Molecular Mechanism Of Nitrogen Microcycle In Tidal Flow Constructed Wetland

Tidal flow constructed wetlands(TFCWs) are increasingly concerned in recent years, as the purification performance to wastewater with high ammonia nitrogen and organic matter was remarkable. The main nitrogen removal process is the microbial metabolic pathway, which was hindered by water conditions with wetland. Therefore, the nitrogen removal process by microbe and the nitrogen removal efficiency were studied in molecular level, which can guide the construction of constructed wetlands with high removal efficiency. These studied was still insufficient in China.This study examined the nitrogen removal efficiencies under different fill time of S1, different flooded time of S2 and different drained time of S3, applied molecular biological techniques(RT-QPCR) to quantitatively evaluate the evolution trend nitrogen transformation microbes and functional genes, and built quantitative response relationships between nitrogen transformation rates and microbes and functional genes. The main conclusions are as follows:(1) The different operation mode has significant impacts on treatment performance, andnitrogen removal process of constructed wetlands. When the flooded time of 12 h, thedrained time of 12 h, the fill time from 0.167 h to 24 h, the S1 system removal efficienciesof COD、NH4+、TN reached 82%~95%,58%~93%,30%~76%;When the fill time of0.167 h, the drained time of 12 h, the flooded time from 12 h to 48 h, the S2 systemremoval efficiencies of COD、NH4+、TN reached 84%~94%,55%~82%,60%~84%;When the fill time of 0.167 h, the flooded time of 12 h, the drained time from 4h to 48 h,the S3 system removal efficiencies of COD、NH4+、TN reached 69%~94%,50%~96%,56%~96%. This study showed that the purification performance of TFCWs wassignificance when the fill time of 0.167 h, the flooded time of 24 h and the drained timeof 48 h.(2) Under the fill time constraint, in S1 system, the nir S was the key rate-limiting factor ofthe NH4+ transformation rate, the nxr A and ANO were the key rate-limiting factors ofthe NO3- transformation rate, the ANO was key rate-limiting factor of the NO2-transformation rate. Under the flooded time constraint, in S2 system, the ANO was thekey rate-limiting factor of the NH4+ transformation rate, the(nap A+nar G) was the keyrate-limiting factor of the NO3- transformation rate, the ANO and qnor B were keyrate-limiting factors of the TN transformation rate. Under the drained time constraint, inS3 system, the amo A was the key rate-limiting factor of the NH4+, NO3- and TNtransformation rate.(3) Under the fill time constraint, in S1 system, the process of NO3-�'NO2- coupled withanammox was the main NO3- removal pathway, the TN removal pathway wastraditional nitrification and denitrification. Under the flooded time constraint, in S2system, the NH4+ removal pathway was the process of anammox coupled withNO3-�'NO2-, the NO3- and TN removal pathway was traditional nitrification anddenitrification. Under the drained time constraint, in S3 system, the NH4+ removalpathway was CANON(Completely Autotrophic Nitrogen removal Over Nitrite), theNO3- removal pathway was the process of NO3-�'NO2- coupled with anammox, the TNremoval pathway was CANON.(4) The results of stepwise regression analysis showed that the quantitative responserelationships between nitrogen transformation rates and microbes and functional geneswas significance in constructed wetlands. There were some coupling mechanisms in thenitrogen transformation processes and the nitrogen transformation rates were limited bythe combined effects of various nitrogen transformation microbes and functional genes.