The evolution of the COVID-19 pandemic can be monitored through the detection of SARS-CoV-2 RNA in sewage. Here, we measured the amount of SARS-CoV-2 RNA at the inflow point of the main waste water treatment plant (WWTP) of Montpellier, France. We collected samples 4 days before the end of lockdown and up to 70 days post-lockdown. We detected increased amounts of SARS-CoV-2 RNA at the WWTP from mid-June on, whereas the number of new COVID-19 cases in the area started increasing a couple of weeks later. Future epidemiologic investigations shall explain such asynchronous finding.

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The understanding of physical phenomena such as flow behaviour and mass transfer performance is needed in order to develop appropriate micromixers for industrial or biomedical applications. In this article, the flow behaviour of the T-shaped and the cross-shaped micromixers with square cross-section are studied through numerical and experimental investigations. The comparisons are based on identical treated fluxes. From the particle image velocimetry (PIV) measurements, the flow topologies in the T-shaped and cross-shaped micromixers are very different. After liquid impact, it is observed that the vortex structures cover a longer part of the outlet channel in the case of the cross geometry. This result indicates that the cross-shaped micromixer could improve the mixing process in comparison with the micromixers having T geometry. A second experimental technique has been used, the electrochemical one, involving microelectrodes placed at several wall positions of the cross-shaped micromixer. The electrochemical method can locally characterize the formation of swirling flows. The high values of wall shear rate, in the impact zone, confirm the near wall disturbance created by the impingement of the flow and also the appearance of vortices that could enhance fluid mixing.

In order to better understand physical and biological clogging in drip-irrigation, a study was conducted on the impacts of hydrodynamic conditions on clay particle deposition and biofilm development in drippers using an optical method. A transparent milli-fluidic system composed of labyrinth channels was used to identify areas most susceptible to particle clogging using two different types of clay suspensions: sodium bentonite and kaolin. The impact of salt addition ([NaCl] =200 mg.L-1) on the clay deposition was also analyzed. Biofilm development was studied using the same methodology using a nutritive solution (chemical oxygen demand, COD = 200 mg.L-1). In addition, fluid dynamics simulations were performed along the labyrinth channel to understand the effect of flow behaviour on the fouling. Computational Fluid Dynamics results show two types of flow topology: high velocity in the main flow (around 1m.s-1) and low velocity in the vortex zones (less than 0.2 m.s-1) found in the channel corners. Using an optical method, kaolin deposition and biofilm growth in the dripper were observed to occur mainly in the inlet channel and initial vortex zones, which are characterized by lower mean velocity and turbulent kinetic energy values. This part of the dripper can be considered as a bottleneck that amplifies the fouling phenomena and which should be optimized. With the addition of NaCl, kaolin particles tend to form bigger flocs. Therefore, more significant particle deposition is observed, but this is not the case of bentonite for which no fouling is observed along the dripper.

The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology. The geometry of the dripper channel has an impact on the flow behaviours and head loss. The objective of this study was to analyse the influence of hydrodynamic parameters of three types of drippers (flow rates of 1, 2 and 4 l.h -1 ) fed by reclaimed wastewater on biofilm development kinetics and on the bacterial community. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers .

Emitter clogging is a major problem in microirrigation systems, which may result from the isolated or combined effects of physical, chemical, and biological agents. Clogging caused by suspended solid particles is the most common plugging form of emitters. Water quality and emitter geometry are key aspects in clogging processes. Any suitable test procedure to assess the sensitivity of drippers to clogging should take into account the predominant factors that influence clogging and must reproduce the field conditions. This research set out to assess the performance and suitability of a laboratory clogging test procedure in order to validate a methodology and to provide scientific results that may support the standardization of a clogging test method. The evaluated methodology has been used by the IRSTEA laboratory since 1974 (Platform of Research and experiment on Science and Technology for Irrigation - PReSTI, formerly LERMI) and its contents are currently being discussed by the ISO TC23/SC18 committee. The aim is to define a standardized testing protocol to evaluate the sensitivity of emitters to clogging due to solid particles. Replications analyzing the clogging resistance of four models of emitting pipes were carried out in a laboratory. The clogging test procedure enabled an accurate assessment of the combinations of concentration and size of particles that caused clogging in each model of dripper. However, a significant variability in degree of clogging was identified when the results of replications for each model of dripper were compared. Several requirements, concerns, and improvements related to the clogging test protocol were discussed.

The evolution of the COVID-19 pandemic can be monitored through the detection of SARS-CoV-2 RNA in sewage. Here, we measured the amount of SARS-CoV-2 RNA at the inflow point of the main waste water treatment plant (WWTP) of Montpellier, France. We collected samples 4 days before the end of lockdown and up to 45 days post-lockdown. We detected increased amounts of SARS-CoV-2 RNA at the WWTP, which was not correlated with the number of newly diagnosed patients. Future epidemiologic investigations may explain such asynchronous finding.