Differences in Cladonia rangiferina nitrogen uptake capacity between ammonium and nitrate with uptake kinetics.

Atmospheric nitrogen (N) deposition could affect the structure and function of terrestrial plants. Non-N2-fixing lichens are used to monitor atmospheric N deposition because they rely on the deposited inorganic N (i.e., ammonium and nitrate) as N sources. However, the uptake capacities of lichen on ammonium and nitrate remain unclear, which hinders the application of lichen N content to accurate bioindication of atmospheric N deposition levels. We investigated ammonium and nitrate uptake capacities of Cladonia rangiferina, which was treated with ammonium alone, nitrate alone, and ammonium and nitrate mixture solutions with different mixing ratios under light and dark conditions. The results showed that N uptake rates increased with ammonium and nitrate concentrations in solutions and generally followed the Michaelis-Menten saturation kinetics. Ammonium uptake of C. rangiferina showed higher values of affinity, and was more efficient than the nitrate uptake. Both rates and amounts of nitrate uptake decreased with increasing ratios of ammonium to nitrate in solutions, while ammonium uptake showed no substantial variations, indicating an inhibition of ammonium on nitrate uptake capability. The darkness significantly decreased the maximum uptake rate and efficiency of nitrate, but had much weaker effects on lichen ammonium uptake. These findings highlight the preference of lichen on ammonium as a key N uptake strategy. It is thus necessary to consider the main types of atmospheric inorganic N deposition when using lichens to monitor atmospheric N pollution levels and evaluate N deposition based on lichen ecophysiology.

Enhanced and robust nitrogen removal using an integrated zeolite and partial denitrification anammox process.

Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO2--N to NH4+-N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO2--N to NH4+-N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment.

Baffled flow constructed wetland-microbial fuel cell coupling systems for combined secondary and tertiary wastewater treatment with simultaneous bioelectricity generation.

Baffled flow constructed wetland-microbial fuel cell (BFCW-MFC) coupling systems were constructed with baffles embedded in cathode chamber. The performance of BFCW-MFCs operated at different hydraulic retention times (HRTs) was evaluated. At the representative HRT of 48 h, embedding 1 or 2 baffles (i.e., BFCW-MFC1 and BFCW-MFC2) produced 32.9 % (29.5 mW/m3) and 53.2 % (34.0 mW/m3) more power density than control system (22.2 mW/m3), respectively. Comparable organics biodegradation efficiencies were observed in BFCW-MFCs at the same HRTs. BFCW-MFC1 and BFCW-MFC2 had higher ammonium and total nitrogen removal efficiency. All systems had decreased nitrogen removal performance as shortening HRT from 72 to 12 h. Multiple nitrogen removal processes were involved, including ammonium oxidation, anammox, and heterotrophic and autotrophic denitrification. The predominant bacteria on electrodes were identified for analyzing bioelectricity generation and wastewater treatment processes. Generally, simultaneous wastewater treatment and bioelectricity generation were obtained in BFCW-MFCs, and embedding 1 or 2 baffles was preferable.

Transcriptomic analysis reveals insights into the responses of Synechocystis sp. PCC 6803 to acidification during cultivation with ammonium salts as a nitrogen source.

Utilizing ammonium in wastewater is a prospective way to reduce costs for bioproduction by photosynthetic organisms. A model cyanobacterium Synechocystis sp. PCC 6803 takes advantage of tolerance to ammonium compared to other microalgae. However, in this study, we report that Synechocystis growth was inhibited when cultured in a medium containing ammonium. This may be due to the pH decreasing below 6 caused by consuming ammonium. Transcriptomic analysis by RNA-seq revealed that the expression of the genes for proteases, chaperones, and antioxidant-scavenging enzymes was induced, but photosynthetic components were repressed. Although these regulations are similar to the previous studies on acidic stress in nitrate-containing culture, the expression of genes such as sigD, slr0042, slr0373, slr0374, and slr1501 was different, indicating that these phenomena are not simply identical to the known responses to acidic stress. The expression of the genes for photosynthesis, gluconeogenesis, and nitrogen assimilation was repressed, and glycolysis and the tricarboxylic acid cycle were induced. Despite the up-regulation of the carbon catabolism and down-regulation of nitrogen assimilation, the 2-oxoglutarate content in the ammonium-grown cells was lower than that in the nitrate-grown cells, and the contents of the major amino acids, such as Glu, Ala, Asp, and Gly were decreased, while the minor amino acids were the same or increased, especially Arg, Lys, Val, and Ile. These results demonstrated that the acidic stress induced by the consumption of ammonium ions differs from the sudden pH drop, and the Synechocystis cell manages amino acid levels to endure carbon limitation under the stress.

Alternative Oxidase Alleviates Mitochondrial Oxidative Stress during Limited Nitrate Reduction in Arabidopsis thaliana.

The conversion of nitrate to ammonium, i.e., nitrate reduction, is a major consumer of reductants in plants. Previous studies have reported that the mitochondrial alternative oxidase (AOX) is upregulated under limited nitrate reduction conditions, including no/low nitrate or when ammonium is the sole nitrogen (N) source. Electron transfer from ubiquinone to AOX bypasses the proton-pumping complexes III and IV, thereby consuming reductants efficiently. Thus, upregulated AOX under limited nitrate reduction may dissipate excessive reductants and thereby attenuate oxidative stress. Nevertheless, so far there is no firm evidence for this hypothesis due to the lack of experimental systems to analyze the direct relationship between nitrate reduction and AOX. We therefore developed a novel culturing system for A. thaliana that manipulates shoot activities of nitrate reduction and AOX separately without causing N starvation, ammonium toxicity, or lack of nitrate signal. Using shoots processed with this system, we examined genome-wide gene expression and growth to better understand the relationship between AOX and nitrate reduction. The results showed that, only when nitrate reduction was limited, AOX deficiency significantly upregulated genes involved in mitochondrial oxidative stress, reductant shuttles, and non-phosphorylating bypasses of the respiratory chain, and inhibited growth. Thus, we conclude that AOX alleviates mitochondrial oxidative stress and sustains plant growth under limited nitrate reduction.

Nutrient removal in floating and vertical flow constructed wetlands using aluminium dross: An innovative approach to mitigate eutrophication.

On global scale, eutrophication is one of the most prevalent environmental threats to water quality, primarily caused by elevated concentration of nutrients in wastewater. This study utilizes aluminum dross (AD), an industrial waste, to create a value-added material by improving its operational feasibility and application for removing phosphate and ammonium from water. The operational challenges of AD such as its powdered nature and effective operation under only extreme pH conditions were addressed by immobilizing in calcium alginate to form calcium alginate aluminium dross (Ca-Alg-Al dross) beads. These Ca-Alg-Al dross beads were further tested for phosphate and ammonium removal from natural wastewater in two different aqueous environment systems: (i) vertical flow constructed wetlands (VF-CWs) followed by Ca-Alg-Al dross beads fixed bed system and (ii) Ca-Alg-Al dross beads mounted floating constructed wetlands (FCW) for remediating polluted lentic ecosystems. Our results show maximum phosphate and ammonium removal of 85 ± 0.41 % and 93.44 %, respectively, in VF-CWs followed by Ca-Alg-Al dross beads fixed bed system. The Ca-Alg-Al dross beads mounted FCW system achieved maximum phosphate removal of 79.18 ± 8.56 % and ammonium removal of 65.45 ± 21.04 %. Furthermore, the treated water from the FCW system was assessed for its potential to inhibit algal growth by artificially inoculating treated water with natural algae to simulate eutrophic conditions. Interestingly, treated water from the FCW system was found capable of arresting the algal growth. Besides, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy confirmed the functional groups and surface properties and probable participation of multiple mechanisms including ion exchange, electrostatic attraction, and ligand complexation for phosphate and ammonium removal. Overall, these results offer a promising way to utilize AD for high-end applications in wastewater treatment.

Potassium and ammonium recovery in treated urine by zeolite based mixed matrix membranes.

Nitrogen, phosphorus and potassium are essential for crop growth, which are abundant in urine. Although numerous studies have developed techniques to recover ammonium and phosphorus from urine, limited research made efforts on the recovery of potassium, which is a non-renewable resource with uneven global distribution. In this study, we explored the possibility of zeolite based mixed matrix membranes (MMMs) to selectively recover ammonium and potassium from urine, with minimal detention of sodium. The findings demonstrated that upon the pre-treatment of zeolites with sodium chloride solution, a 70 wt% zeolite loaded MMM could achieve 69.3 % recovery of potassium and almost full recovery of ammonium. By varying the desorption temperatures and MMMs production process, it was discovered that stepwise backwash at low temperature (276 K) greatly lowered sodium recovery whilst simultaneously enhancing the recovery of potassium and ammonium. This study demonstrates the potential of recovering potassium and ammonium from urine using zeolite-loaded MMMs, coupled with achieving low-sodium recovery.

Adaptation of the anammox process for high ammonium photovoltaic wastewater treatment.

Tunnel Oxide Passivating Contacts (TOPcon) battery in the photovoltaic industry generates high ammonium wastewater during the production process, the adaptability of using the anaerobic ammonia oxidation (Anammox) process for photovoltaic wastewater (PVW) treatment is a research hotspot. Based on the analysis of photovoltaic wastewater quality, the effectiveness of nitrogen removal, sludge characteristics and microbial communities were examined. The results showed that when the influent NH4+-N concentration of PVW was lower than 150 mg·L-1, the nitrogen removal efficiency (NRE) was almost 100 %. In addition, the NRE decreased from 74 % sharply to 20 % when the NH4+-N concentration was increased from 175 mg·L-1 to 200 mg·L-1. The extracellular polymeric substances (EPS) content increased with elevated ammonium concentration in the influent, indicating that microorganisms secreted more EPS to resist elevated nitrogen loading. The main functional populations were Candidatus Kuenenia (0-24 %). The influent ammonium concentration is recommended to be < 200 mg·L-1.

Ammonium carboxylates in the ammonia-Ugi reaction: one-pot synthesis of α,α-disubstituted amino acid derivatives including unnatural dipeptides.

Despite the remarkable developments of the Ugi reaction and its variants, the use of ammonia in the Ugi reaction has long been recognized as impractical and unsuccessful. Indeed, the ammonia-Ugi reaction often requires harsh reaction conditions, such as heating and microwave irradiation, and competes with the Passerini reaction, thereby resulting in low yields. This study describes a robust and practical ammonia-Ugi reaction protocol. Using originally prepared ammonium carboxylates in trifluoroethanol, the ammonia-Ugi reaction proceeded at room temperature in high yields and showed a broad substrate scope, thus synthesizing a variety of α,α-disubstituted amino acid derivatives, including unnatural dipeptides. The reaction required no condensing agents and proceeded without racemization of the chiral stereocenter of α-amino acids. Furthermore, using this protocol, we quickly synthesized a novel dipeptide, D-Leu-Aic-NH-CH2Ph(p-F), which exhibited a potent inhibitory activity against α-chymotrypsin with a Ki value of 0.091 µM.

Revealing degradation pathways of soluble and dissolved organic matter in alluvial-lacustrine aquifer systems impacted by high levels of geogenic ammonium.

The excessive presence of geogenic ammonium (NH4+) in groundwater poses a global environmental concern, commonly linked to the degradation of nitrogen-containing dissolved organic matter (DOM). However, there is a gap in systematic studies on the combination of soluble organic matter (SOM) in sediments and DOM in groundwater, with few indoor incubation experiments to validate their degradation pathways. This study utilized ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to analyze the molecular characteristics of DOM and SOM in aquifer systems affected by geogenic NH4+. Subsequently, indoor incubation experiments spanning up to 140 d were conducted to verify the degradation pathways. The experimental results revealed a two-phase degradation process for both the DOM and SOM. The initial stage was characterized by the degradation of aliphatic compounds (ALC) with the production of polyphenols (PPE) and highly unsaturated compounds (HUC). The second stage was dominated by the degradation of PPE and HUC, accompanied by the re-consumption of some ALC, while more recalcitrant HUC persisted. Notably, the first stage of SOM degradation exceeded that of DOM degradation, indicating that SOM exhibited greater resistance to aging. This phenomenon may be attributed to a wider range of active enzymes in sediments, the rapid replenishment of SOM by organic matter in sediments, or the accelerated degradation of DOM. The experimental results aligned with the molecular characterization of DOM and SOM in actual aquifer systems. It is hypothesized that NH4+ produced through the direct mineralization of SOM may contribute more to the enrichment of NH4+ in groundwater than that produced through the mineralization of DOM. This study is the first to analyze DOM and SOM together in aquifer systems and validate their degradation pathways through incubation experiments, thereby providing novel insights into the enrichment of geogenic NH4+ in groundwater.

Insights into soil autotrophic ammonium oxidization under microplastics stress: Crossroads of nitrification, comammox, anammox and Feammox.

Microplastics (MPs) are widespread in agroecosystems and profoundly impact soil microbiome and nutrient cycling. However, the effects of MPs on soil autotrophic ammonium oxidization processes, including nitrification, complete ammonium oxidation (comammox), anaerobic ammonium oxidation (anammox), and anaerobic ammonium oxidation coupled to iron reduction (Feammox), remain unclear. These processes are the rate-limiting steps of nitrogen cycling in agroecosystems. Here, our work unveiled that exposures of polyethylene (PE), polypropylene (PP), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) MPs significantly modulated ammonium oxidization pathways with distinct type- and dose-dependent effects. Nitrification remained the main contributor (56.4-70.7 %) to soil ammonium removal, followed by comammox (11.7-25.6 %), anammox (5.0-20.2 %) and Feammox (3.3-11.6 %). Compared with conventional nonbiodegradable MPs (i.e., PE and PP), biodegradable MPs (i.e., PLA and PBAT) exhibited more pronounced impacts on soil nutrient conditions and functional microbes, which collectively induced alterations in soil ammonium oxidation. Interestingly, low-dose PLA and PBAT remarkably enhanced the roles of anammox and Feammox in soil ammonium removal, contributing to the mitigation of soil acidification in agroecosystems. This study highlights the diverse responses of ammonium oxidization pathways to MPs, further deepening our understanding of how MPs affect biogeochemical cycling and enriching strategies for agricultural managements amid increasing MPs pollution.

Enhanced-nitrogen removal through Fe(III)-triggered partial dissimilatory nitrate reduction to ammonium coupling with anammox in anammox bioreactor.

Anammox is recognized as a prospective alternative for future biological nitrogen removal technologies. However, the nitrate by-products produced by anammox bacteria limit its overall nitrogen removal efficiency below 88 %. This study introduced Fe(III) into the anammox bioreactor to enhance the nitrogen removal efficiency to approximately 95 %, surpassing the biochemical limit of 88 % imposed by anammox stoichiometry. Anammox sludge was demonstrated to utilize extracellular polymeric substances to reduce Fe(III) into Fe(II), and this process promoted the dominance of Ca. Brocadia. The iron addition improved the abundance of narGHI genes and facilitated the partial dissimilatory nitrate reduction to ammonium, with nitrite as the end product. The accumulated nitrite was then eliminated through the anammox pathway, along with the excess ammonium (30 mg/L) in the influent. Overall, this study deepens our understanding of the enhanced nitrogen removal triggered by Fe(III) in anammox sludge and offers an effective approach to boost anammox process.

Genomic analysis and metabolic characteristics provide insights into inorganic nitrogen metabolism of novel bacterium Acinetobacter pittii J08.

A novel A. pittii J08 with heterotrophic nitrification and aerobic denitrification (HN-AD) isolated from pond sediments could rapidly degrade inorganic nitrogen (N) and total nitrogen (TN-N) with ammonium (NH4+-N) preference. N degradation rate of NH4+-N, nitrite (NO2--N) and nitrate (NO3--N) were 3.9 mgL-1h-1, 3.0 mgL-1h-1 and 2.7 mgL-1h-1, respectively. In addition, strain J08 could effectively utilize most of detected low-molecular-weight carbon (LMWC) sources to degrade inorganic N with a wide adaptability to various culture conditions. Whole genome sequencing (WGS) analysis revealed that assembled genome of stain J08 possessed the crucial genes involved in dissimilatory/assimilatory NO3--N reduction and NH4+-N assimilation. These results indicated that strain J08 could be applied to wastewater treatment in aquaculture.

Microbial nitrogen nutrition links to dissolved organic matter properties in East African lakes.

East African lakes, especially soda lakes, are home habitats for massive numbers of wildlife such as flamingos, mammals, and fishes. These lakes are known for their high primary production due to local high temperatures, light intensities, and alkalinity (inorganic carbon). However, these lakes, normally within remote areas, receive low nutrient inputs. Ammonium (NH4+) recycling and/or nitrogen fixation can become the major N supply mechanisms for phytoplankton. However, the driving forces on microbial N nutrition in lakes with minimal anthropogenic disturbance remain poorly understood. Using stable isotope tracer techniques, NH4+ recycling rates were measured in 18 lakes and reservoirs in East Africa (Tanzania and Kenya) during the dry season in early 2020. Three functional genes (nifH, gdh, and ureC) relating to microbial N nutrition were also measured. The regeneration of NH4+ supported up to 71 % of the NH4+ uptake. Positive community biological NH4+ demands (CBAD) for all lakes and reservoirs indicate an obvious N demand from microbial community. Our study provides clear evidence that microbial NH4+ uptake rates linked closely to the dissolved organic matter (DOM) properties (e.g., the absorption coefficient at 254 nm, percents of total fluorescence intensity contributed by microbial humic-like and protein-like components) and that water residence time drives microbial NH4+ recycling by regulating the duration of in-lake DOM processing and influencing algal growth. Phytoplankton, especially those of Cyanophyceae, showed maximum biomass and higher NH4+ recycling rates at a certain range of water residence time (e.g., 5-8 years). However, CBAD showed a decreasing trend with longer water residence time, which may be influenced by changes in the algal community composition (e.g., % Cyanophyceae vs. % Bacillariophyceae). These results indicate that DOM dynamics and the water residence time have the potential to facilitate the understanding of microbial nitrogen supply status in East African lakes.

Rapid start-up and stable operation of pilot scale denitrification-partial nitritation/anammox process for treating electroplating tail wastewater.

This study explored a novel economical and efficient process for treating actual low-ammonia nitrogen electroplating tail wastewater. A pilot scale system of denitrification-partial nitrification/anaerobic ammonium oxidation (DN-PN/A) was constructed and operated for 190 days. The partial nitrification (PN) reactor, filled with zeolite, increased free ammonia concentration beyond the nitrite oxidizing bacteria threshold and successfully supplied NO2--N, with nitrite accumulation rate exceeding 90 %. Over 109 days, the total nitrogen removal rate achieved was 80.2 ± 7.41 %, and the chemical oxygen demand removal rate reached 79.68 ± 9.53 %. The dominant functional bacteria were Nitrosomonas (5.45 %) and Candidatus Anammoxoglobus (28.84 %) in PN reactor and anaerobic ammonium oxidation (Anammox) reactor. This process, characterized by rapid start-up, strong shock resistance, and low cost, alleviates the pressure of ammonium pollution control, promotes the sustainable development of the electroplating industry and has the potential for application in the treatment of other industrial wastewater.

The adaptive regulation mechanism of Anammox granule sludge under calcium ions stress: Defense modes transformation.

Anammox granular sludge (AnGS) has received considerable attention due to its low carbon footprint (less aeration energy and carbon source consumption) and high biomass density, but growth rate and stability are still the bottlenecks of AnGS process. Calcium ion (Ca2+) is essential for the growth of anaerobic ammonium oxidation bacteria (AnAOB) and plays an important role in the formation and stability of AnGS. Response of AnGS to Ca2+ under different concentrations was comprehensively investigated by multi-spectral and metagenomics analysis in four aspects: nitrogen removal performance, surface morphology, extracellular polymeric substance (EPS) composition and characterization, and microbial community. The nitrogen removal efficiency was significantly enhanced at appropriate Ca2+ concentration (2 mmol/L), owning to the more favorable morphology and functional microbial composition of AnGS. However, the nitrogen removal performance of AnGS declined with the Ca2+concentration increased from 2 to 8 mmol/L, due to the negative effects of excess Ca2+on EPS, mass transfer efficiency, and functional microorganisms. Meanwhile, an unexpected slight "rebound" of nitrogen removal efficiency was observed at Ca2+ = 6 mmol/L and attributed to the defense mode transformation of AnGS (from "ion stabilization" to "precipitate shield" modes) against excess Ca2+ stress. Based on the findings, the response mechanism of AnGS to Ca2+ with different concentrations was established. Our results enhanced the understanding of the interaction between AnGS and Ca2+, which may be valuable for filling the theoretical gap in enhancing the granulation and stability of AnGS and providing a reference for the practical operation of the AnGS process.

Effects of salinity on nitrogen reduction pathways in estuarine wetland sediments.

Denitrification, anammox, and DNRA are three important nitrogen (N) reduction pathways in estuarine sediments. Although salinity is an important variables controlling microbial growth and activities, knowledge about the effects of changing salinity on those three processes in estuarine and coastal wetland sediments are not well understood. Herein, we performed a 60-d microcosms experiment with different salinities (0, 5, 15, 25 and 35 ‰) to explore the vital role of salinity in controlling N-loss and N retention in estuarine wetland sediments. The results showed that sediment organic matter, sulfide, and nitrate (NO3-) were profoundly decreased with increasing salinity, while sediment ammonium (NH4+) and ferrous (Fe2+) varied in reverse patterns. Meanwhile, N-loss and N retention rates and associated gene abundances were differentially inhibited with increasing salinity, while the contributions of denitrification, anammox, and DNRA to total nitrate reduction were apparently unaffected. Moreover, denitrification rate was the most sensitive to salinity, and then followed by DNRA, while anammox was the weakest among these three processes. In other words, anammox bacteria showed a wide range of salinity tolerance, while both denitrification and DNRA reflected a relatively limited dynamic range of it. Our findings could provide insights into temporal interactive effects of salinity on sediment physico-chemical properties, N reduction rates and associated gene abundances. Our findings can improve understanding of the effects of saltwater incursion on the N fate and N balance in estuarine and coastal sediments.

Multi-stage oxic biofilm system for pilot-scale treatment of coking wastewater: Pollutants removal performance, biofilm properties and microbial community.

A multi-stage oxic biofilm system based on hydrophilic polyurethane foam was established and operated for advanced treatment of coking wastewater, in which distinct gradient variations of pollutants removal, biofilm properties and microbial community in the 5 stages were evaluated. The system rapidly achieved NH4+-N removal efficiency of 97.51 ±â€¯2.29 % within 8 days. The biofilm growing attached on the carriers exhibited high biomass (≥10.29 g/L), which ensured sufficient microbial population. Additionally, the rising extracellular polymeric substance and declining proteins/polysaccharides ratios across stages suggested a dense-to-loose transition in the biofilm's structure, in response to the varying pollutant concentrations. The dominance of Nitrosomonas cluster in the first 3 stages and Nitrospira lineage in the following 2 stages facilitated the complete depletion of high NH4+-N concentration without NO2--N accumulation. Overall, the distinct biofilm property and community at each stage, shaped by the multi-stage configuration, maximized the pollutants removal efficiency.

Response of anammox to organics with different degradation characteristics and exposure time: Performance, sludge characteristics and bacterial community.

The effects of typical organic compounds including easily degradable organic matters sodium acetate, yeast and methanol, and refractory organic matter (ROM) humic acid on anaerobic ammonium oxidation (anammox) systems in short-term and medium-term exposure time were studied. During short-term experiments, nitrogen removal activity (NRA) was inhibited at sodium acetate level of 150 mg L-1 total organic carbon (TOC) and methanol level of 30-150 mg L-1 TOC, but humic acid and yeast (≤150 mg L-1 TOC) enhanced nitrogen removal in anammox systems. The greatest NRA of 30.10 mg TN g-1 VSS h-1 was recorded at yeast level of 90 mg L-1 TOC. In medium-term experiments, organics significantly inhibited the nitrogen removal ability. As a ROM, humic acid enhanced sludge aggregation and biological diversity, but decreased the bioactivity and extracellular polymeric substances levels. Due to the endogenous denitrification, the relative abundance of anammox bacteria (AnAOB) was decreased. Candidatus Kuenenia is still dominant in sludge with methanol and humid acid, but AnAOB are not dominant due to the addition of sodium acetate and yeast. This research would be beneficial for the full-scale application of the anammox process in treating real wastewater with organics and ammonia.

Novel insights into Feammox coupled with the NDFO: A critical review.

Ammonium oxidation coupled with Fe(III) reduction, known as Feammox, and nitrate-dependent ferrous oxidation (NDFO) are two processes that can be synergistically achieved through the Fe(III)/Fe(II) cycle. This integrated approach enables the simultaneous removal of ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) from wastewater, representing a novel method for complete nitrogen removal. This study presents a systematic and exhaustive examination of the Feammox-NDFO coupled process. An initial thorough exploration of the underlying mechanisms behind the coupling process is conducted, highlighting how the Fe(III)/Fe(II) cycle enables the concurrent occurrence of these reactions. Further, the functional microorganisms associated with and playing a crucial role in the Feammox-NDFO process are summarized. Next, the key influencing factors that govern the efficiency of the Feammox-NDFO process are explored. These include parameters such as pH, temperature, carbon source, iron source, nitrogen source, and various electron shuttles that may mediate electron transfer. Understanding the impact of these factors is essential for optimizing the process. The most recent trends and endeavors on the Feammox-NDFO coupling technology in wastewater treatment applications are also examined. This includes examining both laboratory-scale studies and field trials, highlighting their successes and challenges. Finally, an outlook is presented regarding the future advancement of the Feammox-NDFO technology. Areas of improvement and novel strategies that could further enhance the efficiency of simultaneous nitrogen removal from the iron cycle are discussed. In summary, this study aspires to offer a thorough comprehension of the Feammox-NDFO coupled process, with a focus on its mechanisms, influencing factors, applications, and prospects. It is anticipated to yield invaluable insights for the advancement of process optimization, thus sparking fresh ideas and strategies aimed at accomplishing the thorough elimination of nitrogen from wastewater via the iron cycle.