus, Web of science, Africa-Wide Nipad, Africa Journals Online (AJOL), Google scholar and International Network for Rational Use of Drugs (INRUD) Bibliography databases to identify primary studies reporting prescribing indicators at primary healthcare centres (PHCs) in Africa. This was supplemented by a manual search of retrieved references. We assessed the quality of studies using a 14-point scoring system modified from the Downs and Black checklist with inclusions of recommendations in the WHO guidelines. Results Forty-three studies conducted in 11 African countries were included in the overall analysis. These studies presented prescribing indicators based on a total 141,323 patient encounters across 572 primary care facilities. The results of prescribing indicators were determined as follows; average number of medicines prescribed per patient encounter = 3.1 (IQR 2.3–4.8), percentage of medicines prescribed by generic name =68.0 % (IQR 55.4–80.3), Percentage of encounters with antibiotic prescribed =46.8 % (IQR 33.7–62.8), percentage of encounters with injection prescribed =25.0 % (IQR 18.7–39.5) and the percentage of medicines prescribed from essential medicines list =88.0 % (IQR 76.3–94.1). Prescribing indicators were generally worse in private compared with public facilities. Analysis of prescribing across two time points 1995–2005 and 2006–2015 showed no consistent trends. Conclusions Prescribing indicators for the African region deviate significantly from the WHO reference targets. Increased collaborative efforts are urgently needed to improve medicine prescribing practices in Africa with the aim of enhancing the optimal utilization of scarce resources and averting negative health consequences