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Talbot P.,Eng-Tips | Martinelli L.,Eng-Tips | Talvy S.,Eng-Tips | Chauveheid E.,Vivaqua | Haut B.,Eng-Tips
Water Research | Year: 2012

In this work, the ozone inactivation of resistant microorganisms is studied and a method to assess the efficiency of a drinking water plant to inactivate resistant microorganisms using ozone is proposed. This method aims at computing the fraction of resistant microorganisms that are not inactivated at the exit of an ozonation step by evaluating the duration of the lag phase of the ozone inactivation of these microorganisms and the contact time distribution of these microorganisms with the ozone in the step. To evaluate the duration of the lag phase of the ozone inactivation of resistant pathogenic microorganisms, an experimental procedure is proposed and applied to Bacillus subtilis spores. The procedure aims at characterizing the ozone inactivation kinetics of B. subtilis spores for different temperature and ozone concentration conditions. From experimental data, a model of the ozone inactivation of B. subtilis spores is built. One of the parameters of this model is called the lag time and it measures the duration of the lag phase of the ozone inactivation of B. subtilis spores. This lag time is identified for different temperature and ozone concentration conditions in order to establish a correlation between this lag time and the temperature and ozone concentration conditions. To evaluate the contact time distribution between microorganisms and the ozone in a disinfection step of a drinking water plant, a computational fluid dynamics tool is used. The proposed method is applied to the ozonation channel of an existing drinking water plant located in Belgium and operated by Vivaqua. Results show that lag times and contact times are both in the same order of magnitude of a few minutes. For a large range of temperatures and ozone concentrations in the Tailfer ozonation channel and for the highest hydraulic flow rate applied, a significant fraction of resistant microorganisms similar to B. subtilis spores is not inactivated. © 2012 Elsevier Ltd.


Talvy S.,Eng-Tips | Debaste F.,Eng-Tips | Martinelli L.,Eng-Tips | Chauveheid E.,Vivaqua | Haut B.,Eng-Tips
Chemical Engineering Science | Year: 2011

Foreseen standards regarding microorganism content for drinking water require assessment of the capability of existing plants to reach the upcoming requirements. This paper presents the development of a tool to assess this capability in a commonly encountered key step of water disinfection: ozonation. In this paper, this tool is applied to the test case of an ozonation channel of the Belgian drinking water producer Vivaqua. This tool is based on a mathematical model of the momentum and mass transport phenomena in an ozonation channel. The gas-liquid flow is coupled to ozone mass transfer and kinetics describing the ozone and microorganisms concentrations decay. The degradation of Bacillus subtilis spores, as a representative of resistant microorganisms, is implemented in the model. The model takes explicitly into account the bubble size variation and its impact on mass transfer. Bubbles sizes and kinetics parameters are estimated based on dedicated experiments. The model is partially validated by comparing simulations results, obtained using computational fluid dynamics, to experimental residence time distributions, residual ozone concentration and Bacillus subtilis spores degradation efficiency measurements obtained on the studied ozonation channel. It is shown that, at the industrial scale, bubble diameter variation has a significant impact on ozone concentration in the liquid at the reactor exit. Using the tool, it is also shown that, the ozonation channel of Vivaqua can be used to achieve degradation of resistant microorganisms but only with its maximal flow rate and concentration of ozone injection. Moreover, at low operating temperature, some microorganisms that present latency towards reaction with dissolved ozone might hardly be destroyed. © 2011 Elsevier Ltd.


Martinelli L.,Eng-Tips | Talvy S.,Eng-Tips | Liegeois S.,Eng-Tips | Liegeois S.,Institute Meurice | And 3 more authors.
Chemical Engineering Science | Year: 2011

This paper proposes a single-phase flow model to simulate the flow induced in a liquid by the injection of gas dispersed in the form of a bubble curtain. It aims at predicting macroscopic liquid flow and mixing time. This single-phase flow model is developed as an alternative to two-phase flow models. The model is based on the assumption that the liquid flow is induced by a density imbalance between the bulk zone and the bubble curtain zone. The density in the bulk is set to the water density while the density in the bubble curtain corresponds to the air-water mixture density and is assessed by numerical simulations, thanks to an iterative procedure. Only the knowledge of the injected air flow rate and the bubble liquid relative velocity is required. The single-phase flow model is applied to assess the liquid flow and the mixing in open quarries having a complex geometry. The liquid velocities and the flow structure in the open quarries simulated with the single-phase flow model are in good agreement with those predicted by numerical simulations based on a two-phase flow model. © 2011 Elsevier Ltd.


Chauveheid E.,Vivaqua | Hansen N.,Vivaqua
Journal Europeen d'Hydrologie | Year: 2010

A dynamic rig test is applied for the evaluation of organic materials in contact with drinking water. The rig test submits only the inner surface of the material to the contact water, under unfavourable conditions created by a long stagnation period (23 h) followed by a controlled flowing regime (1 h). When applied to several polymer materials (uPVC, PEX, PE), the dynamic test rig shows a good repeatability and a great sensitivity for microbiological parameters, allowing an easy discrimination of polymer materials towards microbiological growth. Under these dynamic conditions, materials promoting bacterial growth enhance suspended heterotrophic bacteria by at least a factor 10 when compared to their endogenous concentration in the contact water. On the other hand, materials less prone to bacterial growth show a much lower enhancement of suspended heterotrophic bacteria, less than a factor 5 when compared to their endogenous concentration in the contact water. The long term results show a deterioration of the bacteriological quality of the water for polyethylene materials, but some of these (PE 80, PEX) behave similarly to uPVC, well-known for its poor enhancement of bacterial growth. These unexpected results for some polyethylene materials show that our dynamic rig test can lead to other conclusions concerning bacterial growth from those obtained with the static testing conditions usually recommended. Moreover, the proposed dynamic rig test allows the simultaneous evaluation of the migration (of organic compounds and metals) and also of the degradation of the water quality characterized by global or organoleptic parameters. © ASEES, 2010.

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