Specific methanogenic activity measurements and scanning electron
microscopy (SEM) were used as indirect tools to study the microbial
population and structure of biofilms formed on sand grains. The biofilms
were developed in an anaerobic fluidized bed reactor (diameter 0.08m;
height 0.9m) fed with synthetic sewage wastewater. Biofilm thickness
increased from 10 to 70 um after 510 days of reactor operation. Reactor bed
stratification was observed after one year of operation, and agglomeration
of various biofilms resulted in aggregates (2.0 to 5.0 mm). Microbial
activities were determined through methane production from acetate,
butyrate, propionate and sucrose. Samples were taken from two different
points in the reactor, and the largest aggregates were found nearer the
reactor base. These had 0.01 mmol CH4/gSSV.h of acetoclastic activity.
Bacterial aggregates from the upper part of the reactor presented greater
acetoclastic activity, 0.03 mmol CH4/gSSV.h . Microscopical observations of
both samples revealed the predominant presence of methanogenic bacteria
similar to
Methanothrix
, as well as hydrogenotrophic
methanogen species and
Desulfovibrio
-like bacteria.
