Abstract: The three aerobic denitrifier isolated from sediment of one marine aquaculture farm in Tianjin city were made into aerobic denitrification microbial agent in a ratio of 3∶2∶1, and 5% polyvinyl alcohol, 2% sodium alginate and 3% diatomite was used to embed the aerobic denitrification microbial agent to form immobilized bio-diatomite. The immobilized bio-diatomite was added to the cyclic activated sludge technology （CAST） reactor to investigate the treatment capability of COD, inorganic nitrogen and phosphate in marine aquaculture wastewater by the cyclic activated sludge technology reactor with immobilized bio-diatomite. The results showed that under the same operation condition, the reduction rate of COD, inorganic nitrogen and phosphate by the cyclic activated sludge technology reactor with immobilized bio-diatomite can keep above 83%, 99% and 96%, respectively. It was 30 pecentage points, 28 pecentage points and 55 pecentage points higher than that of the traditional cyclic activated sludge technology reactor, respectively.

Key words: immobilized bio-diatomite, cyclic activated sludge technology, marine aquaculture wastewater