258 research outputs found

    Combined ion exchange / biological denitrification for nitrate removal from ground water

    Get PDF
    This thesis deals with the development of a new process for nitrate removal from ground water. High nitrate concentrations in ground water are a result of fertilization in agriculture. According to a directive of the European Community the maximum admissible concentration of nitrate in drinking water is 11.3 mg NO 3--N/l and the guide level is 5.6 mg NO 3--N/l. To supply water that meets this standard several water supply companies will have to remove nitrate from ground water. Two existing techniques, viz ion exchange and biological denitrification, have serious disadvantages when used separately. Therefore, a new process has been developed that consists of a combination of ion exchange and biological denitrification. In this process nitrate is removed from the ground water by ion exchange. The ion exchange resins are regenerated in a closed circuit through an upflow sludge blanket (USB) denitrification reactor. In this reactor denitrifying bacteria remove nitrate from the regenerant, so that it can be used again and has not to be disposed of. As compared with conventional regeneration of anion exchange resins regeneration salt requirement and brine production are minimized. Further, in contrast with traditional single denitrification procedures, there is no direct contact between ground water and denitrifying bacteria.The first part of this thesis deals with the effect of high salt concentrations, as present in the closed regeneration system, on biological denitrification. Concentrations up to 30 g NaHCO 3 /l or 30 g NaCl/l have only little effect on the activity of denitrifying sludge. With high NaHCO 3 concentrations the sludge yield coefficient decreases and nitrite accumulation is suppressed. High sulfate concentrations (5.5 9 SO 42-/l) do not result in sulfide production in an USB denitrification reactor fed with methanol, when methanol is added in an appropriate ratio to the amount of nitrate to be denitrified.The second part of this thesis deals with the ion exchange part of the combined process. Regeneration of anion exchange resins can be achieved with a solution containing 30 g NaHCO 3 /l provided that a larger flow rate and a longer regeneration time are used as compared with conventional regeneration procedures. With nitrate selective resins it is possible to remove nitrate from ground water that contains high sulfate concentrations, while the nitrate capacity of these resins is not affected by high sulfate concentrations in the regenerant. To safeguard the bacteriological drinking water quality the resins have to be disinfected after each regeneration cycle by rinsing with 0.075% peracetic acid for 15 minutes or by rinsing with 0.20% hydrogen peroxide for 45 minutes. Since the first possibility results in an important loss of resin capacity on the long term, only the latter can be applied in practice.The third part of this thesis deals with the operation of a lab-scale pilot plant. The most important process variables studied were the regenerant composition (NaCl or NaHCO 3 ), the ion exchange resin type (sulfate selective or nitrate selective) and the ground water composition (low sulfate concentration or high sulfate concentration). To explain some phenomena that were observed during this research a computer model has been developed. With this model the regeneration of anion exchange resins in a closed circuit can be optimized

    Drinking water temperature modelling in domestic systems

    Get PDF
    Domestic water supply systems are the final stage of the transport process to deliver potable water to the customers' tap. Under the influence of temperature, residence time and pipe materials the drinking water quality can change while the water passes the domestic drinking water system. According to the Dutch Drinking Water Act the drinking water temperature may not exceed the 25°C threshold at point-of-use level. This paper provides a mathematical approach to model the heating of drinking water within the domestic water supply system. It appears that residence time influences the drinking water temperature more than the ambient temperature itself.</p

    Effectiveness of a MF-59™-adjuvanted pandemic influenza vaccine to prevent 2009 A/H1N1 influenza-related hospitalisation; a matched case-control study

    Get PDF
    Background: During the 2009 influenza A/H1N1 pandemic, adjuvanted influenza vaccines were used for the first time on a large scale. Results on the effectiveness of the vaccines in preventing 2009 influenza A/H1N1-related hospitalisation are scanty and varying.Methods: We conducted a matched case-control study in individuals with an indication for vaccination due to underlying medical conditions and/or age ≥ 60 years in the Netherlands. Cases were patients hospitalised with laboratory-confirmed 2009 A/H1N1 influenza infection between November 16, 2009 and January 15, 2010. Controls were matched to cases on age, sex and type of underlying medical condition(s) and drawn from an extensive general practitioner network. Conditional logistic regression was used to estimate the vaccine effectiveness (VE = 1 - OR). Different sensitivity analyses were used to assess confounding by severity of underlying medical condition(s) and the effect of different assumptions for missing dates of vaccination.Results: 149 cases and 28,238 matched controls were included. It was estimated that 22% of the cases and 28% of the controls received vaccination more than 7 days before the date of onset of symptoms in cases. A significant number of breakthrough infections were observed. The VE was estimated at 19% (95%CI -28-49). After restricting the analysis to cases with controls suffering from severe underlying medical conditions, the VE was 49% (95%CI 16-69).Conclusions: The number of breakthrough infections, resulting in modest VE estimates, suggests that the MF-59™ adjuvanted vaccine may have had only a limited impact on preventing 2009 influenza A/H1N1-related hospitalisation in this setting. As the main aim of influenza vaccination programmes is to reduce severe influenza-related morbidity and mortality from influenza in persons at high risk of complications, a more effective vaccine, or additional preventive measures, are needed

    Рівняння електромагнітної механіки пористого насиченого середовища

    Get PDF
    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

    Factor V Leiden mutation, prothrombin gene mutation, and deficiencies in coagulation inhibitors associated with Budd-Chiari syndrome and portal vein thrombosis: results of a case-control study

    Get PDF
    In a collaborative multicenter case-control study, we investigated the effect of factor V Leiden mutation, prothrombin gene mutation, and inherited deficiencies of protein C, protein S, and antithrombin on the risk of Budd-Chiari syndrome (BCS) and portal vein thrombosis (PVT). We compared 43 BCS patients and 92 PVT patients with 474 population-based controls. The relative risk of BCS was 11.3 (95% CI 4.8-26.5) for individuals with factor V Leiden mutation, 2.1(95% CI 0.4-9.6) for those with prothrombin gene mutation, and 6.8 (95% CI 1.9-24.4) for those with protein C deficiency. The relative risk of PVT was 2.7 (95% CI 1.1-6.9) for individuals with factor V Leiden mutation, 1.4 (95% CI 0.4-5.2) fo
    corecore