SPATIAL DISTRIBUTION OF MICROBIAL ACTIVITIES IN BIOFILMS DETERMINED BY MICROELECTRODES

Microelectrodes, with tip diameters from 3 to 5 μm were fabricated and used to measure the oxygen, ammonium, nitrate and pH microprofiles in an aerobic/anoxic biofilm. Biofilms were cultured in a laboratory scale rotating drum biofilm reactor fed with synthetic wastewater containing 50 mg/L COD and 25 mg/L NH4+-N. Microelectrode measurements were performed after the reactor reached a pseudo-steady state condition with 95% COD removal efficiency, 90% nitrification and partial denitrification. Biofilms removed intact from the removable slats were fixed into the test chamber. The measurements were conducted in a Faraday cage and monitored by a stereomicroscope, a CCD camera and a color monitor. Oxygen, ammonium, nitrate and pH microprofiles were obtained at 50 μm intervals within biofilms having an average thickness of 2000 μm. The spatial distribution of different metabolic activities, including biodegradation of organic matter, nitrification and denitrification, were illustrated. The results presented identify the potential for simultaneous nitrification and denitrification in aerobic/anoxic biofilm systems and provide information for mathematical modeling of such biofilm systems.