Research On Performance And Applications Of Immobilized Microorganisms For In-situ Remediation Of Pollutants In Aquaculture Water

In recent years,with the increasing scale of aquaculture and the increasingly strict national environmental protection requirements,immobilized microbial in-situ remediation technology has received more and more attention.However,there are relatively few practical cases of immobilized microorganisms for the in-situ treatment of aquaculture waters.Therefore,three kinds of immobilized microorganisms（attapulgite,carrageenan and American materials）were selected for laboratory tests in this paper.The properties of immobilized microbial particles,including particle strength,sustained-release performance of microorganisms,kinetics of removal of pollutants by immobilized microbial particles and the main influencing factors of removal efficiency,were studied to find the most suitable immobilized microorganism.It was applied to the in-situ restoration of aquaculture ponds.In order to understand the effect of the in-situ application of an immobilized bacterial agent on the purification of aquaculture water and the microbial community structure in the aquaculture environment,the concentration changes of pollutants(including COD_Mn,ammonia,and TP)in aquaculture wastewater were analyzed during in-situ remediation in the present study.Additionally,the characteristics of the microbial community in the aquaculture environment were evaluated using a high-throughput sequencing method.The aim is to provide theoretical guidance and scientific basis for in-situ purification of aquaculture water by immobilized microorganisms,and to reduce the cost of subsequent tailwater treatment as well as the occupation of land resources.The main results are as follows:（1）The results of the particle performance experiments showed that the crushing rate of the three immobilized microbial particles increased with the extension of time on the whole.Among them,the immobilized microbial particles of attapulgite and American materials had better mechanical strength and the ability to resist disturbance from external environmental forces.The number of sustained-release microorganisms of attapulgite and carrageenan immobilized microbe particles reached a peak at 1 day and remained stable at 1.5×10⁶ CFU/m L and 2.6×10⁵ CFU/m L,respectively,while the number of sustained-release microorganisms of American materials peaked at 3.6×10⁴ CFU/m L at 1 day and then decreased rapidly.The immobilized microorganism particles of attapulgite and carrageenan can release microorganisms continuously in the water containing pollutants to achieve the effect of pollutant treatment.The performance of attapulgite immobilized microbe can better adapt to p H changes in water.The three immobilized microbe sustained-release microbe could well adapt to the optimum temperature of artificial culture（18℃～35℃）and withstand high pollutant load.More microorganisms were released when the aeration rate was moderate 2 L/min（DO=8.3±0.028 mg/L）.Monod equation fitting showed that theμ_max of the three materials were from high to low:American material,carrageenan,attapulgite.And the K_s from high to low:carrageenan,attapulgite,American material.At the same time,theμ_max of ammonia nitrogen was American material,carrageenan,attapulgite from high to low,respectively.And the K_sfrom high to low are attapulgite,carrageenan and American material respectively.（2）The results of the effect of environmental conditions on the degradation of pollutants by immobilized microbial particles showed that the first order rate constant of degradation of COD_Mn was the highest in neutral（p H=7）condition.The efficiency of ammonia nitrogen degradation was better under neutral and alkaline conditions for both attapulgite and American immobilized microbial materials,while carrageenan had the highest k value for ammonia nitrogen degradation under neutral conditions.The value of k of degradation of COD_Mn and ammonia nitrogen by immobilized microbial particles increased with the increase of temperature in the optimum temperature（18℃～35℃）.The values of temperature coefficientsθfor the degradation of COD_Mn at different temperatures for attapulgite,carrageenan and American immobilized microbe were1.003～1.105,0.998～1.006 and 0.089～1.008,respectively.The temperature coefficientsθwere 1.039～1.088,1.031～1.035 and 1.022～1.039,respectively.Under the influence of different initial pollutant concentrations,the value of k increased significantly（P<0.05）with increase of initial pollutant concentrations for all two except the American material.There was no significant difference in the primary reaction rate of COD_Mndegradation by three immobilized microorganisms under three aeration intensities（P>0.05）.For ammonia nitrogen,the primary reaction rates of COD_Mn and ammonia nitrogen degradation by the three immobilized microorganisms fluctuated at the aeration intensities of 2 L/min（DO=8.3±0.028 mg/L）and 3.5 L/min（DO=8.6±0.028 mg/L）.（3）The results showed that the removal of COD_Mn and ammonia in the experimental aquaculture pond was significantly improved（P<0.05）.The removal rate of COD_Mnincreased from 26.14%to 52.49%,and the removal rate of ammonia nitrogen increased from 76%to 90%.The concentration of COD_Mn was lower than the discharge limit of aquaculture wastewater（15 mg/L）,ammonia,and TP at a low level（<0.5 mg/L）.The Shannon index and Chao values of microbial diversity in the experimental group were significantly higher than those of the control group（P<0.05）.The addition of an immobilized bacterial agent increased the number of the total OTU and the unique OTU in the experimental group.The number of common OTUs between the sediment and water from the experimental group was more than those in control group.Principal coordinate analysis（PCo A）showed that the dominant microbial population in the experimental group changed significantly compared with the control group.The increase of Proteobacter promoted the transformation of ammonia,and Actinobacteria,being responsible for the decay of animal and plant remains,was reduced,which might be related to the greatly decreased COD_Mn in the experimental group.Meanwhile,the reduction of Bacteriidota was also caused by improved water quality in the experimental group.Changes in relative abundance at the genus level also reflected that the in-situ application of an immobilized bacterial agent optimized the environmental microbial community structure.