Samuel Lucien Talvy

Ozone inactivation of resistant microorganisms: Laboratory analysis and evaluation of the efficiency of plants

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.

Influence of the nature of hydrodynamic constraints on aerobic biofilms

The aim of this paper is to relate biofilm detachment to local hydrodynamics. Biofilm was submitted to erosion tests in three devices: a Couette Taylor Reactor (CTR) and two Stirred Reactors (SR) Without Baffles (WOB) and With Baffles (WB). Each device involved different hydrodynamics and different impacts on the biofilm detachment. In CTR, the detachment was significant in one specific zone on the biofilm. In SR WOB, poor detachment was observed. In SR WB, major detachment was observed only on the external face. Baffles in SR induced a transient flow and a temporal non-uniformity of shear stress improving biofilm detachment.