Fate, behaviour, and implications of ZnO nanoparticles in a simulated wastewater treatment plant

Abstract

Increased use of engineered nanoparticles (ENPs) has resulted in their entry into municipal wastewater treatment plants (WWTPs) as their final sinks. However, the adverse impact of ENPs on the bacterial activity in the activated sludge WWTPs is not yet well understood, despite their increased release into such systems. In this study, the impacts on WWTPS associated with the disposal of zinc oxide (ZnO) ENPs was investigated using a simulated WWTP developed as per the prescribed Organization for Economic Co-operation and Development (OECD 303A) specifications. Analyses were done to determine zinc concentrations at various stages of the setup, mainly in the raw wastewater and treated effluent, using inductively coupled plasma optical emission spectrometry (ICP-OES). The results obtained indicated low levels of zinc residue (about 50-200 µg/L) in the treated effluent compared to relatively high concentrations of Zn in the sludge (about 3 000 mg/kg). Results reported herein imply precipitation of ZnO ENPs during wastewater treatment processes and hence its high levels in the sludge. The presence of solid Zn in the sludge was determined using X-ray diffraction spectroscopy (XRD). Overall, no significant impact of ZnO ENPs on the performance of the simulated WWTP was observed, in terms of the removal levels of chemical oxygen demand (COD) during the treatment process

Comparison of the effects and distribution of zinc oxide nanoparticles and zinc ions in activated sludge reactors

“…The exposure to 10 and 50 mg/L ZnO NPs further decreased COD removal efficiencies to 72.7% and 65.7%, respectively. This is in disagreement with Chauque et al [25] who reported no effect on COD removal at 20 mg/L ZnO NP. Our findings contradict previous studies of the effects of ZnO NPs on COD removal efficiencies.…”

“…Less Zn 2+ was released from NP because humic acids are known to stabilize ZnO NP and retard dissolution rates. [25] By comparison, in a recent study on the fate and behaviour of ZnO NPs in a simulated WWTP, Musee et al [17] reported an effluent Zn concentration of 1.39 mg/L after 240 hours of exposure. In the present study at 5 hours exposure, 86.3%, 85.1% and 85.8% of zinc from ZnO NPs were retained in the sludge at initial ZnO concentrations of 1.0, 10 and 50 mg/L respectively, showing that a large fraction of the ZnO NPs was removed from the wastewater due to adsorption onto waste activated sludge.…”

Long-term toxicity of ZnO nanoparticles to Scenedesmus rubescens cultivated in different media

“…Nanoparticles (NPs) have always existed in the natural environment (soil, water and atmosphere) 1 . Although exposure to NPs is not a new phenomenon, the rapid development of commercial applications, involving the use of a large variety of engineering NPs, has resulted in the introduction of quite higher amounts into the environment 2 . Engineering NPs have been found in wastewater, which are directed to treatment plants, and then discharged, in the aquatic environment 3 , 4 .…”

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode

“…A continuous supply of NPs in a system may have a major impact on its living organisms (fungi, algae, bacteria, and protozoa) and eventually in the system operation performance. Although WWTPs are the main recipients of NPs and many studies have been performed on the effects of NPs on various organisms, the adverse effects of NPs on bacterial populations in activated sludge need further investigation [5]. Sorption of pollutants on activated sludge is among the main processes for toxic substances removal in wastewater, such as metals, synthetic organic chemicals, suspended solids, and pathogens [6], including NPs.…”