Development And Application Of Immobilized Microbial Water Purification Agent Based On Freshwater Aquaculture

The accumulation of ammonia nitrogen in water sources will cause the aquatic product disease and water eutrophication,which has severely restricted the green and sustainable development of freshwater aquaculture.With the development of microbial technology in recent years,microecological products that can improve the aquatic environment and aquatic product quality have been widely used in the freshwater aquaculture process.In this study,several probiotic bacteria preserved in our laboratory were used as initial strains.The present research investigates the effect of several microorganisms on water purification and their impact on the water environment.The research results specified the conditions for the fermentation and cultivation of composite microorganisms,clarified the preparation process of immobilized composite microbial water purifiers.In addition,these results will enrich the categories of microecological preparations and provide more options for treating ammonia nitrogen in water bodies during freshwater aquaculture.The main results are as follows.(1)Water purification effect of microorganism.In the single microbial water purification experiment with ammonia nitrogen removal as the main indicator,the nitrogen removal effect of Bacillus subtilis(BS),Lactobacillus plantarum(LP)and Rhodopseudomonas palustris(RP)increased with the increase of microbial dosing,while the opposite was true for Saccharomyces cerevisiae(SC),with the best ammonia nitrogen degradation rates of 25.12%,37.94%,20.19%and 21.02%at 72 hours,respectively,when facing the artificial wastewater with ammonia nitrogen concentration of 2 mg/L.After the response surface optimization test,the 72-hour ammonia nitrogen degradation rate was increased to 46.35%when BS,LP,RP and SC were mixed at 0.75%,0.75%,1.0%and0.25%.(2)Expanded culture process of composite microorganisms.The inoculation ratio was BS:RP:LP:SC=3:4:3:1.After optimizing the media composition and fermentation conditions,the maximum viable bacterial count of the fermentation broth was 1.7×10~9cfu/m L.For the freeze-drying process of broth,80.2%of the organisms will keep alive in the bacterial powder with the protective agent of 8.5%alginate,2.5%glycerol and 8.5%skimmed milk powder.(3)Preparation and application of immobilized microbial water purifiers.The spheres were prepared under the conditions of 8%polyvinyl alcohol,0.5%carrageenan,2%biochar,17%bacterial solution,and 2%potassium chloride saturated borate solution cross-linked at room temperature for 21 hours.The immobilized microbial water purifier with an optimum ammonia nitrogen degradation rate of 53.86%for 48 hours towards the artificial wastewater with meets the conditions for freshwater aquaculture.The immobilized microbial water purifier can still remove more than 40%of the ammonia nitrogen from the water body after 3times of repeated use in a water body conforming to the ammonia nitrogen concentration,temperature,p H and carbon to nitrogen ratio of freshwater aquaculture,with good reusability,easy storage,transportation and rapid activation for use.When the water purifier was used in an aquarium for goldfish hatchlings,it reduced the growth rate of ammonia nitrogen by156%in 7 days compared to an aquarium without the water purifier.