Short-term BOD (BODst) as a parameter for on-line monitoring of biological treatment process Part 1. A novel design of BOD biosensor for easy renewal of bio-receptor

A novel design of a biochemical oxygen demand (BOD) biosensor has been developed for on-line monitoring of easily biodegradable organic compounds in aqueous samples. The biological recognition element of the sensor could be easily renewed by injecting new bacterial paste without disassembling the sensor system. The sensor measurements were carried out in the initial-rate mode using a flow injection (FI) system, resulting in 60s for one sample analysis followed by a recovery time less than 10 min. The sensor performance achieved showed a wide detection linearity over the range of 5-700 mg BOD5.1(-1) and a generally good agreement between the BOD values estimated by the biosensor and the conventional 5-day test. Furthermore, the precision test was in the control range (i.e. repeatability less than or equal to+/-7.5%, reproducibility less than or equal to+/-7.3%). The sensor could be used over 1 week in continuous test, however, the best performance was found within the first 24 h where standard deviation of the sensor response was +/-2.4%. The design of the sensor allows easy and fast renewal of the cells used as sensing elements. Replacement of biological recognition element and calibration of the sensor responses can be performed in a rather simple procedure on a daily regular basis. By using a mixed culture as the bio-receptor, one gets a sensor that reacts to a wide range of substrates. The new sensor construction will thus allow fast and convenient replacement of the bio-receptor and on-line assay of a broad range of substrates. This makes the sensor being an interesting and promising candidate for on-line monitoring of biological treatment process. (C) 2004 Elsevier B.V. All rights reserved