Removal and fate of silver nanoparticles in lab-scale vertical flow constructed wetland

Performance of vertical flow constructed wetland for the treatment of effluent from a brassware industry in city of Fez, Morocco: a laboratory scale study

Brassware industry constitutes the second most polluting industrial sector in Fez city, Morocco, owing to its high heavy metal load. The aim of this study is to examine and evaluate the performance of vertical flow constructed wetlands in treating brassware effluents using various plant species. Ten treatment systems were planted with four types of plants: Chrysopogon zizanioides, Typha latifolia, Phragmites australis, and Vitex agnus-castus, while another system remained unplanted. These systems underwent evaluation by measuring various parameters, including pH, electrical conductivity, suspended solids, chemical oxygen demand, biological oxygen demand, sulfates, orthophosphates, total Kjeldhal nitrogen, ammonium, nitrates, nitrites, and heavy metals such as silver, copper, and nickel, using standard methods over of ten weeks. The results obtained demonstrate effectiveness of these systems. When planted with Ch. zizanioides, the systems achieved elimination rates of 83.64%, 98.55%, 91.48%, 86.82%, 80.31%, 96.54%, 98%, and 98.82% for suspended solids, ammonium, nitrites, BOD5, sulfates, orthophosphates, silver, and nickel, respectively. System with V. agnus-castus showed significant reductions in nitrate and copper, with rates of 84.48% and 99.10%, respectively. Considerable decrease in pH and electrical conductivity values was observed in all systems, with a notable difference between planted and control systems regarding effectiveness of treatment for other parameters.

Performance of constructed wetlands with different water level for treating graphene oxide wastewater: Characteristics of plants and microorganisms

Constructed wetlands (CWs) have been expected advantages in emerging pollutant removal, but with less known on their characteristic when treating wastewater containing graphene oxide (GO). In present study, we investigated characteristics of Iris pseudacorus, microorganisms, and pollutant removal in CWs with 60 cm and 37 cm water level (termed HCW and LCW). Plants in LCW had higher chlorophyll content and lower activities of antioxidant enzyme (superoxide dismutase, catalase, peroxidase) as well as malondialdehyde content. Substrate enzyme activities were affected by time and CW type. LCW increased only dehydrogenase activities, while HCW increased catalase, urease, neutral phosphatase, and arylsulfatase activities. Sequencing analysis revealed that microbial community showed higher richness and diversity in LCW, but this dissimilarity could be eased by time-effect. Proteobacteria (25.62-60.36%) and Actinobacteria (13.86-56.20%) were stable dominant phyla in CWs. Ratio of Proteobacteria/Acidobacteria indicated that trophic status of plant rhizosphere zone was lower in LCW. Nitrospirae were enriched to 0.16-0.68% and 0.75-1.42% in HCW and LCW. The enrichment of phyla Proteobacteria and Firmicutes in HCW was attributed to class Gammaproteobacteria and genus Enterococcus. GO transformation showed some reductions in CWs, which could be affected by water depth and substrate depth. Overall, HCW achieved nitrogen and phosphorus removal for 48.78-62.99% and 95.01%, which decreased by 8.41% and 7.31% in LCW. COD removal was less affected reaching 93%. This study could provide some new evidence for CWs to treat wastewater containing GO.

Long-term synergic removal performance of N, P, and CuO nanoparticles in constructed wetlands along with temporal record of Cu pollution in substrate-biofilm

With continued exposure to CuO nanoparticles (NPs) which were toxic to organisms, the performance of wastewater treatment facility might be affected. In present study, the feasibility of constructed wetlands (CWs) for wastewater treatment containing CuO NPs and common pollutants was comprehensively explored. It was found that CWs removed 98.80-99.84% CuO NPs and 90.91-91.83% COD within 300 days. However, N and P removals were affected to varying degrees by CuO NPs. N removal was inhibited only by 0.5 mg/L CuO NPs with 19.75% decreases on the mean from day 200-300. P removal was reduced by 3.80-50.75% and 1.92-7.19% under exposure of 0.5 and 5 mg/L CuO NPs throughout the experiment. Moreover, CuO NPs changed the adsorption potential of P and ammonium-N on sand-biofilm. Cu concentrations in spatial distribution decreased, while they in temporal distribution increased from 36.94 to 97.78 μg/g and from 70.92 to 282.66 μg/g at middle sand layer exposed to 0.5 and 5 mg/L CuO NPs. Mass balance model showed that substrate-biofilm was main pollutant sink for CuO NPs, N, and P. The minor Cu was absorbed by plants exposed to 0.5 and 5 mg/L CuO NPs, which decreased N by 53.40% and 18.51%，and P by 52.35% and 21.62%. Sequencing analysis indicated that CuO NPs also altered spatial microbial community. N-degrading bacteria (Rhodanobacter, Thauera, Nitrospira) changed differently, while phosphate accumulation organisms (Acinetobacter, Pseudomonas, Microlunatus) reduced. Overall, the negative effects of CuO NPs on N and P removal should be noted when CWs as ecological technologies are used to treat CuO NPs-containing wastewater.

Transcriptome analysis reveals the molecular mechanisms of Phragmites australis tolerance to CuO-nanoparticles and/or flood stress induced by arbuscular mycorrhizal fungi

The molecular mechanism of arbuscular mycorrhizal fungi (AMF) in vertical flow constructed wetlands (VFCWs) for the purification of copper oxide nanoparticles (CuO-NPs) contaminated wastewater remains unclear. In this study, transcriptome analysis was used to explore the effect of AMF inoculation on the gene expression profile of Phragmites australis roots under different concentrations of CuO-NPs and/or flood stress. 551, 429 and 2281 differentially expressed genes (DEGs) were specially regulated by AMF under combined stresses of CuO-NPs and flood, single CuO-NPs stress and single flood stress, respectively. Based on the results of DEG function annotation and enrichment analyses, AMF inoculation under CuO-NPs and/or flood stress up-regulated the expression of a number of genes involved in antioxidant defense systems, cell wall biosynthesis and transporter protein, which may contribute to plant tolerance. The expression of 30 transcription factors (TFs) was up-regulated by AMF inoculation under combined stresses of CuO-NPs and flood, and 44 and 44 TFs were up-regulated under single CuO-NPs or flood condition, respectively, which may contribute to the alleviating effect of symbiosis on CuO-NPs and/or flood stress. These results provided a theoretical basis for enhancing the ecological restoration function of wetland plants for metallic nanoparticles (MNPs) by mycorrhizal technology in the future.

Comparative analysis of upward and downward vertical flow constructed wetlands on the nitrogen removal and functional microbes treating wastewater containing Ag nanoparticles

This study investigated impacts of silver nanoparticles (AgNPs) on nitrogen removal within constructed wetlands (CWs) with different flow directions. The obtained results showed that addition of AgNPs at 0.5 and 2 mg/L significantly inhibited NH₄⁺-N removal, resulting from lower abundances of functional genes (amoA and nxrA) within CWs. And higher abundances of amoA and nxrA genes at 0.5 mg/L were observed in downward flow CW, leading to better NH₄⁺-N removal, compared to upward flow CW. Besides, nitrifying genes amoA and nxrA in upward flow CW at 2.0 mg/L exhibited higher than downward flow CW, explaining better NH₄⁺-N removal in upward flow CW. 0.5 mg/L AgNPs significantly declined NO₃^--N and TN removal, resulted from decreasing abundances of nirK, nirS and nosZ. In contrast, abundances of nirK, nirS and nosZ genes had slightly lower or higher than before adding AgNPs in upward flow CW, leading to lower NO₃^--N and TN effluent concentrations. High throughput sequencing also indicated the changes of functional bacterial community after exposing to AgNPs.

Aquatic Macrophytes in Constructed Wetlands: A Fight against Water Pollution

There is growing concern among health institutions worldwide to supply clean water to their populations, especially to more vulnerable communities. Although sewage treatment systems can remove most contaminants, they are not efficient at removing certain substances that can be detected in significant quantities even after standard treatments. Considering the necessity of perfecting techniques that can remove waterborne contaminants, constructed wetland systems have emerged as an effective bioremediation solution for degrading and removing contaminants. In spite of their environmentally friendly appearance and efficiency in treating residual waters, one of the limiting factors to structure efficient artificial wetlands is the choice of plant species that can both tolerate and remove contaminants. For sometimes, the chosen plants composing a system were not shown to increase wetland performance and became a problem since the biomass produced must have appropriated destination. We provide here an overview of the use and role of aquatic macrophytes in constructed wetland systems. The ability of plants to remove metals, pharmaceutical products, pesticides, cyanotoxins and nanoparticles in constructed wetlands were compared with the removal efficiency of non-planted systems, aiming to evaluate the capacity of plants to increase the removal efficiency of the systems. Moreover, this review also focuses on the management and destination of the biomass produced through natural processes of water filtration. The use of macrophytes in constructed wetlands represents a promising technology, mainly due to their efficiency of removal and the cost advantages of their implantation. However, the choice of plant species composing constructed wetlands should not be only based on the plant removal capacity since the introduction of invasive species can become an ecological problem.

Fate of environmental pollutants: A review

A review of the literature published in 2019 on topics associated with the fate of environmental pollutants is presented. Environmental pollutants covered include pharmaceuticals, antibiotic-resistant bacteria and genes, pesticides and veterinary medicines, personal care products and emerging pollutants, PFAS, microplastics, nanomaterials, heavy metals and radionuclides, nutrients, pathogens and indicator organisms, and oil and hydrocarbons. For each pollutant, the occurrence in the environment and/or their fate in engineered as well as natural systems in matrices including water, soil, wastewater, stormwater, runoff, and/or manure is presented based on the published literature. The review includes current developments in understanding pollutants in natural and engineered systems, and relevant physico-chemical processes, as well as biological processes.

Wetlands for environmental protection

This article presents an update on the research and practical demonstration of wetland-based treatment technologies for protecting water resources and environment covering papers published in 2019. Wetland applications in wastewater treatment, stormwater management, and removal of nutrients, metals, and emerging pollutants including pathogens are highlighted. A summary of studies focusing on the effects of vegetation, wetland design and operation strategies, and process configurations and modeling, for efficient treatment of various municipal and industrial wastewaters, is included. In addition, hybrid and innovative processes with wetlands as a platform treatment technology are presented.

Feasibility study of vertical flow constructed wetland for tertiary treatment of nanosilver wastewater and temporal-spatial distribution of pollutants and microbial community

Silver nanoparticles (AgNPs) have the potential to cause negative effects on nutrient removal in constructed wetlands (CWs), further leading to the deterioration of the water. The current work aimed to investigate the feasibility of vertical flow CW (VFCW) for tertiary treatment of AgNPs wastewater, temporal-spatial distribution of pollutants, and microbial community after 450-day exposure. Results reveal that the effluent of VFCW could still meet the discharge limits except the slightly excessive concentration of phosphorus (>0.5 mg/L) from day 390, with the average removal efficiencies of 83%, 61%, 42%, 70%, and 66% for the chemical oxygen demand, total nitrogen, ammonia nitrogen, total phosphorus, and soluble orthophosphate during 450 days, respectively. Results show that AgNPs removal was relatively stable over time, up to 96%. The temporal-spatial analysis reveals that all contaminants were mainly retained in the soil layer. The Ag concentrations in the upper soil layer and plant roots were higher than that in the lower soil layer and plant stems and leaves, respectively. Microbial sequencing analysis reveals the significant differences in the microbial community at different depths on day 450, with the dominant phyla of Proteobacteria, Acidobacteria, Chloroflexi and Bacteroidetes, and dominant genera of Halomonas and Pseudomonas. These results provide much needed knowledge for the implementation of ecological technologies for AgNPs and nutrient removal simultaneously.

Fate of silver nanoparticles in constructed wetlands and its influence on performance and microbiome in the ecosystems after a 450-day exposure

Great controversy still exists on the ecological effects of silver nanoparticles (AgNPs) especially at relatively low concentrations. The performance, fate of AgNPs and microbiome in CWs were evaluated under a long-term exposure to AgNPs (0, 50 and 200 µg/L) for 450 days. Results showed that AgNPs (50, 200 µg/L) caused no obviously negative effects on COD removal whereas nitrogen and phosphorus removals were slightly stimulated. AgNPs could be removed efficiently from wastewater attributed to the accumulations of soil and plant tissues. Mass balance of AgNPs was analysed and soil layer of CWs was the major sink of nanoparticles. High-throughput sequencing further revealed the impact of AgNPs on the ecological structure of CWs. Moreover, the presence of AgNPs altered the relative abundances of key functional bacteria. The ecological risks of persistent exposure to low concentrations AgNPs should not be ignored, even though it did not result in deterioration of the CWs' operating performance in our studies.

The response of nitrogen removal and related bacteria within constructed wetlands after long-term treating wastewater containing environmental concentrations of silver nanoparticles

The wide application of consumer products containing silver nanoparticles (AgNPs) inevitably results in their release into sewer systems and wastewater treatment plants, where they would encounter (and cause potential negative impacts) constructed wetlands (CWs), a complex biological system containing plants, substrate and microorganisms. Herein, the long-term effects of environmental AgNPs concentrations on nitrogen removal, key enzymatic activities and nitrogen-related microbes in constructed wetlands (CWs) were investigated. The short-term exposure (40 d) to AgNPs significantly inhibited TN and NH₄⁺-N removal, and the inhibition degree had a positive relationship with AgNPs levels. After about 450 d exposure, 200 μg/L AgNPs could slightly increase average TN removal efficiency, while presence of 50 μg/L AgNPs showed no difference, compared to control. The NH₄⁺-N removal in all CWs had no difference. The present study indicated that short-term AgNPs loading evidently reduced nitrogen removal, whereas long-term exposure to AgNPs showed no adverse impacts on NH₄⁺-N removal and slightly stimulated TN removal, which was related to the increase of corresponding enzymatic activities. After exposing AgNPs for 450 d, the abundance of relative functional genes and the composition of key community structure were determined by qPCR and high-throughput sequencing, respectively. The results showed that the abundance of amoA and nxrA dramatically higher than control, whereas the abundance of nirK, nirS, nosZ and anammox 16S rRNA was slightly higher than control, but had no statistical difference, which accorded with the TN removal performance. The microbial community analysis showed that different AgNPs concentrations could affect the microbial diversity and structure. The changes of the relative abundance of nitrogen-related genera were associated with the impacts of AgNPs on the nitrogen removal performance. Overall, the AgNPs loading had impacts on the key enzymatic activities, the abundance of nitrogen-related genes and microbial community, thus finally affected the treatment performance of CWs.