Assessment of bacterial communities and prediction of their metabolic functions in vegetation-activated sludge process treating landfill leachate

Optimizing the structure and function of microbial communities is crucial in the design and operation of treatment systems, particularly because the species composition of biomass determines the metabolic pathways, which ultimately impacts the treatment quality. As the impact of landfill leachate (LL) on microbial communities in treatment systems remains poorly understood, this study aimed to analyze the composition of bacterial communities and their variability over time in vegetation-activated sludge process (V-ASP) and modified ASP systems. The predicted metabolic functions of microorganisms and their relationship with nitrogen removal from LL were also determined. Treatment efficiency was associated with the composition of microbial communities. The dominant bacterial phyla in all the treatment systems were Pseudomonadota and Bacteroidota. This study confirmed that landfill leachate supports a unique microbiome that is distinct from other microbiomes. The most abundant bacterial phylum in the LL was Patescibacteria, which reached a maximum abundance of over 30%. However, only a small proportion of Firmicutes (from 1.6% to 3.2%) was recorded in the LL. Biofilms on plant roots favored the occurrence of aerobic denitrifying microorganisms, such as Halomonas, which reached an abundance of up to 20% and may be linked to increased nitrogen removal efficiency. Functional prediction based on PICRUSt2 and KEGG indicated that dissimilatory nitrate reduction and denitrification were the dominant predicted nitrogen-related pathways in all treatment variants, with the highest abundance in Phase II. Microbiological characterization provides new information to help understand the role of bacteria involved in LL treatment and is important for its management.