Study On The Effect Of Nitrogen And Phosphorus Removal By Substrates In Constructed Wetland

Constructed wetland system as an ecological approach, with less investment, low operating costs, lower energy consumption, has been widely used in sewage treatment.Substrates have an important part of removing nitrogen and phosphorus from wastewater.Therefore, the problem studied mostly capabilities, mechanism of removing contamination, in order to seek the substrate with good effect of removing contamination.Seven substrates types, such as zeolite, red mud, slag, ceramic filter, water washing sand, steel slag and shale, were used as sorbents in nitrogen and phosphorus removal tests to find out their adsorption capacity and principles as basic theories in the following tests. Static experiments were mainly carried out. The main results were summarized as following:1. The order of the four substrates of zeolite, red mud, water washing sand and slag adsorption capacity to ammonia nitrogen was followed that zeolite> red mud >slag>water washing sand. The ion exchange function was the main way of removing ammonia nitrogen by zeolite, and zeolite had the worst physical adsorption ability, whereas slag had almost the same physical adsorption and ion exchange capacities. Seen from the ammonia nitrogen desorption rate, the zeolite was the smallest, followed by the red mud, and the other two substrates desorption capacity were very high. Both Langmuir and Freundlich isothermal adsorption equation could well describe the ammonia nitrogen adsorption process of zeolite and red mud substrates under the experimental conditions. For the red mud, the regression level used with Langmuir equation was better than that of Freundlich equation, it was opposite for the zeolite. To some extent, the zeolite was a more suitable substrate for removing ammonia nitrogen in constructed wetland sewage.2. Both Langmuir and Freundlich isothermal adsorption equation could well describe the phosphate adsorption process of ceramic filter and red mud substrates under the conditions of phosphorus (P) concentration for 5~150 mg/L. For the ceramic filter, the regression level used with Langmuir equation was better than that of Freundlich equation, it was opposite for the red mud. The phosphorus adsorption capacity order of the four substrates was followed that red mud>ceramic filter>slag>water washing sand. Seen from the phosphorus desorption rate, the order was followed that slag>water washing sand>ceramic filter>red mud. The desorption rate of water washing sand and slag after adsorbing phosphorus was higher, but the phosphorus desorption proportion of the other two substrates was very low. Comprehensive evaluation, the ceramic filter was more suitable for phosphorus removal in constructed wetland.3. For zeolite, ceramic filter and furnace slag, when at different time the zeolite had a best absorption capacity to ammonia nitrogen, and the ceramic filter had a strong absorption effect to total phosphorus.The concentration of sewage had a bigger effect on the absorption of zeolite to ammonia nitrogen, and the absorption amount increased with the concentration of sewage increasing, while it had little effect on the absorption of blast furnace slag to ammonia nitrogen and total phosphorus, and ceramic filter to ammonia nitrogen.The three substrates absorption amount to ammonia nitrogen and total phosphorus decreased with the adsorbent amount increasing. To achieve a better absorption capacity, tests results could be considered based on the substrate inputs. The pH value had a significant effect on the zeolite absorption to ammonia nitrogen, and it had a best absorption effect when pH was at 6~7,whereas when pH was at 8~12 (alkaline conditions) ,the substrates had a strong absorption to total phosphorus. When temperature was at 30℃~40℃, the substrates had a low removing of nitrogen and phosphorus. So the constructed wetland at high temperature environments had less important in removing of nitrogen and phosphorus.4. In the static adsorption test of combinational substrates, the zeolites and ceramic filter compounded with ratio of 1:2 was confirmed to be the best substrates.