Unveiling the nitrogen removal performance from microbial network establishment in vertical flow constructed wetlands

Area of Science:

• Environmental Engineering
• Microbiology
• Wastewater Treatment

Background:

• Vertical flow constructed wetlands (VFCWs) are crucial for wastewater treatment.
• Understanding substrate and hydraulic retention time (HRT) effects on microbial communities and nutrient removal is vital for optimizing VFCW performance.
• The interplay between substrate type (natural zeolite vs. shale ceramsite) and HRT on VFCW microbial ecology and efficiency requires further investigation.

Purpose of the Study:

• To investigate the combined effects of substrate type (natural zeolite or shale ceramsite) and hydraulic retention time (HRT) on nutrient removal and microbial co-occurrence networks in VFCWs.
• To compare the efficiency of zeolite-packed and ceramsite-packed VFCWs in removing ammonium (NH4+-N) and chemical oxygen demand (COD).
• To analyze the influence of operating conditions on microbial community structure and function, including key nitrogen-cycling genes and phyla.

Main Methods:

• Experimental setup using VFCWs with two substrate types: natural zeolite and shale ceramsite.
• Operation of VFCWs under two different HRTs: 3-day and 6-day.
• Analysis of nutrient removal rates (NH4+-N, COD).
• Assessment of microbial community composition and function using gene abundance analysis (Amx, amoA, nxrA, nosZ) and relative abundance of bacterial phyla (Proteobacteria, Nitrospirae).
• Investigation of microbial co-occurrence networks and ecological strategies (niche sharing vs. niche differentiation) at the species and genus levels.

Main Results:

• Zeolite-packed VFCWs achieved superior removal rates: 93.65% for NH4+-N and 83.84% for COD at a 6-day HRT.
• Longer HRTs (6-day) in zeolite-packed VFCWs increased the abundance of key nitrogen-cycling genes (Amx, amoA, nxrA, nosZ) and the relative abundance of Proteobacteria and Nitrospirae.
• Zeolite-packed VFCWs showed ecological niche sharing at the species level, while ceramsite-packed VFCWs exhibited niche differentiation.
• Both substrate types established functional networks of nitrogen-transforming genera employing niche differentiation.

Conclusions:

• Natural zeolite is a more effective substrate than shale ceramsite for enhancing nutrient removal in VFCWs, particularly at longer HRTs.
• Optimizing HRT and substrate type significantly influences microbial community structure, activity, and nitrogen transformation processes in VFCWs.
• Microbial communities in VFCWs adapt to environmental conditions through distinct ecological strategies, impacting overall treatment efficiency.