The effects of nitrilotriacetic acid (NTA) on methane production and sulfate reduction during the treatment of sulfate laden organic wastewater were investigated in batch assays. The results showed that the methane fermentation was stimulated, while the sulfate reduction was inhibited. At a sodium acetate concentration of 7.0 g/L, temperature of 35 degrees C, and 0.9-15.0 of COD/SO42- ratio, the methane production was increased by 20.8-42.4% and sulfate reduction rate was decreased by 33.0-76.0%, in the presence of 100 mu M NTA. Also, the coenzyme contents of the biomass went up from 0.12 mu mol Ni/g to 0.20 mu mol Ni/g (volatile suspended solids) VSS for F-430 and from 0.30 mu mol/g VSS to 1.06 mu mol/g VSS for CoM. COD removal was also enhanced. Lack of nutrients for MPB greatly affected methane fermentation. By the addition of NTA, NTA-metal complexes formed and speciation of the trace metals in biomass changed. The amount of Co and Ni in the sulfides fraction in the biomass decreased from 145.9 and 50.0 mu g/g (total suspended solids) TSS to 86.3 and 42.9 mu g/g TSS, and their residual fraction increased by 4.4- and 9.0-fold, respectively. NTA boosted the internalization of Co and Ni, consequently enhancing the availability of trace metals for MPB and promoting the methane production. The results indicate that bioavailability of adequate nutrients is an important factor for MPB to compete with SRB (sulfate-reducing bacteria) in methane fermentation of sulfate-containing wastewater. (C) 2008 Elsevier Ltd. All rights reserved.