The insufficient abundance of electron acceptors for ammonia during electron transfer in constructed wetlands (CWs) results in low nitrification rates. This study developed a green, low-carbon CWs enhanced by a bio-electrochemical systems (BESs-CWs) to achieve efficient ammonia (NH4+-N) removal. Electrode enhancement significantly promoted NH4+-N removal. Compared with traditional CWs, the average removal efficiency of NH4+-N in the BESs-CWs increased from 62.9 % to 90.6 %. The intermittent voltage driven by the photovoltaic power system caused minimal plant stress. However, electrode enhancement significantly affected microbial communities involved in short-path nitrification and denitrification within the biofilm. Specifically, the removal rate of NH4+-N by BESs-CWs under electrode enhancement was increased by 27.7 % compared to traditional CWs, enhancing the electron output of NH4+-N in the BESs-CWs. This system provides a method of ammonia nitration for CWs under poor electron acceptor conditions.

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

This study examined the elimination of sulfonamide antibiotics (SAs) by constructed wetland substrates with NaOH-modified corn straw biochar and assessed the impact of environmental conditions on the effectiveness of SAs removal. The study demonstrated that the constructed wetland substrate with NaOH-modified biochar significantly eliminated eight SAs, with a removal rate of over 94 %. During the removal process, the intermediates will undergo regeneration of the parent compounds under low DO concentrations. This was based on the linear stepwise regression analysis and Geodetector models. The results showed that SA types COD, NH4+-N, TN, and DO had a stronger influence. The dominant bacteria in the constructed wetland system were mainly affected by antibiotic concentration, DO, NH4+-N and NO3--N, which affected the removal of antibiotics. Overall, the constructed wetland substrate with NaOH-modified corn straw biochar can be effectively employed as an ecological method for eliminating SAs from the environment.

Pharmaceuticals and personal care products (PPCPs) are insufficiently degraded in saline wastewater treatment processes and are found at high concentrations and detection frequencies in aquatic environments. In this study, the wetland plant Thalia dealbata was selected using a screening plant experiment to ensure good salt tolerance and high efficiency in removing PPCPs. An electric integrated vertical-flow constructed wetland (E-VFCW) was developed to improve the removal of PPCPs and reduce the abundance of antibiotic resistance genes (ARGs). The removal efficiency of ofloxacin, enrofloxacin, and diclofenac in the system with anaerobic cathodic and aerobic anodic chambers is higher than that of the control system (41.84 ± 2.88%, 47.29 ± 3.01%, 53.29 ± 2.54%) by approximately 20.31%, 16.04%, and 35.25%. The removal efficiency of ibuprofen in the system with the aerobic anodic and anaerobic cathodic chamber was 28.51% higher than that of the control system (72.41 ± 3.06%) and promotes the reduction of ARGs. Electrical stimulation can increase the activity of plant enzymes, increasing their adaptability to stress caused by PPCPs, and PPCPs are transferred to plants. Species related to PPCPs biodegradation (Geobacter, Lactococcus, Hydrogenophaga, and Nitrospira) were enriched in the anodic and cathodic chambers of the system. This study provides an essential reference for the removal of PPCPs in saline-constructed wetlands.

On global scale, eutrophication is one of the most prevalent environmental threats to water quality, primarily caused by elevated concentration of nutrients in wastewater. This study focuses on using a cost-effective aluminium dross (AD), an aluminium industrial waste into value-added material, enhancing its operational feasibility and high-end application to remove phosphate and ammonium from water. The operational challenges of AD such as its powdered nature and effective operation under only extreme pH conditions were addressed by immobilizing in calcium alginate to form calcium alginate aluminium dross (Ca-Alg-Al dross) beads. These Ca-Alg-Al dross beads were further tested for phosphate and ammonium removal from natural wastewater in two different aqueous environment systems: (i) vertical flow constructed wetlands (VF-CWs) followed by Ca-Alg-Al dross beads fixed bed system and (ii) Ca-Alg-Al dross beads mounted floating constructed wetlands (FCW) for remediating polluted lentic ecosystems. Our results show maximum phosphate and ammonium removal of 85 ± 0.41 % and 93.44 %, respectively, in VF-CWs followed by Ca-Alg-Al dross beads fixed bed system. The Ca-Alg-Al dross beads mounted FCW system achieved maximum phosphate removal of 79.18 ± 8.56 % and ammonium removal of 65.45 ± 21.04 %. Furthermore, the treated water from the FCW system was assessed for its potential to inhibit algal growth by artificially inoculating treated water with natural algae to simulate eutrophic conditions. Interestingly, treated water from the FCW system was found capable of arresting the algal growth. Besides, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy confirmed the functional groups and surface properties and probable participation of multiple mechanisms including ion exchange, electrostatic attraction, and ligand complexation for phosphate and ammonium removal. Overall, these results offer a promising way to utilize AD for high-end applications in wastewater treatment.

Arbuscular mycorrhizal fungi (AMF) colonization has been used in constructed wetlands (CWs) to enhance treatment performance. However, its role in azole (fungicide) degradation and microbial community changes is not well understood. This study aims to explore the impact of AMF on the degradation of tebuconazole and its metabolites in CWs. Total organic carbon levels were consistently higher with the colonization of AMF (AMF+; 9.63- 16.37 mg/L) compared to without the colonization of AMF (AMF-; 8.79-14.48 mg/L) in CWs. Notably, tebuconazole removal was swift, occurring within one day in both treatments (p = 0.885), with removal efficiencies ranging from 94.10 % to 97.83 %. That\'s primarily due to rapid substrate absorption at the beginning, while degradation follows with a longer time. Four metabolites were reported in CWs first time: tebuconazole hydroxy, tebuconazole lactone, tebuconazole carboxy acid, and tebuconazole dechloro. AMF decreased the abundance of tebuconazole dechloro in the liquid phase, suggesting an inhibitory effect of AMF on dechlorination processes. Furthermore, tebuconazole carboxy acid and hydroxy were predominantly found in plant roots, with a higher abundance observed in AMF+ treatments. Metagenomic analysis highlighted an increasing abundance in bacterial community structure in favor of beneficial microorganisms (xanthomonadales, xanthomonadaceae, and lysobacter), along with a notable presence of functional genes like codA, NAD, and deaD in AMF+ treatments. These findings highlight the positive influence of AMF on tebuconazole stress resilience, microbial community modification, and the enhancement of bioremediation capabilities in CWs.

Constructed wetlands are nature-based solutions able to remove different pollutants from water, including arsenic. Arsenic is a pollutant of concern given its toxicity and its presence in water sources worldwide. Despite the increased interest in investigating the performance of constructed wetlands in the treatment of arsenic-contaminated water at the laboratory scale, the application of these solutions at the pilot and full scale is still limited. To understand and predict the removal of arsenic in constructed wetlands, some numerical models have been developed. Among black box models, only first-order models have been proposed, with unsuccessful results. The model that best describes arsenic retention processes in constructed wetlands is RCB-ARSENIC, a mechanistic model adapted from Retraso-CodeBright that simulates arsenic reactive transport. This model includes arsenic precipitation, arsenic sorption on supporting media, arsenic sorption on plants roots and arsenic uptake by plants; represented in the reactive term of the reactive transport equation. Thus, it includes two of the three main processes that remove arsenic in constructed wetlands: precipitation, sorption, and coprecipitation. Despite this, and what is known about arsenic geochemistry, the formulation of these reactive rates requires improvement. In addition, this model was calibrated and validated using data from a single horizontal subsurface flow constructed wetland system, which treated one type of synthetic water. Therefore, it cannot be applied to other types of arsenic-contaminated water or other constructed wetland systems. Moreover, the reactive transport of relevant species -especially iron- and their role in arsenic removal, along with relevant redox reactions associated to the presence of organic matter, oxides or bacteria-, must be included. A comprehensive mechanistic model able to simulate different design, environmental and operation conditions may be used to guide the design of constructed wetlands targeting the removal of arsenic.

Efficient nitrogen removal in constructed wetlands (CWs) remains challenging when treating agricultural runoff with a low carbon-to-nitrogen ratio (C/N). However, using biochar, iron ore, and FeCl3-modified biochar (Fe-BC) as amendments could potentially improve total nitrogen (TN) removal efficiency in CWs, but the underlying mechanisms associated with adding these substrates are unclear. In this study, five CWs: quartz sand constructed wetland (Control), biochar constructed wetland, Fe-BC constructed wetland, iron ore constructed wetland, and iron ore + biochar constructed wetland, were built to compare their treatment performance. The rhizosphere microbial community compositions and their co-occurrence networks were analyzed to reveal the underlying mechanisms driving their treatment performance. The results showed that iron ore was the most efficient amendment, although all treatments increased TN removal efficiency in the CWs. Ammonia-oxidizing, heterotrophic denitrifying, nitrate-dependent anaerobic ferrous oxidizing (NAFO), and Feammox bacteria abundance was higher in the iron ore system and led to the simultaneous removal of NH4+-N, NO3--N, and NO2--N. Visual representations of the co-occurrence networks further revealed that there was an increase in cooperative mutualism (the high proportion of positive links) and more complex interactions among genera related to the nitrogen and iron cycle (especially ammonia-oxidizing bacteria, heterotrophic denitrifying bacteria, NAFO bacteria, and Feammox bacteria) in the iron ore system, which ultimately contributed to the highest TN removal efficiency. This study provides critical insights into how different iron ore or biochar substrates could be used to treat agricultural runoff in CWs.

Microplastics (MPs) discharging into constructed wetlands pose risks to these ecosystems. Nevertheless, the perturbation of MPs to different types of macrophytes, which play important roles in purifying pollutants of wetlands, has not been fully elucidated. In this study, polystyrene MPs (PS-MPs) perturbation on nitrogen removal and sensory quality of surface flow constructed wetlands planted with emergent and submerged macrophytes were investigated. PS-MPs enhanced N removal efficiencies temporarily, whereas the N removal rate constants were declined as exposure time was prolonged. The NH4+-N removal rate constants declined by 25.78 % and 34.03 % in E and S groups respectively. The NO3--N removal rate constants declined by 22.13 % in the S groups. Denitrifiers including Thiobacillus, Rhodobacter, and Sulfuritalea were stressed. The sensory quality deteriorated after PS-MPs exposure, which was significantly related to changes in Chlorophyll a, particle size distribution, and colored dissolved organic matter. Turbidity in E groups and chroma in S groups were greatly affected by PS-MPs. Overall, under MPs exposure, macrophytes in E groups were more suitable for nitrogen removal, and macrophytes in S groups better purified the turbidity. The study could provide the basis for better allocation of macrophytes in CWs to reduce the purifying risk by PS-MPs disturbance.

Constructed wetlands (CWs) have emerged as effective wastewater treatment systems, mimicked natural wetland processes but engineered for enhanced pollutant removal efficiency. Ammonium (NH4+) and nitrate (NO3-) are among common pollutants in wastewater, posing significant environmental and health risks. The primary objective of this study is to compares the performance of CWs using gravel and three sizes of natural pumice, along with phragmites australis, in horizontal and horizontal-vertical CWs for nitrate and ammonium removal in the complementary treatment of domestic wastewater. Additionally, the study aims to develop and validate a numerical model using MATLAB software to predict the removal efficiency of these pollutants, thereby contributing to the optimization of CW design and operation. The model operates as a zero-dimensional model based on the law of mass conservation, treating the wetland as a completely mixed reactor, thus avoiding complexities associated with solute movement in porous media. It accurately could predict removal efficiency of chemical, biochemical, and biological indicators while considering active and passive absorption mechanisms by plant uptake. Notably, the determination of coefficients in the model equation does not rely on potentially error-prone laboratory measurements due to sampling issues. Instead, optimization techniques alongside field data robustly estimate these coefficients, ensuring reliability and practicality. Results indicate that higher pollutant concentrations increase reaction rates, particularly enhancing CW efficiency in ammonium removal. Pumice, especially in larger sizes, exhibits superior absorption due to increased porosity and surface area. Overall, the model accurately predicts nitrates concentrations, demonstrating its potential for CW performance optimization and confirming the significance of effective pollutant removal strategies in wastewater treatment.