Constructed wetlands: a review

Nutrient dynamics in wetland systems associated with hydrological and anthropogenic variations in the south of Samborombón Bay, Argentina

Wetlands provide numerous ecosystem services to the environment, such as nutrient removal and storage. The aim of this work is to evaluate the nutrient dynamics in different sectors within wetland systems in the south of the Samborombón Bay (Argentina) based on hydrological and/or anthropogenic variations. For this purpose, the hydrological features of the wetland were defined through the analysis of satellite images, precipitation and tidal data, and field surveys. Three sectors were identified in the wetland: one with tidal influence, another which is dependent on rainfall, and another that receives inputs from rainfall and from a sewage effluent treatment plant. In order to analyze the nutrient dynamics, samples of surface water, groundwater, and sediments were collected from these sectors. Measurements of pH and electrical conductivity were determined in situ in water samples, while the concentration of inorganic forms of phosphorus and nitrogen, soluble reactive silica, and organic carbon were determined through laboratory analysis. Also, bioavailable phosphorus, organic matter, pH, and electrical conductivity were determined in the sediment samples collected. Statistical analysis of the data reveals differences between the sectors and allows the interpretation of the dynamics of the studied components in the wetland. Electrical conductivity distinguishes the intertidal sectors of the wetland while components associated with P and N discriminate the sectors with inputs from the sewage effluent treatment plant. On the other hand, soluble reactive silica, organic carbon, and organic matter do not seem to be influenced by the tide or effluent discharge. This study demonstrates that the studied wetland works as a nutrient retention area, providing ecosystem services to local inhabitants. Although these services can be utilized, they require a continuous monitoring over time to provide an early warning in case the variations in P and N cycles could lead to eutrophication or wetland degradation.

Reduction of antimicrobial resistance: Advancements in nature-based wastewater treatment

Water scarcity, affecting one-fifth of the global population, is exacerbated by industrial, agricultural, and population growth pressures on water resources. Wastewater, containing Contaminants of Emerging Concern (CECs) such as antibiotics, presents environmental and health hazards. This study explores a Nature-Based Solution (NBS) using Constructed Wetlands (CWs) for wastewater reclamation and CECs removal. Two CW configurations (Vertical-VCW and Hybrid-HCW) were tested for their efficacy. Results show significant reduction in for all the chemico-physical and biological parameters meeting Italian water reuse standards. Furthermore, Antibiotic Resistant Bacteria (ARB) and Antibiotic Resistant Genes (ARGs) were effectively reduced, emphasizing the potential of the CWs in mitigating Antimicrobial Resistance (AMR). Lettuce seedlings irrigated with the treated wastewater exhibited no ARB/ARGs transfer, indicating the safety of the reclaimed wastewater for agricultural use. Overall, CWs emerge as sustainable Nature Based Solutions (NBS) for wastewater treatment, contributing to global water conservation efforts amid escalating water scarcity challenges.

Wetlands as a potential multifunctioning tool to mitigate eutrophication and brownification

Eutrophication and brownification are ongoing environmental problems affecting aquatic ecosystems. Due to anthropogenic changes, increasing amounts of organic and inorganic compounds are entering aquatic systems from surrounding catchment areas, increasing both nutrients, total organic carbon (TOC), and water color with societal, as well as ecological consequences. Several studies have focused on the ability of wetlands to reduce nutrients, whereas data on their potential to reduce TOC and water color are scarce. Here we evaluate wetlands as a potential multifunctional tool for mitigating both eutrophication and brownification. Therefore, we performed a study for 18 months in nine wetlands allowing us to estimate the reduction in concentrations of total nitrogen (TN), total phosphorus (TP), TOC and water color. We show that wetland reduction efficiency with respect to these variables was generally higher during summer, but many of the wetlands were also efficient during winter. We also show that some, but not all, wetlands have the potential to reduce TOC, water color and nutrients simultaneously. However, the generalist wetlands that reduced all four parameters were less efficient in reducing each of them than the specialist wetlands that only reduced one or two parameters. In a broader context, generalist wetlands have the potential to function as multifunctional tools to mitigate both eutrophication and brownification of aquatic systems. However, further research is needed to assess the design of the generalist wetlands and to investigate the potential of using several specialist wetlands in the same catchment.

Using a retention pond to capture agricultural contaminants from surface waters

To meet the demand of a constantly growing population, agriculture is intensifying, causing an increased use of fertilizers and pesticides. Excessive nutrients transfer to aquatic ecosystems can disrupt the water quality and impact the aquatic life. Pesticides can also have toxic effects on non-target organisms from aquatic systems. The purpose of this study was to evaluate the efficiency of an agricultural retention pond in reducing the supply of nutrients, pesticides and suspended solids to the Nicolet River, a tributary of Lake St. Pierre in the St. Lawrence River. Research combining the study of the fate of a wide range of contaminants in both pond water and sediments, their toxicity to microcrustaceans, microalgae and amphipods, and the effectiveness of contaminant removal, has rarely been carried out in the past. Peak contaminant concentrations occurred one to two months after pesticide and fertilizer applications, and during the months with the highest rainfall. Toxic effects were only observed on microalgae, with suspended solids apparently responsible for this effect through light inhibition on growth rates. However, the pond was not effective in removing this toxicity even if suspended solids were largely removed. Pesticides removal varied widely among sampling dates and pesticide types, with an efficiency reaching 95 % for thiamethoxam, but generally remaining low and often negative (higher concentrations in outflowing water) for other pesticides. On the other hand, the mean fractional removal of suspended solids, phosphorus, and nitrogen based on concentrations was 71 %, 44 % and 22 %, respectively. These are conservative estimations since the removal rates based on loads were above 94 %. The use of retention ponds thus seems an efficient approach to reduce the quantity of fertilizers in rivers draining agriculture areas, but the studied pond was not systematically effective in removing pesticides.

Robust control of water quality in horizontal sub-surface flow wetlands using decentralized quantitative feedback theory based controller

This paper addresses the regulation of water quality influencers such as Organic Nitrogen, Ammonia Nitrogen, Nitrate Nitrogen, Dissolved Organic Carbon and Dissolved Oxygen for a sub-surface flow horizontal wetland in a controlled environment. The plant uncertainty is quantified by using measurement data. The robust control of the process is achieved using a decentralized quantitative feedback theory based control strategy. The control structure also employs a feed-forward mechanism to minimize loop interactions and feedback control to ensure stability, tracking and disturbance rejection. The numerical simulations and hardware-in-loop implementation show that the performance specifications are robustly met.

Factors Influencing Gaseous Emissions in Constructed Wetlands: A Meta-Analysis and Systematic Review

Constructed wetlands (CWs) are an eco-technology for wastewater treatment and are applied worldwide. Due to the regular influx of pollutants, CWs can release considerable quantities of greenhouse gases (GHGs), ammonia (NH₃), and other atmospheric pollutants, such as volatile organic compounds (VOCs) and hydrogen sulfide (H₂S), etc., which will aggravate global warming, degrade air quality and even threaten human health. However, there is a lack of systematic understanding of factors affecting the emission of these gases in CWs. In this study, we applied meta-analysis to quantitatively review the main influencing factors of GHG emission from CWs; meanwhile, the emissions of NH₃, VOCs, and H₂S were qualitatively assessed. Meta-analysis indicates that horizontal subsurface flow (HSSF) CWs emit less CH₄ and N₂O than free water surface flow (FWS) CWs. The addition of biochar can mitigate N₂O emission compared to gravel-based CWs but has the risk of increasing CH₄ emission. Polyculture CWs stimulate CH₄ emission but pose no influence on N₂O emission compared to monoculture CWs. The influent wastewater characteristics (e.g., C/N ratio, salinity) and environmental conditions (e.g., temperature) can also impact GHG emission. The NH₃ volatilization from CWs is positively related to the influent nitrogen concentration and pH value. High plant species richness tends to reduce NH₃ volatilization and plant composition showed greater effects than species richness. Though VOCs and H₂S emissions from CWs do not always occur, it should be a concern when using CWs to treat wastewater containing hydrocarbon and acid. This study provides solid references for simultaneously achieving pollutant removal and reducing gaseous emission from CWs, which avoids the transformation of water pollution into air contamination.

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.

Water quality stress to Amirkalayeh Wetland, Northern Iran

Amirkalayeh Wetland, listed as wetlands of International Importance in the Ramsar Convention, exposes to severe water quality stress resulted from increase in dissolved ions and nutrients concentrations. In addition to in situ measurements of physicochemical parameters (electrical conductivity, pH, and temperature), a total number of 28 water samples were collected from Amirkalayeh Wetland and surrounding surface and groundwater resources to investigate the most important factors increasing trophic state and decreasing the water quality of the wetland. Water samples were analyzed for major ions and dissolved plant nutrients (nitrate, nitrite, ammonium, and phosphate). Up to three-time increase in salinity and dramatic rising in nutrients level was observed in Amirkalayeh Wetland from 2017 to 2021. The excessive nutrients intake resulted in hyper-eutrophication trophic status of Amirkalayeh Wetland. Our hydrological, hydrochemical, and statistical studies investigating the role of a variety of possible water quality degrading factors show that surface and subsurface drainage of agricultural return water into the Amirkalayeh Wetland are the major cause of increase in trophic level and decreasing water quality. Results of this work indicate that Amirkalayeh Wetland is exposed to severe water quality stress that threatens the aquatic life and ecosystem of this wetland. Therefore, preventing the inflow of surface and subsurface agricultural drains to the wetland and providing a sustainable water management plan are vital to improve water quality of the wetland.

The Novel Role of Tyrosinase Enzymes in the Storage of Globally Significant Amounts of Carbon in Wetland Ecosystems

Over the last millennia, wetlands have been sequestering carbon from the atmosphere via photosynthesis at a higher rate than releasing it and, therefore, have globally accumulated 550 × 10¹⁵ g of carbon, which is equivalent to 73% of the atmospheric carbon pool. The accumulation of organic carbon in wetlands is effectuated by phenolic compounds, which suppress the degradation of soil organic matter by inhibiting the activity of organic-matter-degrading enzymes. The enzymatic removal of phenolic compounds by bacterial tyrosinases has historically been blocked by anoxic conditions in wetland soils, resulting from waterlogging. Bacterial tyrosinases are a subgroup of oxidoreductases that oxidatively remove phenolic compounds, coupled to the reduction of molecular oxygen to water. The biochemical properties of bacterial tyrosinases have been investigated thoroughly in vitro within recent decades, while investigations focused on carbon fluxes in wetlands on a macroscopic level have remained a thriving yet separated research area so far. In the wake of climate change, however, anoxic conditions in wetland soils are threatened by reduced rainfall and prolonged summer drought. This potentially allows tyrosinase enzymes to reduce the concentration of phenolic compounds, which in turn will increase the release of stored carbon back into the atmosphere. To offer compelling evidence for the novel concept that bacterial tyrosinases are among the key enzymes influencing carbon cycling in wetland ecosystems first, bacterial organisms indigenous to wetland ecosystems that harbor a TYR gene within their respective genome (tyr⁺) have been identified, which revealed a phylogenetically diverse community of tyr⁺ bacteria indigenous to wetlands based on genomic sequencing data. Bacterial TYR host organisms covering seven phyla (Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Planctomycetes, and Proteobacteria) have been identified within various wetland ecosystems (peatlands, marshes, mangrove forests, bogs, and alkaline soda lakes) which cover a climatic continuum ranging from high arctic to tropic ecosystems. Second, it is demonstrated that (in vitro) bacterial TYR activity is commonly observed at pH values characteristic for wetland ecosystems (ranging from pH 3.5 in peatlands and freshwater swamps to pH 9.0 in soda lakes and freshwater marshes) and toward phenolic compounds naturally present within wetland environments (p-coumaric acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, caffeic acid, catechin, and epicatechin). Third, analyzing the available data confirmed that bacterial host organisms tend to exhibit in vitro growth optima at pH values similar to their respective wetland habitats. Based on these findings, it is concluded that, following increased aeration of previously anoxic wetland soils due to climate change, TYRs are among the enzymes capable of reducing the concentration of phenolic compounds present within wetland ecosystems, which will potentially destabilize vast amounts of carbon stored in these ecosystems. Finally, promising approaches to mitigate the detrimental effects of increased TYR activity in wetland ecosystems and the requirement of future investigations of the abundance and activity of TYRs in an environmental setting are presented.

Spent waste from edible mushrooms offers innovative strategies for the remediation of persistent organic micropollutants: A review

Urgent and innovative strategies for removal of persistent organic micropollutants (OMPs) in soil, groundwater, and surface water are the need of the hour. OMPs detected in contaminated soils and effluents from wastewater treatment plants (WWTPs) are categorized as environmentally persistent pharmaceutical pollutants (EPPPs), and endocrine disrupting chemicals (EDCs), their admixture could cause serious ecological issues to the non-target species. As complete eradication of OMPs is not possible with the extant conventional WWTPs technology, the inordinate and reckless application of OMPs negatively impacts environmental regenerative and resilience capacity. Therefore, the cardinal focus of this review is the bioremediation of persistent OMPs through efficient application of an agro-waste, i.e. spent mushroom waste (SMW). This innovative, green, long-term strategy embedded in the circular economy, based on state of the art information is comprehensively assessed in this paper. SMW accrues ligninolytic enzymes such as laccase and peroxidase, with efficient mechanism to facilitate biodegradation of recalcitrant organic pollutants. It is vital in this context that future research should address immobilization of such enzymes to overcome quantitative and qualitative issues obstructing their widespread use in biodegradation. Therefore, dual benefit is gained from cultivating critical cash crops like mushrooms to meet the escalating demand for food resources and to aid in biodegradation. Hence, mushroom cultivation has positive environmental, social, and economic implications in developing countries like India.

Removal of nitrogen and phosphorus by aboveground biomass of Phragmites australis in Constructed Wetland System under the conditions of temperate continental climate

In this paper, aboveground biomass and basic nutrients removal, nitrogen (N) and phosphorus (P), was analyzed by the use of reed as the main component of Constructed Wetland System (CWS) "Gložan". In almost ideal conditions of temperate continental climate, with favorable substrate humidity, due to the constant inflow of municipal wastewater, reed populations reach a high density, on average 217 ind/m². The reed produces significant aboveground biomass, fresh weight (FW) of 144.21 g/plant and dry weight (DW) of 77.04 g/plant, with the largest share being per tree (87.49 g FW/plant, 48.17 g DW/plant), then leaf (49.45 g FW/plant, 24.89 g DW/plant) and the smallest inflorescence (7.27 g FW/plant, 3.99 g DW/plant). The results obtained in this way indicate that the largest amount of nitrogen was removed by leaves, then by stems and, the smallest by inflorescences, 181.07 g/m², 97.73 g/m², 23.41 g/m², respectively. Thus, an average of 302.21 g/m² of nitrogen was removed by the entire aboveground part of the reed. Also, the largest amount of phosphorus was removed by leaves, then by stems, and the smallest by inflorescences, 5.72 g/m², 4.82 g/m² and 2.57 g/m², respectively, while the entire aboveground part of the reed is on average about 13.11 g/m².

Physicochemical Characterization and Assessment of Magnitude of Pollution to Contribute to Water Sustainability

As in many countries worldwide, deterioration of quality of water in Morocco’s natural reserves continues, such that an inventory of qualities of these reserves has become necessary. Based on statistical analyses of the data collected by measuring nineteen physicochemical variables, and applying an index, the comprehensive pollution index, to those data, the quality of the waters of Lake Dayat Roumi, Morocco, were assessed. Waters of the lake are currently characterized by a salinity of 921.7 mg Cl−/L and 124.2 mg sulfates/L. The concentration of chloride exceeds the value indicated in the standard norms. This can affect the composition of the sediment, overlying water, and specific composition of biota in the lake. Status and trends of values of other parameters also indicate deterioration of water quality in this lake. Multivariate statistical analysis made it possible to differentiate four clusters of samples according to their physicochemical characteristics. These groups are due to inputs from three sources of materials: leaching of rocks from the watershed and plantations, discharge of domestic wastewater and runoff water. Samples taken from deeper parts of the lake indicate a depression of concentrations of dissolved oxygen during the hot season. The analysis results demonstrate the heterogeneous degradation of the water quality in the peripheral areas and deep parts of the lake, favored by the leaching of soils by rainwater, which, when sufficiently severe, can cause repeated mortalities of fishes. This situation requires regular water quality monitoring to develop a management plan for restoration of water quality in the lake to preserve valued ecological services.

Microbial community development in tropical constructed wetland soils in Taiwan

Constructed wetlands are widely used around the world as a low-cost wastewater treatment system that simultaneously provides various ecosystem services. Microorganisms in wetland soils serve as fundamental producers and decomposers that support wetland functions. However, few studies have documented the compositions of soil microorganisms in constructed wetland systems and even fewer have evaluated how soil microorganisms change after a wetland is constructed. In this study, soil samples were collected from four constructed wetlands of different ages and analyzed with a phospholipid fatty acid (PLFA) method to show how soil microbial communities change overtime. The results were that both the bacterial and fungal abundances increased with wetland age, and bacteria comprised about 90% of the soil microbial communities in all ages of constructed wetlands. Although the compositions of microbial communities remained similar among the wetlands, the stress indices showed that microbial stress may be affected by changes in the availability of in situ nutrients, e.g. ammonium, nitrate_, soluble organic nitrogen and total dissolved nitrogen.

The use of treatment wetlands plants for protein and cellulose valorization in biorefinery platform

Different wetland plants were evaluated regarding their potential to be used in further green biorefining platforms to produce soluble protein and cellulose-textile fibers. The results show a higher protein content in the plants grown in treatment wetland conditions, compared with the same species grown in natural conditions, and diverse effect on the content of cellulose, hemicellulose, and lignin, depending on the plant species, more than the growing environment. The TW biomass did not represent a risk regarding accumulation of heavy metals, named Pb, Cd, and Cr, since the studied plants did not present it in their tissues, neither in the roots nor in the leaves. The results regarding cellulose quality of the TW plants showed positive results, having values of molar mass distributions and degrees of polymerization that suggest a suitability to be considered for cellulose-fiber textiles studies. This is one of the first approaches, in the TW field, to establish a new criterion for selecting plant species to be planted in the system, aiming at recovering resources and use them as inputs for biorefineries and sustainable biobased products.

Taxonomic Diversity of Fungi and Bacteria in Azoé-NP® Vertical Flow Constructed Wetlands

Plants, fungi, bacteria and protozoa are highly interconnected in constructed wetlands. These heterogeneous groups of organisms constitute a single system with complex internal trophic interactions. Thus, the joint activity of micro- and macroorganisms in constructed wetlands provides highly efficient wastewater treatment: both nutrients and complex organic substances can be effectively removed in branched trophic chains. The bacterial community of constructed wetlands has recently received much attention, while the fungal component remains less studied, particularly saprotrophic fungi. This paper reveals a taxonomic analysis of the cultivated saprotrophic fungi combined with the bacterial community in vertical flow constructed wetlands (VSCWs) operated by the Azoé-NP® process. These systems have unique features to affect the microbial community, which results in a high treatment efficiency and nitrogen removal. There are very few studies of saprotrophic fungi in VFCWs, while this work shows their abundance and diversity in VFCWs. We found 62 species of cultivated microscopic fungi and described the taxonomic composition of bacterial and fungal community at all wastewater treatment stages. In the studied VFCWs, we identified the species of micromycetes, which proved effective in the removal of contaminants. The data obtained can provide a deeper insight into the characteristics of Azoé-NP® systems and the treatment processes occurring in constructed wetlands.

A Review on Constructed Treatment Wetlands for Removal of Pollutants in the Agricultural Runoff

Constructed wetland (CW) is a popular sustainable best management practice for treating different wastewaters. While there are many articles on the removal of pollutants from different wastewaters, a comprehensive and critical review on the removal of pollutants other than nutrients that occur in agricultural field runoff and wastewater from animal facilities, including pesticides, insecticides, veterinary medicine, and antimicrobial-resistant genes are currently unavailable. Consequently, this paper summarized recent findings on the occurrence of such pollutants in the agricultural runoff water, their removal by different wetlands (surface flow, subsurface horizontal flow, subsurface vertical flow, and hybrid), and removal mechanisms, and analyzed the factors that affect the removal. The information is then used to highlight the current research gaps and needs for resilient and sustainable treatment systems. Factors, including contaminant property, aeration, type, and design of CWs, hydraulic parameters, substrate medium, and vegetation, impact the removal performance of the CWs. Hydraulic loading of 10–30 cm/d and hydraulic retention of 6–8 days were found to be optimal for the removal of agricultural pollutants from wetlands. The pollutants in agricultural wastewater, excluding nutrients and sediment, and their treatment utilizing different nature-based solutions, such as wetlands, are understudied, implying the need for more of such studies. This study reinforced the notion that wetlands are effective for treating agricultural wastewater (removal > 90%) but several research questions remain unanswered. More long-term research in the actual field utilizing environmentally relevant concentrations to seek actual impacts of weather, plants, substrates, hydrology, and other design parameters, such as aeration and layout of wetland cells on the removal of pollutants, are needed.

Materials in constructed wetlands for wastewater remediation: A review

The wastewater treatment industry is constantly evolving to abate emerging contaminants and to meet stringent legislative requirements. The existing technologies need to be modified, or new innovative treatment techniques need to be developed to ensure environmental protection and secure sustainability in the future. Emphasis is mainly on nutrient recovery, energy-efficient systems, zero waste generation, and environmentally friendly techniques. Constructed wetlands (CWs) have evolved as natural, eco-friendly, economical, and low-maintenance alternatives for wastewater remediation. These wetlands employ several materials as adsorbents for the treatment, commonly known as media/substrate. This review paper presents an assessment of various materials that can be used as substrates in CWs for the efficient removal of organic and non-biodegradable pollutants in different types of wastewaters. The effect of pH, mineral composition, specific surface area, and porosity of various natural materials and agricultural and industrial wastes used as media in CWs for wastewater remediation was discussed. The study showed that different substrates like alum sludge, limestone, coal slags, rice husk, and sand had removal efficiency for chemical oxygen demand (COD): 71.8%-82%, total phosphorous (TP): 77%-80%, and total nitrogen (TN): 52%-82% for different types of wastewaters. It also highlights the challenges related to the long-term sustainability of these materials. PRACTITIONER POINTS: Physicochemical characteristics influence the removal efficiency of the materials Life of media is also important along with removal efficiency and cost The sustainability of materials is very crucial for the overall performance of the system.

Remote Sensing Approach for Monitoring Coastal Wetland in the Mekong Delta, Vietnam: Change Trends and Their Driving Forces

Coastal wetlands in the Mekong Delta (MD), Vietnam, provide various vital ecosystem services for the region. These wetlands have experienced critical changes due to the increase in regional anthropogenic activities, global climate change, and the associated sea level rise (SLR). However, documented information and research on the dynamics and drivers of these important wetland areas remain limited for the region. The present study aims to determine the long-term dynamics of wetlands in the south-west coast of the MD using remote sensing approaches, and analyse the potential factors driving these dynamics. Wetland maps from the years 1995, 2002, 2013, and 2020 at a 15 m spatial resolution were derived from Landsat images with the aid of a hybrid classification approach. The accuracy of the wetland maps was relatively high, with overall accuracies ranging from 86–93%. The findings showed that the critical changes over the period 1995/2020 included the expansion of marine water into coastal lands, showing 129% shoreline erosion; a remarkable increase of 345% in aquaculture ponds; and a reduction of forested wetlands and rice fields/other crops by 32% and 73%, respectively. Although mangrove forests slightly increased for the period 2013/2020, the overall trend was also a reduction of 5%. Our findings show that the substantial increase in aquaculture ponds is at the expense of mangroves, forested wetlands, and rice fields/other crops, while shoreline erosion significantly affected coastal lands, especially mangrove forests. The interaction of a set of environmental and socioeconomic factors were responsible for the dynamics. In particular, SLR was identified as one of the main underlying drivers; however, the rapid changes were directly driven by policies on land-use for economic development in the region. The trends of wetland changes and SLR implicate their significant effects on environment, natural resources, food security, and likelihood of communities in the region sustaining for the long-term. These findings can assist in developing and planning appropriate management strategies and policies for wetland protection and conservation, and for sustainable development in the region.

The Role of Wetland Plants on Wastewater Treatment and Electricity Generation in Constructed Wetland Coupled with Microbial Fuel Cell

CWMFC is a novel technology that has been used for almost a decade for concurrent wastewater treatment and electricity generation in varying scopes of domestic, municipal, and industrial applications since its implementation in 2012. Its advantage of low-cost enhanced wastewater treatment and sustainable bioelectricity generation has gained considerable attention. Nevertheless, the overall efficiency of this novel technology is inclined by several operating factors and configuration strands, such as pH, sewage composition, organic loading, electrode material, filter media, electrogens, hydraulic retention time, and macrophytes. Here, we investigate the effect of the wetland plant component on the overall performance of CWMFCs. The macrophyte’s involvement in the oxygen input, nutrient uptake, and direct degradation of pollutants for the required treatment effect and bioelectricity production are discussed in more detail. The review identifies and compares planted and unplanted CWMFC with their efficiency on COD removal and electricity generation based on previous and recent studies.

Impact of climate change on wetland ecosystems: A critical review of experimental wetlands

Climate change is identified as a major threat to wetlands. Altered hydrology and rising temperature can change the biogeochemistry and function of a wetland to the degree that some important services might be turned into disservices. This means that they will, for example, no longer provide a water purification service and adversely they may start to decompose and release nutrients to the surface water. Moreover, a higher rate of decomposition than primary production (photosynthesis) may lead to a shift of their function from being a sink of carbon to a source. This review paper assesses the potential response of natural wetlands (peatlands) and constructed wetlands to climate change in terms of gas emission and nutrients release. In addition, the impact of key climatic factors such as temperature and water availability on wetlands has been reviewed. The authors identified the methodological gaps and weaknesses in the literature and then introduced a new framework for conducting a comprehensive mesocosm experiment to address the existing gaps in literature to support future climate change research on wetland ecosystems. In the future, higher temperatures resulting in drought might shift the role of both constructed wetland and peatland from a sink to a source of carbon. However, higher temperatures accompanied by more precipitation can promote photosynthesis to a degree that might exceed the respiration and maintain the carbon sink role of the wetland. There might be a critical water level at which the wetland can preserve most of its services. In order to find that level, a study of the key factors of climate change and their interactions using an appropriate experimental method is necessary. Some contradictory results of past experiments can be associated with different methodologies, designs, time periods, climates, and natural variability. Hence a long-term simulation of climate change for wetlands according to the proposed framework is recommended. This framework provides relatively more accurate and realistic simulations, valid comparative results, comprehensive understanding and supports coordination between researchers. This can help to find a sustainable management strategy for wetlands to be resilient to climate change.

Futuristic Non-antibiotic Therapies to Combat Antibiotic Resistance: A Review

The looming problem of resistance to antibiotics in microorganisms is a global health concern. The drug-resistant microorganisms originating from anthropogenic sources and commercial livestock farming have posed serious environmental and health challenges. Antibiotic-resistant genes constituting the environmental "resistome" get transferred to human and veterinary pathogens. Hence, deciphering the origin, mechanism and extreme of transfer of these genetic factors into pathogens is extremely important to develop not only the therapeutic interventions to curtail the infections, but also the strategies to avert the menace of microbial drug-resistance. Clinicians, researchers and policymakers should jointly come up to develop the strategies to prevent superfluous exposure of pathogens to antibiotics in non-clinical settings. This article highlights the present scenario of increasing antimicrobial-resistance in pathogenic bacteria and the clinical importance of unconventional or non-antibiotic therapies to thwart the infectious pathogenic microorganisms.

Spatial Changes in Microbial Communities along Different Functional Zones of a Free-Water Surface Wetland

Constructed wetlands (CWs) are complicated ecosystems that include vegetation, sediments, and the associated microbiome mediating numerous processes in wastewater treatment. CWs have various functional zones where contrasting biochemical processes occur. Since these zones are characterized by different particle-size composition, physicochemical conditions, and vegetation, one can expect the presence of distinct microbiomes across different CW zones. Here, we investigated spatial changes in microbiomes along different functional zones of a free-water surface wetland located in Moscow, Russia. The microbiome structure was analyzed using Illumina MiSeq amplicon sequencing. We also determined particle diameter and surface area of sediments, as well as chemical composition of organic pollutants in different CW zones. Specific organic particle aggregates similar to activated sludge flocs were identified in the sediments. The highest accumulation of hydrocarbons was found in the zones with predominant sedimentation of fine fractions. Phytofilters had the highest rate of organic pollutants decomposition and predominance of Smithella, Ignavibacterium, and Methanothrix. The sedimentation tank had lower microbial diversity, and higher relative abundances of Parcubacteria, Proteiniclasticum, and Macellibacteroides, as well as higher predicted abundances of genes related to methanogenesis and methanotrophy. Thus, spatial changes in microbiomes of constructed wetlands can be associated with different types of wastewater treatment processes.

Ferrate effectively removes antibiotic resistance genes from wastewater through combined effect of microbial DNA damage and coagulation

The widespread of antibiotic resistance genes (ARGs) in the environment can pose severe threats to public health. The wastewater treatment plant (WWTP) is regarded as an important hotspot of ARGs in the urban environment, but the removal of ARGs through conventional treatment techniques has been proven not sufficient. In this study, ferrate (Fe(VI)) was applied for the first time to remove intracellular ARGs from the secondary effluent of the WWTP. The results showed that Fe(VI) treatment could effectively remove 15 ARGs covering eight different types as well as intI1, the most common integron important to ARGs horizontal transfer. The removal efficiencies of tested genes could reach 1.10-4.37 log at the Fe(VI) dosage of 10 mg-Fe/L, which is significantly higher than those achieved through traditional disinfection methods. The DNA gel electrophoresis suggested that Fe(VI) could induce microbial DNA damage and consequently resulted in ARGs elimination. The presence of ARGs in settled residues indicated that coagulation initiated by Fe(VI) reduction products also contributed to ARGs removal from wastewater. In addition, the viability and relative abundances of potential ARGs hosts in the wastewater were decreased after Fe(VI) treatment. This study suggested a promising prospect for applying Fe(VI) to efficiently remove ARGs from wastewater, and consequently to control their proliferation and transfer in the environment.

Antibiotics in Food Chain: The Consequences for Antibiotic Resistance

Antibiotics have been used as essential therapeutics for nearly 100 years and, increasingly, as a preventive agent in the agricultural and animal industry. Continuous use and misuse of antibiotics have provoked the development of antibiotic resistant bacteria that progressively increased mortality from multidrug-resistant bacterial infections, thereby posing a tremendous threat to public health. The goal of our review is to advance the understanding of mechanisms of dissemination and the development of antibiotic resistance genes in the context of nutrition and related clinical, agricultural, veterinary, and environmental settings. We conclude with an overview of alternative strategies, including probiotics, essential oils, vaccines, and antibodies, as primary or adjunct preventive antimicrobial measures or therapies against multidrug-resistant bacterial infections. The solution for antibiotic resistance will require comprehensive and incessant efforts of policymakers in agriculture along with the development of alternative therapeutics by experts in diverse fields of microbiology, biochemistry, clinical research, genetic, and computational engineering.

Application of 15N tracing for estimating nitrogen cycle processes in soils of a constructed wetland

Integrated Constructed Wetlands (ICW) area technology for the attenuation of contaminants such as organic carbon (C), nitrogen (N), phosphorous (P) and sulphur (S) in water coming from point or diffuse sources. Currently there is a lack of knowledge on the rates of gross N transformations in soils of the ICW bed leading to losses of reactive N to the environment. In addition, the kinetics of these processes need to be studied thoroughly for the sustainable use of ICW for removal of excessive N in the treatment of waste waters. Gross N transformation processes were quantified at two soil depths (0-15 and 30-45 cm) in the bed of a surface flow ICW using a ¹⁵N tracing approach. The ICW, located in Dunhill village at Waterford in Southeastern Ireland, receives 500 person equivalent waste waters containing large quantities of organic pollutants (ca. mean annual C, N, P and S contents of 240, 60, 5 and 73 mg L^-1). Soil was removed from these depths in December 2014 and incubated anaerobically in the laboratory, with either ¹⁵N labeled ammonium (NH₄⁺) or nitrate (NO₃^-), differentially labeled with ¹⁴NH₄¹⁵NO₃ and ¹⁵NH₄¹⁴NO₃ in parallel setups, enriched to 50 atm% ¹⁵N. Results showed that at both soil depths, NO₃^- production rates were small, which may have resulted in lower NO₃^- reduction by either denitrification or dissimilatory NO₃^- reduction to ammonium (DNRA). However, despite being low, the DNRA rates were greater than denitrification rates. Direct transformation of organic N to NO₃^-, without mineralization to NH₄⁺, was a prevalent pathway of NO₃^- production accounting for 28-33% of the total NO₃^- production. Relative contribution of this process to the total N mineralization was negligible at depth 1 (0.01%) but dominant at depth 2 (99.7%). Total NO₃^-production to total immobilization of NH₄⁺ and NO₃^- was very small (<0.50%) suggesting that ICW soils are not a source of NO₃^-. Despite a large potential of N immobilization existed at both the layers, relative N immobilization to the total N conversion was higher at depth 2 (ca. 2.2) than at depth 1 (ca. 1.5). The NH₄⁺ desorption rate at 30-45 cm was high. However, immobilization in the recalcitrant and labile organic N pools was higher. Mineralization and immobilization of NH₄⁺ processes showed that recalcitrant organic N was the predominant source in ICW soils whereas the labile organic N was comparatively small. Source apportionment of N₂O production showed that the majority of the N₂O produced through denitrification (ca. 92.5%) followed by heterotrophic nitrification (ca. 5.5%), co-denitrification (ca. 1.90%) and nitrification (0.20%). These results revealed that application of a detailed ¹⁵N tracing method can provide insights on the underlying processes of ecosystem based abundances of reactive N. A key finding of this study was that both investigated ICW layers were characterised by large N immobilization which restricts production of NO₃^- and further gaseous N losses.

Review of Dry and Wet Decentralized Sanitation Technologies for Rural Areas: Applicability, Challenges and Opportunities

This paper reviews decentralized sanitation technologies comparing dry and wet solutions currently available, discussing their operational requirements, applicability, effluent output quality, efficiencies, environmental impacts, costs, challenges, as well as their advantages and implementation difficulties. Sanitation technologies vary from conventional centralized systems, typically used on urban areas, to decentralized systems, more common in sparse dwellings and small communities of rural areas. Compared with centralized sanitation, decentralized sanitation is being progressively considered as more sustainable solution. Most do not require energy or expensive or sophisticated operation, being easy to adapt to different geographic contexts. A general lack of consistent regulatory control over most dry rudimentary systems and primary treatment systems may compromise water quality and human health. In the future, a mix of new policies and accurate accounting of the location, performance, and degree of failure of such systems should be performed. However, forcing users and communities to face the capital, operational, or repairing costs may be challenging. Since many of the discussed technologies may be important sources of contamination with nutrients, pathogens and toxic chemicals, new opportunities are still open, which include the conversion of dry rudimentary systems into dry controlled systems.

A critical review on antibiotics and hormones in swine wastewater: Water pollution problems and control approaches

Swine wastewater (SW) is an important source of antibiotics and hormones (A&H) in the environment due to their large-scale application in swine industry. A&H in SW can be released into the water environment through the direct discharge of SW, effluent from SW treatment plants, and runoff and leaching from farmland polluted by swine wastes. The presence of A&H in the water environment has become an increasing global concern considering their adverse effects to the aquatic organism and human. This review critically discusses: (i) the occurrence of A&H in global water environment and their potential risks to water organisms and human; (ii) the management and technical approaches for reducing the emission of A&H in SW to the water environment. The development of antibiotic alternatives and the enhanced implementation of vaccination and biosecurity are promising management approaches to cut down the consumption of antibiotics during swine production. Through the comparison of different biological treatment technologies for removing A&H in SW, membrane-based bioprocesses have relatively higher and more stable removal efficiencies. Whereas, the combined system of bioprocesses and AOPs is expected to be a promising technology for elimination and mineralization of A&H in swine wastewater. Further study on this system is therefore necessary.

A Survey of the Presence of Pharmaceutical Residues in Wastewaters. Evaluation of Their Removal using Conventional and Natural Treatment Procedures

To encourage the reutilization of treated wastewaters as an adaptation strategy to climate change it is necessary to demonstrate their quality. If this is ensured, reclaimed waters could be a valuable resource that produces very little environmental impact and risks to human health. However, wastewaters are one of the main sources of emerging pollutants that are discharged in the environment. For this, it is essential to assess the presence of these pollutants, especially pharmaceutical compounds, in treated wastewaters. Moreover, the different treatment processes must be evaluated in order to know if conventional and natural treatment technologies are efficient in the removal of these types of compounds. This is an important consideration if the treated wastewaters are used in agricultural activities. Owing to the complexity of wastewater matrixes and the low concentrations of pharmaceutical residues in these types of samples, it is necessary to use sensitive analytical methodologies. In this study, the presence of 11 pharmaceutical compounds were assessed in three different wastewater treatment plants (WWTPs) in Gran Canaria (Spain). Two of these WWTPs use conventional purification technologies and they are located in densely populated areas, while the other studied WWTP is based in constructed wetlands which purify the wastewaters of a rural area. The sampling was performed monthly for two years. A solid phase extraction (SPE) coupled to ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was applied for the analysis of the samples, and the 11 pharmaceuticals were detected in all the studied WWTPs. The concentrations were variable and ranged from ng·L^-1 in some compounds like diclofenac or carbamazepine to µg·L^-1 in common pharmaceutical compounds such as caffeine, naproxen or ibuprofen. In addition, removal efficiencies in both conventional and natural purification systems were evaluated. Similar removal efficiencies were obtained using different purifying treatments, especially for some pharmaceutical families as stimulants or anti-inflammatories. Other compounds like carbamazepine showed a recalcitrant behavior. Secondary treatments presented similar removal efficiencies in both conventional and natural wastewater treatment plants, but conventional treatments showed slightly higher elimination ratios. Regarding tertiary system, the treatment with highest removal efficiencies was reverse osmosis in comparison with microfiltration and electrodialysis reversal.

Metal accumulation in dragonfly nymphs and crayfish as indicators of constructed wetland effectiveness

Constructed wetland effectiveness is often assessed by measuring reductions of contaminant concentrations in influent versus departing effluent, but this can be complicated by fluctuations in contaminant content/chemistry and hydrology. We assessed effectiveness of a constructed wetland at protecting downstream biota from accumulating elevated metal concentrations-particularly copper and zinc in effluents from a nuclear materials processing facility. Contaminants distributed throughout a constructed wetland system and two reference wetlands were assessed using six dragonfly nymph genera (Anax, Erythemis, Libellula, Pachydiplax, Tramea, and Plathemis) as biomonitors. Additionally, the crayfish, Cambarus latimanus, were analyzed from the receiving and two reference streams. Concentrations of Cu, Zn, Pb, Mn, Cr, Cd, and Al were evaluated in 597 dragonfly nymph and 149 crayfish whole-body composite samples. Dragonfly genera varied substantially in metal accumulation and the ability to identify elevated metal levels throughout components of the constructed wetland. Genera more closely associated with bottom sediments tended to accumulate higher levels of metals with Libellula, Pachydiplax, and Erythemis often accumulating highest concentrations and differing most among sites. This, combined with their abundance and broad distributions make the latter two species suitable candidates as biomonitors for constructed wetlands. As expected, dragonfly nymphs accumulated higher metal concentrations in the constructed wetland than reference sites. However, dragonfly nymphs often accumulated as high of metal concentrations downstream as upstream of the water treatment cells. Moreover, crayfish from the receiving stream near the constructed wetland accumulated substantially higher Cu concentrations than from downstream locations or reference streams. Despite reducing metal concentrations at base flow and maintaining regulatory compliance, metal fluxes from the wetland were sufficient to increase accumulation in downstream biota. Future work should evaluate the causes of downstream accumulation as the next step necessary to develop plans to improve the metal sequestering efficiency of the wetland under variable flow regimes.

Phytoremediation performance of floating treatment wetlands with pelletized mine water sludge for synthetic greywater treatment

PURPOSE

Buckets containing floating reed (Phragmites australis) simulated floating treatment wetlands (FTWs) and were used to improve the remediation performance of synthetic greywater (SGW). The aim of the study was to investigate the behaviour of FTWs for treatment of key contaminants within artificial greywater.

METHODS

Pelletized ochre based on acid mine water sludge was introduced to selected FTWs, because of its capability in sequestration phosphorus and other trace elements. The impact of the following four operational variables were tested in the experimental set-ups of the FTWs (four replicates each): pollutant strength (high- (HC) and low- (LC) concentrations), treatment time (2- or 7-days of hydraulic retention time (HRT)), presence or absence of macrophytes (P. australis) and cement-ochre pellets.

RESULTS

The results showed that 5 - day biochemical oxygen demand (BOD) and chemical oxygen demands (COD) were significantly (p < 0.05) reduced in all wetlands. Nitrate-nitrogen (NO₃-N) concentrations were significantly (p < 0.05) higher, and those measurements for PO₄-P were significantly (p < 0.05) lower than the corresponding ones determined for the influent. The existence of ochre pellets with P. australis significantly (p < 0.05) decreased B, Cd, Cr, Cu, Mg, Ni and Zn concentrations, but increased Al, Ca, Fe and K concentrations in the effluent, with the exception of sodium (Na).

CONCLUSIONS

The FTW performances can be improved by utilising ochre-cement pellets to increase the pH of greywater. The presence of P. australis acts as a buffer to neutralise the pH of SGW. Rhizomes and biofilms mitigate increases in turbidity, TSS and colour values.

Basins, beaver ponds, and the storage and redistribution of trace elements in an industrially impacted coastal plain stream on the Savannah River Site, SC, USA

Accumulation of eleven trace elements in sediment was evaluated throughout an industrially disturbed headwater stream on the Savannah River Site, SC, USA. Sampling began at upstream sedimentation basins at the margins of industrial areas, continued longitudinally downstream to a beaver pond representing a potential sink in the mid-reaches, and ended in downstream reaches. Additionally, sediment from beaver impacted areas in another industrially disturbed stream and a reference stream were analyzed to assess the natural tendency of these depositional features to settle out trace elements. We further compared trace element accumulation in sediment and biota from downstream reaches before and after an extreme rainy period to evaluate the potential redistribution of trace elements from sink areas. Trace elements accumulated in the headwater basins from which elements were redistributed to downstream reaches. The mid-reach beaver affected area sediments accumulated elevated concentrations of most analyzed elements compared to the free-flowing stream. The elevated accumulation of organic matter in these sink areas illustrated the effectiveness of reduced water velocity areas to settle out materials. The natural tendency of beaver ponds to accumulate trace elements and organic matter was further illustrated by sediments from the reference beaver pond accumulating higher concentrations of several elements than sediments from the free flowing section the stream impacted by industrial activity. However, concentrations in sediment from sedimentation basins and the beaver impacted area of the disturbed stream were highest. Trace elements and organic matter appeared to be redistributed from the sinks after the record rainy period resulting in increased trace element concentrations in both sediment and biota. These data suggest that assessments of contaminants in stream systems should include such slow-water, extreme depositional zones such as beaver impacted areas or basins to verify what contaminants may be pulsing through the stream.

The association of microbial activity with Fe, S and trace element distribution in sediment cores within a natural wetland polluted by acid mine drainage

Natural recovery and remediation of acid mine drainage (AMD) reduces the generation of acidity and transport of trace elements in the runoff. A natural wetland that receives and remediates AMD from an abandoned copper mine at Parys Mountain (Anglesey, UK) was investigated for better understanding of the remediation mechanisms. Water column concentrations of dissolved Fe and S species, trace metal (loid)s and acidity decreased markedly as the mine drainage stream passed through the wetland. The metal (loid)s were removed from the water column by deposition into the sediment. Fe typically accumulated to higher concentrations in the surface layers of sediment while S and trace metal (loid)s were deposited at higher concentration within deeper (20-50 cm) sediments. High resolution X-ray fluorescence scans of sediment cores taken at three sites along the wetland indicates co-immobilization of Zn, Cu and S with sediment depth as each element showed a similar core profile. To examine the role of bacteria in sediment elemental deposition, marker genes for Fe and S metabolism were quantified. Increased expression of marker genes for S and Fe oxidation was detected at the same location within the middle of the wetland where significant decrease in SO₄^2- and Fe²⁺ was observed and where generation of particulate Fe occurs. This suggests that the distribution and speciation of Fe and S that mediates the immobilization and deposition of trace elements within the natural wetland sediments is mediated in part by bacterial activity.

Fate and removal of antibiotics and antibiotic resistance genes in hybrid constructed wetlands

Hybrid design and artificial aeration has been widely applied in wetlands, but little is known about their effectiveness in the removal of antibiotics and antibiotic resistance genes (ARGs). Here we investigated the performance of various mesocosm-scale constructed wetlands (CWs) with artificial aeration and hybrid design in removal of antibiotics and ARGs from antibiotics-spiked domestic sewage. Four hybrid constructed wetland systems with zeolite as substrate and Iris tectorum Maxim as plant were set up to have different artificial aeration designs. The aqueous removal efficiencies of total antibiotics ranged from 87.4% to 95.3%, while those of total ARGs varied from 87.8% to 99.1%. The mass removal of antibiotics by the CWs was attributed mainly to the microbial degradation. The present study imply that sorption of substrates and biological processes could be the two main mechanisms for ARGs elimination. The results from this study showed the hybrid CWs with artificial aeration could enhance treatment efficiencies of antibiotics and ARGs as well as conventional pollutants.

Bacterial community activity and dynamics in the biofilm of an experimental hybrid wetland system treating greywater

The objectives of this study were to determine the biofilm microbial activity and bacterial community structure and successions in greywater treatment filters and to relate the treatment efficiency to the bacterial community parameters. This 10-month study was performed in a newly established experimental system for domestic greywater treatment that consisted of three parallel vertical flow filters (VFs) followed by a horizontal flow filter (HF). A rapid increase in the bacterial community abundance occurred during the first 85 days of filter operations, followed by a short-term decrease and the stabilization of the 16S rRNA gene copy numbers at average levels of 1.2 × 10⁹ and 3.2 × 10⁸ copies/g dw in VFs and HF, respectively, until the end of the experiment. The dominant bacterial phyla and genera differed between the VFs and HF. The temporal variation in the bacterial community structure was primarily related to the species replacement, and it was significantly affected by the influent organic carbon and nitrogen compounds in the VFs and the ammonia and organic carbon in the HF filters. Despite the differences in the community structure and assembly mechanisms, the temporal dynamics of the bacterial community showed high congruence between the filter types. The treatment efficiency was related to the biofilm bacterial community diversity and abundance and the abundance of certain bacterial genera in the VF filters. The results suggest that the dominant pathway of nitrogen removal by greywater treatment VFs occurs via coupled heterotrophic nitrification and denitrification, while the contribution of aerobic denitrification is temporally variable in these filters.

Performance assessment of Etueffont (France) lagooning treatment system: Report from a 16-year survey

This study examined the lagooning treatment system of the Etueffont landfill (France) over a period of 16 years. Outflow concentrations in total suspended solids, biological oxygen demand (BOD₅) and trace metal elements largely met outflow standards and were on average of 5, 8 and 6 times lower than those observed at inflow, respectively. In 2000, however, high levels of BOD₅ were observed in both the influent and effluent, exceeding the authorized outflow limits. At that time the lagooning ponds were subjected temporarily to organic pollution, coinciding with the arrival of the first leachates from a new cell. Though the chemical oxygen demand (COD) and total organic carbon in the influent exceeded authorized limits, overall values conformed to official standards with outflow exhibiting mean concentrations four times lower than those observed at inflow. The first period took place just after the arrival from the new cell of young leachates containing a very high level of COD (>10,000 mg L^-1), causing an organic overload that led to a temporary dysfunctioning of the treatment installation lasting approximately two years. Additionally, the COD in the leachates fell below the strictest limits (125 mg L^-1) at the end of monitoring (2005-2009). The initial nitrogen load brought in by the influent decreased progressively over time, evidence of continuous degradation. At the end of monitoring, regardless of the arriving inflow load, the discharge presented stable concentrations of approximately 30 mg L^-1, appearing to indicate that the limits for nitrogen elimination. Total phosphorus elimination was optimal as the concentrations at outflow were minimal throughout most of monitoring, even though the phosphorus load at inflow was from two to thirty-five times greater. Thus, the findings show that landfill leachates in the methanogenic phase can be treated efficiently by lagooning without risk to the surrounding environment.

Removal of non-point source pollutants from domestic sewage and agricultural runoff by vegetated drainage ditches (VDDs): Design, mechanism, management strategies, and future directions

Domestic wastewater and agricultural runoff are increasingly viewed as major threats to both aquatic and terrestrial ecosystems due to the introduction of non-point source inorganic (e.g., nitrogen, phosphorus and metals) and organic (e.g., pesticides and pharmaceutical residues) pollutants. With rapid economic growth and social change in rural regions, it is important to examine the treatment systems in rural and remote areas for high efficiency, low running costs, and minimal maintenance in order to minimize its influence on water bodies and biodiversity. Recently, the use of vegetated drainage ditches (VDDs) has been employed in treatment of domestic sewage and agricultural runoff, but information on the performance of VDDs for treating these pollutants with various new management practices is still not sufficiently summarized. This paper aims to outline and review current knowledge related to the use of VDDs in mitigating these pollutants from domestic sewage and agricultural runoff. Literature analysis has suggested that further research should be carried out to improve ditch characteristics and management strategies inside ditches in order to ensure their effectiveness. Firstly, the reported major ditch characteristics with the most effect on pollutant removal processes (e.g., plant species, weirs, biofilms, and substrates selection) were summarized. The second focus concerns the function of ditch characteristics in VDDs for pollutant removal and identification of possible removal mechanisms involved. Thirdly, we examined factors to consider for establishing appropriate management strategies within ditches and how these could influence the whole ditch design process. The current review promotes areas where future research is needed and highlights clear and sufficient evidence regarding performance and application of this overlooked ditch system to reduce pollutants.

Inoculation with bacteria in floating treatment wetlands positively modulates the phytoremediation of oil field wastewater

The aim of the present study was to investigate the potential of plant-bacterial synergism in floating treatment wetlands (FTWs) for efficient remediation of an oil field wastewater. Two plants, Brachiara mutica and Phragmites australis, were vegetated on floatable mats to develop FTWs, and inoculated with bacterial cons which were then inoculated with a consortium of hydrocarbon-degrading bacteria (Bacillus subtilis strain LORI66, Klebsiella sp. strain LCRI87, Acinetobacter Junii strain TYRH47, Acinetobacter sp. strain LCRH81). Both plants successfully removed organic and inorganic pollutants from wastewater, but bioaugmentation of P. australis significantly enhanced the plant's efficiency to reduce oil content (97%), COD (93%), and BOD (97%), in wastewater. Analysis of alkane-degrading gene (alkB) abundance and its expression profile further validated a higher microbial growth and degradation activity in water around P. australis as well as its roots and shoots. This study provides insight into the available phytotechnology for remediation of crude oil-contaminated water and introduces a wetland macrophyte, P. australis, with tailor-made bacterial consortium as an effective tool for improved phytoremediation efficiency of FTWs.

Mercury methylation in stormwater retention ponds at different stages in the management lifecycle

Stormwater retention ponds effectively manage erosion, flooding, and pollutant loadings, but are also sources of methylmercury (MeHg), a bioaccumulative neurotoxin which is produced by anaerobic aquatic microorganisms. Stormwater retention ponds have a 10-15 year working life, after which they are dredged and reflooded. In this study, we related MeHg biogeochemistry to the different stages of the management lifecycle. In a new, a dredged, and a mature stormwater retention pond, we measured MeHg and inorganic mercury (IHg) concentrations, and the potential for MeHg formation (Kmeth), during the early summer, peak summer, and fall of 2013. In our study sites, MeHg concentrations appear to be driven by mercury (Hg) methylation, indicated by significant correlations between Kmeth values and MeHg concentrations and the percent of Hg present as MeHg. Relationships between Hg variables and ancillary biogeochemistry suggest that Hg methylation is carried out by sulfate reducing bacteria, but that the process is modulated by the supply of IHg substrate, sediment total and labile organic carbon, and possibly competition with nitrate reducers. Wetlands at different points in the management lifecycle differ in terms of their MeHg biogeochemistry. The organic matter-poor new wetland had low MeHg production (mean Kmeth 0.014 per day) and sediment concentrations (mean 0.015 ng g-1), while the mature wetland both produced and accumulated MeHg about five times more actively. Methylmercury production capacity was only temporarily reduced in the reflooded sediments of the dredged wetland, which experienced rapid increases in Kmeth values from low (mean 0.015 per day) immediately after dredging, to values similar to those in the mature wetland after five months. This pattern may have been related to recolonization of the sediments with mercury methylators or increased microbial activities in response to the addition of fresh organic matter. Additional studies should focus on the applicability of these patterns to stormwater retention ponds in other areas, and particularly investigate the effects of stormwater pond dredging on their microbial ecology and MeHg biogeochemistry.

Bioprocessing for elimination antibiotics and hormones from swine wastewater

Antibiotics and hormones in swine wastewater have become a critical concern worldwide due to the severe threats to human health and the eco-environment. Removal of most detectable antibiotics and hormones, such as sulfonamides (SAs), SMs, tetracyclines (TCs), macrolides, and estrogenic hormones from swine wastewater utilizing various biological processes were summarized and compared. In biological processes, biosorption and biodegradation are the two major removal mechanisms for antibiotics and hormones. The residuals in treated effluents and sludge of conventional activated sludge and anaerobic digestion processes can still pose risks to the surrounding environment, and the anaerobic processes' removal efficiencies were inferior to those of aerobic processes. In contrast, membrane bioreactors (MBRs), constructed wetlands (CWs) and modified processes performed better because of their higher biodegradation of toxicants. Process modification on activated sludge, anaerobic digestion and conventional MBRs could also enhance the performance (e.g. removing up to 98% SMs, 88.9% TCs, and 99.6% hormones from wastewater). The hybrid process combining MBRs with biological or physical technology also led to better removal efficiency. As such, modified conventional biological processes, advanced biological technologies and MBR hybrid systems are considered as a promising technology for removing toxicants from swine wastewater.

Fluoroquinolones (FQs) in the environment: A review on their abundance, sorption and toxicity in soil

The use of fluoroquinolones (FQs) antibiotics as therapeutic agents and growth promoters is increasing worldwide; however their extensive uses are also resulting in antibiotic resistance among world communities. FQs have also become one of the major contaminants in the waste water bodies, which are not even completely removed during the treatment processes. Furthermore, their abundance in agricultural resources, such as the irrigation water, the bio-solids and the livestock manure can also affect the soil micro-environment. These antibiotics in soil tend to interact in several different ways to affect soil flora and fauna. The current review endeavors to highlight the some critical aspects of FQs prevalence in the environment. The review presents a detailed discussion on the pathways and abundance of FQs in soil. The discussion further spans the issue of sorption and FQs transformation into the soil better understand of their behavior and their toxicity to soil flora and fauna.

Treatment of contaminated greywater using pelletised mine water sludge

Precipitated sludge (ochre) obtained from a mine water treatment plant was considered as an adsorbent substance for pollutants, since ochre is relatively free from problematic levels of toxic elements, which could impair on the quality of water to be treated. Artificially created ochre pellets from mixing Portland cement with raw ochre sludge were utilised to remediate either high (HC) or low (LC) contaminated synthetic greywater (SGW) in mesocosm-scale stabilisation ponds at 2-day and 7-day contact times under real weather conditions in Salford. After a specific retention time, treated SGW was agitated before sampling to evaluate pollutant removal mechanisms (other than sedimentation) such as adsorption by ochre pellets, before replacing the treated water with new inflow SGW. The results showed that cement-ochre pellets have a high ability to adsorb ortho-phosphate-phosphorous (PO₄-P) significantly (p < 0.05) by 70.7% and 56.0% at 7-day contact time for HC-SGW and LC-SGW, respectively. After the experiment, an analysis revealed that elements such as boron (B), cadmium (Cd), magnesium (Mg), manganese (Mn), nickel (Ni) and zinc (Zn) accumulated significantly (p < 0.05) within the ochre pellets. The notable accumulation of Cd within ochre pellets reflects the significant (p < 0.05) remediation of greywater during the first 35 and 20 successive times of treatment for HC-SGW at 2- and 7-day contact times, respectively. Cadmium was still adsorbed significantly (p < 0.05) during the treatment of LC-SGW. However, the calcium (Ca) content decreased significantly (p < 0.05) within ochre pellets treating both types of greywaters due to mobilisation. The corresponding increases of Ca in greywater were significant (p < 0.05).

In situ denitrification and DNRA rates in groundwater beneath an integrated constructed wetland

Evaluation of the environmental benefits of constructed wetlands (CWs) requires an understanding of their impacts on the groundwater quality under the wetlands. Empirical mass-balance (nitrogen in/nitrogen out) approaches for estimating nitrogen (N) removal in CWs do not characterise the final fate of N; where nitrate (NO₃^--N) could be reduced to either ammonium (NH₄⁺-N) or N₂ with the potential for significant production of N₂O. Herein, in situ denitrification and DNRA (dissimilatory nitrate reduction to ammonium) rates were measured in groundwater beneath cells of an earthen lined integrated constructed wetland (ICW, used to remove the nutrients from municipal wastewater) using the ¹⁵N-enriched NO₃^--N push-pull method. Experiments were conducted utilising replicated (n = 3) shallow (1 m depth) and deep (4 m depth) piezometers installed along two control planes. These control planes allowed for the assessment of groundwater underlying high (Cell 2, septic tank waste) and low (Cell 3) load cells of the ICW. Background piezometers were also installed off-site. Results showed that denitrification (N₂O-N + N₂-N) and DNRA were major NO₃^--N consumption processes accounting together for 54-79% of the total biochemical consumption of the applied NO₃^--N. Of which 14-16% and 40-63% were consumed by denitrification and DNRA, respectively. Both processes differed significantly across ICW cells indicating that N transformation depends on nutrient loading rates and were significantly higher in shallow compared to the deep groundwater. In such a reduced environment (low dissolved oxygen and low redox potential), higher DNRA over the denitrification rate can be attributed to the high C concentration and high TC/NO₃^--N ratio. Low pH (6.5-7.1) in this system might have limited denitrification to some extent to an incomplete state, evidenced by a high N₂O-N/(N₂O-N+N₂-N) ratio (0.35 ± 0.17, SE). A relatively higher N₂O-N/(N₂O-N+N₂-N) ratio and higher DNRA rate over denitrification, suggest that the end products of N transformations are reactive. This N₂O can be consumed to N₂ and/or emitted to the atmosphere. The DNRA rate and accumulation of NH₄⁺-N indicated that the ICW created a suitable groundwater biogeochemical environment that enhanced NO₃^--N reduction to NH₄⁺-N. This study showed that CWs significantly influence NO₃^--N attenuation to reactive forms of N in the groundwater beneath them and that solely focusing on within wetland NO₃^--N attenuation can underestimate the environmental benefits of wetlands.

Methylmercury production and accumulation in urban stormwater ponds and habitat wetlands

Stormwater management ponds and created habitat wetlands effectively manage erosion, flooding, and pollutant loadings while providing biodiversity and aesthetic benefits, but these structures are also potential sources of methylmercury (MeHg), a bioaccumulative neurotoxin. While MeHg accumulation has been confirmed in habitat wetlands, the extent of MeHg production and accumulation in stormwater ponds is unknown. Additionally, the fine-scale spatial variation in MeHg in these wetlands has never been explored despite the possibility that cycles of wetting and drying, and the presence of aquatic plants may stimulate methylation at their margins. To address these knowledge gaps, we compared MeHg and inorganic mercury concentrations, the percent of total mercury present as MeHg (%MeHg), and potential mercury methylation rate constants (K_meth) in the sediments of terrestrial-aquatic transects through several stormwater and habitat wetlands. We present novel evidence confirming the in situ production of MeHg in both stormwater ponds and habitat wetlands, but observe no systematic differences across the terrestrial-aquatic gradient, suggesting that routine variations in water level do not alter MeHg production and accumulation. Stormwater ponds effectively trap mercury while converting relatively little to MeHg, as evidenced by lower MeHg concentrations, %-MeHg, and K_meth values than habitat wetlands, but often greater inorganic Hg concentrations. The relationship of aquatic vegetation to MeHg accumulation is weak and ambiguous, suggesting plants are not strong drivers of MeHg biogeochemistry in these systems. Although the MeHg hazard associated with individual artificial wetlands is low, they may be important sources of MeHg at the landscape level.

Temporal and spatial variations of contaminant removal, enzyme activities, and microbial community structure in a pilot horizontal subsurface flow constructed wetland purifying industrial runoff

A pilot-scale horizontal subsurface flow constructed wetland (HSSFCW) was operated to purify industrial runoff containing polycyclic aromatic hydrocarbons (PAHs) in Guangzhou, China. Synthetic industrial runoff was fed into the HSSFCW with continuous flow at an average loading rate of 0.128 m(3)/(m(2)/day) for about 2 years. Pollutants such as chemical oxygen demand (COD), total phosphorus (TP), and phenanthrene were mainly removed in the front quarter of the HSSFCW, and in the vertical direction, the average removal rates of COD, TP, total nitrogen (TN), ammonia, and phenanthrene of the upper layer were 64.23, 71.16, 50.81, 65.38, and 92.47 %, which were 1.23, 2.08, 1.48, 1.72, and 1.17 times higher than those of the bottom, respectively. Correlations among pollutant removal, soil environmental indexes, enzyme activities, and soil microbial community structure were evaluated. Enzyme assays (dehydrogenase, catalase, nitrate reductase, and polyphenol oxidase) showed significant associations between enzyme activities and pollutant removal (p < 0.01 and p < 0.05). Soil microbial community structure was assessed with denaturing gradient gel electrophoresis (DGGE) fingerprinting method, and results demonstrated that bacterial communities remained relatively stable in different seasons. Proteobacteria and Bacteroidetes were found to be the dominant phyla of the bacteria communities, and three clones which might be related to the biodegradation of phenanthrene were also detected. Results of the present work would broaden the knowledge of the purification mechanism of contaminants in the constructed wetlands (CWs), and identification of the treatment performances and temporal and spatial variations of biological activities of subsurface flow constructed wetlands (SSFCWs) would help to improve the operations of CWs for surface water protection.

Bacterial community dynamics in surface flow constructed wetlands for the treatment of swine waste

Constructed wetlands are generally used for the removal of waste from contaminated water. In the swine production system, wastes are traditionally flushed into an anaerobic lagoon which is then sprayed on agricultural fields. However, continuous spraying of lagoon wastewater on fields can lead to high N and P accumulations in soil or lead to runoff which may contaminate surface or ground water with pathogens and nutrients. In this study, continuous marsh constructed wetland was used for the removal of contaminants from swine waste. Using pyrosequencing, we assessed bacterial composition within the wetland using principal coordinate analysis (PCoA) which showed that bacterial composition from manure influent and lagoon water were significantly different (P=0.001) from the storage pond to the final effluent. Canonical correspondence analysis (CCA) showed that different bacterial populations were significantly impacted by ammonium--NH4 (P=0.035), phosphate--PO4(3-) (P=0.010), chemical oxygen demand--COD (P=0.0165), total solids--TS (P=0.030), and dissolved solids--DS (P=0.030) removal, with 54% of the removal rate explained by NH4+PO4(3-) according to a partial CCA. Our results showed that different bacterial groups were responsible for the composition of different wetland nutrients and decomposition process. This may be the major reason why most wetlands are very efficient in waste decomposition.

Long-term purification efficiency of a wetland constructed to treat runoff from peat extraction

Peat extraction increases the phosphorus, nitrogen, organic matter, suspended solids, and iron concentrations in runoff, resulting in negative effects on downstream water bodies. Wetlands are commonly used as natural cost-effective solutions to mitigate these negative effects. This study analyzed changes in the quality of runoff water from peat extraction areas and the long-term efficiency of constructed wetlands. The results indicate that the quality of runoff water changed after the initial drainage and during peat extraction. Nitrogen leached at high concentrations in the early stages of peat extraction following drainage, whereas the leaching of iron and phosphorus increased after peat extraction from deeper layers. Comparison of water quality and impurities retained immediately after treatment wetland construction and 14 years later showed that the treatment wetland remained functional, with good retention capacity, over a long period.

Cost-Effectiveness Analysis of Surface Flow Constructed Wetlands (SFCW) for Nutrient Reduction in Drainage Discharge from Agricultural Fields in Denmark

Constructed wetlands have been proposed as cost-effective and more targeted technologies in the reduction of nitrogen and phosphorous water pollution in drainage losses from agricultural fields in Denmark. Using two pig farms and one dairy farm situated in a pumped lowland catchment as case studies, this paper explores the feasibility of implementing surface flow constructed wetlands (SFCW) based on their cost effectiveness. Sensitivity analysis is conducted by varying the cost elements of the wetlands in order to establish the most cost-effective scenario and a comparison with the existing nutrients reduction measures carried out. The analyses show that the cost effectiveness of the SFCW is higher in the drainage catchments with higher nutrient loads. The range of the cost effectiveness ratio on nitrogen reduction differs distinctively with that of catch crop measure. The study concludes that SFCW could be a better optimal nutrients reduction measure in drainage catchments characterized with higher nutrient loads.

Environmental dissemination of antibiotic resistance genes and correlation to anthropogenic contamination with antibiotics

Antibiotic resistance is a growing problem which threatens modern healthcare globally. Resistance has traditionally been viewed as a clinical problem, but recently non-clinical environments have been highlighted as an important factor in the dissemination of antibiotic resistance genes (ARGs). Horizontal gene transfer (HGT) events are likely to be common in aquatic environments; integrons in particular are well suited for mediating environmental dissemination of ARGs. A growing body of evidence suggests that ARGs are ubiquitous in natural environments. Particularly, elevated levels of ARGs and integrons in aquatic environments are correlated to proximity to anthropogenic activities. The source of this increase is likely to be routine discharge of antibiotics and resistance genes, for example, via wastewater or run-off from livestock facilities and agriculture. While very high levels of antibiotic contamination are likely to select for resistant bacteria directly, the role of sub-inhibitory concentrations of antibiotics in environmental antibiotic resistance dissemination remains unclear. In vitro studies have shown that low levels of antibiotics can select for resistant mutants and also facilitate HGT, indicating the need for caution. Overall, it is becoming increasingly clear that the environment plays an important role in dissemination of antibiotic resistance; further studies are needed to elucidate key aspects of this process. Importantly, the levels of environmental antibiotic contamination at which resistant bacteria are selected for and HGT is facilitated at should be determined. This would enable better risk analyses and facilitate measures for preventing dissemination and development of antibiotic resistance in the environment.

Clogging of vertical-flow constructed wetlands treating urban wastewater contaminated with a diesel spill

Clogging often leads to a decrease of the treatment performance of wetlands. The aims of this study were to compare the impact of different design and operational variables on the treatment efficiency and clogging processes and to model suspended solid (SS) accumulation within the saturated wetland zone using the Wang-Scholz model. Different vertical-flow constructed wetlands were operated from June 2011 until April 2014. Four treatment periods were assessed: set-up, first year after set-up period, second year after set-up period and diesel spill (for selected filters only). The filter with the highest chemical oxygen demand (COD) loading but no diesel contamination performed the best in terms of COD and biochemical oxygen demand (BOD) removal for the fourth and final treatment period. Filters contaminated by diesel performed worse in terms of COD and BOD but considerably better regarding nitrate-nitrogen removal. Serious clogging phenomena impacting negatively on the treatment performance and the hydraulic conductivity were not observed. Modelling results were generally poor for the set-up period, adequate for the first 2 years after the set-up period and variable after the diesel spill. The Wang-Scholz model performed well for less complex operations.

The Role of Hydrology in the Polychlorinated Dibenzo--dioxin and Dibenzofuran Distributions in a Lowland River

Persistent organic pollutants such as polychlorinated dibenzo--dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are environmental contaminants that have widespread distribution and pose a serious threat to aquatic ecosystems. We conducted a study to quantify the distribution, patterns, and transport of PCDDs and PCDFs along the Pilica River in central Poland under different hydrological conditions to estimate the loads of these compounds and understand their fate in aquatic systems. Water samples were collected at five sampling points along the river that represent a range of hydrological conditions including flooding and stable and low water flows. Reduced river water flow was associated with lower average total and toxic equivalent (TEQ) concentrations of PCDDs plus PCDFs: 33.6 pg L and 4.21 pg TEQ L for flooding; 28.3 pg L and 3.6 pg TEQ L for stable flow; 18.4 pg L and 1.0 pg TEQ L for low-water flow. Similar results were observed for daily loadings of total and TEQ concentrations: the highest values were observed during flooding (331.1-839.4 mg d and 27.8-110.7 mg TEQ d), medium under stable hydrological conditions (55.8-121.0 mg d and 7.7-15.3 mg TEQ d), and the lowest values during low water flow (30.9 and 40.3 mg d and 1.4-2.4 mg TEQ d). The results demonstrate that diffuse sources of pollution play a key role during periods of high water flow (i.e., flooding season), whereas point sources of pollution, including municipal and industrial wastewater treatment plant discharges, mainly determine the PCDD and PCDF concentrations seen during low water periods.