摘要：The causes of the appreciable increase of dimethyl disulfide (DMDS)-forming bacteria in abnormally conditioned activated sludge were investigated. The strains II-Ab-43 (Corynebacterium) and III-Ab-5 (Pseudomonas), which were isolated from abnormally conditioned activated sludge under high biochemical oxygen demand (BOD) loading, were used to find suitable environmental conditions for DMDS formation and for growth. Both strains formed DMDS at high concentrations and grew well in culture medium with weak alkalinity and a high content of BOD substances, at 20-30°C. Activated sludge was cultured at the BOD load of 0.55 kg-BOD/m3·d at various pHs from 6.0 to 9.5. The state of activated sludge was normal at pH 6.0-8.5, but abnormal at pH 9.5. The DMDS-forming ability of the mixed liquor was constant at low values at pH 6.0-8.5, but increased distinctly at pH 9.5. With an increase of BOD load to 5.5 kg-BOD/m3·d at pH 9.5, the state of activated sludge deteriorated and the DMDS-forming ability rose further. In the aeration tanks of night soil treatment plants, DMDS was detected under conditions of weak alkalinity (pH 8.4-9.1) and high BOD of the influent (BOD 501-5540 mg/l). These results agreed with those obtained in the laboratory. The effluent parameters (BOD, chemical oxygen demand (COD), suspended solids (SS)) from settling tanks in which DMDS was detected in the aeration tanks had higher values than those in cases where DMDS was not detected. It became clear that environmental conditions of weak alkalinity and high BOD, due to abnormally conditioned activated sludge, were suitable for the growth of DMDS-forming bacteria, and DMDS was consequently detected in the aeration tank. It appears that DMDS could be a useful index for evaluating the state of activated sludge.
