In order to develop immobilized microbial agents for purification of water in aquaculture ponds,Bacillus subtilis was immobilized with sodium alginate,different adsorption substrates(zeolite,diatomite,activated carbon)and CaCl2,and the purification effects of immobilized pellets with different adsorption substrates on the simulated aquaculture water were compared.The preparation conditions of immobilized bacterium pellets were optimized by an orthogonal test,and the purification effect of the optimal immobilized bacterium pellets was tested in enclosures in an actual aquaculture pond for 15 days.The indoor test showed that the immobilized bacterium pellets with activated carbon as the adsorption matrix had the best effect on water quality improvement,with final removal rates of 93.65％for total ammonia nitrogen(TAN),44.11％for NO3--N,67.35％for NO2--N and 59.99％for COD in aqua-culture water.The optimal preparation of immobilized pellets was found under conditions of alginate bacterial solu-tion containing 2％sodium alginate and 4％activated carbon cross linked with 4％calcium chloride for 24 hours.The purification effect of the composite carrier immobilized bacterium pellets on the aquaculture water was better and longer in the outdoor enclosure than that in the free bacteria,with significantly lower contents of TAN,NO3--N,NO2--N and COD in enclosures treated by immobilized Bacillus subtilis in the enclosure test at the end of the 21 days than those in the free bacteria groups and the control groups(P＜0.05),only 29.14％,69.23％,12.23％and 68.30％compared to the control group,respectively,indicating that the water purification effect of immobilized bacterium pellets on composite carrier with adsorbent matrix was significantly better than that in single immobilized bacterium pellets and free bacteria without adsorbent matrix.The findings provide reference for the application of immobilized microorganism technology in aquaculture.
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