Layered structure of granules in upflow anaerobic sludge blanket reactor gives microbial populations resistance to metal ions

Metal ions (Cd2+, Cu2+, Ni2+, Zn2+ and Cr3+) did not affect glucose degrada tion or the production of methane during anaerobic digestion with intact an d disintegrated granules from a UASB (Upflow Anaerobic Sludge Blanket) reac tor. However, when Cu2+ was at 500 mg g(-1) VSS (volatile suspended solids) in the media, the glucose degradation rates and methane production rates d ecreased by 14% and 32% in disintegrated granules, respectively, whereas, i n intact granules, decreases were 3% and 14%, respectively. When various el ectroplating metal ions were tested, 50% inhibition of acetate degradation and methane production were produced by 210-770 mg g(-1) VSS and 120-630 mg g(-1) VSS, respectively. The relative toxicity of the electroplating metal s on methane production was in the order of Zn2+ (most toxic) > Ni2+ > Cu2 > Cr3+ > Cd2+ (least toxic).