AOC removal and accumulation of bacteria in experimental sand filters

Ces dix dernières années, les méthodes permettant de déterminer la concentration des composés organiques assimilables par les bactéries dans de l'eau potable ont suscité de plus en plus d'intérêt envers les possibilités de prévision et de contrôle de la croissance des bactéries pendant le stockage et la distribution. La détermination dite "COA" (carbone organique aisément assimilable) introduite par VAN DER KOOIJ et. al. (1982) a été développée et appliquée dans le but de surveiller les concentrations de COA pendant le traitement, le stockage et la distribution. Sur la base des résultats, il a été établi un critère pour de l'eau potable biologiquement stable (VAN DER KOOIJ et HIJNEN, 1990). Ce critère exerce une influence sur la conception du traitement de l'eau. Ceci étant, il convient de porter davantage d'attention à l'effet des processus de traitement - et plus particulièrement des processus de filtration - sur la concentration de COA.Des expériences de filtration ont été effectuées sur de petits filtres à sable, dans des conditions de laboratoire bien déterminées. L'objectif de ces expériences consistait à déterminer (I) l'élimination du carbon organique aisément assimilable (COA) dans le filtre, pour des concentrations d'eaux affluentes différentes, (II) l'effet produit sur l'engorgement du filtre et (III) la qualité bactériologique du filtrat.De l'acétate a été ajouté à l'eau d'entrée des filtres en tant que modèle de substrat, dans une gamme de concentrations allant de 0,01 à 1 mg/l C. L'eau fournie était de l'eau potable préfiltrée à faible teneur en COA (0,005 mg ac-C eq/l). Au cours du temps de fonctionnement, la concentration de COA ainsi que le nombre de colonies dénombrées dans l'eau ont été contrôlés, de même que la perte de charge de la couche filtrante. A l'expiration du temps de fonctionnement, la concentration de matière bactérienne a été déterminée dans le sable des filtres.Dans les filtres à sable dont le temps de contact du lit vide était de 10 minutes, les concentrations d'acétate (Sac) inférieures ou égales à 0,25 mg/1 C ont été totalement éliminées. La réduction de COA pour les valeurs Sac de 0,5 et de 1,0 mg/l C atteignait 90 %. Il en a été conclu que les processus de filtration biologique peuvent fort bien être appliqués pour l'élimination de composés organiques aisément assimilables, tels l'acétate et l'éthanol qui sont fréquemment utilisés dans les processus d'élimination biologique des nitrates au cours du traitement de l'eau potable.La capacité d'élimination de l'acétate, offerte par les filtres à sable expérimentaux, était élevée par comparaison avec la réduction de COA observée dans le cas des filtres à sable utilisés pour la production d'eau potable à partir d'une eau de surface (VAN DER KOOIJ, 1984). La teneur en COA du filtrat dépassait le critère applicable à l'eau potable biologiquement stable, c'est-à-dire 0,01 mg ac-C eq/l, pour des charges volumique d'acétate (LVac), relevées sur les filtres à sable expérimentaux, supérieures à 1600 mg ac-C/(m3.h). La charge volumique critique en COA des filtres à sable, utilisés dans les installations de traitement citées plus haut, au-dessus de laquelle la teneur en COA du filtrat dépasse de critère, est estimée à environ 100 mg COA-C/(m3.h).Ces résultats indiquent que l'acétate est éliminé plus rapidement qu'une quantité équivalente de composés mesurée par détermination du COA.Par suite de la consommation d'acétate, le nombre de bactéries présentes dans le lit filtrant s'est accru. On a constaté qu'un net rapport linéaire existait entre la concentration d'acétate, d'une part, et le nombre de colonies dénombrées (par boite) sur le sable à la surface du filtre, d'autre part. L'accumulation de bactéries a été observée, même pour une concentration de COA de 0,005 mg ac-C/l, tandis que l'engorgement des filtres se produisait sous une concentration d'acétate de 0,01 mg ac-C/l. Des concentrations accrues de carbone organique ont été mesurées sur le sable, dans les premiers millimètres d'épaisseur du lit filtrant. Les résultats obtenus à la suite d'études sur le terrain, relatives à l'infiltration d'eau dans les puits de recharge, ont montré que, pour des valeurs de COA inférieures à 0,01 mg ac-C eq/l, la durée de processus n'atteignait pas un an, du fait de l'engorgement observé dans le sous-sol. Par conséquent, ta concentration de carbone organique assimilable (COA) dans l'eau utilisée pour l'infiltration doit être inférieure à 0,01 mg ac-C eq/l afin d'éviter l'engorgement biologique. Un niveau de COA similaire a été conseillé pour l'eau potable bioiogiquement stable (VAN DER KOOIJ and HIJNEN, 1990).La consommation d'acétate dans les filtres a eu comme autre conséquence l'accroissement du nombre de colonies hétérotrophes dénombrées dans l'eau, selon un rapport linéaire avec la concentration d'acétate dans l'eau affluente. Le nombre de colonies dénombrées présentes dans le filtrat s'est accru pour atteindre une valeur moyenne de 104 cfu/ml, sous une concentration d'acétate de 0,068 mg ac-C/l (charge volumique d'acétate de 400 mg ac-C/(m3.h)). Au vu de ces résultats, il a été conclu que la charge volumique en COA d'une filtration finale dans une installation de traitement des eaux devrait être limitée, entre autre afin d'éviter le recours à une post-désinfection visant à réduire le nombre de germes hétérotrophes.Using small sand filets under well defined laboratory conditions, filtration experiments were performed with tap water supplemented with acetate. The objective of these experiments was to determine the effect of different acetate concentrations on (i) the removal of easily assimilable organic carbon (AOC) in the filter (ii), the clogging of the tiller and (iii) the bacteriological quality of the filtrate.The results of the experiments revealed that the reduction capacity of biological filtration processes for acetate is relatively high. Acetate removal resulted in an increased microbiological activity in the top layer (< 1cm) of the filter bed and accumulation of bacterial matter was observed at an influent AOC concentration as low as 0.005 mg of ac-C eq/l. Clogging of the filter bed occurred at an influent acetate concentration of 0.01 mg C/l. Based on these observations it was concluded that the AOC concentration of water used for infiltration in recharge wells should be less thon 0.01 mg ac-C eq/l. This level is similar to the level advised for biologically-stable drinking water.A linear relationship was found between the acetate removal in the experimental filters and the colony count in the filtrate. It was recommended that the AOC load in the final filtration process in water treatment therefore should be limited to prevent high colony counts in the filtrate, thus leading to the use of post disinfection

Determination of Serum Nucleotidase with Cytidine Monophosphate as Substrate. Part II: Improvement of the procedure

Peer Reviewe

Optimal Scaling transformations to model non-linear relations in GLMs with ordered and unordered predictors

In Generalized Linear Models (GLMs) it is assumed that there is a linear effect of the predictor variables on the outcome. However, this assumption is often too strict, because in many applications predictors have a nonlinear relation with the outcome. Optimal Scaling (OS) transformations combined with GLMs can deal with this type of relations. Transformations of the predictors have been integrated in GLMs before, e.g. in Generalized Additive Models. However, the OS methodology has several benefits. For example, the levels of categorical predictors are quantified directly, such that they can be included in the model without defining dummy variables. This approach enhances the interpretation and visualization of the effect of different levels on the outcome. Furthermore, monotonicity restrictions can be applied to the OS transformations such that the original ordering of the category values is preserved. This improves the interpretation of the effect and may prevent overfitting. The scaling level can be chosen for each individual predictor such that models can include mixed scaling levels. In this way, a suitable transformation can be found for each predictor in the model. The implementation of OS in logistic regression is demonstrated using three datasets that contain a binary outcome variable and a set of categorical and/or continuous predictor variables.Comment: 35 pages, 4 figure

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics

Microfluidic Production of Polymeric Core-Shell Microspheres for the Delayed Pulsatile Release of Bovine Serum Albumin as a Model Antigen

For many vaccines, multiple injections are required to confer protective immunity against targeted pathogens. These injections often consist of a primer administration followed by a booster administration of the vaccine a few weeks or months later. A single-injection vaccine formulation that provides for both administrations could greatly improve the convenience and vaccinee’s compliance. In this study, we developed parenterally injectable core-shell microspheres with a delayed pulsatile release profile that could serve as the booster in such a vaccine formulation. These microspheres contained bovine serum albumin (BSA) as the model antigen and poly(DL-lactide-co-glycolide) (PLGA) with various DL-lactide:glycolide monomer ratios as the shell material. Highly monodisperse particles with different particle characteristics were obtained using a microfluidic setup. All formulations exhibited a pulsatile in vitro release of BSA after an adjustable lag time. This lag time increased with the increasing lactide content of the polymer and ranged from 3 to 7 weeks. Shell thickness and bovine serum albumin loading had no effect on the release behavior, which could be ascribed to the degradation mechanism of the polymer, with bulk degradation being the main pathway. Co-injection of the core-shell microspheres together with a solution of the antigen that serves as the primer would allow for the desired biphasic release profile. Altogether, these findings show that injectable core-shell microspheres combined with a primer are a promising alternative for the current multiple-injection vaccines

Рівняння електромагнітної механіки пористого насиченого середовища

За двоконтинуумного наближення отримано повну систему співвідношень моделі електромагнітомеханіки статистично однорідного та ізотропного пористого насиченого середовища. Враховано наявність подвійного електричного шару в околі межі контакту твердої і рідкої фаз.Complete set of the model equations for electromagnetic mechanics of the porous saturated medium being statistically homogeneous and isotropic is obtained in two-continuum approximation. The presence of a double electrical layer in an environ of contact boundary of solid and liquid phases is taken into account.В двухконтинуумном приближении получено полную систему соотношений модели электромагнитомеханики статистически однородной и изотропной пористой насыщенной среды. Учтено наличие двойного электрического слоя в окрестности границы контакта твердой и жидкой фаз

Non-linear stimulus-response behavior of the human stance control system is predicted by optimization of a system with sensory and motor noise

We developed a theory of human stance control that predicted (1) how subjects re-weight their utilization of proprioceptive and graviceptive orientation information in experiments where eyes closed stance was perturbed by surface-tilt stimuli with different amplitudes, (2) the experimentally observed increase in body sway variability (i.e. the “remnant” body sway that could not be attributed to the stimulus) with increasing surface-tilt amplitude, (3) neural controller feedback gains that determine the amount of corrective torque generated in relation to sensory cues signaling body orientation, and (4) the magnitude and structure of spontaneous body sway. Responses to surface-tilt perturbations with different amplitudes were interpreted using a feedback control model to determine control parameters and changes in these parameters with stimulus amplitude. Different combinations of internal sensory and/or motor noise sources were added to the model to identify the properties of noise sources that were able to account for the experimental remnant sway characteristics. Various behavioral criteria were investigated to determine if optimization of these criteria could predict the identified model parameters and amplitude-dependent parameter changes. Robust findings were that remnant sway characteristics were best predicted by models that included both sensory and motor noise, the graviceptive noise magnitude was about ten times larger than the proprioceptive noise, and noise sources with signal-dependent properties provided better explanations of remnant sway. Overall results indicate that humans dynamically weight sensory system contributions to stance control and tune their corrective responses to minimize the energetic effects of sensory noise and external stimuli

Measuring sustainable employability:psychometric properties of the capability set for work questionnaire

BACKGROUND: The capability set for work questionnaire (CSWQ) is being used to measure the new model of sustainable employability building on the capability approach. However, previous studies on the psychometric properties of the instrument are limited and cross-sectional. This two-way study aimed to (1) evaluate the convergent validity of the CSWQ with the theoretically related constructs person-job fit, strengths use, and opportunity to craft and (2) test the predictive and incremental validity of the questionnaire for the well-established work outcomes, including work ability, work engagement, job satisfaction, and task performance. METHODS: A representative sample of 303 Dutch workers, chosen with probably random sampling, were surveyed using a one-month follow-up, cross-lagged design via the Longitudinal Internet Studies for the Social Sciences panel. The convergent validity was assessed by exploring the strength of associations between the capability set for work questionnaire and the theoretically related constructs using Pearson’s correlations. The predictive and incremental validity was evaluated by performing a series of linear hierarchical regression analyses. RESULTS: We found evidence of the convergent validity of the capability set score by moderate correlations with person-job fit, strengths use, and opportunity to craft (r = 0.51–0.52). A series of multiple regression analyses showed that Time 1 capability set score and its constituents (i.e., importance, ability, and enablement) generally had predictive and incremental validity for work ability, work engagement, job satisfaction, and task performance measured at Time 2. However, the incremental power of the CSWQ over and above conceptually related constructs was modest. CONCLUSIONS: The findings support the convergent, predictive, and incremental validity of the capability set for work questionnaire with not previously investigated work constructs. This provided further evidence to support its utility for assessing a worker’s sustainable employability for future research and practical interventions