Research On Substrate Clogging And Removal Mode Of Floating Vertical Flow Constructed Wetland

As a new type of water treatment technology,constructed wetland is widely used.In actual project operation,the clogging of subsurface wetland is a common problem.To solve this problem,this research intends to use the advantage of lightweight ceramsites to float up and down with the water flow to make the filler voids recombine from time to time,so as to alleviate or even eliminate the problem of clogging of subsurface wetlands.In this study,lightweight ceramsites with three particle sizes of2-4mm,4-8mm,and 8-10mm were used as the research object to construct floating media beds.Chose 5-10mm gravel as a control group to construct a traditional media bed.Chose 2000 mesh zeolite powder(density 1.2-1.4g/cm~3),1500 mesh bentonite(density 2-3g/cm~3)and around 400 mesh corn starch(density 1.48g/cm~3)as suspended particulate matter and studied the water quality purification effect of these four kinds of media beds and the over-current capability changes in clogging process.After the media bed is clogged,the light-weight ceramsite could float up and down with the water level to explore the effect of alleviating the clogging when the packing fluctuates at different heights(10cm,20cm,30cm,40cm)with the water level.According to the results of the previous experiments,the floating vertical flow constructed wetlands were constructed to plant Siberian iris,water bamboo and water calamus.The zeolite powder with the most obvious clogging was selected as the suspended particulate matter,and 20cm was set as the fluctuation range of the filler with the water level,and the effect of light ceramsite on the mitigation of wetland clogging in actual operation and the plant growth were studied.The results of the study are as follows:(1)The four kinds of media beds have the worst water purification capacity for bentonite wastewater,and the removal rate of zeolite powder and starch is better.This shows that the media bed is not conducive to the treatment of suspended solids wastewater with a density greater than 2g/cm~3.Different fillers have different treatment effects on different wastewaters.The water purification effect of the media bed is related to the physical and chemical properties of suspension in the wastewater.In zeolite powder wastewater,the highest removal rate of turbidity and SS is 5-10mm gravel(34.06%,28.67%),and the lowest is 2-4mm ceramsite(17.47%,16.41%);in bentonite wastewater,the highest is 2-4mm(6.96%,10.31%),the lowest is 8-10mm ceramsite(4.00%,4.42%);the highest in starch wastewater is 4-8mm ceramsite(15.77%,21.14%),the lowest is 8-10mm ceramsite(8.97%,11.88%).(2)The smaller the filler particle size,the easier it is to be clogged.The order of the degree of difficulty of clogging of the four media beds is:2-4mm ceramsite>4-8mm ceramsite>5-10mm gravel>8-10mm ceramsite.The four kinds of fillers are more likely to be blocked in zeolite powder and corn starch,which is related to their adsorption and viscosity,and it is easier to compact between the fillers.And in the absence of plants,compared to the clogging of inorganic particles,the degree of clogging of the filler is not obvious when treating wastewater containing organic suspended particles.(3)After the media bed floats 10cm,20cm,30cm,40cm up and down with the water level,the permeability coefficient of the floating media bed can be restored to more than 89%of the initial permeability coefficient after a maximum of 8 times,which has a significant mitigation effect on wetland clogging.And when the wetland is completely clogged,considering the protection height of the wetland is 30cm and the construction cost,the media bed can alleviate or even eliminate the clogging by floating up and down 7-8 times within the protection height of 20cm.(4)The water quality treatment effect of the wetland systems with plants are generally higher than that of the systems without plants.But in the 5-10mm gravel,the removal rate of the plant system is lower than that of the non-plant system.This may be because plants and microorganisms are more firmly attached to the gravel surface,and there are more root exudates and extracellular polymers generated by biochemical reactions,which accelerates the clogging of the wetland,and thus the COD removal effect becomes poor.Different plants have different water quality treatment effects in different fillers.(5)In the process of wetland clogging,2-4mm,4-8mm,8-10mm ceramsite and5-10mm gravel wetland systems are all plant-free systems that take the longest time to achieve clogging(24d,32d,32d,20d),indicating that the growth of plant roots will reduce the gaps between fillers and accelerate wetland clogging.When iris,water bamboo,water calamus and no plants are in 8-10mm ceramsite,it takes the longest time for the wetland system to be clogged(32d,26d,30d,24d),indicating that under the same plant type,the larger the filler particle size,the more difficult it is clogged.(6)After the wetland filler floats up and down 20cm with the water level,the permeability coefficient of most of the media beds can be restored to more than 60%of the initial permeability coefficient.When the wetland is completely clogged,continuous floating 9-10 times within the protection height of 20cm,the wetland can alleviate the clogging formed by the zeolite powder wastewater.Combined with the comparative analysis of plant water content,growth amount and root exudate content before and after wetland clogging,calamus is the best wetland planting plant.