Use of respirometer in evaluation of process and toxicity of thermophilic anaerobic digestion for treating kitchen waste

A thermophilic anaerobic digestion (TAnD, 55 °C) system was adopted to hydrolyze the kitchen waste for 3 days, which was then fermented for a hydraulic retention time (HRT) of 10 days. The TAnD system performed much better than a similar system without thermal pre-treatment. A bubble respirometer was employed to study the effects of thermal pre-treatment, which showed that pre-treatment at 60 °C yielded the highest Total COD (TCOD) removal efficiency (79.2%) after 300 h reaction. Respirometer results also indicated that oil and grease (O and G) began to inhibit the TAnD system at a concentration of approximately 1000 mg/L and the gas production was inhibited by 50% at a concentration of approximately 7500 mg/L of sodium.