| Constructed wetland technology has been widely used in the fields of sewage treatment,water purification and recovery.A large number of research and engineering practice show that after a period of operation,the treatment capacity of constructed wetland will be reduced,and matrix blockage will often occur,which seriously hinders the wastewater treatment function of constructed wetland.The clogged matrix needs to recover through periodic operations,such as dropping dry,stopping bed,trimming and even replacing the filler,which are costly and time consuming.The research on matrix plugging mainly focuses on the causes and mechanism of plugging,with rich theoretical support,but lacking effective and cost-effective practice.This dissertation,taking pore medium as the prototype from the hydrogeological point of view,fully understanding the mechanism of water rock interaction,combining with the change rule of pore medium water physical properties and the reaction process of solution precipitation,adsorption desorption and acid alkali in water rock chemical interaction.Based on the expansion of matrix void space,natural geological materials are selected,suitable grading structure is constructed,multi-scale experimental research is carried out,and the effects of four pollution indexes?COD,TN,NH3-N and TP?are tracked and monitored.Based on the constructed geological model?CGM?,a microbial-water-rock system with pollution and decontamination is established.This study used the CGM to build the constructed wetland engineering matrix and analyzed its blocking mechanism and the attenuation law of removal effect.We then put forward the judgment basis for the occurrence of matrix blocking,explored the feasibility of using grading structure to control physical blocking and active materials to alleviate chemical blocking,and developed appropriate technology to intervene and control matrix blocking,so as to prolong the system operation cycle.The specific research results are as follows:This study selected four kinds of natural geological materials?sand,limestone particles,quartz gravel and quartz sand?and included 8 kinds of particle size samples.The effects of different samples on TN and TP were studied by static adsorption test.The concentrations of TN and TP decreased by 18.70%?54.49%and 16.48%?89.01%respectively after 60 hours;limestone particles,quartz gravel,and sand had better removal effect on nitrogen and phosphorus.The analysis showed that the strength of the sample was affected by the size of the particles.Under the condition of certain sorting and uniform sizes,the increase of quartz gravel particle size had a positive effect on the removal of TN and TP,while the decrease of limestone particle size had a positive effect on the adsorption capacity of TP.In the small-scale test,the selected single gradation matrix was arranged in a certain order to form a multi-layer gradation structure.In the long PVC pipe with L=6m and V=0.05m3,the model was set up according to the grain order from fine to coarse along the water flow direction.Under the condition of continuous water inflow for 36days,the removal rates of COD,TN,NH3-N,and TP can reach 30.74%,53.06%,82.94%,and 63.78%respectively.The results showed that the multi-layer gradation structure could produce the superposition effect,and its effect on nitrogen and phosphorus was stronger than that of single gradation matrix.In the enlarged-scale test,three kinds of CGM models were laid according to different grading methods,i.e.positive particle sequence structure?JP1#?,reverse filter structure?JP2#?and positive anti rhythmic multi-layer composite structure?JP3#?.At the bottom of the model,gas distribution device were set up with a pipe spacing of 0.20m,a hole spacing of 0.20m,and a hole diameter of 0.10×10-1 m;and the air is aerated for 30 min every 3 hours ensuring the oxygen supply.The removal effects of JP2#on COD,TN,NH3-N,and TP were 16.05%,3.35%,30.14%,and 43.93%respectively.The removal effects of JP3#on COD,TN,NH3-N,and TP are 22.81%,4.28%,40.23%,and50.94%respectively.The results showed that the scientific configuration of fillers with different lithology and particle size could effectively improve the sewage treatment capacity.Under the condition of 2.29?3.30mg/l of dissolved oxygen concentration,after 31 days of microbial culture,a stable microbial-water-rock system could be formed to further improve the decontamination efficiency of CGM.The study constructed six groups?1#?6#?of constructed wetland mesoscale test based on JP2#and JP3#CGM models.Each group showed better comprehensive performance under the conditions of inflow of 1.2?1.4m3/d,an actual hydraulic load of0.13?0.16 m3/?m2·d?and total hydraulic retention time of the system for 2d;and the experimental group with more limestone particles has higher removal rate.Group 3#had the best effect on COD?38.06%?,group 5#had the best effect on TN and NH3-N?70.43%and 22.05%?,group 4#had the best effect on TP?97.18%?.The results showed that JP2#was more suitable as a CGM structure.With the increase of influent flow,the actual hydraulic load of the system increased,and the hydraulic retention time decreased.The inverted filter structure?JP2#?could reflect the advantages of regulating the influent flow and hydraulic retention time,and controlling for the effect of a substrate in the constructed wetland.During the experiment,the chemical precipitates attached to the pores could reduce the permeability of the matrix.At the same time,when the limestone granular active materials had dissolution effect with sewage,the surface of the particles form dissolution,and corrosion grooves,expanding the void space of the overall structure to a certain extent.These effects could help the system to achieve the dynamic balance of dissolution and blocking,and effectively reduce the negative impact of chemical precipitation.This study set the direct-current layered water distribution device during the packing laying process and designed the anti-blocking check valve of the water distribution port.The above one patented technology was arranged at the bottom of the CGM functional layer to backwash the pipe and clear flush the internal fillers.The layered water distribution and the gas-water combined backwashing device showed the ability of effective re-oxygenation,de-silting,and alleviating deep blockage.These functions effectively alleviated or reduced matrix blockage but could not completely solve the problem of matrix blockage.In order to further solve the blockage problem,this study introduced a modular detachable device for the constructed wetland construction.The modular device is relatively independent and easy to disassemble.It can realize the gas-water combined backwash without destroying the matrix structure.The matrix module can also be removed for sunlight exposure to shed the mud films.The design enabled the realization of the“in situ regeneration”for the constructed wetland matrix,quick restoration of the matrix function,the continuous operation of the processing system,and the extension of the construction's effective operating cycle.The study showed that it was a feasible way to generalize the matrix of constructed wetland into the theoretical model of pore-aquifer for receiving and decontamination from the perspective of hydrogeology and to study the thinking and technical route of various factors affecting the"runoff"process.CGM solved the problems of low-concentration domestic sewage treatment and long-term operation blockage treatment.The research results provided relevant parameters and theoretical support for the construction of CGM and supplied novel solutions for the sewage treatment and old sewage treatment plant in rural centralized resettlement sites,for the regeneration and utilization of long-term idle constructed wetland,and for improving the tailwater quality and efficiency of small-town sewage treatment plant.These could be potential methods of geological engineering devoted to environmental treatment... |
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