Abstract
The scope of this study was to investigate the toxic effects of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, in long-term semi-batch feeding mode at two different hydraulic retention times (HRTs) (20 and 40 days). A freshwater microalgae, Scenedesmus rubescens, was employed and exposed to a semi-continuous supply of ZnO NPs at a low concentration of 0.081 mg/L for a period of 28 d. Experiments were conducted under controlled environmental conditions. Τhe impact of ZnO NPs on S. rubescens, which was assessed in terms of nutrient removal, biomass growth, and algal lipid content. Semi-batch mode cultures showed that low ZnO NP concentrations at an HRT of 40 d did not have any negative effect on microalgae growth after the fourth day of culture. In contrast, algal growth was inhibited up to 17.5% at an HRT of 20 d in the presence of ZnO NPs. This might be attributed to the higher flow rate applied and ZnO NPs load. A positive correlation between nutrient removal and microalgae growth was observed. The algal lipid content was, in most cases, higher in the presence of ZnO NPs at both HRTs, indicating that even low ZnO NPs concentration cause stress resulting in higher lipid content.
Highlights
Engineered nanomaterials (NMs) are a new technology that have found wide applications in daily life during the last decade
wastewater treatment plants (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]
The present study revealed that hydraulic retention times (HRTs) has a considerable effect on S. rubescens growth during semi-batch culture conditions
Summary
Engineered nanomaterials (NMs) are a new technology that have found wide applications in daily life during the last decade. One of the systems which are affected by the increasing use of NPs are wastewater treatment plants (WWTPs). 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. Chauque et al [5] investigated zinc oxide (ZnO) engineered-NPs disposal using a simulated WWTP and concluded that engineered NPs were aggregated on and attached to the biomass, and engineered NPs were removed from wastewater by sorption processes [5]. Among the predominant NPs, ZnO NPs rank among the top three metal NPs used in consumer products, and estimated global production ranges from 550 to 33,400 tons/year [3,8]
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