Constructed Wetland System Research Articles

The Effect of Effluent Recirculation in a Full-Scale Constructed Wetland System

This study deals with the effect of effluent recirculation (ER) on the pollutant removal efficacy of a full-scale, hybrid treatment system composed of a macrophyte pond and a horizontal flow constructed wetland. The average removals of 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), turbidity, total N (TN), ammonium nitrogen (NH4-N), total phosphorus (TP), sulfates, E. coli and Total coliforms (TC) for the years 2017–2018 (no recirculation), 2019 (50% recirculation) and 2021 (100% recirculation) were compared. Results show a general improvement of the effluent with ER. Removals for 0%, 50% and 100% ER, respectively, were: 59%, 61% and 66% for COD; 90%, 96% and 96% for BOD; 94%, 94% and 99% for TSS; 33%, 40% and 67% for TN; 22%, 30% and 55% for NH4-N; 92%, 98% and 96% for sulfates; 99.6%, 99.7% and 99.9% for E. coli; and 99.5%, 99.7% and 9.9% for TC. No clear effect was observed on the removal of TP and dissolved PO4-P, which were very low. 50% ER improved turbidity removal from 88% to 91%, but 100% ER provided worse results. The removal of NH4-N and TN significantly improved with 100% ER. This indicates that ER can be a simple, economic, and feasible way to upgrade the performance of full-scale natural wastewater treatment systems.

Life Cycle Analysis of Lab-Scale Constructed Wetlands for the Treatment of Industrial Wastewater and Landfill Leachate from Municipal Solid Waste: A Comparative Assessment

Purpose: The objective of this study was to measure the environmental impact of five different laboratory-scale constructed wetland (CW) treatment systems with varying design approaches, which have been employed to treat different types of wastewater. Moreover, the present study also assessed the feasibility of treating landfill leachate using four different hybrid wetlands built outdoors, and analyzed the environmental viability based on the life cycle assessment (LCA). Primarily, the choice of media materials has been the focus of evaluating the sustainability of the systems, as for each system the media materials cover major material consumption and define treatment performance. Methods: This study applied a life cycle assessment using the SimaPro software tool to quantify the environmental impacts from the constructed wetland systems. Primarily, the LCA has been applied by adopting the ReCiPe 2016 method with cross-validation using the Impact 2002+ method. Moreover, an uncertainty analysis has been performed to determine any uncertainties involved in the datasets, along with sensitivity analysis on the inventory. Results and discussions: As the results suggest, the systems employed for wastewater treatment using cement mortar have the highest environmental burden. In contrast, the natural media choices, sugarcane bagasse and coco-peat, have proved to be environmentally favorable. Media employment from recycled materials like brick and steel slag could significantly redeem the previous environmental burdens of these materials, providing treatment efficiency. However, the systems employed for landfill leachate treatment revealed the CW using brick chips as the most vulnerable system with regards to environmental concerns, implying that the media brick chips are certainly the major contributor behind this high leap in the scale. However, both the systems worked very well in the carcinogenic category, providing good treatment performance, and eventually exerting lesser impact. Conclusion: The overall assessments suggested choice of media materials are essential to deciding the sustainability of a CW design. However, the CW is more beneficial and environmentally friendly than the other treatment methods, until the design scale has a high capacity. Nevertheless, the choice of the LCA method is also significant, while measuring impact scales.

Removal of tetracycline and chloramphenicol through constructed wetlands: Roles of plants, substrates, and microbial fuel cells

In this study, wastewater was analyzed for the presence of the antibiotics, tetracycline (Tet) and chloramphenicol (Chlor). Additionally, the antibiotic removal capacities of constructed wetland systems, with interacting macrophytes (Lemna gibba and Azolla filiculoides), substrates (sand and silt) and with or without microbial fuel cells (MFCs), were examined. To find the ideal wetland combination, a randomized 23 factorial design was applied, resulting in eight combinations in triplicate. The initial and final concentrations of antibiotics in the aquatic medium and in plants at the end of the experiment were measured with a high-performance liquid chromatography-diode array detector (HPLC-DAD) to verify the absorption rate. The results showed average Tet and Chlor concentration in wastewater samples 4.25 ± 3.95 and 1.87 ± 0.07 μg/L, respectively. All wetland types performed efficiently, removing a maximum of 100% tetracycline and chloramphenicol and a minimum of 99.45% and 97.84% Tet and Chlor, respectively. The average absorption of Tet and Chlor was 3.13 and 0.36 μg/g, respectively, in A. filiculoides; and the average absorption of Tet and Chlor was 2.08 and 0.08 μg/g, respectively, in Lemna. L. gibba had a higher biomass increase and a better relative growth rate than Azolla. In relation to electrical production, at first, all treatments were affected by the antibiotics; however, production increased as time progressed. Finally, the physicochemical parameters that improved with treatment were oxygen, oxidation-reduction potential and pH, whereas conductivity, dissolved solids, and salinity were most influenced by the silt substrate. Overall, although no wetland was ideal, all combinations were efficient at removing antibiotic contaminants.

Nitrogen removal performance and bacterial community analysis of a multistage step-feeding tidal flow constructed wetland

A multistage mesocosm vertical flow constructed wetland system was designed to treat synthetic domestic wastewater with a high nitrogen (N) load. The study aim was to determine the impact of design and operational variables on N removal efficiency in such systems. A tidal flow operational strategy enhanced aeration and was coupled with a step-feeding approach to promote N removal. Over the 420-day running period N removal rates were between 70 and 77 gN/m3/d, for a step-feeding ratio range of 60:40 to 80:20. The system was able to remove 91–95% of chemical oxygen demand, 74–91% of ammonium and 66–81% of total-N. Tidal flow and step-feeding strategies significantly impacted nitrogen removal with the best performance at a step-feeding ratio of 80:20 providing a carbon to nitrogen (COD/N) ratio of 4–5. The bacterial diversity increased at each stage throughout the system with dominating phyla Proteobacteria, Firmicutes, Planctomycetes, Bacteroidetes, Chloroflexi, Verrucomicrobia and Acidobacteria. Dominant bacteria at the genus level were Thiothrix, Planctomyces, Azonexus, Pseudoxanthomonas, Hydrogenophaga, Gemmobacter and other genera suggesting that N removal was accomplished via diverse metabolic pathways, including autotrophic nitrification, heterotrophic denitrification, autotrophic denitrification, and possibly anammox. This study shows benefits of step-feeding strategies in tidal flow constructed wetlands as a cost-effective solution for minimizing external carbon input to achieve effective N removal.

Performance and microbial community features of tidal-flow biochar-amended constructed wetlands treating sodium dodecyl sulfate (SDS)-containing greywater

A large quantity of surfactants (e.g., sodium dodecyl sulfate (SDS)) are discharged along with greywater especially during the COVID-19 pandemic, while information on the treatment of surfactant-containing greywater using eco-friendly constructed wetlands (CWs) and the impact of surfactants on CW systems has rarely been reported. In the present study, lab-scale CWs amended with a biochar substrate and operated in tidal flow (TF) mode were used to treat SDS-containing greywater. The results showed that the biochar-amended CWs removed NH4+-N significantly better (18.2–37.9%) than the gravel-only CWs (2.5–24.6%) but removed phosphorus (P) and COD less efficiently, and the feeding of SDS at 50 and 100 mg/L led to a notable decrease in N removal. TF not only notably improved the pollutant removal performance but also effectively eliminated SDS stress in the CWs (NH4+-N removal of 67.1–72.1%). Mean SDS removal efficiencies of 75.3–79.3% were obtained in the CWs. TF mode altered the microbial community structure and metabolic pattern and enhanced the abundance of functional bacteria related to N and P removal in the CWs. The bacterial community shifted considerably with SDS feeding, resulting in higher species diversity and more intensive co-occurrence network relationships. TF-CWs filled with composite substrates are highly feasible and promising for the treatment of SDS-containing greywater.

Towards Effective, Sustainable Solution for Hospital Wastewater Treatment to Cope with the Post-Pandemic Era.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread across the globe since the end of 2019, posing significant challenges for global medical facilities and human health. Treatment of hospital wastewater is vitally important under this special circumstance. However, there is a shortage of studies on the sustainable wastewater treatment processes utilized by hospitals. Based on a review of the research trends regarding hospital wastewater treatment in the past three years of the COVID-19 outbreak, this review overviews the existing hospital wastewater treatment processes. It is clear that activated sludge processes (ASPs) and the use of membrane bioreactors (MBRs) are the major and effective treatment techniques applied to hospital wastewater. Advanced technology (such as Fenton oxidation, electrocoagulation, etc.) has also achieved good results, but the use of such technology remains small scale for the moment and poses some side effects, including increased cost. More interestingly, this review reveals the increased use of constructed wetlands (CWs) as an eco-solution for hospital wastewater treatment and then focuses in slightly more detail on examining the roles and mechanisms of CWs' components with respect to purifying hospital wastewater and compares their removal efficiency with other treatment processes. It is believed that a multi-stage CW system with various intensifications or CWs incorporated with other treatment processes constitute an effective, sustainable solution for hospital wastewater treatment in order to cope with the post-pandemic era.

Recent advances in constructed wetlands methane reduction: Mechanisms and methods.

Constructed wetlands (CWs) are artificial systems that use natural processes to treat wastewater containing organic pollutants. This approach has been widely applied in both developing and developed countries worldwide, providing a cost-effective method for industrial wastewater treatment and the improvement of environmental water quality. However, due to the large organic carbon inputs, CWs is produced in varying amounts of CH4 and have the potential to become an important contributor to global climate change. Subsequently, research on the mitigation of CH4 emissions by CWs is key to achieving sustainable, low-carbon dependency wastewater treatment systems. This review evaluates the current research on CH4 emissions from CWs through bibliometric analysis, summarizing the reported mechanisms of CH4 generation, transfer and oxidation in CWs. Furthermore, the important environmental factors driving CH4 generation in CW systems are summarized, including: temperature, water table position, oxidation reduction potential, and the effects of CW characteristics such as wetland type, plant species composition, substrate type, CW-coupled microbial fuel cell, oxygen supply, available carbon source, and salinity. This review provides guidance and novel perspectives for sustainable and effective CW management, as well as for future studies on CH4 reduction in CWs.

Application of Circular Economy in Oil and Gas Produced Water Treatment

The circular economy (CE) is a promising model in industrial waste management, offering viable long-term resource sustainability. The rising costs of the oil and gas industry make circularity a reliable approach for saving materials, money, and energy. In recent years, attention has risen to the need to apply CE within oil and gas produced water (PW) treatment. The most common treatment practice for PW is based on mechanical treatment, with optional disposal of treated water into deep wells. However, this procedure consumes a lot of energy, increases operational costs, and causes environmental risks. This research aims to propose sustainable treatment technology promoting circularity by introducing a novel nature-based solution to treat PW. The main research objective is to develop a circular model for PW treatment by investigating the treatment of PW using constructed wetlands (CWs) to sustainably reduce the amount of waste in oil and gas fields. Additionally, investigate the use of industrial wastes as filtration materials for CW systems. In this study, eight different laboratory-scale CWs models were designed and tested. The CWS operated in two different types of flow directions: vertical (VF) and horizontal flow (HF). The main filter media for the CW system included aggregates, activated carbons, plastic, and shredded tires. The study investigated the removal rates of Total suspended solids (TSS), Total dissolved solids (TDS), Oil and Grease (OG), and Total Petroleum Hydrocarbon (TPH) from the PW. Testing the CWs, it was found that the results of the PW treatment were promising, with the potential for more future shredded tires and plastic applications. All systems were effective at removing contaminants from produced water, with the highest recorded removal efficiencies of 94.8% TSS, 33.7% TDS, 90.2% OG, and 98.4% TPH. The research results were efficient and promoted the circular use of CW in PW treatment in addition to the possibility of reusing the treated effluent in agriculture and irrigation.

Succession dynamics of microbial communities responding to the exogenous microalgae ZM-5 and analysis of the environmental sustainability of a constructed wetland system

Constructed wetlands (CWs) are economical and effective swine tailwater treatment systems. However, nitrogen removal in CWs is limited by the lack of carbon source for denitrification. In this study, we studied the feasibility of dosing the microalgae ZM-5 to improve the nitrogen removal ability in CWs. Compared to the control CW, a 20 % higher removal capacity of COD and TN was observed for the coupled system (EG). The microalgae ZM-5 could interact with denitrifying bacteria to compensate for the deficiency of denitrifying stage in CWs. HT-qPCR chip analysis also provided evidence that denitrification genes significantly increased (p < 0.05). According to the life cycle assessment (LCA), ultrasonic extraction had the best environmental sustainability among four lipid extraction processes. As an improvement strategy, clean energy could be utilized to optimize the electricity source to reduce environmental load (45 %–60 %). These findings offer new insights into the feasibility of EG for environmentally sustainable wastewater treatment.

Landfill leachate treatment by a combination of a multiple plant hybrid constructed wetland system with a solar photoFenton process in a raceway pond reactor

The sustainable and green treatment of landfill leachate (LL), produced by municipal solid waste, represents one of the most relevant challenges in the integrated waste management systems. Accordingly, in this work a green solution was investigated by coupling an innovative hybrid constructed wetland (HCW) to a solar photo-Fenton (SPF) process. A multiple layers HCW pilot plant including different medium substrates (sand, solid compost and carriers) and plant species (Phragmites australis, Arundo donax and A. plinii) was designed. The HCW was functionalised with compost tea solution to simultaneously provide high nutrient content for plants and increase the microorganism biodiversity. Process efficiency was investigated using different real LLs (young and mature) in terms of chemical oxygen demand (COD), nitrogen compounds, chlorides and metals. Removals in the range 75–95% were observed for all the parameters after ten days of leachate recirculation in the pilot plant. Subsequently, the SPF process was carried out in a raceway pond reactor (RPR) as polishing step, significantly improving COD removal (further 49%). HCW combined with SPF in RPR would allow to meet the corresponding limits according to the final use/fate of the effluent by modulating the main parameters of the process.

Influence of sediment quality and microbial community on the functioning capacity of a constructed wetland treating alkaline leachate after 5.5 years in operation

Constructed wetlands (CWs) have been demonstrated as a cost-effective alternative to chemical treatment systems for mine waters, with the microbial communities attributed to promoting carbonation and aiding pH neutralization. However, few data are available for the long-term use of CWs treating alkaline leachates nor the activity of microbes within them. To investigate the feasibility of CW to buffer alkaline pH, a pilot-scale wetland was implemented in 2015 to treat alkaline bauxite residue leachate. After 5.5 years, samples of supernatant water and sediment were taken at 0.5 m increments along the 11 m long wetland. Waters were analysed for pH, EC and metal(loid) content, while sediment was subjected to physico-chemical assessment and element fractionation. Microbial biomass and community were assessed by phospholipid fatty acid analysis (PLFA) and functionality by the Rapid Automated Bacterial Impedance Technique (RABIT).Evidence presented demonstrates that the CW operating for 66 months effectively treats bauxite residue leachate, with reduced influent pH from 11.5 to 7.8. Trace element analysis revealed effective reduction in Al (94.9 %), As (86.7 %) and V (57.6 %) with substrate analysis revealing a frontloading of elevated pH and trace element content in the first 5 m of the wetland. Sediment Al, As and V were present mostly (>94 % of total) in recalcitrant forms. Sediment Na was mostly soluble (48–62 %), but soils were not sodic (ESP < 15 %). Investigations into the microbial community revealed greatest biomass was in the first 5 m of the wetland, where pH, EC and metal contents were greatest. Microbial respiration using endemic Phragmites australis as a substrate demonstrates an ability to cycle recalcitrant carbon sources within a CW system. These novel microbial findings highlight the need for further investigation into the microbial communities in alkaline CWs.

Organic media-based two-stage traditional and electrode-integrated tidal flow wetlands to treat landfill leachate: Influence of aeration strategy and plants

Landfill leachate treatment employing normal and electrode-integrated constructed wetlands is difficult due to the presence of significant amounts of organic compounds, which frequently impede the progression of microbial-based aerobic pollutant removal pathways. As a result, this study examines the effect of supplementary air availability via intermittent and continuous aeration strategies in improving organic, nutrient, and coliform removals of the unplanted, planted (normal and electrode-integrated) two-stage tidal flow constructed wetlands designed to treat landfill leachate. The constructed wetlands were filled with coal and biochar media and planted with Canna indica. Mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages of the externally aerated two-stage unplanted, only planted, planted-microbial fuel cell integrated constructed wetland systems ranged between 96 and 99%, 82 and 93%, 91 and 98%, 86 and 96%, respectively, throughout the experimental campaign. External aeration inhibited the development of a dominant anaerobic environment within the media of the wetland systems and improved overall pollutant removal. The electrode-integrated planted tidal flow wetlands produced better effluent quality than the unplanted or only planted tidal flow systems without electrode assistance. The first stages of the three wetland systems achieved an additional 5–7% COD, 7–12% TN, and 15–22% coliform removal during the continuous aeration period compared to the corresponding performance of the intermittent aeration phase. The pollutant removal performance of the second-stage wetlands decreased during the continuous aeration phase. The media composition supported electrochemically active and inactive microbial-based pollutant removal routes and the chemical adsorption of pollutants. Nitrogen and phosphorus accumulation percentage in plant tissues was low, i.e., 0.4–2.2% and 0.04–0.8%, respectively. During the continuous aeration period, the electrode-integrated tidal flow constructed wetlands achieved higher power density production, i.e., between 859 and 1432 mW (mW)/meter3(m3). This study demonstrates that external aeration might improve pollutant removal performance of the normal, electrodes integrated tidal flow-based constructed wetlands when employed for high organic-strength wastewater treatment such as landfill leachate.

Enhancement of organics and nutrient removal and microbial mechanism in vertical flow constructed wetland under a static magnetic field

Low and unstable pollutant removal is regarded as the bottleneck problem in constructed wetlands (CWs) for wastewater treatment. This study investigated the effect of static magnetic field (MF) on enhancing the purification efficiency and microbial mechanism in vertical flow CW systems for treating domestic wastewater. The results showed that MF-CWs outperformed control systems in terms of treatment performance, with average removal efficiencies of COD, NH4+-N, TN, and TP reaching 92.58%, 73.58%, 72.53%, and 95.83%, respectively. The change of malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD) activity indicated that MF application was beneficial for plant health. Additionally, higher ammonia monooxygenase (AMO) activity in MF-CWs suggested the removal of NH4+-N was facilitated. The high-throughput sequencing results demonstrated that MF application could enrich the functional bacteria such as Patescibacteria phylum, mainly, including Gammaproteobacteria, Betaproteobacteria, and Alphaproteobacteria, which further accelerated pollutants transformation. These findings would be beneficial in understanding pollutant removal processes and their mechanism in CWs with MF application.

Removal of Fe in well water using surface flow constructed wetland system with Eichhornia crassipes and Pistia stratiotes L.

Removal of Fe in well water using surface flow constructed wetland system with Eichhornia crassipes and Pistia stratiotes L.

The different units’ performance and bed length effect of constructed wetland on the removal of organic substances, solids and nutrients from municipal wastewater: a case study, Iran

This study investigated the overall performance and bed length effect of the horizontal subsurface flow constructed wetland (CW) process for full-scale municipal wastewater treatment. 168 samples were collected, including 84 samples in the hot and 84 in the cold season. Seven sampling points were selected as follows: (1) inlet raw wastewater, (2) effluent from an anaerobic pond, (3) from the first 5 m of the selected reed bed, (4) 5 m second, (5) 5 m third, (6) 5 m fourth, and (7) 5 m fifth from the reed bed. The evaluation parameters included biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). The results showed that the removal efficiency for the BOD5, COD, TSS, TN, and TP was equal to 90.6%, 90.1%, 94%, 50.2%, and 35.4%, respectively. In the final treated effluent, the concentration of all studied parameters was less than the maximum allowable amount for discharge to the receiving water. The results showed that although the treatment plant’s pollution load for BOD5 and COD parameters in winter was significantly higher than in summer, the treatment plant efficiency in winter was not significantly different from summer. The results also showed that a 15-m bed in the CW system is suitable for achieving the standard of the environmental protection organization of Iran for municipal wastewater treatment in the hot season; however, it seems not to be enough in the cold season. So, 25 m of reed bed length will be required in practice. Finally, it can be concluded that the Qasr-e-Shirin wastewater treatment plant has the proper capability to remove municipal wastewater pollutants in different temperature conditions and the quality of the final effluent indicates the accuracy of the design criteria for this system.

Peat Soil Ecosystem Restoration for Development of a Wetland- a review

Constructed wetlands are sustainable wastewater treatment technology and have been used to treat a variety of wastewaters for decades, including domestic and industrial wastewaters. They take advantage of many of the same processes that occur in natural wetlands but do so in a more controlled or engineered system. To date, surface flow and subsurface flow wetlands are the two main categories of constructed wetland applications. On the other hand, peat soil is the decomposed organic matter that have built up over thousands of years, with high moisture content. Peat soil management is imperative to maintain the mire ecosystem. The use of rhizosphere biodegradation, phyto-stabilization and phyto-accumulation have shown the possibility of improving water quality of wetland associated with peat soil. Thus, the aim of this work is to present a review in the role of constructed wetland system for peat soil management and the water quality as restoration measures of the peat soil ecosystem to promote its suitability for agricultural purpose.

Nature based-solutions for water reuse: 20 years of performance evaluation of a full-scale constructed wetland system

Water reuse is becoming an important tool in water resource management in regions with recurrent droughts and water shortages, such as the Mediterranean. However, there are still obstacles preventing the multiple application of water reuse projects, such as social acceptability and financial problems. In this context, the use of green infrastructure such as constructed wetlands in combination with conventional mechanical treatments could represent a very practical alternative. In this article, we present the evaluation of the performance and the water quality obtained by a combined system over a long period of 2 decades. The water reuse system is located in Granollers, Barcelona, Spain, and consists of 3 elements: wetland, mechanical reclamation plant and distribution network. The entire system produces >10,000 m3 annually for garden irrigation, and street and sewerage cleaning, and there are plans for a substantial increase of this water reclaimed flow in the next years. The effluent meets the water reuse standards set by the water regional authority for pH, electrical conductivity, TSS, E. coli, Legionella and Nematodes eggs, either as average or as 90th percentiles. Turbidity standard is met as average but not as 90th percentile (being 10.7 NTU, while the limit 10 NTU). The combination of the green infrastructure, represented by the wetland, and the conventional mechanical system, represented by the reclamation plant, results in excellent water quality suitable for the irrigation of public gardens and the cleaning of streets. The integration of both elements increases the reliability of the system and contributes to the social acceptance of water reuse. This work presents long-term and complete evidence at a full-scale of the contribution and benefits of nature-based solutions to sustainable water management.

Kinetics and mineralization fraction of organic matter from sewage sludge mixed with soil under controlled laboratory conditions

The objective of this work was to evaluate the kinetics and mineralization fraction of organic matter from sewage sludge mixed with the soil under controlled laboratory conditions. For this, organic material samples accumulated in layers 0–5 cm, 5–10 cm and 10–15 cm in relation to the surface of a vertical flow constructed wetland system (VF-CW) used for treatment of septic tank sludge, in addition to samples of dewatered sludge from a septic tank and a UASB reactor and non-dewatered sludge from an anaerobic digester were mixed with material collected from the surface layer of a Red Yellow Argisol at rates equivalent to the applications, via organic residues, of 300 and 600 kg ha−1 year−1 of total nitrogen. It was found that the two-phase kinetic equation fit better to the mineralization data of labile and recalcitrant organic carbon. For the lowest nitrogen application rate in the mixtures, the mineralization fractions of the total organic carbon were higher than 73%, while at the highest dose there was a reduction in the mineralization of organic matter by 17% and 63%, respectively in samples collected in layer 10–15 cm from the VF-CW and in the septic tank sludge dewatered in the drying bed.

Removal of Methylene Blue dye from textile wastewater using vertical flow constructed wetland

The aim of this study is to assess the performance of vertical flow constructed wetland system to treat synthetically prepared textile wastewater containing Methylene Blue dye (MB) of two different dye concentrations of 50 mg/L and 100 mg/L. Three lab scale Vertical Flow Constructed Wetland systems (CW1, CW2 and CW3) of size 30 cm diameter and 60 cm depth each were fabricated. CW1, acted as a control system without plants and was packed with sand, zeolite and gravel. CW2 and CW3 were planted with wetland plants - Canna Indica. CW2, was filled with packing media: sand, zeolite and gravel and CW3, with sand and gravel. The wetlands were operated in batch and continuous mode. The systems were evaluated by measuring Colour removal, Chemical Oxygen Demand (COD), pH and Electrical Conductivity (EC). The absorbance of the Methylene Blue dye in the wastewater before and after treatment was measured at the wavelength of maximum absorption using UV/visible spectrophotometer. The results showed that the wetlands CW1, CW2 and CW3 reduced colour by 85 %, 93 % and 74 % for 50 mg/L of MB and 89 %, 99 % and 74 % respectively for 100 mg/L of MB. COD removal of 70 %, 93 % and 89 % was achieved in CW1, CW2 and CW3 respectively for 50 mg/L MB. At 100 mg/L MB, COD removal was 65 %, 89 % and 83 % in CW1, CW2 and CW3 respectively. This study shows that the constructed wetland system with zeolite is a promising technique for the colour removal of methylene blue dyeing textile effluents.

Evaluation of the Richness, Species Diversity, and Biosafety of Saprotrophic Fungal Communities in Constructed Wetlands and Biological Wastewater Ponds

The present study was focused on the characterization of the biocenotic diversity of saprotrophic fungi, taking into account the impact of various treatment systems and technological stages as well as the physicochemical properties of wastewater. The biodegradation potential, the hazard posed to humans, animals, and the environment, and the effectiveness of elimination of propagules were evaluated. The most effective elimination of fungal propagules was recorded in hybrid constructed wetland systems with horizontal (HF-CW) and vertical (VF-CW) wastewater flow, especially in the VF-HF objects. The fungal communities present in wastewater from small constructed wetland (CW) and wastewater stabilization ponds (WSP) were dominated by ubiquitous terrestrial molds accompanied by a minimal number of yeasts. The similarity of the species composition of the fungal communities between the treatment plants was generally low, whereas the species diversity together with the population size was very high at the various stages of wastewater treatment. Species with potential pathogenicity to humans and animals accounted for over 45%, i.e., were classified as BioSafety Level 1 and 2 (BSL-1 and BSL-2 groups), and potentially phytopathogenic fungi represented 31.5% of the mycobiota species composition. The dynamics of fungal growth were correlated with the content of organic pollutants and nutrients (nitrogen and phosphorus) and with oxygen deficiency. The accumulation of nitrates corresponded to the decline in the frequency of fungi in treated wastewater. The lowest efficiency of the removal of fungi was exhibited by the biological wastewater stabilization ponds.