Response of Activated Sludge to Long-Term Nanosilver Input and Changes in Extracellular Polymeric Substances (EPS)
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Response of Activated Sludge to Long-Term Nanosilver Input and Changes in Extracellular Polymeric Substances (EPS) Ferhan Çeçen & Ayse Gul Geyik & Başak Kılıç
Received: 4 May 2020 / Accepted: 22 September 2020 # Springer Nature Switzerland AG 2020
Abstract This study investigates the response of activated sludge to continuous nanosilver (AgNPs) input in a large concentration range. In addition to substrate removal, changes taking place in the different fractions of Extracellular Polymeric Substances (EPS), namely, very loosely bound-EPS (VLB-EPS), loosely boundEPS (LB-EPS), and tightly bound-EPS (TB-EPS), as well as the protein and carbohydrate content of each fraction were examined. At relatively low AgNP concentrations (5 mg/L), production of loosely bound fractions became higher. At AgNP ≥ 12 mg/L, also TB-EPS production was promoted. Seemingly, bacteria were protected from inhibitory effects by regulation of EPS production. Moreover, new proteins emerged in EPS. Respiration tests indicated no effect on substrate removal even at high AgNP concentrations because the nanomaterial lost its effectiveness upon continuous aeration. In WWTPs, AgNP concentrations are normally below 0.8 mg/L. Therefore, no negative impact on Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11270-020-04882-7) contains supplementary material, which is available to authorized users. F. Çeçen (*) : A. G. Geyik : B. Kılıç Institute of Environmental Sciences, Bogazici University, Bebek, 34342 Istanbul, Turkey e-mail: [email protected]
A. G. Geyik e-mail: [email protected] B. Kılıç e-mail: [email protected]
substrate removal and no visible changes in EPS production would be expected. Keywords Activated sludge . Extracellular polymeric substances (EPS) . Inhibition . Nanosilver (AgNP)
1 Introduction Since silver nanoparticles (AgNP) have antimicrobial properties, they are employed in many consumer goods ranging from personal care products to detergents and cloths. Inevitably, they are then found in municipal wastewater. For example, AgNP-containing textiles are reported to emit these nanoparticles into municipal wastewater treatment plants (WWTPs) (Voelker et al. 2015; Wu et al. 2019). AgNPs will also be employed in new areas, and an increase in Ag concentration is thus expected in WWTPs (Benn and Westerhoff 2008; Benn et al. 2010; Geranio et al. 2009; Kaegi et al. 2011; Kaegi et al. 2013). Therefore, studies are still needed to assess the fate and impacts of AgNPs in WWTPs. According to literature values, at μg/L or ppb levels, AgNPs will not have an effect on the activity and abundance of bacteria in activated sludge systems (Blaser et al. 2008). Indeed, recent studies indicated that in the case of relatively short-term contact (10 days and 27 days), 0.5– 1.5 mg/L AgNP did neither affect chemical oxygen demand (COD) nor NH 4 -N removal (Hou et al. 2012; Wang et al. 2012). From the point of inhibition, of utmost importance is the
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speciation of silver. For example, a
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