Nitrification performance and robustness of fixed and moving bed biofilters having identical carrier elements

This study compared moving bed (MB) and fixed bed (FB) biofilter performance. The experimental recir-culating aquaculture system had four equal biofilters in parallel. Each of the two replicated FB biofilters(with heavy elements) and the two MB biofilters (with neutral elements) had 200 l carrier media with asurface specific area to volume ratio of 750 m2/m3.

Total ammonia nitrogen (TAN) and apparent nitriteremoval rates were measured during identical steady-state conditions and during a water treatmentevent where 50 mg/l hydrogen peroxide was applied. FB biofilters were found to perform equal to or bet-ter than MB biofilters during the experimental phases.

The average (n = 2) surface specific TAN removalin the FB biofilters was significantly higher than the MB biofilters (0.20 vs. 0.14; g N/m2/d) at steady state.The FB biofilters had a positive apparent nitrite removal (0.02 g N/m2/d) at steady state in contrast to MBbiofilters releasing nitrite (−0.02 g N/m2/d).

Application of H2O2caused a transient five-fold TAN increaseup to 1.05 mg N/l in the system. Prolonged elevated nitrite levels up to 2.85 mg N/l (>15 fold increase)was observed for one week due to reduced nitrite oxidation particularly in the MB biofilters. The findingsindicate FB biofilters to be more resistant against the sanitizer applied, due to increased organic matterin the biofilters compared to MB biofilters.

Aspects of the experimental setup are discussed in relation toother studies and commercial biofilter operations.