Study On Town Daily Sewage Treated By Composite Floating Bridge Artificial Wetland Technology

This experiment was based on former documents and researches of artificial wetlands. It improved the traditional artificial wetland t echnology and introduced the floating bridge technology, matching the plankton and the submerged plants in the same unit to dispose the sewage and combining the two traditional subsurface flowing wetland units. Thus, a new composed artificial wetland processing system was designed. In this way, a research on domestic sewage in COD, NH3-N, TN, TP of the purification effect of the system was carried out. The results are as follows:(1) Throughout the experiment, the COD inlet concentration of the system ranged from 125.7 to 186.1mg/L, as its effluent concentration ranged from 21.3 to 41.7mg/L, and the removal rate was maintained between 71.0% and 83.7%; The NH3-N inlet concentration ranged from 21.2 to 26.2mg/L, as its effluent concentration ranged from 6.1 to 10.2mg/L,and the removal rate maintained between 53.9% and 71.4%; The TN inlet concentration ranged from 26.4 to 31.3mg/L,as its effluent concentration ranged from 9.9 to 15.3mg/L, and the removal rate maintained between 44.8% and 63.3%; The TP concentration ranged from 1.62 to 2.71mg/L, as its effluent concentration ranged from 0.32 to 0.87mg/L, and the removal rate maintained between 68.0% and 80.3%.(2) Compared to the other two traditional subsurface flowing wetland units, the artificial unit of level two showed a worse capability of COD removal, while its NH3-N, TN and TP removal efficiency was prominent. In the whole system, the COD and TN effluent concentration can reach the standard A of the ’urban sewage treatment plant pollutant discharge standard ’(GB 18918~2002), while its NH3-N and TP effluent concentration can reach the standard B.(3) Pearson correlation analysis of each index in the removal of wetland unit rate showed that, there was a correlation between the removal rates of COD-NH3-N, COD-TN and NH3-N-TN in the HVF1 system; and the removal rates of NH3-N-TN, COD-NH3-N and NH3-N-TP in the HF2 were inseparable. Because of the impact of the low inlet concentration of water in HVF3, in addition to a certain relation between the removal of TN and TP, most indexes showed no evident correlation.(4) Analysis of the characteristics of hydraulics in the wetland system showed that, a certain back mixing phenomenon existed in all levels in the process of sewage flowing wetland units. In subsurface flowi ng wetland units HVF1 and HVF3, the degree of back mixing is smaller. But in horizontal flow wetland unit HF2, the back mixing phenomenon is relatively obvious. When it came to the later period, permeability coefficients showed an uneven distribution, and the removal efficiency of the system began to fall.