DENITRIFYING AND METHANOGENIC BACTERIA IN THE BIOFILM OF A FIXED-FILMREACTOR OPERATED WITH METHANOL NITRATE DEMONSTRATED BY IMMUNOFLUORESCENCE AND MICROSCOPY/

A denitrifying bacterial biofilm population established on a polypropy lene substratum of a fixed-film reactor was characterized by microscop y, scanning electron microscopy and immunofluorescence after 120 days of operation. The reactor, operated at pH 7.0, 22 degrees C, and -180 mV with synthetic wastewater containing methanol/nitrate, achieved a d enitrification rate of 0.24 mol NO3- l(-1) day(-1) with a removal effi ciency for nitrate of 95%-99% at an organic loading rate of 0.325 mol methanol l(-1) day(-1). The gas produced contained 2%-3% (v/v) methane and 3%-4% (v/v) carbon dioxide in addition to nitrogen. The biofilm c ontained mainly cells of Methanobrevibacter arboriphilus antigenically related to strain DC, short, flagellated, gram-negatively staining ro ds of Pseudomonas sp. antigenically related to Pseudomonas stutzeri st rain AN11, non-identified pink-pigmented rods and small lemon-shaped c ells with mono- and bipolar appendages resembling prosthecate Hyphomic robium sp. The biofilm analysis provided evidence for a syntrophy betw een the denitrifying, methylotrophic, bacterial consortium and hydroge notrophic methanogens, which were identified by antigenic fingerprinti ng with 17 antibody probes.