Ten percent of anaerobic sludge inoculum (Table 2) was mixed with tap water to obtain a working volume of 250 mL in 1 L Schott bottles. Assay A contained 2 g/L of C6H12O6$H2O as substrate and 75 mg/L Znþ2 (¼300 mg/L of ZnSO4$7H2O) as the metal inhibitor whereas in assay B no ZnSO4 was added. The control assay C consisted of only 10% inoculum without glucose or a metal inhibitor.The incubation conditions were the same as described in Section 2.3.1.