Acetate treatment in 70 C upflow anaerobic sludge-blanket (UASB) reactors: start-up with thermophilic inocula and the kinetics of the UASB sludges

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Abstract
This study focused on the use of thermophilic anaerobic granulae in the start-up of 70°C acetate-fed upflow anaerobic sludge-blanket (UASB) reactors and the kinetics of granulae grown at 70°C. In the UASB reactors, chemical oxygen demand removal commenced within 48 h of the start-up. The maximum reduction in chemical oxygen demand was 84% with the feed containing yeast and 71% without a yeast supplement. In the bioassays, the yeast-grown sludge converted 98% of the acetate consumed to methane as compared to 92% for the sludge grown without yeast. The highest initial specific methane production rate (µCH4) of the UASB sludges grown at 70°C was 0.088 h−1 at an acetate concentration of 4.6 mM. The higher initial acetate concentration was found to prolong the lag-phase in methane production significantly and to decrease the µCH4. The half-saturation constant (Ks), the inhibition constant (Ki), the inhibition response coefficient (n), and the µCH4max, calculated according to a modified Haldane equation, were 1.5 mM, 2.8 mM, 0.8, and 0.28 h−1, respectively. The prolonged starvation of the 70°C sludge (15 days) decreased the µCH4 from about 0.022 h−1 to 0.011 h−1 and increased the lag phase in methane production from 6 h to 24 h as compared to non-starved sludge.