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

The growth of bacteria on organic compounds in drinking water

Growth ("regrowth") of bacteria In drinking water distribution systems results in a deterioration of the water quality. Regrowth of chemoheterotrophic bacteria depends on the presence of organic. compounds that serve as a nutrient source for these bacteria. A batch-culture technique was developed to study the growth of bacteria in drinking water. The maximum colony counts of selected pure cultures of bacteria grown in drinking water were used as a measure for the concentration of easily assimilable organic carbon compounds (AOC). Three strains of bacteria isolated from drinking water were selected for AOC determinations: (1) Pseudomonas fluorescens strain P17, an organism with a very great nutritional versatility, for general use; (2) a Flavobacterium sp. strain S12, to determine the concentration of maltose and starch-like compounds, and (3) a Spirillum sp. strain NOX to determine the concentration of carboxylic acids. Including oxalic acid. The properties of these bacteria were extensively studied in batch-culture experiments with drinking water supplemented with very low amounts of selected organic compounds. The obtained results prove that growth and growth kinetics of bacteria at concentrations between 1 and 1000 μg of C per liter can be determined in simple experiments using simple equipment. The strains mentioned above were well adapted to growth at concentrations of a few micrograms of substrate C per liter; their substrate saturation constants (K s ) were below 1 μM for many compounds tested. K s values below 0.1 μM were also obtained. Growth measurements with strain P17 in water sampled from various treatment stages revealed that the AOC concentrations in these water types usually varied between 10 and 100 μg of acetate C equivalents per liter. Ozonation caused a strong increase of the AOC concentration. Strain NOX was better suited for the determination of the AOC concentration in ozonated water because of its ability to utilize oxalate. Filtration processes caused significant reductions of the AOC concentrations, at low AOC concentrations (Flavobacterium strain S12. The concentration of these compounds was reduced to non-detectable levels ( Pseudomonas aeruginosa in the filtrate of slow sand filters, and the inability of Aeromonas hydrophila to multiply in this water type.<p/

An Old Dog Learns Some New Tricks: Ready to Embrace Online Learning with Collaborate

https://digitalcommons.winthrop.edu/weeklyreader/1058/thumbnail.jp

Sensory reweighting of proprioceptive input during balance control in healthy elderly

Sensory (re)weighting is the automated and unconscious process of combining sensory inputs, e.g. proprioception, graviception and vision, during human balance control. Typically reliable sensory inputs are weighted more than unreliable and noisy sensory inputs, to prevent deterioration of human balance control. Malfunctioning of sensory reweighting may be an important determinant of balance deficits in elderly with the consequence of falls. In this study we compared sensory (re)weighting of prioprioceptive input of the ankle joints, as one of the available sensory inputs, in healthy young versus healthy elderly during upright stance. Ten healthy young (aged 20-30 years) and ten healthy elderly (aged 75-80 years) were asked to maintain balance while proprioceptive input of each ankle was perturbed by rotations of the support surfaces around the ankle axes. Support surface rotations were applied with specific frequency content and increasing perturbation amplitude over trials. Body sway and reactive ankle torques were recorded. The sensitivity of the ankle torques to perturbation amplitude was determined using system identification techniques. The gain of a sensitivity function describes the ratio of perturbation amplitude and response amplitude as a function of frequency. Overall, elderly had a significant higher gain of the sensitivity function than young subjects. Increasing amplitude of the sensory perturbation resulted in a significant decrease of the gain of the sensitivity function from the perturbation amplitude to the ankle torque. Significant frequency-dependent interactions between group and perturbation amplitude could be established. A significant higher ankle torque sensitivity to perturbations indicates that elderly rely more strongly on proprioceptive input to maintain balance compared to younger subjects. Different reactions of elderly versus young subjects to perturbation amplitudes are indicative of differences in sensory reweighting. Results are important to understand interplay between available sensory inputs in balance and falling

Mathematics in different settings: plenary panel.

When we think about the title “Mathematics in different settings”, a number of questions arise. For example: • How many mathematics are there – one or many? Is there a mathematics that is “prior to”, or independent of, any setting? • What (who) is it that makes settings “different”? And how does this relate to social differences among people? • What is an appropriate typology of different settings – for research or for curriculum design purposes? Relatedly, we might ask: who decides what is “important”? • What is the nature of relations among policy arrangements, research and educational institutional settings? • How are different settings represented in mathematics teaching and assessment? • What is the relationship of mathematics education researchers to any setting

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

Clinical and radiological efficacy of initial vs delayed treatment with infliximab plus methotrexate in patients with early rheumatoid arthritis

= 6 months, IFX was tapered and finally stopped. We aimed to correct for allocation bias using propensity scores. Functional ability was measured by the Health Assessment Questionnaire (HAQ), radiological progression by Sharp/van der Heijde scoring (SHS). Results: Baseline differences between the initial and delayed groups were no longer significant after propensity score adjustment. At 3 years after baseline, patients treated with initial MTX+IFX experienced more improvement in HAQ over time and were less likely to have SHS progression than patients treated with delayed MTX+IFX (p = 0.034). At 2 years after IFX initiation, more patients in the initial group compared with the delayed group could discontinue IFX after a good response (56% vs 29%, p = 0.008). Conclusions: The results of this post hoc analysis suggest that using MTX+IFX as initial treatment for patients with recent onset RA is more effective than reserving MTX+IFX for patients who failed on traditional DMARDs, with more HAQ improvement over time, more IFX discontinuation and less progression of joint damag

Intracellular proliferation of Legionella pneumophila in Hartmannella vermiformis in aquatic biofilms grown on plasticized polyvinyl chloride

The need for protozoa for the proliferation of Legionella pneumophila in aquatic habitats is still not fully understood and is even questioned by some investigators. This study shows the in vivo growth of L. pneumophila in protozoa in aquatic biofilms developing at high concentrations on plasticized polyvinyl chloride in a batch system with autoclaved tap water. The inoculum, a mixed microbial community including indigenous L. pneumophila originating from a tap water system, was added in an unfiltered as well as filtered (cellulose nitrate, 3.0-mum pore size) state. Both the attached and suspended biomasses were examined for their total amounts of ATP, for culturable L. pneumophila, and for their concentrations of protozoa. L. pneumophila grew to high numbers (6.3 log CFU/cm(2)) only in flasks with an unfiltered inoculum. Filtration obviously removed the growth-supporting factor, but it did not affect biofilm formation, as determined by measuring ATP. Cultivation, direct counting, and 18S ribosomal DNA-targeted PCR with subsequent sequencing revealed the presence of Hartmannella vermiformis in all flasks in which L. pneumophila multiplied and also when cyclobeximide had been added. Fluorescent in situ hybridization clearly demonstrated the intracellular growth of L. pneumophila in trophozoites of H. vermiformis, with 25.9% +/- 10.5% of the trophozoites containing L. pneumophila on day 10 and >90% containing L. pneumophila on day 14. Calculations confirmed that intracellular growth was most likely the only way for L. pneumophila to proliferate within the biofilm. Higher biofilm concentrations, measured as amounts of ATP, gave higher L. pneumophila concentrations, and therefore the growth of L. pneumophila within engineered water systems can be limited by controlling biofilm formation