Microbial nitrate removal efficiency in groundwater polluted from agricultural activities with hybrid cork treatment wetlands

Advanced water treatment with antimicrobial silver-lignin nanoparticles sonochemically-grafted on cork granulates in activated carbon packed-bed columns

Cork biomass (C) was grafted with antimicrobial silver phenolated-lignin nanoparticles (AgPLN) using a fast and simple sono-enzymatical process. The AgPLN-functionalised cork (C-AgPLN) exhibited potent antibacterial and antibiofilm properties against the common waterborne pathogens, Escherichia coli and Staphylococcus aureus. Its effects on bacterial cells included alterations in cell morphology and structure, as revealed by electron microscopy (SEM and TEM) and fluorescence microscopy (LIVE/DEAD staining). These effects also included increased oxidative stress (80 % and 31 % in E. coli and S. aureus, respectively), >99 % reduction in viability, a 60 % reduction in E. coli biofilm, and a 44 % reduction in S. aureus biofilm, as quantified by spectroscopic methods (ROS measurement, XTT metabolic activity test, and crystal violet staining). C-AgPLN also demonstrates anti-quorum sensing properties against both Gram-negative and Gram-positive bacteria, crucial for disrupting bacterial communication, thereby preventing biofilm formation. Further, C-AgPLN was combined with activated carbon (AC) at different proportions (1 %, 2 %, and 4 % w/w) in lab-scale packed-bed columns for the disinfection of water contaminated with E. coli or S. aureus. Columns containing 4 % w/w C-AgPLN demonstrated 100 % disinfection efficiency after 1 h of operation in recirculation mode (flow rate = 8.6 mL/min), and were reusable for up to 2 and 4 cycles without losing their disinfection capacity. Noteworthy, silver ion (Ag+) release was not detected in the effluent after 240 h columns operation (ICP-MS detection limit of <0.07 μg/L), confirming the environmental safety on the novel water-disinfection approach. Given that adsorption is a well-established method for advanced wastewater treatment, these results underscore the potential of nano-enabled AC-packed columns for safely and efficiently controlling the spread of water-associated pathogens.

Impact of nature-based solutions on sustainable development goals in Mediterranean agroecosystems: A meta-analysis

Mediterranean agroecosystems' vulnerability to hydroclimatic extremes threatens their resilience and sustainability. Nature-based Solutions present a sustainable strategy to address global challenges. This meta-analysis of 70 studies developed in Mediterranean climates identified solutions to improve soil health and water quality in agroecosystems by estimating their effects on soil organic matter, organic carbon, water, erosion, and Kjeldahl nitrogen, total nitrogen, nitrate, total phosphorus, phosphate, and suspended solids, respectively. Using meta-regression, we analysed how the interaction with biophysical conditions (e.g., soil texture and irrigation practices for soil health and macrophyte species and temperature for water quality) drives the effects of Nature-based Solutions. The results indicate that these solutions can improve soil health and water quality, supporting the achievement of land and water Sustainable Development Goals. Among all the options considered for rehabilitating land ecosystems, afforestation led to significant increases in soil organic carbon up to 137%. Of all tillage practices tested, eliminating soil disturbance combined with using cover crops and mulching revealed the potential to counteract agricultural land degradation, showing significant reductions in erosion as high as 98%. The individual application of organic inputs showed the potential to reverse ongoing agricultural soil degradation trends. Applying olive mill wastewater was associated with a significant increase of 249\% in soil organic matter. However, applying manure compost in no-tilled plots with herbaceous cover reduced the soil water content at field capacity by 46\%.Constructed wetlands have shown the most significant results in improving water quality by reducing pollutants and contributing to protecting and restoring aquatic ecosystems. Polycultural systems with horizontal subsurface flow reduced Kjeldahl nitrogen by 9%, nitrates and phosphorus by 3%, and total suspended solids by 10%. However, in continuous aerated systems, nitrate levels increased by 36%. The reduction in total nitrogen in subsurface vertical flow systems was 11%, while surface flow wetlands with two macrophyte species reduced total suspended solids by 6%. Implementing Nature-based Solutions in Mediterranean agroecosystems depended on biophysical conditions, highlighting the need for site-specific adaptation based on local conditions and objectives. In a global change scenario, mainstreaming these solutions as sustainable land and water management practices is vital for enhancing the resilience and sustainability of Mediterranean agroecosystems, providing ecosystem services beyond soil health and water quality, including climate change mitigation, biodiversity protection and human well-being.

Geochemical evaluation and the mechanism controlling groundwater chemistry using chemometric approach and groundwater pollution index (GPI) in the Kishangarh city of Rajasthan, India

This study is primarily focused on delving into the geochemistry of groundwater in the Kishangarh area, located in the Ajmer district of Rajasthan, India. In pursuit of this research goal, the sampling locations were divided into three parts within the Kishangarh region: Badgaon Rural (KSGR), Kishangarh Urban (KSGU), and the Kishangarh RIICO marble industrial area (KSGI). Various analytical methods have been executed to assess the suitability of groundwater for various purposes based on pH, electric conductivity, total dissolved solids, hardness, salinity, major anions, and cations. The ionic trend of anions and cations was found as HCO3- > Cl- > SO42- > NO3- > Br- > NO2- > F- and Na+  > Ca2+  > Mg2+  > K+, respectively. Applying statistical techniques such as principal component analysis (PCA) and Pearson correlation matrix analysis (PCMA) makes it evident that the physicochemical attributes of water sourced from the aquifers in the study area result from a blend of diverse origins. In addition, Gibbs, Piper, Durov, and scatter plots were used to assess groundwater's geochemical evolution. Piper plot demonstrated the two types of groundwater facies, Na-HCO3- and Na-Cl, implying significant contributions from evaporitic dissolution and silicate weathering. Also, the scatter plots have evaluated the impression of mine acid leachate, evaporitic dissolution, and silicate weathering to upsurge salt formation in the groundwater. The pollution risk evaluation within the study area was conducted using the groundwater pollution index (GPI). This index revealed a prominent concern for pollution, particularly in the northern segment of the study region. As a result, it can be inferred that the fine aeolian sand and silt formations in the northern part are relatively more vulnerable to contamination.

A comparative genomics study of the microbiome and freshwater resistome in Southern Pantanal

This study explores the resistome and bacterial diversity of two small lakes in the Southern Pantanal, one in Aquidauana sub-region, close to a farm, and one in Abobral sub-region, an environmentally preserved area. Shotgun metagenomic sequencing data from water column samples collected near and far from the floating macrophyte Eichhornia crassipes were used. The Abobral small lake exhibited the highest diversity and abundance of antibiotic resistance genes (ARGs), antibiotic resistance classes (ARGCs), phylum, and genus. RPOB2 and its resistance class, multidrug resistance, were the most abundant ARG and ARGC, respectively. Pseudomonadota was the dominant phylum across all sites, and Streptomyces was the most abundant genus considering all sites.

Floating plants reduced methane fluxes from wetlands by creating a habitat conducive to methane oxidation

Wetlands are one of the important natural sources of atmospheric methane (CH4), as an important part of wetlands, floating plants can be expected to affect methane release. However, the effects of floating plants on methane release are limited. In this study, methane fluxes, physiochemical properties of the overlying water, methane oxidation potential and rhizospheric bacterial community were investigated in simulated wetlands with floating plants Eichhornia crassipes, Hydrocharis dubia, and Trapa natans. We found that E. crassipes, H. dubia, and T. natans plants could inhibit 84.31% - 97.31%, 4.98% - 88.91% and 43.62% - 92.51% of methane fluxes at interface of water-atmosphere compared to Control, respectively. Methane fluxes were negatively related to nutrients concentration in water column but positively related to the aerenchyma proportions of roots, stems, and leaves. At the same biomass, root of E. crassipes (36.44%) had the highest methane oxidation potential, followed by H. dubia (12.99%) and T. natans (11.23%). Forty-five bacterial phyla in total were identified on roots of three plants and 7 bacterial genera (2.10% - 3.33%) were known methanotrophs. Type I methanotrophs accounted for 95.07% of total methanotrophs. The pmoA gene abundances ranged from 1.90 × 1016 to 2.30 × 1018 copies/g fresh weight of root biofilms. Abundances of pmoA gene was significantly positively correlated with environmental parameters. Methylotrophy (5.40%) and methanotrophy (3.75%) function were closely related to methane oxidation. This study highlights that floating plant restoration can purify water and promote carbon neutrality partially by reducing methane fluxes through methane oxidation in wetlands.

Use of wood and cork in biofilters for the simultaneous removal of nitrates and pesticides from groundwater

About 13% and 7% of monitored groundwater stations in Europe exceed the permitted levels of nitrates (50 mg NO₃^- L^-1) or pesticides (0.1 μg L^-1), respectively. Although slow sand filtration can remove nitrates via denitrification when oxygen is limited, it requires an organic carbon source. The present study evaluates the performance of the use of wood pellets and granulated cork as carbon sources in bench-scale biofilters operated under water-saturated and water-unsaturated conditions for more than 400 days. The biofilters were monitored for nitrate (200 mg L^-1) and pesticide (mecoprop, diuron, atrazine, and bromacil, each at a concentration of 5 μg L^-1) attenuation, as well as for the formation of nitrite and pesticide transformation products. Microbiological characterization of each biofilter was also performed. The water-saturated wood biofilter achieved the best nitrate removal (>99%), while the cork biofilters lost all denitrification power over time (from 38% to no removal). The unsaturated biofilter columns were not effective for removing nitrates (20-30% removal). As for pesticides, all the biofilters achieved high removal rates of mecoprop and diuron (>99% and >75%, respectively). Atrazine removal was better in the wood-pellet biofilters than the cork ones (68-96% vs. 31-38%). Bromacil was only removed in the water-unsaturated cork biofilter (67%). However, a bromacil transformation product was formed there. The water-saturated wood biofilter contained the highest number of denitrifying microorganisms, with Methyloversatilis as the characteristic genus. Microbial composition could explain the high removal of pesticides and nitrates achieved in the wood-pellet biofilter. Overall, the results indicate that wood-pellet biofilters operated under water-saturated conditions are a good solution for treating groundwater contaminated with nitrates and pesticides.

Recent advances in the source identification and remediation techniques of nitrate contaminated groundwater: A review

Researchers have long been committed to identify nitrate sources in groundwater and to develop an advanced technique for its remediation because better apply remediation solution and management of water quality is highly dependent on the identification of the NO₃^- sources contamination in water. In this review, we systematically introduce nitrate source tracking tools used over the past ten years including dual isotope and multi isotope techniques, water chemistry profile, Bayesian mixing model, microbial tracers and land use/cover data. These techniques can be combined and exploited to track the source of NO₃^- as mineral or organic fertilizer, sewage, or atmospheric deposition. These available data have significant implications for making an appropriate measures and decisions by water managers. A continuous remediation strategy of groundwater was among the main management strategies that need to be applied in the contaminated area. Nitrate removal from groundwater can be accomplished using either separation or reduction based process. The application of these processes to nitrate removal is discussed in this review and some novel methods were presented for the first time. Moreover, the advantages and limitations of each approach are critically summarized and based on our own understanding of the subject some solutions to overcomes their drawbacks are recommended. Advanced techniques are capable to attain significantly higher nitrate and other co-contaminants removal from groundwater. However, the challenges of by-products generation and high energy consumption need to be addressed in implementing these technologies for groundwater remediation for potable use.

Groundwater quality and human health risk assessment in selected coastal and floodplain areas of Bangladesh

Groundwater aquifers are a common source of drinking water in Bangladesh. However, groundwater contamination is a major public health concern across the country. This research aims to examine the groundwater quality and health concerns using a random sampling process. Multivariate statistical and health risk analyses of elements were performed to determine the source of contaminants and their effects on human health. A total of 24 parameters were analyzed, where Na⁺, NH₄⁺, K⁺, Mg²⁺, F^-, NO₃^-, Mn, Fe, Se, U, and As concentrations were found to be high in different sampling points compared to the Department of Environment of Bangladesh (DoE), and the World Health Organization (WHO) groundwater quality standards. Principal Component Analysis (PCA) and Cluster Analysis (CA) identified the dominant and potential sources of contaminants in the groundwater aquifer, including geogenic, salinity intrusion, industrial, and agricultural. The results of the degree of contamination level (C_d) and the heavy metal pollution index (HPI) showed that 28% and 12% of the sampling points had high levels of heavy metal contamination, indicating a high risk for human health issues. Cr concentrations were found to have a higher carcinogenic (cancer) risk than As and Cd concentrations. Hazard quotient (HQ) and hazard index (HI) scores expressed the hazardous status and possible chronic effects in the context of individual sampling points. For both child and adults, 44% and 36% of the sampling points had a high HI score, indicating the possibility of long-term health risks for local populations.

Assessment of a novel microalgae-cork based technology for removing antibiotics, pesticides and nitrates from groundwater

Groundwater pollution has increased in recent years due to the intensification of agricultural and livestock activities. This results in a significant reduction in available freshwater resources. Here, we have studied the long term assessment of a green technology (1-4 L/day) based on a photobioreactor (PBR) containing immobilised microalgae-bacteria in polyurethane foam (PF) followed by a cork filter (CF) for removing nitrates, pesticides (atrazine and bromacil), and antibiotics (sulfamethoxazole and sulfacetamide) from groundwater. The prototype was moderately effective for removing nitrates (58%) at an HRT of 8 days, while its efficiency decreased at a HRT of 4 and 2 days (<20% removal). The combined use of PBR-CF enabled antibiotics and pesticides to be attenuated by up to 95% at an HRT of 8 days, but their attenuation decreased with shorter HRT, with pesticides being the compounds most affected (reducing from 97 to 98% at an HRT of 8 days to 23-45% at an HRT of 2 days). Pesticide transformation products were identified after the CF, supporting biodegradation as the main attenuation process. A gene-based metataxonomic assessment linked the attenuation of micropollutants to the presence of specific pesticide biodegradation species (e.g. genus Phenylobacterium, Sphingomonadaceae, and Caulobacteraceae). Therefore, the results highlighted the potential use of microalgae and cork to treat polluted groundwater.

A Review on Microorganisms in Constructed Wetlands for Typical Pollutant Removal: Species, Function, and Diversity

Constructed wetlands (CWs) have been proven as a reliable alternative to traditional wastewater treatment technologies. Microorganisms in CWs, as an important component, play a key role in processes such as pollutant degradation and nutrient transformation. Therefore, an in-depth analysis of the community structure and diversity of microorganisms, especially for functional microorganisms, in CWs is important to understand its performance patterns and explore optimized strategies. With advances in molecular biotechnology, it is now possible to analyze and study microbial communities and species composition in complex environments. This review performed bibliometric analysis of microbial studies in CWs to evaluate research trends and identify the most studied pollutants. On this basis, the main functional microorganisms of CWs involved in the removal of these pollutants are summarized, and the effects of these pollutants on microbial diversity are investigated. The result showed that the main phylum involved in functional microorganisms in CWs include Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. These functional microorganisms can remove pollutants from CWs by catalyzing chemical reactions, biodegradation, biosorption, and supporting plant growth, etc. Regarding microbial alpha diversity, heavy metals and high concentrations of nitrogen and phosphorus significantly reduce microbial richness and diversity, whereas antibiotics can cause large fluctuations in alpha diversity. Overall, this review can provide new ideas and directions for the research of microorganisms in CWs.

Effect of intermittent induced aeration on nitrogen removal and denitrifying-bacterial community structure in Cork and gravel vertical flow pilot-scale treatment wetlands

In this work, we have evaluated the impact of intermittent induced aeration in total nitrogen (TN), ammonia (NH₄-N) and nitrate-nitrogen (NO₃-N) removal in four pilot-scale vertical flow constructed wetlands (VFCW) (two aerated two non-aerated) using cork by-product or gravel as the filter material and planted with Phragmites australis. Both aerated and non-aerated systems achieved high COD and BOD₅ elimination rates (≥ 90%) at the end of the 5-month test period. However, the aerated systems presented maximal COD and BOD₅ removal from the third month of operation onwards since air supply favored the oxidative bioprocesses occurring within the wetlands. Cork and gravel aerated VFCW also proved to be more efficient (p < 0.05) in NO₃-N removal than the non-aerated systems and this upgraded performance was correlated with a significant higher relative abundance of the nirS gene. The aerated systems also showed a slightly improved NH₄-N removal. Noticeably, cork VFCW showed higher TN removal mean values (∼35%) than gravel wetlands (27-28%) regardless aeration. Moreover, cork VFCW showed higher relative abundance of the nosZ gene. Our results demonstrated a better nitrogen elimination for the aerated cork pilot-scale VFCW, and this behavior was correlated with a higher abundance of both nirS and nosZ, two of the key functional genes involved in nitrogen metabolism.

Change in microbial profile and environmental conditions in a constructed wetland system treating greywater

The objective of this work was to verify the relationships between environmental conditions and microbial processes along a raw-light greywater flow in an improved constructed wetland (CW) system. Physicochemical analysis and high-throughput DNA sequencing were performed in the different zones to investigate the environmental conditions and microbial communities. The results showed that the system operated predominantly under anaerobic conditions, with redox potential (Eh) increasing from the inlet (-342.9 mV) to the outlet (-316.4 mV). Conversely, the chemical oxygen demand (COD) decreased along the greywater flow, suggesting negative correlation between these characteristics. The zones of the evapotranspiration and treatment tank (CEvaT) were characterized by lower community diversity and richness and by the presence of specific groups: Proteobacteria and Synergistetes related to the first steps of the conversion of organic carbon, in the bottom layer inside the anaerobic chamber (AnC); methanogens (Methanosaeta and Methanobacterium) and sulphate-reducing bacteria (Desulfovibrio, Desulforhabdus and Desulfomonile) in the middle layer; and microorganisms associated with the nitrogen cycle and oxygen release (Acinetobacter, Novosphingobium, Candidatus Nitrososphaera) in the top layer. On the other hand, the increase of the ORP and decrease of organic matter concentrations were associated with higher community diversity and richness in the middle layer of the CW, which showed higher abundance of microorganisms involved in methane (Methylobacterium and Candidatus Koribacter) and sulphur (Rhodoblastus and Thiobacillus) oxidation.

Groundwater chemistry, distribution and potential health risk appraisal of nitrate enriched groundwater: A case study from the semi-urban region of South India

In recent years, an elevated concentration of nitrate in groundwater has been a growing problem on a global scale. It directly shows the adverse effects on human health via various intake pathways. Herein, the aim of the present study was to evaluate the nitrate concentration in groundwater and its associated human health risk in various age groups (females, males and children) in the investigated region. For this purposes, thirty groundwater samples were collected and analyzed physico-chemical parameters including nitrate concentration. The results showed that, the concentration of nitrate ranges from 14 to 82 mg/L and about 43.3% of these groundwater samples beyond the safe level of 45 mg/L according to Indian guidelines. The higher nitrate contamination is observed in the vicinity of Sarvepalli and Timmapur villages where groundwater chemistry is majorly influenced by anthropogenic sources. Health risks were assessed through oral/ingestion and dermal contact exposure routes for females, males and children population in the study region. Oral exposure was much higher than dermal contacts. For the non-carcinogenic risk, the HI_Total values of groundwater in the investigated region varied from 0.313 to 1.976 (mean of 0.941) for males, 0.370 to 2.336 (mean of 1.112) for females and 0.443 to 2.694 (mean of 1.314) for children. The health risk assessment for nitrate divulged that 60%, 57% and 50% of groundwater samples pose a non-carcinogenic health risk for children, females and males, respectively.

Review: recent developments of substrates for nitrogen and phosphorus removal in CWs treating municipal wastewater

Substrates are the main factor influencing the performance of constructed wetlands (CWs), and especially play an important role in enhancing the removal of nitrogen and phosphorus from CWs. In the recent 10 years, based on the investigation of emerged substrates used in CWs, this paper summarizes the removal efficiency and mechanism of nitrogen and phosphorus by a single substrate in detail. The simultaneous removal efficiency of nitrogen and phosphorus by different combined substrates is emphatically analyzed. Among them, the reuse of industrial and agricultural wastes as water treatment substrates is recommended due to the efficient pollutant removal efficiency and the principle of waste minimization, also more studies on the environmental impact and risk assessment of the application, and the subsequent disposal of saturated substrates are needed. This work serves as a basis for future screening and development of substrates utilized in CWs, which is helpful to enhance the synchronous removal of nitrogen and phosphorus, as well as improve the sustainability of substrates and CWs. Moreover, further studies on the interaction between different types of substrates in the wetland system are desperately needed.

Variations of soil bacterial diversity and metabolic function with tidal flat elevation gradient in an artificial mangrove wetland

Understanding the sensitivity of soil bacteria to environmental fluctuations can enhance the management of microbial ecosystem services in artificial mangrove wetlands. In this study, the variation in bacterial diversity and metabolic functions in different compartments (bulk soil, rhizosphere soil, and rhizoplane) of the soil and mangrove plant along the tidal elevation gradient was studied in Xiatanwei (Xiamen China) mangrove wetland park, a Kandelia obovata-dominated artificial mangrove stand. With the increase of the tidal flat elevation, the soil pH, total organic matter, and soil moisture contents decreased significantly, while the soil electric conductivity and redox potential increased significantly. The bacterial diversity in the bulk soil and the rhizosphere soil both decreased with the elevation of tidal levels. The relative abundance of the dominant phyla in the bulk and rhizosphere soils decreased with the rise of the tidal flat level. A significant rhizosphere effect was observed in the roots of K. obovata that the rhizosphere soil had higher bacterial diversity and richness than that in the bulk soil nearby. The rhizosphere soil of K. obovata at the low-tidal flat was enriched with the genera Nitrospira and Planctomycetes, which are valuable for the mangrove ecosystem. The Chao1 estimator and Shannon index of the bacterial community in the rhizoplane of K. obovata were much lower than that in the rhizosphere and bulk soils. Results of Biolog-Eco assay show that the bacterial groups in low tidal flat bulk soil had the highest ability in utilizing the carbon sources, which was indicated by the high values of average well color development and the high McIntosh index, and the utilization ability of carbon source decreased with the increase of tidal flat levels. The variation of the soil humidity and Eh jointly shaped the diversity and metabolic function of soil bacterial communities along the tidal flat elevation gradient.

Carbon sources derived from maize cobs enhanced nitrogen removal in saline constructed wetland microcosms treating mariculture effluents under greenhouse condition

This study investigated an alternative carbon source derived from maize cobs (MCs) to enhance nitrogen removal in saline constructed wetlands (SCWs). The main objectives were to select the proper pretreatment method of MCs for rapid carbon release; and to investigate the effects of maize cob pieces (i.e. MCP) and three addition levels of maize cob lixiviums (i.e. L-MCL, M-MCL and H-MCL) on nitrogen purification performance and microbial characteristics of SCWs. Results showed NaOH pretreatment enhanced carbon release of MCs in seawater (from 7.5 ± 0.4 mg_COD g^-1 to 16.4 ± 0.2 mg_COD g^-1). The 80-d trial showed SCWs with M-MCL addition performed well on nitrogen removal: NO₃-N, 88.8 ± 11.6%; NO₂-N, 91.1 ± 3.5%; TAN, 96.5 ± 1.6%; TIN, 89.8 ± 10.4%; with 2 mg L^-1 effluent COD. Denitrification parameters confirmed MCL to be a high quality carbon source: denitrification potential (P_DN) = 0.16 g_N g_COD^-1; heterotrophy anoxic yield coefficient (Y_H) = 0.54 g_COD g_COD^-1. The MCP and H-MCL treatments improved substrate dehydrogenase activity, indicating a higher microbial activity in these SCWs. Sequencing analysis revealed that, regardless of addition manners, carbon sources from MCs changed the rhizosphere microbial community. At genus level, Anaerophaga (10.1%), Granulosicoccus (8.2%) and Sulfurimonas (6.6%) dominated in SCWs under MCP treatment. Increased MCL addition levels improved the relative abundance of Vibrio, Malonomonas and Caldithrix, suggesting the enhancement of denitrification. Relative high proportions of Desulfotignum and Desulfovibrio, and Sulfurimonas were observed in MCP and H-MCL SCWs, implying that sulfate reduction occurred in SCWs with excess carbon sources.

A re-circulating horizontal flow constructed wetland for the treatment of synthetic azo dye at high concentrations

A re-circulating horizontal flow constructed wetland (RHFCW) system was developed in a greenhouse. This system was operated with Typha domingensis to study the phytoremediation capacity of this macrophyte species in different developing stages for synthetic textile wastewater with the pollutant type, the amaranth (AM) azo dye. Experiments were applied with a fixed flow rate Q = 10 L/h corresponding to a theoretical residence time of 3 h. The synthetic feeding to the RHFCW container was re-circulated back until the required water quality was achieved. The performance of this pilot-scale system was compared to an unplanted RHFCW. The effect of the initial dye concentration was studied using four dye concentrations (10, 15, 20, and 25 mg/L). The following parameters pH, color, COD, BOD₅, NO₃^-, NO2^-, and NH₄⁺ were monitored during treatment. The maximum efficiencies obtained for discoloration, COD, NO₃^-, and NH₄⁺ were 92 ± 0.14%, 56 ± 1.12%, 92 ± 0.34%, and 97 ± 0.17% respectively. Experiences demonstrate a decrease of removal efficiencies of studied parameters with the increase of dye concentrations, leading to an increase of the duration of treatment. Changes in activities of antioxidant enzymes (superoxide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), ascorbic peroxidase (APX), and glutathione reductase (GR)) and their relation to plant defense system against stress were studied. Enzymes were evaluated in leaves of T. domingensis during the remediation of the azo dye (amaranth). During treatment, an increase of enzymes activities was observed in accordance with the high removal efficiency.