Misako KURABE
Biological Nitrogen Removal for Seawater
Takashi YAMAGUCHI
This research was intended to marine aquarium seawater. General large aquariums have sand filter and foam fractionator or other aerobic treatment systems for water quality management. These systems are effective for ammonia-oxidation and nitrification. However it has no effect for denitrification and nitrate is accumulated in aquarium water. Currently, the only way to remove nitrate is water exchange and it needs 5-10% of all aquarium water at least. Hence, water exchange is unsuitable way for water quality management of large aquarium. Especially, in marine aquarium, it needs considerable cost for materials of artificial seawater or conveyance and heating seawater. According to this background, this research had developed denitrification reactor in order to reduce exchange water.
This research was organized in the three experiments, selection of electron donor, comparison of reactor type, and selection of inoculum for denitrification. In the selection of electron donor, sodium acetate and sulphur were examined as electron donor using same fixed bed denitrification reactor. Therefore, sodium acetate was effective for denitrification of seawater. Though, fixed bed reactor isn't suitable for seawater. Then in the comparison of reactor type, fixed bed reactor and upflow anaerobic sludge bed reactor were examined. In the result, UASB had great performance for denitrification of seawater. Lastly, the selection of inoculum for denitrification was needed that it is hard to get inoculum acclimated to saline. In this experiment, the coral sand from sand filter in marine aquarium was noticed. And it was effecting for denitrification.
According to those experiment, denitrification reactor for seawater was successfully developed. Denitrification reactor that has highest ability was UASB. In HRT 1.5 hour, nitrate removal efficiency was 95¡Þ2% and nitrate removal rate was 0.61kgN/m3/day. This removal rate was twice as high from previously reported. This fact was possible to contract reactor volume. The reason of effectiveness of UASB was that it had great ability to retain sludge and avoid accumulation of inorganic compounds. In addition, UASB was effective for acclimation of denitrification bacteria that is suitable for salinity of wastewater. On the other side, fixed bed reactor had no capability of adapting to continuous operation. Additionally, coral sand that can be easily obtainable from existing treatment systems for water quality management was effective as inoculum for denitrification. This result also facilitated making denitrification reactor.
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