| With the increase of population,climate change,pollution of water source,over exploitation of groundwater and other problems,the shortage of available water resources on the earth is becoming more and more serious.Artificial recharge technology has become one of the important means to deal with the shortage of water resources and the corresponding environmental geological problems.However,the clogging problem in the process of recharge has a significant adverse effect on the efficiency of managed aquifer recharge,operation cost and project life,which has become the main factor that restricting the promotion and application of managed aquifer recharge technology.Clogging of recharge facilities is the main factor restricting the development of artificial recharge and alleviate the environmental geological problems caused by the shortage of water resources,we studied the law and mechanisms of biological clogging in porous media during artificial recharge through laboratory experiments.Based on the in-depth study of biological clogging,we also analysis the effects of physical and chemical factors on biological clogging in porous media during artificial recharge,which could provide scientific for prevention,control and treatment of biological clogging in porous media during artificial recharge.There are three types of porous media clogging in artificial recharge: physical clogging,chemical clogging and biological clogging.Among them,for biological clogging,because of its many factors,and microorganisms in the environment participate in a variety of hydrogeochemical processes,the laws of biological growth,migration and movement,as well as their impact on clogging are also complex and diverse.In this study,Pseudomonas aeruginosa(P.a)was used as the model microorganism in laboratory experiment to study the mechanism of biological clogging in the process of artificial recharge,and analyze the influence of common physical and chemical clogging substances(suspended solids,Fe(III))on biological clogging.The main conclusions are as follows:1.Under the condition of biological clogging,the whole clogging evolution process has obvious stages: stable in the initial stage,declining in the middle stage and relatively stable in the later stage.In the early stage of the experiment,due to the small adhesion of microorganisms in the quartz sand,under the action of the shear force of water flow,microorganisms fell off the surface of the quartz sand,showing that the permeability of porous media changed little;When some microorganisms adapt to the shear force of water flow,and propagate rapidly under the support of nutrients,they are in the exponential growth stage,with enhanced adhesion and sharply reduced permeability of porous media;When the growth and decay of microorganisms reach a dynamic balance,the biological clogging in porous media reaches a stable stage in the end of experiment.2.With the increase of ionic strength(within the experimental range of 0~200mM),the beginning time of biological clogging is delayed and the degree of biological clogging is reduced.When the ionic strength is in the range of 0~100mM,the external cation neutralizes the negative charge between the microorganism and the quartz sand surface,and promotes the adsorption of the microorganism and the quartz sand,at the same time,the alkaline substances produced by microorganisms promote the dissolution of some substances in the infiltration medium,the interaction between them delays the decrease of permeability;When the ionic strength reaches 200 mM,the growth of microorganisms is limited by the high osmotic pressure,which also causes the delay of microbial plugging time;The increase of ionic strength results in the increase of cell osmotic pressure,which is not conducive to the nutrients absorb by cells,and leads to the degree of biological clogging decreased in porous media.3.With the increase of nutrient concentration(in the experimental range of 0~20mM),the rate of biological clogging is accelerated,the time of clogging is advanced,and the degree of clogging is increased.Nutrition from oligopoly to abundance,the growth and propagation speed of microorganism is accelerated,resulting in the clogging rate of porous media is accelerated;In the same way,with sufficient nutrients and fast growth of microorganisms,the porous media pores are occupied faster than the released rate,which makes the time of biological clogging earlier;Appropriate nutrient concentration promotes the growth and reproduction of microorganisms,increases the volume of microorganisms,generates more extracellular polymers,and aggravates the degree of biological clogging at the end of the experiment.4.The interaction of suspended solids and microorganisms will accelerate the clogging process of porous media and aggravate the degree of clogging.When suspended solids are added,the beginning time of biological clogging is advanced.This is because the suspended solids themselves cause the clogging of porous media,at the same time,the combination of suspended solids and microorganisms will cause more serious agglomeration and flocculation,further accelerating the occurrence of clogging,accelerating the formation of clogging and aggravating the degree of clogging;The suspended solids itself has strong mobility,the comigration of microorganisms and suspended solids in porous media after adhesion increases the clogging depth.5.The interaction of Fe(III)and microorganism will accelerate the clogging process of porous media and aggravate the clogging degree.Under the action of microorganism,the environment is weakly alkaline,which promotes the formation of colloidal Fe(III),increases the volume after adhesion polymerization with microorganism,and advances the beginning time of porous medium clogging;When the concentration of Fe(III)is more than 3mg/L,the adsorption equilibrium of microbe and Fe(III)is exceeded,and the effect of Fe(III)colloid on porous media clogging is increased,which can accelerate the clogging rate;Fe(III)combines with cells to form new substances,and Fe(III)forms iron hydroxide solid under alkaline condition,which results in the aggravation of porous media clogging;Under the influence of Fe(III)migration,the clogging depth of porous media increases further. |
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