Study On Adding Carbon Sources For Better Denitrification In Primary Used Sub-surface Flow Wetlands

Most sub-surface flow wetlands of the VF/HF constructed wetlands can not treat NO₃^- -N efficiently because of the low organic concentration when taken into use at the beginning. This thesis aimed at studying whether adding harvest plant can enhance the effect of the denitrification, which uses denitrification rate constant to quantify.In order to study the effect of living plants, harvest plant with simple pre-treatment and harvest plant with pre-treatment boiling in NaOH, 5 different reactors were set up, which were no living plant-no harvest plant reactor, living plant-no harvest plant reactor, no living plant- harvest plant with simple pre-treatment reactor, living plant- harvest plant with simple pre-treatment reactor, living plant-harvest plant with pre-treatment boiling in NaOH. The experiment results show:(1)Under the same situation, adding harvest plants can enhance the effect of denitrification, and effect of the harvest plants with pre-treatment boiling in NaOH is better than the harvest plants with simple pre-treatment, with the result of the denitrification rate constant of the harvest plants with pre-treatment boiling in NaOH is 3.18 times higher than the harvest plants with simple pre-treatment in the first 33d and the denitrification rate constant of the harvest plants with pre-treatment boiling in NaOH is 2.66 times higher than the harvest plants with simple pre-treatment after 33d. (2)The effect of living plants and harvest plants to denitrification in the sub-surface flow wetland is not equal to the sum of each affection alone , the dentrification rate constant of the system with plants and simple pre-treatment is lower than the sum of constants in the system just having living plants or just adding harvest plants with simple pre-treatment. (3)If using the denitrification rate constant acquired from the experiment, it can be accounted that the area of the constructed wetlands can be saved about 50% if adding harvest plants with simple pre-treatment compared with the constructed wetlands without harvest plants. (4)The molecular biological method PCR-DGGE was used to study the microbial community. After analyzing the DGGE result, it was found that there was no distinct difference of the microbial community and the Shannon index between 5 reactors. After analyzing the result of DGGE bands, it was found that the bacteria were close to Leptolyngbya sp. and Escherichia sp.