Potential of constructed wetland treatment systems for agricultural wastewater reuse under the EU framework

Review on the relationship between microplastics and heavy metals in freshwater near mining areas

Microplastics (MPs), degraded from plastic wastes, have drawn significant attention worldwide due to its prevalence and rapid transition. Contamination of freshwater with MPs has become an emerging global issue. Heavy metals (HMs), a prominent global pollutant, also garnered much attention due to their potential interaction with MPs, presenting a multifaceted environmental threat. The primary source of HM contamination in freshwater has been identified as mining sites. Additionally, the increasing use of plastic materials within mining areas raises concerns about MP release into the surrounding freshwater environments. Recent studies only provide information on the contamination of HMs status with MPs. However, studies on the mechanism responsible for MPs contamination from both external and internal sources of freshwater MPs and HMs are limited. The knowledge gaps in the deposition and fate of MPs in various mining situations and the possibility of combined impacts of heavy metals and MPs in the ecosystem raise ecological concerns. Here, we review the origins of MPs and HM pollution within mining sites and explore the potential combined detrimental impacts on plants and animal life. We found out that polystyrene (PS) and polyethylene (PE) have higher adsorption affinity to heavy metals, and the mingle toxic consequence of the MPs and HM can depend on the MP surface properties, pH, and salinity of the neighboring water solution. The Langmuir and Freundlich isotherm models enable the efficient design of adsorption systems. The Langmuir model describes single-layer adsorption at homogeneous sites, while the Freundlich model addresses multilayer adsorption on heterogeneous surfaces. The crucial mechanism of adsorption and desorption that underlies the occurrence of both MPs and heavy metals is a decisive matter in this issue.

Investigating the effect of hydraulic residence time, artificial aeration and plants presence on different constructed wetland designs treating oil industry effluent

Constructed Wetlands (CW) have gained popularity over the last decades due to their cost-effectiveness, easy and simple operation and environmental compatibility in wastewater treatment. This ecological engineering technology appears particularly ideal for low-income regions. In this study, three widely used CW types (horizontal flow, vertical flow, and hybrid CW) were constructed and evaluated for their effectiveness in removing various pollution parameters (BOD5, COD, TSS, NH4-N, NO3-N, and TP) from an industrial effluent. Different configurations were tested such as CW type, hydraulic residence time, plants presence, and artificial aeration. Results showed that the hybrid CW configuration (i.e., vertical flow CW followed by horizontal subsurface flow CW) achieved the highest removal rates of all pollutants, i.e., more than 90% of BOD5, COD, TSS, and NH4-N. The single horizontal flow and vertical flow CW designs showed variations in the removal of NO3-N and TP (less than 30%), which were significantly improved (50% and 70%, respectively) by using the hybrid CW system. Artificial aeration significantly improves the performance of the CW system, especially for ammonia nitrogen and organic matter removal, while plants presence is also beneficial in the treatment performance. An 8-days HRT seems to be adequate for high removal rates in passive CW designs, though in aerated wetlands a lower HRT of 4 days seems sufficient. These findings suggest that the hybrid CW system could be a promising option for efficient wastewater treatment in developing regions.

Demonstration scale treatment of drainage canal water in the Nile Delta through a combination of facultative lagoons and hybrid constructed wetlands

Drainage canal water (DCW), a mixture of Nile water, drainage water and municipal wastewater, is largely used for irrigation in the Nile Delta. Facultative lagoons (FL) and constructed wetlands (CWs) represent interesting options for DCW treatment before its agricultural re-use, but very few studies investigated their implementation in Egypt. This work aimed at developing at demonstration scale (250 m3 d-1) a FL + CW treatment train capable to turn DCW into an effluent reusable in agriculture. Three types of hybrid CWs were tested in parallel for 530 days. The combination of FL with a cascade hybrid CW, operated at a 200 L d-1 m-2 surface loading rate, led to medium-to-high removal efficiencies (suspended solids 90%, total nitrogen 84%, phosphate 80%, COD 67%, faecal coliforms 2.2 Log) and surface removal rates (COD 47.5 t y-1 ha-1, total nitrogen 10.9 t y-1 ha-1, faecal coliforms 1.5 ∙ 1011 MPN y-1 ha-1). The effluent, compliant with class C of EU 2020/741 regulation, is potentially reusable to irrigate numerous Egyptian crops. The results show that the combination of FLs with cascade hybrid CWs has a great potential for the treatment of DCW and low-strength municipal wastewater, with near-zero energy consumption, null consumption of chemicals and a land requirement varying between 1.1% and 1.5% of the agricultural land irrigated with the treated DCW.

Performance of vertical and horizontal treatment wetlands planted with ornamental plants in Central Chile: comparative analysis of initial operation stage for effluent reuse in agriculture

This study comparatively evaluated effluent reuse from two TWs-a horizontal subsurface flow (HF) and a vertical subsurface flow (VF)-used for rural wastewater treatment in Central Chile during the initial operation stage. The two TWs were planted with Zantedeschia aethiopica and were operated for 10 months at a pilot scale. The water quality of the influent and effluents was measured and compared with reuse regulations. The results showed similarities in the behavior of the effluents from the two TWs, presenting differences only in the chemical oxygen demand (COD) and different forms of nitrogen, suggesting the necessity of complementary treatment stages or modifications to the operation. The effluents from the HF better fulfilled the reuse standards for irrigation, as the VF faced problems associated with its size. However, a complementary disinfection system is necessary to improve pathogen removal in the effluents coming from the two TWs, especially to be reused as irrigation water for crops. Finally, this work showed the potential for applying subsurface TWs for wastewater treatment in rural areas and reusing their effluents as irrigation water, practice that can contribute to reducing the pressure on water resources in Chile, and that can be used as an example for other countries facing similar problems.

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.

Composition of the microbial community in surface flow-constructed wetlands for wastewater treatment

Traditionally constructed wetlands face significant limitations in treating tailwater from wastewater treatment plants, especially those associated with sugar mills. However, the advent of novel modified surface flow constructed wetlands offer a promising solution. This study aimed to assess the microbial community composition and compare the efficiencies of contaminant removal across different treatment wetlands: CW1 (Brick rubble, lignite, and Lemna minor L.), CW2 (Brick rubble and lignite), and CW3 (Lemna minor L.). The study also examined the impact of substrate and vegetation on the wetland systems. For a hydraulic retention time of 7 days, CW1 successfully removed more pollutants than CW2 and CW3. CW1 demonstrated removal rates of 72.19% for biochemical oxygen demand (BOD), 74.82% for chemical oxygen demand (COD), 79.62% for NH4 +-N, 77.84% for NO3 --N, 87.73% for ortho phosphorous (OP), 78% for total dissolved solids (TDS), 74.1% for total nitrogen (TN), 81.07% for total phosphorous (TP), and 72.90% for total suspended solids (TSS). Furthermore, high-throughput sequencing analysis of the 16S rRNA gene revealed that CW1 exhibited elevated Chao1, Shannon, and Simpson indices, with values of 1324.46, 8.8172, and 0.9941, respectively. The most common bacterial species in the wetland system were Proteobacteria, Spirochaetota, Bacteroidota, Desulfobacterota, and Chloroflexi. The denitrifying bacterial class Rhodobacteriaceae also had the highest content ratio within the wetland system. These results confirm that CW1 significantly improves the performance of water filtration. Therefore, this research provides valuable insights for wastewater treatment facilities aiming to incorporate surface flow-constructed wetland tailwater enhancement initiatives.

A critical review of characteristics of domestic wastewater and key treatment techniques in Chinese villages

As of 2022, China's rural sewage treatment rate is only approximately 31 %. Rapid rural development has led to higher demand. However, China's rural areas are complex and face many problems, such as uneven economic development, population distribution, and water availability. Long-lasting and low-cost wastewater treatment measures are needed for application in rural areas. The quantity and quality of rural domestic wastewater in China were characterized first. Next, the hot topic of domestic wastewater in Chinese villages was confirmed via bibliometric analysis using CiteSpace, and the treatment technologies for rural domestic wastewater were compared. Specifically, the technical status and challenges of the most common technology in rural domestic wastewater treatment, constructed wetlands, were summarized.

Meta-analysis review for pilot and large-scale constructed wetlands: Design parameters, treatment performance, and influencing factors

Despite their longstanding use in environmental remediation, constructed wetlands (CWs) are still topical due to their sustainable and nature-based approach. While research and review publications have grown annually by 7.5 % and 37.6 %, respectively, from 2018 to 2022, a quantitative meta-analysis employing advanced statistics and machine learning to assess CWs has not yet been conducted. Further, traditional statistics of mean ± standard deviation could not convey the extent of confidence or uncertainty in results from CW studies. This study employed a 95 % bootstrap-based confidence interval and out-of-bag Random Forest-based driver analysis on data from 55 studies, totaling 163 cases of pilot and full-scale CWs. The study recommends, with 95 % confidence, median surface hydraulic loading rates (HLR) of 0.14 [0.11, 0.17] m/d for vertical flow-CWs (VF) and 0.13 [0.07, 0.22] m/d for horizontal flow-CWs (HF), and hydraulic retention time (HRT) of 125.14 [48.0, 189.6] h for VF, 72.00 [42.00, 86.28] h for HF, as practical for new CW design. Permutation importance results indicate influent COD impacted primarily on COD removal rate at 21.58 %, followed by HLR (16.03 %), HRT (12.12 %), and substrate height (H) (10.90 %). For TN treatment, influent TN and COD were the most significant contributors at 12.89 % and 10.01 %, respectively, while H (9.76 %), HRT (9.72 %), and HLR (5.87 %) had lower impacts. Surprisingly, while HRT and H had a limited effect on COD removal, they substantially influenced TN. This study sheds light on CWs' performance, design, and control factors, guiding their operation and optimization.

Demo-scale up-flow anaerobic sludge blanket reactor coupled with hybrid constructed wetlands for energy-carbon efficient agricultural wastewater reuse in decentralized scenarios

The impact of climate change on water availability and quality has affected agricultural irrigation. The use of treated wastewater can alleviate water in agriculture. Nevertheless, it is imperative to ensure proper treatment of wastewater before reuse, in compliance with current regulations of this practice. In decentralized agricultural scenarios, the lack of adequate treatment facilities poses a challenge in providing treated wastewater for irrigation. Hence, there is a critical need to develop and implement innovative, feasible, and sustainable treatment solutions to secure the use of this alternative water source. This study proposes the integration of intensive treatment solutions and natural treatment systems, specifically, the combination of up-flow anaerobic sludge blanket reactor (UASB), anaerobic membrane bioreactor (AnMBR), constructed wetlands (CWs), and ultraviolet (UV) disinfection. For this purpose, a novel demo-scale plant was designed, constructed and implemented to test wastewater treatment and evaluate the capability of the proposed system to provide an effluent with a quality in compliance with the current European wastewater reuse regulatory framework. In addition, carbon-sequestration and energy analyses were conducted to assess the sustainability of the proposed treatment approach. This research confirmed that UASB rector can be employed for biogas production (2.5 L h-1) and energy recovery from organic matter degradation, but its effluent requires further treatment steps to be reused in agricultural irrigation. The AnMBR effluent complied with class A standards for E. coli, boasting a concentration of 0 CFU 100 mL-1, and nearly negligible TSS levels. However, further reduction of BOD5 (35 mg L-1) is required to reach water quality class A. CWs efficiently produced effluent with BOD5 below 10 mg L-1 and TSS close to 0 mg L-1, making it suitable for water reuse and meeting class A standards. Furthermore, CWs demonstrated significantly higher energy efficiency compared to intensive treatment systems. Nonetheless, the inclusion of a UV disinfection unit after CWs was required to attain water class B standards.

Quantifying carbon pool in ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia

Ex-mining lake-converted constructed wetlands play a significant role in the carbon cycle, offering a great potential to sequester carbon and mitigate climate change and global warming. Investigating the quantity of carbon storage capacity of ex-mining lake-converted constructed wetlands provides information and justification for restoration and conservation efforts. The present study aims to quantify the carbon pool of the ex-mining lake-converted constructed wetlands and characterise the physicochemical properties of the soil and sediment. Pearson's correlation and a one-way ANOVA were performed to compare the different sampling stations at Paya Indah Wetland, Selangor, Malaysia. An analysis of 23 years of ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia, revealed that the estimated total carbon pool in soil and sediment accumulated to 1553.11 Mg C ha-1 (equivalent to 5700 Mg CO2 ha-1), which translates to an annual carbon sink capacity of around 67.5 Mg C ha-1 year-1. The characterisation showed that the texture of all soil samples was dominated by silt, whereas sediments exhibited texture heterogeneity. Although the pH of the soil and sediment was both acidic, the bulk density was still optimal for plant growth and did not affect root growth. FT-IR and WDXRF results supported that besides the accumulation and degradation of organic substances, which increase the soil and sediment carbon content, mineral carbonation is a mechanism by which soil and sediment can store carbon. Therefore, this study indicates that the ex-mining lake-converted constructed wetlands of Paya Indah Wetlands, Selangor, Malaysia have a significant carbon storage potential.

Effect of climate change on the water quality of Mediterranean rivers and alternatives to improve its status

Surface water (SW) quality is particularly vulnerable to increased concentrations of nutrients, and this issue may be exacerbated by climate change. Knowledge of the effects of temperature and rainfall on SW quality is required to take the necessary measures to achieve good SW status in the future. To address this, the aims of this study were threefold: (1) to assess how a changing climate may alter the nitrate, ammonium, phosphorus and biological oxygen demand status (BOD5) of SW; (2) assess the relationship between water quality and flow; and (3) simulate diffuse and point source pollution reduction scenarios in the Júcar River Basin District in the Mediterranean region. A regionalised long-term climate scenario was used following one Representative Concentration Pathway (RCP8.5) with the data incorporated into the coupling of hydrological and water quality models. According to these climate change scenarios, SW with poor nitrate, ammonium, phosphorus and BOD5 status are expected to increase in the future by factors of 1.3, 1.9, 4 and 4, respectively. Furthermore, median ammonium and phosphorus concentration may be doubled in months with low flows. Additional measures are required to maintain current status in the water bodies, and it is necessary to reduce at least 25% of diffuse nitrate pollution, and 50% of point loads of ammonium, phosphorus, and BOD5.

Performance of lagoon and constructed wetland systems for tertiary wastewater treatment and potential of reclaimed water in agricultural irrigation

Climate change poses challenges to agricultural water resources, both in terms of quantity and quality. As an adaptation measure, the new European Regulation (EU) 2020/741 establishes different water quality classes for the use of reclaimed water in agricultural irrigation. Italy is also working on the definition of a new regulation on reclaimed water reuse for agricultural irrigation (in substitution of the current one) that will also include the specific requirements imposed by the European one. Nature-based Solutions (NBS) can be a cost-effective and environmentally friendly way to facilitate water reclamation and reuse. The present study reports the outcomes of a long-term monitoring campaign of two NBS (e.g., a constructed wetland (CW) and a lagoon system (LS)) comparing influent and effluent concentrations of different contaminants (e.g., E. coli, BOD5, TSS, TN and TP) with the threshold values imposed by the new regulations. The results showed that in both the case studies, E. coli (about 100 CFU 100 mL-1) and BOD5 (lower than 25 mg L-1) mean effluent concentration need to be further reduced in reclaimed water to be suitable for unlimited reuse. As a negative aspect, in both the monitored NBS, an increase in TSS mean concentration in the effluent was observed, up to 40 mg L-1 in the case of the LS, making reclaimed water unsuitable for agricultural reuse. The CW has proven to be more effective in nitrogen removal (the effluent mean concentration was 3.4 mg L-1), whereas the LS was better at phosphorus removal (with an effluent mean concentration of 0.4 mg L-1). Based on the results, recommendations were made to further improve the performance of both systems in order to have adequate water quality, even for class A. Furthermore, the capacity of reclaimed water to meet crop water and nutrient needs was analyzed, and total nitrogen removal rate coefficients were calculated for the design of future LSs.

Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.

The integration of nature values and services in the nature-based solution assessment framework of constructed wetlands for carbon-water nexus in carbon sequestration and water security

As the climate change impacts are expected to become increasingly disruptive, affecting water security, environmental health and ecosystem, constructed wetlands receive attention for their functions in delivering various life-sustaining services to human and environmental systems. In this article, a systematic review was conducted through the Preferred Reporting Items for Systematic Reviews and Meta-Analyses standard to identify the current research on constructed wetlands' nature values and services from 2011 to 2020 of two databases, namely Scopus and Web of Science. The criteria of assessment focus on holistic deliberation of subject matters, namely carbon sequestration and water security as regulating and provisioning services, as well as nature values of constructed wetlands, namely instrumental and intrinsic values. As a result, 38 articles were selected and comprehensively examined. As the lack of an interdisciplinary approach makes data and information integration difficult, this study derived an integrated classification of constructed wetlands' services and mapped with its nature values, guided by the Millennium Ecosystem Assessment framework. Besides, mechanisms and factors affecting carbon sequestration and water security were also discussed. The carbon-water nexus was then conceptualised as interlinkages between engineered and natural physicochemical processes at the interface between carbon and water cycles. To fill the gaps, based on the carbon-water nexus concept, a new framework was synthesised at the end of the deliberation for constructed wetlands in regulating local climate through carbon sequestration and ensuring water security through water treatment and purification as well as influencing socio-cultural values, which needs an integrated approach that is the novelty of this work. The framework integrates the dichotomy of the instrumental-intrinsic nature values of constructed wetlands to evaluate the importance and benefit of the carbon-water nexus. The framework that reveals the vitality of nature values provided by constructed wetlands can help improve the decision-making to prioritise ecosystem services and conservation efforts, particularly in the sustainable management of constructed wetlands.

Exploring eco-friendly approaches for mitigating pharmaceutical and personal care products in aquatic ecosystems: A sustainability assessment

Global water scarcity is exacerbated by climate change, population growth, and water pollution. Over half of the world's population will be affected by water shortages for at least a month annually by 2050 due toa lack of clean water sources. Even though recycling wastewater helps meet the growing demand, new pollutants, including pharmaceuticals and personal care products (PPCPs), pose a health threat since conventional methods cannot remove them and their environmental monitoring regulations are yet in place. Therefore, the current review aims to investigate and propose eco-friendly technologies for removing PPCPs from wastewater and their implementation strategies for ecosystem safety. Findings indicated the absence of a single wastewater treatment technology that can remove all PPCPs in a single operation. Instead, biotechnological methods are one of the alternatives that can remove PPCPs from aquatic environments. In this context, community involvement and knowledge transfer are identified keys to clean water resources' long-term sustainability.

Naegleria australiensis isolated from a wastewater treatment station in Santiago Island, Cape Verde

Despite the Naegleria genus being isolated from different natural environments such as water, soil, and air, not all Naegleria species are capable of causing infections in humans, and they are capable of completing their life cycle in environmental niches. However, the presence of this genus may suggest the existence of one of the highly pathogenic free-living amoeba (FLA) species: Naegleria fowleri or the brain-eating amoeba. This facultative parasitic protozoon represents a risk to public health, mainly related to domestic and agricultural waters. In this research, our main objective was to determine the existence of pathogenic protozoa in the Santa Cruz wastewater treatment plant, Santiago Island. Using 5 L of water we confirmed the presence of potentially pathogenic Naegleria australiensis, being the first report on Naegleria species in Cape Verde. This fact demonstrates the low efficiency in the treatment of wastewater and, consequently, a potential threat to public health. Nevertheless, more studies will be needed for the prevention and control of possible infections in this Macaronesian country.

A novel hybrid coagulation-constructed wetland system for the treatment of dairy wastewater

Constructed wetlands (CWs) are a cost-effective and sustainable treatment technology that may be used on farms to treat dairy wastewater (DWW). However, CWs require a large area for optimal treatment and have poor long-term phosphorus removal. To overcome these limitations, this study uses a novel, pilot-scale coagulation-sedimentation process prior to loading CWs with DWW. This hybrid system, which was operated on an Irish farm over an entire milking season, performed well at higher hydraulic loading rates than conventional CWs, and obtained removal efficiencies ≥99 % for all measured water quality parameters (chemical oxygen demand, total nitrogen and phosphorus, total suspended solids and turbidity), which complied with EU directives concerning urban wastewater treatment. Overall, the hybrid coagulation-CW is a promising technology that requires a smaller area than conventional CWs and minimal operator input, and produces high effluent quality.

Escherichia coli removal in a treatment wetland - pond system: A mathematical modelling experience

A full-scale treatment wetland (TW) (100 inhabitants, 14 m³·d^-1), composed of two horizontal subsurface flow wetlands (TW1-400 m² and TW2-200 m²) and a small pond (13 m²), has been evaluated for Escherichia coli (E. coli) removal. The results indicate a global removal from 1.74·10⁶ to 685 MPN·100 mL^-1 (3.41 log units), reducing E. coli sufficiently to reach values suitable for reuse purposes such as agricultural reuse, without energy and reagent consumption. The small pond at the end of the treatment train plays an important role in E. coli removal and biodiversity enhancement. Data from TW1 and TW2 have been fitted to the P-k-C* model, giving values of 134 and 100 m·yr^-1 for the first-order kinetic reaction coefficient. For the pond, a process-based model using continuous stirred-tank reactor (CSTR) and a 3d-CFD model have been implemented and compared. The models indicate that solar disinfection and predation by daphnids are the most important mechanisms in the studied pond, representing 65% and 25% of the removal respectively. It can be concluded that CSTR can provide good results for small ponds and 3d-CFD model provides extra information, useful to enhance their design.

A Review of Hybrid Process Development Based on Electrochemical and Advanced Oxidation Processes for the Treatment of Industrial Wastewater

Nowadays, increased human activity, industrialization, and urbanization result in the production of enormous quantities of wastewater. Generally, physicochemical and biological methods are employed to treat industrial effluent and wastewater and have demonstrated high efficacy in removing pollutants. However, some industrial effluent and wastewater contain contaminants that are extremely difficult to remove using standard physicochemical and biological processes. Previously, electrochemical and hybrid advanced oxidation processes (AOP) were considered a viable and promising alternative for achieving an adequate effluent treatment strategy in such instances. These processes rely on the production of hydroxyl radicals, which are highly reactive oxidants that efficiently break down contaminants found in wastewater and industrial effluent. This review focuses on the removal of contaminants from industrial effluents and wastewater through the integration of electrochemical and advanced oxidation techniques. These processes include electrooxidation, electrocoagulation/electroflocculation, electroflotation, photo-Fenton, ozone-photo-Fenton, sono-photo-Fenton, photo-electro-Fenton, ozone/electrocoagulation, sono-electrocoagulation, and peroxi/photo/electrocoagulation. The data acquired from over 150 published articles, most of which were laboratory experiments, demonstrated that the hybrid process is more effective in removing contaminants from industrial effluent and wastewater than standalone processes.

Study of coliforms and Clostridium bacteria inactivation in wastewaters by a pilot photolysis process and by the maturation lagoons of a low-cost nature-based WWTP

The inactivation processes of coliform bacteria (total and fecal) and sulphito-reducing Clostridium bacteria (vegetative species and spores) in water maturation lagoon of a low-cost nature-based wastewater treatment plant using constructed wetlands and through processes of photolysis in a pilot photoreactor have been comparatively studied. The different inactivation mechanisms by photolysis of these bacteria have been studied following the criteria of different statistical and kinetic models. Clostridium disinfection treatments fit models in which two types of bacteria populations coexist, one sensitive (vegetative species) and the other (spores) resistant to the treatment, the sensitive one (94%) with an inactivation rate of k = 0.24 ± 0.07 min-1 and the resistant one (6%) with k = 0.11 ± 0.05 min-1. Total coliform photolytic disinfection also shows two populations with different physiological state. The time required to reduce the first logarithmic decimal cycle of the different types of bacteria (physiological states) are δ1 = 4.2 ± 0.9 and δ2 = 8.3 ± 1.1 min, respectively. For fecal coliform photolytic disinfection, only bacteria population, with k = 1.15 ± 0.19 min-1, is found. The results obtained confirm the photolytic disinfection processes and maturation lagoon are effective systems for Clostridia bacteria removal after water treatment by nature-based systems. Total removal of coliform bacteria is not achieved by maturation lagoons, but their reduction is significant using low doses of cumulative radiation.

Treated wastewater suitability for reuse in comparison to groundwater and surface water in a peri-urban area: Implications for water quality management

The climate change and population growth led to a severe water shortage that limits fresh water availability in some areas of Togo. Thus, the farmers of Adjougba District have no other choice than using treated wastewater as an alternative for irrigated agriculture. The purpose of this study is to compare the suitability of three types of water for uses with identification of the reliable parameters in the assessment of water suitability for irrigation and domestic purposes. The raw water quality parameters, water quality indices (WQIs) and water suitability indicators for irrigation purpose (WSI-IPs) were applied for the comparison while statistical analysis and, with some experts' consensus were used to identify reliable parameters. The results suggested that the treated wastewater is more suitable than groundwater for irrigation purpose. Treated wastewater constitutes a viable fertilizer supply and is placed like surface water from permissible to excellent classes according to WSI-IPs values. The sodium absorption ratio (SAR), electrical conductivity (EC), residual sodium carbonate (RSC), Cl^- and faecal coliforms (FC) are the most reliable parameters in the detection of water suitability for irrigation purpose. EC, DO, pH, turbidity or TSS, COD or COD_Mn, hardness, FC, NO₃^-, national sanitation foundation's water quality index (NSFWQI), and overall index of pollution (OPI) are the most reliable in the detection of water suitability for domestic use. The reliable parameters identified in this study are potential candidates for the development of a single water quality index for both irrigation and domestic uses in Adjougba District. However further study will be necessary for the identification of reliable parameters and the development of a water quality index at the country scale.

Wastewater fertigation in agriculture: Issues and opportunities for improved water management and circular economy

Water shortages are an issue of growing worldwide concern. Irrigated agriculture accounts for about 70% of total freshwater withdrawals globally, therefore alternatives to use of conventional sources need to be investigated. This paper critically reviews the application of treated wastewater for agricultural fertigation (i.e., water and nutrient recovery) considering different perspectives: legislation, agronomic characteristics, social acceptability, sustainability of treatment technologies. Critical issues that still need further investigation for a wider application of fertigation practices include accumulation of emerging contaminants in soils, microbiological and public health implications, and stakeholders' acceptance. A techno-economic methodological approach for assessing the sustainability of treated wastewater reuse in agriculture is subsequently proposed herein, which considers different possible local conditions (cultivated crops and effluent characteristics). The results showed that tailoring effluent characteristics to the desired nutrient composition could enhance the process economic sustainability; however, water savings have a major economic impact than fertilizers' savings, partly due to limited P reuse efficiency. The developed methodology is based on a practical approach and may be generalized to most agricultural conditions, to evaluate and encourage safe and efficient agricultural wastewater reuse practices.

Increasing chemical oxygen demand and nitrogen removal efficiencies of surface-flow constructed wetlands in macrophyte-dominant seasons by adding artificial macrophytes

The objective was to test the effectiveness of a new strategy, i.e., adding artificial macrophytes (AMs) to surface-flow constructed wetlands (SFCWs) planted with emergent macrophytes (EMs), to improve COD and N removal efficiencies (REs) at the pilot scale. During EM-dominant periods, the SFCWs with only EMs had REs of 78.2%, 59.8%, 50.8% and -54.2% for NH₄⁺-N, NO₃^--N, TN, and COD, respectively, while the SFCWs with both AMs and EMs increased the REs to 85.1%, 72.2%, 73.8%, and 2.0%. The addition of AMs to SFCWs had no significant effect on EM growth (biomass or root activity). Mutual benefit was found between EMs and AMs, i.e., AMs reduced the secondary pollution caused by withered EMs, while EMs improved AM-attached biofilm functions of chemoheterotrophy, nitrate_reduction, and nitrification. Therefore, AM addition is a useful strategy to improve COD and N REs during EM-dominant periods when pollutant removal is a challenge for SFCWs.

Influence of plants on the salinity of constructed wetlands effluents

Reuse of constructed wetlands effluents for fertigation is a promising practice in regions that suffer from water scarcity. Thus this study aimed to evaluate the influence of Vetiver (Chrysopogon zizanioides) and Tifton 85 (Cynodon sp.) grasses cultivation on salinity of the saturated solution of the Horizontal Subsurface Flow Constructed Wetlands (HSSF-CW) porous medium. The grasses were cultivated in HSSF-CW mesocosm and submitted to different levels of salinity for six months. The crop's evapotranspiration, biomass productivity, the electrical conductivity variation (ΔEC) in the solution under treatment and the water use efficiency (WUE) of these grasses were evaluated. The cultivation of Vetiver and Tifton 85 in HSSF-CW provided an increase in the electrical conductivity of the solution mainly for the lowest levels of affluent salinity. The ΔEC in HSSF-CW grown with Vetiver and Tifton 85 grasses were 90.20 and 27.13 mS cm^-1, respectively. Meteorological variables maximize the effect of the vegetative development in ΔEC of the solution. The WUE values of Vetiver and Tifton 85 grasses were 1.77 and 4.18 g kg^-1, respectively. Thus plants with high water use efficiency such as Tifton 85 is indicated for HSSF-CW in which the effluents are used in the fertigation of agricultural crops.

Reclamation of Treated Wastewater for Irrigation in Chile: Perspectives of the Current State and Challenges

Reclamation of treated wastewater is considered a viable option for reducing the agricultural and national water deficit, especially in Mediterranean-type and arid climatic conditions. Given that Chile is a country around 40% of whose territory is classified as semi-arid and desert and 20% as Mediterranean, with serious water scarcity problems, and which uses a great deal of the resource in agricultural irrigation, the present paper offers perspectives on the current state of treated wastewater reuse and considers challenges to improving the development of water reclamation for irrigation in Chile as a case study. The methods followed included a systematic literature review to answer two important questions: (a) What is the state of reclamation of treated wastewater for irrigation in Chile? and (b) What criteria/parameters determine the feasibility of reclaiming treated wastewater for irrigation in Chile? The results showed that Chile has been affected by climate change in a short time: a megadrought has occurred over the last ten years, increasing the necessity for the country to secure alternative water sources for irrigation. The country has advanced greatly in wastewater treatment coverage, achieving almost 100% in urban areas, with technologies that can produce quality water as a new water source for irrigation. However, the lack of regulations and limited frameworks could explain the low direct reuse at present—below 1% of total flow. Regarding challenges, the necessity of updates to Chile’s institutional and legal frameworks, besides the inclusion of rural communities and the study of emerging contaminants, will be discussed. By these means, it will be possible to more efficiently utilize recycled wastewater as a new source for irrigation in this country.

Removal and fate of pesticides in a farm constructed wetland for agricultural drainage water treatment under Mediterranean conditions (Italy)

A non-waterproofed surface flow constructed wetland (SFCW), treating agricultural drainage water in Northern Italy, was investigated to gain information on the potential ability for effective pesticide abatement. A mixture of insecticide imidacloprid, fungicide dimethomorph, and herbicide glyphosate was applied, by simulating a single rain event, into 470-m-long water course of the SFCW meanders. The pesticides were monitored in the wetland water and soil for about 2 months after treatment. Even though the distribution of pesticides in the wetland was not uniform, for each of them, a mean dissipation of 50% of the applied amount was already observed at ≤7 days. The dissipation trend in the water phase of the wetland fitted (r² ≥ 0.8166) the first-order model with calculated DT₅₀ of 20.6, 12.0, 5.8, and 36.7 days for imidacloprid, dimethomorph, glyphosate, and the glyphosate metabolite AMPA, respectively. The pesticide behavior was interpreted based on the chemical and physical characteristics of both the substances and the water-soil system. Despite the fast abatement of glyphosate, traces were detected in the water until the end of the trial. The formation of soluble 1:1 complex between glyphosate and calcium, the most representative cation in the wetland water, was highlighted by infrared analyses. Such a soluble complex was supposed to keep traces of the herbicide in solution.

Potential Use of Constructed Wetland Systems for Rural Sanitation and Wastewater Reuse in Agriculture in the Moroccan Context

Located in a semi-arid to arid region, Morocco is confronting increasing water scarcity challenges. In the circular economy paradigm, the reuse of treated wastewater in agriculture is currently considered a possible solution to mitigate water shortage and pollution problems. In recent years, Morocco has made significative progress in urban wastewater treatment under the National Wastewater Program (PNA). However, rural sanitation has undergone significant delays. Therefore, an alternative technology for wastewater treatment and reuse in rural areas is investigated in this review, considering the region’s economic, social, and regulatory characteristics. Constructed wetlands (CWs) are a simple, sustainable, and cost-effective technology that has yet to be fully explored in Morocco. CWs, indeed, appear to be suitable for the treatment and reuse of wastewater in remote rural areas if they can produce effluent that meets the standards of agricultural irrigation. In this review, 29 studies covering 16 countries and different types of wastewater were collected and studied to assess the treatment efficiency of different types of CWs under different design and operational parameters, as well as their potential application in agricultural reuse. The results demonstrated that the removal efficiency of conventional contamination such as organic matter and suspended solids is generally high. CWs also demonstrated a remarkable capacity to remove heavy metals and emerging contaminants such as pharmaceuticals, care products, etc. The removal of microbial contamination, on the other hand, is challenging, and does not satisfy the standards all the time. However, it can be improved using hybrid constructed wetlands or by adding polishing treatment. In addition, several studies reported that CWs managed to produce effluent that met the requirements of wastewater reuse in agriculture of different countries or organisations including Morocco.

Wastewater Treatment Using Constructed Wetland: Current Trends and Future Potential

Constructed wetlands (CW) is an environmentally friendly technique for removing pollutants from wastewater and has been applied to municipal wastewater, petroleum refinery wastewater, agriculture drainage, acid mine drainage, etc. The past decade has seen a remarkable number of innovations in the exponentially growing field of microbiology. This manuscript covers a critical review of key aspects of CW, such as various types of CW, the contaminants and their removal mechanisms, degradation pathways, challenges and opportunities, materials, applications, and theory with a focus on recent advances in the last three decades. In addition, an attempt has been taken to project future advances in the field of CW and facilitate these advances by framing key unsolved problems in CW. Guidelines are prepared for the fast-growing CW field through the standardization of key design aspects. This review covers the evaluation of the current state-of-the-art of CW technology and provides definitions and performance metric nomenclature in an effort to unify the fast-growing CW community. It also contains an outlook on the emerging trends in CW and proposes future research and development directions.

Constructed Wetlands to Face Water Scarcity and Water Pollution Risks: Learning from Farmers’ Perception in Alicante, Spain

Treated wastewater is constantly produced and relatively unaffected by climatic conditions, while Constructed Wetlands (CWs) are recognized as green technology and a cost-effective alternative to improve treated wastewater quality standards. This paper analyses how farmers consider (1) treated wastewater to face water scarcity risk and (2) CW as mechanisms to face agricultural water pollution in a climate change adaptation context. A survey about climate change perception and adaptation measures was answered by 177 farmers from two irrigation communities near El Hondo coastal wetland and the Santa Pola saltmarshes, both perceived as natural-constructed systems in Alicante, southern Spain. Results highlighted how, even with poor-quality standards, treated wastewater is considered a non-riskier measure and more reliable option when addressing climate change impacts. Overall, physical water harvesting (such as CWs) is the favorite choice when investing in water technologies, being perceived as the best option for users of treated wastewater and those concerned about water quality standards. Consequently, CWs were recognized as mechanisms to increase water supply and reduce water pollution. Policy-makers and water managers can use these learnings from farmers’ experience to identify the main barriers and benefits of using treated wastewater and CWs to address water scarcity and water pollution risks.

Wetland Restoration with Hydrophytes: A Review

Restoration cases with hydrophytes (those which develop all their vital functions inside the water or very close to the water surface, e.g., flowering) are less abundant compared to those using emergent plants. Here, I synthesize the latest knowledge in wetland restoration based on revegetation with hydrophytes and stress common challenges and potential solutions. The review mainly focusses on natural wetlands but also includes information about naturalized constructed wetlands, which nowadays are being used not only to improve water quality but also to increase biodiversity. Available publications, peer-reviewed and any public domain, from the last 20 years, were reviewed. Several countries developed pilot case-studies and field-scale projects with more or less success, the large-scale ones being less frequent. Using floating species is less generalized than submerged species. Sediment transfer is more adequate for temporary wetlands. Hydrophyte revegetation as a restoration tool could be improved by selecting suitable wetlands, increasing focus on species biology and ecology, choosing the suitable propagation and revegetation techniques (seeding, planting). The clear negative factors which prevent the revegetation success (herbivory, microalgae, filamentous green algae, water and sediment composition) have to be considered. Policy-making and wetland restoration practices must more effectively integrate the information already known, particularly under future climatic scenarios.

A GIS-Based Model to Assess the Potential of Wastewater Treatment Plants for Enhancing Bioenergy Production within the Context of the Water–Energy Nexus

The necessity of developing renewable energy sources has contributed to increasing interest in developing the anaerobic digestion for producing biomethane since it both provides green energy and reduces disposal treatment. In this regard, to assure efficient water utilization by finding alternative water sources, sewage sludge collected from the wastewater treatment plant (WWTP) was recently investigated because it could represent a suitable resource for producing biomethane within the context of a circular economy. Therefore, this study aims at improving the current knowledge on the feasibility of biomethane production from sewage sludge by optimizing the logistic-supplying phase. In this regard, a GIS-based model was developed and applied to the Emilia-Romagna region to consider the existing networks of WWTPs and biogas systems to valorize sewage sludge for bioenergy production and minimizing environmental impact. The results of the GIS analyses allowed to localize the highest productive territorial areas and highlighted where sewage sludges are abundantly located and could be better exploited within agricultural biogas plants. Finally, the achieved results could help plan suitable policy interventions that are centered on biomass supply and outputs diversification, governance, and social participation, since the regulatory framework could play a crucial role in planning the reuse of these wastes for developing a more sustainable biomethane sector in line with the green economy goals.

Constructed wetland, an eco-technology for wastewater treatment: A review on types of wastewater treated and components of the technology (macrophyte, biolfilm and substrate)

Constructed wetland (CW) represents an efficient eco-technological conglomerate interweaving water security, energy possibility and environmental protection. In the context of wastewater treatment technologies requiring substantial efficiency at reduced cost, chemical input and low environmental impact, applications of CW is being demonstrated at laboratory and field level with reasonably high contaminant removal efficiency and ecological benefits. However, along with the scope of applications, role of individual wetland component has to be re-emphasized through related research interventions. Hence, this review distinctively explores the concerns for extracting maximum benefit of macrophyte (focusing on interface of pollutant removal, root radial oxygen loss, root iron plaque, endophyte-macrophyte assisted treatment in CW, and prospects of energy harvesting from macrophyte) and role of biofilm (effect on treatment efficiency, composition and factors affecting) in a CW. Another focus of the review is on recent advances and developments in alternative low-cost substrate materials (including conventional type, industrial by-products, organic waste, mineral based and hybrid type) and their effect on target pollutants. The remainder of this review is organized to discuss the concerns of CW with respect to wastewater type (municipal, industrial, agricultural and farm wastewater). Attempt is made to analyze the practical relevance and significance of these aspects incorporating all recent developments in the areas to help making informed decisions about future directions for research and development related to CW.

SARS-CoV-2 from Urban to Rural Water Environment: Occurrence, Persistence, Fate, and Influence on Agriculture Irrigation. A Review

The novel coronavirus disease (COVID-19), originating from China, has rapidly crossed borders, infecting people worldwide. While its transmission may occur predominantly via aerosolization of virus-laden droplets, the possibility of other routes of contagion via the environment necessitates considerable scientific consideration. SARS-CoV-2 viral RNA has been detected in the feces of infected persons, and studies also have reported its occurrence in wastewater and surface water bodies. Therefore, water may be a possible route of virus outbreaks. Agricultural irrigation is the largest use of water globally, accounting for 70% of water use worldwide. Ensuring adequate water quality within irrigation practices is fundamental to prevent harm to plants and soils, maintain food safety, and protect public health. This review aims to gather information on possible SARS-CoV-2 transmission routes within urban and rural water environments, looking into the detection, persistence, and fate of SARS-CoV-2. Based on published literature, the effect of current treatment technologies in wastewater treatment plants (WWTPs) on SARS-CoV-2 inactivation has also been investigated. Preliminary research efforts that concentrated on SARS-CoV-2 indicate that the risk of virus transmission from the aquatic environment may currently be non-existent, although a few studies have reported the presence of SARS-CoV RNA in soils, whereas there are still no studies on the detection of SARS-CoV-2 in crops.

The Use of Constructed Wetland for Mitigating Nitrogen and Phosphorus from Agricultural Runoff: A Review

The loss of nitrogen and phosphate fertilizers in agricultural runoff is a global environmental problem, attracting worldwide attention. In the last decades, the constructed wetland has been increasingly used for mitigating the loss of nitrogen and phosphate from agricultural runoff, while the substrate, plants, and wetland structure design remain far from clearly understood. In this paper, the optimum substrates and plant species were identified by reviewing their treatment capacity from the related studies. Specifically, the top three suitable substrates are gravel, zeolite, and slag. In terms of the plant species, emergent plants are the most widely used in the constructed wetlands. Eleocharis dulcis, Typha orientalis, and Scirpus validus are the top three optimum emergent plant species. Submerged plants (Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans), free-floating plants (Eichhornia crassipes and Lemna minor), and floating-leaved plants (Nymphaea tetragona and Trapa bispinosa) are also promoted. Moreover, the site selection methods for constructed wetland were put forward. Because the existing research results have not reached an agreement on the controversial issue, more studies are still needed to draw a clear conclusion of effective structure design of constructed wetlands. This review has provided some recommendations for substrate, plant species, and site selections for the constructed wetlands to reduce nutrients from agricultural runoff.

The Potential Role of Hybrid Constructed Wetlands Treating University Wastewater—Experience from Northern Italy

University wastewater is a type of wastewater with higher pollutants load and flow rate variability than typical domestic wastewater. Constructed wetlands (CW) could be used for university wastewater treatment and consequently for wastewater reuse. A hybrid CW pilot plant, at the University of Bologna (Italy), was monitored to assess its potential to be used at the university. Its treatment performance was monitored for one year and public acceptance explored through a survey. The pilot plant had two treatment lines, (1) a vertical flow CW (VFCW) and a planted horizontal flow CW (HFCW), and (2) the same VFCW and an unplanted horizontal flow filter (HFF). The HFCW achieved higher removals than the HFF, but it was also found to be prone to higher water losses. However, both treatment lines met the Italian limits for discharge in natural water bodies and some of the limits for wastewater reuse in Italy and the EU. The VFCW alone was not able to meet the same limits, demonstrating the advantages of hybrid over single stage CWs. A positive attitude towards CWs and wastewater reuse was found among the survey participants. Therefore, hybrid CWs (planted and unplanted) are considered a feasible technology for application at universities.