Microbial community and removal of nitrogen via the addition of a carrier in a pilot-scale duckweed-based wastewater treatment system

• The addition of a carrier does not affect duckweed growth or composition.
• The addition of a carrier improves nitrogen (N) removal in a duckweed system.
• Pyrosequencing systematically reveals the microbial community of a duckweed system.
• Abundant N-removal bacteria on the carrier biofilm contribute to improved N removal.
• An efficient N-removal duckweed system with enhanced microorganisms is established.

Carriers were added to a pilot-scale duckweed-based (Lemna japonica 0223) wastewater treatment system to immobilize and enhance microorganisms. This system and another parallel duckweed system without carriers were operated for 1.5 years. The results indicated the addition of the carrier did not significantly affect the growth and composition of duckweed, the recovery of total nitrogen (TN), total phosphorus (TP) and CO2 or the removal of TP. However, it significantly improved the removal efficiency of TN and NH4+-N (by 19.97% and 15.02%, respectively). The use of 454 pyrosequencing revealed large differences of the microbial communities between the different components within a system and similarities within the same components between the two systems. The carrier biofilm had the highest bacterial diversity and relative abundance of nitrifying bacteria (3%) and denitrifying bacteria (24% of Rhodocyclaceae), which improved nitrogen removal of the system. An efficient N-removal duckweed system with enhanced microorganisms was established.