OBJECTIVETo investigate the function of a novel biosensor used for the rapid determination of biochemical oxygen demand (BOD) which is developed by our research group based on suspended immobilized microbial cell system in a completely mixed determining chamber as a substitute of the traditional membrane system.

METHODSActivated sludge was immobilized by PVA gel and used as a bio-sensing element. The novel biosensor was used to measure the short time BOD value and the conventional cultivation method was used for BOD5 measurement.

RESULTSA linear relationship was observed for the difference between the current and the concentration of glucose-glutamic acid (GGA) solution below 200 mg/L with a correlation coefficient of 0.995. The optimal response of the sensor was obtained at pH 7.0 and 30 degrees C. The sensor response was within 15 min and was reproducible within +/- 5% of the mean in a series of eight samples containing 75 mg/L BOD using standard GGA solution. The novel sensor response was found to be fairly constant over a period of 30 days, with +/- 5% fluctuations.

CONCLUSIONA relatively good agreement is found between BOD estimated by the novel BOD biosensor and that determined by the conventional 5-day BOD method. This novel BOD biosensor has good sensitivity, stability and reproducibility.