Bod sensor for wastewater analysis- design and calibration methods

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