Nitrogen removal and N2O emission in subsurface vertical flow constructed wetland treating swine wastewater: Effect of shunt ratio

A comparison study of subsurface vertical flow constructed wetland (VSSF) treating swine wastewater at four different shunt ratios was carried out when the hydraulic loading rate (HLR) was 0.02 m3·(m2 d)−1. The results showed that, the shunt ratio had significantly influence on nitrogen removal of the VSSF, whereas it had no great influence on the removal of COD, BOD, TSS, and TP. As the shunt ratio was 1:2, VSSF had the best performance on treating swine wastewater, especially TN. The quantity of nitrogen transformation bacteria was influenced by the shunt ratio in the system, and the denitrifying bacterial quantity increased as the shunt ratio was increased, leading to enhance the nitrogen removal of VSSF. Besides, the N2O emission from VSSF was also affected significantly by the shunt ratio. The N2O emission flux of VSSF was found to be lowest when the shunt ratio was 1:2. Overall, from the aspects of enhancing the efficiency of nitrogen removal and reducing N2O production, the optimal shunt ratio of VSSF was 1:2.