No abstract

A MEMS approach to obtain an efficient tool for the evaluation of the biochemical oxygen demand (BOD) of wastewaters is introduced. Its operating principle is based on the measurement of oxygen concentration in water samples containing organic pollutants and specific bacteria. The microsystem has been designed to perform multiple and parallel measurements in a poly-wells microfluidic device. The monitoring of the bacterial activity is ensured by optical sensors incorporated in each well of the fluidic network. By using an optode sensor, it is hereby demonstrated that this approach is efficient to measure organic pollutants by testing different Luria Bertani buffer dilutions. These results also show that it is possible to reduce the duration of measurements from 5 d (BOD5) of the standard approach to few hours, typically 3 h–5 h.

The concentration of organic pollutants present in wastewater is classically evaluated by measuring the quantity of dissolved oxygen during five days; it is quantified by the so called BOD5 parameter (Biological Oxygen Demand). This work constitutes the first step of an overall strategy targeting to improve the monitoring of this indicator of the water quality. We focus on the development of a microsystem approach allowing monitoring the O 2 consumption induced by the biodegradation process of organic matter. To evaluate the organic pollutants concentration, we use Escherichia coli as bacterial indicator, confined in a PDMS-glass chip. Their metabolic activity in presence of organic molecules is deduced from their oxygen consumption. These measurements are ensured by optical sensors present in each of the five instrumented chambers of the chip. The results show that the microsystem approach is suitable to measure simultaneously different concentrations of organic load, and that it is possible to reduce the analysis time. By examining the O 2 diffusion towards the walls of the device, we analyze the different part of the experimental results; it allows, on the basis of a theoretical model, to predict a precise evaluation of the BOD value within few hours.