ABSTRACT
In this study, we performed a comprehensive analysis of microbial community compositions in leachate and leachate treatment system (14 processes) during dry and rainy seasons (from February to September and from October to January, respectively), at Khanh Son landfill site, Danang City, Vietnam. In this study, raw leachate in dry and rainy seasons was predominated by Arcobacter, Clostridia, Thermotogales, Methanobacteriaceae, and Methanosaeta. During the two seasons, the system had different microbial community compositions. Orders Methanobacteriales, Clostridiales, MBA08 (order-level clone cluster), and Thermotogales predominated the influent, anaerobic pond, and anoxic pond during the dry season, while Campylobacterales and Pseudomonadales orders were predominant in the anaerobic/anoxic systems during the rainy season. In the facultative pond, aerated ponds, sediment tanks, and polishing ponds, predominant orders during the dry season included Actinomycetales, "Saprospirales", Flavobacteriales, Rhizobiales, Rhodospirillales, Burkholderiales, and Alteromonadales; during the rainy season: Sphingobacteriales, Rickettsiales, Sphingomonadales, and Pseudomonadales. In the final post treatment (polishing ponds with vegetation), significant removal of organic matter, total nitrogen, and colour occurred, while nitrogen-fixing and root-associated or related organisms predominated. This suggested that the vegetation in the ponds was essential to achieve the sufficient leachate treatment.