2.2. Biofilms and BOD sensors
The biofilms were prepared by immobilizing bioelements on a porous cellulose nitrate membrane(20 mm diameter,0.45 mm pore size,Advantec,Japan)as described previously [32]. Calculated culture broths(wet cells 40 mg) were dropped on the cellulose nitrate membrane,and then adsorbed onto the membrane using the suction of an aspirator.The biofilms were washed with 10 mM phosphate buffer.An oxygen electrode with a biofilm is schematically shown in
Fig. 1. The biofilm was placed on the PTFE membrane of the oxygen electrode and fixed in place using 200 mesh nylon and an O-ring.
The oxygen electrode with the biofilm was linked to both a digital
multimeter andanelectronicrecorder.