Effect of organic loading rate on continuous flow anaerobic activated sludge fermentation system for bio-hydrogen production

The effect of organic loading rate on operation of continuous flow anaerobic activated sludge fermentation system for bio-hydrogen production was investigated in a continuous stirred-tank reactor (CSTR). When influent COD concentration rose to 6000 mg/L (OLR 18 kg/(m³·d)) from 4000 mg/L (OLR 12 kg/(m³·d)) with HRT 8 h and (35 ± 1)°C, pH, ALK and ORP had evidently changed. When the system reached at a new stable state, an average hydrogen evolution rate as high as 10.96 L/d was obtained, which was 19.3% and 52.3% higher than that of OLR 6 kg/(m³·d) and OLR 6 kg/m, respectively. When influent COD concentration rose to 8000 mg/L (OLR 24 kg/(m³·d)), the environment in the reactor changed acutely. The pH and ALK dropped to 3.7 and 5 mg/L from 4.1 and 250 mg/L, and ORP rose to -210 mV from -350 mV. The anaerobic activated sludge in the bio-hydrogen production reactor could not endure these changes, and their activity was inhibited. The hydrogen yield of the reactor dropped quickly, and the organic wastewater fermentation type changed from ethanol type fermentation to mixed acids fermentation.