海藻バイオフィルターによる魚類飼育水からの栄養塩の回収

抄録

Nutrient recovery from fish culture water using a seaweed biofilter was investigated. The green alga Ulva onoi was selected for use as a seaweed biomass. The load capacity of ulva per day derived from nitrate (NO₃-N) uptake was 0.9mg-N·g-wet^-1·d^-1. A closed recirculating aquaculture system consisting of a fish tank, an intensive aeration unit, a nitrification unit and a seaweed biofilter tank was constructed. The required amount of seaweed biomass as determined from feed quantity and load capacity was provided into the seaweed biofilter tank, and fish (Oreochromis mossambicus) were cultured in the system. NO₃-N was fixed in the seaweed biomass throughout the experimental period, and did not accumulate in the culture water. The concentrations of ammonium and nitrite were maintained at very low levels of less than 0.15mg-N·l^-1. In addition, the survival rate of the cultured fish was 100%, and the ulva in the seaweed biofilter grew well throughout the experimental period. Each process proceeded smoothly, and the aquaculture system was property maintained. As a result of the nitrogen mass balance in the culture, approximately 70% of all the nitrogen excreted by the fish was fixed by the ulva. For an aquaculture system, a seaweed biofilter is a useful water treatment device for achieving both nutrient removal and seaweed production with low maintenance.