Optimization of metal dosing in anaerobic bioreactors: effect of dosing strategies on the performance and metal retention of methanogenic granular sludge

The effect of trace cobalt dosage and dosing strategies on the performance and cobalt retention of methanol fed upflow anaerobic sludge bed (UASB) reactors were investigated. The three dosing strategies tested (continuous, pre-loading and pulse) showed that continuous dosing at 0.33 muM was effective in minimizing cobalt losses from the granular sludge but only moderately increased the specific methanogenic activity from 110 to 210 mg CH4-COD g VSS-1 d(-1). Pre-loading sludge results in high specific methanogenic activities increasing form 155 to 906 mg CH4-COD. g VSS-1 d(-1), within 30 days of operation. However, cobalt losses are much bigger, 54% of the original 1667 mug g TSS-1 was lost after 77 days of operation. By pulse dosing, 16% of the amount of cobalt present in the pre-loaded sludge, the methanogenic activity of the sludge increased from 155 to 631 mg CH4-COD g VSS-1 d(-1), while the cobalt content increased to only 107 mug g TSS-1, indicating a relatively effective use of the cobalt compared to pre-loading.