The Study Of Constructed Wetland Substrate And Plant Screening

Constructed wetland sewage treatment system is a new way of sewage treatment. Compare with other sewage treatment system it has advantages of less investment low running cost and efficient treatment. Substrates and plants is an important part of the constructed wetland and play an important role in the nitrogen and phosphorus removal. This research mainly studies the adsorption and desorption capacity of different substrates and the ability to remove nitrogen and phosphorus of different plants. Main conclusions are as follows:1 In this study, five substrates(activated coal, ceramsite, sand, volcanic rock, zeolite) were conducted for isothermal adsorption experiment to study the characteristic of ammonia nitrogen adsorption and desorption. The results showed that the adsorption capacities of substrates were increased with the initial concentrations of the ammonia nitrogen solution increasing. The ammonia nitrogen adsorption quantity of the five substrates followed that zeolite>activated coal> volcanic rock > sand> ceramsite. The maximum adsorption quantity was 463.51, 173.00, 92.56, 86.50, 78.00mg·kg-1.The desorption quantity of zeolite was always under other substrates. The desorption quantity of other substrates were increased with the initial concentrations of the ammonia nitrogen solution increasing. When the initial concentrations of the ammonia nitrogen solution was 100 mg·L-1 the desorption quantity was max. The ammonia nitrogen desorption quantity of the five substrates followed that activated coal > volcanic rock > sand > ceramsite. The maximum desorption quantity was 33.88, 28.33, 25.22, 21.43, 14.10, 11.93 mg·kg-1. The desorption rate of the substrates were decreased with the initial concentrations of the ammonia nitrogen solution increasing. The Minimum of desorption rate followed volcanic rock > sand> ceramsite >activated coal >zeolite.The Minimum of desorption rate was 29.74%, 26.68%, 20.45%, 19.45%, 1.43%. The adsorption curve of ceramsite, sand, volcanic rock could be simulated by the Langmuir isothermal adsorption equations. Comprehensive consideration, zeolite was more suitable to be used as the substrate material for constructed wetland to remove the ammonia nitrogen.2 In this study, six substrates(activated coal, zeolite, sand, volcanic rock, ceramsite, iron sand) were conducted for isothermal adsorption experiment to study the characteristic of phosphorus adsorption and desorption. The results showed that the adsorption capacities of substrates were increased with the initial concentrations of the phosphorus solution increasing. The phosphorus adsorption quantity of the six substrates followed that activated coal > iron sand> zeolite >volcanic rock > ceramsite > sand. The maximum adsorption quantity was 260.47, 246.66, 166.44, 110.74, 65.83, 30.25 mg·kg-1.The desorption capacities of substrates were increased with the initial concentrations of the phosphorus solution increasing. The phosphorus desorption quantity of the six substrates followed that activated coal > volcanic rock > zeolite > ceramsite > sand> iron sand. The maximum desorption quantity was 33.88, 28.33, 25.22, 21.43, 14.10, 11.93 mg·kg-1.The desorption rate of substrates were increased with the initial concentrations of the phosphorus solution increasing. The phosphorus desorption quantity of the six substrates followed that sand> ceramsite > volcanic rock > zeolite > activated coal > iron sand. The maximum of desorption rate was 55.94%, 32.75%, 25.63%, 15.22%, 14.63%, 4.90%. The adsorption curve of zeolite, sand, volcanic rock, ceramsite, could be simulated by the Langmuir isothermal adsorption equations. Comprehensive consideration, activated coal and iron sand were more suitable to be used as the substrate material for constructed wetland to remove the phosphorus. But because the iron rust will reduce purification efficiency, activated coal was more suitable to be used as the substrate material for constructed wetland.3In this study, four plants(calamus, reed, iris, typha) were chosen as the constructed wetland plant to study the removal rate of nitrogen and phosphorus of plants in different periods and the best time of sewage stay in constructed wetland. Compare the different parts of plant biomass and nitrogen and phosphorus content before and after the experiment, study the effect of each part on the plant purification efficiency. The results showed that the sewage purification efficiency in growth period was higher than stable period. The purification efficiency was the highest after the sewage stayed in constructed wetland 4 days. Different plants had different removal rate of ammonia nitrogen. The maximum removal rate followed typha> iris> calamus> reed>control. The maximum removal rate was 98.30%, 98.16%, 97.67%, 96.78%, 94.54%. Different plants had different removal rate of phosphorus. The maximum removal rate followed typha> iris> calamus> reed>control. The maximum removal rate was96.68%, 96.42%, 95.92%, 95.23%, 88.31%.The addition of nitrogen and phosphorus content were different in different part of plant. The addition of nitrogen and phosphorus content in above part was higher than under part. The addition of nitrogen in above part followed typha> calamus> iris > reed at 0.82-1.29 mg·g-1. The addition of nitrogen in under part followed typha > iris> calamus > reed at 0.72-0.98 mg·g-1. The addition of phosphorus in above part followed typha> reed > iris> calamus at 0.41-0.56 mg·g-1. The addition of phosphorus in under part followed typha > iris> reed >calamus at 0.36-0.51mg·g-1. The accumulation of nitrogenfollowed that iris > typha > reed >calamus.The accumulation was 7.0,6.37,6.02,5.60 mg·g-1 The accumulation of phosphorus followed that typha > iris> reed >calamus The accumulation was 1.93、1.89、1.81、1.46 mg·g-1。...