Search Results (1,278)

This study investigated the ecological selection and enrichment of anaerobic ammonium-oxidizing bacteria (AnAOB) driven by endogenous carbon cycling in a low-oxygen SBR biofilm system without external carbon addition. The system was operated using dried biofilm inoculation, continuous low oxygen (DO < 0.1 mg/L), and complete drainage. After 117 days, AnAOB were enriched to 8.14% relative abundance and became the dominant functional group. At an influent total nitrogen (TN) of 25 mg/L, the average effluent TN and NH₄⁺-N were 6.37 and 3.75 mg/L, respectively, corresponding to a TN removal efficiency of 75% and meeting the Class A discharge standard. Metagenomic and metatranscriptomic analyses revealed that anammox was the primary nitrogen removal pathway, with nitrite supplied through partial nitrification and endogenous partial denitrification. Higher expression of nitrate reductase genes than of nitrite reductase genes favored nitrite accumulation through endogenous partial denitrification, thereby creating a self-sustaining internal cycle between nitrate reduction and anammox. Extracellular polymeric substances (EPS) served as the key internal carbon source driving this process. This ecological regulation strategy provides an energy-efficient and stable strategy for mainstream low C/N municipal wastewater treatment without external carbon addition. Full article

The Qinghai–Tibet Plateau is undergoing rapid warming and humidification, with altered precipitation regimes increasingly affecting soil nitrogen cycling and N₂O emissions. Denitrification—a key nitrogen transformation pathway—is particularly sensitive to these hydrological changes. Here, we investigated the response of nirK-type denitrifying microbial communities to altered precipitation in an alpine wetland on the northern shore of Qinghai Lake. Using a long-term precipitation manipulation platform with five gradients (ambient, ±25%, and ±50%), we integrated high-throughput sequencing with bioinformatics to systematically assess community shifts. Short-term precipitation treatments did not significantly alter alpha diversity, but markedly restructured community composition. Extreme wetting (+50%) increased within-group heterogeneity. At the phylum level, Proteobacteria remained dominant across all treatments, whereas extreme drought (−50%) suppressed Planctomycetes. At the genus level, Ochrobactrum was enriched under reduced precipitation, while Rhodopseudomonas increased under increased precipitation. Functional predictions indicated that reduced precipitation enhanced nitrogen fixation potential, whereas increased precipitation favored nitrate respiration. Soil pH and carbon fractions were the key environmental filters driving community variation. Ecological process analysis revealed that community assembly was entirely governed by deterministic processes, specifically variable selection. Together, these findings elucidate how precipitation shifts reconfigure the structure and functional potential of denitrifying microbial communities in alpine wetlands, primarily via changes in soil pH and moisture under variable selection. This work provides critical insights into microbial regulation of the nitrogen cycle on the Tibetan Plateau under ongoing climate change. Full article

Nitrous oxide (N₂O) is recognized as a potent greenhouse gas, and 60% of atmospheric N₂O emissions come from cropland soils. Potassium (K) is an important fertilizer for rice paddy fields. K fertilizer decreased the abundance of functional genes mediating nitrification and denitrification processes, thereby mitigating N₂O emissions. However, few studies have explored the effect of K fertilization rates on N₂O emissions and grain yields, as well as the associated soil properties and aboveground N accumulation in paddy fields under different irrigation regimes. This study aimed to propose an optimum combination of K fertilization rate and irrigation regime to increase grain yield while reducing N₂O emissions. Here, a 2-year field experiment using a split-plot design with three replicates was conducted to assess the effect of three K fertilization rates (K₀: 0 kg ha⁻¹, K₇₅: 75 kg ha⁻¹, K₁₅₀: 150 kg ha⁻¹) on N₂O emissions, grain yield, aboveground N accumulation, and soil properties, including soil redox potential (Eh), NH₄⁺, NO₃⁻, soil gene abundance of AOA, AOB, nirK, nirS, nirK/nirS, and nosZ, under continuous flooding irrigation (I_CF) and alternate wetting and drying irrigation (I_AWD). The soil physicochemical properties, the gene abundance and the aboveground N accumulation were evaluated and used to explain how irrigation and K fertilization affect grain yield and N₂O emissions. We found that I_AWD significantly increased N₂O emissions by 38% compared to I_CF, and K fertilizer significantly reduced N₂O emissions by 15% relative to K₀. The effects of I_AWD and K fertilizer on N₂O emissions can be attributed to the combined impact of soil physicochemical properties and the abundance of functional genes governing N₂O emissions. Both irrigation regimes produced equivalent grain yield and aboveground N accumulation. Shifting from I_CF to I_AWD, the increase in N₂O emissions can be mitigated by K fertilization. Moreover, K₇₅ and K₁₅₀ had similar effects in reducing N₂O emissions and yield-scaled N₂O emissions, while K₇₅ had a lower K fertilizer cost and higher K partial factor productivity. Therefore, applying K fertilizer at 75 kg ha⁻¹ under I_AWD is identified as a potentially suitable rate to secure grain yield while effectively mitigating N₂O emissions. Full article

Standing tile inlets are commonly used to drain unwanted surface water from croplands but can exacerbate pollution by facilitating the transport of nutrients to waterways. Blind inlets have increasingly been viewed as a beneficial alternative to standing inlets since they control erosion and capture particulate nutrients. However, conventional blind inlets do little to limit dissolved nutrient transport, and modified blind inlet (MBI) designs have been proposed that incorporate woodchips—a medium that facilitates denitrification. While initial investigations have highlighted MBIs’ remediation potential, their ability to meet prescribed drainage standards has not been well-documented. In this study, we designed and installed MBIs composed of pea gravel and woodchips in two eastern Iowa fields under row crop cultivation. Flow and nitrate were continuously monitored using in situ equipment directly downstream of the MBIs (February 2023–June 2025). Observed flows were very ephemeral, consisting of ~25 distinct events at both sites, with no flow recorded in between. During several wet weather events, flow rates exceeded the MBIs’ design requirements, confirming their sufficient drainage capacity to prevent in-field ponding. Nitrate concentrations varied considerably, with long-term averages of 11.6 and 19.1 mg/L and overall loadings of 4.94 and 7.10 kg during our 28-month study. We also measured phosphate and sulfate during select wet weather events, and discrepancies in concentrations between inlets and outlets suggested that groundwater was often present alongside surficial drainage in our monitoring setup. We believe our results argue for increased adoption of MBIs in conservation and further quantification of their remediation capabilities. Full article

Autotrophic denitrification using sulfur compounds is considered an alternative to heterotrophic denitrification for the treatment of organic carbon-deficient wastewaters. However, the stoichiometric characteristics of denitrification using different sulfur species, particularly thiocyanate (SCN⁻) and sulfite (SO₃²⁻), remain poorly understood. Here, partial autotrophic denitrification driven by thiocyanate or sulfite was studied in two batch reactors. The stoichiometry of thiocyanate-oxidizing denitrification was assessed based on valence and ultimate product analysis. No nitrate removal was observed in the sulfite-fed system, indicating that sulfite could not serve as an effective electron donor for autotrophic denitrification under the tested conditions. In contrast, simultaneous removal of SCN⁻ and NO₃⁻ was achieved in the thiocyanate-fed system, with removal efficiencies of 100% and 92.5 ± 3.6%, respectively. After 36 h, total nitrogen removal reached 63.3%, with nitrite identified as the dominant intermediate product (26.7%). NO₂⁻ and NH₄⁺ accumulated during the process could be further removed through anaerobic ammonium oxidation. Thiocyanate sulfur was primarily oxidized to sulfate via elemental sulfur as a transient intermediate. These findings provide a theoretical basis for applying thiocyanate-driven partial autotrophic denitrification to nitrogen removal from industrial wastewaters, particularly those generated via coal gasification and cyanide-utilizing gold mining processes. Full article

In permanently submerged coastal wetlands, interactions between biogeochemical processes and microbial communities strongly influence greenhouse gas (GHG) fluxes. To improve our understanding of how redox-driven processes shape GHG dynamics in these ecosystems, we investigated the relationships among iron (Fe) pools, microbial dynamics, and the potential GHG production in subaqueous soils from an interdunal wetland in San Vitale Park (Italy), permanently submerged and affected by seasonal oscillations of the saline water table. Two subaqueous soil columns (WAS-2 and WAS-4), collected from similar settings, were analyzed. Surface layers of WAS-4 showed higher salinity and carbonate content, whereas WAS-2 was characterized by overall higher Fe concentrations. Distinct vertical distributions of organic matter and sulfur (S) were shown along depth. Laboratory incubations revealed that nitrous oxide (N₂O) production was up to ten times higher in WAS-2 than in WAS-4, with peaks in the top 13–14 cm, consistent with more active nitrification-denitrification in surface layers. Methane (CH₄) and carbon dioxide (CO₂) fluxes decreased with depth, reflecting reduced availability of labile carbon. Methanomicrobiales dominated CH₄-producing layers, indicating hydrogenotrophic methanogenesis, while amoA-carrying Nitrosomonadales and Thaumarchaeota, occurred in shallow, organic-rich layers where ammonia supported nitrification and denitrification. Denitrifiers mainly belonged to α- and β-Proteobacteria, consistent with their direct contribution to N₂O peaks. Spearman’s correlations showed N₂O positively correlated to sulfur and labile carbon (C), supporting denitrification under moderately reducing conditions. CH₄ and CO₂ positively correlated with organic C (Corg), total nitrogen (TN), and reactive Fe forms, reflecting redox-mediated microbial respiration and methanogenesis. Trace elements (B, Cr, Cu, Ni) acted as micronutrients or inhibitors depending on concentration. Canonical correspondence analysis indicated depth-structured links among gas fluxes, soil chemistry (Corg, TN, S/C, CaCO₃, P), and microbial distributions: surface layers, rich in labile C and nutrients, supported active bacteria and archaea involved in decomposition, nitrification, and denitrification, whereas deeper layers hosted oligotrophic archaea adapted to inorganic substrates. Overall, Fe pools appeared to be associated with soil processes relevant to GHG dynamics, although the extent of their regulatory role remains uncertain due to potential alterations of redox-sensitive Fe fractions during sample handling. These results contribute to broader efforts to predict GHG emissions in submerged wetland soils by linking redox stratification, inorganic chemistry, and microbial functional groups. Full article

Microbial community structure and its carbon, nitrogen, and sulfur metabolic potentials are playing crucial roles in biogeochemical cycles within river ecosystems. However, in karst terrain regions, the impact of the distinctive baijiu industry on these ecosystems remains incompletely understood. This study integrates hydrogeochemical and metagenomic techniques to elucidate how microbial communities and their metabolic potentials respond to the baijiu industry. The results indicate that microbial community richness was higher in the downstream section than in the upstream and core zones. Microbial network modularity decreased from 0.832 upstream to 0.439 downstream, indicating reduced network stability. The migration rate decreased from upstream to downstream, suggesting that species diffusion limitation was gradually enhanced. The NST index gradually decreased from upstream to downstream, reflecting a weakening of random processes and strengthening of deterministic processes within the community. We found significant enrichment of genes associated with dissimilatory nitrate reduction, sulfur oxidation, carbon fixation, and methanogenesis in the core zone, whereas the abundance of denitrification genes decreased. Environmental factor analysis revealed that pH, DO, and elevation are the key hydrochemical parameters driving changes in microbial community structure and metabolic functions. This study reveals the potential impact mechanisms of the baijiu industry on karst river ecosystems from the perspectives of microbial community ecology and metabolic functions, providing a scientific basis for watershed ecological conservation and sustainable management. Full article

To assess the treatment efficiency and spatio-temporal variation characteristics of urban wastewater treatment plants, this study analyzed influent and effluent water quality data, including pH, COD, BOD₅, SS, NH₃–N, TN, and TP, as well as treatment volume data from 19 plants in Changsha from 2020 to 2024. The results revealed significant fluctuations in influent water quality across different plants, though effluent quality generally complied with discharge standards. Removal rates of SS, NH₃–N, and BOD₅ all exceeded 80%, while that of TN ranged between 63% and 79%. The COD/BOD₅ ratios in the influent mostly exceeded 0.3, indicating generally good biodegradability of the municipal wastewater. However, 79% of the plants exhibited SS/BOD₅ > 1.5, and 83.2% had BOD₅/TN < 4, suggesting a widespread carbon deficiency for denitrification. Principal component analysis (PCA) demonstrated that both influent and effluent quality indicators were suitable for dimensionality reduction, with pH, COD, NH₃–N, and TN identified as core evaluation factors. Cluster analysis (CA) indicated phased increases in influent concentrations, while effluent quality showed progressive annual improvement from 2020 to 2024. Urban WWTPs’ influent pollution loads were hydrological period-dependent, with high-flow effluent fluctuations and controllable low-flow loads. This study provides data support for operational optimization of wastewater treatment plants in Changsha. Full article

The anammox technology, as an efficient and energy-saving denitrification method, has been widely used in the field of wastewater treatment. Nevertheless, this process faces two key challenges in actual operation, namely the fluctuation of nitrite substrate supply and the residual nitrate, which greatly limits its promotion and application in a wider range. Although the traditional combined process of partial denitrification/anammox (PD/A) can generate nitrite substances, the coexistence of heterotrophic microorganisms and organic carbon sources in the system may have a significant inhibitory effect on the proliferation of Anammox bacteria. The sulfur-oxidizing bacteria (SOB) involved in the sulfur autotrophic denitrification process (SAD) have overlapping ecological niches with Anammox microorganisms and have stable nitrite enrichment characteristics. In view of this, sulfur-oxidizing bacteria are regarded as a potential candidate for combining with the Anammox process. However, the denitrification efficiency of this process is often restricted by the low solubility and poor bioavailability of substrates. At the same time, there are significant research gaps and data deficiencies regarding the key operating parameters for autotrophic short-range denitrification using elemental sulfur to achieve nitrite accumulation and the coupling application of this process with other wastewater treatment technologies. In view of this, this study is committed to comprehensively sorting out and evaluating the existing optimization methods of the elemental sulfur autotrophic denitrification process, while providing an in-depth analysis of its mechanism of action and environmental control factors. At the same time, this study also carried out innovative exploration on the modification process of the sulfur element from the frontier perspective of materials science and pointed out the key directions for subsequent optimization of the construction path of the elemental sulfur autotrophic denitrification system and for improving the denitrification process efficiency. In summary, this study systematically discusses the mechanism of action, practical application, and improvement scheme of PS⁰AD. Full article

Agricultural drainage water is a significant contributor to a broad spectrum of pollutant loads, including nitrates, ammonium, organic matter, phosphorus, and emerging substances, and thus poses an important environmental and human health concern. This review aims to integrate existing knowledge on bioreactors and natural and constructed wetlands in the treatment of agricultural drainage water. It covers bioreactors from a perspective on categorization, principles, and performance with respect to treatment efficiency. It provides a critical evaluation of constructed wetlands as passive treatment systems, in addition to their importance as nature-based service providers. Some significant issues in bioreactors, such as media durability, greenhouse gas production, and the elimination of emerging pollutants, will be critically described, and this critique will conclude with proposals for possible path methods in bioreactors toward a suitable convergence with a nature-related water treatment system. Full article

Urban wetlands are assumed to contribute to nitrous oxide (N₂O) emissions; however, the microbial mechanisms underlying enhanced N₂O fluxes in urban wetlands and differences in microbial responses between aquatic and soil compartments have not been clearly identified. Here, we characterized the nitrogen (N) cycling microbial communities and their functional metabolic pathways in urban and rural wetlands using metagenomics and N₂O flux measurements. Results showed that urbanization drove a 6~8-fold increase in N₂O fluxes from urban wetlands compared to rural wetlands. Structural equation modeling (SEM) confirmed that urbanization intensity was a primary driver (standardized coefficients: 0.72 for soil and 0.92 for water). In wetland water, N₂O emissions were negatively correlated with inorganic nutrient concentrations (coefficient = −0.62). Aquatic microbial communities exhibited substantial taxonomic shifts but preserved network connectivity, indicating adaptive strategies for surviving urban perturbations at the cost of reduced functional redundancy. In wetland soil, microbial communities maintained stability under urbanization, which was attributed to environmental buffering from heterogeneous microenvironments. Soil N₂O emissions were positively linked to microbial alpha diversity (coefficient = 0.79). Furthermore, urban wetlands enriched genes mediating nitrification and denitrification while depleting genes associated with N fixation and organic N metabolism. This functional shift reflects microbial specialization in processing elevated reactive N (Nr) inputs from urban sources, trapping urban wetlands in an “N loss loop” that reinforces high N₂O fluxes. This study elucidates the microbial mechanisms governing wetland N₂O emissions under urbanization, thereby enhancing understanding of microbially mediated N cycling in the urban wetland ecosystem. Full article

Ammoniacal nitrogen (NH₃-N) is a major pollutant in municipal, industrial, and agricultural wastewaters and is a key driver of eutrophication and aquatic ecosystem degradation. This review paper assessed the potential of water hyacinth (Eichhornia crassipes) as a sustainable phytoremediation option for removing ammoniacal nitrogen from wastewater. This paper focused on the plant’s biological characteristics, nutrient uptake pathways, and adaptability to varying environmental conditions. Specific mechanisms examined include direct root uptake of ammonium, internal translocation, and microbial-assisted nitrification and denitrification within the rhizosphere. The influence of pH, temperature, salinity, retention time, and plant density on removal efficiency was also assessed in this study. Across laboratory, pilot, and field-scale studies, water hyacinth achieved ammoniacal nitrogen removal efficiencies ranging from 74% to 97% under favorable conditions, alongside significant reductions in biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total dissolved solids (TDS). Integration with constructed wetlands, microbial systems, and hybrid treatment approaches further enhanced nitrogen removal and process stability. This paper also highlighted opportunities for biomass valorization through biogas, bioethanol, and compost production while identifying challenges related to salinity sensitivity and biomass management. Overall, water hyacinth emerges as a cost-effective, nature-based solution for decentralized wastewater treatment, with strong potential to support sustainable water management and circular bioeconomy initiatives. Full article

Developed by Marais and Rabinowitz, the A²/O process is a pivotal biotechnology for biological nitrogen and phosphorus removal, developed by optimizing the five-stage Phoredox protocol. Renowned for its efficient configuration and straightforward operation, it has been extensively adopted in municipal and industrial wastewater treatment projects globally, including numerous facilities in China. However, the conventional A²/O process faces inherent operational challenges: the conflicting SRT requirements between autotrophic nitrifying bacteria (needing long SRT for stable nitrification) and PAOs, intense competition for carbon sources among PAOs and denitrifying bacteria, and the inhibitory effects of residual nitrate and DO on phosphorus release and denitrification. To address these issues, a range of optimization strategies has been developed, including SRT adjustment, carbon source distribution optimization, the integration of biofilm carriers, the addition of external carbon sources, and innovative modified configurations such as the Reversed A²/O, JHB, UCT, and MUCT. These approaches synergistically mitigate nitrate interference and enhance nutrient removal efficiency by decoupling microbial SRT demands, supplementing readily biodegradable carbon sources, and optimizing hydraulic flow paths. Future research should focus on deepening the understanding of the metabolic mechanisms underlying nitrogen and phosphorus removal, developing sustainable and efficient external carbon source systems, refining multi-mode reactor design for engineering scalability, optimizing combined processes for ultra-low C/N ratio wastewater treatment, and advancing low-temperature adaptation technologies. These efforts aim to further improve the process’s efficacy, stability, and sustainability, enabling it to meet increasingly stringent environmental discharge standards. Full article

Based on a bibliometric analysis of 2680 publications (1962–2024), this study elucidates the knowledge structure and intellectual evolution of research on climate change-driven nitrogen migration and transformation in inland waters, a critical issue for water security and global climate stability. The field has experienced accelerated growth since 2016, led by the United States and China. Analysis reveals a research framework centered on climate change, nitrogen, and water quality, interconnected with processes like eutrophication and denitrification. The intellectual focus has evolved from early investigations into fundamental chemical mechanisms towards a contemporary emphasis on human–climate interactions (e.g., land use), model-based predictions, and regional management solutions for nonpoint source pollution. A key finding is the bidirectional climate–nitrogen feedback, where climate alters nitrogen pathways and transformations, which in turn release greenhouse gases. The findings underscore a pivotal shift from theoretical understanding to applied, solution-oriented research. Future work must prioritize integrated multi-technique approaches, cross-ecosystem comparisons, and data-driven modeling to advance predictive capabilities and support effective nitrogen management in inland waters under a changing climate. Full article

Research on heterotrophic bioflocs is extensive, whereas investigations into autotrophic bioflocs remain limited. This study established an in situ autotrophic biofloc (ABF) system for intensive Pacific white shrimp (Penaeus vannamei) farming, aiming for zero water exchange and optimized water quality. A 120-day indoor experiment tested three stocking densities (300 (T1), 250 (T2), and 200 shrimp per m³ (T3)) with no water exchange. Water quality was monitored every two days, and bacterial communities were analyzed on days 10 and 70. The results indicated that ABF maturation was achieved by day 70 across all treatments, marked by three key indicators: (1) synchronous declines in nitrite and nitrate concentrations; (2) concurrent decreases in pH and total alkalinity approaching maturation; and (3) sustained high nitrogen removal efficiency (nitrite < 0.7 mg/L, ammonia < 0.6 mg/L). All density groups displayed similar patterns in both water quality dynamics and microbial community evolution. Bacterial analysis revealed that dominant genera such as Ruegeria, Bacillus, Muricauda, SM1A02, and Nitrospira played critical roles in toxic nitrogen removal, while pathogenic Klebsiella and Vibrio significantly decreased post-maturation. Heterotrophic nitrification and aerobic denitrification microorganisms (HNADMs) were identified as potentially responsible for nitrite accumulation. Nitrite accumulation was found in all groups. T2 and T3 achieved satisfactory breeding performance despite pre-maturation nitrate peaks exceeding 40 mg/L, whereas T1 suffered a low survival rate (27.47%) due to severe nitrite accumulation (>50 mg/L). A biofloc volume (BFV) of 4–8 mL/L effectively managed daily feed inputs of 75–110 g/m³. These findings lay a theoretical and technical foundation for the application of in situ ABF cultivation in intensive farming and enhance the sustainability of aquaculture. Full article