Identification of optimal parameters for treatment of high-strength ammonium leachate by mixed communities of heterotrophic nitrifying/aerobic denitrifying bacteria

A green process for total nitrogen removal without extra energy consumption: Synergistic actions for wastewater treatment

Total nitrogen (TN) removal is one of the key issues in improving water quality, while the traditional nitrification-denitrification process with its high energy consumption is unsustainable, due to greenhouse gas (GHG) emission. A method using organic-inorganic pellets and selected microalgae that can operate without electricity consumption was designed for TN removal in actual wastewater treatment. The results showed that the TN removal efficiencies with different pellets were 88.2 % ± 2.2 %, 86.6 % ± 3.0 %, 85.4 % ± 4.3 %, and 82.3 % ± 6.5 %, respectively. Microalgae assimilated inorganic nitrogen within cells, resulting in a significant positive relationship with TN (P < 0.05), and effectively removed TN through sedimentation. The pellets adsorbed nitrogen and microorganisms, released organic substances to regulate the ratio of water chemical oxygen demand (COD) to TN, and correspondingly influenced microbial growth. Microalgae and bacteria such as Romboutsia, Proteiniclasticum, and Rhodopseudomonas cooperated to form a mixed aerobic (water) -anaerobic (pellets) environment in the devices, and acted synergistically to remove TN. This study verifies the feasibility of TN removal with only solar energy in a low flow application in large spaces, benefiting carbon neutrality in wastewater treatment.

Heterotrophic nitrification-aerobic denitrification strains: An overlooked microbial interaction nexus in the anaerobic-swing-anoxic-oxic (ASAO) plug-flow system

This study aims to clarify the overlooked functions of heterotrophic nitrification-aerobic denitrification (HNAD) bacteria in a novel anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system. The dissolved oxygen (DO) levels and aerated hydraulic retention time (HRT) varied in the swing zones, providing a more diverse redox environment. High nitrogen (85.0 %) and phosphorus (80.0 %) removal were achieved by enriched HNAD bacteria (e.g., Thauera and Malikia) and phosphate accumulating organisms (PAO, e.g., Rhodocyclus and Azonexus) under middle DO level (1.0-2.0 mg/L) and longer aerated HRT (5.0 h). More importantly, microbial network revealed that HNAD bacteria became a connection point for other functional microorganisms associated with pollutant metabolism, and promoted the cooperation and functional evolution of microbial communities. The microbial ecology analysis captured the high importance of homogeneous selection, diffusion restriction, and drift for microbial community assembly in the ASAO system. Among them, HNAD bacteria contributed to both deterministic and stochastic processes, whereas the community assembly of PAO was mainly affected by the deterministic processes. The upregulation of denitrification genes (i.e., napA, napB, nirS, norB and norC) further confirmed the nitrogen removal contribution of aerobic denitrification by HNAD bacteria. Through this study, a comprehensive analysis of microbial interactions in the ASAO system was achieved, providing valuable insights into the targeted regulation of functional microorganisms in wastewater biological treatment processes.

High organic volumetric loading rates triggered heterotrophic nitrification in wastewater biological nutrient removal systems

This study confirmed the importance of a higher chemical oxygen demand (COD) volumetric loading rate (CODLR) for triggering heterotrophic nitrification in a lab-scale anoxic/microaerobic biological nutrient removal system for sewage treatment by analyzing the ammonia-oxidizing activities, nitrogen mass balance, and ammonia-oxidizing bacterial communities at four CODLR levels: 0.50 (Phase A), 0.75, 1.10, and 1.50 (Phase D) kg COD m-3 d-1. A higher CODLR led to a significant increase in the potential heterotrophic nitrification activity by 0.4, 0.9, 1.1, and 1.6 mg NH4±-N/g mixed liquor suspended solids h-1, respectively, contributing 7 %, 14 %, 17 %, and 21 % of the ammonia oxidization in the anoxic/microaerobic system. Furthermore, nitrogen balance analysis revealed that heterotrophic nitrifying bacteria contributed 4 % and 12 % of the ammonia oxidization in the anoxic/microaerobic system during Phases A and D, respectively, and that a more plentiful organic carbon supply in the microaerobic zone stimulated heterotrophic nitrification during Phase D.

Enhancement of electron transfer via magnetite in nitrite-dependent anaerobic methane oxidation system

Nitrite-dependent anaerobic methane oxidation (n-DAMO) is a novel denitrification process that simultaneously further removes and utilizes methane from anaerobic effluent from wastewater treatment plants. However, the metabolic activity of n-DAMO bacteria is relative low for practical application. In this study, conductive magnetite was added into lab-scale sequencing batch reactor inoculated with n-DAMO bacteria to study the influence on n-DAMO process. With magnetite amendment, the nitrogen removal rate could reach 34.9 mg N·L-1d-1, nearly 2.5 times more than that of control group. Magnetite significantly facilitated the interspecies electron transfer and built electrically connected community with high capacitance. Enzymatic activities of electron transport chain were significantly elevated. Functional gene expression and enzyme activities associated with nitrogen and methane metabolism had been highly up-regulated. These results not only propose a useful strategy in n-DAMO application but also provide insights into the stimulating mechanism of magnetite in n-DAMO process.

Removal of ammonia nitrogen from residual ammonium leaching solution by heterotrophic nitrification-aerobic denitrification process

The aftermath of mining weathered crust elution-deposited rare earth ore produces a large amount of residual ammonium leaching solution, which causes ammonia and nitrogen pollution to the mine site. Recently, denitrification by heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria has attracted much attention. However, limited studies exist regarding the denitrification process of HN-AD bacteria. In this study, we combined four strains of HN-AD bacteria, Pseudomonas fulva K3, Pseudomonas mosselii K17, Klebsiella oxytoca A12, and Enterobacter hormaechei A16, obtained from rare earth element leaching sites, to select the best microbial consortium for ammonia nitrogen removal. We designed an ammonia removal process applicable to HN-AD bacteria to directly remove ammonia nitrogen from acidic leaching solutions. The experimental results demonstrated that the most efficient microbial consortium for ammonia nitrogen removal to be K3 + K17 + A16, with a removal efficiency of 89.68% for 8 h. In this process, considering the influencing factors of the ammonia removal process, the larger the influent flow rate and influent ammonia nitrogen concentration, the greater the ammonia nitrogen accumulation and pH decrease in the reactor. In consecutive multi-batch experiments, the ammonia removal process was used to remove ammonia nitrogen, at concentrations of 100-600 mg/L, from the simulated leaching solution at pH 4-7, whereby the effluent ammonia nitrogen concentration was lower than 15 mg/L. The results demonstrate that the ammonia removal process is highly feasible and stable. These findings will provide new ideas for the application of HN-AD bacteria and new methods for the removal of ammonia nitrogen from acidic leaching solutions.

Optimizing total ammonia-nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.

Domestication and pilot-scale culture of mixed bacteria HY-1 capable of heterotrophic nitrification-aerobic denitrification

To further investigate the potential of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria for practical applications, the HN-AD mixed bacteria HY-1 were enriched and domesticated in this study. After five generations of domestication, the mixture was able to remove 98% of ammonia nitrogen (400 mg/L) and 81.9% of mixed nitrogen source (nitrate, nitrite). Changes in community structure in the domestication process of mixed microorganisms were studied using 16S rDNA-seq. The results indicated an increase in the abundance of Acinetobacter from 16.9% to 80%. The conditions for the expanded culture of the HY-1 were also optimized. Moreover, A pilot-scale expanded reactor with a capacity of 1000L was constructed, and the HY-1 was successfully expanded from 0.1L to 800L. The community structures of the HY-1 remained stable after the expanded culture, with Acinetobacter as the dominant species. Moreover, the HY-1 demonstrated adaptability to actual high ammonia nitrogen wastewater and showed potential for practical application.

Spatial and temporal dynamic response of abundant and rare aerobic denitrifying bacteria to dissolved organic matter in natural water: A case study of Lake Baiyangdian, China

Revealing the responses of abundant and rare aerobic denitrifying bacteria to dissolved organic matter (DOM) composition is essential for understanding the aquatic N cycle ecosystems. In this study, fluorescence region integration and high-throughput sequencing techniques were used to investigate the spatiotemporal characteristics and dynamic response of DOM and aerobic denitrifying bacteria. The DOM compositions were significantly different among the four seasons (P < 0.001) without spatial differences. Tryptophan-like substances (P2, 27.89-42.67%) and microbial metabolites (P4, 14.62-42.03%) were the dominant components, and DOM exhibited strong autogenous characteristics. Abundant (AT), moderate (MT), and rare taxa (RT) of aerobic denitrifying bacteria showed significant and spatiotemporal differences (P < 0.05). The responses of α-diversity and niche breadth of AT and RT to DOM differed. The DOM explanation proportion for aerobic denitrifying bacteria exhibited spatiotemporal differences based on redundancy analysis. Foliate-like substances (P3) had the highest interpretation rate of AT in spring and summer, while humic-like substances (P5) had the highest interpretation rate of RT in spring and winter. Network analysis showed that RT networks were more complex than AT networks. Pseudomonas was the main genus associated with DOM in AT on a temporal scale, and was more strongly correlated with tyrosine-like substances (P1), P2, and P5. Aeromonas was the main genus associated with DOM in AT on a spatial scale and was more strongly correlated with P1 and P5. Magnetospirillum was the main genus associated with DOM in RT on a spatiotemporal scale, which was more sensitive to P3 and P4. Special operational taxonomic units were transformed between AT and RT with seasonal changes, but not between the two regions. To summarize, our results revealed that bacteria with different abundances utilized DOM components differently, and provides new insight on the spatiotemporal response of DOM and aerobic denitrifying bacteria in aquatic ecosystems of biogeochemical significance.

Low C/N promotes stable partial nitrification by enhancing the cooperation of functional microorganisms in treating high-strength ammonium landfill leachate

Partial nitrification is an effective process for treating high-strength ammonium landfill leachate with low C/N ratio, for the cooperation with denitrification can save almost 40% carbon addition in biological nitrogen removal. However, high ammonia loading often causes the instability of partial nitrification process. Less carbon addition can promote the stability of partial nitrification and increase the nitrite accumulation ratio (NAR). Nevertheless, the microbial mechanisms within remain further elusive. In this study, two laboratory-scale sequencing batch reactors were constructed and operated for 125 days, which were fed with ammonia synthetic wastewater with C/N of 0.6 (CN system) and C/N of 0.0 as the control (N system). CN system performed more stably and had the highest NAR of 100%. Extracellular polymeric substances (EPS) generated from carbon source provided spatial and nutrient niches to tighten the cooperation of functional microorganisms, thus, enhanced the stability and efficiency of partial nitrification. Thauera was the dominant denitrifier in CN system. Nitrosomonas was one of the most important autotrophic ammonia oxidizing bacteria, while Paracoccus and Flavobacterium were the main heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in CN system. The enrichment of HN-AD bacteria outcompeted nitrite oxidizing bacteria (NOB), therefore leaded to higher nitrite accumulation in CN system. The findings of this study may be conducive to increasing the understanding of the microbial collaboration mechanisms of partial nitrification, thereby provides theoretical support for the improvement of biological nitrogen removal technology.

Limited dissolved oxygen facilitated nitrogen removal at biocathode during the hydrogenotrophic denitrification process using bioelectrochemical system

Effects of limited dissolved oxygen (DO) on hydrogenotrophic denitrification at biocathode was investigated using bioelectrochemical system. It was found that total nitrogen removal increased by 5.9%, as DO reached about 0.24 mg/L with the cathodic chamber unplugged (group R_Exposure). With the presence of limited DO, not only the nitrogen metabolic pathway was influenced, but the composition of microbial communities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were enriched accordingly. After metagenomic analysis, enriched genes in R_Exposure were found to be associated with nearly each of nitrogen removal steps as denitrification, nitrification, DNRA, nitrate assimilation and even nitrogen fixation. Moreover, genes encoding both Complexes III and IV constituted the electron transfer chain were significantly enriched, indicating that more electrons would be orientated to the reduction of NO₂^--N, NO-N and oxygen. Therefore, enhanced nitrogen removal could be attained through the co-respiration of nitrate and oxygen by means of NH₄⁺-N oxidation.

Nitrification resistance and functional redundancy maintain the system stability of partial nitrification in high-strength ammonium wastewater system

The sudden change of ammonia loading in high-strength ammonium wastewater treatment can directly affect the system stability by altering microbial community dynamics. To maintain the system stability, the effects of ammonia shock loading on microbial community dynamics must be studied. Two sets of sequencing batch reactors were operated with 6 shock cycles (maximum volumetric loading rate of 1928 mg N/(L·d)). CN system contained both organic carbon and ammonia and N system contained only ammonia. Comparing with N system, CN system operated more stably and had higher nitrite accumulation rate. Free ammonia (FA) was the select stress for the turnover of CN microbial communities, while the N communities didn t shift much. The increase of Nitrosomonas and the appearance of heterotrophic nitrification-aerobic denitrification bacteria in CN system presented its resistance and redundancy against FA impact, while the increase of functional genes exhibited functional genes redundancy which maintained the system stability.

The effect of activated sludge treatment and catalytic ozonation on high concentration of ammonia nitrogen removal from landfill leachate

This study adopted the combination of activated sludge treatment and catalytic ozonation technology to efficiently remove the high concentration of ammonia nitrogen from landfill leachate. Through optimizing the parameters continuously, the COD, NH₄⁺-N, UV₂₅₄ and colority respectively descended to 417.75 ± 6.72 mg/L, 9.77 mg/L, 1.98 ± 0.04 and 40 times, and 3D fluorescence also reduced significantly within 14 days. Target genes of AOB-amoA, nxrA, napA, nirS and nosZ analysis indicated that ammonia-oxidizing bacteria, nitrated bacteria, and denitrifying bacteria played a key role on nitrogen removal, aerobic denitrifying bacteria was dominated especially. The nitrogen removal process was as follows: catalytic ozonation converted nitrogen-containing organic matter into NH₄⁺-N, then NH₄⁺-N was converted into NO₂^--N and NO₃^--N with the action of ammonia oxidation, nitrification and catalytic ozonation. Finally, the denitrification microorganisms transformed NO₃^--N or NO₂^--N to N₂. Therefore, this coupled process realized the nitrogen removal effectively from landfill leachate.

Understanding the effect of residual aluminum salt coagulant on activated sludge in sequencing batch reactor: Performance response, activity restoration and microbial community evolution

To investigate the effect of residual coagulant after coagulation pretreatment on activated sludge system of wastewater treatment plants (WWTPs), comparative evaluation of lab-scale sequencing batch reactors under different poly-aluminum chloride (PAC) concentrations (20 and 55 mg/L), presenting the performance differences of reactors. Results showed that the PAC concentration of 20 mg/L slightly enhanced the average removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN), up to 93.43% and 72.52%. Whereas, an inhibition effect was exerted at the PAC concentration of 55 mg/L, the average removal efficiencies decreased to 88.56% and 57.80% respectively. Similarly, the residual aluminum salts showed a concentration effect of low promotion and high inhibition on sludge activity index. The content of specific oxygen utilization rate (SOUR) and dehydrogenase (DHA) sharply decreased by 30.17% and 53.56% under the high PAC concentration of 55 mg/L. Activity recovery phase showed that the suppression of aluminum salt coagulant on biological system was reversible. High-throughput sequencing presented that the relative abundance of microbes showed obvious variations at different PAC concentrations, and certain bacteria in Chloroflexi and Bacteroidota exhibited better adaptability to the high PAC concentration environment. Nevertheless, the antagonism action between denitrifying genera and other genera as well as the downregulation of functional enzymes regarding nitrogen metabolism gave rise to the deterioration of denitrification under the high PAC concentration of 55 mg/L. This study revealed the influence mechanism of residual aluminum salt coagulant on activated sludge system, providing strategies for efficient decontamination and long-term stable operation of biological system in wastewater treatment plant under the condition of adding PAC.

Applications of Sponge Iron and Effects of Organic Carbon Source on Sulfate-Reducing Ammonium Oxidation Process

The typical characteristics of wastewater produced from seafood, chemical, textile, and paper industries are that it contains ammonia, sulfate, and a certain amount of chemical oxygen demand (COD). The sulfate-reducing ammonium oxidation process is a biochemical reaction that allows both ammonia and sulfate removal, but its low growth rate and harsh reaction conditions limit its practical application. Due to the adsorption properties of the iron sponge and its robust structure, it provides a suitable living environment for microorganisms. To reduce the negative impact on the environment, we employed 4.8 kg of sponge iron in a 2.0 dm3 anaerobic sequencing batch reactor (ASBR). We investigated the effects of the type and concentration of carbon sources on the performance of the sulfate-reducing ammonium oxidation (SRAO) process. The results demonstrated that during a start-up period of 90 days, the average ammonium removal efficiency and the sulfate conversion efficiency of the reactor containing the sponge iron were 4.42% and 8.37% higher than those of the reactor without the sponge iron. The addition of the sponge iron shortens the start-up time of this greenhouse gas-free denitrification process and reduces future costs in practical applications. The removal of total nitrogen (TN) significantly increased after adding organic carbon sources and then declined sharply, while the most considerable reduction of ammonium removal efficiency from 98.4% to 30.5% was observed with adding phenol. The performance of the group employing glucose as the carbon source was recovered on the 28th day, with the average ammonium removal efficiency increasing from 49.03% to 83.5%. The results of this simulation study will help the rapid start-up of SRAO in the water treatment industry and can precisely guide the application of the SRAO process for wastewater containing different organic carbon sources.

Sulfur transformation and bacterial community dynamics in both desulfurization-denitrification biofilm and suspended activated sludge

Types of microbial aggregates have essential effects on bacterial communities' characteristics, thus affecting the pollutants removal. An up-flow biofilm reactor was used to study the different performances of S^2-/NO₂^- removal and functional genes in suspended sludge and biofilms. The metabolic pathways of sulfurous and nitrogenous pollutants in the desulfurization-denitrification process were proposed. The results showed that S⁰ formation dominated the reactor with a high S^2- concentration. Autotrophic Sulfurovum responsible for S^2-/S⁰ oxidation was the only dominant bacteria in suspended sludge. Heterotrophic Desulfocapsa responsible for SO₄^2- reduction coexisted with Sulfurovum and dominated in biofilms. S^2- oxidation to S⁰ was catalyzed via fccA/B and sqr genes in suspended sludge. S₃^2-/S⁰ oxidation to SO₄^2- was catalyzed via dsrA/B gene in biofilms. SO₄^2- and NO₂^- were removed via the dissimilatory sulfate reduction and denitrification pathway, respectively. This work provides a fundamental and practical basis for optimizing suspended sludge/biofilm systems for S^2-/NO₂^- removal.