Removal Efficiency Of Constructed Wetlands Research Articles

Performance and mechanism of falling water enhanced tidal flow constructed wetlands (F-TFCW) for rural grey water treatment

Constructed wetlands (CW) are a promising treatment technology for decentralized rural sewage. However, the pollutant removal efficiency of CW is low due to the limitation of DO concentration. In this study, a falling water enhanced tidal flow constructed wetlands (F-TFCW) was constructed to solve the problems of insufficient oxygen supply and low pollutant removal efficiency in CW. In this regard, the effects of falling water reoxygenation, tidal operation, and flood rest ratio (F/R) on the pollutant removal performance of F-TFCW were examined. Also, the pollutant removal mechanism of F-TFCW was revealed through microbial analysis and biochar XPS characterization. The results showed that the COD, NH4+-N, and TP removal rates of F-TFCW were 99.50 ± 0.21%, 87.16 ± 1.76%, and 88.43 ± 1.35%, respectively, when the F/R was 3:1. The falling water inflow and tidal operation significantly improved the reaeration influence of the constructed wetland. The microbial community analysis represented that the dominant bacteria of the F-TFCW could degrade organic compounds or adapt to tidal flow operation. The tidal operation remarkably changed the core microorganisms of the artificial wetland. In the flood phase of F-TFCW, the COD removal relied mainly on aerobic degradation and the biochar adsorption process. In the experimental step, the microbes degraded the organic matter adsorbed by biochar, which enabled a certain degree of biochar regeneration. This paper provided a new idea to enhance the pollutant treatment efficiency for constructed wetlands.

Characteristic of KMnO4-modified corn straw biochar and its application in constructed wetland to treat city tail water.

Biochar prepared from straw as constructed wetland (CW) substrate reduces straw pollution and simultaneously promotes the wastewater treatment efficiency of CW. In order to further analyze the pollutant removal mechanism of KMnO4-modified biochar substrate, the KMnO4-modified biochar was characterized. The experiment on city tail water treatment by CW with biochar was analyzed. The research showed that the surface property improvement on KMnO4 (0.1mol/L)-modified biochar was the most obvious. The biochar modified by 0.1mol/L KMnO4 increased the SSA and the number of oxygen functional groups and alcohol hydroxyl. KMnO4-modified biochar improved the removal efficiency of NO3--N in CW. KMnO4-modified biochar substrate with plants improved the TP removal efficiency (about 45%). KMnO4 as modifier reduced the influence of biochar on electrical conductivity tracing experiment. This study will improve the utilization value of straw and the removal efficiency of CW.

Pyrite coupled with biochar alleviating the toxicity of silver nanoparticles on pollutants removal in constructed wetlands

Silver nanoparticles (AgNPs) has been widely detected in the substrates of constructed wetlands (CWs), posing threaten to pollutants removal efficiency of CWs. However, the way to alleviate the toxicity of AgNPs on CWs is unclear. In this study, the gravel (GR), biochar (BC), pyrite (PY) and pyrite coupled with biochar matrix (PYBC) were selected as substrates to restore the pollutants removal efficiency of CWs under the exposure to the environment (0.2 mg/L) and accumulation (10 mg/L) concentration of AgNPs. Results showed that the BC and PY showed limited mitigation effects, while the PYBC alleviated the toxicity significantly. Especially in the exposure to the accumulation concentration of AgNPs, the removal of NH4+-N, TN, COD and TP in the PYBC were 10.2%, 8.3%, 9.4% and 10.7% higher than that in the GR, respectively. Mechanism analysis verified that AgNPs were transformed into Ag–Fe–S core shell aggregates (size >200 nm) decreasing bioavailability and the damage to cytomembrane. The PYBC restored the nitrogen removal efficiency by increasing the abundance of Nitrospira and Geothrix, which these bacteria were defined as nitrifiers and Feammox bacteria. This study provides a promising strategy to mitigate AgNPs’ toxicity on the pollutant removal efficiency in CWs.

Field performance investigation for constructed wetland clubbed with tubesettler for hospital wastewater treatment

Pharmaceutical active compounds (PhACs) are a concern owing to their toxicity to the aquatic environment. Several studies have investigated the removal of PhACs from wastewater by employing various treatments. However, hospital wastewater, a primary source of PhACs in wastewater, has yet to gain attention. Hence this study was conducted to investigate the efficiency of constructed wetlands coupled with tube settlers for hospital wastewater treatment. Constructed Wetlands (CWs) and tube settlers are economical and less energy-consuming wastewater treatment systems which can be employed to treat small community wastewater and enhance the effluent quality to conserve the environment. This study evaluates the combination of macrophyte CW-along with a tubesettler system to remove PhACs. The Constructed Wetland system was employed in series with tube settlers. Seven PhACs viz. paracetamol, ketoprofen, carbamazepine, lorazepam, Sulfamethoxazole, Ciprofloxacin, and Fluvastatin were analyzed for wastewater quality characterization. The removal efficiency of CW was 56 %, 72 %, 37 %, 54 %, 54 %, 53 %, and 46 % for PCM, KTF, CAB, LOR, SMZ, CIP and FUT respectively. The study concluded that CW could be successfully used to treat hospital wastewater, and tube settlers can be employed as a polishing treatment for the effluent of CW.

Response of the microbial community to salt stress and its stratified effect in constructed wetlands.

Nitrogen removal in constructed wetlands (CWs) may be inhibited by salinity. The clarification of the response of microbial community to salt stress is a premise for developing strategies to improve nitrogen removal efficiency in CWs under saline conditions. Results showed that the ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), and total nitrogen (TN) removal percentages significantly (p < 0.05) decreased in CWs with increasing salinity. The structure and abundance of the microbial community varied with different salinity levels and sampling depths in CWs. Compared with a non-saline condition, the abundances of some bacteria with a denitrification function (e.g., Arthrobacter) significantly (p < 0.05) decreased in CWs under saline conditions (i.e., EC of 15 and 30 mS/cm). Aerobic bacteria (e.g., Sphingomonas) exhibited more abundance in soil and upper gravel samples in CWs than those in bottom gravel samples, while the abundance of some denitrifying bacteria (e.g., Thauera and Azoarcus) was significantly (p < 0.05) higher in bottom gravel samples compared with soil and upper gravel samples, respectively. This study provides both microbiological evidence for explaining the impact of salt stress on nitrogen removal in CWs and scientific reference for developing enhanced strategies to improve the nitrogen removal capacity of CWs.

Treatment of microcystin (MC-LR) and nutrients in eutrophic water by constructed wetlands: Performance and microbial community

Cyanobacterial harmful algal blooms and microcystins (MCs) pollution pose serious threat to aquatic ecosystem and public health. Planted and unplanted constructed wetlands (CWs) filled with four substrates (i.e., gravel (G-CWs), ceramsite (C-CWs), iron-carbon (I-CWs) and slag (S-CWs)) were established to evaluate nutrients and a typical MCs variant (i.e., MC-LR) removal efficiency from eutrophic water affected by the presence of plant and different substrate. The response of the microbial community to the above factors was also analyzed in this study. The results indicate that the presence of plant can generally enhance nutrients and MC-LR removal efficiency in CWs, except for I-CWs. Throughout the experiment, all CWs exhibited good nitrogen removal efficiency with removal percentages exceeding 90%; TP and MC-LR average removal efficiency of C-CWs and I-CWs were greater than G-CWs and S-CWs irrespective of the presence of plant. The best MC-LR removal efficiency under different MC-LR loads was observed in planted C-CWs (ranged from 91.56% to 95.16%). Except for I-CWs, the presence of plant can enhance relative abundances of functional microorganisms involved in nutrients removal (e.g., Comamonadaceae and Planctomycetaceae) and MCs degradation (e.g., Burkholderiaceae). The microbial community diversity of I-CWs was simplified, while the relative abundance of Proteobacteria was highest in this study. The highest relative abundances of Comamonadaceae, Planctomycetaceae and Burkholderiaceae were observed in planted C-CWs. Overall, ceramisite and iron-carbon were more suitable to be applied in CWs for nutrients and MC-LR removal. This study provides a theoretical basis for practical application of CWs in eutrophication and MCs pollution control.

Effects of nZVI dosing on the improvement in the contaminant removal performance of constructed wetlands under the dye stress

In this study, different dosages of nanoscale zero-valent iron (nZVI) were used to improve the nitrogen removal efficiency in CWs under different C/N ratios and dye stress conditions. The addition of nZVI enhanced the dye and nitrogen removal efficiencies in constructed wetlands (CWs) through chemical reduction and biological denitrification processes. However, total nitrogen (TN) and dye removal efficiencies firstly increased and then decreased with the increases of the nZVI dosage and influent COD/N (C/N) ratio. Under the influent C/N ratio of 5, the higher TN removal efficiencies (80.2%, 55.1%, and 69.14% under 25 mg/L, 50 mg/L, and 75 mg/L dye concentration, respectively) and higher COD removal efficiencies (48.3%, 74.95%, and 30.76% under 25 mg/L, 50 mg/L, and 75 mg/L dye concentration, respectively) were obtained in CWs by adding the optimal nZVI dosage (0.1 g/L). The dye removal efficiencies in CWs with nZVI at C/N = 1 (75%–91%) and at C/N = 5 (81%–97%) were all significantly higher than that in CWs without nZVI (60%–82%). Moreover, the functional bacteria for nitrogen removal in denitrification and the dye degradation (Zoogloea and Acinetobacter) were enriched in CWs with 0.1 g/L nZVI.

Micro-aeration with hollow fiber membrane enhanced the nitrogen removal in constructed wetlands.

The nitrogen removal efficiency in constructed wetlands (CWs) was largely affected by the dissolved oxygen (DO). In this study, micro-aeration with different numbers of hollow fiber membrane modules (HFMEs) was adopted to increase the oxygen availability and improve the nitrogen removal efficiency in CWs under different air temperatures and different hydraulic retention time (HRT). Compared to the plant oxygen release (ROL) of wetland plants and traditional mechanical aeration, HFME increased the oxygen availability and enhanced the nitrogen removal efficiency in CWs. The COD and NH4+-N removal efficiencies increased with the increase of the HMFE. TN removal efficiency was increased by 8~16% after the application of HFME in CWs in the high-temperature stage. However, less HFME in CW-M1 realized the highest TN removal efficiency in low- and medium-temperature stages. At low temperature after 4-day HRT, the DO concentration respectively reached 6.25 mg L-1 and 3.25 mg L-1 in the upper zone and the bottom of CW-M1. The TN removal efficiencies in the upper zone of CW-M1 (60.69%) and the bottom of CW-M1 (64.98%) were all significantly higher than those in the upper zone of CK (35.98%) and the bottom of CK (39.9%). In addition, the microbial biomass and community analyses revealed that CW-M1 showed the most nitrifying bacteria and the best metabolic activity of bacteria. HEMF in CW-M1 also increased the nitrifying capacity from 0.12 to 0.46 mg kg-1 h-1. The application of HFME in CWs accelerated the nitrification process by enhancing nitrifying bacteria and less HFME realized the highest TN removal efficiency through nitrification-denitrification processes. Graphical abstract The application of hollow fiber membrane modules in CWs enhanced the pollutants(TN and COD)removal efficiencyinthe process of biologicalnitrification-denitrification andincreased the number of nitrifying bacteria.

Effects of plant diversity on carbon dioxide emissions and carbon removal in laboratory-scale constructed wetland.

Previous studies have shown that plant diversity can enhance methane (CH4) emission and nitrogen purification efficiency in constructed wetlands (CWs), but effect of plant diversity on carbon dioxide (CO2) flux and carbon removal efficiency in CWs is unknown. Therefore, we established four plant diversity levels (each level containing 4, 3, 2, and 1 species, respectively) in laboratory-scale wetland microcosms fed with simulated wastewater. Results showed that plant species richness enhanced CO2 emissions (84.7-124.7mg CO2 m-2h-1, P < 0.01), carbon fixation rate (P < 0.05), and microbial biomass carbon (P < 0.001), but did not improve carbon removal (P > 0.05). The presence of Pontederia cordata increased CO2 emissions, carbon fixation rate of belowground, and microbial biomass carbon (P < 0.05), whereas the presence of Phragmites australis only enhanced CO2 emission (P < 0.05). However, the presence of Typha orientalis or Lythrum salicaria did not show an influence on CO2 emissions and carbon removal (P > 0.05). Hence, our study highlights the importance of plant diversity in mediating CO2 emission intensity and carbon processes but not carbon removal in CWs.

The adaptability of a wetland plant species Myriophyllum aquaticum to different nitrogen forms and nitrogen removal efficiency in constructed wetlands.

Constructed wetlands (CWs) cultivated with Myriophyllum aquaticum showed great potential for total nitrogen (TN) removal from aquatic ecosystems in previous studies. To evaluate the growth characteristics, photosynthetic pigment content, and antioxidative responses of M. aquaticum, as well as its TN removal efficiency in CWs, M. aquaticum was treated with different levels of ammonium (NH4+) and nitrate (NO3-) for 28days. The results indicated that M. aquaticum had strong nitrogen stress tolerance and was more likely to be suppressed by high levels of NH4+ than NO3-. High levels of NH4+ also led to inhibition of synthesis of photosynthetic pigments and increased peroxidase activity in plant leaves, which was not found in the NO3- treatments. High levels of both NH4+ and NO3- generated obvious oxidative stress through elevation of malondialdehyde content while decreasing superoxide dismutase activity in the early stage. A sustainable increase of TN removal efficiency in most of the CWs indicated that M. aquaticum was a candidate species for treating wastewater with high levels of nitrogen because of its higher tolerance for NH4+ and NO3- stress. However, the increase of TN removal efficiency was hindered in the late stage when treated with high levels of NH4+ of 26 and 36mmol/L, indicating that its tolerance to NH4+ stress might have a threshold. The results of this study will enrich the studies on detoxification of high ammonium ion content in NH4+-tolerant submerged plants and supply valuable reference data for proper vegetation of M. aquaticum in CWs.

Impacts of vegetation and temperature on the treatment of domestic sewage in constructed wetlands incorporated with Ferric-Carbon micro-electrolysis material

ABSTRACTFerric-Carbon Micro-Electrolysis (Fe/C-M/E) material had been widely used for the pretreatment of wastewater. Therefore, we hypothesized that Fe/C-M/E material could enhance the treatment of domestic sewage when it was integrated into constructed wetlands (CWs). In this study, CWs integrated with Fe/C-M/E material were developed. Druing the experiment of effect of vegetation on the performance of CWs, percentages of NH4+-N, NO3−-N, total nitrogen (TN), and Chemical Oxygen Demand (COD) removed in polyculture (W1) were up to 91.8%, 97.0%, 92.3%, and 85.4%, respectively, which were much higher than those in Lythrum salicaria monoculture (W2) and Canna indica monoculture (W3). In the experiment of temperature influences on the removal efficiency of CWs, temperature substantially influenced the performance of CWs. For example, NO3−-N removal percentages of W1, W2, and W3 at high temperature (25.5°C and 19.8°C) were relatively stable and greater than 85.4%. At 8.9°C, however, a sharp decline of NO3−-N removal percentage was observed in all CWs. Temperature also influenced the Chemical Oxygen Demand (COD) removal and soil microbial activity and biomass. Overall, the polyculture (Lythrum salicaria +Canna indica) showed the best performance during most of the operating time, at an average temperature ≥ 19.8°C, due to the functional complementarity between vegetation. All the CWs consistently achieved high removal efficiency (above 96%) for TP in all experiments, irrespective of vegetation types, phosphorous loadings, and temperatures. In conclusion, polyculture was an attractive solution for the treatment of domestic sewage during most of the operating time (average temperature ≥ 19.8°C). Furthermore, CWs with Fe/C-M/E material were ideally suitable for domestic sewage treatment, especially for TP removal.

Plant species diversity reduces N2O but not CH4 emissions from constructed wetlands under high nitrogen levels.

Constructed wetlands (CWs) have been widely used for treating wastewater. CWs also are the sources of greenhouse gas (GHG) due to high pollutant load. It has been reported that plant species diversity can enhance nitrogen (N) removal efficiency in CWs for treating wastewater. However, the influence of plant species diversity on GHG emissions from CWs in habitats with high N levels still lack research. This study established four species richness levels (1, 2, 3, 4) and 15 species compositions by using 75 simulated vertical flow CWs microcosms to investigate the effects of plant species diversity on the GHG emissions and N removal efficiency of CWs with a high N level. Results showed plant species richness reduced nitrous oxide (N2O) emission and N (NO3--N, NH4+-N, and TIN) concentrations in wastewater, but had no effect on methane (CH4) emission. Especially, among the 15 compositions of plant species, the four-species mixture emitted the lowest N2O and had under-depletion of N (DminTIN<0). The presence of Oenanthe javanica had a significantly negative effect on the N2O emission but had no effect on N removal efficiency. The presence of Rumex japonicus significantly reduced the N (NO3--N and TIN) concentrations in wastewater but had no effect on the N2O and CH4 emissions. The N concentrations and GHG emissions in the community of R. japonicus × Phalaris arundinacea were as low as those in the four-species mixture. Assembling plant communities with relatively high species richness (four-species mixture) or particular composition (R. japonicus × P. arundinacea) could enhance the N removal efficiency and reduce the GHG emissions from CWs for treating wastewater with a high N level.

Assessment of treatment efficiency of constructed wetlands in East Ukraine

Abstract The aim of the study was to evaluate the performance of 9 hybrid constructed wetlands (CWs) in the Kharkiv region, East Ukraine. Assessed CWs varied by surface areas (from 760 to 11,000 m 2 ) and treated domestic wastewater discharge (10 m 3 day −1 to 700 m 3 day −1 ). Principal macrophyte species used on these CWs were the Reed Phragmites australis (Cav.) Steud., the Wood Bulrush Scirpus sylvaticus L. and the Broad-leaved Cattail Typha latifolia L . The studied CWs demonstrated high removal efficiency on BOD 5 (82.6 ± 11%), COD (77.3 ± 9%) and suspended solids (72.1 ± 9%). The removal rates of nitrogen, orthophosphates and surfactants ranged from 9% to 52%. The overall removal efficiency of CWs was dependent mainly on inflow pollutant concentrations, design, maintenance parameters and operating conditions. Comparing to conventional domestic wastewater treatment facilities the CWs showed similar efficiency on the majority of controlled parameters. At the same time the estimated construction and operational costs of CWs were significantly lower compared to the conventional wastewater treatment facilities of similar capacities that makes CWs application feasible for small communities in rural areas. In order to improve the removal capacity of studied wetlands, operational conditions should be adjusted to the inflow concentrations and received wastewater volumes.

Comparisons of microbial abundance and community among different plant species in constructed wetlands in summer

The performances of constructed wetlands (CWs) with different plant species have been extensively studied and compared, but no general conclusion has been found, especially in warm temperatures. Wetlands were planted with Phragmites australis (PA), Typha orientalis (TO) and Arundo donax (AD) were set up with unplanted ones as control (CT). The performances of wetlands in summer were measured. The microbial abundance and communities were analyzed with quantitative PCR (qPCR) and pyrosequencing. The summertime removal efficiency in CWs was not significantly different among plant species. Significant differences were found in the microbial community but not in the microbial abundance. Microbial diversities of AD and PA were higher than TO. Proteobacteria and Cyanobacteria were more prevalent than other bacteria in summer. The level of Proteobacteria was higher in PA (47.96%) and AD (45.58%) than in TO (33.54%). Photosynthetic bacteria accounted for 13.55% of the total bacteria in AD, followed by PA (13.07%) and TO (3.42%). However, more Cyanobacteria were in TO (26.09%) than in AD (12.62%) and PA (7.26%). Given that microbial abundances among the three plants had no significant differences, pollutant removal performances in summer were similar among plant species. Furthermore, a high level of Cyanobacteria can potentially be important in pollutant removal in summer.

Plant species richness enhances nitrous oxide emissions in microcosms of constructed wetlands

The coexistence of multiple plant species is an important factor influencing nitrogen removal in constructed wetlands (CWs). However, the influence of plant diversity on nitrous oxide (N2O) emission from the CWs lacks research. In this paper, we examined N2O flux and related parameters in response of plant species richness in microcosms simulating CWs. Results showed that, N2O emissions increased with plant species richness (P<0.05), ranged from 902 to 1848μgN2Om−2d−1; nitrogen removal, abundance of nitrite- and ammonia-oxidizing bacteria, nitrification rate, as well as nitrate reductase activities, also increased with species richness (P<0.05); N2O emission increasing was more sensitive to plant species richness than nitrogen removal rate, however, there was no response in denitrification rates and denitrifier abundance to species richness (P>0.05). Manipulation of plant species richness may provide an opportunity to increase the nitrogen removal efficiency in CWs, with an expense of simultaneously raising greenhouse gas emission.

Synergism of natural and constructed wetlands in Beijing, China

An integrated wetland system (IWS) including constructed wetlands (CWs) and modified natural wetlands (NWs) for wastewater treatment to replenish water to wetlands located at the Beijing Wetland School (BWS) in Beijing, China, is presented in this paper. The synergistic effects of CWs and NWs on treated water quality are investigated. The IWS is proved to be an effective wastewater treatment technique and a better alternative to alleviate the water shortage for conservation of wetlands based on the monitoring data obtained from October 2007 to 2008. The results show that CWs and NWs play different roles in removing contaminants from wastewater. The COD removal efficiency in CWs is higher than that in modified NWs, whereas the modified NWs can compensate for the deficiency of CWs where a stable and sufficient rhizosphere is not fully formed in the start-up period. All removal rates of COD, TN, and TP in CWs and modified NWs vary from 50 to 70%, while the total removal rate of COD, TN, and TP in IWS is about 85–90%. The operational results show that the maximum area loading of organic pollutants in modified NWs (65kg/had) is slightly higher than the empirical one (60kg/had) recommended by USEPA (2000) for free water surface wetlands.