Research On Improving Nitrogen Removal Effects Within Multiplied Vertical Subsurface Flow Wetlands

The constructed wetland is an ecological sewage treatment with good removal effects and low construction and operation cost. However, the pollutant removal efficiency of constructed wetland is really affected by such factors as dissolved oxygen, air temperature, wetland plants, microorganisms in soil, however these factors limit the further improving of purifying effect in wetland, now becoming the locking bottleneck in extending application of wetland.Starting from the change of supplying oxygen condition, three intensifying measures such as aeration, circumfluence and intermittent aeration are put forward in the multiplied vertical surface flow wetland. Nitrogen removal effect of wetlands in three operation conditions upwards is mainly studied. Finally, the effect of the optimum operating conditions in winter is studied.The research results show that the air-water ratio of artificial aeration, the recycling rate and the intermittent aeration have a significant effect in wastewater treatment within one year.(1) When the air-water ratio is3:1, MVSFW can achieve the best nitrogen removal effect with the lowest energy consumption. Removal efficiency of CODcr、NH4+-N and TN is respectively up to90.2%、96.3%and72.8%. The effluent concentration reaches the1st-level A standard of COD and NH4+-N,23.1mg/L and4.2mg/L respectively, but only the1st-level B standard of TN18mg/L. The dissolved oxygen is increased within the wetland, and the aerobic region is expanded. Dissolved oxygen decreases with the deepening of the stroma. There has been significant aerobic hypoxia stratification of the space.(2) The study also founds reflux improves the nitrogen removal effect significantly. When the recycling rate is150%, TN removal effect increased by11.2%compared to no reflux and total nitrogen concentration in the effluent is10.8mg/L, reaching the1st-A standards. But it has little impact on the ammonia nitrogen and COD removal efficiency, only increasing by6.8%and6.2%respectively. The bigger the recycling rate is, the greater the dissolved oxygen is in the returning wetlands. Ultimately, the effective series of aerobic hypoxic region is formed in the upper and lower wetlands.(3) In order to minimize the additional energy consumption, nitrogen removal was improved with the intermittent aeration, compared to continuous aeration, with total nitrogen removal rate81.2%, increased by8.4%. And total nitrogen concentration in the effluent is reduced to12.6mg/L, reaching the1st-A standards. But the removal rate of organic matter and ammonia nitrogen are both decreased,86.8%and91%, respectively.Aeration combined with relux can solve the problem of poor nitrogen removal effect in cold winter, making the removal efficiency of CODcr and TN at over60%and70%. Nitrifying bacteria and denitrifying bacteria can maintain good activity in wetlands.We synthetically estimate the three techincs using an evaluating indicator set used for the decision course to select the techincs.This will be helpful to use the knowledge of fuzzy mathemastics to establish the valuating standard and quantification method, and to optimize the decision from candidates by gray associated analysis. According to the estimate result, we know that the techinc of aeration and circumfluence is the best, and then is intermittent aeration; the feasibility of only aeration is relatively low.The distribution rule of dissolved oxygen and nitrogen transfer in wetlands are studied by suing the experiment achievements in the paper, which has significant value in popularizing the application and development of wetlands in varying areas and conditions.