| In recent years,the technology of constructed wetland sewage treatment has developed rapidly due to the advantages of simple process equipment,less investment,low energy consumption,easy construction,simple operation and maintenance.However,the problem of blockage often occurs in the operation process of the system,resulting in the decrease of the purification capacity and the shortening of the service life of the system.In order to solve this problem,the department designed and manufactured a biological module that can prevent blocking,and built a modular artificial wetland with this biological module as the main filler.During the operation process,the system is in good condition and there is no blocking water.However,the system mainly relies on the experience of traditional constructed wetlands in the design and operation process,which can not play the best sewage purification effect of the system.In this paper,the flow law of modular constructed wetland under different hydraulic conditions is analyzed by using dimensionless hydraulic retention time distribution density curve and hydraulic efficiency from the perspective of hydraulics.Through long-term water quality index detection,the change of pollutants in the system is monitored,the migration law of pollutants in the system is studied,and the most suitable operation conditions for the characteristics of fishery production are found.The tracer test results of modular constructed wetland show that:after planting plants,the plant roots in the upper layer of the wetland internal space have a certain blocking effect on the flow,the effective volume in the system is reduced,also the flow mode is closer to the ideal push flow,and the flow efficiency of the system has been improved to a certain extent;among the different water inlet methods,the hydraulic efficiency of uniform water inlet is the largest.The hydraulic efficiency λ is 0.5222,which is 155.60%higher than that of the middle concentrated inlet and 17.06%higher than that of the side surface uniform inlet,if the hydraulic load of the system is increased within a certain range,the hydraulic efficiency and effective volume ratio of the system also increase,which is linear with the hydraulic load(R2=0.8677,0.7886).The results of water quality test of modular constructed wetland show that rainfall has a great influence on the purification effect of the system when the system is running.When the hydraulic load is adjusted to 500mm/d,the removal rates of suspended solids,ammonia nitrogen,nitrate nitrogen,nitrite nitrogen,total nitrogen,total phosphorus and COD are 77.25%,51.80%,-13.33%,60.21%,21.93%,42.77%and 17.89%,respectively.The change rule of suspended solids concentration in the system is gradually decreasing along the direction of water flow,and the removal of suspended solids is mainly completed at the front of the system;the change rule of ammonia nitrogen concentration is first decreasing and then rising,with the lowest concentration at sampling point 4#;the change rule of nitrate nitrogen concentration is first rising and then falling and then rising;the removal rule of nitrite nitrogen is first decreasing and then rising,with the lowest concentration at sampling point 5#;the change law of total phosphorus concentration is gradually decreasing along the water flow direction,and the main packing area plays a major role in phosphorus removal.When the hydraulic load of the system is 800mm/d,it can better adapt to the needs of fishery production and play the maximum benefit.At this time,the removal rate of ammonia nitrogen and nitrite nitrogen in the system is 76.72%and 74.25%.To sum up,planting plants is conducive to the better operation of the system when the modular constructed wetland is used for the treatment of fishery tail water.The water inlet system should be set with uniform water inflow in full cross section,and the hydraulic load should be set at 800mm/d during operation,and the daily management of the wetland should be strengthened. |
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