Research On Removal Of Nitrogen And Phosphorus In Constructed Wetland Substrates For Domestic Sewage

Presently, soil, sand, pebble and gravel are the conventional substrates used in constructed wetland, but the disadvantages of these substrates are lower purified efficiency, easily absorbed saturation and low removal rates for N and P from domestic wastewater. In allusion to these, the experiment was designed and the text selected five substrates as the object of study that include vermiculite, zeolite, quartz land, anorthite, honeycomb cinder. First, chose the substrates having better adsorption effect on nitrogen and phosphorus through static adsorption test. Then, used the substrates be chosen in the former experiment to compare the competitive removal efficiency of single substrate and combinatorial substrates in the same condition to nitrogen and phosphorus by means of dynamic adsorption test. Finally, taken the vertical-flow constructed wetland as the object of study and used the orthogonal testing method to study the influence of three factors (proportion of substrates, water discharge and wet/dry ratio) on the effect of phosphorus and nitrogen removal, in order to find out the best combined affecting factor. The contents and results were as follows:1. The static adsorption test of several kinds of substrates to nitrogen and phosphorusAdsorption efficiency of five substrates (vermiculite, zeolite, quartz land, anorthite, and honeycomb cinder) on TN and TP with seven different concentrations was studied. It is found that Langmuir adsorption isotherm and Freudlich adsorption isotherm of every kind of substrates and the movement law of adsorption capacity influenced by influent concentration. The result indicated that it is better that the adsorption of zeolite to TN was described in Langmuir, and vermiculite, quartz land, anorthite and honeycomb cinder were described in Freudlich; it is better that the five substrates were described in Freudlich; the adsorption capacity of substrates to TN and TP is increased with concentration increasing; the honeycomb cinder and zeolite are prene to adsorb TN, and the honeycomb cinder and vermiculite have a higher capacity of adsorption to TP. 2. The dynamic adsorption test of substrates to nitrogen and phosphorusBy experimental study on the competitive removal efficiency of single substrate and combined substrates, this paper was set 8 disposal methods: honeycomb cinder, vermiculites, the homogeneous mixture of honeycomb cinder and vermiculite for bulk proportion 1:1 and combined substrates of honeycomb cinder and vermiculite for bulk proportion 1:1 which were barreled respectively, and those four treatment objects were ran in the condition of dry -wet proportion 1:1, inflow discharge 3.6L/h. The result indicated that the most outstanding removal efficiency to TN is vermiculites, and combined substrates secondly, the removal efficiency were 38.12% and 29.10% respectively, the removal efficiency of honeycomb cinder is unapparent, the removal efficiency was 7.16%; and the most outstanding removal efficiency to TP is honeycomb cinder, and combined substrates secondly, the removal efficiency were 19.24% and 9.60% respectively, the most inconspicuous removal efficiency is vermiculite , the removal efficiency was 2.31%. It was testified that combined substrates are better than single substrate to disposal efficiency for TN and TP.3. Study on removal of phosphorus and nitrogen in constructed wetland by different factorsThis experiment took the vertical-flow constructed wetland as the object of study, used the orthogonal testing method to study the influence of three factors (proportion of substrates, water discharge and wet/dry ratio) and the interaction between water discharge and wet/dry ratio on the effect of phosphorus and nitrogen removal, in order to find out the best combined affecting factor. The result showed that the best combined affecting factor is that the proportion of substrates is 1:2, water discharge is 1.2L/h and wet/dry ratio is 1:5.