Toxicity of Long Single-Walled Carbon Nanotubes to the Activated

Downloaded by UNIV OF SYDNEY on October 27, 2015 | http://pubs.acs.org Publication Date (Web): August 26, 2015 | doi: 10.1021/bk-2015-1198.ch009

Chapter 9

Toxicity of Long Single-Walled Carbon Nanotubes to the Activated Sludge Process: Examination of the Effects of Extracellular Polymeric Substances Harshrajsinh Thakor,1 Alex Parise,2 and Xiaoqi (Jackie) Zhang3,* 1MassDEP

20, Riverside Drive, Lakeville, Massachusetts 02347 Engineering Associates, Inc., 779 South Main Street, Manchester, New Hampshire 03102 3Department of Civil and Environmental Engineering, University of Massachusetts Lowell, Lowell, Massachusetts 01854 *Phone: (978) 934-2194; Fax: (978) 934-3052; E-mail: [email protected]

2Loureiro

In this paper, we examined the effect of extracellular polymeric substances (EPS) in protecting the microbial communities when the activated sludge was dosed with long single-walled carbon nanotubes (LSWCNTs). Mix-cultured activated sludge from a local wastewater treatment plant was used in the study and a respiratory inhibition test was performed on the activated sludge without shearing and after shearing to determine the respiratory activity of the activated sludge when the LSWCNTs were introduced. The results showed that the LSWCNTs exhibited toxicity towards the activated sludge microbial communities and more respiratory inhibition was observed when the EPS of the activated sludge was sheared off, illustrating the protective ability of EPS. Keywords: long single-walled carbon nanotubes (LSWCNTs); activated sludge; extracellular polymeric substances (EPS); respiratory inhibition

© 2015 American Chemical Society In Emerging Micro-Pollutants in the Environment: Occurrence, Fate, and Distribution; Mitchell, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Introduction Nanotechnology is an applicable aspect of a broader area of nanoscience. Carbon nanotubes (CNTs) can be released into the environment via wastewater discharge and point source emissions from manufacturing industries (1). Animal inhalation and aspiration studies have demonstrated that exposure to single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) results in acute pulmonary inflammation and long term chronic effects such as thickening of the bronchial wall, fibrosis and granulomas (2). Antimicrobial activity of SWCNTs has been reported after E.coli had been exposed to SWCNTs (3). An activated sludge process is a biological process that is used in the wastewater treatment facility to treat wastewater (4). Parise (5) reported the toxicity effect of different types of SWCNTs on the activated sludge microbial community. Their results showed that long SWCNTs (LSWCNTs) and functionalized SWCNTs were more toxic than the short SWCNTs and non-functionalized SWCNTs. Extracellular polymeric substances (EPS) form a protective layer outside of the microorganisms (6). EPS plays a significant role in the formation and the function of microbial aggregates, including adhesion phenomena, matrix structure formation, microbial physiological processes such as protecting cells against environmental changes in pH, water quality, salt content and hydraulic pressure (7). When the activated sludge is sheared, the EPS layer breaks off and dissolves, and the EPS content can be measured as soluble protein, carbohydrates, deoxyribonucleic acid (DNA), etc. (8). The amount of dissolved protein and carbohydrates detected after shearing indicates the amount of EPS separated from the microorganisms. The ability and degree of EPS protection against a toxin is dependent on the nature of toxin (6). Presently, only limited information is available on the effect of EPS in protecting the microbial communities when CNTs are present. Luongo and Zhang (9) demonstrated that EPS played a significant role in protecting the microbial communities in the activated sludge against the toxicity posed by the MWCNTs. However, the effects of EPS on the activated sludge when the LSWCNTs are present are not yet understood. The objective of this paper is to determine the effect of EPS in protecting the microbial communities when the activated sludge was dosed with the LSWCNTs.

Methods Sludge Preparation Fresh activated sludge was collected from the Lowell Regional Wastewater Utility (Lowell, MA). The sludge was concentrated to 4,000 mg TSS/L. To achieve that, the initial mixed liquor suspended solids (MLSS) and Chemical Oxygen Demand (COD) (10) were measured as soon as the sludge was brought to the environmental laboratory at the University of Massachusetts Lowell (UML). After 168 In Emerging Micro-Pollutants in the Environment: Occurrence, Fate, and Distribution; Mitchell, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

that the sludge was allowed to settle and washed with tap water three times before decanting the supernatant and measuring the MLSS of the sludge again. After washing, tap water was added so that the sludge had 4000 mg/L of MLSS.


Synthetic Feed and Sludge Storage Sludge was stored overnight before the experiment. Synthetic feed was added to the sludge during storage to maintain the same Food/Microorganism ratio as in the original sludge. During storage, the sludge was aerated continuously with an aeration stone. The aeration was set at a rate so that only small bubbles were formed. For every 100 mL of synthetic feed, 1.6 g peptone, 1.1 g meat extract, 0.3 g urea, 0.07 g NaCl, 0.04 g CaCl2•2H2O, 0.02 g MgSO4•7H2O, and 0.28 g K2HPO4 were added (11). To avoid bacterial growth in the feed, fresh synthetic feed was prepared prior to every experiment.

Nanotube Preparation LSWCNTs were purchased from Cheap Tubes Inc. (Brattleboro, VT). The characteristics of the nanotubes are shown in Table 1. The CNTs were sonicated according to Parise, et al. (5).

Table 1. Nanotube Compositions Long Single-Walled CNTs (LSWCNTs) 1-2

Outer Diameter (nm)

5.0-30

Length (µm)

> 90wt%

Purity

0

Functional Content

Toxicity of Long Single-Walled Carbon Nanotubes to the Activated

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