The Effect of Sulfate Concentration on COD Removal and Sludge Granulation in UASB Reactors

Four identical 37.5 Liter UASB reactors R1, R2, R3 and R4 were used to study the effect of sulfate concentration on granule formation. Diluted molasses with COD range 1000–1300 mg/l were used as feed and acclimated cow manure was used as seed. Concentration of sulfate ions in the four reactors were 100, 500, 1000 and 1500mg/l. Granules were observed in R2 after 33 days from startup time, while in  R1 and R3 granules appeared after 45 days. No granules were formed in R4. Sulfate reduction efficiencies were 84, 89, 71.5 and 59.4% while corresponding COD removal efficiencies were 85, 91, 84 and 77% for reactor R1 to R4 respectively. Temperature kept at 30ºC allex periments and the best pH for granulation was found to be 7.00.