Effect of desiccation on ammonia oxidation activity of filter materials in marine biological filters

Abstract

We examined the effects of desiccation on the ammonia oxidation ability of ceramic filter materials to maintain the nitrifier activity during washing procedure of filter. After the ammonia oxidation activity of filters were measured at 25°C, those removed from seawater and kept at 25°C under different conditions (at 30%, 60% humidity in the air , and saturated humidity in plastic bag). After the filters were kept up to 30 days, the ammonia oxidation activity was estimated again. Compared to the initial activity, activity of those kept under the humidity of 30% and 60%, decreased to about 50% on sixth and 21st day, respectively. Activity of filters kept at 30% was lost on the seventh day, but under 60%, filters had 3.2% activity on the 30th day. In saturated humidity, filters had about 50% activity even after 30 days, and an ammonia-oxidizing bacteria and archaea of filters were similar to those at initial condition. When we returned the filters had kept in saturated humidity to the seawater and added an ammonia source, its activity recovered after three days. Therefore, it is necessary to prevent desiccation of the filters in the washing procedure to keep the ammonia oxidation ability.