Abstract
The present study investigated the impacts of temperature shocks on the generation of soluble microbial products (SMPs) in an aerobic activated sludge system, focusing on biopolymers and low molecular weight (LMW) substances that significantly impact the effluent quality. The results indicated that raising the temperature increased SMP production. At 25 and 35 °C, all size fractions of SMPs increased linearly with the aeration time, and biopolymers comprised a large proportion of SMPs. At 5 and 15 °C, in contrast, only biopolymers increased linearly with the aeration time, and LMW substances were the predominant fraction of SMPs. The reduced bio-utilization of SMPs with an increase in temperature was associated with the decreased relative abundance of LMW substances, which is supported by the assimilable organic carbon bioassay measurements. The mass of the biopolymers for the SMPs and extracellular polymeric substances (EPS) was balanced at all temperatures, wherein a negative correlation was observed, indicating that increased SMPs in the water phase led to a decrease in EPS. The results of the reactive oxygen species (ROS) and toxicity assays confirmed that the immune defense reaction of the bacteria (induced by ROS) was the key factor for variations in LMW substances in the SMPs and EPS under temperature stresses.
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