Feasibility of improving nitrogen removal by integrating the rice straw and zeolite with drainage ditches for farmland runoff control

Abstract

Natural zeolite and rice straw have been widely used for removing nitrogen (N) from wastewater due to their different N removal mechanisms. In this study, the N removal performances of three substrate systems composed of zeolite (Z), rice straw (R) and their combination (ZR) were assessed for decontaminating farmland runoff characterized by high loads of ammonium - N or nitrate - N besides of a low carbon content. The N-cycling functional genes were also investigated. The results showed that ZR achieved significantly higher ammonium (48.9%–77.7%) and TN (39.7%–65.9%) removal rates than Z and R ( P < 0.05). ZR also exhibited the highest removal rates of nitrate (67.6%–82.7%) and TN (45.5%–62.1%) in nitrate wastewater treatment. The abundances of 16S rRNA and denitrifying genes (including nirK , nirS , narG and napA ) were significantly enhanced in ZR, which partly explained the higher N removal in the ZR than in the Z and R systems. These findings suggest that it is feasible to combine rice straw with zeolite as a substrate of drainage ditches for considerable N removal enhancement in the control of agricultural runoff. • ZR showed the highest nitrogen (N) removal rate when both NH 4 + -N and NO 3 − -N wastewaters were treated. • TN and NO 3 − -N removal in Z was limited by insufficient denitrification due to low organic carbon source. • The combination of zeolite and rice straw significantly increased the abundances of 16S rRNA and denitrifying genes.