ANAEROBIC TREATMENT OF INTENSIVE FISH CULTURE EFFLUENTS - VOLATILE FATTY-ACID MEDIATED DENITRIFICATION

Denitrifying activity was examined in a laboratory-scale fluidized bed reactor coupled to a digestion basin in which fish feed was anaerobically degraded. Under these conditions volatile fatty acids (VFA; acetate, propionate and butyrate), released during anaerobic feed degradation, were found to fuel the denitrifying activity in the fluidized bed reactor. VFA fatty acid-dependent denitrification was confirmed by laboratory incubation of bacterial consortia, derived from the laboratory-scale fluidized bed reactor and a pilot-plant fluidized bed reactor. Kinetic parameters of denitrification were determined as well as the stoichiometry of VFA uptake and nitrate reduction by these denitrifying consortia. It was concluded that in closed fish culture systems, where nitrate accumulates as a result of nitrification, complete nitrate removal is possible by a combination of denitrification and anaerobic degradation of endogenous organic matter.