Search

Silver nanoparticles (AgNPs) has been widely detected in the substrates of constructed wetlands (CWs), posing threaten to pollutants removal efficiency of CWs. However, the way to alleviate the toxicity of AgNPs on CWs is unclear. In this study, the gravel (GR), biochar (BC), pyrite (PY) and pyrite coupled with biochar matrix (PYBC) were selected as substrates to restore the pollutants removal efficiency of CWs under the exposure to the environment (0.2 mg/L) and accumulation (10 mg/L) concentration of AgNPs. Results showed that the BC and PY showed limited mitigation effects, while the PYBC alleviated the toxicity significantly. Especially in the exposure to the accumulation concentration of AgNPs, the removal of NH 4 +-N, TN, COD and TP in the PYBC were 10.2%, 8.3%, 9.4% and 10.7% higher than that in the GR, respectively. Mechanism analysis verified that AgNPs were transformed into Ag–Fe–S core shell aggregates (size >200 nm) decreasing bioavailability and the damage to cytomembrane. The PYBC restored the nitrogen removal efficiency by increasing the abundance of Nitrospira and Geothrix , which these bacteria were defined as nitrifiers and Feammox bacteria. This study provides a promising strategy to mitigate AgNPs' toxicity on the pollutant removal efficiency in CWs. [Display omitted] • AgNPs inhibited nitrogen and carbon removal in CWs after 60-d exposure. • AgNPs damaged cytomembrane integrity and altered microbial co-occurrence pattern. • The bioavailability of AgNPs was reduced by pyrite coupled with biochar (PYBC). • AgNPs transformed into Ag–Fe–S core-shell aggregates easing the toxicity to microbe. • PYBC enriched nitrifier and Feammox bacteria to restore the nitrogen removal in CWs. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnO 2 was incorporated into PCL, forming NMCS, to enhance nitrogen removal in CWs. • NMCS reduced greenhouse gas emissions from CWs under high nitrogen loads. • NMCS promoted biological nitrogen removal pathways to reduce N 2 O accumulation. • Mn increased methanotrophs and dampened methanogenesis to reduce CH 4 emission. • Mn fostered plant photosynthesis to enhance CO 2 sequestration. Carbon deficits in inflow frequently lead to inefficient nitrogen removal in constructed wetlands (CWs) treating tailwater. Solid carbon sources, commonly employed to enhance denitrification in CWs, increase carbon emissions. In this study, MnO 2 was incorporated into polycaprolactone substrates within CWs, significantly enhancing NH 4 +-N and NO 3 –-N removal efficiencies by 48.26–59.78 % and 96.84–137.23 %, respectively. These improvements were attributed to enriched nitrogen-removal-related enzymes and increased plant absorption. Under high nitrogen loads (9.55 ± 0.34 g/m3/d), emissions of greenhouse gases (CO 2 , CH 4 , and N 2 O) decreased by 147.23–202.51 %, 14.53–86.76 %, and 63.36–87.36 %, respectively. N 2 O emissions were reduced through bolstered microbial nitrogen removal pathways by polycaprolactone and MnO 2. CH 4 accumulation was mitigated by the increased methanotrophs and dampened methanogenesis, modulated by manganese. Additionally, manganese-induced increases in photosynthetic pigment contents (21.28–64.65 %) fostered CO 2 sequestration through plant photosynthesis. This research provides innovative perspectives on enhancing nitrogen removal and reducing greenhouse gas emissions in constructed wetlands with polymeric substrates. [ABSTRACT FROM AUTHOR]

As widely used in many kinds of products, silver nanoparticles (AgNPs) are inevitably released into the aquatic environment. Constructed wetlands (CWs) are essential sinks of AgNPs, while little is known about the responses of microorganisms (biofilm on the substrate surface) and hydrophyte functions to AgNPs accumulation in CWs. Given that, we conducted a 60-day experiment exposing to 1 and 50 mg L−1 of AgNPs in CWs. Results revealed that AgNPs accumulation obviously decreased the relative abundance of genes involved in biofilm formation and microbial nitrogen metabolism, whereas increased those in the glycolysis process; AgNPs also decreased key enzyme activities corresponding to nutrient removal. In addition, AgNPs accumulation decreased the hydrophyte activity, causing a decline in the uptake ability of C (6%–44%), N (17%–54%), and P (14%–56%) elements. Finally, due to the decline in the whole biofilm and hydrophyte functions under AgNPs exposure, the treatment performance of CWs significantly decreased by 40%–56% of total nitrogen and 44%–60% of ammonia nitrogen, respectively. Overall, our results first revealed biofilm and hydrophyte's functional response to AgNPs exposure. We systematically analyzed the changes of vital functional modules of microorganisms based on the metagenomic analysis, as well as the functional emergency response of aboveground and underground tissues of hydrophyte in CWs under AgNPs stress. [Display omitted] • AgNPs accumulation synthetically damaged the metabolic function of the biofilm system. • AgNPs down-regulated the relative abundance of genes in the process of biofilm formation. • AgNPs altered the key enzyme activities of microorganisms and inhibited nitrogen removal. • The presence of AgNPs in plants weakened the photosynthesis and root activity. [ABSTRACT FROM AUTHOR]

Constructed wetlands (CWs) are a promising technique to mitigate trace organic contaminants (TrOCs). The current review used meta-analysis to investigate the TrOC removal in CWs on the basis of 92 selected paper and 2373 observations. The results indicated no regular trend shown for the TrOC removal by using logP ow or pKa, whereas TrOCs with molecular weight greater than 358.60 g mol−1 were found generally more recalcitrant than smaller molecules. It was found that solid–water distribution coefficient (logD) can be effective in distinguishing the readily removable TrOCs. Moreover, different patterns of TrOC removal were found correlated with CW conditions (i.e., CW type, CW scale, CW vegetation, and influent type and quality). By quadratic curves fittings, parameters including pH, DO, Eh, TrOC initial concentration, and CW operational time were found to determine the removal efficiency of TrOCs, whereas logD, COD, NH 4 +-N, and TP were found to be linked to TrOC removal only if the CW conditions were specified. These results also suggested that single factors can hardly determine the fate of TrOCs in CWs. However, some universal patterns could exist for the determination. More attention should be placed in diminishing the scale bias in the future. [Display omitted] • Designs and conditions of CWs were found to determine the fate of TrOCs in CWs. • Conditional parameters included logD, COD, NH 4 +-N, and TP. • Unconditional parameters included pH, DO, Eh, C i , and OT. • Parameter logD 3.2 was effective in distinguishing readily removable TrOCs in CWs. • A knowledge gap exists between small, lab scale and large, full scale studies. [ABSTRACT FROM AUTHOR]

• Plastic particles affect nitrogen removal while mitigating the release of N 2 O. • Large plastics reduce N 2 O release by impeding CO 2 assimilation and NH 2 OH reduction. • Nanoplastics affect N metabolism by disrupting N-ion transmembrane transport. • Nanoplastics block the key N-removing enzyme activity, hindering N 2 O production. Constructed wetlands (CWs) have been proven to effectively immobilize plastic particles. However, little is known about the differences in the impact of varying sized plastic particles on nitrous oxide (N 2 O) release, as well as the intervention mechanisms in CWs. Here, we built a lab-scale wetland model and introduced plastic particles of macro-, micro-, and nano-size at 100 μg/L for 370 days. The results showed that plastic particles of all sizes reduced N 2 O release in CWs, with the degrees being the strongest for the Nano group, followed by Micro and Macro groups. Meanwhile, 15N- and 18O-tracing experiment revealed that the ammoxidation process contributed the most N 2 O production, followed by denitrification. While for every N 2 O-releasing process, the contributing proportion of N 2 O in nitrification-coupled denitrification were most significantly cut down under exposing to macro-sized plastics and had an obvious increase in nitrifier denitrification in all groups, respectively. Finally, we revealed the three mechanism pathways of N 2 O release reduction with macro-, micro-, and nano-sized plastics by impacting carbon assimilation (RubisCO activity), ammonia oxidation (gene amo abundance and HAO activity), and N-ion transmembrane and reductase activities, respectively. Our findings thus provided novel insights into the potential effects of plastic particles in CWs as an eco-technology. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar at lower pyrolysis temperature achieved the higher nitrate removal (NR). • Activities of DHA, ETS, and denitrifying enzymes of CWs were increased by biochar. • Biochar enriched the genes encoding key enzymes in carbon and nitrate metabolism. • The O content, O/C ratio, and EDC of biochar were positively correlated with NR. Constructed wetlands (CWs) amended with biochar have attracted much attention for nitrate removal treating secondary effluent. However, little is acknowledged about the linkage among the nitrate removal performance, microbial metabolic pathway of nitrate, and biochar properties. Herein, biochars pyrolyzed under 300 °C, 500 °C, and 700 °C (BC300, BC500, and BC700, respectively) were used in CWs to reveal the relationship. Results showed that CWs amended with BC300 (59.73%), BC500 (53.27%), and BC700 (49.07%) achieved higher nitrogen removal efficiency, compared with the control (39.51%). Metagenomic analysis showed that biochars could enrich the genes, which encoded key enzymes (adenosine triphosphate production, and electrons generation, transportation, and consumption) involved in carbon and nitrate metabolism. Further, biochar pyrolyzed under lower temperature, with higher oxygen content, molar O/C ratio, and the electron donating capacity, in CWs could obtain higher nitrate removal efficiency. Overall, this research offers new understandings for the promotion of denitrification in CWs amended with biochar. [ABSTRACT FROM AUTHOR]

• Low level of MPs accumulation promoted nitrogen removal under 370-day exposure. • High level of MPs promoted the oxygen mass transfer and OUR for 370-day accumulation. • The microbial and material structure of biofilm attaching on MPs were different from gravel. • Low nitrification rate is a limited step for nitrogen removal of CWs for MPs accumulation. Presence of microplastics (MPs) in wastewater has posed a huge ecosystem risk. Constructed wetlands (CWs) can effectively intercept MPs, while with MPs accumulation the response of CWs' performance is still unclear. In order to evaluate those effects, we conducted a 370-day experiment using CW microcosms fed with different levels (0, 10, 100, and 1000 μg/L) of polystyrene (PS) MPs (diameter: 50−100 μm). Results showed that nitrogen removal efficiency was increased (by 3.9%−24.7%) during the first 60 days and then decreased (by 7.1%−41.3%) with MPs accumulating, but no obvious change in COD and TP removal was observed. From further analysis, MPs accumulation changed the biofilm composition (TOC content increased from 41.4% to 52.7%), substrate porosity (electrical resistivity increased by 1.2–2.4 folds), and oxygen mass transfer (| K L a , O 2 | increased from 3.5% to 18.6%). Moreover, the microbial dynamics presented a higher abundance of nitrifiers (Nitrospira and Nitrosomonas) during the 60-day experiment and a lower abundance in the last days, while denitrifiers (Thauera, Thiobacillus , and Anaerolinea) had a high relative abundance throughout the experiment, being consistent with the variation of nitrification and denitrification rates. Finally, structural equation model analysis proved that due to the changes of substrate characteristics and microbial compositions and activities, the obvious decrease in nitrification efficiency was a direct reason for the decline of nitrogen removal during 370-day MPs accumulation. Overall, our study first prove that MPs accumulation can cause a series of changes in physicochemical and microbial characteristics of substrate, and ultimately affect the nitrogen-transforming process in CWs. Although our conclusions were based on the lab-scale CWs being different from the real wetlands, we hope that the conclusions can provide the effective regulatory strategies to guide the control of MPs in the actual wetlands. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The sustainable reuse of sludge and wetland macrophyte litter was realized. • SBC and CBC promoted nutrient removal and reduced N 2 O emissions fluxes in CWs. • Biochar-derived DOM can supplement carbon source for denitrification in CWs. • SBC significantly enhanced the key enzyme activities and ETSA in CWs. • Biochar enhanced the enrichment of nitrogen and phosphorus removing microorganisms. Constructed wetlands (CWs) are widely used to treat the effluent of wastewater treatment plants (WWTPs) due to their energy-saving and environmentally friendly advantages. Wetland macrophyte litter and sludge are wastes produced by CWs and WWTPs, respectively. However, there are few studies on the reuse of sludge and macrophyte litter as CW filling materials. In this study, sewage sludge and cattail litter were selected as raw materials to prepare biochar, which was used as CW filling materials to enhance the advanced treatment of secondary effluent. The results showed that the sludge biochar CWs (SBC-CWs) and the cattail biochar CWs (CBC-CWs) possessed better total nitrogen removal efficiency (91% and 81%, respectively) compared with the control (67%). Furthermore, SBC-CWs significantly improved total phosphorus removal efficiency by 20% than that of the control (p < 0.05), and reduced nitrous oxide emissions by 66% compared with the control (p < 0.05). The dissolved organic matter (DOM) released in the biochar was beneficial to replenish carbon sources and accommodate adaptive microorganisms. Electrochemical characterization and molecular methods revealed that the sludge biochar had stronger electron transfer capacity (ETC) than the cattail biochar, which could better promote the activities of key enzymes of the pollutant removal procedure. High-throughput sequencing showed that microorganisms such as Thaurea , Rhodocyclaceae , Hydrogenophaga and Fusibacter related to nitrogen removal were well enriched in the SBC-CWs and CBC-CWs. This research shows the potential for the simultaneous energy-saving advanced treatment of WWTP tailwater and waste resource recovery. [ABSTRACT FROM AUTHOR]