Effect of Filter Medium on the Enhancement of Complete Autotrophic Nitrogen Removal over Nitrite Process in a Tidal Flow Constructed Wetland

This study attempted to shorten the time wasted at the startup of a complete autotrophic nitrogen removal over nitrite (CANON) process in a tidal flow constructed wetland (TFCW) to achieve higher nitrogen removal rates. Thus, the starting performance and the related microbiological characteristics of different kinds of filter media filling the TFCW were explored at an appropriate drainage rate. The results showed that the physicochemical properties of the filter medium could significantly affect the quantity and activity of the functional microbes (especially ANAMMOX bacteria) enriched in the TFCWs, leading to fluctuations of the starting time and nitrogen transformation rates of the systems filled with five different kinds of filter media. Compared with that of gravel, the quantity and activity of ANAMMOX bacteria in the bed could be enhanced to different degrees as the TFCW was filled with ceramsite, zeolite, broken bricks, and lobster shells. Correspondingly, the starting times of the TFCWs with the CANON process were shortened, and their nitrogen removal performances could also be optimized. When the hydraulic loading rate of the TFCW was 0.96 m3·(m2·d)-1, the initiation of the CANON process could be accomplished successfully in the system filled with lobster shells within 300 cycles, since AOB and ANAMMOX bacteria could become dominant quickly in the packing bed. Moreover, the TN and NH4+-N removal rates could reach up to (88.37±1.19)% and (91.03±0.66)%, respectively, followed by those of broken bricks, zeolite, ceramsite, and gravel.