have studied the effect of Fe2+ at concentrations 0, 150, 300, 450, 600, and 800 mg/l on the granulation and treatment efficiency of UASB reactors. After 30 days of operation, small granules
with diameters of 0.2–0.6 mm became visible at the bottom of reactors spiked with 300–800 mg/l Fe2+.