Adsorption Characteristics Of Phosphorus In Water By Modified Biochar And Its Resource Reuse

The problem of eutrophication caused by excessive phosphorus content in China’s water body is becoming more and more serious,which has an increasingly serious impact on the structure and function of the ecosystem and the destruction of the freshwater system.At present,the restoration of phosphorus polluted water has become a hot research topic in recent years.Adsorption method has attracted researcher’s attention because of its excellent effect in the improvement of contaminated water.Biochar,as a novel kind of adsorption material,has been widely used in the fields of water restoration.However,there are some difficulties in the adsorption and removal of pollutants by biochar,such as the uneven adsorption performance and the difficulty of recycling.Based on these shortcomings,in this study,cotton straw,corn straw and rice husk were used as raw materials to prepare biochar,and to make the modified biochar materials by ball milling technology and the supported ferromanganese oxygen.The physical and chemical properties of different type biochar are analyzed by batch adsorption test and characterization analysis.Phosphorus adsorption properties and mechanism of biochar in the solution are clarified in this study.Finally,the potential of adsorbed-phosphorus biochar as fertilizer for resource reuse was explored by the pot experiment of lettuce.The main results and conclusions were as follows:（1）The physical and chemical properties of the biochar QMFMBC have been significantly improved after ball milling and Fe/Mn modification.The specific surface area of QMFMBC was 226.5 m²·g^-1-331.49 m²·g^-1,which was 8.27-15.16 times higher than that of the original biochar.In addition,the SEM analysis showed that the fine particles of Fe/Mn oxides were found in the microstructure of QMFMBC.The FTIR showed that the surface of QMFMBC has the same rich functional groups（including-OH,C=C,C-O,etc.）as BC,while the functional groups of Mn-O and Fe-O were also introduced on the surface of QMFMBC.（2）Batch equilibrium method was used to explorethe adsorption kinetics,isothermal adsorption and environmental factors of phosphorus on QMFMBC.It was found that ball milled Fe/Mn modified rice husk biochar（QMFMDK）had the best adsorption effect on phosphorus,and the adsorption capacity was 50.93 m²·g^-1.The fitting results of adsorption kinetic model showed that the adsorption equilibrium time of QMFMBC for phosphorus was about 360 min.The isothermal adsorption results indicated that the modified QMFMBC significantly improved the adsorption of phosphorus compared with the original biochar.The phosphorus adsorption capacity of QMFMBC ranged from 42.07 m²·g^-1to 50.93 m²·g^-1,which were 3.46-7.22 times higher than that in BC.In addition,the increase of temperature and higher acidity of water environment promoted the adsorption of phosphorus by QMFMBC.Generally,the adsorption mechanism of phosphorus by QMFMBC mainly included the electrostatic attraction,ligand exchange and complexation reaction.（3）The results declared that the application of modified rice husk biochar as phosphorus fertilizer could not only significantly promoted the fresh biomass and root of lettuce,but also increased the content of total phosphorus in plant and available phosphorus in soil.The biomass of lettuce in FMDK-P was 1.21-2.47 times and 2.23-7.21 times higher than that in CK,respectively.Both FMDK+P2 and FMDK-P2 had the best promoting effect on the accumulation of total phosphorus in lettuce,which increased by 25.67 times and 24.71 times compared with CK,respectively.FMDK+P2 treatment and FMDK-P2 treatment also significantly increased soil available phosphorus content,which were 24.37 and 12.47 times of CK,respectively.Generally,FMDK-P had better effect on promoting the growth and development of lettuce root system than FMDK+P.In conclusion,compared with the original biochar,the modified biochar not only increased the number and type of functional groups as well as the specific surface area,but also significantly improved the adsorption effect of phosphorus.In this study,the modified biochar such as QMFMDK was prepared by ball milling and loading ferromanganese metal.Moreover,the modified rice husk biochar FMDK-P promoted the growth of lettuce and increased the content of phosphorus in soil.Therefore,iron manganese oxide modified rice husk biochar had a strong ablility of environmental remediation and a great potential of resource reuse,which is expected to be widely applied in the future.