The performance of thermophilic anaerobic co-digestion of coffee grounds and sludge using membrane reactor was investigated for 148days, out of a total research duration of 263days. The OLR was increased from 2.2 to 33.7kg-COD/m3d and HRT was shortened from 70 to 7days. A significant irreversible drop in pH confirmed the overload of reactor. Under a moderately high OLR of 23.6kg-COD/m3d, and with HRT and influent total solids of 10days and 150g/L, respectively, the COD removal efficiency was 44.5%. Hydrogen in biogas was around 100-200ppm, which resulted in the persistent propionate of 1.0-3.2g/L. The VFA consumed approximately 60% of the total alkalinity. NH4HCO3 was supplemented to maintain alkalinity. The stability of system relied on pH management under steady state. The 16SrDNA results showed that hydrogen-utilizing methanogens dominates the archaeal community. The propionate-oxidizing bacteria in bacterial community was insufficient.
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