Spectroscopic fingerprinting of dissolved organic matter in a constructed wetland-reservoir ecosystem for source water improvement-a case study in Yanlong project, eastern China

A double-edged sword: Constructed wetland-microbial fuel cells promote organics removal via entrapment

Recently, constructed wetland-microbial fuel cells (CW-MFCs) are found to enhance the organics removal via the connection of the external circuit. Yet, it is unclear why the energy output is unmatched with the enhancement of the organics removal. This study compared the dynamic changes of the organics in a CW-MFC microcosm operated under the close circuit and open circuit. As a result, the close circuit facilitated the organics removal by 9 % before the proportional discharge of carbon metabolites. This suggested that organics entrapment should account for the huge loss of carbon recovery; and closing the external circuit could further promote the organics entrapment. Besides, polyhydroxybutyrate was found accumulated in the MFC culture experiment, evidencing that the fed-batch mode of operation could result in a feast-famine pattern of microbial metabolism. Despite the fast organics entrapment during the first hours, prolonging the operation time would lead to continuous carbon gas emission, along with the substantially elevated coulombic efficiency. Together, these results explained the substantial COD removal enhancement with low electricity yield, and cautioned the safe use of the MFC integration to spare the system from overaccumulation of organics.

Occurrence, fate and potential health risks of antibiotic resistomes in a constructed wetlands-reservoir ecosystem for drinking water source improvement

The development of effective and feasible engineering technologies to control the transmission of antibiotic resistance genes (ARGs) and pathogenic antibiotic-resistant bacteria (PARB) form drinking water sources is urgently needed for ensuring drinking water safety. In this study, metagenomic analysis was applied to systematically explore the full profiles, removal, and potential health risks of antibiotic resistomes in a large constructed wetlands-reservoir ecosystem (CWs-R) for drinking water source improvement. A total of 343 ARG subtypes belonging to 18 ARG types were identified from water and sediment samples in the CWs-R ecosystem, with an average abundance of 0.339 copies/cell, and bacitracin and multidrug resistance genes were the predominant ARG types in the water and sediment, respectively. The CWs-R ecosystem showed an excellent removal efficiency of ARGs and mobile genetic elements (MGEs) in water, with the total removal rate reaching 64.82 % and 77.09 %, respectively, among which the emergent plant zone and ecological storage unit played major roles. The metagenomic assembly tracked many mobile ARGs and opportunistic pathogens in the CWs-R ecosystem and identified 19 contigs as ARG-carrying pathogens, including Staphylococcus aureus, Salmonella enterica, Escherichia coli, and Klebsiella pneumonia. Overall, the CWs-R ecosystem has an important role in reducing the potential public health risks posed by antibiotic resistomes in drinking water sources but still cannot fully eliminate them. Therefore, we further classified water and sediment samples in the CWs-R ecosystem and identified potential ARGs and PARB indicators based on the metagenomic analysis results by considering the potential for horizontal transfer of ARGs to opportunistic pathogens. Taken together, this work demonstrates the CWs-R ecosystem as an economical and feasible engineering technology to reduce the dissemination of antibiotic resistomes in the drinking water source, provides useful information for monitoring and controlling antibiotic resistance in similar water sources, and ensures biosafety of drinking water.

Identification and evaluation of fishy odorants produced by four algae separated from drinking water source during low temperature period: Insight into odor characteristics and odor contribution of fishy odor-producing algae

Disgusting fishy odor could break out inside oligotrophic drinking waterbody in winter with low temperature. Nevertheless, fishy odor-producing algae and corresponding fishy odorants were not very clear, odor contribution of fishy odorant and odor-producing algae to overall odor profile were also not well understood. In this study, the fishy odorants, produced by four algae separated from Yanlong Lake, were identified simultaneously. Odor contribution of identified odorant, separated algae to overall fishy odor profile were both evaluated. The results indicated Yanlong Lake was mainly associated with fishy odor (flavor profile analysis (FPA) intensity: 6), eight, five, five and six fishy odorants were identified and determined in Cryptomonas ovate, Dinobryon sp., Synura uvella, Ochromonas sp., respectively, which were separated and cultured from water source. Totally sixteen odorants with concentration range of 90-880 ng/L, including hexanal, heptanal, 2,4-heptadienal, 1-octen-3-one, 1-octen-3-ol, octanal, 2-octenal, 2,4-octadienal, nonanal, 2-nonenal, 2,6-nonadienal, decanal, 2-decenal, 2,4-decadienal, undecanal, 2-tetradecanone, were verified in separated algae and associated with fishy odor. Although more odorants' odor activity value (OAV) were lower than one, approximately 89%, 91%, 87%, 90% of fishy odor intensities could be explained by reconstituting identified odorants for Cryptomonas ovate, Dinobryon sp., Synura uvella, Ochromonas sp., respectively, suggesting synergistic effect could exist among identified odorants. By calculating and evaluating total odorant production, total odorant OAV and cell odorant yield of separated algae, odor contribution rank to overall fishy odor should be Cryptomonas ovate (28.19%), Dinobryon sp. (27.05%), Synura uvella (24.27%), Ochromonas sp. (20.49%). This is the first study for identifying fishy odorants from four actually separated odor-producing algae simultaneously, this is also for the first time evaluating and explaining odor contribution of identified odorant, separated algae to overall odor profile comprehensively, this study will supply more understanding for controlling and managing fishy odor in drinking water treatment plant.

Key factors influencing sensory quality of scenic waters and its improvement by constructed wetlands

Sensory quality is very important for scenic waters. It's necessary to find out the key factors influencing sensory quality of scenic waters and then take corresponding measures to improve it. In this study, transparency, turbidity and surface chroma were chosen as the main sensory quality indexes whose key influencing factors were analyzed by structural equation model (SEM). The results indicated that water's transparency, turbidity and surface chroma were all mainly influenced by suspended solid (SS). Meanwhile, transparency was also influenced by Chlorophyll a (Chl a), pH, dissolved oxygen (DO), particle size and nutrients. Turbidity was influenced by Chl a and particle size as well. To verify this result and improve water's sensory quality, three constructed wetlands (CWs) were set up and operated. CWs could effectively improve the sensory quality of water bodies. When hydraulic retention time (HRT) was 2 days, the water' transparency increased from 18.00 ± 2.83 cm to about 100 cm, the removal rate of turbidity was 56.26% ∼ 97.11%, and the average removal rate of surface chroma of the three CWs was 72.56%, 70.31% and 63.36%, respectively. To get a better improvement effect, planting and extending HRT were feasible measures. The mechanism analysis showed that removing SS, especially large particles in water was the main reason for improving sensory quality by CWs, followed by removing Chl a. The operational results of CWs proved that SS was certainly the key influencing factor of water's sensory quality.

Influence of modified biochar supported sulfidation of nano-zero-valent-iron (S-nZVI/BC) on nitrate removal and greenhouse gas emission in constructed wetland

In this study, the biochar (BC) produced from sawdust, sludge, reed and walnut were used to support sulfidation of nano-zero-valent-iron (S-nZVI) to enhance nitrate (NO₃^--N) removal and investigate the impact on greenhouse gas emissions. Batch experiment results showed the S-nZVI/BC_{sawdust (2:1, 500)}, S-nZVI/BC_{sludge (2:1, 900)}, S-nZVI/BC_{reed (2:1, 700)}, and S-nZVI/BC _{walnut (2:1, 700)} respectively improved NO₃^--N removal efficiencies by 22%, 20%, 3% and 0.1%, and the selectivity toward N₂ by 22%, 25%, 22% and 18%. S-nZVI uniformly loaded on BC provided electrons for the conversion of NO₃^--N to N₂ through Fe⁰. At the same time, FeS_x layer was formed on the outer layer of ZVI in the sulfidation process to prevent iron oxidation, so as to improve the electrons utilization efficiency After adding four kinds of S-nZVI/BC into constructed wetlands (CWs), the NO₃^--N removal efficiencies could reach 100% and the N₂O emission fluxes were reduced by 24.17%-36.63%. And the average removal efficiencies of TN, COD, TP were increased by 21.9%, -16.5%, 44.3%, repectively. The increasing relative abundances of denitrifying bacteria, such as Comamonas and Simplicispira, suggested that S-nZVI/BC could also improve the process of microbial denitrification. In addition, different S-nZVI/BC had different effects on denitrification functional genes (narG, nirk, nirS and nosZ genes), methanotrophs (pmoA) and methanogenesis (mcrA). This research provided an effective method to improve NO₃^--N removal and reduce N₂O emission in CWs.

Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response

Polycyclic aromatic hydrocarbons (PAHs) pose a high risk to ecosystems owing to their adverse environmental effects. The use of biochar in constructed wetlands (CWs) to remove PAH has received increased interest, but is frequently challenging because of saturation adsorption. To enhance the microbial degradation, electron acceptors are provided. This study aimed to remove a representative PAH, benzofluoranthrene (BbF), using iron-modified biochar as a supplement to the CW substrate. Results revealed that iron-mediated biochar based CWs increased the removal of BbF by 20.4 % and ammonium by 25.6 %. The BbF retained in substrate with biochar (36.6 % higher content) and further removed with iron modification (40.6 % lower content). Iron-modified biochar increased dissolved organic carbon content, particularly low-aromaticity, and low-molecular-weight organic matters (25.7 % higher tryptophan-like material), which contributed to PAH degradation by microorganisms. Microbial analysis confirmed that iron-mediated biochar enriched the abundance of microbes (e.g., Cellulomonas, Actinotalea, and Sphingomonas) and key enzymes (e.g., catA, lipV, and sdhA) that are involved in PAH degradation. Higher proportion of iron-reducing bacteria (e. g., Thiobacillus, Rhodobacter) played a significant role in driving microbial iron cycle, which was beneficial for PAHs removal. Based on the results, we confirmed that the use of iron-modified biochar in CWs enhance PAH removal.

Fluorescence and molecular signatures of dissolved organic matter to monitor and assess its multiple sources from a polluted river in the farming-pastoral ecotone of northern China

The sources and composition of dissolved organic matter (DOM) in rivers are critical to water quality and aquatic ecosystems. Studies on detailed composition of organic matter in rivers in the farming-pastoral ecotone are relatively limited in the research community. To better understand the characteristics and dynamics of DOM, Yang River in North China was selected as the study area because of its profound influences on the farming-pastoral ecotone nearby. A combination of fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques revealed that the DOM composition of Yang River is driven by land use. DOM in Yang River is predominantly imported from allochthonous inputs, together with agricultural runoff, pastureland, and urban sewage, causing a comprehensive impact on DOM. In detail, DOM associated with cropland inputs was dominated by lignin-like species, with higher nitrogen content. In comparison, DOM related to grassland is more diverse and susceptible to degradation. An increase in urban areas led to an increase in sulfur-containing compounds, while their oxygen, nitrogen, and aromaticity contents were significantly lower than those in cropland. Interestingly, urban-influenced lignin-like compounds may be associated with the effluents from the pulp and paper mill. Additionally, synthetic surfactants from the lower section of the river were also structurally identified by tandem mass spectrometry. Overall, this study could provide valuable insights into the DOM sources and their transformation dynamics at a molecular level, which could be an indicator for riverine water quality management and be applied to other farming-pastoral ecotones straightforward.

Multi-spectroscopic investigation of the molecular weight distribution and copper binding ability of dissolved organic matter in Dongping Lake, China

The properties and metal-binding abilities of dissolved organic matter (DOM) rely on its molecular weight (MW) structure. In this study, the spatial differences of DOM in compositions, MW structures, and binding mechanisms with copper (Cu²⁺) in Dongping Lake were investigated by applying excitation-emission matrix combining parallel factor analysis (EEM-PARAFAC), synchronous fluorescence (SF) spectra, two-dimensional correlation spectra (2D-COS), and Fourier transform infrared (FTIR) spectra. The EDOM for the entrance of the Dawen River and PDOM for the macrophyte-dominated region were divided from DOM of Dongping Lake based on hierarchical clustering analysis (HCA) and principal component analysis (PCA) and were size-fractioned into MW < 500 kDa and <100 kDa fractions. According to EEM-PARAFAC, Dongping Lake was dominated by tryptophan-like substances with MW < 500 kDa. The concentration of PDOM was higher than that of EDOM (p < 0.05). 2D-COS showed that protein-like components preceded humic-like components binding to Cu²⁺ regardless of sample type (215 nm > 285 nm > 310-360 nm). The Cu²⁺ binding capacity of DOM exhibited specific differences in space, components, and molecular weights. The humic-like component 1 (C1) and tryptophan-like component 4 (C4) of PDOM showed stronger binding abilities than those of EDOM. Endogenous tryptophan-like component 4 (C4) had a higher binding affinity for Cu²⁺ than humic-like components (logK_a: C4 > C1 > C2) in PDOM irrespective of MW. Humic-like components with MW < 500 kDa displayed higher binding potentials for Cu²⁺. FTIR spectra showed that the main participants of DOM-Cu complexation included aromatic hydrocarbons, aliphatic groups, amide Ⅰ bands, and carboxyl functional groups. This study provides spatial-scale insights into the molecular weight structure of DOM in influencing the behavior, fate, and bioavailability of heavy metals in lakes.

Automated Monitoring of a High-Speed Flocculation Flat-Bottomed Sludge Blanket Clarifier Pond during Drought and Flood Conditions

The occasional rains that occur during dry seasons often stir up the bottom sediment of reservoirs, which leads to high turbidity and electrical conductivity in raw waters received by water utility companies. A newly developed real-time precision multi-layer sensor (RPMS) system was used to monitor a high-speed flocculation flat-bottomed sludge blanket clarifier (HFSBC) pond in real time to solve the water quality problems caused by drought and flood conditions. The RPMS is capable of monitoring the thickness of a sludge blanket; if the coagulation and sedimentation processes of the HFSBC are not working well, the sludge blanket will be thin and have a low sludge concentration. Conversely, if the HFSBC is working properly, the sludge blanket will have a thick and highly concentrated layer of sludge. Any heavy metals that are not removed by water treatment processes will enter the water supply network, which will result in poor water quality for end users. Against the backdrop of intensifying climate change, the enhancement of automated monitoring systems and adaptation processes will be an important part of efforts to minimize and resolve acute changes in water quality.