Study On Variation Of Microorganisms In Bioremediation Of Eutrophic Waters

This thesis focused on the application of water purification technologies using microbial biofilm and aquatic macrophytes to process effluent from municipal waste plant.During the process,changes on microbial abundance were investigated on the associated four types of aquatic macrophytes:Eichhornia crassipes,Trapa,Nymphaea tetragona,Hydrilla verticillata.Samples were collected from surrounding waters,sediments and the surface of the macrophytes.The impacts of the macrophytes(floating plants,floating leaf plants,submerged plants)on the abundance of microbial communities were analyzed.Furthermore,the patterns of the combination of technologies were explored in situ to purify nutrient rich effluent in storage ponds.The results were listed below:1)In the container experiment,floating macrophytes showed a significant and largest decrement of 16S rRNA;reverse pattern was observed in CK treatment.Abundances of denitrifying genes in water of floating plants showed decrement,or decrement in the early experiment and then stabilized in the experiment,while nirS and nosZ in waters of submerged plants showed a decrement first,and then an increment.Abundances of 16S rRNA on the root surface of the plants increased at the early experiment and then decreased,especially on the root surface of water hyacinth,which ranged from 1.18 to 1.31 × 109mL-1.The nirK and nirS on the root surface of floating macrophytes showed a decrement at the start,then followed by an increment,which ranged between 1.38-1.40×105 mL-1,while the nosZ on the root decreased continuously during the experiment,the same as the denitrifying genes on the root of submerged plants.The abundances of 16S rRNA in sediments of the all treatments decreased and then kept unchanged during the experiment,while the abundance of nosZ in sediment kept increment steadily.The change rate of nosZ in sediment,ordered from the larger to the smaller,was of Hydrilla>water hyacinth>CK>water chestnut>water lettuce.The abundance of nirK in the sediment of submerged treatment decreased steadily;and nirS in the sediment of CK increased significantly first,then decreased.2)Microorganism immobilization technology was used in situ to purify the polluted water.To evaluate the variation of water quality and microorganisms especially denitrifying bacteria before and after the technology application from March to May in subtropical climate zone,and clarify the relationships between microbial abundances and water properties,the changes of water quality(CODMn,NH4+,NO3-,NO2-,TN,TP)were monitored periodically.The temporal and spatial variation of abundances of 16S rRNA and denitrifying genes(nirK,nirS,and nosZ)in waters were analyzed using real-time PCR.The results showed that the concentrations of CODMn,NH4+ and TN in the water were reduced significantly compared with the water from the pond inlet and the transparency of water was improved rapidly.The abundances of 16S rRNA and nosZ genes had the similar variation,which the maximum(the means ware 2.58×108 copies/m L and 2.98×104 copies/m L respectively)occurred at day 3,decreased dramatically at day 17,then increased gradually after using micro-biofilm technology.However,the nirK and nirS abundances did not significantly change,but increased rapidly after one month.The abundance of total bacteria(16S rRNA gene)was significantly correlated with the temperature(R=-0.6597,P<0.0001)and transparency(R=0.4312,P<0.0001)in water.Meanwhile,the nirS gene abundance was significantly correlated with the temperature(R=0.7899,P<0.000),the concentration of NO3-N(R=-0.5559,P<0.000),N02-N(R=-0.7569,P<0.000),and TP(R=-0.4463,P<0.000).The nosZ gene abundance was affected strongly by transparency(R=-0.4534,P<0.0001),NH4+-N concentration(R=-0.5272,P<0.0001),and P043-P concentration(R=-0.4914,P<0.0001).The results indicated that the microorganism immobilization technology is applicable for in-situ to purify the polluted waters and the abundances of microorganisms in the polluted pond were influenced by immobilized microorganism technology and water properties.3)Field experiment using water hyacinth revealed that the abundance of 16S rRNA in waters with water hyacinth was positively correlated with nirK(R=0.449,P<0.001),nirS(R=0.441,P<0.01),TN(R=0.555,P<0.001),NH4+-N content(R=0.411,P<0.01).nirK and nirS were all correlated with transparency(R=0.380,P<0.01,R=0.369,P<0.01).Furthermore,nirK was also correlated with concentrations of TN and NH4+-N(R=0.435,P<0.01,R=0.534,P<0.01);while nirS was only correlated with concentration of NH4+-N(R=0.327,P<0.01).nosZ was correlated with water temperature(R=0.406,p<0.01),DO(R=0.398,P<0.01),concentration of NH4+-N(R=0.330,P<0.01)and NO2--N(R=-0.408,P<0.01).We concluded that the different types of macrophyte affected the purification process differently through modulating the abundances of total bacteria and denitrifying bacteria in the system.Water hyacinth(E.crassipes)is better positioned than other types of aquatic plants and can purify nutrient rich effluent and has more effective functionality if combined with the biofilm technologies to remove nitrogen and to optimize physio-chemical properties of water bodies.