PERFORMANCE OF A TREATMENT SYSTEM FOR INORGANIC NITROGEN REMOVAL IN INTENSIVE AQUACULTURE SYSTEMS

A concrete fish culture unit (50 m3) stocked with common carp at an initial density of 20 kg m-3 was operated on a semi-closed mode with a minimum of fresh water addition (3 m3 day-3). Inorganic nitrogen levels in the unit were controlled by a combination of an aerobic, nitrifying trickling filter and an anoxic, denitrifying fluidized bed reactor. Organic debris accumulating in the culture unit was diverted into a sedimentation basin and supernatant from this sedimentation basin, rich in nitrate and dissolved organic matter, was pumped into the fluidized bed reactor. The effect of this treatment system was examined over a 3-month period and was compared to a similar culture unit operated at different dilution rates using clean, unpolluted water. Levels of inorganic nitrogen (ammonia, nitrite and nitrate) in the treated culture unit were well within the acceptable range of concentrations tolerated by the fish. As compared to previous studies, it was found that denitrification in the fluidized bed reactor was highly improved by the incorporation of a sedimentation basin. In addition, considerable degradation of organic matter was found to take place in the sedimentation basin.