The result showed that growth rate of ammonifying bacteria and nitrifying bacteria were higher than that of denitrifying bacteria, which reach consensus with the results of the change of water index. To be specific, from Fig. 2 it can be seen that the average removal rate of NH4+-N could reach 60.0%, which might be attributed to the high growth rate of ammonifying bacteria. The NH4+-N removal efficiency of water spinach from present study was much higher than 31% for Typha latifolia and 17% for Juncussubulatus, reported by Abissy and Mandi (1999).