A review of research progress of heterotrophic nitrification and aerobic denitrification microorganisms (HNADMs)

Integration of steel slag and zeolite enhances simultaneous nitrification and autotrophic denitrification in ultra-low carbon/nitrogen ratio wastewater: Remodeling microbiota and iron metabolism

Constructed wetlands (CWs) are widely used for nitrogen pollution control in rural aquatic environments, yet their nitrogen removal efficiency often remains suboptimal. This study firstly examines how zeolite robustly stimulates Fe-utilization of steelmaking waste (i.e., steel slag) to improve nitrification and autotrophic denitrification of low carbon-to-nitrogen (C/N) ratio wastewater (C/N ≈ 1). Steel slag, by providing alkalinity for nitrification, also serves as an electron donor for denitrification due to its low-valent iron content. As a result, the total nitrogen (TN) removal efficiency was increased by 153.5% compared to the control group. Zeolite reshaped the microbial consortia, enriching iron autotrophic denitrifying bacteria and aerobic denitrifying bacteria. More importantly, zeolite facilitated microbial iron utilization by enhancing transmembrane iron transport and intracellular iron oxidation to boost nitrification and autotrophic denitrification without additional aeration, external carbon sources, or pH regulation. Our work advances understanding the development of low carbon technologies for wastewater nitrogen removal.

Molecular identification of heterotrophic nitrification and aerobic denitrification bacteria: From methods development to application demonstration

Although heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria, a novel functional group involved in nitrogen conversion, have been isolated and characterized, the lack of specific molecular markers for identification severely limits the study of their role in geochemical cycling and the contribution in ecosystems. Here, a set of molecular markers was developed for the rapid identification of HN-AD bacteria, via delving into the genomics and transcriptomics of a HN-AD isolate (Pseudomonas aeruginosa SNDPR-01). Among the nine candidate genes that were significantly expressed during heterotrophic nitrification, three were involved in the conversion of hydroxylamine to nitrite, a characteristic process of HN-AD. The universality and stability of the identification methods based on the gene primer set were validated using pure HN-AD strains, mixed cultures of pure HN-AD strains, and activated sludge from laboratory-scale and real wastewater treatment plants. In all cases, the amplification outcome was positively correlated with the function and population of HN-AD bacteria, demonstrating its validity as a molecular marker. This study supports the paradigm of heterotrophic nitrification from hydroxylamine to nitrite. As an effective tool for the identification of classic HN-AD bacteria, this study lays the groundwork for research on environmental ecology and biotechnological application of HN-AD bacteria.

Comprehensive revealing the destructive effect and inhibitory mechanism of oxytetracycline on aerobic denitrification bacteria Acinetobacter sp. AD1 based on cell state, electron behavior and intracellular environment

The wide application and low utilization rate of oxytetracycline (OTC) make it often detected in wastewater, which may cause harmful effects on microbial denitrification. Aerobic denitrification (AD) as a new microbial denitrification technology has obvious advantages. However, systematic studies on the effects of OTC on it are lacking. In this study, the effect of OTC on AD was comprehensively explored from multiple perspectives, the main results are as follows. From the perspective of bacterial performance, OTC inhibited AD bacteria growth, denitrification efficiency, and caused serious damage to cell morphological structure, results of CCK-8 confirmed that bacterial activity was significantly affected. From the perspective of electron behavior, OTC decreased electron-producing capacity of carbon metabolism, reduced activity of the electron transport system, inhibited the electron consumption of NAR and NIR to varying degrees, thus increased the risk of nitrite accumulation. From the perspective of intracellular environment, OTC broke redox balance and antioxidant mechanism, related carbon and nitrogen cycle functional genes were down-regulated, affected amino acid, organic acid and nucleotide metabolic processes. The above results provide important information for evaluating the potential risks of antibiotics on the application of AD, and provide key background and theoretical support for stabilizing the technology.

Evaluation of nitrogen removal performance and metabolic mechanism of a novel salt-tolerant strain Pseudomonas aeruginosa SH3

High salinity impedes efficient nitrogen removal from mariculture wastewater, which inhibits the colonization and nitrogen removal capabilities of nitrogen-removing microbes. This study aimed to isolate and characterize a salt-tolerant heterotrophic nitrification-aerobic denitrification bacterial strain. We evaluated 30 bacterial strains isolated from Portunus trituberculatus aquaculture ponds, among which Pseudomonas aeruginosa SH3 exhibited superior nitrogen removal efficiencies (99 % of NH4+-N, 71 % of NO2--N, and 85 % fof NO3--N at a salinity of 30 ‰) than the other strains. Single-factor experiments demonstrated that SH3 effectively removed either NH4+-N or NO2--N across various C/N ratios (10-20), pH levels (7-9), salinity levels (15-35 ‰), and temperatures (25-35 °C), highlighting its promising nitrogen removal capabilities under conditions suitable for mariculture. Genomic analysis showed that SH3 removes NH4+-N through ammonia assimilation and nitrification and converts NO2--N and NO3--N via denitrification and assimilatory nitrate reduction. Bioaugmentation with SH3 reduced the startup period by 14 d, addressing a common challenge of prolonged startup times in a moving-bed biofilm reactor used for nitrogen removal in marine recirculating aquaculture systems. Meanwhile, bioaugmentation maintained minimal fluctuations in nitrogen levels throughout the operational period, resulting in consistently low concentrations of NO2--N and NH4+-N, both below 1 mg/L. Therefore, strain SH3 exhibits robust nitrogen removal capabilities, demonstrating its practicality and reliability in mariculture wastewater treatment along with providing robust data support for industrial-scale applications.

Effect of hydraulic retention time on the nitrogen removal performance of pure biofilm rotating biological contactor system inoculated with heterotrophic nitrification-aerobic denitrification bacteria and its corresponding mechanism

The traditional activated sludge biofilm system struggles with poor removal performance and long hydraulic retention time (HRT) in treating high ammonia nitrogen (NH4+-N) wastewater. To solve these problems, this study introduced a pure heterotrophic nitrification-aerobic denitrification (HN-AD) biofilm system which HN-AD bacteria were inoculated in the rotating biological contactor (PH-RBC), with free microorganisms discharged after biofilm formation. Under short HRT (12 h), PH-RBC exhibited 29.23 % and 31.03 % higher NH4+-N and total nitrogen (TN) removal than pure activated sludge biofilm RBC (PS-RBC) (the influent NH4+-N was 505 ± 45 mg/L). Flavobacterium and Azoarcus were crucial for nitrogen removal in the PH-RBC. Metabolic analysis revealed that genes CS and IDH3 are crucial for carbon metabolism, with dissimilatory nitrate reduction dominates nitrogen metabolism. Bugbase prediction indicated that decreasing HRT increased the presence of Potentially Pathogenic. This study provides a theoretical basis for using pure biofilm system in high NH4+-N wastewater treatment.

Removal of antibiotic resistance from wastewater in aquatic ecosystems dominated by submerged macrophytes

Submerged macrophytes in constructed wetlands (CWs) can effectively improve wastewater quality. However, the effectiveness of different submerged macrophytes in removing antibiotic-resistant genes (ARGs) from wastewater remains unexplored. Additionally, wastewater loading in wetlands can fluctuate due to climate change, potentially affecting ARG removal efficiency. In this study, we systematically constructed microscale wetlands using three submerged plants: Vallisneria natans (VN), Sagittaria pygmaea (SP), and Myriophyllum spicatum (MS). Their effectiveness in ARGs removal was analyzed at hydraulic retention times (HRTs) of 0, 3, 6, and 9 days under high (HWL) and low (LWL) wastewater loading. The results indicated that under LWL conditions, all ecosystems exhibited a higher reduction rate of ARG diversity and relative abundance (RS) compared to HWL conditions. The efficiency of all ecosystems in reducing ARG diversity and abundance followed the order: MS > VN > SP. The sul resistance gene exhibited the highest RS and was degraded most rapidly in all samples. Additionally, sulfadimidine concentrations significantly decreased under LWL conditions, which was significantly correlated with sul reduction. Chemical oxygen demand, total phosphorus, total nitrogen, ammonium nitrogen, and nitrate nitrogen were identified as key factors influencing bacterial and ARG profiles. The increase in rhizobial bacteria and decrease in aerobic denitrifying bacteria likely contributed significantly to ARGs removal. This study offers new insights into ARG removal by submerged macrophytes in CWs, emphasizing the role of wastewater loading and the potential of MS in enhancing ARG degradation. These findings enhance CW design and management to mitigate ARG contamination in wastewater.

Enhanced removal of nitrate, copper, and bisphenol A from immobilized bioreactors by exogenous acyl homoserine lactones-6 (AHLs-6) and iron-cobalt modified biochar

Currently, treating industrial wastewater with complex components and difficult-to-degrade pollutants has become a focal point for research. In this study, sodium alginate (SA), polyvinyl alcohol (PVA), and shell powder (SP) were used as a carrier backbone to embed ferric cobalt-modified biochar (FCBC), exogenous acyl homoserine lactone-6 (AHLs-6), and the salt-tolerant strain Stutzerimonas sp. ZW5, resulting in the preparation of immobilized microbial carriers. Experimental results demonstrated that, under optimal operating conditions, the bioreactor achieved removal efficiencies of 97.11 % for nitrate (NO3--N), 81.20 % for calcium (Ca2+), 93.22 % for chemical oxygen demand (COD), 91.05 % for phosphorus (PO43--P), 98.57 % for copper (Cu2+), and 96.16 % for bisphenol A (BPA). The rough surface and numerous functional groups of the reactor packing effectively adsorbed BPA and Cu2+, thereby reducing the inhibitory effects of these pollutants on microbial metabolic activity. In addition, FCBC provides mass transfer channels and active sites to enhance electron transfer. The introduction of exogenous AHLs-6 markedly increased the abundance of functional microbial communities and the activity of key enzymes by regulating microbial metabolism, thus improving the removal efficiency of complex pollutants. This research offers new perspectives on treating complex industrial wastewater.

Nitrite impairs bioreactor performance due to decreased replication of Candidatus Brocadia sapporoensis by unbalanced energy allocation

The effects of nitrite on anammox activities have been extensively studied. However, the molecular mechanisms of specific microorganisms responding to nitrite in anammox systems remain unexplored. This study investigates how excessive nitrite affects the core metabolisms of AnAOB and symbiotic bacteria, further elucidating the mechanisms by which it regulates microbial growth and nitrogen removal performance. Specifically, the nitrogen removal process in a continuous-flow anammox membrane bioreactor collapsed when the nitrite concentration reached 243 mg N/L. Integrated meta-omics analyses demonstrated that excessive nitrite disrupted the energy metabolism of Ca. Brocadia sapporoensis (AMXB1), reducing the energy available for developing tolerance. Subsequently, it disrupted cell replication by impairing the biosynthesis process of AMXB1, particularly DNA replication and the formation of vital cell structures such as the cell membrane and cell wall, as well as the cellular protection system, leading to the collapse of the anammox system. Additionally, the cross-feeding of amino acids and cofactors between AMXB1 and symbiotic bacteria plays an important role in the recovery of nitrogen removal performance of anammox consortia after nitrite inhibition. The findings provide a novel strategy and direction for improving the tolerance and resilience of anammox consortia in engineered ecosystems.

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.

Acclimation Time Enhances Adaptation of Heterotrophic Nitrifying-Aerobic Denitrifying Microflora to Linear Anionic Surfactant Stress

Linear anionic surfactants (LAS) pose significant stress to microbial denitrification in wastewater treatment. This study investigated the performance and adaptation mechanisms of heterotrophic nitrification-aerobic denitrification (HN-AD) microbial consortia under LAS exposure after short-term (SCM, 2 months) and long-term (LCM, 6 months) acclimation. Results showed a dose-dependent inhibition of total nitrogen (TN) removal, with LCM achieving 97.40% TN removal under 300 mg/L LAS, which was 16.89% higher than SCM. Biochemical assays indicated that LCM exhibited lower reactive oxygen species (ROS) levels, a higher ATP content, and reduced LDH release, suggesting enhanced oxidative stress resistance and membrane stability. EPS secretion also increased in LCM, contributing to environmental tolerance. Metagenomic analysis revealed that long-term acclimation enriched key genera including Pseudomonas, Aeromonas, and Stutzerimonas, which maintained higher expression of denitrification (e.g., nosZ, nirS) and ammonium assimilation genes (glnA, gltB). Although high LAS concentrations reduced overall community diversity and led to convergence between SCM and LCM structures, LCM retained greater functional capacity and stress resistance. These findings underscore the importance of acclimation in sustaining denitrification performance under surfactant pressure and offer valuable insights for engineering robust microbial consortia in complex wastewater environments.

Impacts of sulfamethoxazole on heterotrophic nitrification-aerobic denitrification bacteria and its response strategies: Insights from physiology to proteomics

The effects of sulfonamide antibiotics on heterotrophic nitrification-aerobic denitrification (HN-AD) and the response mechanisms of HN-AD bacteria are not fully understood. This study investigated the physiological changes and proteomic responses of the HN-AD bacteria Pseudomonas stutzeri (P. stutzeri) under varying concentrations of sulfamethoxazole (SMX). Results indicated that SMX inhibited the growth and HN-AD performance of P. stutzeri in a concentration-dependent manner. SMX exposure led to decreased motility, reduced electron transfer system activity, and diminished activities of key denitrifying enzymes, accompanied by increased levels of intracellular reactive oxygen species and compromised cell membrane integrity. Additionally, the production of extracellular polymeric substances and self-aggregation ability of P. stutzeri initially increased and then decreased with rising SMX concentrations. Proteomic analysis revealed that SMX primarily suppressed pathways involved in bacterial chemotaxis, ABC transporters, two-component systems, fatty acid metabolism, and nitrogen metabolism. In response, P. stutzeri upregulated pathways associated with starch and sucrose metabolism, carotenoid biosynthesis, styrene degradation, O-antigen nucleotide sugar biosynthesis, and the pentose phosphate pathway. These findings provide insights into the effects of sulfonamide antibiotics on HN-AD bacteria and their response mechanisms, offering references for the application of HN-AD processes in treating antibiotic-containing wastewater.

Enrichment of a heterotrophic nitrifying and aerobic denitrifying bacterial consortium: Microbial community succession and nitrogen removal characteristics and mechanisms

This study cultivated a bacterial consortium (S60) from landfill leachate that exhibited effective heterotrophic nitrification and aerobic denitrification (HN-AD) properties. Under aerobic conditions, the removal of NH4+-N reached 100 % when the S60 consortium utilised NH4+-N either as the sole nitrogen source or in combination with NO2--N and NO3--N. Optimal HN-AD performance was achieved with sodium acetate as a carbon source and a pH of 7.0-8.0, dissolved oxygen concentration of 4.0-5.0 mg/L, and a C/N ratio of 10. Furthermore, the presence of functional genes (amoA, hao, napA, nirK, nirS, nosZ), hydroxylamine oxidase, nitrate reductase, and nitrite reductase was confirmed in the S60 consortium. Drawing from these findings, two HN-AD pathways were delineated: NH4+-N → NH2OH → NO2--N → NO3--N → NO2--N → NO → N2O → N2 and NH4+-N → NH2OH → N2O → N2. Metagenomic binning analysis of the S60 consortium uncovered complete pathways for dissimilatory nitrate reduction and denitrification within Halomonas, Zobellella, Stutzerimonas, Marinobacter, and Pannonibacter. These findings offer new insights into the application of HN-AD bacteria and their collaborative nitrogen removal in environments with varying nitrogen sources.

Enhancement of aerobic denitrification process on antibiotics removal: Mechanism and efficiency: A review

Traditionally, the removal of nitrogenous pollutants from wastewater relied on conventional anaerobic denitrification as well as aerobic nitrification and anoxic denitrification. However, anaerobic denitrification is complicated since it requires stringent environmental conditions as well as a large land, therefore, denitrification and nitrification were performed in two separate reactors. Although high pollutant removal efficiency has been achieved via aerobic nitrification and anoxic denitrification, the demerits of this approach include high operational costs. Other traditional nitrogen removal methods include air stripping, reverse osmosis, adsorption, ion exchange, chemical precipitation, advanced oxidation process, and breakpoint chlorination. Traditional nitrogen removal methods are not only complicated but they are also uneconomical due to the high operational costs. Researchers have discovered that denitrification can be carried out by heterotrophic nitrification-aerobic denitrification (HNAD) microorganisms which remove nitrogen in a single aerobic reactor that does not require stringent operating conditions. Despite the significant effort that researchers have put in, there is still little information known about the mechanisms of antibiotic removal during HNAD. This review begins with an update on the current state of knowledge on the removal of nitrogenous pollutants and antibiotics from wastewater by HNAD. The mechanisms of antibiotic removal via HNAD were examined in detail. Followed by, the enhancement of antibiotics removal via co-metabolism and oxidation of sulfamethoxazole (SMX) as well as the response of microbial communities to antibiotic toxicity. Lastly, the conditions favorable for antibiotic biodegradation and mechanisms for nitrogen removal via HNAD were examined. The findings in this review show that co-metabolism and oxidation of SMX were the main antibiotic biodegradation mechanisms, pathways for antibiotic removal by co-metabolism and oxidation of SMX were also proposed in the discussion. This research indicated the potential of aerobic denitrification in the removal of antibiotics from wastewater. Understanding the mechanisms and pathways of antibiotic removal by HNAD helps wastewater engineers and researchers apply the technology more efficiently. PRACTITIONER POINTS: The mechanisms of antibiotic removal via HNAD were examined in detail. Co-metabolism and oxidation of SMX were the main antibiotic biodegradation mechanisms. Pathways for antibiotic removal by co-metabolism and oxidation of SMX were also proposed. Conditions favorable for antibiotic biodegradation were examined. This research indicated the potential of aerobic denitrification in the removal of antibiotics from wastewater.

Effective denitrification from landfill leachate using magnetic PVA/CMC/DE carrier immobilized microorganisms

Ammonia nitrogen (NH4+-N) discharge has caused eutrophication of water bodies and harm to humans and organisms. In this work, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), diatomite (DE), and Fe3O4 were used to prepare magnetic immobilized carriers by encapsulating microorganisms for the treatment of NH4+-N wastewater. The response surface methodology was used to explore the optimal ratio of the immobilized carriers. The obtained optimal raw material ratio was 99.10 %. The obtained carriers are spherical (4-5 mm in diameter) with a rich honeycombed pore structure. The magnetic carrier improves the ammonia oxidation activity, and the carrier achieved 99.0 % of NH4+-N and 86.7 % of total nitrogen (TN) removal rates from the simulated wastewater (NH4+-N concentration: 300 mg/L) through nitrification and denitrification under aerobic conditions. Upon applied for a 60 days' treatment of landfill leachate (NH4+-N concentration of 300 mg/L), the daily removal rates for NH4+-N and TN reached 93.7 % and 78.3 %, respectively. The analysis of the microbial community showed that the abundances of heterotrophic nitrifying-aerobic denitrifying bacteria including Enterobacter, Pseudomonas, and Bacillus increased with prolonging treatment days, which accelerated nitrification and denitrification, consequently promoting the nitrogen removal effect.

Impact of carbon/nitrogen ratio on sequencing batch biofilm reactors initiated with different seed sludges for treating actual mariculture effluents

The impact of carbon/nitrogen (C/N) ratio on sequencing batch biofilm reactor (SBBR) initiated with different seed sludges for treating actual mariculture effluent was explored. Increasing the C/N ratio significantly enhanced the nitrogen removal efficiency, achieving average removal efficiency of 95% for ammonia nitrogen and 73% for total nitrogen at ratio of 30, while the impact of seed sludge was minimal. High C/N ratio promoted the secretion of tightly bound extracellular polymeric substances (TB-EPS), which showed significant correlation with nitrogen removal. Interactions between bacteria and archaea were enhanced and conditionally rare or abundant taxa were the keystone taxa. High C/N ratio inhibited the relative abundance of ammonia-oxidizing archaea (Candidatus_Nitrosopumilus) and bacteria (Nitrosomonas), but promoted the heterotrophic nitrification-aerobic denitrification bacteria (Halomonas). The expression of nitrogen removal functional genes significantly correlated with functional genera. This study emphasized the crucial role of high C/N ratios in biological nitrogen removal from actual mariculture effluent.

Synchronous control of nitrogen and phosphorus release from sediments in shallow lakes under wind disturbance by modified zeolite and Ca/Al-based sludge combination

To inhibit eutrophication caused by endogenous pollutants release, the experiment explored the efficiency and mechanism of the synchronous control of nitrogen (N) and phosphorus (P) release from sediments in shallow lakes under wind disturbance by modified Ca/Al-based sludge (MS) and modified zeolite (MZ). High-temperature calcination and NaCl impregnation increased the pore volume of MS and Na+ content of MZ, and the adsorption capacity of MS for PO43--P and MZ for NH4+-N was as high as 42.01 and 20.28 mg g-1. The results of a 90-day incubation experiment showed that the addition of MS and MZ increased the abundance of Thauera, Nitrospira, Denitratisoma, and Clostridium, while decreasing the proportion of Proteus Hauser and Saccharimonadales, thereby reducing the active N and P contents in sediments through microbial transformation. At the same time, the efficient adsorption performance of the MS and MZ resulted in a significant decrease in pollutants in the interstitial water and sediments. In addition, sediment resuspension caused by wind disturbance increased the contact between sediments and remediation agents, resulting in the action depth of covering materials exceeding 100 mm. Compared to adding MS or MZ alone, the combination of the two (MSZG) could synchronously, efficiently, and stably inhibit N and P release. Under the coupling effects of physical interception, physicochemical adsorption, and biotransformation, the average TN, NH4+-N, TP, and PO43--P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants.

Feedstock optimization with low carbon to nitrogen ratio during algal sludge aerobic composting: Quality and gaseous emissions

This study investigated compost quality and gaseous emissions during the algal sludge composting. The experiment explored the feasibility of low initial carbon to nitrogen (C/N) ratio composting by using different volume ratios of algal sludge and spent mushroom substrates (1:1, 1:2, 1:3, and 1:4, corresponding to C/N ratios of 9.5, 12.3, 14.6, 16.0, respectively). The results showed that increasing the proportion of algal sludge in the initial material led to a longer maturation time and higher nitrogen losses but also enhanced the mineralization of organic nitrogen (converted to NH4+ and NO3-) and reduced carbon losses. The addition of carbon-rich bulking agents within a certain range improved the diversity and interactions of bacterial communities during algal sludge composting. In conclusion, considering the nitrogen and carbon lost, retained, and made available across the four treatments, treatment 3 (C/N = 14.6) appears to be the optimal choice for low C/N composting.

Pollutant removal and greenhouse gas emissions in horizontal subsurface flow constructed wetlands with iron ore treating ammonium-rich wastewater

Horizontal subsurface flow constructed wetlands (HFCWs) are capable of eliminating organic matter and nitrogen while emitting less methane (CH4) and nitrous oxide (N2O) than free water surface flow wetlands. However, the simultaneous removal of pollutants and reduction of greenhouse gases (GHG) emissions from high-strength wastewater containing high levels of organic matter and ammonium nitrogen (NH4+-N) has not get been investigated. The influent COD concentration affected the efficiency of nitrogen removal, GHG emissions and the presence of iron from iron ore, but the COD and TP removal efficiencies remained unaffected. CO2 and CH4 fluxes were significantly influenced by influent COD concentrations, whereas less N2O emissions were obtained during 7d. The highest CO2 and CH4 fluxes, along with the GHG emissions, were observed in HFCWs with COD concentrations of 375.6 mg/L and NH4+-N concentrations of 159.0 mg/L at a COD/N ratio of 2.4. Conversely, the lowest CH4 (-1.72 mg/m2/h) and N2O fluxes (0.13 mg/m2/h) were recorded in HFCWs with COD concentrations of 375.6 mg/L and NH4+-N concentrations of 162.4 mg/L at a COD/N of 4.5, although nitrogen removal was weak in these HFCWs. HFCWs at a COD/N ratio of 3.6 exhibited greater removal of nitrogen and other pollutants, along with a lower global warming potential (GWP). In conclusion, the concentrations of organic matter and NH4+-N in wastewater affected both pollutant removal and GHG emissions. The simultaneous enhancement of pollutant removal and the reduction of GHG emissions can be achieved in HFCWs with a COD/N ratio of 3.6.

The simultaneous addition of chitosan and peat enhanced the removals of antibiotics resistance genes during biogas residues composting

Direct reuse of biogas residue (BR) has the potential to contribute to the dissemination of antibiotic resistance genes (ARGs). Although high-temperature composting has been demonstrated as an effective method for the harmless treatment of organic waste, there is few researches on the fate of ARGs in high-temperature composting of BR. This research examined the impact of adding 5% chitosan and 15% peat on physicochemical characteristics, microbial communities, and removal of ARGs during BR-straw composting in 12 Biolan 220L composters for 48 days. Our results showed that the simultaneous addition of chitosan and peat extended the high-temperature period, and increased the highest temperature to 74 °C and germination index. These effects could be attributed to the presence of thermophilic cellulose-decomposing genera (Thermomyces and Thermobifida). Although the microbial communities differed compositionally among temperature stages, their dissimilarity drastically reduced at final stage, indicating that the impact of different treatments on microbial community composition decreases at the end of composting. Peat had a greater impact on aerobic genera capable of cellulose degradation at thermophilic stage than chitosan. Surprisingly, despite the total copy number of ARGs significantly decreased during composting, especially in the treatment with both chitosan and peat, intl1 gene abundance significantly increased 2 logs at thermophilic stage and maintained high level in the final compost, suggesting there is still a potential risk of transmission and proliferation of ARGs. Our work shed some lights on the development of waste resource utilization and emerging contaminants removal technology.

Activation of algicidal bacteria and nitrogen-phosphorus removal bacteria during controlling cyanobacteria bloom in Taihu lake by artemisinin algaecide

Cyanobacterial harmful algal blooms (CyanoHABs) in Taihu Lake pose a persistent environmental challenge. This study investigated the inhibitory effects of artemisinin algaecide (AMA) on cyanobacteria in Taihu Lake and assessed its impact on nutrients, as well as the structures of particle-attached (PA) and free-living (FL) bacterial communities and potential ecological mechanisms. The results indicated that A-3 (0.8 g artemisinin/L) effectively inhibited CyanoHABs (inhibition rate = 93 %) and significantly increased the alpha diversity of PA and FL bacterial communities during the stationary phase， thereby promoting the proliferation of algicidal bacteria (AB) (e.g., Acinetobacter, Stenotrophomonas, and Exiguobacterium) and heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria (e.g., Acinetobacter, Stenotrophomonas, and Bacillus) through the utilization of dissolved organic carbon (DOC) from the dead cyanobacteria. This proliferation enhanced nitrogen metabolism and increased the abundance of nitrogen-cycling functional genes, improving nutrient cycling and enhancing system stability. The increased abundance of AB continuously suppressed cyanobacteria, while the proliferation of HN-AD bacteria removed nitrogen and phosphorus from the water, thus limiting nutrients available for cyanobacterial growth. Our findings demonstrate that AMA effectively inhibits CyanoHABs and prevents secondary blooms, providing a scientific foundation for the widespread application in cyanobacterial management, enhancing the effectiveness and sustainability of CyanoHAB control efforts.

Efficient strategy for employing HN-AD bacterium enhanced biofilter reactors to remove NH3 and reduce secondary pollution

Heterotrophic nitrification-aerobic denitrification (HN-AD) strain (Paracoccus denitrificans HY-1) was employed in this study to enhance the removal efficiency of NH3 in a biological trickling filter (BTF) reactor. The results demonstrated that inoculation with HY-1 and packed with bamboo charcoal as filler significantly improved the RE of NH3 in BTF, reaching 96.52 % under 27 s of empty bed residence time (EBRT) and 812.56 ppm of inlet gas concentration. Meanwhile, the titer of NH4+-N, NO2--N, and NO3--N in the circulating fluid were merely 8.52 mg/L, 5.14 mg/L, and 18.07 mg/L, respectively. Microbial community and metabolism analyses revealed that HY-1 have successfully colonized in the BTF, and the high expression of denitrification-related genes (nar, nap, nir, nor and nos) further confirmed that the inoculation of HY-1 greatly improved both nitrification and denitrification metabolism. Furthermore, the biofilter reactor inoculated with HY-1 was applied at a large-scale piggery and exhibited remarkable odor removal effect, in which 99.61 % of NH3 and 96.63 % of H2S were completely eliminated. In general, the HN-AD bacterium could strengthen the performance of BTF reactor and reduce the secondary pollution of circulating fluid during bio-deodorization.

A novel Zobellella endophytica W14 strain for nitrogen removal from hypersaline wastewater through simultaneous nitrification and denitrification

To address the challenges associated with biological treatment of high-salinity wastewater, a novel salt-tolerant strain, Zobellella endophytica W14, was isolated. This strain exhibited heterotrophic nitrification-aerobic denitrification (HN-AD) capabilities. Strain W14 could grow and remove ammonium in high-salinity environments with salinity levels ranging from 0 to 11% (w/v). At 5% salinity, strain W14 demonstrated high removal efficiencies for nitrite, ammonium, and nitrate (100%, 99.58%, and 98.85%, respectively), when these compounds were provided as the single source of nitrogen. In cases of mixed nitrogen sources, total nitrogen removal efficiency of strain reached 95.22%. The nitrogen balance analysis confirmed the utilization of nitrogen sources by strain W14 through both assimilation and dissimilation. Through the amplification of functional genes involved in nitrogen metabolism (i.e., hao, napA, nirS, and nosZ), the nitrogen metabolism pathway of strain W14 was predicted to be: NH₄⁺ → NH₂OH → NO₂⁻ → NO₃⁻ → NO₂⁻ → NO → N₂O → N₂. The study reveals that the novel W14 strain can efficiently remove total nitrogen from high-salinity wastewater and has significant potential for biological treatment of such wastewater.

Enhanced nutrients removal from low C/N ratio rural sewage by embedding heterotrophic nitrifying bacteria and activated alumina in a tidal flow constructed wetland

Rural sewage treatment facilitates nitrogen and phosphorus removal yet can be costly. To address this challenge, a cost-effective embedding material mainly consisting of heterotrophic nitrifying bacteria, activated alumina (AA), and a solid carbon source (HPMC) was applied to a tidal flow constructed wetlands (TFCWs); aimed at stable nitrogen and phosphorus removal under low carbon-to-nitrogen (C/N) ratios. The TFCWs could be shortened to 16 d of startup duration time compared with the control group; and improved the ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) removal efficiencies to 98 %, 93 %, and 68 %, respectively. Also, effluent NH4+-N, TN, and TP in the enhanced TFCWs could be stable at 0.52 ± 0.18, 1.23 ± 0.45, and 0.75 ± 0.25 mg/L, respectively. Microbial community analysis revealed that AA and HPMC were enriched Pseudomonas sp., which potentially accelerated the NH4+-N assimilation pathway and phosphate biological removal. Embedding materials-TFCWs can provide new solutions for integrated rural sewage technology.

Fulvic acid mediated highly efficient heterotrophic nitrification-aerobic denitrification by Paracoccus denitrificans XW11 with reduced C/N ratio

Reducing the C/N ratio requirements for heterotrophic nitrification-aerobic denitrification (HNAD) is crucial for its practical application; however, it remains underexplored. In this study, a highly efficient HNAD bacterium, Paracoccus denitrificans XW11, was isolated. The HNAD characteristics of XW11 were studied, and the redox mediator fulvic acid (FA) was used to reduce the C/N requirements. Whole-genome sequencing revealed multiple denitrification genes in XW11; however, nitrification genes were not identified, because heterotrophic nitrification-related gene sequences were not included in the database. However, the nitrogen removal related enzyme activity test revealed complete nitrification and denitrification pathways. Reverse transcription PCR showed that the membrane-bound nitrate reductase (NarG), rather than the periplasmic nitrate reductase, was responsible for aerobic denitrification. The conventional nitrite reductase (NirS) also does not mediate nitrite denitrification. When the C/N ratio was 10, the ammonia removal efficiency of the Control was 71.71 % and the addition of FA increased it to 86.12 %. Transcriptomic analysis indicated electron flow from the carbon source to FA without proton transmembrane transport, and the presence of FA constructs another electron transfer system. The redox potential of oxidized FA/reduced FA is 0.3679 V, avoiding competition for electrons from Complex III. Thus, ammonia monooxygenase obtains electrons more easily, thereby promoting nitrification. The enzyme activity test of the nitrification process confirmed this view. In addition, NarG expression increased, and the denitrification process was enhanced. Overall, FA improved HNAD efficiency by facilitating electron transfer to the nitrogen dissimilation process, offering a novel approach to reduce the C/N requirement of HNAD.

Nitrate removal by a novel aerobic denitrifying Pelomonas puraquae WJ1 in oligotrophic condition: Performance and carbon source metabolism

Reducing nitrate contamination in drinking water has become a critical issue in urban water resource management. Here a novel oligotrophic aerobic denitrifying bacterium, Pelomonas puraquae WJ1, was isolated and purified from artificial lake sediments. For the first time, excellent aerobic denitrification capabilities were demonstrated. At a carbon-to‑nitrogen ratio of 5.0, strain WJ1 achieved 100.0 % nitrate removal and 84.92 % total nitrogen removal within 24 h, with no nitrite accumulation. PCR amplification and sequencing confirmed the presence of the denitrification genes napA, nirS, and nosZ in the strain. The nitrogen balance demonstrated that approximately 74.95 % of the initial nitrogen was eliminated as gaseous products under aerobic conditions. Furthermore, carbon balance analysis showed that most electron donors from strain WJ1 were directed towards oxygen, with limited availability for nitrate reduction. A combination of bio-ECO analysis and network modeling indicated that strain WJ1 has robust metabolic capabilities for diverse carbon sources and exhibits high adaptability to complex carbon environments. Overall, Pelomonas puraquae WJ1 removed approximately 45.89 % of the nitrates in raw water, demonstrating significant potential for practical applications in oligotrophic denitrification.

Efficient nitrogen removal by heterotrophic nitrification-aerobic denitrification yeast Candida boidinii L21: Performance, pathway and application

Efficient nitrogen removal yeasts are rarely encountered. Here, a heterotrophic nitrification-aerobic denitrification strain of Candida boidinii L21 was isolated. The optimal removal conditions for strain L21 were glucose as carbon source, C/N of 15, salinity of 10 ppt, pH of 7, shaking speed of 120 rpm, and temperature of 30 °C. Strain L21 removed NH4+-N, NO2--N, NO3--N (14---140 mg/L) and achieved nearly complete NO2--N, removal. Nitrogen balance and enzyme activity analysis indicated the nitrogen removal pathway of strain L21 through assimilation, nitrification, and denitrification pathways. When applied in wastewater and sludge, strain L21 reduced inorganic nitrogen levels within 4 days, with a 58-fold increase in nitrite removal compared to controls. These findings demonstrate that strain L21 holds great potential for enhancing nitrogen removal in wastewater treatment processes, providing valuable insights for improving environmental management practices.

Evaluation of agricultural non-point source pollution infiltration on clogging and nitrogen leaching effects in BRCs with different plants in dryland areas

As high-standard farmland rapidly expands, agricultural non-point source pollution has emerged as a main environmental issue in China. To tackle nitrogen pollution, green infrastructure (GI), especially bioretention cells (BRCs), has been extensively adopted. However, the long-term effectiveness of these systems may be hindered by clogging and nitrogen leaching. In this study, we designed three BRCs simulation devices to investigate the effects of different plants on the removal of TSS TN and NO3-N from runoff through simulated pollutant infiltration experiments. To address this issue, laboratory research has explored the contributions of woody plants like Buxus and herbaceous plants such as Ophiopogon in BRCs, concentrating on their impact on system clogging and nitrogen leaching. The results indicated that, although the total suspended solids (TSS) removal rates in the Buxus and Ophiopogon treatment groups were slightly lower than in the control group, permeability experienced a notable enhancement, with the Buxus group showing a 24.47% increase in permeability. The removal rates of TN and NO3-N in the Buxus group were significantly reduced, decreasing by 31.82% and 41.25%, respectively, in comparison to the control group. After five months, Ophiopogon demonstrated considerably better root growth, with its root length, volume, and surface area all significantly exceeding those of the Buxus group. The choice of plants significantly influenced nitrogen cycling and system clogging, with the reduced removal rates in the Buxus group potentially linked to its weaker root system, lower abundance of actinomycetes, and reduced soil enzyme activity.

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.

Enhanced anammox-mediated nitrogen removal in bioelectrochemical systems at prolonged negative electrode potentials

Bioelectrochemical anaerobic ammonium oxidation (anammox) systems allow eco-friendly removal of nitrogen from reject wastewater coming from biogas processing as the anammox bacteria have previously shown to have c-type cytochromes acting in the extracellular electron transport (EET) mechanism between the bacteria and electrode. The anammoxosome compartment present in anammox bacteria features a highly curved membrane and contains tubular structures along with electron-dense particles that contain iron, which could enhance the process of EET and enhance nitrogen removal by properly applied potentials. In this study, nitrogen removal was investigated in the electrostimulated anammox nitrogen removal (EANR) cells operated comparatively at open circuit and at applied potentials of - 300 mV, - 500 mV, and - 700 mV vs. Ag/AgCl. At peak performance (at - 700 mV vs. Ag/AgCl), the EANR showed up to 140% higher specific nitrogen removal rate (11.2 ± 0.3 g N/m2/day) compared to the control reactors without applied potential (8.3 ± 0.2 g N/m2/day). The microbial community on the cathode with the applied potential had a higher relative proportion of unclassified Candidatus Brocadia (7.5%) compared to inoculum (> 0.01%), in contrast to cathode without potential (0.74%) and control (0.2%). The EANR system demonstrated to achieve ammonium and nitrite removal efficiencies of 91% and 53%, respectively, during a 24-h test cycle from an initial TN concentration of ~ 100 mg N/L. After 150 h, it achieved complete removal of all nitrogen compounds, reaching a 100% removal efficiency. The EANR would be very useful in the establishment of field-scale bilateral anammox-bioelectrochemical technology combining microbial fuel cell bioanodes and EANR biocathodes for wastewater treatment.

Beyond Earth: Harnessing Marine Resources for Sustainable Space Colonization

The quest for sustainable space exploration and colonization is a challenge in its infancy, which faces scarcity of resources and an inhospitable environment. In recent years, advancements in space biotechnology have emerged as potential solutions to the hurdles of prolonged space habitation. Taking cues from the oceans, this review focuses on the sundry types of marine organisms and marine-derived chemicals that have the potential of sustaining life beyond planet Earth. It addresses how marine life, including algae, invertebrates, and microorganisms, may be useful in bioregenerative life support systems, food production, pharmaceuticals, radiation shielding, energy sources, materials, and other applications in space habitats. With the considerable and still unexplored potential of Earth's oceans that can be employed in developing space colonization, we allow ourselves to dream of the future where people can expand to other planets, not only surviving but prospering. Implementing the blend of marine and space sciences is a giant leap toward fulfilling man's age-long desire of conquering and colonizing space, making it the final frontier.

Genome-centric metagenomics provides insights into the core microbial community and functional profiles of biofloc aquaculture

Bioflocs are microbial aggregates that play a pivotal role in shaping animal health, gut microbiota, and water quality in biofloc technology (BFT)-based aquaculture systems. Despite the worldwide application of BFT in aquaculture industries, our comprehension of the community composition and functional potential of the floc-associated microbiota (FAB community; ≥3 µm size fractions) remains rudimentary. Here, we utilized genome-centric metagenomic approach to investigate the FAB community in shrimp aquaculture systems, resulting in the reconstruction of 520 metagenome-assembled genomes (MAGs) spanning both bacterial and archaeal domains. Taxonomic analysis identified Pseudomonadota and Bacteroidota as core community members, with approximately 93% of recovered MAGs unclassified at the species level, indicating a large uncharacterized phylogenetic diversity hidden in the FAB community. Functional annotation of these MAGs unveiled their complex carbohydrate-degrading potential and involvement in carbon, nitrogen, and sulfur metabolisms. Specifically, genomic evidence supported ammonium assimilation, autotrophic nitrification, denitrification, dissimilatory nitrate reduction to ammonia, thiosulfate oxidation, and sulfide oxidation pathways, suggesting the FAB community's versatility for both aerobic and anaerobic metabolisms. Conversely, genes associated with heterotrophic nitrification, anaerobic ammonium oxidation, assimilatory nitrate reduction, and sulfate reduction were undetected. Members of Rhodobacteraceae emerged as the most abundant and metabolically versatile taxa in this intriguing community. Our MAGs compendium is expected to expand the available genome collection from such underexplored aquaculture environments. By elucidating the microbial community structure and metabolic capabilities, this study provides valuable insights into the key biogeochemical processes occurring in biofloc aquacultures and the major microbial contributors driving these processes.

IMPORTANCE

Biofloc technology has emerged as a sustainable aquaculture approach, utilizing microbial aggregates (bioflocs) to improve water quality and animal health. However, the specific microbial taxa within this intriguing community responsible for these benefits are largely unknown. Compounding this challenge, many bacterial taxa resist laboratory cultivation, hindering taxonomic and genomic analyses. To address these gaps, we employed metagenomic binning approach to recover over 500 microbial genomes from floc-associated microbiota of biofloc aquaculture systems operating in South Korea and China. Through taxonomic and genomic analyses, we deciphered the functional gene content of diverse microbial taxa, shedding light on their potential roles in key biogeochemical processes like nitrogen and sulfur metabolisms. Notably, our findings underscore the taxa-specific contributions of microbes in aquaculture environments, particularly in complex carbon degradation and the removal of toxic substances like ammonia, nitrate, and sulfide.

Destabilization mechanisms of Semi-aerobic aged refuse biofilters under harsh treatment conditions: Evidence from fluorescence and microbial characteristics

Semi-aerobic aged refuse biofilters (SAARB) are commonly-used biotechnologies for treating landfill leachate. In actual operation, SAARB often faces harsh conditions characterized by high concentrations of chemical oxygen demand (COD) and Cl-, as well as a low carbon-to-nitrogen ratio (C/N), which can disrupt the microbial community within SAARB, leading to operational instability. Maintaining the stable operation of SAARB is crucial for the efficient treatment of landfill leachate. However, the destabilization mechanism of SAARB under harsh conditions remains unclear. To address this, the study simulated the operation of SAARB under three harsh conditions, namely, high COD loading (H-COD), high chloride ion (Cl-) concentration environment (H-Cl-), and low C/N ratio environment (L-C/N). The aim is to reveal the destabilization mechanism of SAARB under harsh conditions by analyzing the fluorescence characteristics of effluent DOM and the microbial community in aged refuse. The results indicate that three harsh conditions have different effects on SAARB. H-COD leads to the accumulation of proteins; H-Cl- impedes the reduction of nitrite nitrogen; L-C/N inhibits the degradation of humic substances. These outcomes are attributed to the specific effects of different factors on the microbial communities in different zones of SAARB. H-COD and L-C/N mainly affect the degradation of organic matter in aerobic zone, while H-Cl- primarily impedes the denitrification process in the anaerobic zone. The abnormal enrichment of Corynebacterium, Castellaniella, and Sporosarcina can indicate the instability of SAARB under three harsh conditions, respectively. To maintain the steady operation of SAARB, targeted acclimation of the microbial community in SAARB should be carried out to cope with potentially harsh operating conditions. Besides, timely mitigation of loads should be implemented when instability characteristics emerge, and carbon sources and electron donors should be provided to restore treatment performance effectively.

Nitrogen removal pathways in lake restoration using microalgal-bacterial granular sludge: Unraveling influence of organics and carbon to nitrogen ratio

This study investigated the performance of microalgal-bacterial granular sludge (MBGS) in the restoration of Qingling Lake and Huangjia Lake, focusing on nitrogen removal under varying water quality conditions. Significant color changes in MBGS and differences in granule characteristics were observed, with Qingling Lake demonstrating superior removal efficiencies for ammonia nitrogen, nitrate nitrogen, and total nitrogen compared to Huangjia Lake. Stoichiometric analysis revealed that when the chemical oxygen demand (COD) and carbon-to-nitrogen (C/N) ratios were less than 20 mg/L and 20, respectively, assimilatory nitrate reduction was positively correlated with both, whereas denitrification was negatively correlated. Gene function analysis showed that Qingling Lake had a more active microbial community supporting efficient nitrogen metabolism. The findings highlighted the enormous potential of MBGS in lake restoration, demonstrating its ability to adapt to different COD concentrations and C/N ratios by altering its nitrogen removal pathways.

Efficient nitrogen removal via simultaneous ammonium assimilation and heterotrophic denitrification of Paracoccus denitrificans R-1

Although diverse microorganisms can remove ammonium and nitrate simultaneously, their metabolic mechanisms are not well understood. Paracoccus denitrificans R-1 showed the maximal NH4 + removal rate 9.94 mg L-1·h-1 and 2.91 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. Analysis of the nitrogen balance calculation and isotope tracing experiment indicated that NH4 + was consumed through assimilation. The maximal NO3 - removal rate of strain R-1 was 18.05 and 19.76 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. The stoichiometric consumption ratio of acetate to nitrate was 0.902 and NO3 - was reduced to N2 for strain R-1 through 15NO3 - isotopic tracing experiment, which indicated a respiratory process coupled with the oxidation of electron donors. Genomic analysis showed that strain R-1 contained genes for ammonium assimilation and denitrification, which effectively promoted each other. These findings provide insights into microbial nitrogen transformation and facilitate the simultaneous removal of NH4 + and NO3 - in a single reactor.

Hormesis and synergistic effects of disinfectants chloroxylenol and benzethonium chloride on highly efficient heterotrophic nitrification-aerobic denitrification functional strain: From performance to mechanism

The heterotrophic nitrification-aerobic denitrification (HNAD) strain Exiguobacterium H1 (H1) was isolated in this study. The changes in nitrogen metabolism functions of H1 strain were discussed in presence of disinfectants chloroxylenol (PCMX) and benzethonium chloride (BEC) alone and combined pollution (PCMX+BEC). The H1 strain could use NH4+-N, NO2--N and NO3--N as nitrogen sources and had good nitrogen removal performance under conditions of C/N ratio 25, pH 5-8, 25-35 oC and sodium acetate as carbon. PCMX and BEC alone exhibited hormesis effects on H1 strain which promoted the growth of H1 strain at low concentrations but inhibited it at high concentrations, and combined pollution showed synergistic inhibitory on H1 strain. H1 strain owned a full nitrogen metabolic pathway according to functional genes quantification. PCMX encouraged nitrification process of H1, while BEC and combined pollution mostly blocked nitrogen removal. PCMX, but not BEC, mainly led to the enrichment of resistance genes. These findings will aid in systematic assessment of contaminant tolerance characteristics of HNAD strain and its application prospects.

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.

Growth performance of African catfish (Clarias gariepinus) in aquaponic systems with varying densities of Vietnamese coriander (Persicaria odorata)

Mass cultivation of high-value aromatic herbs such as Vietnamese coriander and Persicaria odorata required specific soil, nutrients, and irrigation, mostly found in the limited natural wetland. This study aimed to evaluate the capacity of P. odorata at different densities in nutrient removal and the growth performance of African catfish, Clarias gariepinus in aquaponic systems. P. odorata was cultivated for 40 d with less than 10% water exchange. The effects of increasing crop densities, from zero plants for the control, 0.035 ± 0.003 kg/m2 in Treatment 1, 0.029 ± 0.002 kg/m2 in Treatment 2, and 0.021 ± 0.003 kg/m2 in Treatment 3, were tested on the growth performance of C. gariepinus with an initial density of 3.00 ± 0.50 kg/m3. The specific growth rate (SGR), daily growth rate of fish (DGRf), and survival rate (SR) of the C. gariepinus were monitored. Nutrient removal, daily growth rate of plant (DGRp), relative growth rate (RGR), and the sum of leaf number (Ʃn) of the P. odorata plant were also recorded. It was found that nutrient removal percentage significantly increased with the presence of P. odorata at different densities. The growth performance of C. gariepinus was also affected by P. odorata density in each treatment. However, no significant difference was observed in the DGRp and RGR of the P. odorata (p>0.05), except for Ʃn values. Treatment 1 had the highest Ʃn number compared to Treatment 2 and Treatment 3, showing a significant difference (p<0.05). This study demonstrates that the presence of P. odorata significantly contributes to lower nutrient concentrations, supporting the fundamental idea that plants improve water quality in aquaponic systems.

Acid-tolerant Pseudomonas citronellolis YN-21 exhibits a high heterotrophic nitrification capacity independent of the amo and hao genes

Heterotrophic nitrifying bacteria are found to be promising candidates for implementation in wastewater treatment systems due to their tolerance to extreme environments. A novel acid-resistant bacterium, Pseudomonas citronellolis YN-21, was isolated and reported to have exceptional heterotrophic nitrification capabilities in acidic condition. At pH 5, the highest NH4+ removal rate of 7.84 mg/L/h was displayed by YN-21, which was significantly higher than the NH4+ removal rates of other strains in neutral and alkaline environments. Remarkably, a distinct accumulation of NH2OH and NO3- was observed during NH4+ removal by strain YN-21, while traditional amo and hao genes were not detected in the genome, suggesting the possible presence of alternative nitrifying genes. Moreover, excellent nitrogen removal performance was displayed by YN-21 even under high concentrations of metal ion stress. Consequently, a broad application prospect in the treatment of leather wastewater and mine tailwater is offered by YN-21.

Simultaneous removal of ammonia nitrogen, phosphate, zinc, and phenol by degradation of cellulose in composite mycelial pellet bioreactor: Enhanced performance and community co-assembly mechanism

In this experiment, the prepared tea biochar-cellulose@LDH material (TB-CL@LDH) was combined with mycelium pellets to form the composite mycelial pellets (CMP), then assembled and immobilized with strains Pseudomonas sp. Y1 and Cupriavidus sp. ZY7 to construct a bioreactor. At the best operating parameters, the initial concentrations of phosphate (PO43--P), ammonia nitrogen (NH4+-N), chemical oxygen demand (COD), zinc (Zn2+), and phenol were 22.3, 25.0, 763.8, 1.0, and 1.0 mg L-1, the corresponding removal efficiencies were 80.4, 87.0, 83.4, 91.8, and 96.6%, respectively. Various characterization analyses demonstrated that the strain Y1 used the additional carbon source produced by the strain ZY7 degradation of cellulose to enhance the removal of composite pollutants and clarified the principle of Zn2+ and PO43--P removal by adsorption, co-precipitation and biomineralization. Pseudomonas and Cupriavidus were the dominant genera according to the high-throughput sequencing. As shown by KEGG results, nitrification and denitrification genes were affected by phenol. The study offers prospects for the simultaneous removal of complex pollutants consisting of NH4+-N, PO43--P, Zn2+, and phenol.

Microbial mechanisms in nitrogen fertilization: Modulating the re-mobilization of clay mineral-bound cadmium in agricultural soils

Soil cadmium (Cd) can affect crop growth and food safety, and through the enrichment in the food chain, it ultimately poses a risk to human health. Reducing the re-mobilization of Cd caused by the release of protons and acids by crops and microorganisms after stabilization is one of the significant technical challenges in agricultural activities. This study aimed to investigate the re-mobilization of stabilized Cd within the clay mineral-bound fraction of soil and its subsequent accumulation in crops utilizing nitrogen ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N), at 60 and 120 mg kg-1. Furthermore, the study harvested root exudates at various growth stages to assess their direct influence on the re-mobilization of stabilized Cd and to evaluate the indirect effects mediated by soil microorganisms. The results revealed that, in contrast to the NO3--N treatment, the NH4+-N treatment significantly enhanced the conversion of clay mineral-bound Cd in the soil to NH4NO3-extractable Cd. It also amplified the accumulation of Cd in edible amaranth, with concentrations in roots and shoots rising from 1.7-6.0 mg kg-1 to 4.3-9.8 mg kg-1. The introduction of NH4+-N caused a decrease in the pH value of the rhizosphere soil and stimulated the production and secretion organic and amino acids, such as oxalic acid, lactic acid, stearic acid, succinic acid, and l-serine, from the crop roots. Furthermore, compared to NO3--N, the combined interaction of root exudates with NH4+-N has a more pronounced impact on the abundance of microbial genes associated with glycolysis pathway and tricarboxylic acid cycle, such as pkfA, pfkB, sucB, sucC, and sucD. The effects of NH4+-N on crops and microorganisms ultimately result in a significant increase in the re-mobilization of stabilized Cd. However, the simulated experiments showed that microorganisms only contribute to 3.8-6.6 % of the re-mobilization of clay mineral-bound Cd in soil. Therefore, the fundamental strategy to inhibit the re-mobilization of stabilized Cd in vegetable cultivation involves the regulation of proton and organic acid secretion by crops.

Asymmetries among soil fungicide residues, nitrous oxide emissions and microbiomes regulated by nitrification inhibitor at different moistures

Carbendazim residue has been widely concerned, and nitrous oxide (N2O) is one of the dominant greenhouse gases. Microbial metabolisms are fundamental processes of removing organic pollutant and producing N2O. Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) can change soil abiotic properties and microbial communities and simultaneously affect carbendazim degradation and N2O emission. In this study, the comprehensive linkages among carbendazim residue, N2O emission and microbial community after the DMPP application were quantified under different soil moistures. Under 90% WHC, the DMPP application significantly reduced carbendazim residue by 54.82% and reduced soil N2O emission by 98.68%. The carbendazim residue was negatively related to soil ammonium nitrogen (NH4+-N), urease activity, and ratios of Bacteroidetes, Thaumarchaeota and Nitrospirae under 90% WHC, and the N2O emission was negatively related to NH4+-N content and relative abundance of Acidobacteria under the 60% WHC condition. In the whole (60% and 90% WHC together), the carbendazim residue was negatively related to the abundances of nrfA (correlation coefficient = -0.623) and nrfH (correlation coefficient = -0.468) genes. The hao gene was negatively related to the carbendazim residue but was positively related to the N2O emission rate. The DMPP application had the promising potential to simultaneously reduce ecological risks of fungicide residue and N2O emission via altering soil abiotic properties, microbial activities and communities and functional genes. ENVIRONMENTAL IMPLICATION: Carbendazim was a high-efficiency fungicide that was widely used in agricultural production. Nitrous oxide (N2O) is the third most important greenhouse gas responsible for global warming. The 3, 4-dimethylpyrazole phosphate (DMPP) is an effective nitrification inhibitor widely used in agricultural production. This study indicated that the DMPP application reduced soil carbendazim residues and N2O emission. The asymmetric linkages among the carbendazim residue, N2O emission, microbial community and functional gene abundance were regulated by the DMPP application and soil moisture. The results could broaden our horizons on the utilizations DMPP in decreasing fungicide risks and N2O emission.

Wastewater treatment from a science faculty during the COVID-19 pandemic by using ammonium-oxidising and heterotrophic bacteria

During and after the pandemic caused by the SARS-CoV-2 virus, the use of personal care products and disinfectants increased in universities worldwide. Among these, quaternary ammonium-based products stand out; these compounds and their intermediates caused substantial changes in the chemical composition of the wastewater produced by these institutions. For this reason, improvements and environmentally sustainable biological alternatives were introduced in the existing treatment systems so that these institutions could continue their research and teaching activities. For this reason, the objective of this study was to develop an improved culture medium to cultivate ammonium oxidising bacteria (AOB) to increase the biomass and use them in the treatment of wastewater produced in a faculty of sciences in Bogotá, D.C., Colombia. A Plackett Burman Experimental Design (PBED) and growth curves served for oligotrophic culture medium, and production conditions improved for the AOB. Finally, these bacteria were used with total heterotrophic bacteria (THB) for wastewater treatment in a pilot plant. Modification of base ammonium broth and culture conditions (6607 mg L-1 of (NH4)2SO4, 84 mg L-1 CaCO3, 40 mg L-1 MgSO4·7H2O, 40 mg L-1 CaCl2·2H2O and 200 mg L-1 KH2PO4, 10% (w/v) inoculum, no copper addition, pH 7.0 ± 0.2, 200 r.p.m., 30 days) favoured the growth of Nitrosomonas europea, Nitrosococcus oceani, and Nitrosospira multiformis with values of 8.23 ± 1.9, 7.56 ± 0.7 and 4.2 ± 0.4 Log10 CFU mL-1, respectively. NO2- production was 0.396 ± 0.0264, 0.247 ± 0.013 and 0.185 ± 0.003 mg L-1 for Nitrosomonas europea, Nitrosococcus oceani and Nitrosospira multiformis. After the 5-day wastewater treatment (WW) by co-inoculating the three studied bacteria in the wastewater (with their self-microorganisms), the concentrations of AOB and THB were 5.92 and 9.3 Log10 CFU mL-1, respectively. These values were related to the oxidative decrease of Chemical Oxygen Demand (COD), (39.5 mg L-1), Ammonium ion (NH4+), (6.5 mg L-1) Nitrite (NO2-), (2.0 mg L-1) and Nitrate (NO3-), (1.5 mg L-1), respectively in the five days of treatment. It was concluded, with the improvement of a culture medium and production conditions for three AOB through biotechnological strategies at the laboratory scale, being a promising alternative to bio-augment of the biomass of the studied bacteria under controlled conditions that allow the aerobic removal of COD and nitrogen cycle intermediates present in the studied wastewater.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03961-4.

Enhancing wastewater treatment efficiency: A hybrid technology perspective with energy-saving strategies

The study aimed to investigate how hybrid technology, combined with various intermittent aeration (IA) strategies, contributes to reducing the energy costs of wastewater treatment while simultaneously ensuring a high treatment efficiency. Even with IA subphases lasting half as long as those without aeration, and oxygen levels reduced from 3.5 to 1.5 mg O2/L, pollutants removal efficiency remains robust, allowing for a 1.41-fold reduction in energy consumption (EO). Hybrid technology led to a 1.34-fold decrease in EO, along with improved denitrification efficiency from 74.05 ± 4.71 to 81.87 ± 2.43 % and enhanced biological phosphorus removal from 35.03 ± 4.25 to 87.32 ± 3.64 %. The high nitrification efficiency may have been attributed to the abundance of Pseudomonas, Acinetobacter, and Rhodococcus, which outcompeted the genera of autotrophic nitrifying bacteria, suggesting that the hybrid system is favorable for the growth of heterotrophic nitrifiers.

Enhanced ammonia removal in tidal flow constructed wetland by incorporating steel slag: Performance, microbial community, and heavy metal release

Utilizing alkaline solid wastes, such as steel slag, as substrates in tidal flow constructed wetlands (TFCWs) can effectively neutralize the acidity generated by nitrification. However, the impacts of steel slag on microbial communities and the potential risk of heavy metal release remain poorly understood. To address these knowledge gaps, this study compared the performance and microbial community structure of TFCWs filled with a mixture of steel slag and zeolite (TFCW-S) to those filled with zeolite alone (TFCW-Z). TFCW-S exhibited a much higher NH4+-N removal efficiency (98.35 %) than TFCW-Z (55.26 %). Additionally, TFCW-S also achieved better TN and TP removal. The steel slag addition helped maintain the TFCW-S effluent pH at around 7.5, while the TFCW-Z effluent pH varied from 3.74 to 6.25. The nitrification and denitrification intensities in TFCW-S substrates were significantly higher than those in TFCW-Z, consistent with the observed removal performance. Moreover, steel slag did not cause excessive heavy metal release, as the effluent concentrations were below the standard limits. Microbial community analysis revealed that ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and complete ammonia-oxidizing bacteria coexisted in both TFCWs, albeit with different compositions. Furthermore, the enrichment of heterotrophic nitrification-aerobic denitrification bacteria in TFCW-S likely contributed to the high NH4+-N removal. In summary, these findings demonstrate that the combined use of steel slag and zeolite in TFCWs creates favorable pH conditions for ammonia-oxidizing microorganisms, leading to efficient ammonia removal in an environmentally friendly manner.

Removal of sulfur and nitrogen pollutants in a sediment microbial fuel cell coupled with Vallisneria natans: Efficiency, microbial community structure, and functional genes

The rapid development of the economy has led to an increase in the sulfur and nitrogen load in surface water, which has the potential to cause river eutrophication and the emission of malodorous gases. A lab-scale sediment microbial fuel cell coupled with Vallisneria natans (P-SMFC) was designed for surface water remediation. The enhancement of pollutant removal performance of P-SMFC was evaluated in contrast to the SMFC system without plants (SMFC), the open-circuit control system with plants (C-P), and the open-circuit control system without plants (C-S), while illustrating the mechanisms of the sulfur and nitrogen transformation process. The results demonstrated that the effluent and sediment of P-SMFC had lower concentrations of sulfide compared to other systems. Furthermore, P-SMFC exhibited higher removal efficiency for COD (73.1 ± 8.7%), NH4+-N (80.5 ± 19.8%), and NO3--N (88.5 ± 11.8%) compared to other systems. The closed-circuit conditions and growth of Vallisneria natans create a favorable ecological niche for functional microorganisms involved in power generation, sulfur oxidation, and nitrogen transformation. Additionally, metagenomic analysis revealed that multifunctional bacteria possessing both denitrification and sulfur oxidation genes, such as Thiobacillus, Dechloromonas, and Bacillus, may play simultaneous roles in metabolizing sulfur and nitrogen, thus serving as integral factors in maintaining the performance of P-SMFC. In summary, these findings provide a theoretical reference for the concurrent enhancement of sulfur and nitrogen pollutants removal in P-SMFC and will facilitate its practical application in the remediation of contaminated surface water.

Involvement of functional metabolism promotes the enrichment of antibiotic resistome in drinking water: Based on the PICRUSt2 functional prediction

Biofilters are the important source and sink of antibiotic resistance genes (ARGs) and antibiotic resistance bacteria (ARB) in the drinking water. Current studies generally ascribed the prevalence of BAR in biofilter from the perspective of gene behavior, i.e. horizontal gene transfer (HGT), little attentions have been paid on the ARGs carrier- ARB. In this study, we proposed the hypothesis that ARB participating in pollutant metabolism processes and becoming dominant is an important way for the enrichment of ARGs. To verify this, the antibiotic resistome and bacterial functional metabolic pathways of a sand filter was profiled using heterotrophic bacterial plate counting method (HPC), high-throughput qPCR, Illumina Hiseq sequencing and PICRUSt2 functional prediction. The results illustrated a significant leakage of ARB in the effluent of the sand filter with an average absolute abundance of approximately 102-103 CFU/mL. Further contribution analysis revealed that the dominant genera, such as Acinetobacter spp., Aeromonas spp., Elizabethkingia spp., and Bacillus spp., were primary ARGs hosts, conferring resistance to multiple antibiotics including sulfamethoxazole, tetracycline and β-lactams. Notably, these ARGs hosts were involved in nitrogen metabolism, including extracellular nitrate/nitrite transport and nitrite reduction, which are crucial in nitrification and denitrification in biofilters. For example, Acinetobacter spp., the dominant bacteria in the filter (relative abundance 69.97 %), contributed the majority of ARGs and 53.79 % of nitrite reduction function. That is, ARB can predominate by participating in the nitrogen metabolism pathways, facilitating the enrichment of ARGs. These findings provide insights into the stable presence of ARGs in biofilters from a functional metabolism perspective, offering a significant supplementary to the mechanisms of the emergence, maintenance, and transmission of BARin drinking water.

bacLIFE: a user-friendly computational workflow for genome analysis and prediction of lifestyle-associated genes in bacteria

Bacteria have an extensive adaptive ability to live in close association with eukaryotic hosts, exhibiting detrimental, neutral or beneficial effects on host growth and health. However, the genes involved in niche adaptation are mostly unknown and their functions poorly characterized. Here, we present bacLIFE ( https://github.com/Carrion-lab/bacLIFE ) a streamlined computational workflow for genome annotation, large-scale comparative genomics, and prediction of lifestyle-associated genes (LAGs). As a proof of concept, we analyzed 16,846 genomes from the Burkholderia/Paraburkholderia and Pseudomonas genera, which led to the identification of hundreds of genes potentially associated with a plant pathogenic lifestyle. Site-directed mutagenesis of 14 of these predicted LAGs of unknown function, followed by plant bioassays, showed that 6 predicted LAGs are indeed involved in the phytopathogenic lifestyle of Burkholderia plantarii and Pseudomonas syringae pv. phaseolicola. These 6 LAGs encompassed a glycosyltransferase, extracellular binding proteins, homoserine dehydrogenases and hypothetical proteins. Collectively, our results highlight bacLIFE as an effective computational tool for prediction of LAGs and the generation of hypotheses for a better understanding of bacteria-host interactions.

A review of the phosphorus removal of polyphosphate-accumulating organisms in natural and engineered systems

Increasing eutrophication has led to a continuous deterioration of many aquatic ecosystems. Polyphosphate-accumulating organisms (PAOs) can provide insight into the human response to this challenge, as they initiate enhanced biological phosphorus removal (EBPR) through cyclical anaerobic phosphorus release and aerobic phosphorus uptake. Although the limiting environmental factors for PAO growth and phosphorus removal have been widely discussed, there remains a gap in the knowledge surrounding the differences in the type and phosphorus removal efficiencies of natural and engineered PAO systems. Furthermore, due to the limitations of PAOs in conventional wastewater treatment environments, there is an urgent need to find functional PAOs in extreme environments for better wastewater treatment. Therefore, it is necessary to explore the effects of extreme conditions on the phosphorus removal efficiency of PAOs as well as the types, sources, and characteristics of PAOs. In this paper, we summarize the response mechanisms of PAOs, denitrifying polyphosphate-accumulating organisms (D-PAOs), aerobic denitrifying polyphosphate-accumulating organisms (AD-PAOs), and sulfur-related PAOs (S-PAOs). The mechanism of nitrogen and phosphorus removal in PAOs is related to the coupling cycles of carbon, nitrogen, phosphorus, and sulfur. The genera of PAOs differ in natural and engineered systems, but PAOs have more diversity in aquatic environments and soils. Recent studies on the impact of several parameters (e.g., temperature, carbon source, pH, and dissolved oxygen) and extracellular polymer substances on the phosphorus removal efficiency of PAOs in natural and engineered systems are further discussed. Most of the PAOs screened under extreme conditions still had high phosphorus removal efficiencies (>80.0 %). These results provide a reference for searching for PAOs with different adaptations to achieve better wastewater treatment.

Kinetic analysis and mechanism of nitrate, calcium, and cadmium removal using the newly isolated Pseudomonas sp. LYF26

The co-existence of heavy metals and nitrate (NO3--N) pollutants in wastewater has been a persistent global concern for a long time. A strain LYF26, which can remove NO3--N, calcium (Ca(II)), and cadmium (Cd(II)) simultaneously, was isolated to explore the properties and mechanisms of synergistic contaminants removal. Different conditions (Cd(II) and Ca(II) concentrations and pH) were optimized by Zero-, Half-, and First-order kinetic analyses to explore the environmental parameters for the optimal effect of strain LYF26. Results of the kinetic analyses revealed that the optimal culture conditions for strain LYF26 were pH of 6.5, Cd(II) and Ca(II) concentrations of 3.00 and 180.00 mg L-1, accompanied by Ca(II), Cd(II), and NO3--N efficiencies of 53.10%, 90.03%, and 91.45%, respectively. The removal mechanisms of Cd(II) using strain LYF26 as a nucleation template were identified as biomineralization, lattice substitution, and co-precipitation. The differences and changes of dissolved organic matter during metabolism were analyzed and the results demonstrated that besides the involvement of extracellular polymeric substances in the precipitation of Cd(II) and Ca(II), the high content of humic acid-like species revealed a remarkable contribution to the denitrification process. This study is hopeful to contribute a theory for further developing microbially induced calcium precipitation used to treat complex polluted wastewater.

Simultaneous inorganic nitrogen and phosphate removal by aerobic-heterotrophic fungus Fusarium keratoplasticum FSP1: Performance, pathway and application

Fungi with multiple contaminant removal function have rarely been studied. Here, a novel fungal strain Fusarium keratoplasticum FSP1, which was isolated from halophilic granular sludge, is reported for first time to perform simultaneous nitrogen and phosphate removal. The strain showed wide adaptability under C/N ratios of 30-35, salinities of 0 %-3 % (m/v), and pH of 7.5-9.5. The maximum removal rates of ammonium, nitrate and nitrite were 4.43, 4.01 and 2.97 mg N/L/h. The nitrogen balance, enzyme activity and substrate conversion experiments demonstrated a single strain FSP1 can assimilate inorganic nitrogen and convert inorganic nitrogen to gaseous nitrogen through heterotrophic nitrification or aerobic denitrification. About 39 %-42 % of the degraded phosphorus was in the extracellular polymeric substances (EPS). Orthophosphate was the main phosphorus species in the cell, whereas phosphate monoester and diester were in the EPS. The novel strain FSP1 is a potential candidate for wastewater treatment.