| Due to the rapid development of modern industrial and agricultural science and technology,the problem of urban river sediment pollution is becoming more and more serious.The water environment pollution of rivers mainly includes the discharge of exogenous pollutants and the release of endogenous pollutants.After the exogenous pollution is controlled to a certain extent,the phenomenon of endogenous release of sediment becomes more prominent.At present,most cities in China have the phenomenon of endogenous release of sediment to varying degrees,which not only leads to the deterioration of water quality,but also causes great harm to the aquatic ecosystem.Therefore,the key to solving the problem of river water environmental pollution is to control the endogenous pollution of sediment,and to explore how to curb the release of endogenous pollution from sediment is particularly critical for controlling polluted water bodies such as rivers.In this paper,ceramsite was prepared from river sediment,bentonite,starch and limestone.The physical properties,specific surface area,pore structure,phase composition,surface morphology and heavy metal leaching concentration of ceramsite were analyzed.Using the self-designed biological aerated filter,the comparative experiments of domestic sewage treatment by sediment ceramsite BAF and commercial ceramsite BAF were carried out.The effects of BAF start-up,hydraulic retention time and gas-water ratio on the removal of pollutants by BAF system were investigated.A multi-functional ecological blanket for in-situ remediation of polluted rivers was designed.The effect and mechanism of ecological blanket coverage on the release of sediment pollutants were discussed through indoor sediment release simulation experiments.In the practical engineering application of field fish pond,the effect of ecological blanket coverage on the release of sediment pollutants was further investigated,which made the application of ecological blanket wider.The results are as follows:（1）According to the ratio of raw materials,river sediment:bentonite:starch:limestone=70:30:10:13,preheated at 400°C for 10 min,calcined at 1000°C for 15 min,the sediment ceramsite was prepared.Its bulk density is 750.08 kg/m3,apparent density is1345.29 kg/m3,porosity is 44.24%,water absorption is 27.17%,compressive strength is 3.03MPa,specific surface area is 1.5911 m2/g,all meet the requirements of’artificial ceramsite filter for water treatment’.（2）The phase composition of the sediment ceramsite is Si O2（quartz）,Fe2O3（hematite）,Al PO4（aluminum phosphate）and albite（Na Al Si3O8）,which together form the skeleton structure of the ceramsite.Through SEM analysis,it can be seen that the surface of the sediment ceramsite is rough,the pore structure is rich,and there is a strong adsorption potential.The heavy metal content of the sediment ceramsite leaching solution is lower than the’hazardous waste identification standard’standard.（3）The removal rates of COD,NH3-N and TP in SSC-BAF based on sediment ceramsite were basically stable at more than 75%on the 15 th day of biofilm formation.Compared with CTC-BAF based on commercial ceramsite,the removal rates of COD,NH3-N and TP were increased by 9.19%,7.55%and 11.42%respectively.When the hydraulic retention time was 22 h and the gas-water ratio was 6:1,the BAF treatment effect was better and more stable.At this time,the removal rates of COD,NH3-N and TP by SSC-BAF and CTC-BAF were 75.17%,71.21%,73.92%and 70.09%,67.28%,70.84%,respectively.At the same time,the mass concentrations of COD and TP in the effluent of the two BAFs met the first level A standard of GB 18918-2002.The mass concentration of NH3-N in the effluent met the first level B standard of GB 18918-2002.（4）Through the indoor water tank simulation experiment,it was determined that the inhibitory effect on the total nitrogen release in the sediment was that the ecological blanket group was greater than the ceramsite group,and the inhibitory effect on the total phosphorus release was that the ecological blanket group was greater than the ceramsite group.When the thickness of the cover layer was 3 cm,the effect of in-situ coverage of ecological blanket on inhibiting the release of nitrogen and phosphorus from sediment was the best,and the reduction rates of TN and TP reached 81.85%and 88%,respectively.（5）The concentration of TP and TN in the overlying water of the control area was 2.36mg/L and 5.72 mg/L,respectively,and the concentration of the experimental area was 0.53mg/L and 2.06 mg/L,respectively.The reduction rate of TP and TN by ecological blanket coverage was 77.54%and 63.99%,respectively.Therefore,ecological blanket coverage has a good inhibitory effect on the release of nitrogen and phosphorus in fish pond sediment. |
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