Experimental evaluation of nitrate reduction from water using synthesis nanoscale zero-valent iron (NZVI) under aerobic conditions

The aim of this research was to study the potential of synthesized nanoscale zero-valent iron for nitrate reduction in aqueous solution. Batch technique was used to determine the kinetics and effective parameters. The effects of initial pH level, initial nitrate concentration and nanoscale Fe̊ concentration on nitrate reduction were studied. Nanoscale zero-valent iron was synthesized by chemical reduction method. The TEM image showed that synthesized nano Fe̊ has a size in the range of 40-120 nm. Experimental results exhibited that reduction efficiency of nitrate decreases with increasing initial pH and increases significantly due to increasing the concentration of zero-valent iron nanoparticles. Also, it was illustrates that initial concentration of nitrate has little effect on the nitrate reduction efficiency. Under acidic and neutral conditions, pH level of the reaction solution increased considerably after 60 min. However, under alkaline conditions, pH level of the reaction solution decreased. The reduction rate of nitrate reached 80% in 60 min with nanoscale Fe° dosage of 1.0 gl-1 and pH in4. The observed reaction rate constant was determined to be 0.0255 in min-1 for nanoscale concentration 1.0 gl -1. The experimental results indicated that the nitrate reduction with zero-valent iron nanoparticles do not comply the first-order reaction model with respect to nitrate concentration

Wastewater treatment plants as a pathway for microplastics: Development of a new approach to sample wastewater-based microplastics

Wastewater effluent is expected to be a pathway for microplastics to enter the aquatic environment, with microbeads from cosmetic products and polymer fibres from clothes likely to enter wastewater treatment plants (WWTP). To date, few studies have quantified microplastics in wastewater. Moreover, the lack of a standardized and applicable method to identify microplastics in complex samples, such as wastewater, has limited the accurate assessment of microplastics and may lead to an incorrect estimation. This study aimed to develop a validated method to sample and process microplastics from wastewater effluent and to apply the developed method to quantify and characterise wastewater-based microplastics in effluent from three WWTPs that use primary, secondary and tertiary treatment processes. We applied a high-volume sampling device that fractionated microplastics in situ and an efficient sample processing procedure to improve the sampling of microplastics in wastewater and to minimize the false detection of non-plastic particles. The sampling device captured between 92% and 99% of polystyrene microplastics using 25 μm–500 μm mesh screens in laboratory tests. Microplastic type, size and suspected origin in all studied WWTPs, along with the removal efficiency during the secondary and tertiary treatment stages, was investigated. Suspected microplastics were characterised using Fourier Transform Infrared spectroscopy, with between 22 and 90% of the suspected microplastics found to be non-plastic particles. An average of 0.28, 0.48 and 1.54 microplastics per litre of final effluent was found in tertiary, secondary and primary treated effluent, respectively. This study suggests that although low concentrations of microplastics are detected in wastewater effluent, WWTPs still have the potential to act as a pathway to release microplastics given the large volumes of effluent discharged to the aquatic environment. This study focused on a single sampling campaign, with long-term monitoring recommended to further characterise microplastics in wastewater

Wastewater treatment plant effluent as a source of microplastics: review of the fate, chemical interactions and potential risks to aquatic organisms

Wastewater treatment plant (WWTP) effluent has been identified as a potential source of microplastics in the aquatic environment. Microplastics have recently been detected in wastewater effluent in Western Europe, Russia and the USA. As there are only a handful of studies on microplastics in wastewater, it is difficult to accurately determine the contribution of wastewater effluent as a source of microplastics. However, even the small amounts of microplastics detected in wastewater effluent may be a remarkable source given the large volumes of wastewater treatment effluent discharged to the aquatic environment annually. Further, there is strong evidence that microplastics can interact with wastewater-associated contaminants, which has the potential to transport chemicals to aquatic organisms after exposure to contaminated microplastics. In this review we apply lessons learned from the literature on microplastics in the aquatic environment and knowledge on current wastewater treatment technologies, with the aim of identifying the research gaps in terms of (i) the fate of microplastics in WWTPs, (ii) the potential interaction of wastewater-based microplastics with trace organic contaminants and metals, and (iii) the risk for aquatic organisms

Environmentally relevant concentrations of polyethylene microplastics negatively impact the survival, growth and emergence of sediment-dwelling invertebrates

Microplastics are a widespread environmental pollutant in aquatic ecosystems and have the potential to eventually sink to the sediment, where they may pose a risk to sediment-dwelling organisms. While the impacts of exposure to microplastics have been widely reported for marine biota, the effects of microplastics on freshwater organisms at environmentally realistic concentrations are largely unknown, especially for benthic organisms. Here we examined the effects of a realistic concentration of polyethylene microplastics in sediment on the growth and emergence of a freshwater organism Chironomus tepperi. We also assessed the influence of microplastic size by exposing C. tepperi larvae to four different size ranges of polyethylene microplastics (1-4, 10-27, 43-54 and 100-126 mu m). Exposure to an environmentally relevant concentration of microplastics, 500 particles/kg(sediment), negatively affected the survival, growth (i.e. body length and head capsule) and emergence of C tepperi. The observed effects were strongly dependent on microplastic size with exposure to particles in the size range of 10-27 mu m inducing more pronounced effects. While growth and survival of C tepperi were not affected by the larger microplastics (100-126 mu m), a significant reduction in the number of emerged adults was observed after exposure to the largest microplastics, with the delayed emergence attributed to exposure to a stressor. While scanning electron microscopy showed a significant reduction in the size of the head capsule and antenna of C. tepperi exposed to microplastics in the 10-27 mu m size range, no deformities to the external structure of the antenna and mouth parts in organisms exposed to the same size range of microplastics were observed. These results indicate that environmentally relevant concentrations of microplastics in sediment induce harmful effects on the development and emergence of C. tepperi, with effects greatly dependent on particle size. (C) 2018 Elsevier Ltd. All rights reserved

Effects of polyethylene microplastics on the acute toxicity of a synthetic pyrethroid to midge larvae (Chironomus tepperi) in synthetic and river water

Microplastics are ubiquitous pollutants in the aquatic environment. However, our understanding of the interaction of chemicals, particularly synthetic pyrethroids, with microplastics and the potential toxic effects of sorbed contaminants on aquatic organisms under realistic conditions is still extremely limited. In this study, we examined whether the presence of polyethylene (PE) microplastics can affect the acute toxicity of the synthetic pyrethroid bifenthrin to an invertebrate Chironomus tepperi in both synthetic and river water. Bifenthrin alone was, as expected, acutely toxic to exposed larvae (LC50 of 0.5 mu g/L after 48 h exposure). The addition of microplastics to synthetic water significantly reduced the toxicity of bifenthrin (apparent LC50 = 1.3 mu g/L), most likely because sorption of bifenthrin to microplastics reduced its bioavailability to the exposed larvae. A sorption capacity experiment showed that >92% of bifenthrin was sorbed to microplastics. In river water containing 9.6 mg/L organic carbon, bifenthrin alone was less toxic (LC50 = 1.3 mu g/L) than in synthetic water. Strikingly, the addition of microplastics to river water did not mitigate bifenthrin toxicity (apparent LC50 = 1.4 mu g/L), most likely due to greater interaction of bifenthrin with organic carbon than with microplastics. While PE microplastics reduced the negative effects of bifenthrin in synthetic water, the presence of organic carbon in river water without microplastics also reduced toxicity. This suggests that while sorption of contaminants to microplastics does occur, it may not be as relevant under environmentally realistic conditions with mg/L concentrations of organic matter. (C) 2019 Elsevier B.V. All rights reserved

Microplastics profile in constructed wetlands : Distribution, retention and implications

Wastewater and stormwater are both considered as critical pathways contributing microplastics (MPs) to the aquatic environment. However, there is little information in the literature about the potential influence of constructed wetlands (CWs), a commonly used wastewater and stormwater treatment system. This study was conducted to investigate the abundance and distribution of MPs in water and sediment at five CWs with different influent sources, namely stormwater and wastewater. The MP abundance in the water samples ranged between 0.4 ± 0.3 and 3.8 ± 2.3 MP/L at the inlet and from 0.1 ± 0.0 to 1.3 ± 1.0 MP/L at the outlet. In the sediment, abundance of MPs was generally higher at the inlet, ranging from 736 ± 335 to 3480 ± 4330 MP/kg dry sediment and decreased to between 19.0 ± 16.4 and 1060 ± 326 MP/kg dry sediment at the outlet. Although no significant differences were observed in sediment cores at different depth across the five CWs, more MPs were recorded in silt compared to sandy sediment which indicated sediment grain size could be an environmental factor contributing to the distribution of MPs. Polyethylene terephthalate (PET) fibres were the dominant polymer type found in the water samples while polyethylene (PE) and polypropylene (PP) fragments were predominantly recorded in the sediment. While the size of MPs in water varied across the studied CWs, between 51% and 64% of MPs in the sediment were smaller than 300 μm, which raises concerns about the bioavailability of MPs to a wider range of wetland biota and their potential ecotoxicological effects. This study shows that CWs can not only retain MPs in the treated water, but also become sinks accumulating MPs over time.</p

Analysis of the literature shows a remarkably consistent relationship between size and abundance of microplastics across different environmental matrices

Microplastics come in a variety of shapes, polymer types and sizes. Due to the lack of a harmonised approach to analyse and quantify microplastics, there are huge disparities in size detection limits and size classifications used in the literature. This has caused large variations in reported microplastic data and has made comparing microplastic abundance between studies extremely challenging. Herein, we applied a simple mathematical approach that allows for a meaningful comparison between size and abundance (number of particles) of microplastics irrespective of the size classifications used. This method was validated using two separate datasets (microplastics in air and sediment) and applied to re-analyse 127 publications reporting microplastics in various environmental matrices. We demonstrate a strong negative linear relationship between microplastic concentrations and their sizes with comparable slopes across all matrices. Using this method, it is possible to compare the concentration of microplastics of various sizes between studies. It also allows estimation of the abundance of microplastics of a specific size where data are not available. This enables researchers to predict environmentally relevant concentrations of microplastics (particularly for smaller microplastics) and provide realistic exposure scenarios in future toxicity studies, which will greatly improve our understanding of the risks that microplastics pose to living organisms