Tao Lv

Phytoremediation of imazalil and tebuconazole by four emergent wetland plant species in hydroponic medium.

Pollution from pesticide residues in aquatic environments is of increasing concern. Imazalil and tebuconazole, two commonly used systemic pesticides, are water contaminants that can be removed by constructed wetlands. However, the phytoremediation capability of emergent wetland plants for imazalil and tebuconazole, especially the removal mechanisms involved, is poorly understood. This study compared the removal of both pesticides by four commonly used wetland plants, Typha latifolia, Phragmites australis, Iris pseudacorus and Juncus effusus, and aimed to understand the removal mechanisms involved. The plants were individually exposed to an initial concentration of 10 mg/L in hydroponic solution. At the end of the 24-day study period, the tebuconazole removal efficiencies were relatively lower (25%-41%) than those for imazalil (46%-96%) for all plant species studied. The removal of imazalil and tebuconazole fit a first-order kinetics model, with the exception of tebuconazole removal in solutions with I. pseudacorus. Changes in the enantiomeric fraction for imazalil and tebuconazole were detected in plant tissue but not in the hydroponic solutions; thus, the translocation and degradation processes were enantioselective in the plants. At the end of the study period, the accumulation of imazalil and tebuconazole in plant tissue was relatively low and constituted 2.8-14.4% of the total spiked pesticide in each vessel. Therefore, the studied plants were able to not only take up the pesticides but also metabolise them.

Treatment of anaerobic digested effluent in biochar-packed vertical flow constructed wetland columns: role of media and tidal operation

Three types of vertical flow constructed wetland columns (VFCWs), packed with corn cob biochar (CB-CW), wood biochar (WB-CW) and gravel (G-CW) under tidal flow operations, were comparatively evaluated to investigate anaerobic digested effluent treatment performance and mechanisms. It was demonstrated that CB-CW and WB-CW provide significantly higher removal efficiencies for organic matter (>59%), NH4+-N (>76%), TN (>37%) and phosphorus (>71%), compared with G-CW (22%-49%). The higher pollutants removal ability of biochar-packed VFCWs was mainly attribute to the higher adsorption ability and microbial cultivation in the porous biochar media. Moreover, increasing the flooded/drained ratio from 4/8h to 8/4h of the tidal operation further improved around 10% of the removal of both organics and NH4+-N for biochar-packed VFCWs. The phosphorus removal was dependent on the media adsorption capacities through the whole experiment. However, the NH4+-N biodegradation by microbial communities was demonstrated to become the dominant removal mechanism in the long term treatment, which compensated the decreased adsorption capacities of the media. The study supported that the use of biochar would increase the treatment performance and elongate the lifespan of CWs under tidal operation.

Functionality of microbial communities in constructed wetlands used for pesticide remediation: Influence of system design and sampling strategy

The objective of this study was to compare the microbial community metabolic function from both unsaturated and saturated constructed wetland mesocosms (CWs) when treating the pesticide tebuconazole. The comparison was performed for both interstitial water and substrate biofilm by community level physiological profiling (CLPP) via BIOLOG™ EcoPlates. For each CW design (saturated or unsaturated), six mesocosms were established including one unplanted and five planted individually with either Juncus effusus, Typha latifolia, Berula erecta, Phragmites australis or Iris pseudacorus. Microbial activity and metabolic richness of interstitial water from unsaturated CWs were significantly lower than that from saturated CWs. However, in general, the opposite result was observed for biofilm samples. Wetland plants promoted significantly higher biofilm microbial activity and metabolic richness than unplanted CWs in both CW designs. Differences in the microbial community functional profiles between plant species were only found for saturated CWs. Biofilm microbial metabolic richness was generally statistically higher than that of interstitial water in both unsaturated (1.4-24 times higher) and saturated (1.2-1.7 times higher) CWs. Carbon source (guild) utilization patterns were generally different between interstitial water and biofilm samples. Functionality of the biofilm microbial community was positively correlated to the removal of all pollutants (TN, NH4+-N, TP, TOC and tebuconazole) for both unsaturated and saturated CWs, suggesting the biofilm plays a more important role in pollutant removal than the interstitial water microbial community. Thus, merely observing the interstitial water microbial communities may underestimate the role of the microbial community in CW performance. Interestingly, the ability for the biofilm microbial community to utilize amino acids and amines/amides was positively correlated with tebuconazole removal in all system types.

Effects of constructed wetland design on ibuprofen removal – A mesocosm scale study

This study aimed to investigate the effects of constructed wetland design (unsaturated, saturated and aerated saturated) and plant species (Juncus, Typha, Berula, Phragmites and Iris) on the mass removal and removal kinetics of the pharmaceutical ibuprofen. Planted systems had higher ibuprofen removal rates (29%-99%) than in the unplanted ones (15%-85%) in all designs. The use of forced aeration improved ibuprofen removal only in the unplanted mesocosms. In general, ibuprofen removal followed an area-based first-order removal kinetics model with removal rate coefficients (kA) varying between 3 and 35cm/d. The ibuprofen removal was mainly attributed to microbial degradation by the fixed bed biofilm, but plant uptake and degradation within plant tissues also occurred. The ibuprofen removal was positively correlated with the oxygen concentration in the water and the removal of nutrients, indicating that degradation may be due to co-metabolisation processes.

Microbial density and diversity in constructed wetland systems and the relation to pollutant removal efficiency

Microbes are believed to be at the core of the wastewater treatment processes in constructed wetlands (CWs). The aim of this study was to assess the microbial biomass carbon (MBC) and Shannons diversity index (SDI) in the substrate of CWs planted with Phragmites australis, Hymenocallis littoralis, Canna indica and Cyperus flabelliformis, and to relate MBC and SDI to the pollutant removal in the systems. Significant higher MBC was observed in CWs with H. littoralis and C. indica than in CWs with P. australis, and the MBC differed with season and substrate depth. The microbial community in the wetlands included four phyla: Cyanobacteria, Proteobacteria, Chloroflexi, and Acidobacteria, with a more diverse community structure in wetlands with C. flabelliformis. The MBC in the substrate and the SDI of the 15-20 cm depth correlated with the removal of biochemical oxygen demand, NH4-N and NO3-N. Our results indicate that substrate SDI and MBC can both be regarded as bioindicators of the pollutant removal ability in CWs.

Treatment of anaerobic digestate supernatant in microbial fuel cell coupled constructed wetlands: Evaluation of nitrogen removal, electricity generation, and bacterial community response

The objective of this study was to assess whether the improved configuration of vertical upflow constructed wetlands (CWs) coupled with aeration in the centre part and effluent recirculation can strengthen the treatment performance of high strength anaerobic digestate supernatant. Moreover, electricity generation and bacterial community characteristics were also examined. The results indicated that intermittent aeration in vertical upflow CWs significantly enhanced organic matter (>69%, 214-401g/m2d) and ammonium (>92%, 62-138g/m2d) removal, regardless of aeration position. However, the removal efficiency of total nitrogen (TN) was limited to 24%-40%. Effluent recirculation was examined to enhance TN removal up to 69% in the central aerated CW, as compared to 44% observed in the bottom aerated CW. Accordingly, significantly higher abundances of denitrifiers (nirK and nirS) and anaerobic ammonium oxidation bacteria (anammox) were found in the bottom layer of the central aerated CW. In addition, the central aerated CW coupled with effluent recirculation generated significantly higher electricity (maximum power density of 112mW/m2) than traditional bottom aerated CWs when integrated with a microbial fuel cell (MFC). Results confirmed the application potential of this new configuration of upflow CW integrated with central aeration and effluent recirculation.