| Constructed wetland is a kind of ecological wastewater treatment technology. It has the advantages of low investment, easy to administer and good treatment effect, constructed wetland is suitable for domestic sewage treatment in small and medium town. This experiment use reeds and cannas as constructed wetland plants. I built two constructed wetland systems, the canna artificial wetland system and the reed constructed wetland system respectively. Combined constructed wetland system composited by three tandem vertical flow constructed wetland treatment units. This experiment take simulated sewage as research objects to study impact of hydraulic retention time, aeration and step feed on constructed wetland system removal of COD, N, P and antibiotic. The main conclusions are as follows:(1) When HRT was 3.0 days, the canna artificial wetland system and the reed constructed wetland system had the highest removal rate for all kinds of pollutants. The reed constructed wetland system had higher removal rate than the canna artificial wetland system for COD, TN, NH3-N,TP and PO43-. With the increase of HRT, removal rates of TP, PO43-, tetracycline, oxytetracycline and chlortetracycline in canna artificial wetland system and reed constructed wetland system increased quickly at first and then slowly increased, the highest removal rates were 80.72±1.21%, 65.67±5.26%, 61.82±2.64%, 97.27%, 91.18%, 83.43% and 86.99±1.86%, 79.38±5.45%, 78.08±3.26%, 97.71%, 91.46%, 86.68% respectively. However, with the increase of HRT, removal rate of TN and NH3-N had been slowly increased in canna artificial wetland system and reed constructed wetland system, which the highest removal rates were 33.60±0.86%, 29.13±2.71% and 38.27±4.86%, 36.68±3.15% respectively. Under different HRT condition, the removal of COD and nitrogen in constructed wetland system were mainly depended on the degradation of the first two vertical flow wetland units. Dephosphorization was completed by three vertical flow constructed wetland treatment units. Tetracycline, oxytetracycline and chlortetracycline were mainly completed by the first vertical flow constructed wetland treatment unit.This antibiotics were mostly rely on substrate adsorption to be removed.(2) With the increased of gas-water ratio, removal rates of COD, TN, NH3-N, TP and PO43- in canna artificial wetland system and reed constructed wetland system increased quickly at first and then slowly increased. However, with the increased of gas-water ratio, the removal rates of tetracycline, oxytetracycline and chlortetracycline had little change. The reed constructed wetland system of TN and NH3-N removal rates were higher than that of canna constructed wetland system.But the removal rates of COD, TP, PO43-, tetracycline, oxytetracycline and chlortetracycline were similar to the canna artificial wetland system. When gas-water ratio were 15 to 45, the removal rates of COD, TP and PO43- had a little change in the two constructed wetland systems, at this point, the COD removal rate was between 83% and 85%, the removal rates of TP and PO43- were higher than 98%. When gas-water ratio were 15, 30 and 45, TN removal rate increased by 14.72%, 31.58%, 31.58% and 14.72%, 72.69%, 73.52%, respectively in the canna artificial wetland system and the reed constructed wetland system compared to no aeration, the removal rate of NH3-N increased by 37.15%, 68.69%, 68.69% and 37.15%, 81.54%, 84.24%, respectively compared to no aeration. The removal rates of tetracycline, oxytetracycline and chlortetracycline were between 75.65% and 79.78%, between 78.83% and 80.46% and between 75.65% and 54.69% in the canna artificial wetland system and the reed constructed wetland system. Under the condition of the comprehensive consideration, the best gas-water ratio is 30.(3)Step feed can slightly improve the removal rates of COD, TN, NH3-N and TP and PO43- in the artificial wetland system. At the same time, it can obviously increase the removal rates of tetracycline, oxytetracycline and chlortetracycline in the constructed wetland system. The best influent flow distribution ratio of removing COD in the canna artificial wetland system and the reed constructed wetland system were 1:2 and 2:1 respectively, which the removal efficiency were 86.38±2.84% and 86.38±3.53% respectively. The best influent flow distribution ratio of removing TN, NH3-N, TP, PO43-, tetracycline, oxytetracycline and chlortetracycline were 1:1. When the influent flow rate was 1:0, the removal efficiency of each pollutant was the lowest. At this moment, the removal efficiency of COD, TN, NH3-N, TP, PO43-, tetracycline, oxytetracycline and chlortetracycline in the canna artificial wetland system and reed constructed wetland system were 82.34±5.06%, 47.31±2.44%, 86.84±2.38%, 94.91±0.59%, 96.71±0.08%, 77.37%, 79.74%, 50.50% and 82.16±3.20%, 91.50±0.18%, 96.50±1.42%, 94.64±0.32%, 98.54±0.32%, 82.39%, 77.70%, 58.98% respectively. |
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