| Harmless treatment and resource utilization of wastes such as garbage,sludge and sewage is the concept of international environmental geotechnical engineering,and the focus of research in the field of environmental geotechnical engineering.According to the research on sludge treatment methods at home and abroad,it is technically feasible and economically reasonable to use the solidified material modified sludge as the covering layer of landfill.In this paper,the municipal sludge from Wu Han San Jin Tan sewage treatment plant were used as research subjects to carry out laboratory tests.Under the condition of natural curing in the laboratory,three industrial solid wastes including desulfurized gypsum,fly ash and slag were selected to modify the sludge,the modified sludge was prepared by activating and pyrolysis of sludge with 4 factors and 3 levels.The mechanical properties of the modified sludge with well mechanical properties by cracking and shrinkage test,moisture content test and compression test,and the best ratio of the modified sludge was optimized by combining the characteristics of shear resistance and permeability.The wetting-drying test,nuclear magnetic resonance(NMR)test,scanning electron microscope(SEM)test and X-ray diffraction test(XRD)were carried out for the cured sludge with different contents of modified materials.And through the simulation calculation of VS2 DI software,the change rule of water in the interior of the modified sludge mulch under the conditions of precipitation and evaporation was obtained.Through the experiments,the following conclusions are drawn.(1)A new type of modified material is presented,which is used to modifiy municipal sludge with desulfurized gypsum,fly ash and slag from industrial solid waste.The results show that: when sludge: desulfurized gypsum: fly ash: slag = 1:0.6:0.6:0.2(mass ratio),the modified sludge is the most suitable covering material for sealing field.(2)Through laboratory tests,the change rules of the mechanical properties of the modified sludge,such as moisture content,volume shrinkage,compressive strength,shearing strength and permeability coefficient were studied.The results showed that the desulfurized gypsum,fly ash,slag and municipal sludge were uniformly mixed to form a cementing material with good mechanical properties,which played a good role as the skeleton in the modified sludge.(3)Wetting and drying cycles tests were carried out,with compressive strength,permeability coefficient and pore structure as the research objects.The results showed that: After three times of wet and dry cycling,the total pore capacity distribution and permeability coefficient of the modified sludge changed greatly,and the impact on the compressive strength was small and favorable.After two times of wet and dry cycling,the compressive strength and permeability coefficient of the modified sludge began to stabilize.(4)The micromorphology and mineral composition of solidified sludge were revealed by means of SEM and XRD tests.The results indicate that: The composition of solidified sludge is complex,mainly including lamellar,rod-like and needle-like minerals,and ettringite,silicide,ovum,bioclast and various organic flocculating substances and so on.The main mineral composition in undisturbed sludge is quartz.After adding different amount of modified material,the main chemical substance is calcium sulfate.(5)VS2DI software was used to simulate the change rule of water in the interior of the modified sludge cover during rainfall and evaporation,the physical and mechanical parameters of plant growth layer and modified sludge were obtained by laboratory test,and a simple landfill covering layer model was established to analyze the moisture variation under four working conditions. |
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