Abstract
The increased use of engineered nanoparticles (ENPs), such as copper oxide nanoparticles (CuO NPs), in commercial products and applications raises concern regarding their possible release into freshwater sources. Therefore, their removal from water is important to eliminate adverse environmental and human health effects. In this study, the effects of pH and natural organic matter (NOM), i.e., humic acid (HA) and salicylic acid (SA) on the removal of CuO NPs by coagulation/flocculation/sedimentation (C/F/S) were evaluated. The results indicated that pH significantly affects the coagulation efficiency, where 10–60% CuO NPs removal was achieved under extreme acidic/alkaline conditions. However, at neutral pH, removal of up to 90% was observed with a lower ferric chloride (FC) dosage (0.2 mM). The coagulation efficiency and mechanism were strongly affected by the type of Fe species present in the aqueous phase, which is mainly controlled by pH. Higher concentrations of both HA and SA decrease the CuO NPs agglomeration rate, and thereby improve the colloidal stability due to the NOM molecules adsorbed onto the NPs surface. The presence of hydrophobic HA needs a higher FC dosage of 0.5–0.8 mM than a dosage of hydrophilic SA of 0.25–0.35 mM, to obtain a similar CuO coagulation efficiency. Moreover, higher removals of dissolved organic carbon (DOC) and UV254 were observed more in hydrophobic NOM than in hydrophilic. The results of the Fourier transform infrared (FT-IR) analysis of FC composite flocs confirm that the charge neutralization and enmeshment of coagulant might be a possible removal mechanism. The findings of the current study may provide critical information in the prediction of the fate, mobility, and removal of CuO NPs during C/F/S in water treatment.
Highlights
The usage of metal-based nanomaterials (NMs) in commercial products and applications is increasing rapidly, because of the current advances in nanotechnology
The hydrodynamic diameter (HDD) of the CuO NPs suspension was measured as 225 ± 27 nm by dynamic light scattering (DLS) at pH 7.0 (Figure S1B of the SM), indicating a much larger size of NPs in DI water, as compared to the vendor reported size (
This study showed that C/F/S is an effective process to remove CuO NPs from aqueous environments
Summary
The usage of metal-based nanomaterials (NMs) in commercial products and applications is increasing rapidly, because of the current advances in nanotechnology. Amongst several NMs, copper oxide nanoparticles (CuO NPs) are widely used in many industries, environmental remediation, agricultural activities, and antimicrobial agents due to their unique specific structural properties [1,2]. The global annual production of CuO NPs was approximately 570 tons/year in 2014 and is predicted. The large production and application of CuO NPs have raised environmental concerns because of their release into the aqueous system, increasing the potential risk to human health and aquatic organisms [4]. The CuO NPs can dissociate into Cu2+ ions and a high concentration of Cu2+ is harmful to both humans and aquatic life. A recent study [6] reported the adverse effect of Cu2+ ions on the impaired growth of Triticum aestivum, and the increased levels of oxidative stress in microalgae
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