Plants In Constructed Wetlands Research Articles

Removal of Reactive Yellow 86 from Synthetic Wastewater in Lab-Scale Constructed Wetlands Planted with Cattail and Papyrus

Synthetic wastewater was treated in lab-scale constructed wetlands (CWs) in sequencing batch mode to evaluate roles of aquatic plants for removing an azo dye: Reactive Yellow 86 (RY86). Under hydraulic retention time (HRT) of 5 days, removal by unplanted CWs was less than 20% for RY86 of 10–50 mg/L. The CWs planted with cattail and papyrus demonstrated RY86 removal of 50–68% and 73–84%, respectively. For wastewater containing 50 mg/L RY86, removal in the unplanted CW was <12%, even under a 15 day HRT, although it was 22–71% in CWs planted with cattail and 34–81% in CWs planted with cattail, with increasing values under HRTs of 1 day to 15 days. Both cattail and papyrus grew well, extending their roots in the CWs for 90 days. RY86-decolorizing microorganisms were detected in CW effluent. Overall, RY86 removal was positively correlated with evapotranspiration in the CWs, indicating the plant uptake as the main removal mechanism. Papyrus and cattail, especially the former, are suitable plants for CWs intended to treat RY86-containing wastewater.

Effects of coagulation pre-treatment on chemical and microbial properties of water-soil-plant systems of constructed wetlands

Chemical coagulation has gained recognition as an effective technique to enhance the removal efficiency of pollutants in wastewater prior to their entry into a constructed wetland (CW) system. However, its potential impact on the chemical and microbial properties of soil and plant systems within CWs requires further research. This study investigated the impact of using ferric chloride (FeCl3) as a pre-treatment stage for dairy wastewater (DWW) on the chemical and microbial properties of water-soil-plant systems of replicated pilot-scale CWs, comparing them to CWs treating untreated DWW. CWs treating amended DWW had better performance than CWs treating raw DWW for all water quality parameters (COD, TSS, TP, and TN), ensuring compliance with the EU wastewater discharge directives. Soil properties remained mostly unaffected except for pH, calcium and phosphorus (P), which were lower in CWs treating amended DWW. As a result of lower nitrogen (N) and P loads, the plants in CWs receiving FeCl3-amended DWW had lower N and P contents than the plants of raw DWW CWs. However, the lower loads of P into amended DWW CWs did not limit the growth of Phragmites australis, which were able to accumulate trace elements higher than CWs receiving raw DWW. Alpha and Beta-diversity analysis revealed minor differences in community richness and composition between both treatments, with only 3.7% (34 genera) showed significant disparities. Overall, the application of chemical coagulation produced superior effluent quality without affecting the properties of soil and plant of CWs or altering the functioning of the microbial community.

Carbon slow-release and enhanced nitrogen removal performance of plant residue-based composite filler and ecological mechanisms in constructed wetland application

Stable carbon release and coupled microbial efficacy of external carbon source solid fillers are the keys to enhanced nitrogen removal in constructed wetlands. The constructed wetland plant residue Acorus calamus was cross-linked with poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) to create composite solid carbon source fillers (Ac-BDPs). The study demonstrated the slow release of carbon sources from Ac-BDPs with 35.27 mg/g under an average release rate of 0.88 mg/(g·d). Excellent denitrification was also observed in constructed wetlands with Ac-BDPs. Moreover, the average removal rate of nitrate nitrogen (NO3−-N) was increased by 1.94 and 3.85 times of the blank groups under initial NO3−-N inputs of 5 and 15 mg/L, respectively. Furthermore, the relatively high abundances of nap, narG, nirKS, norB, qnorZ and nosZ guaranteed efficient denitrification performance in constructed wetlands with Ac-BDPs. The study introduced a reliable technique for biological nitrogen removal by using composite carbon source fillers in constructed wetlands.

Promoting Aquatic Health in Constructed Wetlands: Removal of Pathogens and Nitrogen

Due to urbanization and population growth, freshwater resources have become a long-term concern for most developing countries. With the growth of population, the demand for fresh water is increasing and the requirement for sewage treatment is also increasing. In recent years, the demand for sewage recycling has increased sharply. Constructed wetlands (CWs) are an effective sewage treatment system with low energy consumption, minimal maintenance requirements, and a low operation cost, which will meet the current demand for the removal of nutrients and pathogens. The application of CWs in sewage treatment has attracted more and more attention because it is also a nature-based solution (NbS). These systems are capable of removing not only nitrogen (N) and phosphorus (P), but also pathogen indicators, such as fecal coliform and Escherichia coli. The presence of these indicators also suggests the influx of other pathogens into aquatic systems, thereby threatening aquatic ecological health. However, research on the removal of pathogens in CWs is relatively scare and their removal mechanisms are not fully understood. Despite their widespread application, the role of plants in CWs, particularly in the specific mechanism of pathogens and nitrogen removal, remains largely unknown. This article will help us to better understand this technology and provide help for our further research. In this paper, the coupled denitrification mechanism between microorganisms and plants in the process of nitrogen transformation was discussed. Plants affect nitrogen transformation microorganisms by releasing oxygen and secretions from their roots and provide substrates for bioremediation. The removal effects of different types of CWs on pathogen and nitrogen species were also summarized. Overall, the removal effect of subsurface flow wetlands outperforms that of surface flow wetlands, with multi-stage wetland systems being the most effective. The main factors affecting the removal of pathogens and nitrogen species in CWs include plants, substrates, operating parameters, UV radiation, temperature, water composition, and pH. Finally, the research frontiers on the removal of pathogens in CWs were prospected.

Study on the performance of vertical flow constructed wetland microcosm with Canna sps. for treatment of high chromium-containing wastewater

Chromium (Cr (VI)) pollution has plagued the environment due to chromite mining and various industrial actions. Constructed wetlands (CW) have emerged as a potential wastewater management technique that utilizes physical, chemical, and biological processes. The present study investigates the use of vertical flow-constructed wetlands (CW) using manure-rich garden soil and sand as substrates in planted CW (CW–P) and unplanted CW (CW-UP) to remove Cr (VI) from simulated wastewater. The experiment was performed in two phases, i.e., Phase I and II, in the same system. In Phase I, initial Cr (VI) concentrations were varied between 5 and 200 mg/l at a fixed hydraulic retention time (HRT) of 48 h, while in Phase II, the effect of HRT (24 h, 48 h, and 96 h) was studied at a fixed Cr (VI) concentration of 200 mg/L in the influent. At 24 h, HRT removal efficiencies were 90.20% for CW-P and 86.41% for CW-UP. However, at 96 h of HRT, the system showed nearly the same removal efficiency. Scanning electron microscopy with energy dispersion X-Ray spectroscopy analysis suggested the conversion of Cr (VI) to Cr (III) in soil precipitate and the translocation of Cr (VI) in plant tissues (Canna sps.). Moreover, microbial diversity profiling indicated that microbial diversity involved in pollutant removal differed in both systems. The phytotoxicity test clearly showed the decrease in toxicity level in the treated effluent, concluding the reusability of treated water. This exploratory study suggested that the CW can potentially remove a higher concentration of hexavalent chromium at longer HRT.

A review of emerged constructed wetlands based on biochar filler: Wastewater purification and carbon sequestration/greenhouse gas reduction

Constructed wetlands (CWs) are a promising ecological wastewater treatment technology. The method of biochar (BC) filler to enhance CWs has been widely researched in the past decade. This article summarizes the applications of BC-added CWs technology and consolidates the various impacts of BC filler on the operation of CWs, which can be divided into two aspects. One is to enhance the wastewater purification performance of CWs ecosystems, and the other is to improve the abilities of CWs to sequester carbon and reduce greenhouse gas (GHG) emissions. These two aspects are precisely among the environmental challenges facing humanity globally. The BC prepared from CWs plants used as CWs filler can solve excess biomass in CWs. Moreover, the large specific surface area of BC, excellent adsorption performance, and good biocompatibility improve the sewage treatment effect of CWs. The BC has a high potential for stimulating the growth of CWs plants, biomass carbon sequestration, inhibition of organic carbon mineralization in CWs substrates, and reducing GHG emissions, which mitigates global climate change. In short, the BC-added CWs is a technology that combines wastewater purification and carbon sequestration/GHG reduction. This study provides solid references for the engineering promotion of CWs based on BC filler.

Do mycorrhizal symbiosis affect wastewater purification in constructed wetlands with different substrates?

Arbuscular mycorrhizal fungi (AMF) can play important roles in pollutant removal in the terrestrial system. However, the functional role of AMF in wetland systems is still unclear. This study evaluated the effects of AMF on the purification of the pharmaceuticals and personal care products (PPCPs) containing wastewater in constructed wetlands (CWs) filled with different substrate types (sand, perlite, vermiculite or biochar). Results indicated that the removal efficiencies of total organic carbon (TOC), phosphate (PO43−-P), and total nitrogen (TN) in CWs with different substrates were in the following order: biochar > vermiculite > perlite > sand. Compared with sand systems, the removal efficiencies of TOC, PO43−-P, ammonium (NH4+-N), and TN in CWs filled with adsorptive substrates (biochar, vermiculite, or perlite) were enhanced by 3.8–11.4 %, 11.6–30.6 %, 16.5–31.2 %, and 6.2–34.6 %, respectively. AM symbiosis increased TOC, TN, and PO43−-P removal in CWs but the adsorptive substrates showed more significant influences on wastewater purification than AMF symbiosis. Besides, plant (Glyceria maxima) presence also improved the performance of CWs on wastewater purification. Overall, all the findings indicated that the interaction effects of AM symbiosis and adsorptive substrates (e.g., biochar, vermiculite, or perlite) could enhance the removal performance of pollutants from wastewater in planted CWs.

The removal of ciprofloxacin from synthetic wastewater in constructed wetland

Considering the health effects of antibiotics in the environment, effective monitoring and treatment technologies are needed to mitigate social and environmental impacts. The present study was carried out to investigate the efficiency of the constructed wetland (CW) on the removal of Ciprofloxacin (CIP) from aqueous samples. Experiments were conducted in pilot scale CWs planted with single plants of Cyperus alternifolius, Canna indica and one planted with both plant species. Analysis of CIP concentrations in the influent and effluent samples was done using Cary 60 UV–Vis spectrophotometer, while physical-chemical parameters were monitored for the influent and effluent samples. The removal efficiency of physico-chemical parameters was ˃70% for Nitrate, ˃60% for Phosphate, ˃70% for BOD and ˃77% for COD. The maximum removal of CIP (77.1%) was observed in CW planted with Cyperus alternifolius during a 7 days hydraulic retention time (HRT). The results of this study show superior performance of Cyperus alternifolius than Canna indica. There was no significance difference (p > 0.05) produced by mixing the two plants in a CW. However, mixing of plants especially ornamental plants in CWs brings good visual impression of the systems while treating the wastewater. This study demonstrate that CW can remove antibiotics from wastewater. The best performance depends on best selection and best combination of the plants.

Constructed wetlands for the treatment of household organic micropollutants with contrasting degradation behaviour: Partially-saturated systems as a performance all-rounder

The degradability of specific organic micropollutants in constructed wetlands (CWs) may differ depending on the prevalence of oxic or anoxic conditions. These conditions are governed, among other factors, by the water saturation level in the system. This study investigated the removal of three environmentally-relevant organic micropollutants: bisphenol-group plasticizer bisphenol S (BPS), household-use insecticide fipronil (FPN) and non-steroidal anti-inflammatory drug ketoprofen (KTP) in the model CWs set up in an outdoor column system. BPS and KTP, in contrast to FPN, exhibit higher biodegradability potential under oxic conditions. The experimental CWs were operated under various saturation conditions: unsaturated, partially saturated and saturated, and mimicked the conditions occurring in unsaturated, partially-saturated intermittent vertical-flow CWs and in horizontal-flow CWs, respectively. The CWs were fed with synthetic household wastewater with the concentration of the micropollutants at the level of 30–45 μg/L. BPS and KTP exhibited contrasting behaviour against FPN in the CWs in the present experiment. Namely, BPS and KTP were almost completely removed in the unsaturated CWs without a considerable effect of plants, but their removal in saturated CWs was only moderate (approx. 50%). The plants had only a pronounced effect on the removal of BPS in saturated systems, in which they enhanced the removal by 46%. The removal of FPN (approx. 90%) was the highest in the saturated and partially-saturated CWs, with moderate removal (66.7%) in unsaturated systems. Noteworthy, partially-saturated CWs provided high or very high removal of all three studied substances despite their contrasting degradability under saturated and unsaturated conditions. Namely, their removal efficiencies in planted CWs were 95.9%, 94.5% and 81.6%, for BPS, KTP and FPN, respectively. The removal of the micropollutants in partially-saturated CWs was comparable or only slightly lower than in the best treatment option making it the performance all-rounder for the compounds with contrasting biodegradability properties.

Constructed Wetlands as Nature-Based Solutions for the Removal of Antibiotics: Performance, Microbial Response, and Emergence of Antimicrobial Resistance (AMR)

Antibiotics and antibiotic resistance genes (ARGs) have been regarded as emerging pollutants and pose significant threats to the aquatic environment and to human health. This study aimed to investigate the removal of nutrients, antibiotics, and the emergency of ARGs in domestic sewage by means of constructed wetlands (CWs) filled with an electroconductive media, i.e., coke. In this study, the antibiotics removal efficiencies ranged from 13% to 100%, which were significantly higher in the system filled with coke compared with the CWs filled with common quartz sand (7~100%). Moreover, the presence of wetland plants could also significantly improve the removal of nutrients and tetracyclines. The results also demonstrated the importance of substrate selection and wetland plants in CWs on the alternation of microbial communities and structures, where the electroconductive media showed a promising effect on increasing the removal of antibiotics in CWs. In terms of the emergency of ARGs, the CWs filled with coke retained the most ARGs (10,690 copies/g) compare with the control groups (8576–7934 copies/g) in the substrate. As the accumulated ARGs could be released back to the watercourse due to the environmental/operation condition changes, the application of such an advanced substrate in CWs may pose a more significant potential threat to the environment. With these results, this study provided new insight into selection of the substrates and plants for wastewater treatment to achieve a sustainable and secure water future.

Random Forest modelling and evaluation of the performance of a full-scale subsurface constructed wetland plant in Egypt

This article presents a methodology to evaluate and model the performance of subsurface horizontal constructed wetland (SHCW) in Samaha village, Egypt's Delta. The influent and effluent biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total phosphorus (TP), and total nitrogen (TN) were measured and analyzed for the period 2018–2020. The Random Forest process (RF) was applied to predict the removal efficiency of BOD, COD, and TSS using 112 samples, 90% of samples were used as training and 10% as a test. The results show removal efficiency of 72, 77, 78, 49, and 31%, for BOD, COD, TSS, TP, and TN respectively. The Random Forest modeling fit the results well with coefficient of determination (R2) for removal efficiency of BOD, COD, and TSS equal to 0.66, 0.68, and 0.79, respectively. The Random Forest process is a good way to come up with effective management and mitigation strategies.

Removal of Heavy Metals from Acid Mine Drainage with Lab-Scale Constructed Wetlands Filled with Oyster Shells

The present study investigated the applicability of constructed wetlands (CWs) filled with oyster shells (OSs) for removing heavy metals from acid mine drainage (AMD). Lab-scale CWs consisted of columns (ID 12.5 cm, H 50 cm) packed with OSs or limestone, which were left unplanted or planted with cattails. Synthetic and real AMD containing 7.3 mg/L of Zn, 38.0 mg/L of Fe, and other minerals (pH = 4.0) were fed to the CWs (1 L/column) under a hydraulic retention time of 7 days in a sequencing batch mode. The effluent pH values of the CWs reached 6.9–8.3. Results show that OSs with high CaCO3 contents had higher neutralizing capability for AMD than limestone had. During 7 months of operation, all CWs were highly effective for removing Zn (88.6–99.2%); Fe (98.7–99.7%); and Cd, Cu, Pb, As, and Mn (48.2–98.9%) from both real and synthetic AMD. The mass balance in the CWs indicated accumulation in OSs or limestone as a main pathway for removing heavy metals, representing 44.8–99.3% of all metals, followed by biomass (8.8–29.9%) in the planted CWs. Other processes examined for this study only played a minor role in removing heavy metals. The higher metal treatment performance of OS CWs demonstrated the value of this aquaculture byproduct as a CW substrate.

Phytoremediation potential of Schumannianthus dichotomus in vertical subsurface flow constructed wetland

Schumannianthus dichotomus (Murta) is a naturally abundant wetland plant species in Bangladesh that has significant economic and aesthetic values. This species is perennial, and fast-growing in the nutrient-abundant swamp and marshes, moreover, it can thrive in a shaded and semi-shaded environment. Although it has all the potential to be a prominent Constructed Wetlands (CW) plant, no considerable study has yet been reported on the phytoremediation potential of the plant. The study was conducted to scrutinize the contaminants removal efficiency of the Murta plant in a lab-scale vertical subsurface flow constructed wetland (VSSFCW). Two CW columns were installed for the experiment: one kept planted (experimental) with the Murta plants and the another remained unplanted (control). Afterward a two months stabilization period, water samples were analyzed from the influent storage tank and both the experimental and control systems effluent at 24 h hydraulic retention time (HRT) for one month study period. The CWs were operated in the batch mode, for completing one cycle it run for one day, in keeping the flow 0.012m3/d and the hydraulic loading rate (HLR) 0.13 m3/d/m2. The results indicated higher reduction capability in the planted CW: 61.60 ± 2.85% Biochemical oxygen demand (BOD5), 53.98 ± 11.84% Chemical oxygen demand (COD), 70.25 ± 15.33% Nitrate (NO3-N), and 39.36 ± 30.85% Nitrite (NO2-N) reduction occurred in the column. Conversely, the unplanted CW reduced 43.31 ± 9.37% BOD5, 45.34 ± 8.88% COD, 9.92 ± 5.32 % NO3-N, and 15.87 ± 25.07% NO2-N. The study reports the reduction efficacy of the biochemical pollutants enhanced with the increase of the influent concentration. The average concentration of physical parameters of the influent, planted and unplanted CW was, respectively: 7.62±0.28, 6.8±0.16, 6.94±0.14 pH; 1107±140.50, 1199.03±57.48, 1050.75±96.18 μS/cm electrical conductivity (EC); 545.67±72.26, 533.51±84.12, 596.34±33.13 mg/L total dissolved solids (TDS); 0.55±0.07, 0.59±0.03, 0.52±0.02% salinity; 919.06±111.64, 835.27±39.53, 952.20±66.01 Ώ-cm resistivity; and 3.20±1.77, 5.15±1.00, 5.03±0.96 mg/L dissolved oxygen (DO). Therefore, 62% dissolved oxygen (DO) increased in the planted CW column than the influent sample water, whereas 59% DO enhance in the control. After all, the study suggests that S. dichotomus has significant organic reduction efficacy in the VSSFCW system, and could be regarded as an efficient CW plant.

Constructed Wetland Tipe Horisontal Subsurface Flow Menggunakan Rumput Odot untuk Pengolahan Efluen IPAL Tahu

The effluent of tofu’s anaerobic digester contains organic matter and require further treatment. Constructed wetland (CW) using forage grass plant is one of the alternatives. The study is aimed to observe the effect of CW’s stage variation and planting duration on TSS and COD effluent. Plant growth also observed duringoperation. Two CWs horizontal subsurface tank of dimension 100 cm x 50 cm x 50 cm were arranged in series as stage 1 and 2. Tank was planted with Pennisetum purpureum c.v Mott at spacing of 25 cm, tank without plants as control, and operated at hydraulic loading rate of 0.1 m3/m2.day. Temperature, pH and plant height was measured every 2 days, TSS and COD every 1-2 week. The study showed, there was relatively no temperature difference between control and planted CW. The pH effluent increased with the pH of stage II being higher than stage IThe TSS and COD removal efficiency in planted CW was 61-90 % and 27-85 %, while for control was 8-85 % and 13-79 %, respectively. Plant can grow, indicated by the addition of plant height and plant weight during harvesting. In conclusion, CW stage and planting duration had effect on TSS and COD effluent.

Iris pseudacorus as precursor affecting ecological transformation of graphene oxide and performance of constructed wetland

The role of plants is largely unknown in constructed wetlands (CWs) exposed to phytotoxic nanomaterials. Present study investigated transformation of graphene oxide (GO) and performance of CWs with Iris pseudacorus as precursor. GO was trapped by CWs without dependence on plants. GO could move to lower substrate layer and present increases on defects/disorders with stronger effects in planted CW. Before adding GO, planted CW achieved better removal both of phosphorus and nitrogen. After adding GO, phosphorus removal in planted CW was 93.23–95.71% higher than 82.55–90.07% in unplanted CW. However, total nitrogen removal was not improved, showing 48.20–56.66% and 53.44–56.04% in planted and unplanted CWs. Plant improved urease, phosphatase, and arylsulfatase, but it decreased β-glucosidase and had less effects on dehydrogenase and catalase. Pearson correlation matrix revealed that plant enhanced microbial interaction with high degree of positive correlation. Moreover, there were obvious shifts in microbial community at phylum and genus level, which presented closely positive action on substrate enzyme activities. The functional profile was less affected due to functional redundancy in microbial system, but time effects were obvious in CWs, especially in planted CW. These findings could provide the basis on understanding role of plants in CWs for treating nanoparticles wastewater.

Nitrogen metabolism in different configuration design constructed wetlands under exposure of graphene oxide

With occurrence of emerging contaminants in wastewater, nitrogen metabolism in constructed wetlands (CWs) should be re-evaluated at different environmental variables to withstand adversely exogenous contaminants. This study investigated functional gene, key enzyme, and microbe regulating nitrogen metabolism in three different configuration design CWs (planted W1 and W3 with full and low water level, unplanted W2 with full water level) when exposed to graphene oxide, one of most popular carbon-based nanomaterials. It was found that nitrogen removal was achieved by classical nitrification and denitrification, which was limited by nitrification in W2 and denitrification in planted CWs, presenting optimal balance between nitrification and denitrification in W1. Compared to W2, ammonium removals increased by 48% and 107% in W1 and W3, conversely total nitrogen removals decreased by 6% and 14% due to nitrate accumulation. Ammonia monooxygenase was the most sensitive to variables among four key enzymes. Bacteria were more abundant than archaea in CWs, both of functional genes and nitrifying populations were obviously affected by plant and water level in later period. The dominant denitrification populations were class Gammaproteobacteria followed by Alphaproteobacteria with the highest abundance observed in W2. Their species richness at genus level was higher on day 30 in W2 than planted CWs, but similar on day 120 in three CWs. The cooccurrence network and associated heatmap evidenced complex interaction among key enzymes, functional genes, and functional genera for nitrogen removal. KEGG annotations revealed specific differences in six core pathways of nitrogen metabolism in three CWs.

Effects of Constructed Wetlands Plants on Phosphorus Removal from Domestic Wastewater in Gaborone, Botswana

The United Nations, Sustainable Development Goal (SDG) Target 6.3. aims at “halving the proportion of untreated waste water and substantially increasing recycling and safe reuse globally” by 2030. To achieve this target, sustainable and context-specific wastewater treatment systems are urgently needed. Constructed wetlands (CW) is one of the wastewater treatment technological options available. CW have been widely accepted and acknowledged as simple, low cost, alternative and appropriate domestic wastewater treatment technology. CW were piloted by the Department of Water Affairs, Gaborone, Botswana to assess their treatment performance. Specifically, the study investigated the effects of CW plants on Phosphorus (P) removal from domestic wastewater. The first CW cell (CA) was a control which was filled with sand only, the second cell (CB) was planted with Typha Latifolia, the third (CC) with Cyperus Papyrus and the fourth (CD) with Phragmites Mauritianus. Each cell had a surface area of 100m2 and received a wastewater discharge of 4m3 /day. River sand with porosity of 0.44 and particle size diameter ranging from 2-7mm was used as plants growing media. Wastewater samples were analysed in accordance with Standard Methods for Examination of Water and Wastewater. The results showed that the P treatment performance efficiencies for CA, CB, CC, and CD were 93.6%, 97.4%, 98.1% and 98.4% respectively. Despite that there was CW plants contribution towards P removal from domestic wastewater, there was however no statistically significant performance difference (p>0.05) in P removal between the CW cells planted with different plant species. The mean effluent P concentrations from the different CW cells were; CA 0.62mg/l, CB 0.28mg/l, CC 0.19mg/l and CD 0.16mg/l. Thus, the mean P concentration from the effluent of C1 was above the Botswana Bureau of Standards Limits of 0.5mg/l. Hence the effluent was non-compliant with Botswana standards for the discharge of effluent into the environment.

Preparation of biochar from constructed wetland plant and its adsorption performance towards Cu2.

In order to solve problems in the treatment and disposal of huge production of artificial wetland plants and heavy metal pollution, two constructed wetland plants of reed and gladiolus were selected as raw materials to prepare biochar for adsorbing heavy metals from aqueous solutions. The experimental results showed that reed biochar prepared at 600℃ and activated by KOH with an impregnation ratio of 1:3 (KRAC-3) exhibited relatively high adsorption ability towards Cu2+. The optimal results analyzed by Design-Expert software showed that the maximum adsorption rate of KRAC-3 towards Cu2+ was obtained under the optimal conditions of adsorbent dosage of 1.2g/L, pH of 4.96, and reaction time of 137.43min. The adsorption of Cu2+ followed pseudo-second-order kinetics and the Langmuir adsorption model. The theoretical maximum adsorption capacity of KRAC-3 calculated from the Langmuir isotherm model was 148.08mg/g. Microscopic tests with the help of SEM, EDS, and XRD revealed that physical adsorption, ion exchange, electrostatic adsorption, surface complexation, and precipitation were the main adsorption mechanism of Cu2+ loading onto KRAC-3. This study will provide a theoretical basis for the application of biochar prepared from constructed wetland plants and the treatment of heavy metal-containing wastewater.

Plants inhibit the relative abundance of sulfonamide resistance genes and class 1 integron by influencing bacterial community in rhizosphere of constructed wetlands

Antibiotic resistance genes (ARGs) commonly detected in wastewater can potentially lead to a health crisis. Constructed wetlands (CWs) remove ARGs and sulfonamides (SAs) from wastewater, but the importance of plants in the process is seldom reported. We compared the effect of three wetland plant species (Cyperus alternifolius, Juncus effuses, and Cyperus papyrus), sample distance from the root, and SA presence on the environmental abundance of class 1 integron (intI1) and SA resistance genes (sul) using specially designed CW rhizoboxes. Quantitative polymerase chain reaction revealed that the relative abundance of the target genes in planted CWs, especially in C. alternifolius planted CWs, was significantly lower than that in unplanted CWs (P < 0.05). The substrate in the rhizosphere or near-/moderate-rhizosphere (closest to the root) showed the lowest average relative abundance of the target genes, while the bulk substrate (without the root) showed the highest abundance of these genes, irrespective of the planted species. Further, the influence of plants was more evident after 8 weeks of wastewater treatment. The trend was the same in SA-treated and untreated groups, although the relative abundance of the target genes was significantly higher in the former (P < 0.05). The weaker correlation between the intI1 and sul genes in the rhizosphere and near-/moderate-rhizosphere in comparison to the bulk substrate in the SA group suggested that the risk of horizontal gene transfer was probably higher in the bulk substrate and unplanted CW. A partial least-squares path model revealed that dissolved organic carbon and oxygen content significantly influenced SA concentration, microbial community, and intI1 genes, and then shaping the sul genes together. Finally, redundancy analysis suggested that abundance of sul genes was influenced by bacteria enriched in the bulk substrate and unplanted CWs. The findings provide new insights into the importance for controlling risk of ARGs by wetland plants.

Efficient Microcystis removal and sulfonamide-resistance gene propagation mitigation by constructed wetlands and functional genes analysis

Increasingly prevalent Microcystis blooms and the propagation of the associated resistance genes represent global environmental problems. Constructed wetlands (CWs) are a cost-effective technology used for wastewater treatment. In this study, the herb Alisma orientale and three industrial byproducts, namely, blast furnace slag, biochar, and sawdust, were selected to construct mini-CW units. Their potential to remediate toxic Microcystis and their influences on the behaviors of antibiotic-resistant genes (ARGs, sul1, sul2, and intl1) were analyzed. Approximately 98.46% of Microcystis cells were removed by the sawdust-based CW in just 2 d, wherein <0.37 μg/L residual microcystin (MC)-LR was detected, with a removal efficiency of >96.47%, which is potentially caused by the higher relative abundance of MC-degrading gene mlrA on the substrate. Lower target ARG accumulations in the sawdust-based CW may be attributed to the lower intl1 relative abundance and microbial function mobile element content, which could influence horizontal gene transfer. In three sequential batches for the treatment of eutrophic lake water, six sawdust-based CW units were assembled into CW microcosms. The efficiency of removal of Microcystis and MC-LR by planted CW microcosms ranged between 92.00% and 95.88% and between 86.48% and 94.82%, respectively; this was significantly (P < 0.05) higher than that by unplanted ones. Less accumulation of target ARGs was also observed in planted CWs. Planting considerably improved nitrogen removal, possibly owing to the enrichment of genes involved in the KEGG nitrogen metabolism pathway in the substrate through metagenomic analysis.