Methane yield and microscopic observation as monitoring biofilm behaviour parameters, during start up phase of anaerobic inverse fluidized bed reactor

Abstract

Anaerobic biofilm behavior on polyethylene and Extendosphere™ supports was evaluated during start-up of an inverse fluidized bed reactor using methane yield and microscopic observation as parameter monitoring techniques. Two anaerobic inverse fluidized bed reactors were used, one filled with triturated polyethylene as solid carrier material (diameter = 380 μm, density = 926 kg/m³) and the other with Extendosphere™ (diameter = 147 μm, density = 700 kg/m³). Each support material was used at up to 25% of its working volume (polyethylene = 1.2 l, Extendosphere™ = 1.9 l). Both reactors were started up in sequencing batch mode, applying organic loading rates of 0.5 to 14 g COD/l.d. Both supports exhibited rapid biofilm growth during start-up. Maximum surface colonization was 46% with the polyethylene and 100% with Extendosphere™. Both supports had a methane yield of 0.298 l CH₄/g COD at 10 and 14 g COD/l.d, respectively. Digital microscopic observation results coincided with methane yield results, confirming each to be viable for parameter monitoring of biofilm growth. Data generated by these two techniques is different and complementary, and in conjunction they constitute a highly effective monitoring method of biofilm growth.

Key words: Anaerobic digestion, biofilm, inverse fluidized bed reactor, methane yield.