X. France’s scientific contributions

To relate population structure and activity to wastewater volume and composition, field trials were conducted at the outlets of two urban catchments that have different population structures (residential-only and mixed). Macropollution and metal micropollution were both considered. In the residential-only catchment, a diurnal pattern with a morning peak (at 10:00) and an evening peak (at 20:00, corresponding to dinner) was observed for all seasons. No difference was observed throughout the year; patterns in summer days, in which daily mobility out of the catchments should be reduced, were similar to those observed in other seasons. For both catchments, N-NH4 (from urine) and chemical oxygen demand (from urine and grey water) correlated with Cu, Zn, Al, Fe and Mn but not with alkaline earth metals. The observed diurnal pattern is associated with work and school mobility and with the general lifestyle of the population. Such an approach is useful to model expected domestic pollution patterns, with respect to lifestyle changes in the future.

The knowledge of sediment transport characteristics is an important issue in terms of sewer and surface water management. In order to monitor these phenomena in sewage, the Suspended Solids Concentration (SSC) is usually measured either by ad hoc analysis on samples or by optical turbidity which is the most commonly used continuous measurement technology for SSC. After adequate calibration, it can be linearly linked to the SSC. However, it should be noted that it is a point measurement which might not be representative of the whole flow. The use of acoustic multi-frequency instruments allows to monitor the particle size and concentration. Inversion techniques exist and are satisfying in flows with limited particle size and nature. This is unfortunately not the case in wastewater for which some attempts have been made but no systematic inversion technique exists. Without regular calibration, both optical and acoustic turbidity give a rough estimation of the SSC. As in the complex medium that is wastewater, inversion techniques are still discussed, we focused on the general optical and acoustic turbidity trends during long time observation trying to highlight their similitudes or differences.

In order to monitor these phenomena, the Suspended Solids Concentration is usually measured either by ad hoc analyzes on samples or continuously by optical turbidity. We compared these conventional techniques to explain, in terms of particle presence, the variations of real time acoustic turbidity. The Ultrasonic Doppler Velocity Profiler (UVP) also provides velocity and water height data. Major differences have been observed between dry weather and storm event conditions. .

Optical sensors, namely a submersible UV-visible spectrophotometer, a fluorescence probe for dissolved organic matter and a fluorimeter with a circulation cuvette dedicated to tryptophan-like fluorescence measurement have been deployed for the real-time monitoring of a periurban stream. Biofouling was a main issue for the UV-visible spectrophotometer and the tryptophan-like fluorimeter. However nitrates variation could be monitored by UV-vis spectroscopy based on the maximum of the second derivative of the spectrum in the UV-range.

This paper focuses on the use of the raw acoustical turbidity and velocity data as a flow online monitoring tool. Its aim is to demonstrate that, with adequate instrumental settings, interesting results can directly be seen on the raw data. As illustration, some experimental results on a combined acoustic turbidity and velocity analysis on a river are shown. It demonstrates the great potential of the acoustic measurements in sediment transport studies by the combined information on velocity and turbidity. Another application is the study of a wastewater collector inlet for which the comparison with standard measurement methods is possible. The acoustic turbidity raw data can easily be used for qualitative suspended solids concentration studies. It is also shown that more accurate results on the water height can be obtained through the acoustic turbidity.

Two field fluorometers, devoted either to natural organic matter (NOM) or to tryptophan-like fluorescing substances, were tested for the characterization of a large set of water samples (n = 263) impacted to various degrees by untreated or poorly treated urban sewage. Both fluorometers yielded consistent results when testing discrete samples. A nonlinear correlation (coefficient of determination = 0.98) was found between the tryptophan concentration given by the tryptophan field fluorometer and the fluorescence intensity given by a bench-top fluorometer (excitation = 285 nm, emission = 335 nm), corresponding to tryptophan-like fluorescing substances. A linear correlation with a mediocre coefficient of determination (0.63) was found between the NOM concentration given by the NOM field fluorometer and the fluorescence intensity given by the bench-top fluorometer (excitation = 355 nm, emission = 405 nm). This could be related to the diversity of NOM present, as illustrated by the different shapes of synchronous fluorescence spectra collected for the same samples.

An index based on wastewater flowrate entropy, sensitive to both rainfall intensity and time since the last rainfall, has been developed to discuss the variability of biofilm development on combined sewer walls in response to the hydrodynamic stress related to rapid variations of water height.

This paper focuses on the use of acoustic turbidity as an online monitoring tool. Some experimental results on river and sewer network are shown. The river data analysis demonstrates the great potential of the acoustic measurements in sediment transport studies. The sewer data shows different application as suspended sediments concentration or water height measurements. A comparison of the acoustical data to the most usual methods used for the total suspended solids concentration evaluation, namely sampling and optical turbidity is also done.

The occurrence in urban wastewater of eight micropollutants (erythromycin, ibuprofen, 4-nonylphenol (4-NP), ofloxacin, sucralose, triclosan, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS)) originating from household activities and their fate in a biological wastewater treatment plant (WWTP) were investigated. Their concentrations were assessed in the liquid and solid phases (sewage particulate matter and wasted activated sludge (WAS)) by liquid chromatography-tandem mass spectrometry.

The efficiency of an in-line stormwater physic-chemical treatment system combining sand removal, flocculation-coagulation and subsequent settling has been assessed by simulation. Such a system is designed to both reduce the discharge of pollution during storm events in receiving water bodies and to avoid disturbances on the downstream wastewater treatment plant. The stormwater treatment model, based on an existing system, is combined to the Benchmark Simulation Model 2 wastewater treatment plant. It is demonstrated that such a stormwater treatment system can improve the wastewater treatment plant performance by reducing the violations of the effluent quality constraints, but that such improvement is mostly due to a hydraulic effect.