Application of iron oxides modified volcanic rock in continuous phenol wastewater anaerobic treatment: Performance and underlying mechanisms

In this study, volcanic rocks (VR) or iron oxides modified volcanic rocks (IOVR) were added into the upflow anaerobic sludge bed reactor to serve as the supporting materials for improving phenol containing wastewater treatment efficiency. Results showed that with the presence of supporting materials the anaerobic digestion efficiency was effectively improved. In stage Ⅳ, in VR reactor and IOVR reactor the organics removal efficiency were 97.5% and 120.0% higher than that in control reactor, and the methane production were 71.2% and 105.3% higher than that in control reactor, respectively. Mechanisms exploration indicated that the activity of the electron transport system (ETS) and Coenzyme F420 were obviously improved in both VR reactor and IOVR reactor, which played an important role in organics decomposition and methanogenesis process, respectively. Microbial community analysis indicated that the frequency of functional genomes encoding key enzymes was effectively improved with the existence of supporting materials, especially in IOVR reactor, which meant the total microbial activity was significantly enhanced. Besides, the abundance of syntrophic bacteria (i.e. Clostridium and Longilinea) and syntrophic archaea (i.e. Methanothrix and Methanobacterium) also increased in these two reactors, which meant that syntrophic metabolism was potentially established and played an important role during anaerobic digestion.