| Currently,the phenomenon of excessive nitrogen concentration in maricultural water appears frequently,which has seriously threatened the health of fish and shrimp in marine aquaculture.Simultaneously,the effluent of aquacultural wastewater aggravates the nitrogen pollution in nearby sea areas,excessive nitrogen has become an important cause of eutrophication of water body.Therefore,and it is of great significance to strengthen the research of nitrogen removal from aquaculture wastewater.biological nitrogen removal technique is more popular thant chemical and physical techniques in wastewater purification because of its several advantages,such as low cost,no secondary pollution,simple operation and so on.The selection of excellent strains plays an important role in biological nitrogen removal.Heterotrophic nitrification-aerobic denitrifying bacteria are newly found denitrifying bacteria in recent years,which broke through people's traditional understanding on nitrogen removal theory,the simultaneous nitrification and denitrification is conducted by using organic matter and nitrogen as the source of carbon and nitrogen to achieve biological nitrogen removal.At present,study on heterotrophic nitrification-aerobic denitrifying bacteria mostly focused on the isolation and selection of bacteria strains and their nitrogen removal characteristics,the reports on their application technologies on mariculture wastewater purification are poor.In this paper,studies on the application of 3 heterotrophic nitrification-aerobic denitrifying bacteria strains screened and preserved in our laboratory was carried out in prufication of Verasper variegates farming water and manufacturing simulated biological filter,aimed at exploring the application methods and effect of these strains and providing the basis for its further application in real mariculture.The mainexperimental results are as follows:(1)Litopenaeus vannmei weighted(10.2±1.3)g were selected and divided into 4groups randomly,with 30 per group,and was farmed continuesly without water change.During farming,the various combinations of Bacillus hwajinpoensis(SLWX2),Halomonas alkaliphila(X3)and their mix were inoculated into the culture tanks respectively.The purification effect of diffirent combinations were detected by determining the change of concentrations of inorganic nitrogen and organic matter in the various combinations.The results showed that,the concentrations of ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,total nitrogen and chemical oxygen demand in the control group showed continuous increasing trend during the whole experiment,The indicators in experimental groups were lower than those of then control group on the 4th days,The results suggested that the addition of these 3 heterotrophic nitrification-aerobic denitrification bacteria strains can effectively improve the water quality through nitrification and denitrification without adding carbon sources.(2)Verasper variegates weighted(98±6)g were selected and divided into 8groupsrandomly,with 30 per group,and was farmed continuesly without water change.During farming,the various combinations of Bacillus hwajinpoensis(SLWX2),Halomonas alkaliphila(X3)and Alteromonas macleodii(SLNX2)were inoculated into the culture tanks respectively.The purification effect of diffirent combinations were detected by determining the change of concentrations of inorganic nitrogen and organic matter in the various combinations.The results showed that the concentrations of ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,total nitrogen and chemical oxygen demand in the control group showed continuous increasing trend during the whole experiment,rising from 0.21mg/L to 15.94mg/L,0.08mg/L to5.68mg/L,1.10mg/L to 7.05mg/L,1.74mg/L to 38.86mg/L,1.19mg/L to 22.87mg/L,respectively.The concentrations of the indexes in the trial groups were significantly lower than those of control group.Among the trial groups,the group SLWX2+X3+SLNX2 showed the best purification effect to keep good water quality for Verasper variegates farming,with the concentrations of ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,total nitrogen and chemical oxygen demand 68.55%,48.36%,58.38%,40.02% and 27.47% lower than those in the control group respectively.In addition,the group SLWX2+X3 showed the second best purification effect.During the experiment,massive dead fish appeared on the 21 stday in the control group,but there were few dead fish in the trial groups,The results suggested that the addition of these 3 heterotrophic nitrification-aerobic denitrification bacteria strains can effectively improve the water quality through nitrification and denitrification without adding carbon sources and have no toxic or morbigenous effect on Verasper variegatus,but increasing their survival rate by improving the living condition.(3)Simulated bio-filter was manufactured,the various combinations of Bacillus hwajinpoensis(SLWX2),Halomonas alkaliphila(X3)and Alteromonas macleodii(SLNX2)were inoculated to the carrier to form biofilters respectively.in first stage,the effect of different combination-formed biolilters to remove ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,total nitrogen and chemical oxygen demand in quantitative aquaculture wastewater was studied.In the later stage of the experiment,the combination of SLWX2+X3+SLNX2 with the best removal efficiency of inorganic nitrogen was selected as the dominant bacteria to form bio-film again.The effect to remove ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen in the flowing aquaculture wastewater was analyzed by comparing the dominant bacteria formed bio-film and the naturally formed bio-film.The results of the stable aquaculture wastewater showed that the removal effect of inorganic nitrogen and organic matter in the trial groups was better than those of control group,Among the trial groups,the group SLWX2+X3+SLNX2showed the best removal effect,with the removal rate of ammonia-nitrogen,nitrite-nitrogen,chemical oxygen demand,total nitrogen of 95.8%,82%,60.8% and100%,100%,80.7%,59.5% in 24 hour and 48 hour,respectively.In the first 24 hour,the concentration of nitrite in the naturally formed biofilm group increased,After 48 hours,the removal rate of ammonia-nitrogen,nitrite-nitrogen,chemical oxygen demand,total nitrogen was 95.5%,50.52%,38.1%,13.44%,respectively.In the trial groups,nitrate-nitrogen concentration increased at beginning and then decreased.However,nitrate-nitrogen concentration has continued to rise in the control group.The results showed that heterotrophic nitrification-aerobic denitrification bacteria could be used to remove nitrogen from maricultural wastewater,and to reduce the concentration ofnitrogen and organic matter.The later period result showed that the removal efficiency of inorganic nitrogen of trial group was better than those of natural bio-film group.The group of 108cfu/mL showed the best removal effect of ammonia-nitrogen,nitrite-nitrogen,nitrate-nitrogen,with the maximum removal rate of 31.6%,11.33%,15.6%,respectively.The group of 107cfu/ml showed the second best removal effect,suggesting the dominant bacteria-formed biofilter has sustainable purification effect for continueslly flowing maricultural water. |
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