Particle characterization of urban wet-weather discharges: methods and related uncertainties

Abstract

Urban wastewater particles play a major role in the impact of wet weather discharges in the environment. So particle characterization is of particular interest to assess their impacts and understand their behaviour in sewers. The classical method of uncertainty combination, the Monte Carlo simulation and the experimental repetition method were used to evaluate the uncertainties for the measurement of the following particle characteristics: wet and dry densities with a water pycnometer, particle size distribution by laser diffraction, concentrations in suspended solids and particulate chemical oxygen demand (standardized methods). The advantages and complementarities of the different methods for uncertainty determination are discussed and illustrated by several intra- and inter-laboratory examples. Those examples show the utility of the uncertainty determination to optimize the test portions, or to specify the validity range of a measuring instrument, or by identifying the most influential steps of a measurement procedure, to improve its reliability (operator effect) and/or accuracy.

Keywords::

• density
• measurement uncertainty
• particle sizing
• suspended solids
• urban discharges
• wastewater

Acknowledgements

This study was realized with wastewater samples taken from several sites of the sewerage system of the urban community of Nantes. The authors thank the urban community of Nantes Metropole for its contribution to the sampling campaigns during this study.