Study On Phragmites Based Biochar And Its Application In The Ecological Remediation Of Tai Lake

The nutrients in the water and the releasing of N and P from the sediment were the major contributions of eutrophication in Tai lake.Phytoremediation had the potential to be applied in the water treatment in Tai lake in a large scale by the advantage of lower coat,remarkable effect and complete integration with the ecological system.Biochar based on the aquatic plants after phytoremediation could not only avoid secondary pollution from the withered plants,but also adsorbe N and P in the water with the properties of high surface area,porous structure and environmental-friendly,which could deliver multiple benefits on the eco-system.However,the problems of limited adsorption capacity for N and P on the biochar and laking of practical application have not been solved.Phragmites,which was the mostly used aquatic plants in Tai lake,was selected to be studied in the thesis.The MgCl2 modified biochar(MPB)was successfully synthesized based on the Phragmites,which was loaded nano-size MgO particles on the surface and could effectively adsorb NH4-N and PO4-P in the water.The biochar’s adsorption process and mechanism for NH4-N and PO4-P were studied.Furthermore,the experiments to explore the application potential of MgCl2 modified biochar on the ecological remediation of Tai lake were also carried out.MgCl2 was used to produce modified biochar based on the Phragmites.The impacts of temperature and impregnation ratio on the properties of biochar were studied.It suggested MgCl2 impregation could largely increase the surface area of the biochar and help form the porous structure.The MgCl2 modified biochar successfully loaded nano-size MgO particles on the surface,with the maxium surface area being 254.91 g/m2 and the pore diameters in average was 3.07 nm.Following,adsorption experiments were designed and carried out to study on the adsorption process and mechanism for NH4-N and PO4-P onto the MPB.The results demonstrated that the MPB presented high adsorption capacity to both simulated NH4-N and PO4-P with the maximum adsorption capacity exceeding 30 mg/g and 100 mg/g respectively.The dominant mechanism for ammonium adsorption was Mg2+exchange instead of functional groups and surface areas and the Mg-P precipitation was the main mechanism for phosphate adsorption.The MPB also showed high TP removal ratio on the practical water in the Tai lake.After the adsorption experiments of MPB for 24 h,the concentration of TP decresed from 0.152 mg/L to 0.02 mg/L,with the removal ratio more than 90%.The impacts of MPB addition on the sediment’s remediation in the Tai lake was also studied by carrying out the incubation experiments under the overlying wter/sediment system.It was found that the MPB could decrease the amount of NH4-N and immobilize NH4-N in the sediment of Tai lake by adsorbing.MPB addition could also dramatically change the microbial community structure.It turned out that MPB could promote the growth of Proteobacteria by offering carbon source,which was the dominant bacteria in the sediment of Tai lake.The OUTs of Nitrospira in the sediment adding MPB showed minor decreasing compared with the controlling group,which demonstrated that the addition of MPB had the potential to restrain the nitrification process.To further explore the application potential of MPB on the ecological remediation of Tai lake,engineering pilot-scale experiments were carried out in the south of Tai lake.The Phragmites in the south Tai lake was harvested in a large scale to produce biochar which was further added in the Tai lake after mixing with the sediments in advance.Up to now,Phragmites harvesting and biochar production were completed and some 1 t biochar based on the Phragmites was derived.The biochar addition experiments was about to carry on.The study in this thesis combined the preparing of adsorption material of nutrients and resourse utilization of aquatic plants after phytomediation.A modified biochar which could effectively adsorb NH4-N and PO4-P was successfully systhesized.The lab experiments and engineering pilot-scale experiments were both used to study on the Tai lake’s ecological remediation by MPB.The initializing results showed that the MPB had the potential to be used in the Tai lake.