Removal Performance Of Constructed Wetlands Research Articles

Spatiotemporal dynamics of root exudates drive microbial adaptation mechanisms under day-night alterations in constructed wetlands

Root exudates, as plant-derived metabolites, play a pivotal role in shaping the assembly of rhizosphere microorganisms by acting as nutrients and signals. However, the spatial–temporal dynamics of root exudates remained unknown and thus also, if the dynamic changes in root exudates mediated the assembly of rhizosphere microorganisms. In this study, we conducted an in-depth assessment of root exudates, examining the composition and functional attributes of rhizosphere microorganisms, alongside the pollutant removal performance of constructed wetlands (CWs) under spatial–temporal conditions. Results suggested that nutrient-rich root exudates potentially facilitate the emergence of intricate and resilient microbial communities harboring a plethora of functional microorganisms under light conditions. The function prediction results indicated that the relative abundances of genes related to C and N transformation were enhanced under light conditions. Accordingly, increased microbial metabolic activity would enhance the pollutant removal performance in CWs. Remarkably, the removal efficiencies of COD (82.79 %), NH4+-N (76.72 %), TN (28.29 %), and NO3–-N (94.73 %) were enhanced under light conditions. Furthermore, a higher content of root exudates was discerned at the upper layer, leading to an enhancement in the carbon and nitrogen metabolisms of CWs. These findings emphasized root exudate-induced divergence in microbiota dynamics and pollutant removal in CWs, providing valuable mechanistic insights for the adaption of microbiota in response to spatial–temporal variation.

Exploring the resilience of constructed wetlands to harmful algal blooms disturbances: A study on microbial response mechanisms

Constructed wetlands (CWs) have emerged as a promising environmentally sustainable technique for wastewater treatment. However, the susceptibility of CWs to disturbances caused by harmful algal blooms (HABs) raises concerns. This study aimed to investigate the impact of HABs on the pollutants’ removal performance of CWs and the response of rhizosphere microbial community. Results revealed that CWs possessed an adaptive capacity that enabled them to recover caused by HABs. The rhizosphere was found to stimulate the occurrence of Acinetobacter, which played a critical role to help resist HABs disturbance. This study also observed an increased dissimilatory nitrate reduction metabolic pathway which promoted denitrification and enhanced the nitrogen removal efficiency of CWs. Additionally, the structural equation model further suggested that dissolved oxygen exerted a significant influence on the microbial activities and then affected the pollutants removal performance. Overall, our findings shed light on the mechanism for CW stability maintenance during HABs disturbance.

Constructed wetlands treating synthetic wastewater in response to day-night alterations: Performance and mechanisms

Constructed wetlands (CWs), as nature-based wastewater treatment systems, continuously maintain exchanges of material and energy with the natural environment. However, it is unclear how pollutant removal performance in CWs occurs in response to diurnal variation. Herein, we investigated the effects of day-night alterations on the rhizosphere microbial community in CWs. The results revealed that a dynamic alternate mechanism existed in the inner environment when the CWs were in steady operation, which was validated by rhythmic changes in the core microbial community, microbial metabolism activity, and pollutant removal shown in this study. The results showed that pollutant removal (e.g., total nitrogen) due to microbial processes was 1.31 times higher under daytime conditions than under nighttime conditions. Core microbial taxa of the rhizosphere that evolved with circadian rhythm (e.g., Chloroflexus and Beijerinckia) were mostly associated with carbon, nitrogen, phosphorus, and energy metabolism, with lower average relative abundance identified at night. Although higher activity of microbial metabolism was also observed in the daytime, nighttime conditions demonstrated higher gene levels that were related to carbon and nitrogen metabolic functions. Structural equation model (SEM) analysis further suggested that environmental factors exerted a significant influence in driving microbial processes for pollutant removal and that the microbial community played a greater role in promoting pollutant removal under nighttime conditions than under daytime conditions.

Multi-metabolism regulation insights into nutrients removal performance with adding heterotrophic nitrification-aerobic denitrification bacteria in tidal flow constructed wetlands

Constructed wetlands (CWs) usually exhibit limits in functional redundancy and diversity of microbial community contributing to lower performances of nutrients removal in decentralized domestic sewage treatment. To address this quandary, heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was added in tidal flow CWs (TFCWs) developing for nitrogen (N) and phosphorus (P) removal. With addition of HN-AD bacteria, TFCWs could be setup more rapidly and obtained better removal efficiencies of 66.9%–70.1% total nitrogen (TN), and 88.2%–92.4% total phosphorus (TP) comparing with control systems (TN: 53.9%; TP: 83.9%) during stable operation. Typical-cycles variations showed that TFCWs with addition of HN-AD bacteria promoted NO3−-N and NH4+-N removal respectively under hydraulic retention time (HRT) of 14 h and 8 h with slight NO2−-N accumulation. Activated alumina (AA) coupled with HN-AD bacteria decreased P release and relieved its poor removal performance in CWs. Based on metagenomic taxa and functional annotation, Pseudomonas and Thauera played pivotal roles in N removal in TFCWs. Furthermore, gradient oxic environments by 8 h-HRT promoted co-occurrence of heterotrophic nitrifiers (mostly Pseudomonas stutzeri) and autotrophic nitrifiers (mostly Nitrosomonas europaea. and Nitrospira sp.) which potentially accelerated NH4+-N transformation by elevated nitrification and denitrification related genes (e. g. amoABC, hao, napA and nirS genes). Meanwhile, the addition of HN-AD bacteria stimulated nirA and gltD genes of N assimilation processes probably leading to NH4+-N directly removal. The conceptual model of multi-metabolism regulation by HN-AD process highlighted importance of glk, gap2 and PK genes in glycolysis pathway which were vital drivers to nutrients metabolism. Overall, this study provides insights into how ongoing HN-AD bacteria-addition effected microbial consortia and metabolic pathways, serving theoretical basis for its engineered applications of TFCWs in decentralized domestic sewage treatment.

Impacts of salinity on degradation of pollutions in hybrid constructed wetlands

To investigate the impact of salinity on the pollution removal performance of constructed wetlands (CWs), four sets of hybrid CWs (HCW) were considered herein. The HCWs were composed of free water surface flow (FWS) and subsurface flow (SSF) CWs that were planted with cattail (Typha orientalis Presl.) and reed (Phragmites communis Trin.), respectively. After a preliminary experiment of almost seven months with influent fresh wastewater, NaCl was added at concentrations of 5 ppt, 10 ppt, and 20 ppt to simulate the impact of salinity. The removal performance was compared with that of the control CWs, and the impact of salinity on FWS CWs, SSF CWs, and HCWs were investigated. According to the experimental results, the biochemical oxygen demand (BOD) removal ratio in FWS CWs decreased from 70.3% to 58.3% as salinity increased from 0 ppt to 20 ppt, while that in SSF CWs fell significantly from 53.5% to 36.9% as salinity increased to ≧10 ppt. However, hybrid CWs offered more stable BOD removal and ammonia-nitrogen (NH3-N) removal under salinity impact. Salinity≧10 ppt stimulated the removal performance of NH3-N in FWS CWs to 19.4% while salinity≦5 ppt had no significant effect. In SSF CWs, a linear relationship was observed between removal loading and salinity, and NH3-N removal completely ceased at a salinity of 30.6 ppt. All removal ratios of NO3─-N>94.9% in FWS CWs revealed that salinity had almost no impact because the environment was anaerobic and contained sufficient organic carbon. The TP removal ratio in FWS CWs decreased from 14.7% to 9.2% as salinity increased from 0 ppt to 20 ppt and that in SSF CWs decreased monotonically from 7.2% to −0.2%. The impact period of salinity showed versatile reaction patterns of pollution removals in FWS CWs, SSF CWs, and HCWs. It distributed from 28 days to 186 days, after which the removal performance of CWs was restored.

Intensified nitrogen removal in immobilized nitrifier enhanced constructed wetlands with external carbon addition

Nitrogen removal performance response of twelve constructed wetlands (CWs) to immobilized nitrifier pellets and different influent COD/N ratios (chemical oxygen demand: total nitrogen in influent) were investigated via 7-month experiments. Nitrifier was immobilized on a carrier pellet containing 10% polyvinyl alcohol (PVA), 2.0% sodium alginate (SA) and 2.0% calcium chloride (CaCl2). A batch experiment demonstrated that 73% COD and 85% ammonia nitrogen (NH4-N) were degraded using the pellets with immobilized nitrifier cells. In addition, different carbon source supplement strategies were applied to remove the nitrate (NO3-N) transformed from NH4-N. An increase in COD/N ratio led to increasing reduction in NO3-N. Efficient nitrification and denitrification promoted total nitrogen (TN) removal in immobilized nitrifier biofortified constructed wetlands (INB-CWs). The results suggested that immobilized nitrifier pellets combined with high influent COD/N ratios could effectively improve the nitrogen removal performance in CWs.