Metagenomic analysis reveals the methanogenic, ATP, and potassium-transport metabolisms of anaerobic systems with different ammonia concentrations

Excessive ammonia is a well-known inhibitor of anaerobic wastewater treatment systems. In this study, responses of methanogenic activity and pathway, microbial communities, adenosine triphosphatases (ATPase) system, and potassium (K⁺) transport system to different ammonia concentrations were investigated. The long-term acclimation with 1 g NH₄⁺-N/L of ammonia decreased the methanogen abundance by more than 13% and shifted the dominant methanogen from Methanothrix to Methanosarcina. In the acetate-substrate reactor, genes encoding methanogenesis, ATPase, and K⁺ transport systems were suppressed. However, in the reactor fed with ethanol and acetate, the long-term acclimation with ammonia enriched ammonia-tolerant syntrophic bacteria (i.e., Geobacter) with a high abundance of ATPase and K⁺ transport genes. The robust ethanol oxidation and ammonia-detoxicate activities benefited the subsequent methanogenesis (including acetoclastic methanogenesis), increasing 78% of the maximum methane production rate, compared with the control reactor. Direct interspecies electron transfer-capable partners and PilA genes were both detected under 1 g NH₄⁺-N/L of ammonia condition.