Exploring influence mechanism of small-molecule carbon source on heterotrophic nitrification-aerobic denitrification process from carbon metabolism, nitrogen metabolism and electron transport process

Simultaneous removal of carbamazepine, nitrate, and copper in a biofilm reactor filled with FeMn-modified ceramsite

Mixtures of pollutants are a significant challenge for conventional wastewater treatment processes. In the present work, the potential of a biofilm reactor to simultaneously remove nitrate (NO3--N), carbamazepine (CBZ), and copper ions (Cu2+) was evaluated. The reactor was filled with FeMn-modified ceramsite (CS@FeMn) and inoculated with the strains of Cupriavidus sp. HY129 and Pantoea sp. MFG10, which contributed to the redox cycling of Mn. Under optimum conditions with the HRT, C/N and pH of 9.0 h, 2.0, and 7.0, respectively, the bioreactor incorporating CS@FeMn demonstrated a significant increase in nitrogen removal capacity compared to the CS carrier, achieving a NRE of 96.7 %. Moreover, the removal efficiencies of CBZ and Cu²⁺ reached the values of 91.8 % and 85.6 %, respectively. The experimental results indicated that the removals of CBZ and Cu²⁺ were closely associated with microbial activity, involving the combined effects of microbial metabolism, adsorption of CS@FeMn, and bioprecipitation. Analyses through high-throughput sequencing and KEGG pathway revealed that the presence of CBZ and Cu²⁺ reshaped the structure of microbial community within the bioreactor, driving the regulation of functional genes and nitrogen metabolism-related genes to maintain metabolic stability. These findings indicated that the CS@FeMn bioreactor system presents an effective solution for simultaneously addressing multiple pollutants in water treatment, achieving high efficiencies in NO3--N, CBZ, and Cu2+ removal.

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.

Strategic carbon source supplementation enhances nitrite degradation by Pantoea sp. A5 in variable temperature conditions

The expanding global demand for sustainable aquaculture underscores the need for efficient water quality management, particularly in controlling harmful nitrogenous compounds like nitrites. This study explores the effectiveness of Pantoea sp. A5, a nitrite-degrading bacterium isolated from food waste, reduces nitrite levels in aquaculture systems, focusing on the role of carbon sources like glucose and glycerol. The experiments showed that these carbon sources, especially glycerol, significantly enhanced the bacterium's ability to degrade nitrites across a range of temperatures without promoting growth, suggesting a cost-effective alternative to glucose. Unlike acetic acid, which did not enhance nitrite degradation, glycerol and glucose regulated metabolic pathways, evidenced by reduced malate dehydrogenase (MDH) activity and increased glutamate dehydrogenase (GDH) levels, facilitating efficient ammonia assimilation. These findings highlight the potential of using targeted carbon sources to manage nitrite levels in aquaculture, improving sustainability and contributing to global food supply efforts.

Identification of novel strain Acinetobacter baumannii H1 and its improvement capacity for nutrient removal after coimmobilized on activated carbon and CaCO3 in real aquaculture wastewater

A new strain H1, Acinetobacter baumannii, exhibited the 96 % nitrogen and 76 % phosphate removal efficiencies in suspension environment after 48 h, and the optimal conditions were obtained at pH of 7-8, temperature of 30 °C, carbon source of succinate, carbon-nitrogen ratio of 10 and phosphorus-nitrogen ratio of 0.2, respectively. The immobilization experiments with activated carbon and CaCO3 were carried out, the optimal formula was 30 g/L CaCO3, 15 g/L activated carbon-bacteria complex, 2 % CaCl2 and a 1:1 embedding agent ratio. The removal efficiency of NH4+-N, total nitrogen, total phosphorus and chemical oxygen demand in immobilized H1 was 288.89 %, 121.87 %, 135.69 % and 667.21 % higher than that by free strain in group With Indigenous Bacteria, respectively. Under the real water environment, the nitrogen concentrations in the immobilization groups were 3-4 times lower than those of the suspension groups, and the abundances of N and P metabolism-associated bacterial communities (Proteobacteria and Patescibacteria) were higher in the immobilization groups. These results provided an approach for the practical application in aquaculture tailwater treatment.

Effects of arsenic and trace metals on bacterial denitrification process from estuarine sediments and associated nitrous oxide emission

Coastal ecosystems currently face significant challenges due to nutrient enrichment and trace metal contamination. However, the effects of arsenic (As) and other trace metals (copper, lead, zinc, cadmium, mercury) on denitrification processes and nitrous oxide (N2O) emissions in estuarine sediments remain poorly understood. Here, we examined the influence of As and other trace metals on denitrification and N2O emissions in a single denitrifying strain, Marinobacter sp. MSD-1, isolated from metal-contaminated estuarine sediments based on its As(III)-oxidizing and denitrifying abilities and functional microbial composition. The results showed that As did not significantly affect the denitrification or N2O emission of MSD-1. However, Cd(II) at concentrations of 5-10 mg/L significantly induced the accumulation of N2O, while not significantly affecting the reduction of nitrate (NO3-) and nitrite (NO2-). The presence of As(III) further inhibited the N2O reduction under Cd exposure, but it had no significant effect on the N2O reduction after exposure to other trace metals. A negative correlation was observed between N2O reductase (NO2R) activity and N2O emissions, indicating that Cd(II) inhibits the reduction process of N2O mainly by suppressing the activity of NO2R. This study highlights the detrimental effects of cadmium on microbial denitrification and subsequent emissions of the greenhouse gas N2O, thereby improving our understanding of how estuarine and coastal ecosystems respond and adapt to trace metal pollution.

Nitrogen removal characteristics and mechanism of the aerobic denitrifying bacterium Stutzerimonas stutzeri os3 isolated from shrimp aquaculture sediment

To overcome the limitations of denitrification under high dissolved oxygen conditions, an efficient aerobic denitrifier, Stutzerimonas stutzeri os3, was isolated from shrimp aquaculture sediment. The strain os3 achieved complete removal of nitrate without significant nitrite accumulation, when sodium citrate was used as the carbon source, with a C/N ratio of 5, and at a shaking speed of 50 r/min. Moreover, the strain os3 demonstrated a high TIN removal efficiency, reaching 98.29 % - 99.28 % under various nitrogen sources. Whole-genome sequencing revealed the presence of denitrification genes (napAB, nirS, norBC and nosZ) in the strain os3, which combined with nitrogen balance analysis, confirmed that the strain os3 primarily utilized aerobic denitrification for nitrate removal under aerobic conditions, as follows: NO3--N→NapABNO2--N→NirSNO→NorBCN2O→NosZN2. Furthermore, the strain os3 significantly increased the removal efficiencies of TIN and NO3--N in shrimp aquaculture wastewater, reaching 90.20 % and 94.43 %, respectively. Therefore, the strain os3 contributes to enhancing aerobic denitrification, providing a biotechnological solution for improving nitrogen cycling in shrimp aquaculture water.

Nitrogen conversion and mechanisms related to reduced emissions by adding exogenous modified magnesium ore during aerobic composting

In this study, modified products with a higher specific surface area and pore volume were prepared by light burning magnesite (MS) to increase its magnesium content and surface activity. MS heated at 650 °C (MS650) was applied in aerobic composting to assess its effect on nitrogen transformation during composting and the possible related chemical and microbial mechanisms. Adding MS650 reduced the NH3 emissions (0.74-52.4%), N2O emissions (29.0-57.9%), and greenhouse gas emissions (41.8-60.3%), and its effect on reducing nitrogen emissions was negatively correlated with the amount added, where the optimum proportion of MS650 was 2.5%. Struvite precipitation and physical adsorption were the chemical mechanisms responsible for nitrogen retention. MS650 inhibited the growth of nitrifying, nitrate reducing, and denitrifying bacteria. The total organic carbon content, electrical conductivity, and N2O together explained most of the variation (52.7%) in nitrogen functional genes, followed by Proteobacteria (28.6%). These findings have important implications for reducing nitrogen and greenhouse gas emissions, and improving the quality of compost products.

New Insight Into the Mechanism of Nitrite Enhancement on Heterotrophic Nitrification and Aerobic Denitrification Bacterium in Gene Expression

The growth and nitrogen metabolism of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are affected by nitrite, but the mechanisms underlying this for strain Acinetobacter johnsonii EN-J1 are unclear. In this study, the addition of 10 mg/L nitrite increased the reduction rate of ammonium by 1.0 mg/L/h, and 20 mg/L nitrite increased the reduction rate of nitrate by 3.9 mg/L/h. Compared with the control, the nitrate reductase activity, electron transfer activity, and adenosine triphosphate content of EN-J1 were enhanced by 142.0%, 278.0% and 279.0%, respectively, in the nitrate removal process after the addition of 20 mg/L nitrite. The whole genome was annotated with nitrogen removal genes such as narGHI, narK, nsrR, nirBD, nasA, glnA, gltB, gdhA and amt. Transcriptome analysis showed that nitrite triggered significant upregulation of several key pathways, including nitrogen metabolism, the tricarboxylic acid cycle, and amino acid metabolism for enhancing denitrification. The expression of key denitrification genes (narG, narK, hmp, nirBD, glnA and nasA) was detected by real-time quantitative polymerase chain reaction. These results suggested that nitrite enhances denitrification by increasing the expression of denitrification genes, electron transfer and adenosine triphosphate levels, which is important for elucidating the mechanism of nitrite promotion of biological nitrogen removal efficiency.

Characteristics and Mechanism of Ammonia Nitrogen Removal by Heterotrophic Nitrification Bacterium Klebsiella pneumoniae LCU1 and Its Application in Wastewater Treatment

In this study, a novel strain exhibiting heterotrophic nitrification was screened; subsequently, the strain was identified as Klebsiella pneumoniae LCU1 using 16S rRNA gene sequencing. The aim of the study was to investigate the effects of external factors on the NH4+-N removal efficiency of strain LCU1 in order to elucidate the optimal conditions for NH4+-N removal by the strain and improve the removal efficiency. The findings indicated that the NH4+-N removal efficiency of the strain exceeded 80% under optimal conditions (sodium succinate carbon source, C/N ratio of 10, initial pH of 8.0, temperature of 30 °C, and speed of 180 rpm). The genome analysis of strain LCU1 showed that key genes involved in nitrogen metabolism, including narGHI, nirB, nxrAB, and nasAB, were successfully annotated; hao and amo were absent, but the nitrogen properties analysis determined that the strain had a heterotrophic nitrification ability. After 120 h, the NH4+-N removal efficiency of strain LCU1 was 34.5% at a high NH4+-N concentration of 2000 mg/L. More importantly, the NH4+-N removal efficiency of this strain was above 34.13% at higher Cu2+, Mn2+, and Zn2+ ion concentrations. Furthermore, strain LCU1 had the highest NH4+-N removal efficiency of 34.51% for unsterilised (LCU1-OC) aquaculture wastewater. This suggests that with intensive colonisation treatment, the strain has promising application potential in real wastewater treatment.

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.

Heterotrophic nitrification processes driven by glucose and sodium acetate: New insights into microbial communities, functional genes and nitrogen metabolism from metagenomics and metabolomics

Heterotrophic nitrification (HN) bacteria use organic carbon sources to remove ammonia nitrogen (NH4+-N); however, the mechanisms of carbon and nitrogen metabolism are unknown. To understand this mechanism, HN functional microbial communities named MG and MA were enriched with glucose and sodium acetate, respectively. The NH4+-N removal efficiencies were 98.87 % and 98.91 %, with 88.06 % and 69.77 % nitrogen assimilation for MG and MA at 22 h and 10 h, respectively. Fungi (52.86 %) were more competitive in MG, and bacteria (99.99 %) were dominant in MA. Metagenomic and metabolomic analyses indicated that HN might be a signaling molecule (NO) in the production and detoxification processes when MG metabolizes glucose (amo, hao, and nosZ were not detected). MA metabolizes sodium acetate to produce less energy and promotes nitrogen oxidation reduction; however, genes (hao, hox, and NOS2) were not detected. These results suggest that NO and energy requirements induce microbial HN.

Effect of carbon source on carbon and nitrogen metabolism of common heterotrophic nitrification-aerobic denitrification pathway

Pseudomonas sp. ZHL02, removing nitrogen via ammonia nitrogen (NH4+) → hydroxylamine (HN2OH) → nitrite (NO2-) → nitrate (NO3-) → NO2- → nitric oxide (NO) → nitrous oxide (N2O) pathway was employed for getting in-depth information on the heterotrophic nitrification-aerobic denitrification (HNAD) pathway from carbon oxidation, nitrogen conversion, electron transport process, enzyme activity, as well as gene expression while sodium succinate, sodium citrate, and sodium acetate were utilized as the carbon sources. The nitrogen balance analysis results demonstrated that ZHL02 mainly removed NH4+-N through assimilation. The carbon source metabolism resulted in the discrepancies in electron transport chain and nitrogen removal between different HNAD bacteria. Moreover, the prokaryotic strand-specific transcriptome method showed that, amo and hao were absent in ZHL02, and unknown genes may be involved in ZHL02 during the HNAD process. As a fascinating process for removing nitrogen, the HNAD process is still puzzling, and the relationship between carbon metabolism and nitrogen metabolism among different HNAD pathways should be studied further.

A pilot-scale anoxic-anaerobic-anoxic-oxic combined with moving bed biofilm reactor system for advanced treatment of rural wastewater

Rural domestic poses a significant challenge to treatment technologies due to significant fluctuations in both water quality, particularly in terms of carbon concentration, and quantity. Conventional biological technology, such as anaerobic-anoxic-oxic (A2O) systems, is inefficient. In this work, a continuous pilot-scale anoxic-anaerobic-anoxic-oxic (A3O) reactor with a moving bed biofilm reactor (MBBR) system was constructed and optimized to improve the treatment efficiency of rural domestic wastewater. The sludge return ratio, volume ratio of the oxic-to-anoxic zone (Voxi/Vano), step-feeding and hydraulic retention time (HRT) at low temperature were considered the main parameters for optimization. Microbial analysis was performed on both the mixed liquor and carrier of the A3O-MBBR system under initial and post-optimized conditions. The results indicated that the A3O-MBBR improved the treatment efficiency of rural domestic wastewater, especially for total phosphorus (TP), which increased by 20 % compared with that of the A2O-MBR. In addition, the removal efficiencies of nitrogen and phosphorus were further optimized, and the average concentrations of total nitrogen (TN) and TP in the effluent reached 2.46 and 0.364 mg/L, respectively, at a sludge reflux ratio of 100 or 150 %, Voxi/Vano =200 %, step-feeding of 0.5Q/0.5Q (anaerobic/anoxic) and HRT of 15 h at low temperature in the A3O-MBBR, which met standard A of GB18918-2002, China (TN < 15 mg/L, TP < 0.5 mg/L). The average rate of attaining the standard increased by 58.63 % (post optimization). The microbial analysis showed an increase in species diversity and richness after the parameters were optimized. Moreover, compared to the microbial community structure before optimization, the post-optimization exhibited a more stable microbial structure with a significant enrichment of functional bacteria. Defluviimonas, Novosphingobium and Bifidobacterium, considered as the dominant nitrification or denitrifying bacteria, were enriched in the suspended sludge of the MBBR reactor, which the relative abundance increased by 3.11 %, 3.84 %, and 3.24 %, respectively. Further analysis of the microbial community in the carrier revealed that the abundance of Nitrospira and the denitrifying bacteria carried by the carrier were much greater than those in the suspended sludge. Consequently, the microorganism cooperation between suspended sludge and biofilm might be responsible for the improved performance of the optimized A3O-MBBR.

Significantly Enhanced Nitrate and Phosphorus Removal by Pyrite/Sawdust Composite-Driven Mixotrophic Denitrification with Boosted Electron Transfer: Comprehensive Evaluation of Water-Gas-Biofilm Phases during a Long-Term Study

Further reducing total nitrogen (TN) and total phosphorus (TP) in the secondary effluent needs to be realized effectively and in an eco-friendly manner. Herein, four pyrite/sawdust composite-based biofilters were established to treat simulated secondary effluent for 304 days. The results demonstrated that effluent TN and TP concentrations from biofilters under the optimal hydraulic retention time (HRT) of 3.5 h were stable at <2.0 and 0.1 mg/L, respectively, and no significant differences were observed between inoculated sludge sources. The pyrite/sawdust composite-based biofilters had low N2O, CH4, and CO2 emissions, and the effluent's DOM was mainly composed of five fluorescence components. Moreover, mixotrophic denitrifiers (Thiothrix) and sulfate-reducing bacteria (Desulfosporosinus) contributing to microbial nitrogen and sulfur cycles were enriched in the biofilm. Co-occurrence network analysis deciphered that Chlorobaculum and Desulfobacterales were key genera, which formed an obvious sulfur cycle process that strengthened the denitrification capacity. The higher abundances of genes encoding extracellular electron transport (EET) chains/mediators revealed that pyrite not only functioned as an electron conduit to stimulate direct interspecies electron transfer by flagella but also facilitated EET-associated enzymes for denitrification. This study comprehensively evaluates the water-gas-biofilm phases of pyrite/sawdust composite-based biofilters during a long-term study, providing an in-depth understanding of boosted electron transfer in pyrite-based mixotrophic denitrification systems.

Novel adaptive activated sludge process leverages flow fluctuations for simultaneous nitrification and denitrification in rural sewage treatment

The fluctuating characteristics of rural sewage flow pose a significant challenge for wastewater treatment plants, leading to poor effluent quality. This study establishes a novel adaptive activated sludge (AAS) process specifically designed to address this challenge. By dynamically adjusting to fluctuating water flow in situ, the AAS maintains system stability and promotes efficient pollutant removal. The core strategy of AAS leverages the inherent dissolved oxygen (DO) variations caused by flow fluctuations to establish an alternating anoxic-aerobic environment within the system. This alternating operation mode fosters the growth of aerobic denitrifiers, enabling the simultaneous nitrification and denitrification (SND) process. Over a 284-day operational period, the AAS achieved consistently high removal efficiencies, reaching 94 % for COD and 62.8 % for TN. Metagenomics sequencing revealed HN-AD bacteria as the dominant population, with the characteristic nap gene exhibiting a high relative abundance of 0.008 %, 0.010 %, 0.014 %, and 0.015 % in the anaerobic, anoxic, dynamic, and oxic zones, respectively. Overall, the AAS process demonstrates efficient pollutant removal and low-carbon treatment of rural sewage by transforming the disadvantage of flow fluctuation into an advantage for robust DO regulation. Thus, AAS offers a promising model for SND in rural sewage treatment.

Biological performance and membrane fouling of a microalgal-bacterial membrane photobioreactor for wastewater treatment without external aeration and carbonation

Biological nutrient removal processes involving the use of activated sludge (AS) to treat municipal wastewater normally result in high aeration energy consumption and significant greenhouse gas (GHG) emissions. Therefore, developing cost-efficient and environmentally friendly processes for wastewater treatment is vital. In this work, a novel non-aerated microalgal-bacterial membrane photobioreactor (MB-MPBR) was proposed, and its feasibility for organic contaminant and nutrient removals was evaluated, for the first time. The effects of inoculation ratio (microalgae to bacteria (M/B)) on the biological performance and membrane fouling were systematically investigated. The results showed that 95.9% of the chemical oxygen demand (COD), 74.5% of total nitrogen (TN), 98.5% of NH4+-N and 42.0% of total phosphorus (TP) were removed at an inoculation M/B ratio of 3:2 at steady state, representing a significant improvement compared to the M/B inoculation ratio of 1:3. Additionally, the higher inoculation M/B ratio (3:2) significantly promoted the biomass production owing to the favorable mutual exchange of oxygen and carbon dioxide between microalgae and bacteria. Cake layer formation was the primary fouling mechanism owing to the absence of aeration scouring on the membrane surface. The membrane fouling rate was slightly higher at the higher inoculation ratio (M/B = 3:2) owing to the increased biomass and extracellular polymeric substances (EPS) productions, despite the larger particle size. These results demonstrated that the non-aerated MB-MPBR could achieve superior biological performance, of which the inoculation M/B ratio was of critical importance for the initiation and maintenance of microalgal-bacterial symbiotic system, yet possibly caused severer membrane fouling in the absence of external aeration and carbonation. This study provides a new perspective for further optimizing and applying non-aerated MB-MPBR to enhance municipal wastewater treatment.