Integrated Vertical-flow Constructed Wetland Research Articles

Enhancing nitrogen removal in constructed wetlands: The role of influent substrate concentrations in integrated vertical-flow systems

Recent advancements in constructed wetlands (CWs) have highlighted the imperative of enhancing nitrogen (N) removal efficiency. However, the variability in influent substrate concentrations presents a challenge in optimizing N removal strategies due to its impact on removal efficiency and mechanisms. Here we show the interplay between influent substrate concentration and N removal processes within integrated vertical-flow constructed wetlands (IVFCWs), using wastewaters enriched with NO3−-N and NH4+-N at varying carbon to nitrogen (C/N) ratios (1, 3, and 6). In the NO3−-N enriched systems, a positive correlation was observed between the C/N ratio and total nitrogen (TN) removal efficiency, which markedly increased from 13.46 ± 2.23% to 87.00 ± 2.37% as the C/N ratio escalated from 1 to 6. Conversely, in NH4+-N enriched systems, TN removal efficiencies in the A-6 setup (33.69 ± 4.83%) were marginally 1.25 to 1.29 times higher than those in A-3 and A-1 systems, attributed to constraints in dissolved oxygen (DO) levels and alkalinity. Microbial community analysis and metabolic pathway assessment revealed that anaerobic denitrification, microbial N assimilation, and dissimilatory nitrate reduction to ammonium (DNRA) predominated in NO3−-N systems with higher C/N ratios (C/N ≥ 3). In contrast, aerobic denitrification and microbial N assimilation were the primary pathways in NH4+-N systems and low C/N NO3−-N systems. A mass balance approach indicated denitrification and microbial N assimilation contributed 4.12–47.12% and 8.51–38.96% in NO3−-N systems, respectively, and 0.55–17.35% and 7.83–33.55% in NH4+-N systems to TN removal. To enhance N removal, strategies for NO3−-N dominated systems should address carbon source limitations and electron competition between denitrification and DNRA processes, while NH4+-N dominated systems require optimization of carbon utilization pathways, and ensuring adequate DO and alkalinity supply.

Microbial community structure in a constructed wetland based on a recirculating aquaculture system: Exploring spatio-temporal variations and assembly mechanisms

The diversity, composition and performance of microbial communities within constructed wetlands (CW) were markedly influenced by spatio-temporal variations. A pilot-scale integrated vertical-flow constructed wetland (IVCW) as the biological purification unit within a recirculating aquaculture system (RAS) was established and monitored in this study. The investigation aimed to elucidate the responses of community structure, co-occurrence networks, and assembly mechanisms of the microbial community to spatial and temporal changes. Spatially, all a-diversity indices and microbial networks complexity were significantly higher in the upstream pool of the IVCW than in the downstream pool. Temporally, the richness increased over time, while the evenness showed a decreasing trend. The number of nodes and edges of microbial networks increased over time. Notably, the stable pollutant removal efficiencies were observed during IVCW operations, despite a-diversity and bacterial community networks exhibited significant variations across time. Functional redundancy emerged as a likely mechanism contributing to the stability of microbial ecosystem functions. Null model and neutral model analyses revealed the dominance of deterministic processes shaping microbial communities over time, with deterministic influences being more pronounced at lower a-diversity levels. DO and inorganic nitrogen emerged as the principal environmental factor influencing microbial community dynamics. This study provides a theoretical foundation for the regulation of microbial communities and environmental factors within the context of IVCW.

Response of remediation performances and microbial communities of integrated vertical-flow constructed wetlands with different configurations after chronic exposure to pharmaceuticals and personal care products

Integrated vertical-flow constructed wetlands (IVCWs) received increasing concern on pollutant elimination with high cost-effectiveness, even for emerging contaminants such as pharmaceuticals and personal care products (PPCPs). However, it will be beneficial for the further reduction of input costs if the correlation between different construction strategies and corresponding removal performance can be clearly elucidated. In this study, three IVCWs with different configurations were constructed to clarify the effect of artificial aeration and planting on pollutant removal after chronic exposure to PPCPs. The CW-A with artificial aeration and planting exhibited superior nitrogen removal performance (>90 %) over the other two systems, though along with increased input expenses. All types IVCWs showed satisfying removal performance of CODCr, TP, MEA, and 2-php after maturity of CWs. The participation of planting Canna indica improved the elimination of sulfamethoxazole (SMX), evidenced by a higher removal efficiency of 92.42 % in CW-A and 90.86 % in CW-B, compared to 69.58 % in CW-C. No obvious differences were observed in all groups for removing mefenamic acid (MEA) and 2-phenylphenol (2-php) with a satisfying removal rate of over 90 %. Ammonia-oxidizing bacteria (AOB) were limited after exposure in all IVCWs while denitrifying bacteria still existed in high abundance. Notably, results showed that the main pathway of PPCPs removal was biodegradation according to the mass balance. Findings from this work could provide informative references for the construction and maintenance of IVCWs with minimized expenses in practical applications while preserving excellent removal efficiencies of nitrogen and PPCPs.

Performance evaluation and microbial profiling of integrated vertical flow constructed wetland (IVFCW) for simultaneous treatment of domestic and pulp and paper industry waste water

The present study demonstrates the potential of an integrated vertical flow-constructed wetland (IVFCW) for simultaneously treating black liquor and domestic wastewater. IVFCW was operated and monitored for 12 samples with the frequency of one sample per week with the following specifications viz,4 L of wastewater, a blend of 1:1 of pulp and paper industry effluent (black liquor BL), and domestic wastewater, was fed daily in a continuous mode with organic loading rate (OLR) of 1230 mg COD/L-Day, at a temperature range of 40-45℃ (natural temperature of the workstation). Valves controlled each chamber's hydraulic retention time (HRT) of 3 days and flow rate of 10 mL/minute. The IVFCW showed remarkable efficiency in removing various pollutants, including total suspended solids (TSS) and total dissolved solids (TDS), by 100 % and 83 %, respectively, and organic contaminants such as chemical oxygen demand (COD) and biological oxygen demand (BOD) by 80 % and 81 %, respectively. Moreover, the IVFCW efficiently reduced nutrients such as sulfates (SO₄-2), phosphates (PO₄-3), and total nitrogen by about 81 %, 63 %, and 61 %, respectively. The treatment also led to the reduction of lignin content by 83 %. Microbiological analysis revealed a significant reduction in fecal coliforms, and microbial profiling of Typha latifolia roots confirmed the presence of bacteria involved in lignin degradation. Seed germination and seedling survival were found to be negativelyaffected by untreated wastewater in a phytotoxicity study, suggesting that the wastewater's toxic chemicals could be harmful to plant life.This study highlights the effectiveness of IVFCW as a sustainable, economically viable, and resilient wastewater treatment system for mitigating environmental concerns related to the release of untreated wastewater.

Construction of hybrid constructed wetlands for phosphorus chemical industry tailwater treatment in the middle Yangtze river basin: Responses of plant growth and root-associated microbial communities

Constructed wetlands are commonly utilized to treat industrial wastewater due to their effectiveness, affordability, and environmental benefits. Many phosphorus chemical enterprises in the middle Yangtze River basin are facing high pollution load challenges and efforts are needed to improve removal efficiency of pollutants. This work was the first to use constructed wetlands for phosphorus chemical industry tailwater (PCITW) treatment. The new hybrid constructed wetlands (CWs) proposed were the aeration horizontal subsurface flow constructed wetland (AHSCW) and the integrated vertical flow constructed wetland (IVCW), which were constructed on a pilot scale. Here, the effectiveness of pollutant removal along hybrid CWs, wetland plant growth, and root-associated microbial community responses to the PCITW were investigated. The results showed that there was spatial variation in removal of carbon, nitrogen, and phosphorus in the hybrid CWs, and that the AHSCW and the IVCW played synergistic roles in the removal of pollutants. Compared with influent, the toxic effect of effluent to embryos of a rare minnow (Gobiocypris rarus) was alleviated. Exposure to the effluent resulted in no malformation or death for embryos. Plants and microorganisms in the wetland system of the phosphate chemical tailwater were then compared with the control system of municipal tailwater. Plants in the former system had lower root density, and higher average root diameter, root shoot ratio, specific root length, and specific surface area. Plant roots also had decreased NH4+ uptake ability but increased Ca2+ uptake to adapt to the high load and complex pollution stress. Unlike the control system, stochastic mechanisms had a more important role than deterministic processes in shaping the microbial community assembly associated with the PCITW. Meanwhile, analysis of microbial network-level topological characteristics demonstrated substantial reduction in network interactions complexity and microbiome stability in the treatment system. Findings from this study suggest wetlands will be helpful for efficient purification of phosphorus chemical industry wastewater in the Yangtze River basin.

An anoxic-aerobic system combined with integrated vertical-flow constructed wetland to highly enhance simultaneous organics and nutrients removal in rural China

The biggest problem in the treatment of rural domestic sewage is that the existing treatment projects require the big investment and the high operation and maintenance costs. To overcome this problem, cost-effective, low-consuming, resource-recovering and easy-maintenance technologies are urgently demanded. To this end, a novel anoxic-aerobic system combined with integrated vertical-flow constructed wetland (IVFCW) with source separation was proposed for treating rural sewage in this study. The anoxic-aerobic system contained the anoxic filter (ANF), two-stage waterwheel driving rotating biological contactors (ts-WDRBCs). Key parameters of ts-WDRBCs were identified to be 0.6 m drop height and 4 r/min rotational speed found on oxygenated clean water experiments. Then, the optimal operating parameters were determined to be 200% reflux ratio and 3 h hydraulic retention time of ts-WDRBCs. During the 80-day operation, 91.58 ± 1.86% COD, 96.17 ± 0.92% NH4+-N, 82.71 ± 3.92% TN and 92.28 ± 2.78% TP were removed under the optimal operating parameters. Compared with other treatment technologies, this combined bio-ecological system could achieve the higher simultaneous organics and nutrients removal. The effluent NO3−-N/NH4+-N concentration ratio of ts-WDRBCs was 2.15 ± 0.54, which was proved to be beneficial for plants growth. The microbial communities coexisted in each section ensured the desired removal performance of combined bio-ecological system. Summarily, high performance together with low investment costs and cheap operation costs are characteristics that make this system a promising and competitive alternative for rural sewage treatment.

Controlling methane emissions from Integrated Vertical-Flow Constructed Wetlands by using potassium peroxymonosulfate as oxidant

It is very important to control methane emissions to reduce global warming. In this study, a new attempt of one oxidant (potassium peroxymonosulfate (PMS)) was made to adjust the oxidation-reduction potential (Eh) by adding different mass of (0 g, 31.25 g, 62.5 g, 125 g, 250 g and 500 g) for the reduction of methane emissions from integrated vertical-flow constructed wetland (IVCW), where the IVCW system has been divided into the root-water system and the stem-leaf system of methane emissions. Results show that the reduced CH4 emission from IVCW was the highest with decreased by 43.5% compared to blank group (PMS = 0), when adding 125 g PMS. Importantly, the reduced CH4 from the root-water system of IVCW was higher than that of the stem-leaf system of IVCW, when adding PMS. It's found that Eh not only has a significant correlation with CH4 flux, but also has a significant relationship between PMS quality, DO, water temperature and sampling time (yEh = −0.44XPMS + 6.82XDO + 0.38t - 264.1, R2 = 0.99). It concludes that PMS, as an oxidant, is a very feasible method for controlling methane emissions from IVCW. It's concluded from this study that it is a feasible engineering method by using PMS as an oxidant for reducing methane emissions from IVCWs when treating artificial domestic sewage. Further research may combine other methods together such as microbiology, physical control and hydrology control for mitigating the CH4 emissions from constructed wetlands for more types of wastewater.

Enhancement effects and pathways of nitrogen removal by plant-based carbon source in integrated vertical flow constructed wetlands

Nitrogen removal in integrated vertical flow constructed wetlands (IVCW) is often limited by denitrification processes due to the lack of carbon sources. This study aims to elucidate the enhancement effects and mechanisms of alkali pretreated reeds as plant-based carbon source on the nitrogen removal process of IVCW. The results show near-complete removal of both COD and NH4+-N, with removal efficiencies of circa 98.0%. The alkali pretreated reeds were demonstrated to increase the removal efficiencies of NO3−-N and TN from −15.97% and 53.13% to 95.5% and 93.7%. The plant-based carbon source release organic matter primarily composed of tryptophan-like, fulvic acid-like and humic acid-like substances. Among these substances, the low molecular weight organic matter closely related to the carboxyl functional group showed high bioavailability. 16S rRNA gene sequencing demonstrated the plant-based carbon source to increase the relative abundance of nitrogen removal functional microbial genera up to 24.12%. Consequently, total nitrogen (TN) removal increased notably from 47.77% to 89.10%, primarily driven by a significant increase in denitrification from 0.16 mg/L to 14.11 mg/L. The TN removal was further enhanced by a considerable increase in anaerobic ammonia oxidation from 0.18 mg/L to 1.73 mg/L. The findings could support efficient nitrogen removal in CW via the enhancement of denitrification pathways.

Stereoselective degradation pathway of amide chiral herbicides and its impacts on plant and bacterial communities in integrated vertical flow constructed wetlands

This study demonstrates the stereoselective degradation patterns and biodegradation mechanisms of metolachlor (MET) and napropamide (NAP) in integrated vertical flow constructed wetlands (IVCW). The higher interphase transferability of NAP resulted in higher degradation rates of 90.60 ± 4.09%. The enantiomeric fraction (EF) values of 0.38 ± 0.02 and 0.54 ± 0.03, respectively, recorded for the enantiomers S-MET and R-NAP, with higher herbicidal activities, demonstrated their highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants showed positive correlations with the degradation efficiency and enantioselectivity of MET and NAP. Adaptive regulations by plants promoted the proliferation of microbial genera like Enterobacter and unclassified_Burkholderiales, which could facilitate plant growth. Moreover, enrichment of the herbicide-degrading functional bacteria Terrimonas (5.10%), Comamonas (4.05%) Pseudoxanthomonas (4.49%) and Mycobacterium (1.42%) demonstrably promoted the preferential degradation of S-MET and R-NAP. Furthermore, the abundance of Ferruginibacter favored the use of R-NAP as carbon source to achieve co-removal of R-NAP and NO3–-N.

Phytoremediation mechanisms and plant eco-physiological response to microorganic contaminants in integrated vertical-flow constructed wetlands

Vegetations play a vital role in the ecological function of constructed wetlands (CW), but the systemic phytoremediation mechanism of CW is still unclear. An integrated vertical-flow constructed wetland (IVCW) was established to elucidate the phytoremediation mechanisms and plants eco-physiological response to an emerging contaminant, sulfamethoxazole (SMX). Attenuation of SMX in IVCW with and without vegetation (Acorus calamus) are comparatively analyzed. The results showed significant enhancement of removal efficiencies of total nitrogen (via intensified denitrification) and SMX by up to 10% respectively with vegetation. A unique micro-rhizo environment was created by stimulating the denitrifiers, Clostridium_sensu_stricto, Ignavibacterium, Rhodanobacter, and Geobacter. Free-living plant growth-promoting bacteria, unclassified_Burkholderiales and unclassified_Betaproteobacteria, proliferated in the rhizosphere, protecting the growth mechanism of A. calamus and, consequently, promoting performance of the IVCW. Overall, A. calamus exhibited tolerance to SMX, maintaining its photosynthesis rate and stabilizing the plant cell structure by an effective antioxidant system. The growth and defense mechanisms of A. calamus appeared to positively correlate with the IVCW performance, whereby the photosynthetic rate and antioxidant enzymes activities peaked together with the maximum removal efficiency of TN (77.81%) and SMX (99.88%). The contribution of vegetation to ecotoxicity reduction in CW might be underrated as absorbed SMX could be phytodegraded into less toxic metabolites via specific enzymes.

Fate of an antibiotic and its effects on nitrogen transformation functional bacteria in integrated vertical flow constructed wetlands

• IVCW could achieve simultaneous nitrogen and antibiotic removal. • Sulfamethoxazole (SMX) removal exceeds 95% primarily via biodegradation. • Enrichment of Pseudomonas , Bradyrhizobium , Sphingomonas , Luteimonas for SMX removal. • SMX transforms nitrogen transformation process to favor ANAMMOX. This study aims to provide insights into the fate and effects of the antibiotic sulfamethoxazole (SMX) on nitrogen transformation processes in integrated vertical-flow constructed wetlands (IVCW), which is useful to create strategies to improve their degradation and combat antibiotic resistance dissemination. Findings indicated chronic exposure to SMX to cause moderate deterioration of IVCW performance for nitrogen removal (p < 0.05), with average TN removal efficiency reductions of circa 10%. High-throughput sequencing and network analysis demonstrated chronic exposure of antibiotics to impact functional bacteria, ammonium oxidizing bacteria (AOB) and ANAMMOX, significantly. ANNAMMOX emerged as a potential pathway of nitrogen removal in the IVCW, albeit with considerable accumulation of NO 3 − -N (12.76 mg/L) and carbon deficiency (C/N = 0.99). Nonetheless, IVCW provides a promising technology for the advanced treatment of antibiotic-containing wastewater, demonstrated by a high and stable removal efficiency (circa 95%) of sulfamethoxazole. Biodegradation, primarily in the first stage of the IVCW, represented the major removal pathway of SMX. Microbial network analysis and the enrichment of Pseudomonas , Bradyrhizobium , Sphingomonas and Luteimonas demonstrated potential for the biodegradation of SMX. These results provide a theoretical reference for the enhancement of nitrogen and antibiotics removal in constructed wetlands.

Comparison of performance of two large-scale vertical-flow constructed wetlands treating wastewater treatment plant tail-water: Contaminants removal and associated microbial community

The removal efficiency of contaminants in large-scale integrated vertical-flow constructed wetland (IVCW) and vertical-flow constructed wetland (VCW) for wastewater treatment plant (WWTP) tail-water was evaluated, and the microbial community was also investigated in this study. The results for 14 months study period indicated that 40.05% chemical oxygen demand (COD), 45.47% ammonia nitrogen (NH4+-N), 62.55% total phosphorus (TP), 55.53% total nitrogen (TN) and 57.20% total suspended solids (TSS) average removal efficiencies were achieved in the IVCW. There was a poor performance of TN removal in the VCW, with an average removal efficiency of 38.13%. There was no significant seasonal difference in TP removal, and a strong positive correlation between influent TP load and removed load. The high-throughput sequencing analysis revealed that Proteobacteria, Planctomycetes, Bacteroidetes and Acidobacteria were dominant in nature and wetland systems. The relative abundance of nitrifying bacteria, denitrifying bacteria and anammox bacteria confirmed that nitrification, denitrification and anammox may be the main processes for nitrogen removal in the IVCW.

Efficiency and kinetics of conventional pollutants and tetracyclines removal in integrated vertical-flow constructed wetlands enhanced by aeration

The integrated vertical-flow constructed wetland (IVCW) is considered as a potential alternative for domestic wastewater treatment of towns and small cities. Oxygen supply is the main limitation of pollutants removal in IVCWs. In the present study, a field experiment was conducted to evaluate the capacity and kinetics of pollutants removal in IVCWs with/without artificial aeration. Two IVCWs constructed with Canna indica and Phragmites australis were running in continuous flow to remove high concentrations of conventional pollutants and low concentrations of tetracyclines (TETs), which are at similar levels of domestic wastewater. The results showed that IVCWs had a good performance on COD, phosphorus, and TETs with removal efficiencies over 80%, 64%, and 75%, respectively, with a hydraulic retention time (HRT) of 3.0 d. However, the removal of nitrogen was limited, showing as TN removal efficiency of about 30%. The IVCW with Phragmites australis had a higher removal efficiency and rate. A kinetics based on Monod Equation and solved with Matlab 2018a could describe the degradation of conventional pollutants. Artificial aeration improved the oxygen supply and remarkably raised the removal capacity for COD, N, and P in IVCWs. The q1/2 values, which was defined as the average removal loading before half of the pollutants was removed and represented the removal capacity without limitation of pollutants concentration, were increased by 5–30 times after aeration. In conclusion, IVCWs could remove conventional pollutants and TETs simultaneously showing a great potential in domestic wastewater treatment. Artificial aeration enhanced removal capacity of IVCWs on conventional pollutants while showed little influence on TETs.

Effects of plant on denitrification pathways in integrated vertical-flow constructed wetland treating swine wastewater.

Plant is an important part of constructed wetland (CW), while, its potential effect on nitrogen cycling is complicated. Herein, integrated vertical-flow constructed wetland (IVCW) in pilot-scale planted with Arundo donax (Planted System, PS) was constructed to treat swine wastewater. The removal performance of nitrogen in PS, effects of plant on the microbial community structure and nitrogen related function genes were revealed. Results showed that, Arundo donax planting enhanced the removal rate of TN, compared to unplanted IVCWs, the absolute abundance of Pseudomonas, Acinetobacter and Bacillus in PS was significantly increased, as well as the absolute abundance of functional gene (amoA, nxrA, nirK, nirS and nosZ). The denitrification process was mainly occurred in down-flow cell of PS with significantly higher abundant of nirK and nosZ (P<0.05). These findings suggested that Arundo donax planting in IVCWs with zeolite as substrate promoted the growth of denitrifying microorganisms under higher pollutant load. In addition, the increased abundant of nosZ and the ratio of nosZ/∑nir indicating a lower genetic potential for N2O release. Our research provides new insight into the potential application of plant on the purification of swine wastewater.

Removal performance of antibiotics and antibiotic resistance genes in swine wastewater by integrated vertical-flow constructed wetlands with zeolite substrate

Antibiotics and antibiotic resistance genes (ARGs) in swine wastewater have an irreversible impact on the surrounding water and soil ecosystems. Herein, integrated vertical-flow constructed wetlands (IVCWs) were constructed to assess the effects of zeolite and plants on the removal of sulfonamides (SMs), tetracyclines (TCs), and related ARGs (tetW, tetO, tetM, sul I, sul II, and sul III) from digested swine wastewater. The microorganism community structure was also investigated. Results showed that IVCWs with a zeolite substrate and plant system (ZP) exhibited a favorable removal performance for N, antibiotics, and ARGs at 97.9%, 95.0%, and 95.1%, respectively. Moreover, zeolite systems showed higher adsorption of SMs, lower adsorption of TCs. The higher removal rate of antibiotics in ZP systems might be due to the enhanced microbial degradation with the enrichment of Pseudomonas, Acinetobacter, and Bacillus in zeolite. Furthermore, Arundo donax had limited impact on antibiotics removal and was not conducive to the removal of ARGs. The absolute abundances of sul(I), sul(II), sul(III), tet(M), and tet(O) were significantly positively correlated with the absolute abundance of 16S rDNA. However, no significant correlation was found between the concentration of antibiotics and the abundance of related ARGs in the effluent.

Waste Brick as Constructed Wetland Fillers to Treat the Tail Water of Sewage Treatment Plant.

Adopting the concept of "using waste to treat waste", the waste bricks will be used for constructed wetland filling. Integrated vertical-flow constructed wetland (IVCW) studied on the purification effect in influent water under three hydraulic loads (0.15, 0.25, 0.35m/day). The results show that the waste bricks can be used as the carrier for the growth of the system biofilm, and have positive effects on the removal of pollutants in the influent water. Under three different hydraulic load conditions, the vertical flow of CWs can significantly reduce the load of water intake. In the low hydraulic load condition of 0.15m/day, the average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) can reach 66.52%, 72.10%, 56.53% and 91.55% in this system, respectively. The influent pool on removal efficiency of pollutants was obviously higher than that of the upper pool, especially in the inlet surface 0-30cm ranges. This research has achieved the effect of using "waste" to treat wastewater, which has strong practical significance and popularization value.

Behavior of selected organophosphate flame retardants (OPFRs) and their influence on rhizospheric microorganisms after short-term exposure in integrated vertical-flow constructed wetlands (IVCWs)

Considering its ubiquitous occurrence and potential adverse effects of organophosphorus flame retardant (OPFR), it is urgent to explore the efficient treatment for OPFRs wastewater. Thus, integrated vertical-flow constructed wetlands (IVCWs) were set up to comparatively evaluate their nitrogen removal capacity under tidal flow operations and to investigate environmental behavior and rhizosphere microbial responses after short-term exposure to three OPFRs. The results show that IVCWs have an excellent TN removal rate (628.13 ± 110.63 mg m−2 d−1) and moderate mitigation efficiencies (48.37 ± 9.52 to 82.28 ± 7.48%) for target OPFRs when treating low-C/N ratio wastewater. Moreover, the sorption of selected OPFRs to soil (28.85–308.41 ng g−1, dry weight (dw)), igneous rock (659.85–970.80 ng g−1 dw) and zeolite (1045.60–1351.70 ng g−1 dw) and accumulation in tissues of C. alternifolius (0–289.68 ng g−1 dw) and P. australis (0.56–108.22 ng g−1 dw) showed a hydrophobicity-specific feature. Namely, the highly hydrophobic compound tricresyl phosphate (TCrP) partitioned preferentially to sediment, and the chlorinated analytes were more easily taken up and then translocated into the plant body. Simultaneously, further mass balance analysis revealed the fate of OPFRs in IVCW components. A total of 53.25% of the highly hydrophobic TCrP inflow mass settled in sediment, while tris (2-chloroethyl) phosphate (TCEP) and tris (1-chloro-2-propyl) phosphate (TCPP) were more liable to discharge (35.33–50.89%) and other pathways (38.77–39.87%). Furthermore, the abundance of aerobic denitrifying bacteria (AD) in rhizosphere soil (2.25–5.12%), jointly with the prevalence of nitrobacteria (NOBs, 1.84–13.60%) and denitrifying bacteria (DNBs, 5.84–7.89%) in sublayer matrices, was responsible for superior TN removal. Additionally, the rhizosphere microbial richness, diversity and nitrogen-related microorganisms were clearly influenced by the presence of OPFRs. Notably, the genera Pseudomonas and Sphingobium might be the functional microorganisms for mixture OPFRs biodegradation.

Performance of different macrophytes in the decontamination of and electricity generation from swine wastewater via an integrated constructed wetland-microbial fuel cell process

Plants constitute a major element of constructed wetlands (CWs). In this study, a coupled system comprising an integrated vertical flow CW (IVCW) and a microbial fuel cell (MFC) for swine wastewater treatment was developed to research the effects of macrophytes commonly employed in CWs, Canna indica, Acorus calamus, and Ipomoea aquatica, on decontamination and electricity production in the system. Because of the different root types and amounts of oxygen released by the roots, the rates of chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N) removal from the swine wastewater differed as well. In the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, the COD removal rates were 80.20%, 88.07%, 84.70%, and 82.20%, respectively, and the NH4+-N removal rates were 49.96%, 75.02%, 70.25%, and 68.47%, respectively. The decontamination capability of the Canna indica system was better than those of the other systems. The average output voltages were 520±42, 715±20, 660±27, and 752±26mV for the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, respectively, and the maximum power densities were 0.2230, 0.4136, 0.3614, and 0.4964W/m3, respectively. Ipomoea aquatica had the largest effect on bioelectricity generation promotion. In addition, electrochemically active bacteria, Geobacter and Desulfuromonas, were detected in the anodic biofilm by high-throughput sequencing analysis, and Comamonas (Proteobacteria), which is widely found in MFCs, was also detected in the anodic biofilm. These results confirmed the important role of plants in IVCW–MFCs.

Methane Emissions Driven by Adding a Gradient of Ethanol as Carbon Source in Integrated Vertical-Flow Constructed Wetlands

This work aims to investigate the methane emissions from integrated vertical-flow constructed wetlands (IVCWs) when ethanol is added as an external carbon source. In this study, a gradient of ethanol (0, 2, 4, 8, 16 and 32 mmol/L) was added as the carbon source in an IVCW planted with Cyperus alternifolius L. The results showed that the methane emission flux at an ethanol concentration of 32 mmol/L was 32.34 g CH4 m−2 day−1 less than that of the control experiment (0 mmol/L) and that the methane emission flux at an ethanol concentration of 16 mmol/L was 5.53 g CH4 m−2 day−1 less than that at 0 mmol/L. In addition, variations in the water quality driven by the different ethanol concentrations were found, with a redox potential range of −64 mV to +30 mV, a pH range of 6.6–6.9, a chemical oxygen demand (COD) removal rate range of 41% to 78%, and an ammonia nitrogen removal rate range of 59% to 82% after the ethanol addition. With the average CH4-C/TOC (%) value of 35% driven by ethanol, it will be beneficial to understand that CH4-C/TOC can be considered an ecological indicator of anthropogenic methanogenesis from treatment wetlands when driven by carbon sources or carbon loading. It can be concluded that adding ethanol as an external carbon source can not only meet the water quality demand of the IVCW treatment system but also stimulate and increase the average CH4 emissions from IVCWs by 23% compared with the control experiment. This finding indicates that an external carbon source can stimulate more CH4 emissions from IVCWs and shows the importance of carbon sources during sewage treatment processes when considering greenhouse emissions from treated wetlands.

Organic matter and ammonia removal by a novel integrated process of constructed wetland and microbial fuel cells.

A novel approach, combining a microbial fuel cell (MFC) with an integrated vertical flow constructed wetland (IVCW), was developed, and its ability to simultaneously produce electrical energy while treating swine wastewater was verified. The system combined the singular water flow path of a traditional vertical flow constructed wetland (upflow and downflow)-microbial fuel cell (CW-MFC), which demonstrates better characteristics in the aerobic, anoxic, and anaerobic regions. It not only enhanced the anti-pollution load ability and the organic compound removal effect, but also improved the gradient difference in the redox potential of the system. The results showed that the structure and substrate distribution in the device could both improve swine wastewater treatment and increase bioelectricity generation capabilities. The average chemical oxygen demand (COD) and ammonia nitrogen (NH4+–N) removal efficiencies were as high as 79.65% and 77.5%, respectively. Long-term and stable bioelectricity generation was achieved under continuous flow conditions. The peak values of the output voltage and power density were 713 mV and 456 mW m−3. The activated carbon layer at the bottom of this system provided a larger surface for the growth of microbes. It showed significant promotion of the relative abundance of electrochemically active bacteria, which might result in the increase of bioelectricity generation in integrated vertical flow constructed wetland-microbial fuel cells (IVCW-MFCs). The electrochemically active bacteria, Geobacter and Desulfuromonas, were detected in the anodic biofilm by high-throughput sequencing analysis.