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.

The fate and behavior of perfluorooctanoic acid (PFOA) in constructed wetlands: Insights into potential removal and transformation pathway.

Although constructed wetland (CW) technology is widely used to eliminate emerging organic pollutants, the removal pathway of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in CW system have not been fully understood yet. This study aims to deeply probe into the fate and behavior of perfluorooctanoic acid (PFOA) in CW system. Findings indicated that the removal efficiency of PFOA by CW system was 49.69-73.63 % with initial concentrations at 100-1000 µg/L. Substrate was the main "sink" of PFOA into the CWs (46.22-50.83 %), and the plant uptake (1.99-2.48 %) accounted for a small proportion. Transformation products in the effluent of CW systems included a series of short-chain perfluorinated carboxylic acids (PFCAs), hydrogen-containing perfluoroalkanes and other organic fluorides. Activated pathways of xenobiotics biodegradation suggested that enzyme-mediated biochemical reactions might be responsible for the PFOA transformation. The transformation pathway included enzymatic decarboxylation, hydroxylation, hydrolysis, dehydrogenation and dehalogenation, as well as non-enzymatic reactions. These discoveries provide new insights into the in-depth understanding environmental behavior of PFOA in ecosystem and lay the foundation for further ecological remediation.

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.

Evaluation of the ecological impacts of short- and long-chain perfluoroalkyl acids on constructed wetland systems: Perfluorobutyric acid and perfluorooctanoic acid.

Perfluoroalkyl substances (PFASs) contamination of aquatic system has attracted widespread attention in recent years. From both plant and microbial perspectives, the ecological risk of CWs by comparing PFASs with different chain lengths have not been fully understood. In this study, the influences of perfluorobutyric acid (PFBA) and perfluorooctanoic acid (PFOA) as typical of short- and long-chains on the ecological effect of CWs have been specifically studied. The results showed that plants produced oxidative stress response and the activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves were stimulated by 17.23-28.13% and 10.49-14.17% upon 10 mg/L PFBA and PFOA exposure. Under the high level of PFBA and PFOA stress, the chlorophyll content was reduced by 15.20-39.40% and lipid peroxidation was observed in leaves with the accumulation of malondialdehyde (MDA) at 1.20-1.22 times of the control. Dehydrogenase (DHA) exhibited the most sensitivity in the presence of PFBA and PFOA with an inhibition ratio of over 90%. The biotoxicity of PFOA was higher than that of PFBA in terms of the inhibition degree of several substrate enzymes. The information of Illumina Miseq sequencing indicated that the diversity and structure of microbial community in CWs were significantly altered by PFBA and PFOA addition and led to an enrichment of more PFASs-tolerant bacteria.

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.