Determination of BOD-values of starch-containing waste water by a BOD-biosensor

The control of waste water plants is difficult or even impossible using the classical determination method for biological oxygen demand (BOD), because of its high time consumption of five days. A determination within some minutes is possible by microbial BOD-sensors. However, high molecular weight substances cannot be detected, a problem which can be overcome by the use of additional enzymes. For the application in a flow-through system to analyse starch containing waste water, alpha-amylase and amyloglucosidase were immobilized by adsorption to polystyrene or polypropylene carriers followed by crosslinking. Furthermore, covalent coupling to different nylon carriers, derivatives of chitin, silanized glass beads and silanized beads of foamed glass was tried. Chitin and Lewatit were the best suited carriers for the immobilization of alpha-amylase and amyloglucosidase. Two glass columns were filled with the immobilized enzymes and inserted into a commercial BOD-sensor containing the yeast Trichosporon cutaneum as biological component. The system was stable for more than two months under storage and one month under working conditions. A comparison of different starch types resulted in a hydrolysis of more than 80% in case of potato starch whereas grain starch was hydrolized only for 40-50%. Sensor-determined BOD-values of waste water with potato starch were nearly identical with BOD5-values resulting from the classical method.