Effects of plant diversity on nutrient retention and enzyme activities in a full-scale constructed wetland

CH4 control and nitrogen removal from constructed wetlands by plant combination

Global warming trend is accelerating. This study proposes a green and economical methane (CH4) control strategy by plant combination in constructed wetlands (CWs). In this study, a single planting of Acorus calamus L. hybrid constructed wetland (HCW-A) and a mixed planting of Acorus calamus L. and Eichhornia crassipes (Mart.) Solms hybrid constructed wetland (HCW-EA) were constructed. The differences in nitrogen removal performance and CH4 emissions between HCW-A and HCW-EA were compared and analyzed. The findings indicated that HCW-EA demonstrated significant improvements over HCW-A, with NH4+-N and TN removal rates increasing by 21.61% and 16.38% respectively, and CH4 emissions decreased by 43.36%. The microbiological analysis results showed that plant combination promoted the enrichment of Proteobacteria, Alphaproteobacteria and Bacillus. More nitrifying bacteria carrying nxrA genes and denitrifying bacteria carrying nirK genes accelerated the nitrogen transformation process. In addition, the absolute abundance ratio of pmoA/mcrA increased, reducing the release of CH4.

Performance of vertical flow constructed wetland for the treatment of effluent from a brassware industry in city of Fez, Morocco: a laboratory scale study

Brassware industry constitutes the second most polluting industrial sector in Fez city, Morocco, owing to its high heavy metal load. The aim of this study is to examine and evaluate the performance of vertical flow constructed wetlands in treating brassware effluents using various plant species. Ten treatment systems were planted with four types of plants: Chrysopogon zizanioides, Typha latifolia, Phragmites australis, and Vitex agnus-castus, while another system remained unplanted. These systems underwent evaluation by measuring various parameters, including pH, electrical conductivity, suspended solids, chemical oxygen demand, biological oxygen demand, sulfates, orthophosphates, total Kjeldhal nitrogen, ammonium, nitrates, nitrites, and heavy metals such as silver, copper, and nickel, using standard methods over of ten weeks. The results obtained demonstrate effectiveness of these systems. When planted with Ch. zizanioides, the systems achieved elimination rates of 83.64%, 98.55%, 91.48%, 86.82%, 80.31%, 96.54%, 98%, and 98.82% for suspended solids, ammonium, nitrites, BOD5, sulfates, orthophosphates, silver, and nickel, respectively. System with V. agnus-castus showed significant reductions in nitrate and copper, with rates of 84.48% and 99.10%, respectively. Considerable decrease in pH and electrical conductivity values was observed in all systems, with a notable difference between planted and control systems regarding effectiveness of treatment for other parameters.

Saturated constructed wetland-microbial fuel cell system and effect on dissolved oxygen gradient, electricity generation and ammonium removal

The aim of this work was to assess effect of saturated constructed wetland-Microbial fuel cell system on dissolved oxygen gradient, electricity generation and ammonium removal. Two laboratory-scale systems, one planted with Schoenoplectus californicus (SCW1-MFC) and other without plant (SCW2-MFC), were fed discontinuously with synthetic wastewater over 90 days. Both systems were operated at different organic loading rate (12 and 28 g COD/m2d) and ammonium loading rate (1.6 and 3.0 g NH4+- N/m2 d) under open circuit and close circuit mode. The results indicate that between lower and upper zones of wetlands the average values were in the range of 1.22 ± 0.32 to 1.39 ± 0.27 mg O2/L in SCW1-MFC and 1.28 ± 0.24 to 1.56 ± 0.31 mg O2/L in SCW2-MFC. The effect of operating mode (closed and open circuit) and vegetation on DO was not significant (p > 0.05). Chemical oxygen demand (COD) removal efficiencies, fluctuated between 90 and 95% in the SCW1-MFC and 82 and 94% in the SCW2-MFC system. Regarding NH4+- N, removal efficiencies were above 85% in both systems reaching values maximus 98%. The maximum power density generated was 4 and 10 mW/m2 in SCW1-MFC, while SCW2-MFC recorded the highest values (12 and 22 mW/m2).

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

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

Unveiling the nitrogen removal performance from microbial network establishment in vertical flow constructed wetlands

The combined effects of substrate types (natural zeolite or shale ceramsite) and hydraulic retention time (HRT, 3-day or 6-day) on nutrient removal and microbial co-occurrence networks in vertical flow constructed wetlands (VFCWs) remains to be elucidated. In this study, zeolite-packed VFCWs demonstrated superior removal rates, achieving 93.65% removal of NH4+-N and 83.84% removal of COD at 6-day HRT. The activity and establishment of microbial community were influenced by combined operating conditions. The abundances of Amx, amoA, nxrA, and nosZ genes increased with longer HRTs in zeolite-packed VFCWs. Additionally, a 6-day HRT significantly increased the relative abundances of Proteobacteria and Nitrospirae. At the species level, zeolite-packed VFCWs exhibited ecological niche sharing as a coping strategy in response to environment changes, while ceramsite-packed VFCWs displayed ecological niche differentiation. Both zeolite-packed and ceramsite-packed VFCWs established functional networks of nitrogen-transforming genera that utilized ecological niche differentiation strategies.

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

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

Both species richness and growth forms affect nutrient removal in constructed wetlands: A mesocosm experiment

Introduction

Plant richness is thought to improve the function of constructed wetlands (CWs), but most CWs are planted with monocultures, with only a few employed polycultures, which have drawn contradictory conclusions. We suppose functional diversity is the key to better performance of plant communities and hypothesize that CWs planted with diverse growth forms are superior in plant growth and nutrient removal.

Methods

In this study, six emergent plant species categorized into slender type (Schoenoplectus tabernaemontani, Typha orientalis), fan type (Iris sibirica, Acorus calamus) and large type (Canna indica and Thalia dealbata) were planted in monocultures, combinations (two species of the same growth form) and mixed polycultures (six species of three growth forms). We then compared how plant growth and nutrient uptake differed among treatments.

Results

It showed that the polyculture considerably increased the removal of total nitrogen (TN) and total phosphorus (TP), but the combination did not outperform monoculture. High consistency in the patterns between underground biomass and total biomass indicated that plant roots were essential for nutrient consumption. Compared with slender and fan plants, the large plants had a greater biomass increase in polycultures, which greatly accelerated the absorption and assimilation of TN and TP.

Conclusion

Our study indicated that plant community with various growth forms reduced the intensity of interspecific competition, increased the functional diversity, and greatly enhanced the ability of pollutant removal. Our results also provide some suggestions for plant selection and combination designs in CWs.

Immobilization of chromium enhanced by arbuscular mycorrhizal fungi in semi-aquatic habitats with biochar addition

Arbuscular mycorrhizal fungi (AMF) exhibit great potential in heavy-metal immobilization in semi-aquatic habitats. Under high heavy-metal stress, however, the role of AMF is limited, and the detoxification mechanism of AMF in heavy metals' stabilization remains unclear. This study investigated the effects of AMF on a wetland plant (Iris pseudacorus) and chromium (Cr) immobilization at different water depths in semi-aquatic habitats with biochar addition. Results showed that AMF increased the physiological and photosynthetic functions in I. pseudacorus under Cr exposures. Besides, AMF alleviated the accumulation of reactive oxygen species and lipid peroxidation by enhancing the antioxidant enzyme activities. AMF and biochar significantly decreased Cr concentrations in outlet water and increased Cr accumulation in I. pseudacorus. Besides, biochar also vastly improved Cr accumulation in the substrate under the fluctuating water depth. AMF reduced Cr bioavailability in the substrate, with Cr (Ⅵ) concentrations and acid-soluble forms of Cr decreased by 0.3-64.5% and 19.0-40.8%, respectively. Micro-proton-induced X-ray emission was used to determine element localization and revealed that AMF improved the nutrients uptake by wetland plants and inhibited Cr translocation from roots to shoots. Overall, this study demonstrated that the interaction between AMF and biochar could significantly enhance the immobilization of high Cr concentrations in semi-aquatic habitats.

Meta-analysis shows that plant mixtures increase soil phosphorus availability and plant productivity in diverse ecosystems

Soil phosphorus (P) availability is critical to plant productivity in many terrestrial ecosystems. How soil P availability responds to changes in plant diversity remains uncertain, despite the global crisis of rapid biodiversity loss. Our meta-analysis based on 180 studies across various ecosystems (croplands, grasslands, forests and pot experiments) shows that, on average, soil total P, phosphatase activity and available P are 6.8%, 8.5% and 4.6%, respectively, higher in species mixtures than in monocultures. The mixture effect on phosphatase activity becomes more positive with increasing species and functional group richness, with more pronounced increases in the rhizosphere than in the bulk soil. The mixture effects on soil-available P in the bulk soil do not change, but with increasing species or functional group richness these effects in the rhizosphere soil shift from positive to negative. Nonetheless, enhanced soil phosphatase activity stimulated available P in diverse species mixtures, offsetting increased plant uptake effects that decrease soil-available P. Moreover, the enhancement effects of species richness on soil phosphatase activity are positively associated with increased plant productivity. Our findings highlight that preserving plant diversity could increase soil phosphatase activity and P availability, which sustain the current and future productivity of terrestrial ecosystems.

Performance and mechanism of the in situ restoration effect on VHCs in the polluted river water based on the orthogonal experiment: photosynthetic fluorescence characteristics and microbial community analysis

Volatile halogenated hydrocarbons (VHCs) attracted many attentions due to its toxicity and persistence in the environment. In this research, a novel in situ ecological restoration reactor was applied to the degradation of VHCs in polluted river water. The optimized working condition adaptation of the in situ restoration technique was evaluated through orthogonal tests. The experiments showed that when the water depth was 0.4 m, the HRT was 5 days, and the current velocity was 1 m/s, the optimal removal efficiency of VHCs in the reactor was achieved. And the removal rates of CHCl₃, CCl₄, C₂HCl₃, and C₂Cl₄ reached 70.27%, 70.59%, 67.74%, and 81.82%, respectively. The results showed that both HRT and water depth were significantly related to the removal efficiency of reactor. The physiological state of the plants was analyzed by fitting rapid light curve (RLC) model, which showed that the accumulation of VHCs inhibited the photosynthetic performance of plants. Moreover, the microbial community structures of fillers were tested by high-throughput sequencing, and the findings supported that the microbial community made a great response to adapt to the changes in environment of the reactor. The relative abundance of Rhodocyclaceae increased slightly, which hinted that it had good adaptability to VHCs in polluted river water. The research results confirmed that in situ ecological restoration reactor was a potential approach for removal VHCs in polluted river water.

Constructed wetlands as a sustainable technology for wastewater treatment with emphasis on chromium-rich tannery wastewater

Water scarcity is a major threat to agriculture and humans due to over abstraction of groundwater, rapid urbanization and improper use in industrial processes. Industrial consumption of water is lower than the abstraction rate, which ultimately produces large amounts of wastewater such as from tannery industry containing high concentration of chromium (Cr). Chromium-contaminated tannery industry wastewater is used for irrigation of food crops, resulting in food safety and public health issues globally. In contrast to conventional treatment technologies, constructed wetlands (CWs) are considered as an eco-friendly technique to treat various types of wastewaters, although their application and potential have not been discussed and elaborated for Cr treatment of tannery wastewater. This review briefly describes Cr occurrence, distribution and speciation in aquatic ecosystems. The significance of wetland plant species, microorganisms, various bedding media and adsorbents have been discussed with a particular emphasis on the removal and detoxification of Cr in CWs. Also, the efficiency of various types of CWs is elaborated for advancing our understanding on Cr removal efficiency and Cr partitioning in various compartments of the CWs. The review covers important aspects to use CWs for treatment of Cr-rich tannery wastewater that are key to meet UN's Sustainable Development Goals.

Performance and mechanism of sulfamethoxazole removal in different bioelectrochemical technology-integrated constructed wetlands

Sulfamethoxazole (SMX) has a high concentration and detection frequency in aquatic environments due to the poor removal efficiency of traditional biological treatment processes. Bioelectrochemical technology-integrated constructed wetlands (CWs) have great potential for SMX removal; however, the process of SMX removal in different bioelectrochemical technology-integrated CWs (microbial fuel cell (MFC) and direct current (EC)) remains unclear. To address this, we examined the mechanism of SMX removal in MFCCW and ECCW. The results revealed that the SMX removal efficiency can reach 96.0 ± 2.4% in the ECCW and 97.2 ± 2.2% in the MFCCW. The enhancement of MFC for SMX removal in CW was slightly better than that in direct current (p > 0.05). It was found that the adsorption process of SMX in the substrate promoted by EC was more enhanced than that by MFC. Furthermore, bioelectrochemical technology improved plant activity, including root and enzymatic (superoxide dismutase, peroxidase, and catalase) activities, and fluorescence parameters (photochemical quenching coefficient, non-photochemical quenching coefficient, and quantum efficiency of PS II). Significant differences were found between CW and ECCW (p < 0.05), while no significant differences were found between CW and MFCCW (p > 0.05). The microbial activity and abundance in CW were improved by bioelectrochemical technology, and the microbial community structure was optimised to be simpler and more stable. However, EC tended to promote microbial and plant activity in CW, whereas MFC tended to optimise the microbial community and improve the tightness and stability of the module. The enhanced difference might also account for the changes in the SMX degradation pathway. 4-aminobenzenesulfonic acid (TP174), 3-amino-5-methylisoxazole (TP99) and 5-methylisoxazole (TP84) were all common products in the three reactors, whereas TP99 underwent further ring-opening in MFCCW and TP174 underwent further hydrolysis in ECCW. This study provided an important reference for the targeted regulation of plants and microorganisms in constructed wetlands via different bioelectrochemistry to enhance characteristic pollutants degradation.

The role of plants and soil properties in the enzyme activities of substrates on hard coal mine spoil heaps

Knowledge about biotic (plant species diversity, biomass) and/or abiotic (physicochemical substrate parameters) factors that determine enzyme activity and functional diversity of the substrate on hard coal spoil heaps is limited. Spontaneously developed vegetation patches dominated by herbaceous species commonly occurring on these spoil heaps: grasses (Poa compressa, Calamagrostis epigejos) and forbs (Daucus carota, Tussilago farfara), were examined. The activity of dehydrogenase and alkaline phosphatase was twice as high in plots dominated by grass species compared with those dominated by forbs. Significant positive correlations were found between the activity of dehydrogenase and alkaline phosphatase with pH, available P, soil moisture, and water holding capacity and negative correlations between the activity of urease and soil organic carbon. Strong positive correlations were found between values for Shannon–Wiener diversity index, evenness, species richness and soil functional diversity in plots dominated by grasses. We found that the soil physicochemical parameters had a greater impact on enzyme activity of the substrate than plant biomass and species diversity. However, grasses, through their extensive root system, more effectively increased enzyme activity and health of the substrate than other herbaceous species, and as they stabilize the substrate and form dense plant cover, they can be recommended for reclamation purposes.

The improvement of pollutant removal efficiency in saturated vertical flow constructed wetlands by tubifex tubifex

Pilot-scale saturated vertical flow constructed wetlands (VF-CWs) were established to identify whether T. tubifex has the similar performance in saturated VF-CWs to that in surface flow CWs in improving pollutant removal efficiency (RE). The saturated VF-CWs with T. tubifex achieved REs of 67.3% total nitrogen (TN) and 39.8% chemical oxygen demand (COD), which were significantly higher than treatments without T. tubifex (42.2% TN and 31.4% COD). There existed significant interactions between macrophytes and T. tubifex. T. tubifex greatly improved the dissolved oxygen by increasing the connectivity between layers, and enhanced dehydrogenase activity and fluorescein diacetate. Adding T. tubifex improved the bacterial diversity and relative abundance of both N-cycle bacteria and fermentation bacteria in the biofilms. The improvements of ammonia oxidation and anammox were the main pathways for the increased nitrogen removal by T. tubifex. Therefore, T. tubifex is a useful tool for improving pollutant REs in saturated VF-CWs.

Microbial coupling mechanisms of nitrogen removal in constructed wetlands: A review

Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs.

Nitrogen removal in vertical flow constructed wetlands: influence of bed depth and high nitrogen loadings

The aim of the study was to evaluate the nitrogen removal and its effects on the plant's growth and leaves morphology. using two subsurface vertical flow (VF bed), with different depths (0.24 m² × 0.70 m; 0.24 m² × 0.35 m) and nitrogen load increments. The VF bed were planted with Vetiveria zizanioides, filled with light expanded clay aggregates (Leca®NR 10/20) and fed in parallel mode with synthetic wastewater. High ammonium nitrogen concentration ([NH₄ ⁺-N] from 68 ± 3 to 290 ± 8 mg L^-1) was used without toxicity symptoms in plants, although the effects of ammonium nitrogen load were stopped the growth of the plants. Significant differences between ammonium nitrogen removed in each VF bed obtained for total nitrogen (TN_infl.) ≥ 27 ± 0.8 g m^-2 d^-1. The nitrification was contributed to ammonium nitrogen removal because was found higher values of nitrate and nitrite in the effluent. These values were more higher in VF bed 1 than in the VF bed 2, since ammonium nitrogen removal were also more higher in VF bed 1 than in the VF bed 2. Total nitrogen mass balance was carried out and the results show that the nitrification/denitrification process occurred with nitrogen plants uptake. It was observed that the VF bed depth has an influence on all nitrogen removal processes. As higher the depth root system it is seemed to favour the creation of zones with different oxidations conditions that allow the nitrogen compounds to be removed intensively.

Enhanced performance of pilot-scale hybrid constructed wetlands with A/O reactor in raw domestic sewage treatment

The aim of this study was to improve the nutrient removal efficiency by optimizing aeration time, hydraulic loading rate (HLR) and combination type in hybrid constructed wetlands (HCWs) with anoxic/oxic (A/O) reactor. The results showed that, the highest removal percentages of TN, NH₄-N, TP, PO₄-P and COD were 87.9%, 98.1%, 86.1%, 85.3% and 95.2%, respectively, in horizontal subsurface flow (HF) - surface flow - vertical subsurface flow CW with A/O reactor at 0.1 m/d HLR and 2 h aeration. HLR, aeration time and combination type had a significant impact on the removal of nutrients, though plant diversity did not have any significant influence. Presence of the A/O reactor improved the removal of TN in the HCWs by reducing influent loading and changing influent characteristics, thereby affecting the role of nitrification, anammox, and denitrification processes. The anammox process was the dominant pathway in the 1^st HF CWs during the aeration period, where the highest removal of phosphorus was observed.

Can Constructed Wetlands be Wildlife Refuges? A Review of Their Potential Biodiversity Conservation Value

The degradation of wetland ecosystems is currently recognized as one of the main threats to global biodiversity. As a means of compensation, constructed wetlands (CWs), which are built to treat agricultural runoff and municipal wastewater, have become important for maintaining biodiversity. Here, we review studies on the relationships between CWs and their associated biodiversity published over the past three decades. In doing so, we provide an overview of how wildlife utilizes CWs, and the effects of biodiversity on pollutant transformation and removal. Beyond their primary aim (to purify various kinds of wastewater), CWs provide sub-optimal habitat for many species and, in turn, their purification function can be strongly influenced by the biodiversity that they support. However, there are some difficulties when using CWs to conserve biodiversity because some key characteristics of these engineered ecosystems vary from natural wetlands, including some fundamental ecological processes. Without proper management intervention, these features of CWs can promote biological invasion, as well as form an ‘ecological trap’ for native species. Management options, such as basin-wide integrative management and building in more natural wetland components, can partially offset these adverse impacts. Overall, the awareness of managers and the public regarding the potential value of CWs in biodiversity conservation remains superficial. More in-depth research, especially on how to balance different stakeholder values between wastewater managers and conservationists, is now required.

Exposure of Juncus effusus to seven perfluoroalkyl acids: Uptake, accumulation and phytotoxicity

The extensive use of poly- and perfluoroalkyl substances (PFAS) has led to perfluoroalkyl acids (PFAAs) contamination in various environmental matrices. To remove PFAAs from contaminated water, this study investigated plant uptake of PFAAs by a native wetland plant species in the US, Juncus effusus. The results showed that J. effusus translocated selected PFAAs, including perfluoropentanoic acid (PFPA), perfluorobutanesulfonic acid (PFBS), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). During the 21-day experimental period, the uptake of PFAAs increased with increasing PFAAs exposure concentration and time. PFOS was largely accumulated in the roots with limited upward translocation. PFAAs with shorter carbon chain length were taken up by J. effusus roots and tended to accumulate in plant shoots. The highest removal efficiency (11.4%) of spiked PFAAs by J. effusus was achieved when it was exposed to PFAAs at around 4.6 mg/L for 21 days. The exposure to PFAAs stimulated the antioxidative defense system in J. effusus shoots but inhibited the superoxide dismutase (SOD) and catalase (CAT) activities and damaged the antioxidative defense system in J. effusus roots. These results warrant further studies to evaluate J. effusus's long-term performance in a PFAAs contaminated environment.

Plant diversity increases N removal in constructed wetlands when multiple rather than single N processes are considered

Biodiversity has a close relationship with ecosystem functioning. For most biodiversity-ecosystem-functioning studies, biodiversity has been linked to a single indicator variable of ecosystem functioning. However, there are generally multiple ecosystem processes contributing to ecosystem functioning and they differ in their dependence on biodiversity. Thus, the relationship between biodiversity and ecosystem functioning can be stronger when multiple rather than single ecosystem processes are considered. Using both mass-balance and stable-isotope approaches, we explored the effects of plant diversity on nitrogen (N) removal sustained by multiple N-cycling processes in experimental microcosms simulating constructed wetlands, an ecosystem treating wastewater with high N loading. Four species were used to assemble different plant communities, ranging in richness from one to four species. The removal of N, indicated by low levels of total inorganic N concentration (TIN) present in the effluent, was considered as an integrated measure of ecosystem functioning, combining three constituent N-cycling processes: plant uptake, denitrification, and substrate adsorption. Our results showed that (1) species richness had a positive effect on N removal, in particular, the four-species mixture reduced effluent TIN to a lower level than any monoculture; however, polycultures (two-, three-, and four-species mixtures) did not outperform the most efficient monoculture when each of the three constituent N-cycling processes was considered by itself; (2) species identity had significant impacts on single processes. Communities with the species Coix lacryma-jobi showed the greatest capacity for N uptake and communities with Phragmites australis had the highest denitrification rates; (3) isotope fractionation in the rhizosphere of Coix lacryma-jobi was primarily due to microbial denitrification while multistep isotope fractionation was detected for Phragmites australis and Acorus calamus (indicating recycling of N), suggesting that species differed in the way they transformed N; (4) the enhanced N removal at high diversity may be due to mutualistic interactions among species belonging to different functional types. Our findings demonstrated that although plant species richness had negligible effects on individual N-cycling processes, it enhanced the overall ecosystem functioning (N removal) when these processes were considered collectively. Our study thus contributes to improve the treatment efficiency of constructed wetlands through proper vegetation management.

High performance of integrated vertical-flow constructed wetland for polishing low C/N ratio river based on a pilot-scale study in Hangzhou, China

We investigated the treatment efficiency of micro-polluted NO₃^--dominated river water with low C/N ratio by five parallel pilot-scale IVCWs with different plant and substrate collocation. When the mean concentration was 2.24 and 0.193 mg L^-1 in influent, IVCWs achieved an average (mass) removal rate of (0.09 g m^-2 day^-1) 46.8% and (0.77 g m^-2 day^-1) 62.3% for TN and TP, respectively, during 1 year of operation. Water quality was significantly improved from grade V to meet the criterion of grade IV of surface water. Through the comparison of removal rate by different IVCWs, we found that lack of carbon sources in influent limited the denitrification in the middle and bottom layers (ML, BL) of IVCW. Zeolites deployed in the upper layer (UL) of IVCW reduced the overall N removal efficiency compared with gravels, due to a stronger nitrification but weaker denitrification. Canna indica (C. indica) was superior to Arundo donax (A. donax) and Thalia dealbata (T. dealbata) for N removal in the UL of IVCW due to higher aboveground biomass accumulation and microbial removal during the first 10 months. Stronger nitrification and denitrification were simultaneously facilitated near the rhizosphere of C. indica. When entered into Dec., A. donax performed higher N removal efficiency than the other two species. The internal replenishment of peats in the ML as carbon sources significantly improved N and P removal efficiency. Zeolites with stronger capacity of ammonium (NH₄⁺) adsorption was more in favor of anammox in the BL, when compared with roseites, but both of them were not conducive to the growth of denitrifiers. However, the deployment of shale ceramisites obtained an opposite result. Gemmata and Pirellula as anammox bacteria were more enriched in the zeolite layer, whereas some anaerobic denitrifiers (Corynebacterium and Paludibacter) and heterotrophic denitrifiers including Bacillus, Geobacter, Pseudomonas, and Lactococcus were more found in shale ceramisite. Supply of peats as carbon sources in the ML was beneficial for the adhesion of anammox bacteria and denitrifiers in the BL of shale ceramisites. An ideal model composed of C. indica + A. donax (DFU)-gravel (UL)-anthracite+peat (ML)-zeolite+shale ceramsite (BL)-Acorus calamus (UFU) was proposed for treating this type of river water to achieve high efficiency.

Environmental, Ecological, and Economic Benefits of Biofuel Production Using a Constructed Wetland: A Case Study in China

Here we show a constructed wetland (CW), a viable alternative wastewater treatment system, be used to produce biofuels from biomass by using nitrogen contained in domestic wastewater. We summarize the potential biomass yield evaluated as cellulosic ethanol bioenergy production, and combine the life cycle analysis with a mass balance approach to estimate the energetic, environmental, and economic performance of a CW biofuel system. The results showed that the annual aboveground biomass yield of a CW in Zhoushan, Zhejiang Province, China, averaged 37,813 kg ha⁻¹ year⁻¹ as the by-product of treating waste N, which is about one order of magnitude larger than traditional biofuel production systems. The biomass yield in the Zhoushan CW system had life cycle environment benefits of 8.8 Mg (1 Mg = 10⁶ g) CO₂ equivalent ha⁻¹ year⁻¹ of greenhouse gas emission reduction. The CW in Zhoushan had a net energy gain of 249.9 GJ (1 GJ = 10⁹ J) ha⁻¹ year⁻¹ while the wastewater treatment plant (WTP) consumes 7442.5 GJ ha⁻¹ year⁻¹. Moreover, the CW reduced greenhouse gas emissions to 2714 times less than that of the WTP. The CW also provided various ecosystem services, such as regional climate regulation and habitat conservation. We suggest that the potential use of a CW as biofuel production and carbon sequestration via nitrogen-negative input can be explored more widely in the future.

Electricity production and the analysis of the anode microbial community in a constructed wetland-microbial fuel cell

The objective of this study is to assess bioelectricity generation, pollutant removal (COD, ammonium, nitrate) and the bacterial communities on anodes in constructed wetlands coupled with microbial fuel cells (CW-MFCs), through feeding the systems with three different types of synthetic wastewater (system 1: normal wastewater; system 2: ammonium-free wastewater; system 3: nitrate-free wastewater). Three CW-MFCs were operated with different wastewater concentrations and hydraulic retention times (HRTs) over a long time period (6 months). The results indicate that the maximum open circuit voltage (775.63 mV) and maximum power density (0.628 W m⁻³) were observed in system 3 (period 3), and that bioenergy production was inhibited in system 2, when feeding with ammonium-free wastewater continuously. COD removal rates in the three systems were similar during each period and ranged from 82.2 ± 6.8% to 98.3 ± 2.2%. Ammonium removal occurred at the air cathode of the CW-MFCs through nitrification, and a higher level of ammonium removal was found in system 1 (period 3) compared with the others. Meanwhile, denitrification occurred at the anaerobic anode of the CW-MFCs, and a large amount of nitrate was removed effectively. The highest nitrate removal rate was 98.8 ± 0.5% in system 2 (period 3). Additionally, four genera related to electricity generation were detected at the anode: Geothrix; Desulfovibrio; Desulfobulbus; and Geobacter. The relative abundances of Desulfovibrio, Desulfobulbus and Geothrix gradually increased during the three periods in system 3, which might be beneficial for bioelectricity generation. Further investigations are needed to optimize the CW-MFC performance and explain the mechanism behind the pollutant degradation and electron motion in the CW-MFCs.

The objective of this study is to assess bioelectricity generation, pollutant removal and the bacterial communities on anodes in constructed wetlands coupled with microbial fuel cells, through feeding the systems with three different types of synthetic wastewater.

Integrated biomarker responses of the submerged macrophyte Vallisneria spiralis via hydrological processes from Lake Poyang, China

Vallisneria spiralis, a widely distributed wetland plant, was used to reveal how the light intensity at the top of the plant, plant morphology and antioxidant enzyme activity respond to different hydrologic conditions from Lake Poyang, China. By designing a laboratory experiment simulating historical water levels of low, normal and high wetland plant submersion, this study aimed to elucidate the effects of different levels of flooding on growth and antioxidant enzyme activity for V. spiralis. The results showed that the plant crown light intensity of the treated group and control group (CG) first decreased and then increased along with the seasonal variation of the water level. The maximum and minimum values of the plant crown light intensity were observed in April and July, respectively. Similar to the CG, V. spiralis from the normal and low water level (LWL) groups was measured and had higher plant height growth in the flooding period from May to June, and the entire plant biomass also showed a steady growth trend in the same period. However, the plant growth of the high water level (HWL) group was lower during the whole simulation period, with negative growth in July. Antioxidant enzyme activities changed with the seasonal temperature, and the activity of the CG showed a rising trend. Compared with those of the CG, the antioxidant enzyme activities of the HWL group showed a 'bell shaped' trend, which was first significantly induced and then significantly inhibited. In addition, the peroxidase (POD) and catalase (CAT) activities from the LWL group in April were also significantly induced. The integrated biomarker response (IBR) index showed that a comprehensive biological index could well reflect the effects of seasonal water levels in Poyang Lake on the growth of the wetland plant V. spiralis. This study indicated that high flooding levels had the strongest negative effect on the growth and enzyme activity of the submerged plant V. spiralis.

Integrated perspectives on the use of bacterial endophytes in horizontal flow constructed wetlands for the treatment of liquid textile effluent: Phytoremediation advances in the field

Constructed wetlands (CWs) have emerged as cost-effective and sustainable treatment systems for the remediation of industrial wastewaters; nevertheless, their potential has mostly been evaluated in laboratory-scale studies. Likewise, endophytic bacteria can enhance plant growth and reduce phytotoxicity under polluted conditions, but their application with pilot-scale CWs has rarely been evaluated. The present study aims to evaluate on-site performance of endophyte-assisted pilot-scale horizontal flow constructed wetlands (HFCWs) for the remediation of effluent from a textile industry. The HFCWs were established by planting Leptochloa fusca in the presence of three endophytic bacterial strains with dye degrading, and plant growth promoting capabilities. We found that the system was able to remove a significant proportion of both organic and inorganic pollutants. Maximum reduction of pollutants was observed in endophyte-augmented HFCWs, where the COD and BOD reduced from 493 to 70 mg l^-1 and 190 to 42 mg l^-1, respectively, within 48 h. Additionally, survival of endophytic bacteria in different components of the HFCWs was also recorded. Treated wastewater was found to be non-toxic and the inoculated bacteria showed persistence in the wastewater as well as rhizo- and endosphere of L. fusca. Accordingly, a positive impact on plant growth was observed in the presence of bacterial augmentation. The system performance was comparable to the vertical flow constructed wetlands (VFCWs) as high nutrients reduction was seen in the presence of this partnership. This pilot-scale study is a step forward toward the field-scale application of phytoremediation coupled with bacterial endophytes as a cost-effective means of on-site wastewater remediation. To the best of our knowledge, this is among the first pilot-scale studies on use of HFCWs for improvement in quality of textile industry effluent as most previous studies are limited either in the context of engineering or lack effective interplay of plant and bacteria.

Taxonomic and phylogenetic diversity of vascular plants at Ma'anling volcano urban park in tropical Haikou, China: Reponses to soil properties

Anthropogenic processes and socio-economic factors play important roles in shaping plant diversity in urban parks. To investigate how plant diversity of Ma' anling urban volcano park in Hainan Province, China respond to these factors, we carried out a field investigation on the taxonomic and phylogenetic diversity of vascular plants and soil properties in this area. We found 284 species of vascular plants belonging to 88 families and 241 genera, which included 194 native species, 23 invasive species, 31 naturalized species, 40 cultivars, and 4 rare / endangered plant species. Tree composition and richness significantly varied between different vegetation formations (plantation, secondary forest, and abandoned land). Plant species richness and community composition were significantly affected by elevation (El), soil water content (WC), total soil nitrogen (TN) and soil organic matter (SOM). There were significant diversity differences between plantations and abandoned lands, but not between the plantations and secondary forests. The flora in the study site was tropical in nature, characterized by pantropic distributions. Compared to adjacent areas, floristic composition in the study site was most similar to that of Guangdong, followed by that of Vietnam. Our study revealed the diversity patterns of volcanic plants and provided the basis for future planning of plant conservation, such as preserving plant species, maintaining plant habitats, and coordinating plant management in this region.

Elevated tropospheric CO2 and O3 concentrations impair organic pollutant removal from grassland soil

The concentrations of tropospheric CO₂ and O₃ have been rising due to human activities. These rising concentrations may have strong impacts on soil functions as changes in plant physiology may lead to altered plant-soil interactions. Here, the effects of eCO₂ and eO₃ on the removal of polycyclic aromatic hydrocarbon (PAH) pollutants in grassland soil were studied. Both elevated CO₂ and O₃ concentrations decreased PAH removal with lowest removal rates at elevated CO₂ and elevated O₃ concentrations. This effect was linked to a shift in soil microbial community structure by structural equation modeling. Elevated CO₂ and O₃ concentrations reduced the abundance of gram-positive bacteria, which were tightly linked to soil enzyme production and PAH degradation. Although plant diversity did not buffer CO₂ and O₃ effects, certain soil microbial communities and functions were affected by plant communities, indicating the potential for longer-term phytoremediation approaches. Results of this study show that elevated CO₂ and O₃ concentrations may compromise the ability of soils to degrade organic pollutants. On the other hand, the present study also indicates that the targeted assembly of plant communities may be a promising tool to shape soil microbial communities for the degradation of organic pollutants in a changing world.

Effect of vegetation type on treatment performance and bioelectric production of constructed wetland modules combined with microbial fuel cell (CW-MFC) treating synthetic wastewater

An operation of microcosm-constructed wetland modules combined with microbial fuel cell device (CW-MFC) was assessed for wastewater treatment and bioelectric generation. One of the crucial aims of the present experiment is also to determine effect of vegetation on wastewater treatment process and bioelectric production in wetland matrix with microbial fuel cell. Accordingly, CW-MFC modules with vegetation had higher treatment efficiency compared to unplanted wetland module, and average COD, NH₄⁺, and TP removal efficiency in vegetated wetland modules were ranged from 85 to 88%, 95 to 97%, and 95 to 97%, respectively. However, the highest NO₃^- removal (63%) was achieved by unplanted control module during the experiment period. The maximum average output voltage, power density, and Coulombic efficiency were obtained in wetland module vegetated with Typha angustifolia for 1.01 ± 0.14 V, 7.47 ± 13.7 mWatt/m², and 8.28 ± 10.4%, respectively. The results suggest that the presence of Typha angustifolia vegetation in the CW-MFC matrix provides the benefits for treatment efficiency and bioelectric production; thus, it increases microbial activities which are responsible for biodegradation of organic compounds and catalyzed to electron flow from anode to cathode. Consequently, we suggest that engineers can use vegetated wetland matrix with Typha angustifolia in CW-MFC module in order to maximize treatment efficiency and bioelectric production.

Chromium removal from wastewater using HSF and VF pilot-scale constructed wetlands: Overall performance, and fate and distribution of this element within the wetland environment

The current experimental work aimed at the investigation of the overall chromium removal capacity of constructed wetlands (CWs) and the chromium fate-distribution within a wetland environment. For this purpose, the experimental setup included the parallel operation and monitoring of two horizontal subsurface flow (HSF) pilot-scale CWs and two vertical flow (VF) pilot-scale CWs treating Cr-bearing wastewater. Samples were collected from the influent, the effluent, the substrate and the plants. Apart from the continuous experiment, batch experiments (kinetics and isotherm) were conducted in order to investigate the chromium adsorption capacity of the substrate material. According to the findings, HSF-CWs demonstrated higher removal capacities in comparison to VF-CWs, while in both types the planted units indicated better performance compared to the unplanted ones. Analysis in various wetland compartments and annual mass balance calculation highlighted the exceptional contribution of substrate to chromium retention, while Cr accumulation in plant was not so high. Finally, experimental data fitted better to the pseudo-second-order and Langmuir models regarding kinetics and isotherm simulation.

Bacterial communities and enzymatic activities in the vegetation-activated sludge process (V-ASP) and related advantages by comparison with conventional constructed wetland

A new-developed vegetation-activated sludge process (V-ASP) was implemented for decentralized domestic wastewater treatment, and studied in lab-scale and full-scale. The main purpose of this work was the investigation of biomass activities and microbial communities in V-ASP by comparison with conventional constructed wetland (CW), to unveil the causations of its consistently higher pollutants removal efficiencies. Compared with CWs, V-ASP has greater vegetation nitrogen and phosphorus uptake rates, higher biomass and enzymatic activities, and more bacteria community diversity. The microbial community structure was comprehensively analyzed by using high-throughput sequencing. It was observed that Proteobacteria was dominated in both CWs and V-ASPs, while their subdivisions distribution was rather different. V-ASPs contained a higher nitrite-oxidizing bacteria (Nitrospira) abundances that resulted in a consistently better nitrogen removal efficiency. Hence, a long-term experiment of full-scale V-ASP displayed stably excellent capability in resistance of influent loading shocks and seasonal temperature effect.

Evaluation of an innovative approach based on prototype engineered wetland to control and manage boron (B) mine effluent pollution

A major environmental problem associated with boron (B) mining in many parts of the world is B pollution, which can become a point source of B mine effluent pollution to aquatic habitats. In this study, a cost-effective, environment-friendly, and sustainable prototype engineered wetland was evaluated and tested to prevent B mine effluent from spilling into adjoining waterways in the largest B reserve in the world. According to the results, average B concentrations in mine effluent significantly decreased from 17.5 to 5.7 mg l(-1) after passing through the prototype with a hydraulic retention time of 14 days. The results of the present experiment, in which different doses of B had been introduced into the prototype, also demonstrated that Typha latifolia (selected as donor species in the prototype) showed a good resistance to alterations against B mine effluent loading rates. Moreover, we found that soil enzymes activities gradually decreased with increasing B dosages during the experiment. Boron mass balance model further showed that 60 % of total B was stored in the filtration media, and only 7 % of B was removed by plant uptake. Consequently, we suggested that application of the prototype in the vicinity of mining site may potentially become an innovative model and integral part of the overall landscape plan of B mine reserve areas worldwide. Graphical Abstract ᅟ.

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.

Bioaugmentation in a pilot-scale constructed wetland to treat domestic wastewater in summer and autumn

In order to determine whether bioaugmentation is an effective technique in wetlands before the plants were harvested, the nitrogen (N) removal from a constructed wetland (CW) planted with Phragmites was evaluated after inoculating with Paenibacillus sp. XP1 in Northern China. The experiment was loaded with secondary effluent of rural domestic wastewater (RDW) using the batch-loaded method for over a 17-day period in summer and autumn. Chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N), and total nitrogen (TN) decreased significantly in the CW with Phragmites inoculated with Paenibacillus sp. XP1. Four days after treatments were set up, the removal efficiencies were found to be 76.2 % for CODcr, 83 % for NH3-N, and 63.8 % for TN in summer and 69.5 % for CODcr, 76.9 % for NH3-N, and 55.6 % for TN in autumn, which were higher than the control group without inoculation during the entire 17-day experiment. The inoculated bacteria did not have a noticeable effect on total phosphorus (TP) removal in autumn. However, bioaugmentation still keep a low P concentration in the whole CW. First-order kinetic model represented well the CODcr, TN, and TP decay in CWs with bioaugmentation, resulting in very good coefficients of determination, which ranged from 0.97 to 0.99. It indicated that bioaugmentation would be an effective treatment for pollutant removal from RDW in the CWs.

Purifying capability, enzyme activity, and nitrification potentials in December in integrated vertical flow constructed wetland with earthworms and different substrates

The response of purifying capability, enzyme activity, nitrification potentials, and total number of bacteria in the rhizosphere in December to wetland plants, substrates, and earthworms was investigated in integrated vertical flow constructed wetlands (IVFCW). The removal efficiency of total nitrogen (TN), NH4-N, chemical oxygen demand (COD), and total phosphorus (TP) was increased when earthworms were added into IVFCW. A significantly average removal efficiency of N in IVFCW that employed river sand as substrate and in IVFCW that employed a mixture of river sand and Qing sand as substrate was not found. However, the average removal efficiency of P was higher in IVFCW with a mixture of river sand and Qing sand as substrate than in IVFCW with river sand as substrate. Invertase activity in December was higher in IVFCW that used a mixture of river sand and Qing sand as substrate than in IVFCW which used only river sand as substrate. However, urease activity, nitrification potential, and total number of bacteria in December was higher in IVFCW that employed river sand as substrate than in IVFCW with a mixture of river sand and Qing sand as substrate. The addition of earthworms into the integrated vertical flow constructed wetland increased the above-ground biomass, enzyme activity (catalase, urease, and invertase), nitrification potentials, and total number of bacteria in December. The above-ground biomass of wetland plants was significantly positively correlated with urease and nitrification potentials (p < 0.01). The addition of earthworms into IVFCW increased enzyme activity and nitrification potentials in December, which resulted in improving purifying capability.

Enhanced nitrogen removal in constructed wetlands: effects of dissolved oxygen and step-feeding

Four horizontal subsurface flow constructed wetlands (HSFCWs), named HSFCW1 (three-stage, without step-feeding), HSFCW2 (three-stage, with step-feeding), HSFCW3 (five-stage, without step-feeding) and HSFCW4 (five-stage, with step-feeding) were designed to investigate the effects of dissolved oxygen (DO) and step-feeding on nitrogen removal. High removal of 90.9% COD, 99.1% ammonium nitrogen and 88.1% total nitrogen (TN) were obtained simultaneously in HSFCW4 compared with HSFCW1-3. The excellent TN removal of HSFCW4 was due to artificial aeration provided sufficient DO for nitrification and the favorable anoxic environment created for denitrification. Step-feeding was a crucial factor because it provided sufficient carbon source (high COD: nitrate ratio of 14.3) for the denitrification process. Microbial activities and microbial abundance in HSFCW4 was found to be influenced by DO distribution and step-feeding, and thus improve TN removal. These results suggest that artificial aeration combined with step-feeding could achieve high nitrogen removal in HSFCWs.

How to increase microbial degradation in constructed wetlands: influencing factors and improvement measures

Microorganisms play a vital role in degradation of multiple pollutants in constructed wetlands (CWs). Thus, the search for methods to improve microbial degradation in CWs is crucial. This study provides a review of critical parameters including availability of organic carbon, redox condition, temperature, pH, presence of plants, media characteristics and their influences on microbial processes. Current strategies focusing on regulation of carbon source, redox condition, and choice of substrates to enhance microbial activity in CWs are also described. A special emphasis is given to the application of bioaugmentation to enhance microbial activities in wetland in future research.

Effects of monocot and dicot types and species richness in mesocosm constructed wetlands on removal of pollutants from wastewater

The effects of planting type and species richness on removal of BOD5, COD, nitrogen and phosphorus were studied in mesocosms with monocot alone (M), dicot alone (D) and mixed planting of M+D, where each planting type had four species richness levels. Above- and below-ground plant biomasses increased with the M and M+D species richness as shown by one-way ANOVA. The M+D type had the highest above-ground biomass, whereas the M type had the highest below-ground biomass among planting types. Carbon, nitrogen and phosphorus in the microbial biomass increased with the richness of the M and M+D type. Removals of BOD5, COD, inorganic P and total P did not change with the richness, but removals of NH4-N, NO3-N increased. Planting type impacted only removal of inorganic P, with higher removal of inorganic P in the M type.

Statistical modelling of organic matter and emerging pollutants removal in constructed wetlands

Multiple regression models, clustering tree diagrams, regression trees (CHAID) and redundancy analysis (RDA) were applied to the study of the removal of organic matter and pharmaceuticals and personal care products (PPCPs) from urban wastewater by means of constructed wetlands (CWs). These four statistical analyses pointed out the importance of physico-chemical parameters, plant presence and chemical structure in the elimination of most pollutants. Temperature, pH values, dissolved oxygen concentration, redox potential and conductivity were related to the removal of the studied substances. Plant presence (Typha angustifolia and Phragmites australis) enhanced the removal of organic matter and some PPCPs. Multiple regression equations and CHAID trees provided numerical estimations of pollutant removal efficiencies in CWs. These models were validated and they could be a useful and interesting tool for the quick estimation of removal efficiencies in already working CWs and for the design of new systems which must fulfil certain quality requirements.

Effects of dissolved oxygen on extracellular enzymes activities and transformation of carbon sources from plant biomass: implications for denitrification in constructed wetlands

Dissolved oxygen (DO) concentrations have often been shown to be important to decomposition rates of plant litter and thus may be a key factor in determining the supply of dissolved organic carbon (DOC) and carbon-dependent denitrification in wetlands. During the 2 months operation, DOC accumulation in anaerobic condition was superior to aerobic condition due to higher activities of hydrolase enzymes and lower hydrolysates converted to gaseous C. Also, much higher denitrification rates were observed in wetland when using anaerobic litter leachate as the carbon source, and the available carbon source (ACS) could be used as a good predictor of denitrification rate in wetland. According to the results of this study, extracellular enzymes activities (EEAs) in wetland would change as a short-term consequence of DO. This may alter balance of litter carbon flux and the characteristics of DOC, which may, in turn, have multiple effects on denitrification in wetlands.

Comprehensive assessment of the design configuration of constructed wetlands for the removal of pharmaceuticals and personal care products from urban wastewaters

Seven mesocosm-scale constructed wetlands (CWs) of different configurations were operated outdoors for nine months to assess their ability to remove pharmaceuticals and personal care products (PPCPs) from urban wastewaters. CWs differed in some design parameters, namely the presence of plants, the species chosen (i.e., Typha angustifolia vs Phragmites australis), flow configuration (i.e., surface flow vs subsurface flow) and the presence of a gravel bed. A nearby conventional activated-sludge wastewater treatment plant (WWTP) fed with the same sewage was simultaneously monitored for comparison. The PPCPs ketoprofen, naproxen, ibuprofen, diclofenac, salicylic acid, carbamazepine, caffeine, galaxolide, tonalide and methyl dihydrojasmonate were monitored. The presence of plants favoured the removal of some PPCPs. The performance of the mesocosm studied was compound-dependant, soilless CWs showing the highest removal efficiency for ketoprofen, ibuprofen and carbamazepine, while free-water CWs with effluent leaving through the bottom of the tank performed well for the degradation of ketoprofen, salicylic acid, galaxolide and tonalide. Finally, subsurface horizontal flow CWs were efficient for the removal of caffeine. Significant linear correlations were observed between the removal of some PPCPs and temperature or redox potential. Hence, microbiological pathways appear to be the most probable degradation route for PPCPs in the CWs studied.