Bod sensor for wastewater analysis- design and calibration methods

Abstract

Water quality monitoring is an important aspect of water management concerning to thepollution control. The removal of biodegradable organic substances is a very importantaspect of evaluation the treatment efficiency in a wastewater treatment plant (WWTP).The amount of oxygen consumed by microorganisms to oxidise organic substances ischaracterised by biochemical oxygen demand (BOD), a widely used parameter inenvironmental analysis. The conventional method BOD determination is uneffective fromthe point of view of short-term in situ measurements or on-line monitoring because itmeasures the microorganisms endogenous and exogenous oxygen consumption over aperiod of 5 or 7 days. BOD biosensors provide much faster results thereby allowing theresearches to overcome the weaknesses of the conventional method.BOD sensor studied in present work is based on an amperometric oxygen sensor and aneasily replaceable biomembrane of mixed culture of microorganisms. Biosensor outputsignal depends on the concentration of substrate that indicates the organic pollution ofwaters. Biosensor output signal is analysed classically according to the steady-stateparameters and by the dynamic change of the response and also by the elaboratedmathematical model. The calibration of biosensor by steady-state method is based on thechange of biosensor response between an initial value and the stable end-point of thesignal. The dynamic method of measurement is based on the determination of themaximum rate of change of output signal during experiment and the mathematical modelenables us to find the time constants characterising the non-steady-state processes inBOD sensor. Studied biosensor can be used for the measurements of biochemical oxygendemand in the concentration range 10-90 mg/L.