Intensified nitrogen removal in intermittently-aerated vertical flow constructed wetlands with agricultural biomass: Effect of influent C/N ratios

The poor nitrogen removal due to the low denitrification caused by lack of carbon sources in vertical flow constructed wetlands (VFCWs) especially for treating low carbon sewage. In this study, agricultural biomass materials including wheat straw, apricot pit and walnut shell had been tested as substrates in intermittently-aerated VFCWs for enhancing the nitrogen removal, and the effect of C/N ratios on the nitrogen removal was also studied. The results showed that intermittently-aerated VFCWs by adding agricultural biomass could intensify the denitrification process significantly, and the system with wheat straw performed much better than the systems with walnut shell and apricot pit. Four microcosms with different agricultural biomass showed different trends with the rising C/N ratio of influent. Moreover, the best removals (COD 97%, NH₄⁺-N 99% and TN 96%) have been obtained at an influent C/N ratio of 0.5, which indicated that the dosage of biomass addition and influent C/N should be further optimized for achieving the sustainable nitrogen removal in VFCWs for low carbon wastewater treatments.