The ability to sequentially inject more than 70 samples in 20 days while achieving highly reproducible results (RSD = 4.48%) attests to the robustness of the assay and the long-term stability of the sensor system. No detectable clogging was observed. The results obtained in this study indicate that this novel COD determination method, which is based on a thermal biosensor with a flow injection system, is a viable one. The sensitivity and repeatability of the assay are high enough to allow the sensor to be used in practical applications. The system is easy to operate, environmentally friendly, and highly stable. More importantly, it has a small response time (approximately 8 to 10 min). The assay system is thus suitable for the real-time monitoring of the COD values of water from rivers and lakes