Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications

Spatial and temporal dynamics of microbes and genes in drinking water reservoirs: Distribution and potential for taste and odor generation

Numerous reservoirs encounter challenges related to taste and odor issues, often attributed to odorous compounds such as geosmin (GSM) and 2-methylisoborneol (2-MIB). In this study, two large reservoirs located in northern and southern China were investigated. The Jinpen (JP) reservoir had 45.99 % Actinomycetes and 14.82 % Cyanobacteria, while the Xikeng (XK) reservoir contained 37.55 % Actinomycetes and 48.27 % Cyanobacteria. Most of the 2-MIB produced in surface layers of the two reservoirs in summer originated from Cyanobacteria, most of the 2-MIB produced in winter and in the bottom water originated from Actinomycetes. Mic gene abundance in the XK reservoir reached 5.42 × 104 copies/L in winter. The abundance of GSM synthase was notably high in the bottom layer and sediment of both reservoirs, while 2-MIB synthase was abundant in the surface layer of the XK reservoir, echoing the patterns observed in mic gene abundance. The abundance of odor-producing enzymes in the two reservoirs was inhibited by total nitrogen, temperature significantly influenced Actinomycetes abundance in the JP reservoir, whereas dissolved oxygen had a greater impact in the XK reservoir. Overall, this study elucidates the molecular mechanisms underlying odor compounding, providing essential guidance for water quality management strategies and the improvement of urban water reservoir quality.

Insights into the azo dye decolourisation and denitrogenation in micro-electrolysis enhanced counter-diffusion biofilm system

In this study, electron transport pathways were activated and diversified by coupling counter-diffusion biofilms with micro-electrolysis for Alizarin yellow R (AYR) denitrogenation. Due to the binding of AYR to two residues of EC 4.1.3.36 with higher binding energy, the expression of EC 4.1.3.36 was down-regulated, causing the EC 3.1.2.28 and EC 2.5.1.74 for menaquinone synthesis (redox mediator) undetectable in Membrane aerated biofilm reactors (MABR). Spontaneous electron generation in the micro electrolysis-coupled MABR (ME-MABR) significantly activated two enzymes. Activated menaquinone up-regulated decolourisation related genes expression in ME-MABR, including azoR (2.12 log2), NQO1 (2.97 log2), wrbA (0.45 log2), and ndh (0.47 log2). The diversified electron flow pathways also promoted the nitrogen metabolism coding genes up-regulation, accelerating further inorganic nitrogen denitrogenation after AYR mineralisation. Compared to MABR, the decolourisation, mineralisation, and denitrogenation in ME-MABR increased by 25.80 %, 16.53 %, and 13.32 %, respectively. This study provides new insights into micro-electrolysis enhanced removal of AYR.

Enhanced remediation of real agricultural runoff in surface-flow constructed wetlands by coupling composite substrate-packed bio-balls, submerged plants and functional bacteria: Performance and mechanisms

Import of agricultural runoff containing nutrients considerably contributes to eutrophication of receiving water bodies. Surface-flow constructed wetlands (SFCWs) are commonly applied for agricultural runoff purification, but the performance is usually unsatisfactory. In this study, suspended bio-balls filled with zeolite and iron-carbon (Fe-C) composite substrates, submerged macrophyte (Ceratophyllum demersum) and functional denitrifying bacteria were collectively added into SFCW microcosms to enhance the remediation efficiency for real agricultural runoff with high nutrient concentrations and low content of bioavailable organic matter. The bio-ball added SFCWs achieved notably higher pollutant removal efficiencies (21.1%, 80.2% and 47.5% for chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), respectively) than the control (COD: 6.9%, TN: 64.4%, TP: 27.9%), because of the versatile functions of filling materials for pollutant removal. C. demersum plantation (COD: 44.2%, TN: 82.8% and TP: 53.7%) and functional bacteria inoculation (COD: 51.8%, TN: 85.8% and TP: 55.1%) further enhanced the efficiency of the SFCWs for agricultural runoff remediation. Bio-ball addition and C. demersum plantation significantly increased the humification degree and reduced the molecular weight of dissolved organic matter (DOM) in the agricultural runoff. Moreover, the two intensification measures also notably reduced organic and nitrogen contents in the wetland sediment. Remarkable distinction in bacterial community distribution patterns was observed in the SFCW sediment and filling substrates in bio-balls. Keystone genera including Clostridium_sensu_stricto_1 and Bacillus in the zeolite, Sphingomonas and Exiguobacterium in the Fe-C substrates and Sediminibacterium in the sediment might be critical for agricultural runoff remediation in the SFCW microcosms. The study highlights a high potential of the intensified SFCWs by these coupling measures for agricultural runoff remediation.

Illuminating the role of powder carrier materials in shaping sludge aggregation in wastewater treatment: Insights from extended operation performance to microbial response mechanism

This study uncovered the response of novel micro-granule wastewater treatment technology to different powder carrier materials. Characteristics and distinctions among different systems were assessed based on process performance, sludge aggregation capacity, and microbial metabolism. Zeolite carrier system exhibited remarkable nitrogen removal efficiency of 89.6 ± 0.9 %, while diatomite carriers, in conjunction with intermittent aeration, enhanced simultaneous nitrification and denitrification from 2.6 % to 27.1 %. Iron-based carriers demonstrated efficient phosphorus removal (94.7 ± 1.2 %) through both chemical and microbial pathways. Specific surface area, pore structure and biocompatibility of powder carriers determined the formation and size of micro-granules. Tryptophan-like substances, C-(C/H), and Npr in extracellular polymeric substances strongly correlated with sludge hydrophobicity and granulation. Significant enrichment in norank_Comamonadaceae and Nitrosomonas in zeolite powder carrier system promoted partial nitrification and endogenous denitrification. Differences in metabolic pathways elucidated the up-regulation of amino acid synthesis, energy metabolism, and membrane transport as potential mechanisms driving micro-granule formation and efficient treatment performance.

Hydrogen generated by electrochemical water splitting as electron donor for nitrate removal from micro-polluted reservoir water

Extremely limited organic carbon sources and aerobic environment in micro-polluted reservoir water make conventional denitrification exceptionally challenging. As a result, total nitrogen (TN) concentration in most reservoir waters exceeds standard value year-round. In this study, for the first time, we constructed a mini water-lifting and aeration system (mini-WLAS) to remove nitrate in actual reservoir water. In the mini-WLAS, H2 was produced through electrolysis of reservoir water without adding any electrolyte, and the ascending water flow carried the generated H2 from lower layer to upper bacteria layer. The maximum denitrification rate reached 0.29 mg (L·d)-1 under dissolved oxygen (DO) concentration of 6-8 mg L-1, 6.04 times higher than that of the control group. There is almost no accumulation of NH4+-N, NO2--N, and N2O, and the concentration of CODMn decreased by 55.2 %. More importantly, the pH stayed near-neutral steadily throughout the whole process. Microbial community analysis showed that the abundances of hydrogenotrophic denitrifying bacteria (HDB) were 2 orders higher than those in the control system. Some HDB could work under aerobic conditions, providing an explanation for the excellent denitrification performance under high DO. This study provides a novel perspective for TN removal from reservoir water.

Weak magnetic field promotes denitrification by stimulating ferromagnetic ion-containing metalloprotein expression

Weak magnetic field (WMF) has been recognized to promote biological denitrification processes; however, the underlying mechanisms remain largely unexplored, hindering the optimization of its effectiveness. Here, we systematically investigated the effects of WMF on denitrification performance, enzyme activity, microbial community, and metaproteome in packed bed bioreactors treating high nitrate wastewater under different WMF intensities and C:N ratios. Results showed that WMFs significantly promoted denitrification by consistently stimulating the activities of denitrifying reductases and NAD+/NADH biosynthesis across decreasing C:N ratios. Reductases and electron transfer enzymes involved in denitrification were overproduced due to the significantly enriched overexpression of ferromagnetic ion-containing (FIC) metalloproteins. We also observed WMFs' intensity-dependent selective pressure on microbial community structures despite the effects being limited compared to those caused by changing C:N ratios. By coupling genome-centric metaproteomics and structure prediction, we found the dominant denitrifier, Halomonas, was outcompeted by Pseudomonas and Azoarcus under WMFs, likely due to its structural deficiencies in iron uptake, suggesting that advantageous ferromagnetic ion acquisition capacity was necessary to satisfy the substrate demand for FIC metalloprotein overproduction. This study advances our understanding of the biomagnetic effects in the context of complex communities and highlights WMF's potential for manipulating FIC protein-associated metabolism and fine-tuning community structure.

Capabilities of Microbial Consortia from Disparate Environment Matrices in the Decomposition of Nature Organic Matter by Biofiltration

Dissolved organic matter (DOM) plays a pivotal role in drinking water treatment, influencing the performance of unit processes and final water quality (e.g. disinfection byproduct risk). Biofiltration is an effective method of reducing DOM, but currently lacks a comprehensive appreciation of the association between microbial profiles and biofiltration performance. In this study, bench-scale biofiltration units inoculated with microbial consortia from river and soil matrices were operated successively for comparing their efficacy in terms of DOM removal. The results showed that biofiltration units receiving soil microbes were significantly superior (p < 0.05) to those receiving river inoculated microbes in terms of decomposing DOM recalcitrant fractions and reducing DBP formation potential, resulting in DOC and DBP precursor removals of up to 58.4 % and 87.9 %, respectively. Characterization of the taxonomic composition revealed that differences in the microbial assembly of the two biofilter groups were subject to deterministic rather than stochastic factors. Furthermore, more complicated interspecific relationships and niche structures in soil inoculated biofilters were deciphered by co-occurrence network, providing a plausible profile on a taxonomic division of labor in DOM stepwise degradation. Accordingly, the contribution of microbial compositions was found to be of greater importance than the GAC mass and biomass attached to the media. Thus, this study has advanced the understanding of microbial-mediated DOM decomposition in biofiltration, and also provided a promising strategy for enhancing the process for water use via developing appropriate engineered consortia of bacteria.

Mixotrophic aerobic denitrification facilitated by denitrifying bacterial-fungal communities assisted with iron in micro-polluted water: Performance, metabolic activity, functional genes abundance, and community co-occurrence

Low-dosage nitrate pollutants can contribute to eutrophication in surface water bodies, such as lakes and reservoirs. This study employed assembled denitrifying bacterial-fungal communities as bio-denitrifiers, in combination with zero-valent iron (ZVI), to treat micro-polluted water. Immobilized bacterial-fungal mixed communities (IBFMC) reactors demonstrated their ability to reduce nitrate and organic carbon by over 43.2 % and 53.7 %, respectively. Compared to IBFMC reactors, IBFMC combined with ZVI (IBFMC@ZVI) reactors exhibited enhanced removal efficiencies for nitrate and organic carbon, reaching the highest of 31.55 % and 17.66 %, respectively. The presence of ZVI in the IBFMC@ZVI reactors stimulated various aspects of microbial activity, including the metabolic processes, electron transfer system activities, abundance of functional genes and enzymes, and diversity and richness of microbial communities. The contents of adenosine triphosphate and electron transfer system activities enhanced more than 5.6 and 1.43 folds in the IBFMC@ZVI reactors compared with IBFMC reactors. Furthermore, significant improvement of crucial genes and enzyme denitrification chains was observed in the IBFMC@ZVI reactors. Iron played a central role in enhancing microbial diversity and activity, and promoting the supply, and transfer of inorganic electron donors. This study presents an innovative approach for applying denitrifying bacterial-fungal communities combined with iron enhancing efficient denitrification in micro-polluted water.

Simultaneous removal of nitrogen, phosphorus, and organic matter from oligotrophic water in a system containing biochar and construction waste iron: Performances and biotic community analysis

The issue of combined pollution in oligotrophic water has garnered increasing attention in recent years. To enhance the pollutant removal efficiency in oligotrophic water, the system containing Zoogloea sp. FY6 was constructed using polyester fiber wrapped sugarcane biochar and construction waste iron (PWSI), and the denitrification test of simulated water and actual oligotrophic water was carried out for 35 days. The experimental findings from the systems indicated that the removal efficiencies of nitrate (NO3--N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP) in simulated water were 88.61%, 85.23%, 94.28%, and 98.90%, respectively. The removal efficiencies of actual oligotrophic water were 83.06%, 81.39%, 81.66%, and 97.82%, respectively. Furthermore, the high-throughput sequencing data demonstrated that strain FY6 was successfully loaded onto the biological carrier. According to functional gene predictions derived from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, the introduction of PWSI enhanced intracellular iron cycling and nitrogen metabolism.

Synergistic mechanisms of denitrification in FeS2-based constructed wetlands: Effects of organic carbon availability under day-night alterations

In constructed wetlands (CWs), carbon source availability profoundly affected microbial metabolic activities engaged in both iron cycle and nitrogen metabolism. However, research gaps existed in understanding the biotransformation of nitrogen and iron in response to fluctuations in organic carbon content under day-night alterations. Results demonstrated increased removal efficiency of NO3--N (95.7 %) and NH4+-N (75.70 %) under light conditions, attributed to increased total organic carbon (TOC). This enhancement promoted the relative abundance of bacteria involved in nitrogen and iron processes, establishing a more stable microbial network. Elevated TOC content also upregulated genes for iron metabolism and glycolysis, facilitating denitrification. Spearman correlation analysis supported the synergistic mechanisms between FeS2-based autotrophic denitrification and TOC-mediated heterotrophic denitrification under light conditions. The significant impact of carbon sources on microbial activities underscores the critical role of organic carbon availability in enhancing nitrogen removal efficiency, providing valuable insights for optimizing FeS2-based CWs design and operation strategies.

Microbial communities assembly in wastewater treatment plants in China

Community assembly processes determine community structure. Deterministic processes are essential for optimizing activated sludge (AS) bioreactor performance. However, the debate regarding the relative importance of determinism versus stochasticity remains contentious, and the influencing factors are indistinct. This study used large-scale 16S rRNA gene data derived from 252 AS samples collected from 28 cities across China to explore the mechanism of AS community assembly. Results showed that the northern communities possessed lower spatial turnover and more significant dispersal limitation than those in the south, whereas the latter had more substantial deterministic processes than the former (14.46 % v.s. 9.12 %). Meanwhile, the communities in the south exhibited lower network complexity and stability. We utilized a structural equation model to explore the drivers of deterministic processes. Results revealed that low network complexity (r = -0.56, P < 0.05) and high quorum sensing bacteria abundance (r = 0.25, P < 0.001) promoted deterministic assembly, which clarifies why determinism was stronger in southern communities than northern ones. Furthermore, total phosphorus and hydraulic retention time were found to be the primary abiotic drivers. These findings provide evidence to understand the community deterministic assembly, which is crucial for resolving community structure and improving bioreactor performance.

Norfloxacin affects inorganic nitrogen compound transformation in tailwater containing Corbicula fluminea

The Asian clam, Corbicula fluminea, commonly used in engineered wetlands receiving tailwater, affects nitrogen compound transformation in water. This study investigates how a commonly observed antibiotic in tailwater, norfloxacin, impact nitrogen compound transformation in tailwater containing C. fluminea. The clam was exposed to artificial tailwater with norfloxacin (0, 0.2, 20, and 2000 μg/L) for 15 days. Water properties, C. fluminea ecotoxicity responses, microorganism composition and nitrification- or denitrification-related enzyme activities were measured. Results revealed norfloxacin-induced increases and reductions in tailwater NH4+ and NO2- concentrations, respectively, along with antioxidant system inhibition, organ histopathological damage and disruption of water filtering and digestion system. Microorganism composition, especially biodiversity indices, varied with medium (clam organs and exposure water) and norfloxacin concentrations. Norfloxacin reduced NO2- content by lowering the ratio between microbial nitrifying enzyme (decreased hydroxylamine oxidoreductase and nitrite oxidoreductase activity) and denitrifying enzyme (increased nitrate reductase and nitrite reductase activity) in tailwater. Elevated NH4+ content resulted from upregulated ammonification and inhibited nitrification of microorganisms in tailwater, as well as increased ammonia emission from C. fluminea due to organ damage and metabolic disruption of the digestion system. Overall, this study offers insights into using benthic organisms to treat tailwater with antibiotic residues, especially regarding nitrogen treatment.

Peracetic acid (PAA)-based pretreatment effectively improves medium-chain fatty acids (MCFAs) production from sewage sludge

Peracetic acid (PAA), known for its environmentally friendly properties as a oxidant and bactericide, is gaining prominence in decontamination and disinfection applications. The primary product of PAA oxidation is acetate that can serve as an electron acceptor (EA) for the biosynthesis of medium-chain fatty acids (MCFAs) via chain elongation (CE) reactions. Hence, PAA-based pretreatment is supposed to be beneficial for MCFAs production from anaerobic sludge fermentation, as it could enhance organic matter availability, suppress competing microorganisms and furnish EA by providing acetate. However, such a hypothesis has rarely been proved. Here we reveal that PAA-based pretreatment leads to significant exfoliation of extracellular polymeric substances (EPS) from sludge flocs and disruption of proteinic secondary structures, through inducing highly active free radicals and singlet oxygen. The production of MCFAs increases substantially to 11,265.6 mg COD L-1, while the undesired byproducts, specifically long-chain alcohols (LCAs), decrease to 723.5 mg COD L-1. Microbial activity tests further demonstrate that PAA pretreatment stimulates the CE process, attributed to the up-regulation of functional genes involved in fatty acid biosynthesis pathway. These comprehensive findings provide insights into the effectiveness and mechanisms behind enhanced MCFAs production through PAA-based technology, advancing our understanding of sustainable resource recovery from sewage sludge.

Overlooked in-situ sulfur disproportionation fuels dissimilatory nitrate reduction to ammonium in sulfur-based system: Novel insight of nitrogen recovery

Sulfur-based denitrification is a promising technology in treatments of nitrate-contaminated wastewaters. However, due to weak bioavailability and electron-donating capability of elemental sulfur, its sulfur-to-nitrate ratio has long been low, limiting the support for dissimilatory nitrate reduction to ammonium (DNRA) process. Using a long-term sulfur-packed reactor, we demonstrate here for the first time that DNRA in sulfur-based system is not negligible, but rather contributes a remarkable 40.5 %-61.1 % of the total nitrate biotransformation for ammonium production. Through combination of kinetic experiments, electron flow analysis, 16S rRNA amplicon, and microbial network succession, we unveil a cryptic in-situ sulfur disproportionation (SDP) process which significantly facilitates DNRA via enhancing mass transfer and multiplying 86.7-210.9 % of bioavailable electrons. Metagenome assembly and single-copy gene phylogenetic analysis elucidate the abundant genomes, including uc_VadinHA17, PHOS-HE36, JALNZU01, Thiobacillus, and Rubrivivax, harboring complete genes for ammonification. Notably, a unique group of self-SDP-coupled DNRA microorganism was identified. This study unravels a previously concealed fate of DNRA, which highlights the tremendous potential for ammonium recovery and greenhouse gas mitigation. Discovery of a new coupling between nitrogen and sulfur cycles underscores great revision needs of sulfur-driven denitrification technology.

Induced domestication of humic reduction-denitrification coupled bacteria improved treatment of sediment: Performance, remediation effect, and metabolic mechanisms

The high organic matter in river sediment primarily induces black and odorous rebound. Traditional humic-reducing bacteria demonstrate relatively single metabolic functions and restrain the remediation within complex sediment environments. In addition, Ca(NO3)2 is commonly utilized in synergistic with bioremediation to improve the reducing environment of sediments. In this study, a multifunctional bacterial community with humic reduction-denitrification coupled bacteria was domesticated by the step-feeding strategy in an anaerobic baffle reactor (ABR). The performance, remediation effect, and metabolic mechanisms were analyzed. The results indicated that humic-reducing bacteria (HRB) and denitrifying-humic-reducing bacteria (DF/HRB) have quinone-reduction and denitrification capabilities. The synergistic effect of DF/HRBs and Ca(NO3)2 was superior to HRBs and Ca(NO3)2 on the removal of total organic matter(TOM). Microbial community structure analysis revealed an enhanced relative abundance of denitrification and humic-reducing bacteria (e.g., Thauera, Pseudomonas, Sulfurospirillum, Desulfovibrio, Geobacter) in the DF/HRB, resulting in a superior synergistic effect of DF/HRBs with Ca(NO3)2. This work helps to present an innovative approach to domesticate humic-reducing bacteria suited for the remediation environment effectively. It also expands the application of humic-reducing bacteria for in-situ anaerobic remediation of river sediments.

Algicidal activity synchronized with nitrogen removal by actinomycetes: Algicidal mechanism, stress response of algal cells, denitrification performance, and indigenous bacterial community co-occurrence

The harmful algal blooms (HABs) can damage the ecological equilibrium of aquatic ecosystems and threaten human health. The bio-degradation of algal by algicidal bacteria is an environmentally friendly and economical approach to control HABs. This study applied an aerobic denitrification synchronization algicidal strain Streptomyces sp. LJH-12-1 (L1) to control HABs. The cell-free filtrate of the strain L1 showed a great algolytic effect on bloom-forming cyanobacterium, Microcystis aeruginosa (M. aeruginosa). The optimal algicidal property of strain L1 was indirect light-dependent algicidal with an algicidal rate of 85.0%. The functional metabolism, light-trapping, light-transfer efficiency, the content of pigments, and inhibition of photosynthesis of M. aeruginosa decreased after the addition of the supernatant of the strain L1 due to oxidative stress. Moreover, 96.05% nitrate removal rate synchronized with algicidal activity was achieved with the strain L1. The relative abundance of N cycling functional genes significantly increased during the strain L1 effect on M. aeruginosa. The algicidal efficiency of the strain L1 in the raw water was 76.70% with nitrate removal efficiency of 81.4%. Overall, this study provides a novel route to apply bacterial strain with the property of denitrification coupled with algicidal activity in treating micro-polluted water bodies.

Ecological evolution of algae in connected reservoirs under the influence of water transfer: Algal density, community structure, and assembly processes

Reservoir connectivity provides a solution for regional water shortages. Understanding the water quality of reservoirs and the response of algal communities to water transfer could provide the basis for a long-term evolutionary model of reservoirs. In this study, a water-algal community model was established to study the effects of water transfer on water quality and algal communities in reservoirs. The results showed that water transfer significantly decreased total nitrogen and nitrate concentrations. However, the water transfer resulted in an increase in the CODMn concentration and conductivity in the receiving reservoir. Additionally, the algal density and chlorophyll-a (chl-a) concentration showed an increase with water transfer. Bacillariophyta, Cyanophyta, and Chlorophyta were the dominant algal phyllum in all three reservoirs. Water transfer induced the evolution of the algal community by driving changes in the chemical parameters of the receiving reservoir and led to more complex relationships within the algal community. The effects of stochastic processes on algal communities were also enhanced in the receiving reservoirs. These results provide specific information for water quality safety management and eutrophication prevention in connected reservoirs.

Nanoscale zero-valent iron alleviate antibiotic resistance risk during managed aquifer recharge (MAR) by regulating denitrifying bacterial network

The frequent occurrence of antibiotics in reclaimed water is concerning, in the case of managed aquifer recharge (MAR), it inevitably hinders further water purification and accelerates the evolutionary resistance in indigenous bacteria. In this study, we constructed two column reactors and nanoscale zero-valent iron (nZVI) amendment was applied for its effects on water quality variation, microbial community succession, and antibiotic resistance genes (ARGs) dissemination, deciphered the underlying mechanism of resistance risk reduction. Results showed that nZVI was oxidized to iron oxides in the sediment column, and total effluent iron concentration was within permissible limits. nZVI enhanced NO3--N removal by 15.5% through enriching denitrifying bacteria and genes, whereas made no effects on oxacillin (OXA) removal. In addition, nZVI exhibited a pivotal impact on ARGs and plasmids decreasing. Network analysis elucidated that the diversity and richness of ARG host declined with nZVI amendment. Denitrifying bacteria play a key role in suppressing horizontal gene transfer (HGT). The underlying mechanisms of inhibited HGT included the downregulated SOS response, the inhibited Type-Ⅳ secretion system and the weakened driving force. This study afforded vital insights into ARG spread control, providing a reference for future applications of nZVI in MAR.

Multivariate statistical and bioinformatic analyses for the seasonal variations of actinobacterial community structures in a drinking water reservoir

Actinobacterial community is a conspicuous part of aquatic ecosystems and displays an important role in the case of biogeochemical cycle, but little is known about the seasonal variation of actinobacterial community in reservoir ecological environment. In this study, the high-throughput techniques were used to investigate the structure of the aquatic actinobacterial community and its inducing water quality parameters in different seasons. The results showed that the highest diversity and abundance of actinobacterial community occurred in winter, with Sporichthya (45.42%) being the most abundant genus and Rhodococcus sp. (29.32%) being the most abundant species. Network analysis and correlation analysis suggested that in autumn the dynamics of actinobacterial community were influenced by more factors and Nocardioides sp. SX2R5S2 was the potential keystone species which was negatively correlated with temperature (R = -0.72, P < 0.05). Changes in environmental factors could significantly affect the changes in actinobacterial community, and the dynamics of temperature, dissolved oxygen (DO), and turbidity are potential conspicuous factors influencing seasonal actinobacterial community trends. The partial least squares path modeling further elucidated that the combined effects of DO and temperature not only in the diversity of actinobacterial community but also in other water qualities, while the physiochemical parameters (path coefficient = 1.571, P < 0.05) was strong environmental factors in natural mixture period. These results strengthen our understanding of the dynamics and structures of actinobacterial community in the drinking water reservoirs and provide scientific guidance for further water quality management and protection in water sources.

Enhanced nitrate removal efficiency and microbial response of immobilized mixed aerobic denitrifying bacteria through biochar coupled with inorganic electron donors in oligotrophic water

The nitrogen removal characteristics and microbial response of biochar-immobilized mixed aerobic denitrifying bacteria (BIADB) were investigated at 25 °C and 10 °C. BIADB removed 53.51 ± 1.72 % (25 °C) and 39.90 ± 4.28 % (10 °C) nitrate in synthetic oligotrophic water. Even with practical oligotrophic water, BIADB still effectively removed 47.66-53.21 % (25 °C), and 39.26-45.63 % (10 °C) nitrate. The addition of inorganic electron donors increased nitrate removal by approximately 20 % for synthetic and practical water. Bacterial and functional communities exhibited significant temperature and stage differences (P < 0.05), with temperature and total dissolved nitrogen being the main environmental factors. The dominant genera and keystone taxa exhibited significant differences at the two temperatures. Structural equation model analysis showed that dissolved organic matter had the highest direct and indirect effects on diversity and function, respectively. This study provides an innovative pathway for utilizing biochar and inorganic electron donors for nitrate removal from oligotrophic waters.

Antibacterial Hydrophilic ZnO Microstructure Film with Underwater Oleophobic and Self-Cleaning Antifouling Properties

Super-hydrophilic and oleophobic functional materials can prevent pollution or adsorption by repelling oil, and have good circulation. However, traditional strategies for preparing these functional materials either use expensive fabrication machines or contain possibly toxic organic polymers, which may prohibit the practical application. The research of multifunctional ZnO microstructures or nanoarrays thin films with super-hydrophilic, antifouling, and antibacterial properties has not been reported yet. Moreover, the exploration of underwater oleophobic and self-cleaning antifouling properties in ZnO micro/nanostructures is still in its infancy. Here, we prepared ZnO microstructured films on fluorine-doped tin oxide substrates (F-ZMF) for the development of advanced self-cleaning type super-hydrophilic and oleophobic materials. With the increase of the accelerators, the average size of the F-ZMF microstructures decreased. The F-ZMF shows excellent self-cleaning performance and hydrophilic (water contact angle ≤ 10°) and oleophobic characteristics in the underwater antifouling experiment. Under a dark condition, F-ZMF-4 showed good antibacterial effects against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with inhibition rates of 99.1% and 99.9%, respectively. This study broadens the application scope of ZnO-based material and provides a novel prospect for the development of self-cleaning super-hydrophilic and oleophobic materials.

Aerobic Denitrification Promoting by Actinomycetes Coculture: Investigating Performance, Carbon Source Metabolic Characteristic, and Raw Water Restoration

The coculture theory that promotes denitrification relies on effectively utilizing the resources of low-efficiency denitrification microbes. Here, the strains Streptomyces sp. PYX97 and Streptomyces sp. TSJ96 were isolated and showed lower denitrification capacity when cultured individually. However, the coculture of strains PYX97 and TSJ96 enhanced nitrogen removal (removed 96.40% of total nitrogen) and organic carbon reduction (removed 92.13% of dissolved organic carbon) under aerobic conditions. Nitrogen balance analysis indicated that coculturing enhanced the efficiency of nitrate converted into gaseous nitrogen reaching 70.42%. Meanwhile, the coculturing promoted the cell metabolism capacity and carbon source metabolic activity. The coculture strains PYX97 and TSJ96 thrived in conditions of C/N = 10, alkalescence, and 150 rpm shaking speed. The coculturing reduced total nitrogen and CODMn in the raw water treatment by 83.32 and 84.21%, respectively. During this treatment, the cell metabolic activity and cell density increased in the coculture strains PYX97 and TSJ96 reactor. Moreover, the coculture strains could utilize aromatic protein and soluble microbial products during aerobic denitrification processes in raw water treatment. This study suggests that coculturing inefficient actinomycete strains could be a promising approach for treating polluted water bodies.

Simultaneously enhanced autotrophic-heterotrophic denitrification in iron-based ecological floating bed by plant biomass: Metagenomics insights into microbial communities, functional genes and nitrogen metabolic pathways

In this study, the ecological floating bed supporting with zero-valent iron (ZVI) and plant biomass (EFB-IB) was constructed to improve nitrogen removal from low-polluted water. The effects of ZVI coupling with plant biomass on microbial community structure, metabolic pathways and functional genes were analyzed by metagenomic sequencing, and the mechanism for nitrogen removal was revealed. Results showed that compared with mono-ZVI system (EFB-C), the denitrification efficiencies of EFB-IB were effectively enhanced, with the higher average NO3--N removal efficiencies of 22.60-59.19%. Simultaneously, the average NH4+-N removal efficiencies were 73.08-91.10%. Metagenomic analyses showed that EFB-IB enriched microbes that involved in iron cycle, lignocellulosic degradation and nitrogen metabolism. Plant biomass addition simultaneously increased the relative abundances of autotrophic and heterotrophic denitrifying bacteria. Network analysis showed the cooperation between autotrophic and heterotrophic denitrifying bacteria in EFB-IB. Moreover, compared with EFB-C, plant biomass addition increased the relative abundances of genes related to iron cycle, lignocellulose degradation and glycolysis processes, ensuring the production of autotrophic and heterotrophic electron donors. Therefore, the relative abundances of key enzymes and functional genes related to denitrification were higher in EFB-IB, being beneficial to the NO3--N removal. Additionally, the correlation analysis of nitrogen removal and functional genes verified the synergistic mechanism of iron-based autotrophic denitrification and plant biomass-mediated heterotrophic denitrification in EFB-IB. In summary, plant biomass has excellent potential to improve the nitrogen removal of iron-based EFB from low-polluted water.

Iron-based multi-carbon composite and Pseudomonas furukawaii ZS1 co-affect nitrogen removal, microbial community dynamics and metabolism pathways in low-temperature aquaculture wastewater

Aerobic denitrification is the key process in the elimination of nitrogen from aquaculture wastewater, especially for wastewater with high dissolved oxygen and low carbon/nitrogen (C/N) ratio. However, a low C/N ratio, especially in low-temperature environments, restricts the activity of aerobic denitrifiers and decreases the nitrogen elimination efficiency. In this study, an iron-based multi-solid carbon source composite that immobilized aerobic denitrifying bacteria ZS1 (IMCSCP) was synthesized to treat aerobic (DO > 5 mg/L), low temperature (<15 °C) and low C/N ratio (C/N = 4) aquaculture wastewater. The results showed that the sequencing batch biofilm reactor (SBBR) packed with IMCSCP exhibited the highest nitrogen removal performance, with removal rates of 95.63% and 85.44% for nitrate nitrogen and total nitrogen, respectively, which were 33.03% and 30.75% higher than those in the reactor filled with multi-solid carbon source composite (MCSC). Microbial community and network analysis showed that Pseudomonas furukawaii ZS1 successfully colonized the SBBR filled with IMCSCP, and Exiguobacterium, Cellulomonas and Pseudomonas were essential for the nitrogen elimination. Metagenomic analysis showed that an increase in gene abundance related to carbon metabolism, nitrogen metabolism, extracellular polymer substance synthesis and electron transfer in the IMCSCP, enabling denitrification in the SBBR to be achieved via multiple pathways. The results of this study provided new insights into the microbial removal mechanism of nitrogen in SBBR packed with IMCSCP at low temperatures.

Indigenous mixotrophic aerobic denitrifiers stimulated by oxygen micro/nanobubble-loaded microporous biochar

The prevalence of hypoxia in surface sediment inhibits the growth of aerobic denitrifiers in natural waters. A novel oxygen micro/nanobubble-loaded microporous biochar (OMB) was developed to activate indigenous aerobic denitrifiers in this study. The results indicate a thin-layer OMB capping mitigates hypoxia effectively. Following a 30-day microcosm-based incubation, a 60 % decrease in total nitrogen concentration was observed, and the oxygen penetration depth in the sediment was increased from <4.0 mm to 38.4 mm. High-throughput sequencing revealed the stimulation of indigenous mixotrophic aerobic denitrifiers, including autotrophic denitrifiers such as Hydrogenophaga and Thiobacillus, heterotrophic denitrifiers like Limnobacter and unclassified_f_Methylophilaceae, and heterotrophic nitrification aerobic denitrification bacteria, including Shinella and Acidovorax, with total relative abundance reaching up to 38.1 %. Further analysis showed OMB enhanced the overall collaborative relationships among microorganisms and promoted the expression of nitrification- and denitrification-related genes. This study introduces an innovative strategy for stimulating indigenous aerobic denitrifiers in aquatic ecosystems.

Promoting aerobic denitrification in reservoir water with iron-activated carbon: Enhanced nitrogen and organics removal efficiency, and biological mechanisms

Carbon scarcity limits denitrification in micropolluted water, especially in drinking water reservoirs. Therefore, a Fe-activated carbon (AC) carrier was used in this study to enhance the nitrogen removal capacity of aboriginal denitrification in drinking water reservoirs under aerobic conditions. Following carrier addition, total nitrogen (TN) and permanganate index (CODMn) removal efficiencies reached 81.89% and 72.66%, respectively, and were enhanced by 40.45% and 39.65%. Nitrogen balance analysis indicated that 77.86% of the initial TN was converted into gaseous nitrogen. Biolog analysis suggested that the metabolic activity of denitrifying bacteria was substantially enhanced. 16S rRNA gene sequencing indicated that organic degradation bacteria, hydrogen-consuming, Fe-oxidizing, and Fe-reducing denitrifying bacteria (e.g., Arenimonas, Hydrogenophaga, Zoogloea, Methylibium, and Piscinibacter) evolved into the dominant species. Additionally, napA, nirS, nirK, and nosZ genes were enriched by 3.17, 6.68, 0.40, and 6.70 folds, respectively, which is conducive to complete denitrification. These results provide a novel pathway for the use of Fe-AC to promote aerobic denitrification in micropolluted drinking water reservoirs.

Simultaneous removal of phosphorus, zinc, and lead from oligotrophic ecosystem by iron-driven denitrification: Performance and mechanisms

Based on the current situation of complex pollution caused in surface water by oligotrophic condition and heavy metal release from river and lake bottom sediments. This study aimed to achieve the simultaneous removal of nitrate, phosphorus, Zn2+ and Pb2+ through microbial approach. At nitrate concentration of 4.82 mg L-1, carbon to nitrogen ratio of 1.5, pH of 6.0, and Fe2+ concentration of 5.0 mg L-1, the nitrate removal efficiency of Zoogloea sp. FY-6 reached 95.17%. The addition of pollutants under these conditions resulted in 88.76% removal of total phosphorus at 18 h, and 85.46 and 78.59% removal of Zn2+ and Pb2+ respectively, and there was competition for adsorption between Zn2+ and Pb2+. Extracellular polymers and fluorescence excitation-emission substrates confirmed that Fe2+ reduced heavy metal toxicity through promoting bacterial production of secretions and promotes denitrification as a carbon source. Meanwhile, contaminant removal curves and Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy demonstrated the synchronous removal of Zn2+ and Pb2+ mainly through biological action and the formation of nanoscale iron oxides. Biological-iron precipitation also provided adsorption sites for phosphorus. This research provides the theoretical foundation for applying microorganisms to restore oligotrophic source water (rivers and lakes) containing complex pollutants.

Extracellular electron transfer for aerobic denitrification mediated by the bioelectric catalytic system with zero-carbon source

The slow rate of electron transfer and the large consumption of carbon sources are technical bottlenecks in the biological treatment of wastewater. Here, we first proposed to domesticate aerobic denitrifying bacteria (ADB) from heterotrophic to autotrophic by electricity (0.6 V) under zero organic carbon source conditions, to accelerate electron transfer and shorten hydraulic retention time (HRT) while increasing the biodegradation rate. Then we investigated the extracellular electron transfer (EET) mechanism mediated by this process, and additionally examined the integrated nitrogen removal efficiency of this system with composite pollution. It was demonstrated that compared with the traditional membrane bioreactor (MBR), the BEC displayed higher nitrogen removal efficiency. Especially at C/N = 0, the BEC exhibited a NO3--N removal rate of 95.42 ± 2.71 % for 4 h, which was about 6.5 times higher than that of the MBR. Under the compound pollution condition, the BEC still maintained high NO3--N and tetracycline removal (94.52 ± 2.01 % and 91.50 ± 0.001 %), greatly superior to the MBR (10.64 ± 2.01 % and 12.00 ± 0.019 %). In addition, in-situ electrochemical tests showed that the nitrate in the BEC could be directly converted to N2 by reduction using electrons from the cathode, which was successfully demonstrated as a terminal electron acceptor.

Pollutants reduction via artificial mixing in a drinking water reservoir: Insights into bacterial metabolic activity, biodiversity, interactions and co-existence of core genera

Endogenous pollution due to long periods of hypolimnetic anoxia in stratified reservoirs has become a worldwide concern, which can threaten metabolic activity, biodiversity, water quality security, and ultimately human health. In the present study, an artificial mixing system applied in a drinking water reservoir was developed to reduce pollutants, and the biological mechanism involved was explored. After approximately 44 days of system operation, the reservoir content was completely mixed resulting in the disappearance of anoxic layers. Furthermore, the metabolic activity estimated by the Biolog-ECO microplate technique and biodiversity was enhanced. 16S rRNA gene sequencing indicated a great variability on the composition of bacterial communities. Co-occurrence network analysis showed that interactions among bacteria were significantly affected by the proposed mixing system. Bacteria exhibited a more mutualistic state and >10 keystone genera were identified. Pollutants, including nitrogen, phosphorus, organic matter, iron, and manganese decreased by 30.63-80.15 %. Redundancy discriminant analysis revealed that environmental factors, especially the temperature and dissolved oxygen, were crucial drivers of the bacterial community structure. Furthermore, Spearman's correlation analysis between predominant genera and pollutants suggested that core genus played a vital role in pollutant reduction. Overall, our findings highlight the importance and provide insights on the artificial mixing systems' microbial mechanisms of reducing pollutants in drinking water reservoirs.

Activation of indigenous denitrifying bacteria and enhanced nitrogen removal via artificial mixing in a drinking water reservoir: Insights into gene abundance, community structure, and co-existence model

Nitrogen pollution poses a severe threat to aquatic ecosystems and human health. This study investigated the use of water lifting aerators for in situ nitrogen reduction in a drinking water reservoir. The reservoir was thoroughly mixed and oxygenated after using water-lifting aerators for 42 days. The average total nitrogen concentration, nitrate nitrogen, and ammonium nitrogen-in all water layers-decreased significantly (P < 0.01), with a reduction efficiency of 35 ± 3%, 34 ± 2%, and 70 ± 6%, respectively. Other pollutants, including organic matter, phosphorus, iron, and manganese, were also effectively removed. Quantitative polymerase chain reactions indicated that bacterial nirS gene abundance was enhanced 26.34-fold. High-throughput sequencing, phylogenetic tree, and network analysis suggested that core indigenous nirS-type denitrifying bacteria, such as Dechloromonas, Simplicispira, Thauera, and Azospira, played vital roles in nitrogen and other pollutant removal processes. Furthermore, structural equation modeling revealed that nitrogen removal responded positively to WT, DO, and nirS gene abundance. Our findings provide a promising strategy for nitrogen removal in oligotrophic drinking water reservoirs with carbon deficiencies.

Enhanced nitrogen removal of micropolluted source waterbodies using an iron activated carbon system with siliceous materials: Insights into metabolic activity, biodiversity, interactions of core genus and co-existence

Aerobic denitrification technology can effectively abate the nitrogen pollution of water source reservoirs. In this study, 40% siliceous material was used as the carrier to replace the activated carbon in Fe/C material to enhance denitrification and purify water. The removal efficiency of new material for target pollutants were nitrate nitrogen (95.68%), total phosphorus (68.23%) and chemical oxygen demand (46.20%). Aerobic denitrification of water samples and anaerobic denitrification of sediments in three systems jointly assisted nitrogen removal. In a reactor with new material, diversity and richness of denitrifying bacterial communities were enhanced, and the symbiotic structure of aerobic denitrifying bacteria was more complex (Bacillus and Mycobacteria as the dominant bacteria); the microbial distribution better matched the Zif and Mandelbrot models. This system significantly increased the abundance of key enzymes in water samples. The new material effectively removed pollutants and represents a promising and innovative in-situ remediation method for reservoirs.

Actinobacteria produce taste and odor in drinking water reservoir: Community composition dynamics, co-occurrence and inactivation models

Taste and odor (T&O) has become a significant concern for drinking water safety. Actinobacteria are believed to produce T&O during the non-algal bloom period; however, this has not been widely investigated. In this study, the seasonal dynamics of the actinobacterial community structure and inactivation of odor-producing actinobacteria were explored. The results indicated that the diversity and community composition of actinobacteria exhibited significant spatiotemporal distribution. Network analysis and structural equation modeling showed that the actinobacterial community occupied a similar environmental niche, and the major environmental attributes exhibited spatiotemporal dynamics, which affected the actinobacterial community. Furthermore, the two genera of odorous actinobacteria were inactivated in drinking water sources using chlorine. Amycolatopsis spp. have a stronger chlorine resistance ability than Streptomyces spp., indicating that chlorine inactivates actinobacteria by first destroying cell membranes and causing the release of intracellular compounds. Finally, we integrated the observed variability in the inactivation rate of actinobacteria into an expanded Chick-Watson model to estimate its effect on inactivation. These findings will deepen our understanding of the seasonal dynamics of actinobacterial community structure in drinking water reservoirs and provide a foundation for reservoir water quality management strategies.

Reduced sulfide and methane in rising main sewer via calcium peroxide dosing: Insights from microbial physiological characteristics, metabolisms and community traits

Although the biocidal effect of calcium peroxide (CaO2) has attracted increasing attention in wastewater and sludge management, its potential in the reduction of sulfide and methane from sewer is not tapped. This study aims to fill this gap through the long-term operated sewer reactors. Results showed one-time dose of 0.2% (w/v) CaO2 with 12-h exposure decreased the average sulfide and methane production by 80% during one week. The electron paramagnetic resonance and free radical quenching tests indicated free radicals from CaO2 decomposing posed a major contribution on sewer biofilms (•OH>•O2->alkali). Mechanistic analysis revealed extracellular polymeric matrix breakdown (e.g., protein secondary structure) and cell membrane damage were caused by the increased lipid peroxidation of cells and exacerbated intracellular reactive oxygen species under CaO2 stress. Moreover, the intracellular metabolic pathways, such as electrons provision and transfer, as well as pivotal enzymatic activities (e.g., APS reductase, sulfite reductase and coenzymes F420) were significantly impaired. RT-qPCR analysis unveiled the absolute abundances of dsrA and mcrA were decreased by 7.53-40.37% and 67.00-74.85%, respectively. Although this study broadens the application scope of CaO2 and provides in-depth understanding of advanced oxidation-based technology in sewer management, the pipe scale risk due to the release of calcium ions warrants further investigation.

Plant and microbial communities responded to copper and/or tetracyclines in mycorrhizal enhanced vertical flow constructed wetlands microcosms with Canna indica L

Arbuscular mycorrhizal fungi (AMF) play a significant role in pollutants removal in constructed wetlands (CWs). However, the purification effects of AMF on combined copper (Cu) and tetracycline (TC) pollution in CWs remains unknown. This study investigated the growth, physiological characteristics and AMF colonization of Canna indica L. living in vertical flow CWs (VFCWs) treated for Cu and/or TC pollution, the purification effects of AMF enhanced VFCWs on Cu and TC, and the microbial community structures. The results showed that (1) Cu and TC inhibited plant growth and decreased AMF colonization; (2) the removal rates of TC and Cu by VFCWs were 99.13-99.80% and 93.17-99.64%, respectively; (3) the growth, Cu and TC uptakes of C. indica and Cu removal rates were enhanced by AMF inoculation; (4) TC and Cu stresses reduced and AMF inoculation increased bacterial operational taxonomic units (OTUs) in the VFCWs, Proteobacteria, Bacteroidetes, Firmicutes and Acidobacteria were the dominant bacteria, and AMF inoculation decreased the relative abundance of Novosphingobium and Cupriavidus. Therefore, AMF could enhance the pollutants purification in VFCWs by promoting plant growth and altering the microbial community structures.

Aerobic Denitrification Enhanced by Immobilized Slow-Released Iron/Activated Carbon Aquagel Treatment of Low C/N Micropolluted Water: Denitrification Performance, Denitrifying Bacterial Community Co-occurrence, and Implications

The key limiting factors in the treatment of low C/N micropolluted water bodies are deficient essential electron donors for nitrogen removal processes. An iron/activated carbon aquagel (IACA) was synthesized as a slowly released inorganic electron donor to enhance aerobic denitrification performance in low C/N micropolluted water treatment. The denitrification efficiency in IACA reactors was enhanced by more than 56.72% and the highest of 94.12% was accomplished compared with those of the control reactors. Moreover, the COD_Mn removal efficiency improved by more than 34.32% in IACA reactors. The Illumina MiSeq sequencing consequence explained that the denitrifying bacteria with facultative denitrification, iron oxidation, and iron reduction function were located in the dominant species niches in the IACA reactors (e.g., Pseudomonas, Leptothrix, and Comamonas). The diversity and richness of the denitrifying bacterial communities were enhanced in the IACA reactors. Network analysis indicated that aerobic denitrifying bacterial consortia in IACA reactors presented a more complicated co-occurrence structure. The IACA reactors presented the potential for long-term denitrification operation. This study affords a pathway to utilize IACA, promoting aerobic denitrification during low C/N micropolluted water body treatment.

Novel insights into aerobic denitrifying bacterial communities augmented denitrification capacity and mechanisms in lake waters

Scanty attention has been paid to augmenting the denitrification performance of polluted lake water by adding mix-cultured aerobic denitrifying bacterial communities (Mix-CADBCs). In this study, to solve the serious problem of nitrogen pollution in lake water bodies, aerobic denitrifying bacteria were added to lake water to enhance the nitrogen and carbon removal ability. Three Mix-CADBCs were isolated from lake water and they could remove >94 % of total nitrogen and dissolved organic carbon, respectively. The balance of nitrogen analysis shown that >70 % of the initial nitrogen was converted to gaseous nitrogen, and <11 % of the initial nitrogen was converted into microbial biomass. The batch experiments indicated that three Mix-CADBCs could perform denitrification under various conditions. According to the results of nirS-type sequencing, the Hydrogenophaga sp., Prosthecomicrobium sp., and Pseudomonas sp. were dominated genera of three Mix-CADBCs. The analysis of network indicated Pseudomonas I.Bh25.14 and Vogsella LIG4 were correlated with the removal of total nitrogen (TN) and dissolved organic carbon in the Mix-CADBCs. Compared with lake raw water, the addition of three Mix-CADBCs could promote the denitrification capacity (the removal efficiencies of TN > 78.72 %), microbial growth (optical density increased by 0.015-0.138 and the total cell count increased by 2 times), and organic degradation ability (the removal efficiency chemical oxygen demand >38 %) of lake water. In general, the findings of this study demonstrated that Mix-CADBCs could provide a new perspective for biological treatment lake water body.

Nitrogen reduction by aerobic denitrifying fungi isolated from reservoirs using biodegradation materials for electron donor: Capability and adaptability in the lower C/N raw water treatment

Biological denitrification was considered an efficient and environmentally friendly way to remove the nitrogen in the water body. However, biological denitrification showed poor nitrogen removal performance due to the lack of electron donors in the low C/N water. In this study, three novel aerobic denitrifying fungi (Trichoderma sp., Penicillium sp., and Fusarium sp.) were isolated and enhanced the performance of aerobic denitrification of fungi in low C/N water bodies combined with polylactic acid/polybutylene adipate-co-terephthalate (PLA/PBAT). In this work, the aerobic denitrifying fungi seed were added to denitrifying liquid medium and mixed with PLA/PBAT. The result showed that Trichoderma sp., Penicillium sp., and Fusarium sp. could reduce 89.93 %, 89.20 %, and 87.76 % nitrate. Meanwhile, the nitrate removal efficiency adding PLA/PBAT exceeded 1.40, 1.68, and 1.46 times that of none. The results of material characterization suggested that aerobic denitrifying fungi have different abilities to secrete proteases or lipases to catalyze ester bonds in PLA/PBAT and utilize it as nutrients in denitrification, especially in Penicillium brasiliensis D6. Besides, the electron transport system activity and the intracellular ATP concentration were increased significantly after adding PLA/PBAT, especially in Penicillium brasiliensis D6. Finally, the highest removal efficiency of total nitrogen in landscape water by fungi combined with PLA/PBAT was >80 %. The findings of this work provide new insight into the possibility of nitrogen removal by fungi in low C/N and the recycling of degradable resources.

Effects of copper sulfate algaecide on the cell growth, physiological characteristics, the metabolic activity of Microcystis aeruginosa and raw water application

Harmful cyanobacteria blooms (HCBs) occurred frequently and become a serious scientific challenge. Copper sulfate (CuSO₄) is a broad-spectrum chemical algaecide to control algae blooms. Herein, the Microcystis aeruginosa was exposed to different CuSO₄ (0.0, 0.2 and 0.5 mg/L) to assess the variations in algal physiological process and metabolic profiles. The results indicated that exposure to CuSO₄ of 0.5 mg/L at 72 h could significantly inhibit the cell growth and photosynthetic capacity of M. aeruginosa, including chl-a content and chlorophyll fluorescence parameters. Plasma membrane damage causing cell lysis of M. aeruginosa increased the K⁺ release. The increase of SOD and CAT suggested that CuSO₄ treatment caused oxidative stress in algal cells. Different doses of CuSO₄ modified the carbon metabolic potential, algal cells had their unique metabolic mode thereby. Moreover, the research further verified that CuSO₄ would also inhibit algal growth and change algal community structure in site-collected water application. Overall, laboratory results of M. aeruginosa to CuSO₄ and site-collected water application of algal responses to CuSO₄ might be conducive to uncovering the controlling mechanism of algae and the potential effect of carbon cycling in an ecological environment.

Aerobic denitrifying using actinobacterial consortium: Novel denitrifying microbe and its application

The aerobic denitrifying capacity of actinomycete strain has been investigated recently, while little is known about nitrogen and carbon substrate removal by mix-cultured aerobic denitrifying actinobacteria (Mix-CADA) community. Hence, three Mix-CADA consortiums, named Y23, X21, and Y27, were isolated from urban lakes to investigate their aerobic denitrification capacity, and their removal efficiency for nitrate and dissolved organic carbon were >97 % and 90 %, respectively. Illumina Miseq sequencing revealed that Streptomyces was the most dominant genus in the Mix-CADA consortium. Network analysis indicated that Streptomyces exfoliates, as the core species in the Mix-CADA consortium, majorly contributed to dissolved organic carbon and total nitrogen reduction. Moreover, the three Mix-CADA consortiums could remove 78 % of the total nitrogen and 61 % of the permanganate index from the micro-polluted l water. Meanwhile, humic-like was significantly utilized by three Mix-CADA consortiums, whereas Mix-CADA Y27 could also utilize aromatic protein and soluble microbial by-product-like in the micro-polluted raw water purification. In summary, this study will offer a novel perspective for the purification of micro-polluted raw water using the Mix-CADA consortium.

Novel insights in seasonal dynamics and co-existence patterns of phytoplankton and micro-eukaryotes in drinking water reservoir, Northwest China: DNA data and ecological model

Although associations between phytoplankton and micro-eukaryotes have been studied in aquatic ecosystems, there are still knowledge gaps in comprehending their dynamics and interactions in drinking water reservoirs. Here, the seasonal dynamics of phytoplankton and micro-eukaryotic diversities and their co-existence patterns were studied in a drinking water reservoir, Northwest China. The highest phytoplankton diversity was observed in summer, and Chlorella sp. that belongs to Chlorophyta was the most abundant genus. The highest eukaryotic diversity was also detected in summer, and Rimostrombidium sp. that belongs to Ciliophora was the most dominant genus. Mantel test showed that the phytoplankton diversity was significantly correlated with ammonia nitrogen (r = 0.561, p = 0.001) and dissolved organic carbon (r = 0.267, p = 0.017), while the eukaryotic diversity was significantly associated with ammonia nitrogen (r = 0.265, p = 0.034) and temperature (r = 0.208, p = 0.046). PLS-PM (Partial Least Squares Path Modeling) further revealed that nutrients (P < 0.01) significantly affected the phytoplankton diversity, while nutrients (P < 0.01) and temperature (P < 0.01) significantly influenced the eukaryotic diversity. Co-occurrence network displayed the primarily positive interactions (77.66% positive and 22.34% negative) between phytoplankton and micro-eukaryotes. These findings could deepen our understanding of interactions between phytoplankton and micro-eukaryotes and their driving factors under changing aquatic environments of drinking water reservoirs.

Transcriptome analysis reveals the molecular mechanisms of Phragmites australis tolerance to CuO-nanoparticles and/or flood stress induced by arbuscular mycorrhizal fungi

The molecular mechanism of arbuscular mycorrhizal fungi (AMF) in vertical flow constructed wetlands (VFCWs) for the purification of copper oxide nanoparticles (CuO-NPs) contaminated wastewater remains unclear. In this study, transcriptome analysis was used to explore the effect of AMF inoculation on the gene expression profile of Phragmites australis roots under different concentrations of CuO-NPs and/or flood stress. 551, 429 and 2281 differentially expressed genes (DEGs) were specially regulated by AMF under combined stresses of CuO-NPs and flood, single CuO-NPs stress and single flood stress, respectively. Based on the results of DEG function annotation and enrichment analyses, AMF inoculation under CuO-NPs and/or flood stress up-regulated the expression of a number of genes involved in antioxidant defense systems, cell wall biosynthesis and transporter protein, which may contribute to plant tolerance. The expression of 30 transcription factors (TFs) was up-regulated by AMF inoculation under combined stresses of CuO-NPs and flood, and 44 and 44 TFs were up-regulated under single CuO-NPs or flood condition, respectively, which may contribute to the alleviating effect of symbiosis on CuO-NPs and/or flood stress. These results provided a theoretical basis for enhancing the ecological restoration function of wetland plants for metallic nanoparticles (MNPs) by mycorrhizal technology in the future.

Enhanced anaerobic digestion of waste activated sludge with periodate-based pretreatment

The potential of periodate (PI) in sludge anaerobic digestion is not tapped, although it has recently attracted great research interest in organic contaminants removal and pathogens inactivation in wastewater treatment. This is the first work to demonstrate significant improvement in methane generation from waste activated sludge (WAS) with PI pretreatment and to provide underlying mechanisms. Biochemical methane potential tests indicated that methane yield enhanced from 100.2 to 146.3 L per kg VS (VS, volatile solids) with PI dosages from 0 to 100 mg per g TS (TS, total solids). Electron spin resonance showed PI could be activated without extra activator addition, which might be attributed to the native transition metals (e.g., Fe²⁺) in WAS, thereby generating hydroxyl radical (•OH), superoxide radicals (•O₂ ^-), and singlet oxygen (¹O₂). Further scavenging tests demonstrated all of them synergistically promoted WAS disintegration, and their contributions were in the order of •O₂ ^- > •OH > ¹O₂, leading to the release of substantial biodegradable substances (i.e., proteins and polysaccharides) into the liquid phase for subsequent biotransformation. Moreover, fluorescence and ultraviolet spectroscopy analyses indicated the recalcitrant organics (especially lignocellulose and humus) could be degraded by reducing their aromaticity under oxidative stress of PI, thus readily for methanogenesis. Microbial community analysis revealed some microorganisms participating in hydrolysis, acidogenesis, and acetoclastic methanogenesis were enriched after PI pretreatment. The improved key enzyme activities and up-regulated metabolic pathways further provided direct evidence for enhanced methane production. This research was expected to broaden the application scope of PI and provide more diverse pretreatment choices for energy recovery through anaerobic digestion.

Sediment nitrogen contents controlled by microbial community in a eutrophic tributary in Three Gorges Reservoir, China

Nitrogen pollution caused serious environmental problems in reservoir ecosystems. Reducing nitrogen pollution by enhancing nitrogen removal in river sediments deserved intensive research. Distributions of nitrogen contents in sediment-water interface were characterized along the Xiangxi bay (XXB), a eutrophic tributary in Three Gorges Reservoir, China. More than 47% of total Kjeldahl nitrogen (TKN) and 67% of total organic nitrogen (TON) were degraded during burial. Higher TN, TON and NH₄⁺ consuming at downstream sites indicated stronger nitrogen mineralization and release due to higher turbulence of the overlying density currents. Nitrifying bacteria, denitrifying bacteria, anaerobic ammonium oxidizing (anammox) bacteria and nitrite/nitrate-dependent anaerobic methane oxidation (N-DAMO) bacteria were detected in nitrate-ammonium transition zone. Nitrogen contents transitions were responded to microbial stakeholders indicated microbially mediated nitrogen cycling in sediments. The dissolved oxygen and nitrate availabilities were the key limits of denitrification and associated reactions. These results suggested microbial mediated nitrogen cycling processes in sediments were critical for nitrogen removal in aquatic ecosystems, and replenishing dissolved oxygen and nitrate was expected to enhance sediment denitrification and strengthen potential environmental self-purification.

The scale-dependence of spatial distribution of reservoir plankton communities in subtropical and tropical China

Distance-decay relationships (DDRs) represent a very useful approach to describing the spatial distribution of biological communities. However, plankton DDR patterns and community assembly mechanisms are still poorly understood at different spatial scales in reservoir ecosystems. We collected phytoplankton, zooplankton and water samples in 24 reservoirs from subtropical and tropical China from July to August 2018. We examined DDR patterns across three distinct spatial scales, i.e., within-reservoir, within-drainage (but between reservoirs) and between drainages. We tested whether the rate of change (i.e., slope) of DDRs is consistent across different spatial scales. We assessed the relative importance of spatial and environmental variables in shaping the community distribution of plankton and quantitatively distinguished the community assembly mechanisms. We observed significant DDR curves in phytoplankton and zooplankton communities, in which slopes of the DDRs were steepest at the smallest spatial scale. Both spatial and environmental factors had significant impacts on DDR and dispersal assembly was a slightly stronger process in reservoir phytoplankton and zooplankton community assembly than niche-based process. We conclude that DDRs of reservoir phytoplankton and zooplankton vary with spatial scale. Our data shed light on how spatial and environmental variables contribute to plankton community assembly together. However, we revealed that dispersal process contributes to the biogeography of reservoir plankton slightly more strongly than environmental filtering. Collectively, this study enhances the understanding of plankton biogeography and distribution at multiple spatial scales.

Bacterial community structure and metabolic activity of drinking water pipelines in buildings: A new perspective on dual effects of hydrodynamic stagnation and algal organic matter invasion

Eutrophication and algal blooms have become global issues. The drinking water treatment process suffers from pollution by algal organic matter (AOM) through cell lysis during the algal blooms. Nevertheless, it remains unclear how AOM invasion affects water quality and microbial communities in drinking water, particularly in the stagnant settings. In this study, the addition of AOM caused the residual chlorine to rapidly degrade and below the limit of 0.05 mg/L, while the NO₂^--N concentration ranged from 0.11 to 3.71 mg/L. Additionally, total bacterial counts increased and subsequently decreased. The results of Biolog demonstrated that the AOM significantly improved the utilization capacity of carbon sources and changed the preference for carbon sources. Full-length 16S rRNA gene sequencing and network modeling revealed a considerable reduction in the abundance of Proteobacteria, whereas that of Bacteroidetes increased significantly under the influence of AOM. Furthermore, the species abundance distributions of the Microcystis group and Scenedesmus group was most consistent with the Mandelbrot model. According to redundancy analysis and structural equation modeling, the bacterial community structure of the control group was most positively regulated by the free residual chlorine concentrations, whereas the Microcystis group and Scenedesmus group were positively correlated with the total organic carbon (TOC) concentration. Overall, these findings provide a scientific foundation for the evolution of drinking water quality under algae bloom pollution.

Patterns of internal nitrogen and phosphorus loadings in a cascade reservoir with a large water level gradient: Effects of reservoir operation and water depth

Internal nutrient loadings pose a high risk of being an additional N and P source, exacerbating eutrophication and deteriorating water quality. In this study, we selected the Daheiting Reservoir (DHTR) in North China, with a pronounced water level gradient, to investigate internal N and P loadings, estimate N and P fluxes across the sediment‒water interface based on the pore water profiles, and reveal the potential effects of water discharge from an upstream reservoir and high-intensity cage aquaculture on the risks of internal N and P release. The results indicated that DHTR presented with severe internal nutrient loadings, and the N and P fluxes showed significant spatiotemporal variations. NH₄⁺-N and soluble reactive phosphorus (SRP) fluxes were higher in deep areas (averages of 26.14 and 9.9 mgm^-2d^-1, respectively) than in shallow areas near inflows (averages of 5.0 and 1.24 mgm^-2d^-1, respectively). Unexpectedly, the estimated NH₄⁺-N and SRP fluxes were the lowest in summer (averages of 3.94 and 0.33 mgm^-2d^-1, respectively), which may have been influenced by seasonal thermal stratification and copious discharge from the hypolimnion of the upstream reservoir (Panjiakou Reservoir). Comparison of annual internal and external N and P loadings revealed that water discharge from the upstream Panjiakou Reservoir was the dominant source of N and P to the reservoir, contributing up to 83.6% of N input and 55.4% of P input. The internal P loading also contributed to water eutrophication to a great extent, accounting for 34.7% of the total P input. Our results highlight the impact of upstream reservoir discharge operation on downstream reservoir water quality and the importance of controlling the internal nutrient loading in cascade reservoirs, and further provide theoretical and practical foundations for the development of policies and strategies to conserve reservoir ecosystems.

Autochthonous sources and drought conditions drive anomalous oxygen-consuming pollution increase in a sluice-controlled reservoir in eastern China

Freshwater reservoirs are an important type of inland waterbody. However, they can suffer from oxygen-consuming pollution, which can seriously threaten drinking water safety and negatively impact the health of aquatic ecosystems. Oxygen-consuming pollutants originate from both allochthonous and autochthonous sources, and have temporally and spatially heterogeneous drivers. Datanggang Reservoir, China, is located in a small agricultural watershed; it is controlled by multiple sluice gates. Anomalously high oxygen consumption indicators were observed in this reservoir in March 2021. Here, it was hypothesized that autochthonous sources were the primary drivers of oxygen-consuming pollution in the reservoir under drought conditions. Datasets of water quality, precipitation, primary productivity, and sediment were used to analyze water quality trends in the reservoir and inflow rivers, demonstrating the effects of allochthonous inputs and autochthonous pollution. No correlation was found between reservoir oxygen consumption indicators and allochthonous inputs; reservoir oxygen consumption indicators and chlorophyll-a concentration were significantly positively correlated (p < 0.05). Substantially lower precipitation and higher water temperature and pH (compared to historical levels) were also observed before the pollution event. Therefore, during this period the hydrological conditions, water temperature, pH, and other variables caused by short-term drought conditions may have facilitated phytoplankton growth in the reservoir. This contributed to a large increase in autochthonous oxygen-consuming pollutants, as reflected by the abnormally high indicators. Sediments contaminated with organic matter may also have been an important contributor. As the effects of environmental management and pollution control continue to emerge, exogenous pollutants imported from the land to reservoirs are currently effectively controlled. However, endogenous pollutants driven by a variety of factors, such as meteorology and hydrology, will likely become the main drivers of short-term changes in oxygen-consuming pollution in freshwater reservoirs in the foreseeable future.

Biological nitrogen removal and metabolic characteristics of a novel cold-resistant heterotrophic nitrification and aerobic denitrification Rhizobium sp. WS7

For improving the poor de-nitrogen efficiency and effluent quality faced by wastewater treatment plants in winter, a novel cold-resistant strain, Rhizobium sp. WS7 was isolated. Strain WS7 presented dramatic de-nitrogen efficiencies including 98.73 % of NH₄⁺-N, 99.98 % of NO₃^--N, 100 % of NO₂^--N and approximately 100 % of mixed nitrogen (NH₄⁺-N and NO₃^--N) at 15 °C. Optimum parameters of WS7 for aerobic denitrification were determined. Additionally, functional genes (amoA, napA, nirK, norB, and nosZ) and key enzymes (nitrate reductase and nitrite reductase) activities were determined. Nitrogen balance analysis suggested that assimilation played a dominant role in de-nitrogen by WS7, the NH₄⁺-N metabolic pathway was deduced as NH₄⁺-N → NH₂OH → NO → N₂O → N₂, and the NO₃^--N/NO₂^--N metabolic pathway was deduced as NO₃^--N → NO₂^--N → NO → N₂O → N₂. The cold-resistant Rhizobium sp. WS7 has great application feasibility in cold sewage treatment.

Iron-Based Nanocatalysts for Electrochemical Nitrate Reduction

Nitrate has a high level of stability and persistence in water, endangering human health and aquatic ecosystems. Due to its high reliability and efficiency, the electrochemical nitrate reduction reaction (NO₃ RR) is regarded as the best available option for mitigating excess nitrate in water and wastewater, especially for the removal of trace levels of nitrate. One of the most critical factors in the electrochemical reduction are the catalysts, which directly affect the reaction efficiency of nitrate removal. Iron-based nanocatalysts, which have the advantages of nontoxicity, wide availability, and low cost, have emerged as a promising electrochemical NO₃ RR material in recent years. This review covers major aspects of iron-based nanocatalysts for electrochemical NO₃ RR, including synthetic methods, structural design, performance enhancement, electrocatalytic nitrate reduction test, and reduction mechanism. The recent progress of iron-based nanocatalysts for electrochemical NO₃ RR and the mechanism of functional advantages for modified structures are reviewed from the perspectives of loading, doping, and assembly strategies, in order to realize the conversion from pollutant nitrate to harmless nitrogen or ammonia and other sustainable products. Finally, challenges and future directions for the development of low-cost and highly-efficient iron-based nanocatalysts are explored.

Synchronous N and P Removal in Carbon-Coated Nanoscale Zerovalent Iron Autotrophic Denitrification─The Synergy of the Carbon Shell and P Removal

Fe⁰ is a promising electron donor for autotrophic denitrification in the simultaneous removal of nitrate and phosphorus in low C/N wastewater. However, P removal may inevitably inhibit bio-denitrification. It has not been well recognized and led to an overdose of iron materials. This study employed carbon-coated zerovalent iron (Fe⁰@C) to support autotrophic denitrification to mitigate the inhibition effects of P removal and enhance both N and P removal. The critical role of the carbon shell in Fe⁰@C was to block the direct contact between Fe⁰ and P and NO₃^--N, to maintain the Fe⁰ activity. Besides, P inhibited the chemical reduction of NO₃^--N by competing for Fe⁰ active sites. This indirectly boosted H₂ generation and promoted bio-denitrification. P removal displayed negligible effects on microbial species but indirectly enhanced the nitrogen metabolic activities because of promoted H₂ in Fe⁰@C-based autotrophic denitrification. Bio-denitrification, in turn, strengthened Fe-P co-precipitation by promoting the formation of ferric hydroxide as a secondary adsorbent for P removal. This study demonstrated an efficient method for simultaneous N and P removal in autotrophic denitrification and revealed the synergistic interactions among N and P removal processes.