Pollutant removal performance and microbial enhancement mechanism by water-lifting and aeration technology in a drinking water reservoir ecosystem

Optimization of carbon membrane performance in reverse osmosis systems for reducing salinity, nitrates, phosphates, and ammonia in aquaculture wastewater

This study investigates the performance of various types of carbon membranes in reverse osmosis systems aimed at reducing salinity, nitrates, phosphates, and ammonia in aquaculture wastewater. As sustainable aquaculture practices become increasingly essential, effective treatment solutions are needed to mitigate pollution from nutrient-rich effluents. The research highlights several carbon membranes types, including carbon molecular sieves, activated carbon membranes, carbon nanotube membranes, and graphene oxide membranes, all of which demonstrate exceptional filtration capabilities due to their unique structural properties. Findings reveal that these carbon membranes can achieve removal efficiencies exceeding 90 % for critical pollutants, thereby significantly improving water quality and supporting environmental sustainability. The study also explores the development of hybrid membranes and nanocomposites, which enhance performance by combining the strengths of different materials, allowing for customized solutions tailored to the specific requirements of aquaculture wastewater treatment. Additionally, operational parameters such as pH, temperature, and feed water characteristics are crucial for maximizing membrane efficiency. The integration of real-time monitoring technologies is proposed to enable prompt adjustments to treatment processes, thereby improving system performance and reliability. Overall, this research emphasizes the importance of interdisciplinary collaboration among researchers and industry stakeholders to drive innovation in advanced filtration technologies. The findings underscore the substantial potential of carbon membranes in tackling the pressing water quality challenges faced by the aquaculture sector, ultimately contributing to the sustainability of aquatic ecosystems and ensuring compliance with environmental standards for future generations.

Biotic Interaction Underpins the Assembly Processes of the Bacterial Community Across the Sediment-Water Interface in a Subalpine Lake

The sediment-water interface is the most active region for biogeochemical processes and biological communities in aquatic ecosystems. As the main drivers of biogeochemical cycles, the assembly mechanisms and the distribution characteristics of microbial communities at this boundary remain unclear. This study investigated the microbial communities across the sediment-water interface in a natural subalpine lake in China. The results indicated that the diversity of bacterial communities in middle sediment was significantly higher than that in overlying water and other sediments (p < 0.001). Pearson's correlation analysis indicated that the diversity was significantly influenced by biotic factors (e.g., diversity of fungus, protozoan and alga) and physicochemical parameters (e.g., total carbon, total organic carbon, nitrate, ammonium and pH) (p < 0.01). Null model analysis revealed that the homogeneous selection dominated the assembly of the bacteria community in sediment, whereas the heterogeneous selection dominated that in overlying water. The least squares path analysis showed that interactions between protozoa and bacteria had a greater impact on bacterial community assembly (p < 0.001). Important taxa influence the assembly by regulating biotic interactions. These findings provided a basis for understanding the importance of biotic interactions in maintaining subalpine lakes' ecosystems across the sediment-water interface.

Aerobic denitrifying bacterial community with low C/N ratio remove nitrate from micro-polluted water: Metagenomics unravels denitrification pathways

The efficient nitrogen removal from micro-polluted source water is an international challenge to be solved urgently. However, the inner denitrification mechanism of native aerobic denitrifying bacterial communities in response to carbon scarcity remains relatively unclear. Here, the bacterial community XT6, screened from an oligotrophic reservoir, exhibited aerobic denitrifying capacity under low-carbon environments. Up to 76.79-81.64 % of total organic carbon (TOC) and 51.48-67.60 % of NO3--N were removed by XT6 within 48 h at C/N ratios of 2.0-3.0. Additionally, the nitrogen balance experiments further manifested that 26.27-38.13 % of NO3--N was lost in gaseous form. As the C/N ratio decreased, XT6 tended to generate more extracellular polymeric substances (EPS), with the tightly bound EPS showing the largest increase. Pseudomonas and Variovorax were quite abundant in XT6, constituting 59.69 % and 28.65 % of the total sequences, respectively. Furthermore, metagenomics analysis evidenced that XT6 removed TOC and nitrate mainly through the tricarboxylic acid cycle and aerobic denitrification. Overall, the abovementioned results provide a deeper understanding of the nitrogen metabolic pathways of indigenous aerobic denitrifying bacterial communities with low C/N ratios and offer useful guidance for controlling nitrogen pollution in oligotrophic ecosystems.

Dissolved oxygen facilitates efficiency of chlorine disinfection for antibiotic resistance

Controlling the dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is a global concern. While commonly used chlorine disinfectants can damage or even kill ARB, dissolved oxygen (DO) may affect the formation of reactive chlorine species. This leads to the hypothesis that DO may play roles in mediating the effectiveness of chlorine disinfection for antibiotic resistance. To this end, this study investigated the impacts of DO on the efficiency of chlorine disinfection for antibiotic resistance. The results revealed that DO could increase the inactivation efficiency of ARB under chloramine and free chlorine exposure at practically relevant concentrations. Reactive species induced by DO, including H2O2, O2-, and OH, inactivated ARB strains by triggering oxidative stress response and cell membrane damage. In addition, the removal efficiency of extracellular ARGs (i.e. tetA and blaTEM) was enhanced with increasing dosage of free chlorine or chloramine under aerobic conditions. DO facilitated the fragmentation of plasmids, contributing to the degradation of extracellular ARGs under exposure to chlorine disinfectants. The findings suggested that DO facilitates disinfection efficiency for antibiotic resistance in water treatment systems.

Unveiling the power of COD/N on constructed wetlands in a short-term experiment: Exploring microbiota co-occurrence patterns and assembly dynamics

Constructed wetlands (CWs) are a cost-effective and environmentally friendly wastewater treatment technology. The influent chemical oxygen demand (COD)/nitrogen (N) ratio (CNR) plays a crucial role in microbial activity and purification performance. However, the effects of CNR changes on microbial diversity, interactions, and assembly processes in CWs are not well understood. In this study, we conducted comprehensive mechanistic experiments to investigate the response of CWs to changes in influent CNR, focusing on the effluent, rhizosphere, and substrate microbiota. Our goal is to provide new insights into CW management by integrating microbial ecology and environmental engineering perspectives. We constructed two groups of horizontal subsurface flow constructed wetlands (HFCWs) and set up three influent CNRs to analyse the microbial responses and nutrient removal. The results indicated that increasing influent CNR led to a decrease in microbial α-diversity and niche width. Genera involved in nitrogen removal and denitrification, such as Rhodobacter, Desulfovibrio, and Zoogloea, were enriched under medium/high CNR conditions, resulting in higher nitrate (NO3--N) removal (up to 99 %) than that under lower CNR conditions (<60 %). Environmental factors, including water temperature (WT), pH, and phosphorus (P), along with CNR-induced COD and NO3--N play important roles in microbial succession in HFCWs. The genus Nitrospira, which is involved in nitrification, exhibited a significant negative correlation (p < 0.05) with WT, COD, and P. Co-occurrence network analysis revealed that increasing influent CNR reduced the complexity of the network structure and increased microbial competition. Analysis using null models demonstrated that the microbial community assembly in HFCWs was primarily driven by stochastic processes under increasing influent CNR conditions. Furthermore, HFCWs with more stochastic microbial communities exhibited better denitrification performance (NO3--N removal). Overall, this study enhances our understanding of nutrient removal, microbial co-occurrence, and assembly mechanisms in CWs under varying influent CNRs.

Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement

Artificial mixing and oxygenation induced by water-lifting aerations (WLAs) have the potential to improve water quality in reservoirs. However, there is a limited understanding of the bacterial community composition, assembly, and mechanisms behind water quality improvement under the influence of WLAs, especially in a water transfer reservoir. Here, the dynamics and relationship between water quality, bacterial diversity, and composition during the pre-operation, in-operation, and post-operation stages of WLAs were analyzed using high-throughput sequencing technology to explore the effects of artificially regulated bacteria on water quality improvement. WLAs operation led to the elimination of water stratification, significant bottom oxygenation, and reduction in nutrient concentrations. In addition, the operation of WLAs significantly changed the bacterial community composition, with an increase in richness, negligible difference in diversity, and a significant increase in the abundance of species with pollutant degradation functions, resulting in a shift from stochastic to deterministic processes of the bacterial community assembly. As a result, enhancement of the dominant bacteria responsible for organic matter degradation and denitrification and suppression of the emergence of algae-related bacteria were observed during the WLAs operation, and the ecosystem stability improved. Multiple analyses indicated a direct correlation between artificial mixing and oxygenation; changes in the bacterial community; and the reduction of nitrogen, phosphorus, and permanganate index in the water column. This study provides novel insights into in situ water quality enhancement and a valuable reference for understanding bacterial change patterns under artificially intervened conditions in water transfer reservoirs.

Microbial interactions strengthen deterministic processes during community assembly in a subtropical estuary

Systematic studies on the assembly process and driving mechanisms of microbial communities in estuaries with diverse seasonal and spatial scales are still limited. In this study, high-throughput sequencing, and microbial network analysis were combined to decipher the impact of environmental changes and biological interactions on the maintenance of microbial diversity patterns in the Jiulong River Estuary (JRE). The results showed that overall, stochastic processes dominated the bacterioplankton community assembly in the estuary, accounting for 49.66-74.78 % of the total. Additionally, bacterioplankton community diversity varied significantly across seasons and subzones. Specifically, the concentration of soluble reactive phosphorus (SRP) in the estuary steadily reduced from winter to summer, and the corresponding bacterioplankton community interactions gradually shifted from the weakest interaction in winter to the strongest in summer. The deterministic processes contributed more than half (50.34 %) to microbial assembly in the summer, but only 25.22 % in winter. Deterministic processes prevailed in the seaward with low SRP concentrations and strong bacterioplankton community interactions, while stochastic processes contributed 70.14 % to the assembly of microbial communities riverward. Biotic and abiotic factors, such as nutrients and microbial interactions, jointly drove the seasonal and spatial patterns of bacterioplankton community assembly, but overall, nutrients played a dominant role. Nevertheless, the contributions of nutrients and microbial interactions were equivalent in spatial assembly processes, albeit nutrients were the primary seasonal driver of the bacterioplankton community assembly process. This study emphasizes the significance of microbial interactions in the bacterioplankton community assemblage. These findings provide new and comprehensive insights into the microbial communities' organization in estuaries.

Microbial community structure and functional prediction in five full-scale industrial park wastewater treatment plants

The development of industrial parks has become an important global trend contributing significantly to economic and industrial growth. However, this growth comes at a cost, as the treatment of multisource industrial wastewater generated in these parks can be difficult owing to its complex composition. Microorganisms play a critical role in pollutant removal during industrial park wastewater treatment. Therefore, our study focused on the microbial communities in five full-scale industrial park wastewater treatment plants (WWTPs) with similar treatment processes and capacities. The results showed that denitrifying bacteria were dominant in almost every process section of all the plants, with heterotrophic denitrification being the main pathway. Moreover, autotrophic sulfur denitrification and methane oxidation denitrification may contribute to total nitrogen (TN) removal. In plants where the influent had low levels of COD and TN, dominant bacteria included oligotrophic microorganisms like Prosthecobacter (2.88 % ~ 10.02 %) and hgcI_clade (2.05 % ~ 9.49 %). Heavy metal metabolizing microorganisms, such as Norank_f__PHOS-HE36 (3.96 % ~ 5.36 %) and Sediminibacterium (1.86 % ~ 5.34 %), were prevalent in oxidation ditch and secondary settling tanks in certain plants. Functional Annotation of Prokaryotic Taxa (FAPROTAX) revealed that microbial communities in the regulation and hydrolysis tanks exhibited higher potential activity in the nitrogen (N) and sulfur (S) cycles than those in the oxidation ditch. Sulfate/sulfite reduction was common in most plants, whereas the potential occurrence of sulfide compounds and thiosulfate oxidation tended to be higher in plants with a relatively high sulfate concentration and low COD content in their influent. Our study provides a new understanding of the microbial community in full-scale industrial park WWTPs and highlights the critical role of microorganisms in the treatment of industrial wastewater.

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.

Coupling effect of DOM and microbe on arsenic speciation and bioavailability in tailings soil after the addition of different biologically stabilized sludges

Dissolved organic matter (DOM) and microbes co-mediate the transformation of heavy metals in soil. However, few previous studies have investigated the effects of interaction between DOM and microbes on the transformation and bioavailability of heavy metals in tailings soil at the molecular level after the addition of organic wastes. This study used co-occurrence network analysis based on Fourier-transform ion cyclone resonance mass spectrometry and high-throughput sequencing to investigate the molecular mechanisms of different bio-stabilized sludge addition on arsenic fraction transformation and bioavailability in tailings soil. It was found that sludge amendments decreased the arsenic bioavailable fraction from 3.62% to 1.74% and 1.68% and promoted humification of DOM in soil. The extra inorganic salt ions introduced with sludge desorb the adsorbed As(V) into soil solution. Specifically, bio-stabilized sludge increased the contents of labile compounds that provided nutrients for microbial metabolism and shaped the microbial community composition into a more copiotrophic state, which increased the abundance of As(V)-reducing bacteria and then converted the As(V) into As(III) and precipitated as As₂S₃. This work innovatively explores the transformation mechanisms of As fractions through the perspectives of microbial community and DOM molecular characterization, providing an important basis for the remediation of As-contaminated soil using biosolids.

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.

Water-lifting and aeration system improves water quality of drinking water reservoirs: Biological mechanism and field application

Reservoirs have been served as the major source of drinking water for dozens of years. The water quality safety of large and medium reservoirs increasingly becomes the focus of public concern. Field test has proved that water-lifting and aeration system (WLAS) is a piece of effective equipment for in situ control and improvement of water quality. However, its intrinsic bioremediation mechanism, especially for nitrogen removal, still lacks in-depth investigation. Hence, the dynamic changes in water quality parameters, carbon source metabolism, species compositions and co-occurrence patterns of microbial communities were systematically studied in Jinpen Reservoir within a whole WLAS running cycle. The WLAS operation could efficiently reduce organic carbon (19.77%), nitrogen (21.55%) and phosphorus (65.60%), respectively. Biolog analysis revealed that the microbial metabolic capacities were enhanced via WLAS operation, especially in bottom water. High-throughput sequencing demonstrated that WLAS operation altered the diversity and distributions of microbial communities in the source water. The most dominant genus accountable for aerobic denitrification was identified as Dechloromonas. Furthermore, network analysis revealed that microorganisms interacted more closely through WLAS operation. Oxidation-reduction potential (ORP) and total nitrogen (TN) were regarded as the two main physicochemical parameters influencing microbial community structures, as confirmed by redundancy analysis (RDA) and Mantel test. Overall, the results will provide a scientific basis and an effective way for strengthening the in-situ bioremediation of micro-polluted source water.

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.

Aerobic denitrification of oligotrophic source water driven by reduced metal manganese

The lack of organic electron donors limits the potential utility of aerobic denitrification in treatment of oligotrophic source water. Here, reduced manganese (Mn) was used as an inorganic electron donor to improve the denitrification of oligotrophic source water under the high dissolved oxygen condition (7-9 mg L^-1). Over 30 days, the total nitrogen removed by the treatment with reduced Mn was 76.21 ± 2.11% (maximum), substantially higher than that of the control treatment, which was 41.48 ± 2.33%. Furthermore, the addition of Mn resulted in the directional evolution of the microbial community. Water samples with Mn added showed a higher abundance of Limnohabitans, the dominant denitrifying genus, reaching 51.02%, 36.79%, and 20.19% (with 30, 50, and 70 g Mn, respectively), versus only 5.54% in the control. In biofilm, Mn promoted Hydrogenophaga and Brevundimonas growth while Pseudarthrobacter growth was promoted by 30 and 50 g Mn, but inhibited by 70 g Mn. This study demonstrates an improved performance in aerobic denitrification of water sources through the use of inorganic electron donors.

NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model

The nirS-type denitrifying bacterial community is the main drivers of the nitrogen loss process in drinking water reservoir ecosystems. The temporal patterns in nirS gene abundance and nirS-type denitrifying bacterial community harbored in aerobic water layers of drinking water reservoirs have not been studied well. In this study, quantitative polymerase chain reaction (qPCR) and Illumina Miseq sequencing were employed to explore the nirS gene abundance and denitrifying bacterial community structure in two drinking water reservoirs. The overall results showed that the water quality parameters in two reservoirs had obvious differences. The qPCR results suggested that nirS gene abundance ranged from (2.61 ± 0.12) × 10⁵ to (3.68 ± 0.16) × 10⁵ copies/mL and (3.01 ± 0.12) × 10⁵ to (5.36 ± 0.31) × 10⁵ copies/mL in Jinpen and Lijiahe reservoirs, respectively. The sequencing results revealed that Paracoccus sp., Azoarcus sp., Dechloromonas sp. and Thauera sp. were the dominant genera observed. At species level, Cupriavidus necator, Dechloromonas sp. R-28400, Paracoccus denitrificans and Pseudomonas stutzeri accounted for more proportions in two reservoirs. More importantly, the co-occurrence network analysis demonstrated that Paracoccus sp. R-24615 and Staphylococcus sp. N23 were the keystone species observed in Jinpen and Lijiahe reservoirs, respectively. Redundancy analysis indicated that water quality (particularly turbidity, water temperature, pH and Chlorophyll a) and sampling time had significant influence on the nirS-type denitrifying bacterial community in both reservoirs. These results will shed new lights on exploring the dynamics of nirS-type denitrifying bacteria in aerobic water layers of drinking water reservoirs.

New insights into the mechanism of ammonia toxicity: Focus on Cactus

The NF-κB signaling pathway is the most critical pathway in innate immunity. IκB (Cactus) is the primary cytoplasmic inhibitor of NF-κB (Dorsal). In this study, we found that ammonia exposure could significantly induce the expression of Cactus, in a dose-dependent manner in different tissues, with the highest expression in the gill of Corbicula fluminea. The expression pattern-related elements (Tube and Dorsal) in the NF-κB signaling pathway were also analyzed, showing significant up-regulation in 48 h. There was an inhibitory effect between up-regulated Cactus and Dorsal in 72 h, which may regulate Dorsal as a negative feedback pathway function to control the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). Besides, through molecular docking simulation, we found that the Cactus could be directly activated by NH₃, complementing the regulatory mechanism of the Cactus. To further test our hypothesis, the levels of pro-inflammatory cytokines decreased after adding PDTC (the antioxidant of Cactus/IκB), suggesting that PDTC can prevent the degradation of Cactus, inhibit Dorsal translocating into the nucleus, and activate the pro-inflammatory cytokines. This revealed the inhibitory effect of Cactus on activating Dorsal/NF-κB factors in the NF-κB signaling pathway. Thus, we suggested that the Cactus is an essential regulator of ammonia-activated inflammation in C. fluminea, which was reported to be activated only by bacteria and immune stimulators. Our study provides a new perspective on the mechanism of ammonia toxicity in invertebrates.

The importance of rest phase and pollutant removal mechanism of tidal flow constructed wetlands (TFCW) in rural grey water treatment

This paper explored the effects of the rest phase of tidal flow constructed wetlands (TFCW) on pollutant removal and microbial communities, and further analyzed the mechanism of TFCW removal of pollutants from grey water. The results showed that the removal rate of organic matter was 69.91 ± 2.44% in the control group (NR-TFCW) without the rest phase, 94.95 ± 1.17% in the experimental group (TFCW), and 96.95 ± 2.43% in the control group (P-TFCW) with the ventilation pipe enhanced rest phase. Limiting and enhancing the oxygen supply in the emptying stage of TFCW will enhance the overlap rate of microorganisms in the upper, middle and lower layers of the reactor. Enhancing the rest phase of TFCW leaded to better aerobic removal of organic matter in the microbial community, while limiting the rest phase of TFCW results in the opposite. In addition, the species overlap rate of the top, middle and bottom layers of NR-TFCW (69.98%) and P-TFCW (54.29%) was higher than that of TFCW (11.34%). The removal of organic matter by TFCW mainly relied on the adsorption of biochar in the flood phase, and the microorganisms aerobic degraded the organic matter adsorbed on the biochar in the rest phase. And thus form a continuous cycle of adsorption and biological regeneration. The microbial community in TFCW did not have the ability to nitrify, but had the ability to remove phosphorus. Ammonia nitrogen in the influent was adsorbed by biochar or converted into cytoplasm. While the phosphorus in the influent was adsorbed by the biochar, it was also being biologically removed.

Performance and microbial community of MBBRs under three maintenance strategies for intermittent stormwater treatment

Maintaining microbial activities is a critical problem for biological treatment processes of stormwater runoff because of its intermittent nature. In this study, the suitability of the moving bed biofilm reactor (MBBR) was assessed for stormwater treatment by long-term dry - rainy alternation operation. Three strategies to maintain microbial activities during the dry period, including keeping idle (MBBR_I), introducing river water throughout the period (MBBR_C), and ahead of a rainy day (MBBR_M), were investigated. COD and NH₄⁺-N removal efficiencies declined linearly from 94.2 % and 94.7 % to 51.7 % and 64.6 %, respectively, after the 61-day operation with microbial activity and biomass decreased. Introducing river water adversely affected the process performance as MBBR_C presented the highest declining rates of COD and NH₄⁺-N removal efficiencies. Most genera in MBBRs decayed and their microbial communities developed towards individualization, especially in MBBR_M because of its highest environmental variability. Keeping idle slightly alleviated the performance decline and formed a more stable microbial community structure. However, significantly deteriorating performance in all MBBRs after the long-term operation indicated that MBBRs were unsuitable for treating stormwater independently of intermittent nature.

Extending improvements of eutrophication and water quality via induced natural mixing after artificial mixing in a stratified reservoir

Induced (natural) mixing proposed by our teams can solve a big problem of low-energy water situation improvement of stratified reservoirs by minimizing operating periods of water-lifting aerators (WLAs) to advance a complete natural mixing. Here, the mechanisms influencing water situation via induced mixing were systematically explored using a combination of multi-water-environment assessment methods including trophic level index (TLI), water quality index (WQI), and minimum WQI (WQI_min) based on long-term field data (i.e., non-operational and operational years of WLAs). The results showed that induced mixing after WLA deactivation improved the levels of eutrophication and water quality (into "light-eutrophic" and "good" status) with a decrease in TLI values (56.0-56.2) and increase in WQI (79.0-79.9) and WQI_min (81.5-89.3) values, compared to mixing of the non-operational year (TLI: 69.6, WQI: 73.4, WQI_min: 76.1). Induced mixing was launched by deactivating the WLAs in cooling seasons (i.e., in late September within a subtropical monsoon climate zone), which advanced and prolonged the periods of naturally complete mixing by 2-3 months. Water temperature (WT), Dissolved oxygen (DO), relative water column stability (RWCS) and inflow were primary drivers for the water situation succession in the study years. Induced mixing extended the well-oxygenated and mixed conditions (temperature difference <1.0 °C, DO > 8.5 mg/L, RWCS< 20) following artificial mixing to improve the water status from single index level (improvement of 18.8%-73.7% than mixing before the operational years) to integrated evaluation results by changing WT, DO, and RWCS. This study presents a successful case for energy-saving pollution control using mixing systems.

Deciphering the core seed endo-bacteriome of the highland barley in Tibet plateau

Highland barley (Hordeum vulgare var. nudum (L.) Hook.f., qingke) has unique physical and chemical properties and good potential for industrial applications. As the only crop that can be grown at high altitudes of 4200-4500 m, qingke is well adapted to extreme habitats at high altitudes. In this study, we analysed the seed bacterial community of 58 genotypes of qingke grown in different regions of Tibet, including qingke landraces, modern cultivars, and winter barley varieties, and characterised endophytic bacterial communities in seeds from different sources and the core endo-bacteriome of qingke. This study aim to provide a reference for the application of seed endophytes as biological inoculants for sustainable agricultural production and for considering microbe-plant interactions in breeding strategies. A total of 174 qingke seed samples from five main agricultural regions in Tibet were collected and subjected to investigation of endophytic endo-bacteriome using high-throughput sequencing and bioinformatics approaches. The phyla of endophytic bacteria in qingke seeds from different sources were similar; however, the relative proportions of each phylum were different. Different environmental conditions, growth strategies, and modern breeding processes have significantly changed the community structure of endophytic bacteria in seeds, among which the growth strategy has a greater impact on the diversity of endophytic bacteria in seeds. Seeds from different sources have conserved beneficial core endo-bacteriome. The core endo-bacteriome of qingke seeds dominated by Enterobacteriaceae may maintain qingke growth by promoting plant growth and assisting plants in resisting pests and diseases. This study reveals the core endo-bacteriome of qingke seeds and provides a basis for exploiting the endophytic endo-bacteriome of qingke seeds.

Effect of wastewater treatment plant discharge on the bacterial community in a receiving river

The effluent of wastewater treatment plants (WWTPs) is an important water resource for some rivers in regions with relatively low precipitation, which may pose ecological risks. Various pollutants and microorganisms are discharged into rivers, along with the WWTP effluent, but this process has not been thoroughly studied. The objective of this study was to evaluate the effect of WWTP effluent on the bacterial community in the sediment and water column of an urban river and to identify the relationship between the total and active bacterial communities. Five sites were sampled in the river, including the most upstream site of the river (Up-most), 200 m upstream of the WWTP (Up-200), at the point of effluent discharge of the WWTP (Eff-pl) and 50 m (Down-50) and 1000 m (Down-1000) downstream of the WWTP. Compared with the two upstream sites (Up-most and Up-200), the bacterial species composition of Eff-pl was significantly different (p < 0.05) in both the sediment and water columns, while the bacterial species composition at Down-1000 was significantly different (p < 0.05) in the sediment but not in the water. The relative abundance of Proteobacteria, Actinobacteriota and Verrucomicrobiota was significantly different (p < 0.05) at Eff-pl in both the sediment and water columns compared with that at the upstream sites. The shared bacterial species between the DNA and RNA 16 S rRNA analyses were only 45.5-62.2% and 43.2-52.3% for the sediment and water, respectively. Accordingly, WWTP effluent drainage significantly alters (p < 0.05) the bacterial composition in the receiving river but can be recovered in water within a short distance. However, in sediment, a longer recovery space is probably needed. Analyses of the combination of total and active bacterial compositions are recommended to evaluate the ecological consequences of WWTP effluent drainage on the bacterial composition.

An assessment of the purification performance and resilience of sponge-based aerobic biofilm reactors for treating polluted urban surface waters

Pollutants are continuously released into surface waters, which decrease the dissolved oxygen (DO) concentration and leads to the formation of black-odorous water, especially in slow-flowing urban lakes and enclosed small ponds. In situ treatment by artificial aeration or water cycling, coupled with biofilm, can address this problem without occupying large amounts of land. In this study, we designed a novel sponge-based aerobic biofilm reactor (SABR) and evaluated its performance in purifying urban surface water under different conditions. In the urban lake water treatment, the continuous inflow results revealed that the NH₄⁺-N and NO₂^--N concentrations in the effluent were stable and remained lower than 0.10 mg/L and 0.05 mg/L, respectively. Abrupt increases in the NH₄⁺-N and NO₂^--N concentrations in the influent and sudden increases in the NH₄⁺-N and NO₂^--N concentrations in the effluent were observed, and only 4 to 8 days were required for the concentrations to decline below 0.10 mg/L and 0.05 mg/L, respectively. Increases in the polyurethane sponge filling ratios in the SABRs can reduce the DO concentration but do not affect NH₄⁺-N removal. When no biodegradable organic matter was present in the enclosed surface water, the degradation time of NH₄⁺-N from 14.22 to 0.10 mg/L was only 9 days when SABRs were combined with water cycling, which was shorter than the time needed by water cycling alone (16 days), and most of the NH₄⁺-N was converted to NO₃^--N. When massive amounts of biodegradable organic matter were present in the enclosed surface water, 22 days were required to remove the NH₄⁺-N when SABRs were combined with water cycling. Our results indicated that organic matter could be used as a carbon source to eliminate the produced NO₃^--N in SABRs. Therefore, the newly developed bioreactor provides an effective approach for treating N-polluted urban surface waters.

Spatial and temporal dynamics of actinobacteria in drinking water reservoirs: Novel insights into abundance, community structure, and co-existence model

The control of taste and odor (T&O) in drinking water reservoirs is the main challenge for water supply. T&O is mainly derived from actinobacteria during non-algal blooms. However, few studies have investigated the actinobacterial community in reservoirs, especially the effects of water quality parameters on actinobacteria. This study analyzed the environmental driving force of the actinobacterial community composition and change in time and space through structural equations and network in drinking water reservoirs. The results showed a high abundance of actinobacteria, up to 2.7 × 10⁴ actinobacteria per 1 L, in the hypolimnion of the Lijiahe reservoir in September, which is one order of magnitude greater than that in the Jinpen reservoir. The two drinking water reservoirs had similar dominant genera, mainly Sporichthya sp., and Mycobacterium sp., and difference in the actinobacterial proportions. However, there was a large difference at the dominant species. Rhodococcus fascians (4.02%) was the dominant species in the Lijiahe reservoir, while Mycobacterium chlorophenolicum (6.64%) was the dominant species in the Jinpen reservoir. Network analysis revealed that the structure of the network in the Lijiahe reservoir was more unstable; thus, it was vulnerable to environmental disturbances. In addition, a low abundance of species may play a critical role in the actinobacterial community structure of aquatic ecosystems. Structural equation modeling analysis suggested that water temperature, dissolved oxygen, and nutrition were the dominant factors affecting the abundance and community of actinobacteria. Overall, these findings broaden the understanding of the distribution and co-existence of actinobacterial communities in drinking water reservoirs and provide valuable clues for the biological controls of T&O and reservoir management.

Role of nano-Fe3O4 particle on improving membrane bioreactor (MBR) performance: Alleviating membrane fouling and microbial mechanism

This study would investigate the effect of nano-Fe3O4 particles on the performance of membrane bioreactor (MBR), including membrane fouling, membrane rejection and microbial community. It can effectively alleviate membrane fouling and improve the effluent quality in MBR by bio-effect rather than nanoparticle adsorption. The lowest membrane fouling resistance was achieved at R4-MBR (sludge and membrane surface with nano-Fe3O4), which decreased by 46.08%. Meanwhile, R3-MBR (sludge with nano-Fe3O4) had the lowest concentration of COD in effluent which was below 20 mg/L in the stable phase of MBR operation. After applying nano-Fe3O4, the content of extracellular polymeric substances (EPS) and soluble microbial products (SMP) were both reduced with a lower molecular weight. From the microbial community analysis, the abundance of Proteobacteria increased from 25.06 to 45.11% at the phylum level in R3-MBR. It contributed to removing organic substances in MBRs. Moreover, the nano-Fe3O4 restricted Bacteroidetes growth, especially in R4-MBR, leading to a more excellent performance of membrane flux. Besides, the applied nano-Fe3O4 promoted the abundance of Quorum Quenching (QQ) microorganism, and declined the percentage of Quorum Sensing (QS) bacteria. Then, a lower content of N-Acyl-l-Homoserine Lactones (AHLs) in containing nano-Fe3O4 sludge. That was also prone to control membrane fouling. Overall, this study indicates the nano-Fe3O4 particle is appropriate for elevating MBR performance, such as membrane fouling and effluent quality, by bio-effect.

Effect of AM Fungi Inoculation on Litter Bacterial Community Characteristics under Heavy Metal Stress

Because microorganisms are the primary driving force behind litter decomposition, they play an important role in maintaining ecosystem material and chemical cycling. Arbuscular mycorrhizal (AM) fungi can improve host plant tolerance to various environmental stressors, making their application in mining area remediation important. In this study, litter from the dominant plant species (Imperata cylindrica) in a copper tailings mining area was selected as the experimental material. We conducted a greenhouse-based heavy metal stress experiment to investigate how AM fungi affect litter microbial community characteristics and key ecological factors. Results showed that AM fungi species, heavy metal treatments, and their combined interaction had significant impacts on litter pH. Additionally, enzyme activities in litter were significantly affected by interactions between AM fungi species and heavy metal contaminates. Ralstonia was significantly positively correlated to lead (Pb) content, indicating that Ralstonia had a certain tolerance to Pb pollution. Sucrase and urease activity were increased when plants were inoculated with Rhizophagus irregularis under Pb stress. Furthermore, Microbacterium, Brevundimonas, and Pseudonocardia all may play important roles in litter decomposition, while a certain tolerance was observed in Kushneria and Roseivivax to heavy metal pollution when plants were inoculated with Glomus mosseae. Results showed that AM fungi affected litter bacterial community structure and function by influencing plant litter properties. By exploring interactions between AM fungi and bacterial communities in plant litter under heavy metal stress, we will better understand associative processes that promote the cycling of soil organic matter and nutrients contaminated by non-ferrous metal tailings.

Direct and indirect effects of fenoxycarb on freshwater systems dominated by Neocaridina palmata (Decapoda: Atyidae) and macrophyte Ceratophyllum demersum

Few studies have been conducted with regard to the effects of insecticides on population dynamics of shrimps and associated groups such as macrophytes, phytoplankton, microorganisms etc. In the present study, effects of a single application of fenoxycarb were tested using indoor freshwater systems dominated by Neocaridina palmata and Ceratophyllum demersum (Dicotyledons: Ceratophyllales). The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for the N. palmata, as scaled by liberated chitobiase, were 6.48 μg/L and 27.76 μg/L, and the dose-related effect lasted for 14 days. Results of principal components analysis (PCA) and that of principal response curves (PRC) method showed that the biomass of C. demersum and concentrations of chlorophyll-a were suppressed, while the concentrations of phycocyanin were promoted. Illumina high-throughput sequencing was adopted to determine the diversity of bacteria and fungi in the media. Result of PCA and PRC showed that the fenoxycarb promoted photosynthetic bacteria (e.g. Cyanobacteria and Rhodobacterales) and suppressed groups involved in nitrogen and sulfur the transformation (e.g. Flavobacterium, hgcI_clade, Cystobasidium, Rhodotorula and Rhizobiales). Promotion in pathogen such as Pseudomonas and Cercozoa and suppression in beneficial taxa such as Novosphingobium and Rhodotorula were also sighted. Result of study suggested a water quality deterioration due to fenoxycarb applications.

Inducing an extended naturally complete mixing period in a stratified reservoir via artificial destratification

Naturally complete mixing (i.e., ΔT <1 °C across the entire water column) driven by convection in winter is an ideal state for maintaining good water quality, as it spontaneously redistributes dissolved oxygen (DO) over the entire water column and prevents hypolimnetic anoxia and associated pollution. A complete mixing duration is quite short under natural mixing conditions, whereas artificial destratification systems can artificially induce an earlier occurrence of complete mixing, thereby prolonging the span of the naturally complete mixing period by several months. Based on multi-year in situ water quality measurements and meteorological data during natural and artificial mixing periods, this study evaluates the effects of water-lifting aerators (WLAs) and climatic factors on convective mixing processes and their duration. WLA-supplied turbulent kinetic energy (TKE) and WLA-induced hypolimnion warming significantly decrease the water stability and extend the naturally complete mixing period for 2.6-fold. The results indicate that an optimal WLA implementation should immediately achieve complete mixing when surface mixing occurs in autumn. By evaluating the influence of WLAs and other factors on convective mixing, this study provides insights for successful destratification system operations (i.e., WLAs) to replenish oxygen concentrations across the water column and minimize operating costs by taking advantage of climatic conditions. Although our study focuses on WLA-induced mixing, these observations can be applicable to other destratification systems in most of the stratified reservoirs and lakes.

Reservoir water stratification and mixing affects microbial community structure and functional community composition in a stratified drinking reservoir

To investigate how the aquatic bacterial community of a stratified reservoir drives the evolution of water parameters, the microbial community structure and network characteristics of bacteria in a stratified reservoir were investigated using Illumina MiSeq sequencing technology. A total of 42 phyla and 689 distinct genera were identified, which showed significant seasonal variation. Additionally, stratified variations in the bacterial community strongly reflected the vertical gradient and seasonal changes in water temperature, dissolved oxygen, and nutrition concentration. Furthermore, principal coordinate analysis indicated that most microorganisms were likely influenced by changes in water stratification conditions, exhibiting significant differences during the stratification period and mixing period based on Adonis, MRPP, and Anosim. Compared to the stratification period, 123 enhanced operational taxonomic units (OTUs; 29%) and 226 depleted OTUs (52%) were identified during the mixing period. Linear discriminant analysis effect size results showed that 15 major genera were enriched in the mixing period and 10 major genera were enriched in the stratification period. Importantly, network analysis revealed that the keystone species belonged to hgcI_clade, CL500-29, Acidibacter, Paucimonas, Flavobacterium, Prochlorothrix, Xanthomonadales, Chloroflexia, Burkholderiales, OPB56, KI89A_clade, Synechococcus, Caulobacter or were unclassified. Redundancy analysis showed that temperature, dissolved oxygen, pH, chlorophyll-α, total phosphorus, nitrate, and ammonia were important factors influencing the water bacterial community and function composition, which were consistent with the results of the Mantel test analysis. Furthermore, random forest analysis showed that temperature, dissolved oxygen, ammonia, and total dissolved phosphorous were the most important variables predicting water bacterial community and function community α- and β-diversity (P < 0.05). Overall, these results provide insight into the interactions between the microbial community and water quality evolution mechanism in Zhoucun reservoir.

Keystone taxa of water microbiome respond to environmental quality and predict water contamination

The human activity introduces strong environmental stresses, and results in great spatiotemporal heterogeneity for the environment. Although the effects of environmental factors on the microbial diversity and succession have been widely studied, knowledge about how keystone taxa respond to environmental stresses remains poorly understood. We examined bacterial and archaeal communities from 45 wetland ponds covering a wide range of waters in Hangzhou. We found that shifts in bacterial and archaeal communities were strongly correlated with water pollution as indicated by the comprehensive water quality identification (CWQI). The SEGMENTED analysis suggested that there were non-linear responses of microbial communities and keystone taxa to the water pollution gradient. Moreover, these significant tipping points (e.g., CWQI > 4.0) would afford a warning line for urban wetland management. Notably, keystone taxa of bacterial communities could be used to successfully (~88.9% accuracy) predict water contamination levels. This study provides new insights into the potential for keystone bacterial taxa to predict water contamination.

Linking Shifts in Bacterial Community Composition and Function with Changes in the Dissolved Organic Matter Pool in Ice-Covered Baiyangdian Lake, Northern China

The relationship between CDOM (Chromophoric dissolved organic matter) and the bacterial community was investigated in ice-covered Baiyangdian Lake. The results showed that environmental parameters significantly differed in Baiyangdian Lake, whereas a-diversity was not significantly different. Moreover, the microbial and functional communities exhibited significant differences, and T (Temperature), pH, ORP (Oxidation-reduction potential), DO (Dissolved oxygen), NO₃⁻-N, NH₄⁺-N, and Mn (Manganese) were the main environmental factors of these differences, based on redundancy analysis and the Mantel test. Biomarkers of the microbial and functional communities were investigated through linear discriminant analysis effect size and STAMP analysis. The number of biomarkers in the natural area was highest among the typical zones, and most top functions were related to carbohydrate metabolism. Two protein-like components (C1 and C2) and one humic-like component (C3) were identified by parallel factor analysis, and C1 was positively related to C2 (R = 0.99, p < 0.001), indicating the same sources. Moreover, CDOM significantly differed among the typical zones (p < 0.001). The high biological index, fluorescence index, β:α, and low humification index indicated a strong autochthonous component and aquatic bacterial origin, which was consistent with the results of UV-vis absorption spectroscopy. Network analysis revealed non-random co-occurrence patterns. The bacterial and functional communities interacted closely with CDOM. The dominant genera were CL500-29_marine_group, Flavobacterium, Limnohabitans, and Candidatus_Aquirestis. Random forest analysis showed that C1, C2, and C3 are important predictors of α- and β-diversity in the water bacterial community and its functional composition. This study provides insight into the interaction between bacterial communities and DOM (Dissolved organic matter) in ice-covered Baiyangdian Lake.

Characteristics and Driving Factors of the Aerobic Denitrifying Microbial Community in Baiyangdian Lake, Xiong'an New Area

Here, the ion-exchangeable form of nitrogen (IEF-N), weak-acid extractable form of nitrogen (WAEF-N), strong-alkali extractable form of nitrogen (SAEF-N), strong-oxidant extractable form of nitrogen (SOEF-N), residue nitrogen (Res-N), and total nitrogen (TN) showed spatial differences, and most of the sediment nitrogen fractions exhibited positive correlations in Baiyangdian Lake. High-throughput sequencing analysis revealed that the aerobic denitrification microbial community was composed of proteobacteria (42.04%–99.08%) and unclassified_bacteria (0.92%–57.92%). Moreover, the microbial community exhibited significant differences (R² = 0.4422, P < 0.05) on the basis of the adonis analysis. T(temperature), Moisture content (MC), sediment total phosphorus (STP), ion-exchangeable form of ammonia (IEF-NH₄⁺-N), weak-acid extractable form of ammonia (WAEF-NH₄⁺-N), weak-acid extractable form of nitrate (WAEF-NO₃⁻-N), and strong-alkali extractable form of ammonia (SAEF-NH₄⁺-N) were the dominant environmental factors and explained 11.1%, 8.2%, 10.7%, 6.9%, 9.3%, 8.1%, 10.5%, 7.5%, and 7% variation, respectively, of the total variation in the microbial community. Furthermore, the network analysis showed that symbiotic relationships accounted for a major percentage of the microbial networks. The keystone aerobic denitrifying bacteria belonged to Comamonas, Rhodobacter, Achromobacter, Aeromonas, Azoarcus, Leptothrix_Burkholderiales, Pseudomonas, Thauera, unclassified_Burkholderiales, and unclassified_bacteria. The composition of the keystone aerobic denitrifying microbial community also exhibited significant differences (R² = 0.4534, P < 0.05) on the basis of the adonis analysis. T, STP, IEF-NH₄⁺-N, ion-exchangeable form of nitrate (IEF-NO₃⁻-N), WAEF-NO₃⁻-N, SAEF-NH₄⁺-N, and TN were the dominant environmental factors that explained 8.4%, 6.2%, 4.6%, 5.9%, 5.9%, 4.5%, and 9.4% variation, respectively, of the total variation in the keystone aerobic denitrifying microbial community. The systematic investigation could provide a theoretical foundation for the evolution mechanism of the aerobic denitrifying microbial community in Baiyangdian Lake.