Long-term performance of nutrient removal in an integrated constructed wetland

Greenhouse gas emissions from rotating biological contactors combined with hybrid constructed wetlands treating polluted river

The rotating biological contactors combined with hybrid constructed wetlands (R-HCWs) has promising treatment performance, however, concerns persisted regarding greenhouse gases (GHGs) emissions. In this study, GHGs in the R-HCWs was evaluated, and results revealed that R-HCWs facilitated nitrogen conversion and provided alternating oxygen environments, thereby promoting the reduction of N2O and CH4 emissions. Therefore, the comprehensive global warming potential (8.7±2.7 g CO2-eq·m-3·d-1) for handling unit volume of river water was low, thus, greater ecological benefits were achieved. The relative abundance of functional microorganisms such as Bacillus, Acinetobacter, Nitrospira and norank_f__norank_o__SBR1031, increased due to warm season, which promoted the nitrogen cycle and N2O emission reduction. Anammox and denitrifying bacteria showed significantly correlated with N2O and CH4 emissions (p < 0.01). This study provides valuable insights for the potential adoption of biological and ecological integrated treatment approach optimized for improving water and mitigating GHGs emissions.

Assessment of secondary metabolites in Pennisetum purpureum planted into constructed wetlands using shale and laterite as substrate for wastewater treatment

Constructed wetlands (CWs) are systems designed to maximize pollutants removal by various mechanisms, most of which are associated with the presence of plants. However, the substances secreted by plants to defend themselves against external aggressions during their growth are very little studied in these systems. This study aimed to characterize the chemical constituents of Pennisetum purpureum extracts used in an experimental mesocosm filled with shale and laterite treating domestic wastewater. Above-ground biomass, strain diameter and secondary metabolites of P. purpureum plants grown on the different substrates (shale and laterite) were monitored, as were those grown on the experimental site (control). In addition, the removal performance of chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total Kjedahl nitrogen (TKN) and Total Phosphorus (TP) was determined at the outlet of CWs. Plant biomass measured on the shale bed (13.7 ± 0.5 kg m-2) was higher than on the laterite bed (12.5 ± 0.1 kg m-2), both lower than the biomass obtained in the natural environment (14.9 ± 0.6 kg m-2). Performances ranged from 83 ± 5.4 to 76.9 ± 7 % (COD), 84.7 ± 6.8 to 78 ± 8.1 % (BOD5), 72.2 ± 10.7 to 55.5 ± 16.4 % (NTK) and 72.4 ± 4.9 to 58.4 ± 3.4 % (TP), with higher efficiencies in the shale-filled bed. Plant extracts from the experimental site were richer in secondary metabolites (total polyphenol [73.5 mgEAG/gMS], total flavonoids [18.1 mgEQ/gMS] and condensed tannin [13.3 mgEC/gMS]) than those from plants grown in CWs. However, plants in the shale-filled bed secreted more total polyphenol (57.7 mgEAG/gMS), total flavonoids (12.1 mgEQ/gMS) and condensed tannin (12 mgEC/gMS) than those in the laterite-filled bed. In short, wastewater and filtration materials have an influence on the secretion of secondary plant metabolites. However, of the two materials, shale seems to be better suited to CWs, as it promotes an environment close to the natural environment.

Microbial community and antimicrobial resistance niche differentiation in a multistage, surface flow constructed wetland

Free-living (FL) and particulate-associated (PA) communities are distinct bacterioplankton lifestyles with different mobility and dissemination routes. Understanding spatio-temporal dynamics of PA and FL fractions will allow improvement to wastewater treatment processes including pathogen and AMR bacteria removal. In this study, PA, FL and sediment community composition and antimicrobial resistance gene (ARG; tetW, ermB, sul1, intI1) dynamics were investigated in a full-scale municipal wastewater free-water surface polishing constructed wetland. Taxonomic composition of PA and FL microbial communities shifted towards less diverse communities (Shannon, Chao1) at the CW effluent but retained a distinct fraction-specific composition. Wastewater treatment plant derived PA communities introduced the bulk of AMR load (70 %) into the CW. However, the FL fraction was responsible for exporting over 60 % of the effluent AMR load given its high mobility and the effective immobilization (1-3 log removal) of PA communities. Strong correlations (r2>0.8, p < 0.05) were observed between the FL fraction, tetW and emrB dynamics, and amplicon sequence variants (ASVs) of potentially pathogenic taxa, including Bacteroides, Enterobacteriaceae, Aeromonadaceae, and Lachnospiraceae. This study reveals niche differentiation of microbial communities and associated AMR in CWs and shows that free-living bacteria are a primary escape route of pathogenic and ARG load from CWs under low-flow hydraulic conditions.

Nitrogen and phosphorus removal performance of sequential batch operation for algal cultivation through suspended-solid phase photobioreactor

Nitrogen (N) and phosphorus (P) absorbed by algae in the suspended-solid phase photobioreactor (ssPBR) have emerged as an efficient pathway to purify the effluent of wastewater treatment plants (WWTPs). However, the key operational parameters of the ssPBR need to be optimized. In this study, the stability of the system after sequential batch operations and the efficiency under various influent P concentrations were evaluated. The results demonstrated that the ssPBR maintained a high N/P removal efficiency of 96 % and 98 %, respectively, after 5 cycles. When N was kept at 15 mg/L and P ranged from 1.5 to 3.0 mg/L, the system yielded plenty of algae products and guaranteed the effluent quality that met the discharge standards. Notably, the carriers were a key contributor to the high metabolism of algae and high performance. This work provided theoretical ideas and technical guidance for effluent quality improvement in WWTPs.

Analysis of long-term spatio-temporal wetland change reveals the complex nature of habitat alterations - A case study from the Czech Republic 1842-2017

Wetlands fulfil a number of functions in the landscape, especially non-productive ones. Information on landscape and biotope changes is important not only from a theoretical point of view for understanding the forces and pressures that cause changes in the landscape, but also from a practical point of view, as we can take inspiration from history when planning the landscape. The main goal of this study is to analyse the dynamics and trajectories of changes in wetlands, including testing the influence of the main natural conditions (climate, geomorphology) on their changes, for a large area of 141 cadastral territories (1315 km2), which will allow the results to be sufficiently generalized. The results of our study confirmed the global trend of rapid wetland loss, with almost three quarters of wetlands disappearing, mostly on arable land (37 %). The results of the study are of great importance in the field of the ecology of landscapes and wetlands, both in the national and international context, not only because they make it possible to understand the regularities and forces that affect changes in wetlands and landscapes, but also have significance due to the methodology. The specific methodology and procedure are based on the application of advanced GIS functions (Union and Intersect functions) to identify the location and area of individual change dynamics and types of wetland (new, extinct, continuous), using accurate old large-scale maps and aerial photographs. The proposed and tested methodological procedure can generally be used for wetlands in other locations, but also for studying the dynamics of changes and trajectories of other biotopes in the landscape. The greatest potential for using the results of this work in the field of environmental protection is the possibility of using the places of extinct wetlands for their restoration.

A three-year study on the treatment of domestic-industrial mixed wastewater using a full-scale hybrid constructed wetland

Three full-scale constructed wetlands (CWs), namely vertical flow (VFCW), surface flow (SFCW), and horizontal flow (HFCW) systems, were combined in a series process to form a hybrid CW, which was used for the treatment performance of domestic-industrial mixed wastewater and investigated over a three-year period. The hybrid CW demonstrated that it is effective and stable during the long-term treatment of high-loading mixed wastewater under different operation years, season changes, and technology processes, with the average removal efficiencies of suspended solids, chemical oxygen demand, biological oxygen demand, total nitrogen, ammonia nitrogen, nitrate nitrogen, and total phosphorous being 84, 40, 54, 54, 70, 40, and 46%, respectively. The effluent quality of the hybrid CW reached the highest discharge standard for wastewater treatment plants. First, a variety of pollutants from the mixed wastewater were effectively removed in the subsurface processes (VFCW and HFCW) via substrate adsorption and degradation of the attached biofilm. The higher dissolved oxygen content and oxygen transfer capacity values in the VFCW were favourable for the occurrence of aerobic pathways (such as nitrification and inorganic phosphorus oxidation). In addition, with the large consumption of oxygen in the previous process, the oxygen-enriching capacity of the SFCW processes, provided aerobic potential for the next stage. In particular, the plant debris in the SFCW temporarily increased the organics and suspended solids, further increasing the C/N ratio, which was beneficial for denitrification as the main nitrogen removal pathway in the HFCW.

Ecological restoration performance enhanced by nano zero valent iron treatment in constructed wetlands under perfluorooctanoic acid stress

Perfluorooctanoic acid (PFOA) of widespread use can enter constructed wetlands (CWs) via migration, and inevitably causes negative impacts on removal efficiencies of conventional pollutants due to its ecotoxicity. However, little attention has been paid to strengthen performance of CWs under PFOA stress. In this study, influences of nano zero valent iron (nZVI), which has been demonstrated to improve nutrients removal, were explored after exemplifying threats of PFOA to operation performance in CWs. The results revealed that 1 mg/L PFOA suppressed the nitrification capacity and phosphorus removal, and nZVI distinctly improved the removal efficiency of ammonia and total phosphorus in CWs compared to PFOA exposure group without nZVI, with the maximum increases of 3.65 % and 16.76 %. Furthermore, nZVI significantly stimulated dehydrogenase (390.64 % and 884.54 %) and urease (118.15 % and 246.92 %) activities during 0-30 d and 30-60 d in comparison to PFOA group. On the other hand, nitrifying enzymes were also promoted, in which ammonia monooxygenase increased by 30.90 % during 0-30 d, and nitrite oxidoreductase was raised by 117.91 % and 232.10 % in two stages. Besides, the content of extracellular polymeric substances (EPS) under nZVI treatment was 72.98 % higher than PFOA group. Analyses of Illumina Miseq sequencing further certified that nZVI effectively improved the community richness and caused the enrichment of microorganisms related to nitrogen and phosphorus removal and EPS secreting. These results could provide valuable information for ecological restoration and decontamination performance enhancement of CWs exposed to PFOA.

Demonstration study of bypass multipond wetland system to enhance river water quality

This study focused on the water quality of a river in Wuhan City, China, which is surrounded by ponds that were transformed into a bypass multipond wetland system to improve river water quality. The bypass multipond wetland system included surface-flow artificial wetlands, modified partition ponds, aeration reoxygenation ponds, ecological ponds, and other processes. After the stable operation of the process, the water transparency was higher than 60 cm and the dissolved oxygen (DO) was higher than 5 mg/L, while the ammonia nitrogen (NH₃-N) concentration was less than 1.0 mg/L, total phosphorus (TP) was lower than 0.2 mg/L, and chemical oxygen demand (COD) was lower than 20 mg/L, achieving the treatment target. After monitoring the results of each process, the process which best enhanced the water transparency enhancement was the surface-flow of the artificial wetlands and ecological ponds. The aeration reoxygenation pond had the best effect on DO enhancement. The processes that most affected NH₃-N and TP removal were the surface-flow artificial wetlands and ecological ponds. The modified parthenogenic pond had the greatest effect on COD removal. The bypass multipond wetland system not only improved the river water quality but also enhanced the river landscape, and can act as a reference for similar river water quality improvement actions.