Evaluation of ecological impacts with ferrous iron addition in constructed wetland under perfluorooctanoic acid stress.

In this study, ferrous ion (Fe(II)) had the potential to promote ecological functions in constructed wetlands (CWs) under perfluorooctanoic acid (PFOA) stress. Concretely, Fe(II) at 30 mg/L and 20-30 mg/L even led to 11.37% increase of urease and 93.15-243.61% increase of nitrite oxidoreductase respectively compared to the control. Fe(II) promotion was also observed on Nitrosomonas, Nitrospira, Azospira, and Zoogloea by 1.00-6.50 folds, which might result from higher expression of nitrogen fixation and nitrite redox genes. These findings could be explanation for increase of ammonium removal by 7.47-8.75% with Fe(II) addition, and reduction of nitrate accumulation with 30 mg/L Fe(II). Meanwhile, both Fe(II) stimulation on PAOs like Dechloromonas, Rhodococcus, Mesorhizobium, and Methylobacterium by 1.58-2.00 folds, and improvement on chemical phosphorus removal contributed to higher total phosphorus removal efficiency under high-level PFOA exposure. Moreover, Fe(II) raised chlorophyll content and reduced the oxidative damage brought by PFOA, especially at lower dosage. Nevertheless, combination of Fe(II) and high-level PFOA caused inhibition on microbial alpha diversity, which could result in decline of PFOA removal (by 4.29-12.83%). Besides, decrease of genes related to nitrate reduction demonstrated that enhancement on denitrification was due to nitrite reduction to N2 pathways rather than the first step of denitrifying process.

Modified basalt fibers boost performance of constructed wetlands: Comparison between surface coating and chemical grafting.

Modified basalt fiber (MBF) is a potential material that has been applied in wastewater treatment fields. In this study, superior performances of MBFs by calcium (Ca-MBF) and polyethyleneimine modification (PEI-MBF) were compared in constructed wetlands (CWs). Via chemical grafting, higher biofilm contents were observed on the surface of PEI-MBF, compared to Ca-MBF. Moreover, MBF increased key enzyme activities particularly in lower substrate layer, contributing to positive responses of microbial community in CWs. For instance, PEI-MBF boosted microbial richness and diversity and improved the abundances of denitrifying functional bacteria and biomarkers like Thauera, Vulcanibacillus, and Maritimimonas, probably promoting nitrate removal compared with Ca-MBF group. By contrast, Ca-MBF enriched more functional genera involved in nutrients removal, with the highest removal of ammonium (43.9 %), total nitrogen (66.2 %), and total phosphorus (37.1 %). Overall, this work provided new findings on improved performance of CWs with MBF.

Comparison of eco-improvement on constructed wetlands with nano zero valent iron introduction under different levels of PFOA stress: Perspectives on plant, microbe, and PFOA removal.

The ecological hazards of perfluoro octanoic acid (PFOA, a typical perfluoroalkyl substances) have been continually reported in constructed wetlands (CWs) for wastewater treatment. In present study, nano zero valent iron (nZVI) was adopted to alleviate PFOA stress at different levels (1 and 10 mg/L) in CWs. It was revealed that the effects of nZVI on specific ecological parameters varied at different PFOA dosages. PFOA influenced plant photosynthetic and antioxidant parameters with significant concentration-dependence. NZVI addition caused more obvious promotion of chlorophyll (25.30-31.84 %) and reduction of catalase (172.64 %) and malondialdehyde (83.01 %) with 10 mg/L PFOA exposure. For microbe, nZVI was prone to stimulate enzyme activities under 1 mg/L PFOA, in which the relative activity of dehydrogenase, urease, phosphatase, and four nitrogen cycling enzymes increased by 86.25-375.56 %, 43.10-71.16 %, 1.52-29.38 %, and 4.49-315.18 %. However, nZVI caused more abundant of functional bacteria (like nitrifying bacteria and phosphorus-accumulating organisms) and function genes (like amoA, hao, and ppx) with PFOA at 10 mg/L. On the whole, changes in bacterial community confirmed the enhancement potential of nZVI on ammonium and phosphorous removal. PFOA removal at 10 mg/L was higher compared to 1 mg/L, resulting from higher abundance of class Gammaproteobacteria, and nZVI addition further contributed to the highest removal efficiency (73.54 %). This study provided evidence on nZVI as a possible manner for optimizing eco-function in CWs with PFOA stress at different levels.

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.

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.

Ecological restoration performance enhanced by nano zero valent iron treatment in constructed wetlands under perfluorooctanoic acid stress.

Perfluorooctanoic acid (PFOA) of widespread use can enter constructed wetlands (CWs) via migration, and inevitably causes negative impacts on removal efficiencies of conventional pollutants due to its ecotoxicity. However, little attention has been paid to strengthen performance of CWs under PFOA stress. In this study, influences of nano zero valent iron (nZVI), which has been demonstrated to improve nutrients removal, were explored after exemplifying threats of PFOA to operation performance in CWs. The results revealed that 1 mg/L PFOA suppressed the nitrification capacity and phosphorus removal, and nZVI distinctly improved the removal efficiency of ammonia and total phosphorus in CWs compared to PFOA exposure group without nZVI, with the maximum increases of 3.65 % and 16.76 %. Furthermore, nZVI significantly stimulated dehydrogenase (390.64 % and 884.54 %) and urease (118.15 % and 246.92 %) activities during 0-30 d and 30-60 d in comparison to PFOA group. On the other hand, nitrifying enzymes were also promoted, in which ammonia monooxygenase increased by 30.90 % during 0-30 d, and nitrite oxidoreductase was raised by 117.91 % and 232.10 % in two stages. Besides, the content of extracellular polymeric substances (EPS) under nZVI treatment was 72.98 % higher than PFOA group. Analyses of Illumina Miseq sequencing further certified that nZVI effectively improved the community richness and caused the enrichment of microorganisms related to nitrogen and phosphorus removal and EPS secreting. These results could provide valuable information for ecological restoration and decontamination performance enhancement of CWs exposed to PFOA.

Iris pseudacorus as precursor affecting ecological transformation of graphene oxide and performance of constructed wetland.

The role of plants is largely unknown in constructed wetlands (CWs) exposed to phytotoxic nanomaterials. Present study investigated transformation of graphene oxide (GO) and performance of CWs with Iris pseudacorus as precursor. GO was trapped by CWs without dependence on plants. GO could move to lower substrate layer and present increases on defects/disorders with stronger effects in planted CW. Before adding GO, planted CW achieved better removal both of phosphorus and nitrogen. After adding GO, phosphorus removal in planted CW was 93.23-95.71% higher than 82.55-90.07% in unplanted CW. However, total nitrogen removal was not improved, showing 48.20-56.66% and 53.44-56.04% in planted and unplanted CWs. Plant improved urease, phosphatase, and arylsulfatase, but it decreased ß-glucosidase and had less effects on dehydrogenase and catalase. Pearson correlation matrix revealed that plant enhanced microbial interaction with high degree of positive correlation. Moreover, there were obvious shifts in microbial community at phylum and genus level, which presented closely positive action on substrate enzyme activities. The functional profile was less affected due to functional redundancy in microbial system, but time effects were obvious in CWs, especially in planted CW. These findings could provide the basis on understanding role of plants in CWs for treating nanoparticles wastewater.

Unveiling changes of microbial community involved in N and P removal in constructed wetlands with exposing to silver nanoparticles.

Constructed wetlands (CWs) are environmentally friendly engineered systems to purify wastewater, with low-cost and easy maintenance. However, it is not clear on responses of functional microbes for nitrogen (N) and phosphorus (P) biotransformation in CWs to silver nanoparticles (Ag NPs). The high throughput sequencings were employed to reveal microbial communities in vertical flow subsurface CWs with stable operation for 120 days. The results indicated that NH4+-N, TN and TP removal of soil layer decreased by 43.56%, 15.7% and 22.7% under stress of Ag NPs. Microbial richness index and compositions were affected, and control wetland enriched Sulfurospirillum, Desulfarculaceae and Flavobacterium whereas CWs exposed to Ag NPs enriched Desulfosporosinus and Desulfurispora from LEfSe analysis. Moreover, after dosing Ag NPs, relative abundances of functional genes amoA and hao for nitrification, nirK and norB for denitrification and ppx and phoA/phoD for phosphorus conversions in upper soil were significantly downregulated. Inhibition on functional bacteria and genes of Ag NPs explained poor removal efficiencies of nitrogen and phosphorus pollutants in CWs. Our findings give an insight into ecological toxicity of Ag NPs on CWs with N and P bioconversions and provide the understanding of response of nitrifiers, denitrifies and PAOs.

Response of constructed wetland for wastewater treatment to graphene oxide: Perspectives on plant and microbe.

The wide application of graphene oxide (GO) increases its release into environment with less known on environmental effects. This work investigated 120-day interaction between GO (500 and 5000 µg/L) and constructed wetlands (CWs) planted with Iris pseudacorus. CWs showed the effective retention for GO via mature biofilm but less biodegradation. GO significantly induced enzyme activities (urease, neutral phosphatase, and catalase), which was attributed to increases in ecological association and enzyme abundance. GO decreased microbial biomass on day 30, but it had no impacts on day 120. The microbial community showed gradual self-adaption with time due to protection of antioxidant defense system (L-ascorbate oxidase, superoxide reductase, and glutathione related enzyme). The antioxidant enzymes (superoxide dismutase and peroxidase) and lipid peroxidation of Iris pseudacorus were increased by GO, accompanied by reduction on chlorophyll biosynthesis. Overall, the separate effects of GO on micro-regions and individual bodies in CWs were obvious, but it was acceptable that variations in pollutant removal were not evident due to synergetic role of plant-substrate-microbe. Organic matter and phosphorus removals reached to above 93%, and ammonia and total nitrogen removals in GO groups were reduced by 7-8% and 9-13%, respectively.

Comprehensive metagenomic and enzyme activity analysis reveals the negatively influential and potentially toxic mechanism of polystyrene nanoparticles on nitrogen transformation in constructed wetlands.

The widespread use of nanoplastics inevitably leads to their increasing emission into constructed wetlands (CWs). However, little is known about the impacts of nanoplastics on nitrogen transformation in CWs. In this study, the influence of polystyrene nanoparticles (PS NPs), one of the most widely used plastics, on the nitrogen transformation in CWs was comprehensively investigated, and the influential and toxic mechanism was evaluated through metagenomic analysis (DNA level) and key enzyme activities (protein level) related to N-transformation metabolism and antioxidant systems. The results showed that over 97% of PS NPs were retained in CWs, and the biofilm of sand was the main sink of PS NPs. Exposure to 1 and 10 mg/L PS NPs suppressed the nitrogen transformation, causing a certain degree of inhibition in TN removal, especially in the relatively short term of the exposure experiment (p < 0.05). At the protein level, 1 and 10 mg/L PS NPs negatively affect enzyme activities involved in denitrification (nitrate reductase and nitrite reductase) and electron transport system activity (ETSA). In contrast, 10 mg/L of PS NPs significantly suppressed the activities of nitrifying enzymes (ammonia monooxygenase, hydroxylamine dehydrogenase and nitrite oxidoreductase), whereas 1 mg/L PS NPs showed no impacts on nitrifying enzymes. Metagenomic analysis further certified that PS NPs restrained the relative abundances of genes involved in nitrogen transformation including nitrification and denitrification biochemical metabolisms (the electron production, electron transport and electron consumption processes). It also indicated that PS NPs could affect nitrogen transformation by reducing the abundance of genes for electron donor and ATP production involved in carbon metabolism (glycolysis and tricarboxylic acid cycle metabolism). In our study, the potential toxic mechanisms of PS NPs attributed to over production of reactive oxygen species and variations of antioxidant systems in macrophytes and microorganisms. These results provided valuable information for evaluating the impacts of PS NPs on CWs and arouse more attention to their impacts on the global geochemical nitrogen and carbon cycles.

Hydraulic flow direction alters impacts of AgNPs on pollutant removal and silver spatial distribution in vertical flow constructed wetlands.

This study investigated the effects of AgNPs on pollutant removals in constructed wetlands (CWs) with different flow patterns and spatial distributions of silver. Before exposure to AgNPs, upward flow constructed wetland (UCW) had better nitrogen removal than down-flow CW (DCW). And 0.5 mg/L AgNPs evidently inhibited nitrogen and phosphorus removal, including ammonia, nitrate, and TP (total phosphorus), with average effluent concentrations increasing by 70.83% of NH4+-N in UCW, 18.75% of TP in UCW, and 28.33% and 25.06% of NO3--N in DCW and UCW, respectively, while COD (chemical oxygen demand) was not affected. Moreover, presence of 2 mg/L AgNPs slightly inhibited organic compounds and NH4+-N removal in two systems during stage 4 (dosing 2 mg/L AgNPs). However, the response of NO3--N and TN removal to 2 mg/L AgNPs in two systems were different, and nitrogen concentrations in effluent at the end of stage 4 significantly increased in DCW. Addition of 2 mg/L AgNPs significantly affected TP removal in two systems. Two wetlands showed high removal efficiencies of about 98% on AgNPs, indicating that CWs could provide a feasible approach for ecological restoration of nanoparticles pollution. This study also found that AgNPs mainly accumulated in the upper layer with the Ag content of 17.55-20.26 mg/kg dry weight in sand layer and 7.25-10.85 mg/kg dry weight in gravel layer. Plant roots absorbed AgNPs, with Ag content at 50.80-101.40 mg/kg and bioconcentration factors 2.80-5.00. The obtained results showed that up-flow CWs had better performance and higher resistance to the exposure of AgNPs pollution, compared with down-flow CWs.

Impacts of Ag and Ag2S nanoparticles on the nitrogen removal within vertical flow constructed wetlands treating secondary effluent.

In this study, the effects of silver (Ag NPs) and sliver sulfide nanoparticles (Ag2S NPs) on nitrogen removal and nitrogen functional microbes in constructed wetlands were investigated. The obtained results demonstrated that inhibition extent on nitrogen removal relied on NPs types and high concentrations NPs showed higher negative effects. 0.5 mg/L Ag NPs had no influence on NH4+-N removal, amoA and nxrA gene copies, whereas Ag2S NPs and Ag+ decreased NH4+-N removal by reducing abundances of nitrifying genes. The concentrations of NO3--N and TN in all 0.5 mg/L obviously increased compared with control, resulting from decreasing functional genes and denitrifying bacteria. And 0.5 mg/L Ag NPs exhibited largest inhibitory effects, with the highest NO3--N effluent concentrations. 2 mg/L Ag NPs decreased NH4+-N removal, but adverse effects gradually vanished with extension of time, whereas both Ag2S NPs and Ag+ at 2 mg/L influenced NH4+-N transformation and decreased the abundance of amoA and nxrA genes and the AOB Nitrosomonas in CWs. Moreover, 2 mg/L of Ag NPs reduced NO3--N removal by decreasing abundance of nirS and key denitrifying bacteria. To sum up, the inhibition mechanisms concluded from current results were possibly in that Ag NPs exhibited nanotoxicity rather than ionic toxicity.

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.

Effects of PVP-coated silver nanoparticles on enzyme activity, bacterial and archaeal community structure and function in a yellow-brown loam soil.

The undesirable effects of silver nanoparticles (AgNPs) on soil environment have caused much concern. The previous studies, however, focused on sandy soil, with little known on others. In present study, the effects of polyvinylpyrrolidone-coated AgNPs (0, 1, 10, and 100 mg kg- 1 soil) on enzyme activities (urease and dehydrogenase), ammonia-oxidizing bacteria (AOB) and archaea (AOA), bacterial and archaeal communities, and microbial function profile in a yellow-brown loam soil were investigated. The significant dose-response inhibitions of AgNPs on enzyme activities were observed, with dehydrogenase more susceptible to AgNPs. Both of bacterial and archaeal amoA genes were reduced by AgNPs above 10 mg kg- 1, with AOB more susceptible to AgNPs than AOA. AgNPs at 100 mg kg- 1 caused reductions on the dominant Nitrosospira and Nitrosomonas, and even disappearance on Nitrosovibrio, while increase on Nitrososphaera significantly. AgNPs also changed bacterial and archaeal community structure. Exposure to AgNPs at 100 mg kg- 1 caused significant increases by 186.79% and 44.89% for Bacteroidetes and Proteobacteria, while decreases by 47.82%, 44.09%, 43.67%, and 80.44% for Actinobacteria, Chloroflexi, Planctomycetes, and Verrucomicrobia, respectively. Moreover, three dominant archaeal phyla (Thaumarchaeota, Euryarchaeota, and Parvarchaeota) were also reduced in the presence of AgNPs, especially Thaumarchaeota with the significant reduction of 13.71%. PICRUSt prediction revealed that AgNPs indeed had the potential to change soil microbial community's functional contributions. It must be cautious on the interference of AgNPs to soil ecological functions in the future.

Long-term effects of silver nanoparticles on performance of phosphorus removal in a laboratory-scale vertical flow constructed wetland.

Silver nanoparticles (AgNPs) have been widely used in many fields, which raised concerns about potential threats to biological sewage treatment systems. In this study, the phosphorus removal performance, enzymatic activity and microbial population dynamics in constructed wetlands (CWs) were evaluated under a long-term exposure to AgNPs (0, 50, and 200 µg/L) for 450 days. Results have shown that AgNPs inhibited the phosphorus removal efficiency in a short-term exposure, whereas caused no obviously negative effects from a long-term perspective. Moreover, in the coexisting CW system of AgNPs and phosphorus, competition exhibited in the initial exposure phase, however, cooperation between them was observed in later phase. Enzymatic activity of acid-phosphatase at the moderate temperature (10-20°C) was visibly higher than that at the high temperature (20-30°C) and CWs with AgNPs addition had no appreciable differences compared with the control. High-throughput sequencing results indicated that the microbial richness, diversity and composition of CWs were distinctly affected with the extension of exposure time at different AgNPs levels. However, the phosphorus removal performance of CWs did not decline with the decrease of polyphosphate accumulating organisms (PAOs), which also confirmed that adsorption precipitation was the main way of phosphorus removal in CWs. The study suggested that AgNPs and phosphorus could be removed synergistically in the coexistence system. This work has some reference for evaluating the influences of AgNPs on the phosphorus removal and the interrelation between them in CWs.

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.

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.

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.

Comparison of Iris pseudacorus wetland systems with unplanted systems on pollutant removal and microbial community under nanosilver exposure.

Rapidly developing industry raises concerns about the environmental risks of silver nanoparticles (AgNPs), but the effects of AgNPs on the performance and microbial community in the constructed wetlands remain unclear. In this study, long-term exposure of AgNPs in two VFCWs was conducted to determine the effects of AgNPs on the pollutant removal and microbial community structure. Before exposing AgNPs, the water quality of effluent was better in planted wetland (CW2), compared with unplanted wetland (CW1). After continuous exposure of 100µg/L AgNPs, the COD (chemical oxygen demand) removal of two CWs had no difference. However, addition of AgNPs reduced the nitrogen and phosphorus removal in two CWs, with decreasing average removal efficiencies of ammonia nitrogen from 46.31% to 32.09% and 59.66% to 51.06%, total nitrogen from 57.76% to 43.78% and 67.35 to 60.58%, total phosphorus from 71.29% to 59.31% and 67.35% to 60.58%, respectively. The vegetable wetlands showed higher resistances to AgNPs loading than unplanted wetlands. In addition, AgNPs accumulated in the wetland substrate, especially in the soil layer with the silver concentration of approximately 4.32µg/g. The small portion of silver was found in plant tissues, and plants played a minor role to remove the AgNPs from wastewater. Moreover, the constructed wetlands could effectively remove the AgNPs from the synthetic wastewater. The illumine high-throughput sequencing results demonstrated the variations of the bacterial community structure at the exposure of AgNPs. The results showed that the dominant phyla were Proteobacteria, Acidobacteria and Bacteroidetes. Compared with unplanted wetlands, the contents of several nitrifying bacteria such as Candidatus Nitrososphaera (AOA) and Nitrospira (NOB) at genus level increased, leading to the higher nitrogen removal in the planted wetlands.

Shifts of system performance and microbial community structure in a constructed wetland after exposing silver nanoparticles.

The increasing utilization of silver nanoparticles (Ag NPs) in industry and commerce inevitably raises its release into wastewater. In this work, effects of Ag NPs on system performance and microbial community along the way of a vertical flow constructed wetland (VFCW) were investigated, along with the removal and fate of Ag NPs within the system. Results showed that the performance of control wetland kept stable during the experimental period, and the top substrate layer (soil layer) of wetland could remove most of pollutants in the influent. The study also suggested that addition of Ag NPs did not significantly affect organic matters removal. However, adverse effects were observed on the nitrogen and phosphorus removal. Removal efficiencies of TN, NH4+-N and TP approximately obviously reduced by approximately 10.10%, 8.42% and 28.35% respectively in contrast to before dosing after exposing 100 µg/L Ag NPs for 94 d, while the no dosing wetland with the stable performance. It was found that Ag NPs accumulated in the upper soil layer more than in the lower soil layer, and Ag NPs could enter into the plant tissues. After continuous input of Ag NPs, removal efficiency of Ag NPs was measured as 95.72%, which showed that the CW could effectively remove Ag NPs from the wastewater. The high-throughput sequencing results revealed that Ag NPs caused the shifts in microbial community structures and changed the relative abundances of key functional bacteria, which finally resulted in a lower efficiency of biological nitrogen and phosphorus removal.