Impact of temperature on ammonium and nitrite removal rates in RAS moving bed biofilters

The impact of temperature on bacterial processes is well known; however temperature related data on nitrification rates in aquaculture systems are fragmented and compiled from different studies. We sought to determine ammonium and nitrite removal kinetics over a temperature range from 6 to 36 °C by using moving bed bio-elements from a freshwater RAS in steady state operated at 18 °C. The impact of temperature on ammonium and nitrite oxidation rates was evaluated by transferring the colonized bio elements to six liter batch reactors (triplicated setup). Each reactor was acclimatized for 24 h at each of the six temperatures (6, 12, 18, 24, 30 and 36 °C) and then spiked with ammonium chloride or sodium nitrite under identical conditions. The average surface specific TAN removal (STR) increased a six-fold from 6 to 30 °C (0.04-0.25 g TAN m−2 day−1) and dropped significantly at 36 °C-0.14 g TAN m−2 day−1. The surface specific nitrite removal (SNR) increased linearly from 0.04 g N m−2 d−1 at 6 °C-0.14 g N m−2 day−1 at 30 °C, decreasing to 0.12 g N m−2 day−1 at 36 °C. Throughout the temperature range tested, STR remained significantly larger than SNR. The temperature coefficient, Ɵ (6-30 °C) for ammonium oxidation was 1.079; for nitrite oxidation the temperature coefficient was found to be 1.054. The data provided by this study can be applied dimensioning future RAS that utilizes temperature ranges below 10 and above 30 °C.