The potential of oxygen to improve the stability of anaerobic reactors during unbalanced conditions: Results from a pilot-scale digester treating sewage sludge

摘要

A well-functioning pilot reactor treating sewage sludge at approximately 4.4NL/m~3/d of oxygen supply and 18d of hydraulic retention time (HRT) was subjected to a hydraulic overload to investigate whether oxygen benefits successful operation in stressful circumstances. Only a mild imbalance was caused, which was overcome without deterioration in the digestion performance. Volatile solids (VS) removal was 45% and 43% at 18 and 14d of HRT, respectively. Biogas productivity remained around 546NmL/g_(VS), but it was slightly higher during the period of imbalance. Thereafter, similar performances were achieved. Under anaerobic conditions, VS removal and biogas productivity were respectively 41% and 525NmL/g_(VS), hydrogen partial pressure rose, and acetic acid formation became less favourable. Oxygen seemed to form a more stable digestion system, which meant increased ability to deal successfully with overloads. Additionally, it improved the biogas quality; methane concentration was negligibly lower, while hydrogen sulphide and oxygen remained around 0.02 and 0.03%v/v, respectively.