Basic Research On The Application Of Constructed Wetlands In The Treatment Of Town Landfill Leachate

In order to deal with the high cost and complex management of small town landfill leachate,Horizontal sub-surface flow constructed wetlands?HFCW,partial-area aeration?and vertical sub-surface flow constructed wetlands?VFCW,full-area aeration?were set up to investigate the removal effect of organic matter and nitrogen and phosphorus in the actual landfill leachate of small towns in this study.Moreover,this study aimed to explore the operation strategy of short-cut nitrification and denitrification in the constructed wetlands?CWs?,in order to achieve low-cost treatment of town landfill leachate.Firstly,this study investigated the start-up differences of two CWs through the low-temperature start-up and continuous operation.Secondly,the treatment effect of two CWs on the town landfill leachate and the realization of short-cut nitrification were explored through different intermittent aeration modes.Finally,the removal ways of pollutants were investigated by analyzing the change of water quality in different CWs.The main results and conclusions are as follows:?1?The experiment was started up in low-temperature with the mixed domestic sewage and town LL?volume ratio 30:1?.The results exhibited that two CWs could be started at the low temperature of 6.1?under continuous aeration with air-water ratio of40:1.The town landfill leachate was treated without aeration after two CWs entered stable stage,and VFCW exhibited better performance to remove organic matter and nitrogen than HFCW.?2?The experiment results of intermittently aerated CWs showed that the removal effect of organic matter in both CWs increased firstly and then declined with the aeration amount gradually decreased from 488L/d?high intensity?to 288?medium intensity?and 144L/d?low intensity?under the condition of high-frequency intermittent aeration?2h aeration/4h rest?.In the three stages,when the average influence concentration of COD was 2623.54mg/L,the average COD removal rates of HFCW were 74.23%,89.08%and 83.44%respectively,while the corresponding value of VFCW were 80.70%,84.51%and 80.05%respectively.It showed that partial-area aeration CWs was more conducive to the removal of organic matter in landfill leachate under low oxygen supply conditions.?3?Compared with full-area aeration,partial-area aeration would delay the removal of NH₄⁺-N in CWs.At the same time,it would lead to the different approaches to nitrogen removal between two CWs.Nitrogen removal in HFCW was mainly through short-cut nitrification and denitrification,while nitrogen removal in VFCW was through nitrification and denitrification.Under the conditions of high-frequency/low-intensity intermittent aeration and high-frequency/medium-intensity intermittent aeration,the DO concentration of HFCW was low?0.59mg/L?,which could improve stable short-cut nitrification and make the average nitrite accumulation rate reach 50.96%.However,full-area aeration in VFCW resulted in a high DO concentration?1.09mg/L?,which made short-cut nitrification difficult to maintain.Furthermore,short-cut nitrification and denitrification could improve the nitrogen removal effect of CWs.When the average concentration of total nitrogen in the influent was 1393.44mg/L,the average removal rate of total nitrogen in VFCW reached 71.77%.Due to the existence of short-cut nitrification and denitrification in HFCW,the average removal rate of total nitrogen increased slightly,reaching a maximum of 73.22%.?4?The results of water quality along the CWs exhibited that the main functional areas of two CWs were at the front of wetlands.HFCW was mainly at the water inlet to35 cm,while VFCW was mainly at the wetland surface to a depth of 20 cm.Under the same influent concentration,the contribution rates of COD and TN removal in the region of 0?35 cm of HFCW were 66.26%and 49.28%,respectively.The contribution rates of COD and TN removal in the 0?20 cm region of VFCW were 73.47%and51.88%,respectively.Therefore,partial-area aeration might save more carbon sources for the denitrification of CWs,which was beneficial to improve the nitrogen removal effect.?5?The analysis results of nitrogen and phosphorus removal in CWs showed that the contribution rates of nitrogen removal by microbial transformation,gravel adsorption and plant absorption were 84.72%?15.16%and 0.12%in HFCW,respectively.The corresponding values were 85.15%?14.71%and 0.14%in VFCW,respectively.The contribution rates of CWs sediment storage,gravel adsorption and plant absorption to phosphorus removal were 80.04%?18.39%and 1.57%in HFCW,respectively.The corresponding values were 80.39%?17.36%and 2.25%in VFCW,respectively.