In the present study,the fate and long-term effect of TiO_2 nanoparticles( NPs) on anaerobic granular sludge( AGS) was evaluated in an anaerobic methanogenic system. In the short-term experiment,the methane production rate decreased when the dosage of TiO_2 NPs was greater than 150 mg·g~(-1). However,no significant difference in the products of acidification and methanation between the control and 150 mg·g-1( as VSS) of TiO_2 NPs assays was observed,indicating low bacteria cytotoxicity of TiO_2 NPs on AGS i...