Studies On The Effect Of Plant Carbon Source In Partial Nitrification Denitrification In Vertical Flow Constructed Wetland

In this experiment, wetland plants of Arundo donax and Pontederia cordata L were studied to reveal the pattern of carbon source generating by different strategies of plant anaerobic fermentation, and the components and contents of volatile fatty acid(VFAs) in fermentation broth were also analyzed by gas chromatography. The impacts on the denitrification by single plant carbon source and complex plants carbon source were compared by artificial denitrification simulation experiments. Small scale plots of vertical flow constructed wetland were utilized to study the effects on partial nitrification denitrification by different plant carbon source addition and to understand the vertical variation of nitrogen chemical in vertical flow constructed wetland. The nitrogen transformation gene(the nxr A gene of NOB, the amo A gene of AO B and the nir S gene of denitrifying bacteria) in vertical flow constructed wetland were also quantified by fluorescence quantitative PC R(QPCR). The main results are as follows:(1) Arundo donax, Pontederia cordata L and complex plants were fermented by 7 days. In these fermentation broth, the total nitrogen contents were less than 5 mg/L, CODCr were higher than 1800 mg/L, while the maximum emission reached 7560.45mg/L, which met high-carbon but low-nitrogen requirement. Moreover, large amounts of volatile fatty acids were produced by the fermentation processes, and the main ingredients were acetic acid and isovaleric acid, wherein the maximum content was acetic acid. The highest volatile fatty acids content was in(Arundo donax) broth which reached 2140.82mg/L.(2) In artificial denitrification simulation experiments, denitrification rate in added Arundo donax, Pontederia cordata L and complex plants carbon source systems were 0.453 mg/L·h, 0.459 mg/L·h and 0.509 mg/L·h, respectively. The TN removal rate in vertical flow constructed wetland affected by Arundo donax, Pontederia cordata L and complex plants carbon source were 79.55%, 87% and 92.78% respectively. However the control group was only 33.78%. Differential analysis by SPSS showed that the carbon source of all plant materials had a very significant impact on TN removal. And the TN removal affected by complex plants carbon source was significantly higher than the other two plants carbon source(single plant material, Arundo donax and Pontederia cordata L), which indicated that plants carbon source by complex plants material was more suitable as an organic carbon source for denitrification than signal plant material.(3) In all the small-scale plots of vertical flow constructed wetland system, the number of NOB(103-104copy/g) was far less than that of AOB(106-107copy/g) and the denitrifying bacteria(106-108copy/g). It demonstrated that the AO B and the denitrifying bacteria were predominant nitrogen transformation bacteria. Partial nitrification-denitrification appeared to be the N removal route in vertical flow artificial wetland. The number of denitrifying bacteria in the system which was added complex plants carbon source was significantly higher than the other two plants carbon source( P = 0.012), which indicated that the complex plants was more suitable organic carbon source in terms of the number of denitrifying bacteria.