| Recent years,reusing of urban reclaimed water has become one of important measures to alleviate water resources crisis,because of its properties of abundance,local accessible and economical.However,the reuse of reclaimed water,as a complex multi-material coexistence system,can cause the infiltration system clogging.A thorough understanding of seepage-clogging mechanism in river-Lake vadose zone recharged by urban reclaimed water is critical to ensure safely reclamation and improve the reclaimed water recharging efficiency.In the first part,through constructing the simulated columns system,the natural seepage-clogging process of infiltration vadose zone recharged by urban reclaimed water was developed.We found that,in the upper 5m depth of typical sections in Beiyun river,the percolation mediums were plain fill and sandy silt in Tugou,fine sand and silty sand in Hehezhan,separately.The infiltration rate in Hehezhan column was higher than Tugou column,and both of the infiltration relationships fitted the power correlation.The penetration time was 78.83 h in Hehezhan column,and 152 h in Tugou column.According to the porosity simulation result obtained from Thullner(0.75)model,the clogging degrees were 19.3%in Tugou column and 14.4%in Hehezhan column respectively;physical clogging occurred in 0-30d,and physical-biological clogging occurred in 31-77d.The second part of this study examined the clogging process of porous media recharged by reclaimed water and the particles retention rules under the influence of different porous media clogging degree.The result indicates that the relative permeability coefficient had a great fluctuation in the first 40d,with less effect of biological clogging;and the relative permeability coefficient gradually decline in 41-122d,with a great influence of biological clogging.There were a larger significant correlation between the relative permeability coefficient and porous medium size,and the influence of surface morphology and flow velocity to the permeability was relatively small.Combined the simulation result of porosity and dispersion,the result can be deduced that the clogging degree was about 200%,and the clogging degree increased with the decrease of midum size.With the clogging degree increased,the particles transport ability decreased sharply,which showed that biological clogging can accelerate particles retention capacity significantly.Both the third part and the fourth part of this study examined the effects of dissolved organic matter(DOM)contained in reclaimed water,ionic strength(IS),porous media surface morphology and flow velocity on the retention and transport of particles in water-saturated porous media.The result indicates that DOM showed remarkable effect on the deposition of particles,the retention rate increased with the particle diameter increasing.When IS and roughness of medium increased,deposition of particles in the porous media increased.When flow velocity increased,the mobility of particles in porous media enhanced.DOM showed solubilization capacity to nanoparticles.When DOM combined lower IS,they enhanced 260nm and 960nm particles mobility;when DOM combined higher IS,they improved 260nm and 960nm particles retention.The last part of this study developed the dynamic analysis on particles attachment efficiency in porous media under the influence of DOM on the basis of DLVO theory coupled with the Maxwell extended model.Theoretical analysis indicated that Zeta potential was decreased under the influence of DOM,and resulted in lower repulsive energy barrier and deeper secondary minimum.Maxwell extended model predicted that the smaller particles was adsorbed in primary minimum,the primary minimum attachment efficiency increased with the ionic strength increasing;the bigger particles was adsorbed in both primary minimum and secondary minimum.The presence of DOM increased the particles primary minimum attachment efficiency by two orders of magnitude,secondary potential attachment efficiency increased by one order of magnitude. |
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