Effects Of Peroxymonosulfate On The Nitrifying Activity And Microbial Community Structure Of Polyurethane Sponge Biofilms

At present,while aquaculture provides a large amount of high-quality protein and promotes economic development around the world,its negative impact on the environment is attracting increasing attention.The traditional culture mode in a pond mainly relies on water exchange to maintain good water quality,resulting in large discharge of aquaculture tail water and serious consumption of water resources.Recirculating aquaculture system（RAS）uses nitrifying microorganisms to construct autotrophic biofilms to achieve effective removal of ammonia and nitrite and reuse of water resources,which is an important development direction of aquaculture.However,some disinfectants,and insecticides were widely used due to the increasing of cultured density and the continuous deterioration of water environment as well as the high pathogenic rate of aquaculture organisms which is caused by the invasion of bacteria,viruses and parasites.Peroxymonosulfate（KMPS）is an inorganic peroxide,which,with oxidation,produces small molecule free radicals with high energy and activity,reactive oxygen derivatives,etc.in water.Thus,KMPS is widely used in aquaculture field as a disinfectant and a bottom-altering agent,with the advantage of small environmental impact,high efficiency,low toxicity and low residue.However,the effects of KMPS on nitrifying microbial activity and biofilm community structure in aquaculture systems are unclear.In this study,based on the autotrophic biofilm culture of polyurethane sponge,the effects of KMPS on ammonia oxidation activity and nitrite oxidation activity of polyurethane biofilm under different concentrations,salinity and action time were determined.Litopenaeus vannamei were used as subjects in this study,and the effects of different KMPS dosages on water quality and growth of Litopenaeus vannamei were analyzed.The composition and diversity of biofilm bacterial community were analyzed by high-throughput sequencing technology.The conclusions are as follows:（1）To analyze the effects on the ammonia oxidation oxidation activity and nitrite oxidation activity,the polyurethane sponge was treated with KMPS of 0 mg/L（Group CK）,1.0 mg/L（Group A）,2.0 mg/L（Group B）,3.0 mg/L（Group C）,4.0 mg/L（Group D）and 5.0 mg/L（Group E）for 2 hours,respectively.The results showed that the removal of NH₄⁺-N in Group CK and Group A at 48 hours were 33.50%and 32.15%,respectively,without significant difference（p>0.05）,and the removal rates in Group B,Group C,Group D and Group E were significantly lower than those in Group CK and Group A（p<0.05）.The removal rate of NO₂^--N in group CK was significantly higher than that in other five groups（p<0.05）.When the concentration of KMPS was higher than 2.0 mg/L and 1.0 mg/L,the ammonia oxidation activity and nitrite oxidation activity of polyurethane sponge are inhibited,and the inhibition effect is enhanced with the increase of KMPS concentration.With the increase of treatment times,the inhibition of KMPS on ammonia oxidation activity and nitrite oxidation activity weakened.Compared with the first treatment,the total removal time of NH₄⁺-N in Group D and Group E was reduced by 50%,and the time of NO₂^--N was reduced by 75%.（2）To analyze the effects of salinity on the oxidation activity of ammonia and nitrite,polyurethane sponge was treated with 2.0 mg/L KMPS at the salinity of 3‰（Group CK）,10‰（Group A）,15‰（Group B）,20‰（Group C）,25‰（Group D）and30‰（Group E）for 2 hours,respectively,The results showed that the removal rates of NO₂^--N in Group D and Group E were 2.66 mg/L·h^-1and 2.52 mg/L·h^-1,respectively,with no significant difference（p>0.05）,but they were significantly lower than those in other treatment groups（p<0.05）.There was no significant difference in removal rate between the second and third treatments,and the degradation rate was significantly higher than that of the first treatment.（3）To analyze the effects of treatment time on ammonia oxidation activity and nitrite oxidation activity,polyurethane sponge was treated with 2.0 mg/L KMPS for 0hour（Group CK）,2 hours（Group A）,4 hours（Group B）,6 hours（Group C）,8 hours（Group D）and 10 hours（Group E）,respectively.The results showed that it took more than 216 hours for the complete removal of 5.12 mg/L NH₄⁺-N in Group E,and the NH₄⁺-N removal rate was significantly lower than that in Group CK（p<0.05）.There was no significant difference in NO₂^--N removal rate among Group CK,Group A and Group B（p>0.05）.The NO₂^--N removal rate in group D and E was significantly different from that in Group CK,Group A,Group B and Group C（p<0.05）.At the third treatment,there was no significant difference in NH₄⁺-N removal rate among all groups（p>0.05）,and there was no significant difference in NO₂^--N removal rate between Groups D and E compared with the first treatment（p>0.05）.（4）The polyurethane sponge with precultured biofilm（5%V/V）was inserted into Litopenaeus vannamei culture tanks,and the seedling density was 800 fish/m³.The KMPS concentration was 0 mg/L（CK）,2.0 mg/L（T1）,4.0 mg/L（T2）and 8.0mg/L（T3）respectively and the effects of water quality and shrimp growth were studied.The results showed that DO,p H and turbidity in different treatment groups had no significant effect.The average concentrations of NH₄⁺-N and NO₂^--N were0.02±0.002 mg/L,0.02±0.004 mg/L,0.04±0.005 mg/L,0.05±0.007 mg/L and0.35±0.02 mg/L,1.09±0.05 mg/L,2.14±0.07 mg/L and 3.47±0.12 mg/L,respectively.The average concentrations of NH₄⁺-N and NO₂^--N were significantly different among different groups during the whole experiment（p<0.05）.The peak concentrations of NH₄⁺-N were all less than 0.1 mg/L,and the peak concentrations of NO₂^--N were 0.75 mg/L,2.74 mg/L,4.28 mg/L and 5.13 mg/L,respectively.The final weight of Litopenaeus vannamei was affected by the dose of KMPS,and the survival rate and FCR of Litopenaeus vannamei were affected by the high dose of KMPS（8.0mg/L）.（5）High-throughput sequencing method was used to analyze the bacterial community structure diversity of polyurethane sponge biofilms in different KMPS treatment groups.The Alpha diversity showed that adding KMPS could reduce the richness and diversity of bacterial community in the culture system.The results of Beta diversity analysis showed that P0＿0 had the largest difference in bacterial community composition from others.There were significant differences in bacterial community composition between T1＿15,T2＿15 and T3＿15 samples on 15 d and T0＿30,T1＿30,T2＿30 and T3＿30 samples on 30 d.（6）Proteobacteria,Bacteroidetes,Acidobacteria,Planctomycetes and Chloroflexi were the dominant phyla of each biofilm sample.The relative abundance of Bacteroidetes and Alphaproteobacteria was positively correlated with the addition level of KMPS.The relative abundance of Nitrospirota,Nitrococcus and Nitrosomonas,which were related to nitrogen cycling,decreased with the increase of the addition level of KMPS.The relative abundance of Acidobacteria,Chloroflexi,Actinobacteria,Phycisphaerae,Bacilli,Woeseia and norank＿f＿＿Rhodobacteraceae in the 15 d and 30 d was decreased with the increase of KMPS dosage.