Effect of short-term exposure to thallium on SBR activated sludge performance
In this study,using the Sequencing Batch Reactor(SBR)process as an example,the short-term disturbances and recovery behavior of activated sludge performance with respect to Tl exposure concentration were investigated,focusing on nitrogen and phosphorus removal,microbiological and enzyme activity.The results indicated that both nitrogen and phosphorus removal efficiency and COD removal rate of activated sludge were susceptible to the influence of Tl.When Tl was at a concentration of 500µg/L,nitrogen and phosphorus removal processes were inhibited,but upon the elimination of Tl exposure,the performance could recover.However,at a Tl concentration of 1000µg/L,although the phosphorus removal efficiency could be restored to 65%,the nitrogen removal process was completely inhibited and the inhibition of the nitrogen removal process was irreversible.Low concentrations of Tl increased the COD removal rate,and the effect of high concentrations of Tl on the COD removal rate was reversible.Furthermore,a Tl concentration of 200µg/L was found to increase microbial activity,but at 1000µg/L,Tl led to a significant reduction in the relative production of catalase and superoxide dismutase by 71.9%and 30.8%,which greatly inhibited microbial activity.The specific oxygen uptake rate was highly sensitive to the presence and elimination of Tl,making it an indicator for Tl exposure in wastewater treatment plants.Characterization through Fourier-Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy revealed that Tl bound to hydroxyl groups in extracellular polymeric substances or oxidized from Tl+to Tl3+,which might have been the mechanism by which activated sludge mitigated Tl cytotoxicity.Therefore,when exposed to short-term Tl,it was necessary to enhance the nitrogen and phosphorus removal performance of activated sludge and strengthened its ability to remove Tl to ensure the stable operation of wastewater treatment plants.This study revealed the potential impacts of short-term Tl exposure on activated sludge systems and proposed mitigation strategies.
thalliumSBRnitrogen and phosphorus removalenzymatic activity
NETL
NSTL
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