A new biosensor for rapid BOD estimation by using immobilized growing cell beads.
A closed, reactor-type sensor system for rapid estimation of BOD by the use of immobilized growing whole cells of a facultative bacterium, Bacillus polymyxa D-21, in kappa-carrageenan and an oxygen electrode is described. This system consists of a transformer, a recorder, a thermostated water bath (30 +/- 1 degree C), a magnetic stirrer (200 rpm), an oxygen electrode, and a flask containing 10 g (wet weight) immobilized cell beads of 2-3 mm in diameter. The total time required for an assay is less than 15 min. The calibration curves obtained show a linear relationship between the rate of oxygen consumption and the concentration of standard wastewater solution which contains equal amounts of glucose and L-glutamic acid each at a concentration below 10 mg/l. The measurement is independent of the pH of the wastewater solution under investigation. The rate of oxygen consumption was reproducible with an average relative error of 5.89% when a standard wastewater solution containing 12 mg/l of glucose and 12 mg/l of L-glutamic acid was assayed 54 times. When the immobilized cell beads were suspended in a 0.1 M phosphate buffer (pH 6.0) and stored at 25 degrees C, the response of the sensor system remained unchanged for about 30 days. However, based on the observed linear relationship between the rate of oxygen consumption and the concentration of standard wastewater solution, the sensor system should remain usable for at least 2 months. There is a good correlation between BOD5 determined by a conventional method and BOD5 determined by the proposed method when wastewater samples from a local fermentation factory were assayed.