The Removal Efficiency Of Pollutants In Series Combination Of Substrate Beds

In recent years, the scientific research of constructed wetlands has turned to the impact factors of the pollutant removal efficiency from the decontamination mechanism and further to the design and methodology of building efficient constructed wetlands. As the important influencing factors of the pollutant removal efficiency, wetland combinations and residence time has always been the focus of the study. Many studies indicate that the pollutant removal efficiency of multiple constructed wetland systems is higher than individual wetland’s, especially N removal; In the3-stage wetland combination, the removal rates of COD, TN and TP of wetlands of different stage have significant differences. The experimental studies of hydraulic conditions have shown that there is an optimum value of the residence time in the actual operation of the constructed wetland, and the removal rate on other residence times that is greater than or less than the value will decline. However, the current domestic and international researches just separately study the effects of different wetland combinations or residence time, which don’t combine the two factors. Furthermore, these studies don’t have comprehensive analysis of wetland combinations of surface wetland and subsurface wetland, and don’t study the effect of the pollutant removal efficiency of different wetland locations. In addition, the micro-electrolytic method which can improve the removal rate is widely used in dyes, printing and dyeing, oil, heavy metals, pesticides, pharmaceuticals and other wastewater treatment. While the study on the effect of constructed wetlands with it is very few. Therefore, this study constructed four substrate beds with three-step series which consisted of surface flow and subsurface flow substrate beds, and the residence time of wastewater in each bed was1h,3h and5h, respectively. We fully studied the effect of the number of substrate bed and analyzed the pollutant removal efficiencies of different substrate bed’s locations in four substrate bed combinations. Furthermore, we analyzed two factors of different substrate bed combinations and different residence times using two-way analysis of variance (ANOVA). On this basis, we respectively compare the pollutant removal rates of the mass ratio of5:1iron sheet and copper and unreinforced matrix before in individual substrate bed and substrate bed combinations. We design the experiments to provide the scientific basis for substrate bed’s reasonable construction and operation.The results showed that:(1) The removal of organic, N and P was mainly through sedimentation and adsorption of the substrate and microbial oxidation-reduction because there were not plants in this experiment. With the increase of the number of substrate bed, the removal rates of COD, TN and TP of the substrate bed system are improved, especially the efficiency of the3-stage substrate bed combination was significantly higher than that of single substrate bed. The results demonstrate the pollutant removal efficiency of multiple substrate bed is better than that of individual substrate bed.(2) The pollutant removal efficiencies of substrate beds of different locations were different. In the3-stage substrate bed combination, the removal rates of COD, TN and TP of the third stage substrate bed were higher than that of the first stage and the second stage substrate bed. This result is different from the conclusion that the pollutant removal efficiency of the second stage wetland is significantly higher than that of the first stage wetland and the third stage wetland which is concluded by Seo et al in the3-stage combination of horizontal flow-vertical flow-horizontal flow. The results may be due to the lack of plants in the system which leads to the factor of plants on the removal of organic matter, N and P is ignored. (3) Substrate bed combination had significant effects on the pollutant removal efficiency. In four substrate bed combinations, the removal rates of CODMn, NH4+-N and PO43--P of the combination of two surface substrate beds and one subsurface substrate bed were highest than others. Residence time had significant effects on the pollutant removal efficiency. And extending the residence time to some extent could improve the removal rates of CODMn, NH4+-N and PO43--P of the substrate bed system. The removal rates of CODMn, NH4+-N and PO43-P were not significantly affected by interactions between combination and residence time. This indicates that in the actual operation of the substrate bed system, we can directly ignore the interactions between combination and residence time and independently consider the net pollution effect of them. The result provides some reference value and referential significances to further expand the efficiently substrate bed.(4) Using micro-electrolysis in the system by adding an appropriate amount of intensive matrix could improve the pollutant removal efficiency of single substrate bed and substrate bed combination. In the case of the consistency of other operating conditions, adding5:1Fe and Cu could improve the removal rates of CODMn, NH4+-N and PO3--P of substrate bed system, especially in the case of shorter residence time.In summary, increasing the number of substrate bed could increase the pollutant removal efficiency. The pollutant removal efficiencies of different locations of substrate bed had significant differences.