Effect of chemical oxygen demand (COD) on hydrogen production from waste molasses in continuous stirred tank reactor (CSTR)

The performance of anaerobic hydrogenation was evaluated in a continuous stirred-tank reactor (CSTR) operated at different influent chemical oxygen demand (COD) concentration with selectively enriched anaerobic mixed consortia in this present study. Waste molasses was used as a model substrate. The CSTR was started at a hydraulic retention time (HRT) of 8 hours with a temperature of (35±1)°C. Four OLRs were examined, ranging from 6.0 to 24.0 kg/m³·d, with influent glucose concentrations ranging from 2000 to 8000 mgCOD/L. The highest H₂ production (10.96 L/d) was obtained at 18 kg/m³·d of OLR. When influent COD concentration rose to 8000 mg/L, The pH and ALK dropped to 3.7 and 5 mg/L from the level of 4 and 250 mg/L. and Oxidation-Reduction Potential (ORP) rose to -210 mV from -350 mV. The biomass concentration in the CSTR system could not endure these changes, and its activity was restrained. The H₂ yield had quick descent. The changed influent COD concentration would have direct impact on the activity of hydrogen producing bacteria and metabolic characteristics of microbial community in the fermentative process.