Rhizosphere Microorganisms in Subsurface Flow Garden Constructed Wetland and their Influence on Nitrogen Removal Efficiency

Subsurface flow garden constructed wetland (SFGCW) is a type of constructed wetland with garden characteristics. This study explores the efficiency of SFGCW in the removal of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) from domestic sewage and examines the structure of the rhizosphere microbial community and prevalence of nitrifying and denitrifying bacteria. An L₄(2³) orthogonal experiment was conducted using different factors such as substrates, plants, and hydraulic retention times (HRT). The results of range and variance analyses revealed that HRT and substrate considerably influenced nitrogen removal by SFGCWs, with plant factors playing a notable role. The use of fluidized bed slag as the substrate enhanced nitrogen removal, particularly when HRT was set at 3 or 6 days. At the phylum level, Proteobacteria predominated the rhizosphere microbial abundance, comprising 42.58%–55.38% of the microbial population, followed by Chloroflexi (7.19%–17.16%). It exhibited higher counts in winter than in autumn. Anaerolineaceae, which belongs to Chloroflexi, was predominant in each wetland group. Seasonal variations significantly impacted the abundance of ammonia-oxidizing and nitrite-oxidizing bacteria among nitrifying bacteria in the rhizosphere microbial community, with higher levels observed in autumn than in winter, and played a crucial role in NH₄⁺-N transformation. Additionally, a correlation was observed between the nitrogen removal effectiveness and abundance of rhizosphere microbial nitrifying bacteria, providing technical insights for further optimization of the structure and operational parameters of SFGCW.