Metal ions have an adverse effect on anaerobic digestion. In an acetate degradation test of upflow of anaerobic sludge blanket granules with Cu2+, not all of the acetate that disappeared was stoichiometrically converted to methane. In the presence of 400 mg/g-VSS (volatile suspended solids) Cu2+, only 26% of the acetate consumed was converted to methane. To study acetate conversion by other anaerobic microorganisms, sulfate and nitrate reductions were investigated in the presence of Cu2+ Sulfate and nitrate reductions exhibited more resistance to Cu2+than methanogenesis, and the granules reduced 2.2 mM and 5.4 mM of nitrate and sulfate, respectively, in the presence of 400 mg/g-VSS copper ion. However, the acetate degraded by sulfate and nitrate reductions was only 24% of the missing acetate that could have been stoichiometrically converted to $CO2. Accordingly, 76% of the acetate consumed appeared to have been converted to other unknown compounds.