Subsurface Flow Constructed Wetlands Research Articles

Evaluation of Wastewater Treatment by Microcosms of Vertical Subsurface Wetlands in Partially Saturated Conditions Planted with Ornamental Plants and Filled with Mineral and Plastic Substrates.

The current knowledge about the role terrestrial ornamental plants play in constructed wetlands (CWs) has scarcely been evaluated. Likewise, little attention has been given towards the use of new support or fill media for subsurface flow CWs, which may result in the reduction of costs when implemented on a large scale. This study evaluated, during nine months, the effect of three terrestrial ornamental plants and two substrates on the elimination of pollutants in wastewaters by using fill-and-drain vertical subsurface flow CWs (FD-CWs). Sixteen microcosms were used, nine filled with polyethylene terephthalate (PET) and nine with porous river stone (PRS). For each type of substrate, duplicates of microcosms were used, utilizing Anthurium sp., Zantedeschia aethiopica, and Spathiphyllum wallisii as vegetation and two other CWs without vegetation as controls. The environmental conditions, number of flowers, and height of the plants were registered. The results revealed that both substrates in the FD-CWs were efficient in removing pollutants. The average removal of pollutants in systems with vegetation revealed a positive effect on the reduction of the biochemical oxygen demand (55–70%), nitrates (28–44%), phosphates (25–45%), and fecal coliforms (52–65%). Meanwhile, in units without vegetation, the reduction of pollutants was nearly 40–50% less than in those with vegetation. The use of PET as a filling substrate in CWs did not affect the growth and/or the flowering of the species; therefore, its use combined with the species studied in CWs may be replicated in villages with similar wastewater problems. This may represent a reduction in implementation costs when utilizing PET recycled wastes and PRS as substrates in these systems in comparison with the typical substrates used in CWs. More studies are needed to better understand the interactions among these novel support media and the commercial terrestrial ornamental plants.

First Two Years of Operation of Subsurface Flow-constructed Wetland System with Methane Fermentation Digestion Effluent Treated by Polymeric Flocculation

First Two Years of Operation of Subsurface Flow-constructed Wetland System with Methane Fermentation Digestion Effluent Treated by Polymeric Flocculation

Electroactive biofilm-based constructed wetland (EABB-CW): A mesocosm-scale test of an innovative setup for wastewater treatment

Constructed wetlands (CWs) performance enhancement can be done with intensification strategies. A recent strategy still in study is the coupling with Microbial Electrochemical Technologies (MET). An alternative system using electro-conductive biofilters instead of electrodes and circuits used in MET, resulted in the development of a Microbial Electrochemical-based CW (METland). This system relies on electroactive bacteria (EAB) metabolism to transfer electrons to an electro-conductive material, thus boosting substrate consumption, and diminishing electron availability for biomass build-up and methane generation. In previous studies this biofilters have shown an improvement in biodegradation rates in comparison with subsurface flow CW. However, this set-up is still in development, hence there are uncertainties regarding the dynamics involve in the removal of pollutants. Considering that, this work aimed at establishing the capacity and removal kinetics of organic matter and nutrients in an Electroactive Biofilm-Based CW (EABB-CW). Two electro-conductive materials were tested (PK-A and PK-LSN) in planted and non-planted mesocosms and compared with sand. The systems were operated in a continuous upflow mode for 32 weeks and fed with real wastewater. The electro-conductive systems reached removal efficiencies up to 88% for BOD5, 90% for COD, 46% for NH4-N, and 86% for PO4-P. Organic matter removal in electro-conductive systems was possible even at loading rates 10-fold higher than recommended for horizontal flow CWs. First-order area-based removal constants (k), calculated for organic matter and nutrients are higher than values typically reported for saturated CW and in certain cases comparable with vertical flow CW. The organic removal was correlated with electron current densities measures, as indicator of the presence of EAB. The tested EABB-CW profiles as a promising CW type for the removal of organic matter and PO4-P with margin for modifications to improve nitrogen removal. Future studies with pilot/real scale systems are proposed to validate the findings of this study.

Storage mechanisms in constructed wetlands: Should we modify heterotrophic bacteria modelling?

This study investigated the occurrence of storage mechanisms in biofilm from constructed wetlands (CWs) through respirometric studies and calculated the corresponding heterotrophic growth yields. Respirometric tests were performed in biofilm extracted from horizontal sub-surface flow CWs batch loaded with three different COD mass loads: 7.0., 15.6 and 35.2 g COD/(m2∙day). The bed removal efficiency remained above 96% for all mass loads and COD mass removal rates increased from 6.8 g COD/(m2∙day) for the lowest load to 34.5 g COD/(m2∙day) for the highest load. The percentage of tests with storage evidence decreased from 85% to 10% with increasing mass loads and the responses of the microbial community to the acetate pulse showed an adaptation to the feast-famine conditions, through storage mechanisms, for lower loads, and a metabolic shift to the use of COD for growth for higher loads. Heterotrophic biomass yield values varied from 0.54–0.56 g COD/g COD for low mass loads to 0.69–0.71 for higher mass loads, indicating that greater substrate availably triggers growth and reduces the occurrence of storage. Storage yield values supported this trend varying between 0.89 and 0.94 with increasing mass loads. Given the significant storage evidence obtained in the present study, it is suggested that a modified modelling architecture, which includes storage mechanisms, should be considered in future simulations of CW systems.

Nitrogen removal in response to the varying C/N ratios in subsurface flow constructed wetland microcosms with biochar addition

Biochar as a substrate has great potential to promote pollutant removal efficiency in subsurface flow constructed wetlands (SSFCWs). However, information about the effect of different influent C/N ratios on treatment efficiency in SSFCWs with biochar is still scarce. In this study, SSFCW microcosms added with and without biochar were performed to investigate comparatively nitrogen removal in response to the domestic wastewater with varying C/N ratios. The results demonstrated that nitrogen removal increased at influent C/N ratios from1 to 3, and then decreased with the rising influent C/N ratios from 3 to 15 in different SSFCWs. Much higher removal efficiencies for COD (92%), NH4+-N (50%), and TN (50%) were obtained in the biochar-added SSFCW especially at the C/N ratio of 3 when comparing to CW without biochar. The higher pollutants removal ability of biochar-added SSFCWs was mainly attributed to the stronger adsorption ability in the porous biochar. However, poor nitrification was observed at various influent C/N ratios in SSFCWs with and without biochar due to lack of enough oxygen. This study supported that the use of biochar could increase the treatment performance in SSFCWs under various influent C/N ratios.

Elucidating the impact of influent pollutant loadings on pollutants removal in agricultural waste-based constructed wetlands treating low C/N wastewater

In this study, the common agricultural wastes (wheat straw, apricot pit and walnut shell) were exploited as the potential organic substrates in subsurface flow CWs (SSFCWs) with intermittent aeration to investigate the impacts of the varied influent loadings on the removal performance of pollutants. The results indicated that an application of agricultural wastes in CWs presented the different role in improving removal efficiency as influent pollutant loadings increased. In middle and high influent pollutant loadings, CWs with walnut shell strengthened the denitrification process significantly, and could achieve preferable purification of COD (97.36%), NH4+-N (98.83%), TN (51.78%), and TP (80.33%), respectively. However, N2O emission fluxes were higher in CWs with agricultural biomass and increased clearly as the influent pollutant loadings increasing. The results indicated that combination of agricultural material addition and aeration could be an appropriate intensifying strategy in SSFCWs especially for treating medium-strength low-carbon wastewaters.

Contaminants removal and bacterial activity enhancement along the flow path of constructed wetland microbial fuel cells

Microbial fuel cells implemented in constructed wetlands (CW-MFCs), albeit a relatively new technology still under study, have shown to improve treatment efficiency of urban wastewater. So far the vast majority of CW-MFC systems investigated were designed as lab-scale systems working under rather unrealistic hydraulic conditions using synthetic wastewater. The main objective of this work was to quantify CW-MFCs performance operated under different conditions in a more realistic setup using meso-scale systems with horizontal flow fed with real urban wastewater. Operational conditions tested were organic loading rate (4.9 ± 1.6, 6.7 ± 1.4 and 13.6 ± 3.2 g COD/m2·day) and hydraulic regime (continuous vs. intermittent feeding) as well as different electrical connections: CW control (conventional CW without electrodes), open-circuit CW-MFC (external circuit between anode and cathode not connected) and closed-circuit CW-MFC (external circuit connected).Eight horizontal subsurface flow CWs were operated for about four months. Each wetland consisted of a PVC reservoir of 0.193 m2 filled with 4/8 mm granitic riverine gravel (wetted depth 25 cm). All wetlands had intermediate sampling points for gravel and interstitial liquid sampling. The CW-MFCs were designed as three MFCs incorporated one after the other along the flow path of the CWs. Anodes consisted of gravel with an incorporated current collector (stainless steel mesh) and the cathode consisted of a graphite felt layer. Electrodes of closed-circuit CW-MFC systems were connected externally over a 220 Ω resistance.Results showed no significant differences between tested organic loading rates, hydraulic regimes or electrical connections, however, on average, systems operated in closed-circuit CW-MFC mode under continuous flow outperformed the other experimental conditions. Closed-circuit CW-MFC compared to conventional CW control systems showed around 5% and 22% higher COD and ammonium removal, respectively. Correspondingly, overall bacteria activity, as measured by the fluorescein diacetate technique, was higher (4% to 34%) in closed-circuit systems when compared to CW control systems.

Arsenic Removal Using Horizontal Subsurface Flow Constructed Wetlands: A Sustainable Alternative for Arsenic-Rich Acidic Waters

Constructed wetlands (CW) have been widely used to treat different types of water, including acid mine drainage (AMD). However, little is known about their performance in the removal of As from AMD. In this study, a laboratory-scale horizontal subsurface flow (HSSF) CW system was tested to evaluate its capacity to treat highly acidic, As-rich contaminated water resembling AMD. Vegetated and non-vegetated cells, having limestone or zeolite as the main supporting media, were built and operated to evaluate the effect of the media type and the presence of Phragmites australis on the removal of arsenic, iron (Fe), lead (Pb), and zinc (Zn), and on the neutralization capacity. The four types of cells were highly effective in the removal of As and Pb (removal > 99%), and Fe (removal > 98%), whereas Zn removal rates depended on the cell type. Limestone cells raised the pH from ~1.9 to ~7.5, while zeolite cells raised it to ~4. These results suggest that the media type has a key role in the neutralization capacity, and that the presence of vegetation affected mainly the removal of Zn. Knowledge from this study will contribute to guiding the implementation of HSSF CW for treating As-rich AMD.

Removal Processes of Carbamazepine in Constructed Wetlands Treating Secondary Effluent: A Review

It is widely believed that constructed wetlands (CWs) own great potentiality as polishing wastewater treatment methods for removing carbamazepine (CBZ). Although the typical CBZ removal efficiencies in CWs are quite low, the CBZ removal performance could be improved to some extend by optimizing the CW design parameters. A comparison of current relevant studies indicates that horizontal sub-surface flow CWs (HSSF-CWs) and hybrid wetlands are attracting more interest for the treatment of CBZ wastewater. According to CBZ’s physicochemical properties, substrate adsorption (25.70–57.30%) and macrophyte uptake (22.30–51.00%) are the two main CBZ removal pathways in CWs. The CBZ removal efficiency of CWs employing light expanded clay aggregate (LECA) as a substrate could reach values higher than 90%, and the most favorable macrophyte species is Iris sibirica, which has shown the highest total CBZ assimilation capacity. Several methods for enhancement have been proposed to optimize CBZ removal in CWs, including development of hydraulic models for optimization of CW operation, introduction of extra new CBZ removal ways into CW through substrate modification, design of combined/integrated CW, etc.

Denitrification- and anammox-dominant simultaneous nitrification, anammox and denitrification (SNAD) process in subsurface flow constructed wetlands

Simultaneous nitrification, anammox and denitrification (SNAD) process was developed in subsurface flow constructed wetlands (SFCWs) to treat polluted surface water. The effects of vegetation, hydraulic retention time (HRT), C/N, and influent nitrogen forms on nitrogen removal and microbial communities were investigated. Results showed that denitrification- and anammox-dominant SNAD corresponded to nitrate- and ammonia-dominant influent, respectively, and both could achieve more efficient nitrogen removal in planted SFCWs than the unplated. These higher efficiencies were due to the microbial growth, organic carbon release, oxygen supply and plant uptake promoted by vegetation. The electron donors accelerated denitrification but inhibited ammonia oxidation with deficient oxygen. Anammox contributed to nitrogen removal of 27.34% under oxygen-limited conditions without vegetation. Anammox combined with denitrification and plant uptake were over 90% in planted SFCWs. For the investigated factors, the ammonia, nitrate and C/N were the most significant ones influencing the microbial communities, further nitrogen removal pathways and performances.

Constructed wetland microcosms for the removal of organic micropollutants from freshwater aquaculture effluents

The presence of organic micropollutants (MPs) in the aquatic environment is strongly related to their difficult elimination by conventional water and wastewater treatment processes. Therefore, alternative treatment technologies are required to overcome this problem. In this domain, constructed wetlands (CWs) have gained increasing attention in the last years, mainly due to the low-cost, simple operation/maintenance and environmental friendliness of these systems. However, studies on the application of CWs to remove MPs from freshwater aquaculture effluents are still scarce. In this work, planted (Phragmites australis) vertical subsurface flow CWs, at microcosm scale, were investigated for the removal of MPs found in non-spiked freshwater aquaculture effluents, namely atrazine, isoproturon, perfluorooctanesulfonic acid (PFOS), clarithromycin, erythromycin, fluoxetine, norfluoxetine, and 2-ethylhexyl-4-methoxycinnamate (EHMC). A wider multi-component set of 36 MPs was also studied by adding these MPs at 100 ng L−1 to the same matrix (alachlor, atrazine, chlorfenvinphos, isoproturon, PFOS, azithromycin, clarithromycin, erythromycin, diclofenac, methiocarb, acetamiprid, clothianidin, thiacloprid, thiamethoxam, EHMC, simazine, atorvastatin, bezafibrate, carbamazepine, cephalexin, ceftiofur, citalopram, clindamycin, clofibric acid, diphenhydramine, enrofloxacin, fluoxetine, ketoprofen, metoprolol, norfluoxetine, ofloxacin, propranolol, tramadol, trimethoprim, venlafaxine, and warfarin). High weekly removal efficiencies (>87%) were observed for all MPs in both non-spiked and spiked experiments, with the exception of EHMC (removal rates between 0 and 86%). These results emphasize the potential of CWs to remove MPs from freshwater aquaculture effluents, but also the need to enhance the performance of these systems for the elimination of some recalcitrant MPs, such as EHMC, which was found at high concentrations in the studied effluents.

Nitrogen and organic matter removal and enzyme activities in constructed wetlands operated under different hydraulic operating regimes

Constructed wetlands (CWs) are environmentally-friendly methods for mariculture wastewater purification. The hydraulic regime is a key factor in the effectiveness of sub-surface flow CW treatment. The objectives of this study were to investigate the effects of five hydraulic operating regimes (i.e. Intermittent, Continuous, Batch I, Batch II and Batch III) on the purification performance of CW treated with mariculture wastewater and to assess the correlations between enzyme activities (i.e. urease, dehydrogenase) and purification performance of CW. Fifteen pilot sub-surface CWs with Salicornia bigelovii were investigated for the performance of CW as well as urease activity (UA) and dehydrogenase activity (DA). Over the experiment, removal efficiencies of TAN, NO3−-N, TN and COD under five hydraulic operating regimes were 26.6 to 37.2%, −6.0 to 16.5%, 9.4 to 16.8% and 33.9 to 44.6% respectively, corresponding to removal rates of 147.6 to 456.9 mg m−2 d−1, −18.1 to 229.2 mg m−2 d−1, 174.0 to 603.6 mg m−2 d−1 and 501.9 to 1421.6 mg m−2 d−1 respectively. CW with a Batch III operating regime had the best treatment performance, with mean removal efficiencies of TAN, NO3−-N, TN and COD of 37.2%, 16.5%, 14.9% and 34.0% respectively, with the corresponding removal rates of 456.9, 229.2, 603.6 and 873.6 mg m−2 d−1. As for enzyme activities, the UA was significantly higher in CW under Batch II than in Intermittent and Continuous operating regimes and the DA in CW with Batch I was significantly higher than under an Intermittent operating regime. UA and DA had significant positive correlations with COD concentrations but negative correlations with TAN and TN concentrations. The correlation analysis results showed that UA and DA can be an important indicator in evaluating removal performance of CW with Salicornia bigelovii in marine aquaculture wastewater treatment.

Influence of Biochar Application on Growth and Antioxidative Responses of Macrophytes in Subsurface Flow Constructed Wetlands

Constructed wetlands (CWs) have high potential for wastewater treatment in developing countries because of their operational convenience and low maintenance costs. However, rapid accumulation of macrophytes in these wetlands, as a result of plant litter recycling, can lead to lower removal efficiencies. Periodic harvesting is consider to be the effective measure to maintain the wastewater treatment performance, and so a lot of harvested plant waste needs to be properly disposed of. However, in China, plant waste is usually used for agricultural burning and the greenhouse gas emissions bring adverse effects on the atmospheric environment. In the traditional subsurface flow CW, the dissolved oxygen (DO) concentration is low, resulting in long-term anoxic or anaerobic conditions, which will bring damages to plant body, such as membrane lipid peroxidation and protein and DNA damage. Generally, the addition of biochar to CWs is beneficial for aeration, and improves the internal environment of wetlands. Hence, the effects of plant biochar on the pollutant purification efficiencies in CWs were studied, and the role of biochar in macrophyte growth and antioxidative response was investigated. Based on the results of biochar application in agricultural fields, the harvested wetland plant straw was pyrolyzed to biochar at 500 ℃ under a dynamic high-purity nitrogen atmosphere. The wetland plant Acorus calamus L. (AC) was chosen for this study. The impact characteristics of biochar on AC were studied in five independent CWs built in a greenhouse, by combining the analyses of growth and antioxidative responses of plants. Results showed that the removals of ammonium (NH4+-N) and total nitrogen (TN) were significantly enhanced when biochar was added to CWs and that higher long-term nitrogen removal rates were achieved when the biochar application rate was increased. The photosynthetic pigment content in AC increased significantly with increasing biochar application rate. This stimulated photosynthesis and increased the soluble protein (SP) and plant biomass amounts. Further, glutamine synthetase (GS) activity was strengthened with the addition of biochar. This helped enhance the NH4+-N metabolism and increased the relative uptake rate of AC. This study confirmed that long-term anoxic or anaerobic conditions in CWs cause membrane lipid oxidation in plants. However, the activity of the antioxidative response system was promoted with the addition of biochar, significantly decreasing the malonic dialdehyde (MDA) content in the plants.

Removal of acidic pharmaceuticals by small-scale constructed wetlands using different design configurations

To better understand the performance of constructed wetlands (CWs) to remove acidic pharmaceuticals (APs) in wastewaters in subtropical areas and to optimize CW design criteria, six small-scale CWs under different design configurations were operated. The factors (environmental parameters, water quality, and seasonality) influencing the APs removal were also analyzed to illustrate the removal mechanisms. The results indicated that the best performances of CWs were up to 80–90%. Subsurface flow (SSF) CWs showed high removal efficiency for ibuprofen, gemfibrozil and naproxen, but surface flow (SF) CWs performed better for ketoprofen and diclofenac. The positive relationship between the removal efficiencies of ibuprofen, gemfibrozil, and naproxen with dissolved oxygen and ammonia nitrogen reveals that SSF CWs under aerobic conditions benefit the biodegradation, while the favorable conditions created by SF CWs for receiving solar radiation promote the effective photolysis of ketoprofen and diclofenac. Planted SSF CWs had significantly higher removal efficiencies of ibuprofen and gemfibrozil than the unplanted controls had in all seasons. The removal of all APs was higher in summer and autumn than those in winter. Furthermore, an inverse relationship between removal efficiency and the distribution coefficient (logDow) was observed in SF CWs. Overall, CWs that provide aerobic degradation and photolysis would benefit APs removal in subtropical areas in the south of China.

A comparative study on the enhanced operation of a BFB and SFCW coupling process for domestic wastewater treatment

In this study, a new coupling process system of BFB (biological filter bed) and SFCW (subsurface-flow constructed wetland) based on the auto-ventilation network was proposed, and the comparative pollutant removal efficiency of the pilot test coupling system with different substrates configurations were investigated. The study found that: the influent concentration of the system fluctuated greatly and effluent concentration of the comparison system (b) was 20.22 ± 13.37 mg/L, 2.70 ± 2.49 mg/L, 4.40 ± 3.05 mg/L and 1.09 ± 0.62 mg/L, respectively. The comparison system (b) had better removal rates than that of the original system (a), which was 81.30 %, 90.28 %, 88.57 % and 75.36 % for CODcr, NH4+-N, TN and TP, respectively. The removal of the above main water indexes of the comparison system (b) promoted to 4.20 %, 9.20 %, 7.66 % and 13.61 % respectively when compared to the original system (a), which showed that the optimized configuration of various kinds of substrates was significant and was more beneficial to the degradation and removal of pollutants. The adsorption and interception function of substrates in the constructed wetland was the main way of phosphorus removal. The function of auto-ventilation ensured the amount of DO in the coupling system, making the phosphorus removal was less affected comparing to structure of traditional wetland.

Evaluation of attenuation of pharmaceuticals, toxic potency, and antibiotic resistance genes in constructed wetlands treating wastewater effluents

The performance of constructed wetlands (CWs) in the removal of pharmaceutically active compounds (PhACs) is generally evaluated on the basis of chemical analysis. In this work, we used a combination of chemical, toxicological, and molecular analyses to assess the attenuation of PhACs, toxic potency and antibiotic resistance genes (ARGs) in a field study of three CWs serving as tertiary treatment of wastewater treatment plants. First, 17 PhACs were analysed chemically, of which 14 were detected and seven at concentrations >0.1μg/l. Even though some of the individual PhACs were moderately or highly removed in the CWs investigated, median removal of overall PhACs was approximately 50% in the vertical subsurface flow CW (VSF-CW) with a lower hydraulic loading rate while the removal in the other two free water surface flow CWs (SF-CWs) was negligible. Second, toxic potency of wastewater extracts was assessed in a range of bioassays. Estrogenicity was overall attenuated in CWs, while the neurotoxic potency of wastewater extracts did not decrease after passage through the two CWs investigated. Third, the VSF-CW and one of the SF-CW showed a positive removal of an integrase gene and three ARGs tested. The increased concentrations of ARGs in the other SF-CW, as well as the increase of total bacteria in all CWs, may relate to regrowth of resistance-carrying bacteria. Finally, multivariate analysis shows that most PhACs are positively correlated to the observed toxic potency. Additionally, low removal of organics and nutrients seems to parallel with low removal of PhACs. ARGs positively correlated with organics, nutrients and some PhACs, and the integrase gene but not to the respective antibiotics. The insufficient removal of PhACs, toxic potency, and ARGs indicates the need of an optimal design of CWs as tertiary treatment facilities.

Effectiveness and Temporal Variation of a Full-Scale Horizontal Constructed Wetland in Reducing Nitrogen and Phosphorus from Domestic Wastewater

Cultural eutrophication stimulated by anthropogenic-derived nutrients represents one of most widespread water quality problems worldwide. Constructed wetlands (CWs) have emerged as an aesthetic, sustainable form of wastewater treatment, but, although they have shown adequate levels of organic matter removal in wastewaters, the effectiveness of nutrient removal has been less successful. An eleven-month monitoring program was undertaken in a horizontal subsurface flow CW (HSSF-CW) treating domestic wastewater from a village in Centre Region of Portugal, to evaluate the influence of climatic conditions (Continental-Mediterranean Climate region) and seasonal variations on removal. This CW uses gravel and sand as substrate and Phragmites australis as wetland plants. Samples were collected at the inlet and outlet from wetland bed and analyzed for pH, TN, Org-N, NH4+-N, NOx-N, TP and DP. The removal efficiencies (RE) of nitrogen and phosphorus compounds were relatively poor, but the results allow us to conclude that season had a significant (p < 0.05) effect on the RE of TN, NH4+-N, NOx-N, TP and DP, with higher values in warmest period (10.4%, 10.4%, 3.4%, 27.5% and 26.1%, respectively) than in coldest period (0%, −7.7%, −9.8%, 12.9% and 0%, respectively). Although lower hydraulic loading rate (HLR) generally resulted in better RE of all N and P compounds analyzed, no significant linear relationship was observed between these two variables. TN and NH4+-N concentrations in the effluent tend to significantly (p < 0.05) decrease with increasing respective incoming mass load rates for whole monitoring period and during spring–summer period, while the correlation between outlet TP concentrations and the inlet loading rate are not significant. The results indicate that the system is not effective for removal of nutrients, probably because it operated on overload and with a low hydraulic retention time (HRT) (average = 2.4 days). The results also showed that the RE of N and P followed seasonal trends, with higher values during spring–summer period.

Elevated salinity inhibits nitrogen removal by changing the microbial community composition in constructed wetlands during the cold season

In the present study we investigated whether subsurface flow constructed wetlands (SSF-CWs) can remove nitrogen from saline waste water and whether salinity affects nitrogen removal during the cold season (mean water temperature <10°C). Eight Iris pseudacorus-planted SSF-CWs were fed with normal (salinity 1.3–1.5‰; CWP) or saline (salinity 6.3–6.5‰; CWP+) waste water; similarly, eight unplanted SSF-CWs were fed with normal (CWU) or saline waste water (CWU+). The systems were run continuously at a hydraulic loading rate of 187.5mmday–1 and a hydraulic retention time of 4 days. Nitrogen removal efficiency, plant parameters and bacterial abundance and community composition were measured. In CWP, 80% of NH4+-N and 52% of total nitrogen (TN) were removed. In contrast, the removal rates of NH4+-N and TN in CWP+ were reduced by 27 and 37% respectively. In the presence of higher salinity, not only were there decreases in plant biomass (32.1%) and nitrogen uptake (50.1%), but the growth, activity and oxygen release of roots were also reduced (by 37.8, 68.0 and 62.9% respectively). Bacterial community composition also differed under conditions of elevated salinity. Elevated salinity is associated with lower nitrogen removal in SSF-CWs, which we speculate is a result of suppressed wetland macrophyte growth and activity, as well as changes in microbial community composition.

Fate of estrone in laboratory-scale constructed wetlands

A horizontal, subsurface, laboratory-scale constructed wetland (CW) consisting of four cells in series was used to determine the attenuation of the steroid hormone estrone (E1) present in animal wastewater. Liquid swine manure diluted 1:80 with farm pond water and dosed with [14C]E1 flowed through the series of cells containing floating vegetation (duckweed, family Lemnaceae) and a sand:gravel sediment layer. The aqueous layer within each cell was sampled across time, and at 168h duckweed and sediment were sampled for E1 and/or its metabolites. Control and Blank systems consisted of single cells with no vegetation or no vegetation/sediment, respectively. Only 5% of the dose was detected in the effluent at 168h. With the use of mass spectrometry and thin layer chromatography, it was determined that E1 was metabolized into estriol (E3) and to polar metabolites. The largest compartment for [14C] was duckweed (42.1% of administered dose) at 168h followed by sediment (17.3%) and the liquid layer (15.1% of the dose). Most of the vegetative removal of E1 occurred in the first cell, and thereafter, sediment:liquid layer interactions governed E1 movement suggesting particle-bound transport on either colloids or dissolved organic matter. Horizontal, subsurface flow CW were able to remove approximately 95% of the influent E1, and demonstrated the importance of vegetative matter in removal of this potent steroid hormone.

Macroinvertebrate Community in Subsurface-Flow Constructed Wetlands for Wastewater Treatment under High and Low Pollutant Stress in China

Constructed wetlands (CWs) for wastewater treatment had drawn much attention for their additional function of conserving freshwater ecosystems. The purpose of this study was to evaluate the macroinvertebrate biodiversity of two subsurface-flow and surface-flow hybrid CW systems (Qimei CW system (QCWS) and Kejiyuan CW system (KCWS)) under high and low pollutant stress in China. Nonmetric multidimensional scaling (NMDS) and canonical correspondence analysis (CCA) were used to analyze the water quality and aquatic macroinvertebrates community data. The results indicated that the subsurface-flow CW could conserve significant macroinvertebrate biodiversity (total taxon richness 17). The community structure was influenced by habitat types (i.e., subsurface-flow vs. surface-flow CWs) under low pollutant stress, and this influence was somehow masked by influence of water quality under high pollutant stress. Good pollutant removal rates were obtained in decreasing the concentrations of total nitrogen (66.37% and 27.28%), total phosphorus (58.93% and 37.55%), and loadings of biochemical oxygen demand (28.38% and 73.71%) in QCWS and KCWS, respectively. This study implied that subsurface-flow CWs could achieved good performance in both water purification and biodiversity conservation, which could provide a more solid basis for the application of subsurface-flow CWs.