Study On Enhanced The Tailwater Deep Nitrogen Removal Performance Of Constructed Wetland With Sulfur Autotrophic Denitrification

Large quantities of nitrogen and phosphorus present in lakes,rivers,etc,is the main causes of eutrophication.According to the Action Plan for Prevention and Control of Water Pollution,9.2%of the water bodies among the surface water control section in China had lost their function(bad V),and 24.6%of the key lakes were eutrophic.Due to C/N?2,TN?20 mg/L in tail water.Advanced treatment by constructed wetland could not meet to the IV criterion specified in the Environmental Quality Standards for Surface Water(GB3838-2002),therefore,it was urgent to develop advanced technologies for waste water treatment to retrofit constructed wetland.Focused on the problem of total nitrogen(TN),pilot scale subsurface flow constructed wetlands with sulfur/limestone denitrification section for municipal waste water treatment were established on site and the operating parameters were explored.Based on abve results,two units of the Ducunsi aritifical Wetlands were re-constructed,the engineering process was monitored for months and a systemical re-designing drafts of the Wetlands was provided.The major results were as following:The natural hanging-film method was adopted to the on-site HSFCW to cultivate the system dominant bacteria microorganisms.The optimal process conditions for denitrification of traditional HSFCW systems were:T 25?28?,HRT>11 h,with removal rates of 45%,95%,65%and 50%for COD,NH4+-N,TN and NO3--N.The denitrification performance was decreased to only 30%at low temperature.The average removal rates of TN for the subsurface constructed wetland with sulfur/limestone section for municipal wastewater treatment were 65%with HRT 6.5 h.And the ultimate results was reached 80%,which was ascribed to the high performance of denitrifying bacteria of the sulfur-based autotrophic denitrification process.Established an on-site pilot plant with waste water treatment capacity of 6 m3/d to carry out related technical studies(Horizontal Subsurface flow constructed wetland(HSFCW),Vertical flow constructed wetland(VFCW),Integrated vertical flow constructed wetland).The monitoring data suggested that the effluent quality of VFCW was superior to the HSFCW.To the VFCW system filled with sulfur/limestone/zeolite/volcanic rock(volume ratio 1:1:1:1),the removal rate of NO3--N and TN reached about 97%and 85%,respectively,with the influent concentration of TN 24-26 mg/L,NO3--N 22?23 mg/L temperature 25?29.1? and hydraulic retention time(HRT)3.5 h.The effluent concentration of the pollutants basically meet the standards of IV criterion specified.The reconstruction of two units of the micro-aeration vertical up flow wetland of the Ducunsi Wetland was completed.Three months of monitoring data showed that the level of the overlying water could be easily controlled by the collecting pipes.After the reconstruction by the sulfur-based autotrophic denitrification process,the TN removal rate was increased about 10%comparing to the original process.And the water quality indicators,such as COD and TP,basically meet the surface water IV standards.According to the monitoring results of the on-site pilot equipments and the engineering operation results of the two units of Ducunsi Wetland,the systemical re-designing drafts of the Ducunsi Wetlands with sulfur-based autotrophic denitrification process was conducted,which provided an operational and engineering designing example for such tail water treatment.