Effect of Aluminum (Al3+) on Granulation in Upflow Anaerobic Sludge Blanket Reactor Treating Low-Strength Synthetic Wastewater

The effect of aluminum on agglomeration in the sludge bed and chemical oxygen demand (COD) removal efficiency in laboratory-scale upflow anaerobic sludge blanket (UASB) reactors treating low-strength synthetic wastewater (approximately 665 to 738 mg/L of COD) was investigated. Continuous application of aluminum chloride (200 mg/L) caused poor COD removal, less sludge density, and adversely affected agglomeration in the sludge bed. An adverse effect on granulation also was observed when 300 mg/L aluminum chloride was added only during the startup, and the effect continued even after it was discontinued. A lower concentration of aluminum chloride (50 mg/L) added for 30 days after the reactors reached steady-state did not affect the COD removal efficiency, but adversely affected the growth of agglomerates and caused temporary degeneration of existing agglomerates. The adverse effect of aluminum appeared to stem from the precipitation of aluminum hydroxide on the surfaces of agglomerates. The effect of aluminum on agglomeration was shown to be a function of influent strength.