| Water eutrophication is one of the more serious water environment problems in China.Studies have shown that the phosphorus concentration in water reaches 0.02mg·L-1 can cause blooms to erupt.The river sediment can adsorb a large amount of soluble reactive phosphorus from external input,thus becoming an important reservoir of phosphorus in the aqueous environment.As an important part of sediment,the composition and content of organic matter have an important influence on the change of phosphorus flux between sediment and overlying water.In-situ passivation technology can effectively control the release of phosphorus in sediment,but the effect of light organic matter on the control of phosphorus release in sediment by passivator is still unclear.In this paper,the effects of removal of light organic matter on phosphorus adsorption-release characteristics and phosphorus control effect of lanthanum zeolitewere studied by taking the X river sediment with serious phosphorus pollution as the research object,and the lanthanum zeolite was used as the representative of the passivator,and the following conclusions were obtained:(1)The pH of the X river sediment was 7.64～8.88,and the average particle size was smaller than that in summer and spring.The total phosphorus content of sediment was 870.00～2173.00mg/kg,and the evaluation of single-factor index method showed that some points were seriously polluted with phosphorus.The adsorption kinetics showed that the adsorption amount of phosphorus from 0～2h sediment fluctuated between positive and negative.The adsorption capacity increased rapidly in 2～4h,and the adsorption rate also reached the peak(22.14～48.46 mg/kg·h-1).After that,the adsorption capacity increases slowly,reaching equilibrium at 48h.The adsorption isotherm showed that the equilibrium concentration of phosphorus adsorption-desorption(EPC0)of the sediment was 0.39～2.21mg/L,which was higher than the phosphorus concentration in the overlying water in the same period,and had a high release risk.The maximum buffer capacity of phosphorus MBC and Freundlich constant KF showed the regularity of autumn>>summer>spring.The adsorption energy of most samples was 8.45～11.18 KJ/mol,indicating that the adsorption mechanism was ion exchange.The correlation analysis showed that the phosphorus adsorption rate constant of sediment was positively correlated with the calcium content(P<0.05).The EPC0 value was positively correlated with total phosphorus and easily released phosphorus in sediment(P<0.01),average particle size and organic matter of sediment(P<0.05),and pH(P<0.05).(2)After removing light group organic matter,the organic matter content in the sediment decreased from 3.54%of the original sediment(R-S)to 2.36%of the removal of light group organic matter sediment(LFOR-S),a decrease of 0.18%.pH increased from 7.35 for R-S to 10.21 for LSOF-R,an increase of 38.9%.Compared with R-S,the phosphorus content of NH4Cl-P,BDP and Org-P decreased by 0.42%,0.91%and 0.89%,respectively,while the content of NaOH-P,HCl-P and Res-P increased by 0.11%,1.34%and 0.77%.The maximum release of R-S phosphorus was 179.39mg/kg,and the maximum release of LFOR-S increased to 289.03mg/kg,an increase of 1.61 times.The release rate of LFOR-S increased by 1.86 times within 0-0.08h.The EPC0 for R-S is 2.60mg P/L and the EPC0 for LFOR-S is 7.07mg P/L.The maximum adsorption capacity of R-S for phosphorus was 556.30mg/kg,and the maximum adsorption capacity of LFOR-S for phosphorus was 371.04mg/kg.The influence of temperature on R-S is manifested as the decrease of phosphorus release with the increase of temperature,and the phosphorus release of LFOR-S increases with the increase of temperature.The phosphorus release of sediment has a parabolic(U-shaped)relationship with pH.(3)The addition of LMZ increased the maximum phosphorus adsorption capacity of R-S and LFOR-S from 2568 mg·kg-1 and 2071 mg·kg-1 to 4054 mg·kg-1 and 4014 mg·kg-1,respectively.When the temperature increased from 5℃ to 30℃,the phosphorus release control rate of LMZ on R-S gradually increased,while the phosphorus release control rate of LFOR-S decreased from 90%to 76%and returned to the original level.XPS characterization found that ligand exchange was the main mechanism by LMZ to control phosphorus release from the two sediments.LMZ can convert unstable phosphorus in sediment into a stable state,but the reduced unstable phosphorus in LFOR-S is not completely converted to a stable state,but enters the aqueous phase to make its phosphorus release higher than R-S,resulting in poor phosphorus control effect. |
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