RESPONSE CHARACTERISTICS OF A DEAD-CELL BOD SENSOR

Bacillus subtilis cells, thermally killed by exposing dried cells to 280°C for 2.5 mins, were used for fabricating the biofilm attached to a dissolved oxygen probe. The dead cell biosensor showed good sensing characteristics for the BOD of aqueous organic solutions and wastewaters in regard to its response and recovery times, reproducibility and stability. It has a significantly long life span of several months, requiring only simple storage at room temperature in phosphate buffer in between measurements and even over extended idling periods for which microbial sensors would normally require food and nutrient additions for their sustenance. The sensitivity of the biosensor towards 24 organic solutes were generally comparable with biosensors using living Bacillus subtilis cells and the American Public Health Association (APHA) method of measurement using activated sludge. The high diffusion resistance of the membranes was experimentally verified to have caused the long response time for soluble starch. The BOD8 of some real wastewater and synthetic water samples were determined and compared with the BOD5 obtained by the APHA method. The deviation of the biosensor values from the APHA values depends on the difference in the sensitivity of the device and the microbial system towards the compounds in the test sample. Nevertheless the deviation was similar to those generally observed among the APHA values reported for a given substrate by different analysts and laboratories.