Optimization Of Intermittent Aeration In The Vertical Flow Constructed Wetland On Wastewater Purification Efficiency

Lake Chaohu has been suffering from the pollution problem for quite a long time.Existing literatures showed that the external pollution loads accounted for 98% of the total pollution loads.Most of the external loads are from the inflowing rivers,among which the Nanfei River has the maximum amount of pollutants input.The present water quality of Nanfei River was classified as inferior Ⅴ,belonging to severe pollution level.This situation has been posing a serious threat to Lake Chaohu.Therefore,a water purification demonstration project of the multi-stage bypass constructed wetland system was built aside the Nanfei River in May 2013 to reduce pollutants from the Nanfei River into Lake Chaohu.The whole system includes a pretreatment unit,a vertical flow constructed wetland unit,and a horizontal flow constructed wetland unit.This paper took the whole systems the research object.Experiments have been carried out to study the removal efficiencies of pollutants in the water of Nanfei River for each unit.Specific focuses has been given on the seasonal variations of the removal efficiencies.Moreover,the effect of intermittent aeration on wastewater purification efficiency in the vertical flow constructed wetland unit was studied.Furtherly,the high-throughput sequencing and three-dimensional fluorescence spectrum techniques were used to study the purification mechanisms of pollutants.The whole research was expected to develop an effective technique to improve the wastewater purification efficiency of the process.The main results are as follows:（1）The system presented strong buffering capacity and high removal efficiency,accompanied with stable effluent quality.The total average removal rates of CODMn,TN,NH₄⁺-N,and TP reached 58.1%,37.1%,29.2%,and 56.2%,respectively.It could be seen that the removal efficiencies of CODMn and TP were superior to that of nitrogen.Lacking of carbon source,short hydraulic retention time,and low removal rate of NH₄⁺-N might be the main cause of the poor denitrification efficiency.Significant differences on the pollutant removal efficiency among different purification units were discovered.The pretreatment unit played a leading role in the removal of CODMn,while the vertical flow constructed wetland unit was mostly responsible for the removal of TN,NH₄⁺-N,and TP.（2）The removal efficiencies of the studied pollutants varied significantly between different seasons.The removal rates of CODMn and TP decreased in the sequence of summer > autumn > spring > winter.The removal rate of TN decreased in the sequence of autumn > spring > summer > winter.And the removal rate of NH₄⁺-N was in the order of autumn > summer > spring > winter.（3）The optimized operating conditions of the vertical flow constructed wetland combined with intermittent aeration were a gas-water ratio of 4:1 and an aeration time of 1 h.Under these conditions,the artificial wetland still had high removal efficiency of pollutants and stable effluent quality.After the optimization of the process,the total average removal rates of CODMn,DOC,NH₄⁺-N,TN,and TP increased by2.1%,19.1%,30.1%,24.0%,and 14.8%,respectively.（4）The optimization of the process had significant influence on the removal of nitrogen.While the acceleration of the removal of organic matter and phosphorus was not as effective as that of nitrogen.The results of microbial diversity and three-dimensional fluorescence spectrum analysis showed that intermittent aeration significantly promoted the removal of dissolved organic matter and nitrogen in the vertical flow constructed wetland.In addition,the removed organic matter was mostly dissolved protein material.