An improved nitrifying enrichment to remove ammonium and nitrite from freshwater aquaria systems

The total ammonium nitrogen (TAN) concentration is often a key limiting water quality parameter in intensive aquaculture systems. Removing ammonia (NH3) through biological activity is thus an important objective in aquaria and aquaculture system designs. In this study, the performance characteristics of a suspension of nitrifying cells (named ammonia binding inoculum liquid, ABIL) have been explored. This aqueous suspension contains a highly active, nitrifying microbial consortium that can be used to shorten the start-up period of a biofilter. Tests were performed in freshwater at lab scale (70 1, 20-24 degreesC). Results showed that the application of the consortium at a dose of 5 mg volatile suspended solids (VSS) l(-1) assures a total removal of ammonium (NE4+) and nitrite species from 10 mg N l(-1) to below the detection limit within a period of 4 days. Experimentally, at a substrate level of 10 mg TAN l(- 1), a rate of biological ammonium and nitrite conversion of the order 0.3-0.5 g TAN g(-1) VSS-1 day(-1) could be achieved by the consortium in the freshwater aquaria systems tested. Provided adequate aeration and dissolved oxygen (DO) levels of 6 mg l(-1) or more, no important intermediary nitrite concentrations were found. Only a small amount of TAN was not recovered as nitrate and might have been lost through ammonia stripping. Pre-inoculating the nitrifiers in polyurethane (PU) sponges and installation of such sponges in the freshwater aquaria did not improve the effect compared to adding the consortium directly to the water. After 12 months preservation of the inoculum at 4 degreesC, no important decrease in ammonium removal activity and only a minor decrease in the nitrite removal rate of the consortium were noticed, (C) 2002 Elsevier Science B.V. All rights reserved.