Study On Treatment Of Secondary Effluent Water By A Combined Constructed Wetland With Aquatic Plants And Bio-cords

China’s current urban sewage treatment plant effluent quality is still not able todirectly reuse, and it still contains high concentrations of pollutants, in order toreduce the pollution to the water environment, further purification is requiredurgently. The traditional sewage reuse facilities are complex and running costs arevery high, which is unbearable for the majority of the sewage treatment plant.Constructed wetland technology has a good purifying effect, small in vestment, andcost low. Model test method was used in this article, the traditional structure ofsubsurface-flow constructed wetlands have been improved, and was combined withbio-cord paddings, for treatment of simulating secondary effluent. It was studied thatthe effects of factors such as bio-cord paddings, different aquatic plants, anddifferent hydraulic retention time on efficiency of subsurface flow constructedwetland for artificial wastewater purification. The main conclusions include:The biofilm-plants combination system, consisted of newly bio-cord paddingsand floating plants, used a hydraulic retention time （HRT） for24h to treat secondaryeffluent water. The results showed that the average removal rate of COD was78%and25.9%respectively in device A filled with bio-cord and Alternantheraphiloxeroides and device B only plant Alternanthera philoxeroides. The averageremoval rate of NH₄⁺-N was45.8%and6.2%, for TN it was27.7%and6.3%, andTP was25.6%and5.9%.While HRT was12h, The average removal rate of CODwas67.7%and22.9%, for NH₄⁺-N was35%and5.4%, for TN it was21.8%and4.8%, and TP was18.2%and5.4%. Under different conditions of HRT for treatmenteffect analysis, it turned out that the overall effect of the system was ideal atHRT24h.The biofilm-plants combination system, consisted of newly bio-cord paddingsand floating plants, used a hydraulic retention time （HRT） for24h to treat secondary effluent water. The treatment effect of COD、NH₄⁺-N、TN and TP was studied. Theresults showed that the average removal rate of COD was81.1%and29.6%respectively in device A filled with bio-cord and Eichhornia crassipes and device Bonly plant Eichhornia crassipes. Besides, the average removal rate of NH₄⁺-N was49.6%and8.4%, for TN it was42.8%and9.7%, and TP was51.7%and7.65%. Thewastewater after treated in device A could meet rank1of the integrated wastewaterdischarge standard of China.The results show that, the direct absorption of the plants of nitrogen andphosphorus in wastewater is not the most important removal mechanism for sewagetreatment, however, it has a synergistic role in promoting the removal of pollutants inwater, then improves the ability of nitrogen and phosphorus removal. In secondaryeffluent water treatment process, the three-dimensional elastic packing PP+K-45produced by Shanghai TBR corporation and used in experiment, which efficiency isthe best combined with Eichhornia crassipes in HRT for24hours.