The influence of the ethanol concentration on the composition and activity of a developed biofilm
in a denitrifying submerged unidirectional filter was studied. Process yields (represented as
inorganic nitrogen removal), total platable bacteria, denitrifying bacteria, nitrate- and sulphatereducing
bacteria and denitrifying activity (N20 production) were compared at different ethanol
concentrations (0 to 46.74 mg/-1). The biofdm exhibited a diverse bacterial composition and
higher microbial development at the entrance of the unidirectional biofilter. The number of ,cells
per gram of dry weight of biofilm was increased when the ethanol concentration increased, ,with
the exception of nitrate reducers, for which the number of cells decreased per gram of biofilm in
relation to height. Five different species of denitrifying bacteria were isolated from the biof'dm, all
of which were gram-negative rods. All of the species manifested an increase in denitrifying activity
when the ethanol concentration was increased. In this sense, the number of denitrifying bacteria
in the biof'dm was positively correlated with the ethanol concentration. Both nitrate- and sulphate-
reducing bacteria were present in the biofilm in the lower and higher part of the column.
Nitrate-nitrogen removal in the submerged filter showed a high correlation with the influent ethanol
concentration.