Effect of La ₂ O ₃ and CeO ₂ on anaerobic methanogenesis process: kinetics analysis and process mechanism study

La O and CeO , as main rare earth oxides, with unique physical and chemical properties have been widely used in catalyst and grinding industry. In this study, the effects of La O and CeO on the anaerobic process were investigated. The biological methane production tests showed that 0-0.05 g/L La O and 0-0.05 g/L CeO enhanced anaerobic methanogenesis process. The result showed maximum specific methanogenic rate of La O and CeO were 56.26 mL/(h·gVSS) and 49.43 mL/(h·gVSS), and compared to the control, increased 4% and 3% respectively. La O significantly reduced the accumulation of volatile fatty acids (VFA), while CeO had no similar effect. Dissolution experiments demonstrated that the content of extracellular La in the anaerobic granular sludge reached 404 μg-La/g volatile suspended solid (VSS), which was 134 times higher than that of extracellular Ce (3 μg-Ce/gVSS). The content of intracellular La reached 206 μg-La/gVSS, which was 19 times higher than that of intracellular Ce (11 μg-Ce/gVSS). The different stimulation between La and Ce could be attributed to the different dissolution of La O and CeO . The result of this work is helpful to optimize anaerobic processes and to develop novel additives.