Insights into the role of extracellular polymeric substances in Zn2+ adsorption in different biological sludge systems
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The adsorption behavior of Zn2+ in four different biological sludge systems, i.e. activated sludge, denitrification sludge, short-cut nitrification sludge, and anammox granules, was investigated. The results indicated that all sludge samples possessed considerable potential for Zn2+ adsorption. Short-cut nitrification sludge possessed the highest Zn2+ maximum adsorption capacity (qm) of 36.4 mg g SS−1, which was much higher than other sludges applied (12.8–14.7 mg g SS−1). Besides, the adsorption rate for short-cut nitrification sludge was fastest among the four types of sludge after fitting with a pseudo-second-order rate equation. Comparing with the physicochemical properties of the four sludges, the soluble extracellular polymeric substances (EPS), especially soluble polysaccharide (PS), played a prior role in binding metal cations (i.e., Zn). The present study also showed that with less than 30% of Zn2+ trapped by EPS, 61.6–71.9% of Zn2+could be harvested directly by cells, indicating that the protecting capability by EPS was limited. Therefore, it is important to remove metal ions as early as possible if the activated sludge processes encountered high stress of heavy metal.
KeywordsActivated sludge Zinc Adsorption EPS Anammox Nitrification
This work is partially supported by the National Natural Science Foundation of China (51878662, 51674305), the key projects of the Science and Technology of Hunan Province (2017SK2420), the Innovation-Driven Project (2017CX010) of Central South University, and the Opening Fund of Jiangsu Key Laboratory of Anaerobic Biotechnology (Jiangnan University) (JKLAB201706). Dr. Tang C.-J. is supported by the 2017 Huxiang Provincial Scholar Program (2017RS3005).
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