Nitrogen Removal Rate Research Articles

Study on the enhancement of low carbon-to-nitrogen ratio urban wastewater pollutant removal efficiency by adding sulfur electron acceptors.

The effective elimination of nitrogen and phosphorus in urban sewage treatment was always hindered by the deficiency of organic carbon in the low C/N ratio wastewater. To overcome this organic-dependent barrier and investigate community changes after sulfur electron addition. In this study, we conducted a simulated urban wastewater treatment plant (WWTP) bioreactor by using sodium sulfate as an electron acceptor to explore the removal efficiency of characteristic pollutants before and after the addition of sulfur electron acceptor. In the actual operation of 90 days, the removal rate of sulfur electrons' chemical oxygen demand (COD), ammonia nitrogen, and total phosphorus (TP) with sulfur electrons increased to 94.0%, 92.1% and 74%, respectively, compared with before the addition of sulfur electron acceptor. Compared with no added sulfur(phase I), the reactor after adding sulfur electron acceptor(phase II) was demonstrated more robust in nitrogen removal in the case of low C/N influent. the effluent ammonia nitrogen concentration of the aerobic reactor in Pahse II was kept lower than 1.844 mg N / L after day 40 and the overall concentration of total phosphorus in phase II (0.35 mg P/L) was lower than that of phase I(0.76 mg P/L). The microbial community analysis indicates that Rhodanobacter, Bacteroidetes, and Thiobacillus, which were the predominant bacteria in the reactor, may play a crucial role in inorganic nitrogen removal, complex organic degradation, and autotrophic denitrification under the stress of low carbon and nitrogen ratios. This leads to the formation of a distinctive microbial community structure influenced by the sulfur electron receptor and its composition. This study contributes to further development of urban low-carbon-nitrogen ratio wastewater efficient and low-cost wastewater treatment technology.

Novel Start-up for Moving Bed Biological Reactors for Nitrogen Removal with High C/N Influent by Heterotrophic Nitrification and Aerobic Denitrification

A novel start-up strategy for MBBR systems was implemented that achieved removal rates of ammonia and total nitrogen of more than 90% and 70%, respectively, with influent C/N ratio of nine. The strategy consists of operating the MBBR with non-nitrified secondary effluent (C/N=2) until ammonia removal is sustained and gradually increase the C/N ratio of the feed to the target value of nine, when the MBBR system is fed primary effluent. Before using the start-up sequence, the MBBR system treating primary effluent (C/N=9) showed negligible ammonia removal after 120 days of operation, indicating the absence of nitrifying bacteria. It was assumed that heterotrophs were outcompeting autotrophs, and the C/N ratio was decreased to allow autotrophs to proliferate. Genomic analysis indicated the presence of bacterial and fungal populations, which can perform nitrification and denitrification. The most abundant heterotrophs observed were Proteobacteria at 31%, Bacteroidetes at 22%, and Actinobacteria at 8%. The most abundant fungal population belonged to Ascomycota (10%), Basidiomycota (10%), and Mucoromycota (1%). Heterotrophic nitrification and aerobic denitrification were found to play an important role in nitrogen removal at C/N=9. Autotrophs may have proliferated at lower C/N ratio as total nitrogen removal was low, but at higher C/N a shift in microbial population should have taken place as indicated by the dominance of heterotrophs.

Effects of different cathode conditions on electricity generation and removal of heavy metal pollutants in CW-MFC

The effect of treating copper-containing wastewater by CW-MFC technology was discussed. The power generation and wastewater purification efficiency of CW-MFC are affected by electrode spacing, cathode electrode area and influent copper concentration. Smaller electrode spacing may destroy the anaerobic environment in the wastewater, while larger electrode spacing will increase the total internal resistance of the system, resulting in a decrease in electricity generation efficiency. With the increase of cathode area, the removal efficiency of pollutants in wastewater will be improved. However, when the cathode area is too large, it will increases the internal resistance of the system, which will affect the electric production performance. When the best electrode spacing is 10 cm and the cathode electrode area is 75 cm2, CW-MFC shows the best power generation and wastewater purification effect. When the concentration of copper in the wastewater increases, the power generation and wastewater purification efficiency of the system will also increase. When the copper concentration reaches 50 mg/L, the system shows the best effect, its open circuit voltage reaches the maximum, and the removal rate of copper and total nitrogen is also the highest. When the concentration of copper in wastewater reaches 100 mg/L, the microbial activity is inhibited, resulting in a significant decline in the performance of CW-MFC.

Effect of phosphorus on the performance of sulfur autotrophic denitrification

Autotrophic denitrification, recognized as a biological denitrification method, has garnered increasing interest in the field of ecological water environment denitrification technology. This study focuses on the utilization of the sulfur autotrophic denitrification process for the deep denitrification treatment of wastewater. Furthermore, it investigates the impact of phosphorus on nitrogen removal efficiency and bacterial community structure of sulfur autotrophic denitrification. In the experiment, a column containing an autotrophic denitrification filter with a carbon-sulfur filler was constructed. This study aimed to examine the impact of phosphorus on the initiation and denitrification efficiency of the autotrophic denitrification filter column. High-throughput sequencing was used to examine alterations in the structure of the bacterial community. The experimental findings indicated that the absence of phosphorus in the influent considerably extended the initiation period of the autotrophic denitrification filter column. The average Total Inorganic Nitrogen (TIN) removal rate was determined to be 80.26%, while the effluent exhibited an accumulation concentration of NO2−-N ranging from 7 to 11 mg/L. After the addition of phosphate, the removal rate of NO3−-N in the autotrophic denitrification process increased to more than 97%, with no2−-N accumulation. As the influent phosphorus concentration increased, the ability of the sulfur autotrophic denitrification filter column to resist hydraulic impact load improved. At a NO3−-N concentration of 30 mg/L and Hydraulic Retention Time (HRT) = 2 h, the mean NO3−-N removal rate increased from 73.22% to 81.71%. The concentration of phosphorus affected the quantity and variety of primary bacteria in the sulfur autotrophic denitrification system, as their domination changed from Pseudomonas to Ferritrophicum and Thiobacillus, and from a mixed culture to complete autotrophy.

Isolation of a marine-derived yeast with potential applications in industrial nitrite utilizing.

The nitrite efficient utilization microorganism Wickerhamomyces anomalus RZWP01 was identified. Using nitrite and ammonium as the sole nitrogen source, the nitrogen removal rate of W. anomalus RZWP01 was 97.4% and 87.1%, respectively. W. anomalus RZWP01 grew well in the nitrite medium with glucose or xylose as the only carbon source. However, the W. anomalus RZWP01 cannot live on the nitrite medium with lactose, citric acid, and methanol as the only carbon source. The maximal cell concentration occurred in the nitrite medium with glucose as the only carbon source at a C/N ratio of 20 for 48h, reaching 8.92 × 108 cell mL-1. W. anomalus RZWP01 was the first reported yeast that can efficiently utilize nitrite. The isolation and identification of W. anomalus RZWP01 enriched the microbial resources of nitrite-degrading microorganisms and provided functional microorganisms for the water treatment of sustainable aquaculture.

AnCMBR-AFB-integrated process for the treatment of high nitrogen and phosphorus wastewater.

Improving the nitrogen and phosphorus removal rates and efficiently controlling membrane fouling are the keys to fully exploiting the applicability of anaerobic membrane bioreactor (AnMBR) process in high-concentration wastewater treatment. To that purpose, an integrated reactor composed of an anaerobic ceramic membrane bioreactor and N anaerobic fluidized bed (AnCMBR-AFB) was built and pollutant removal efficiency, nitrogen and phosphorus recovery characteristics, and membrane pollution features of this integrated reactor were investigated. The results revealed that the integrated reactor had good pollutant removal efficiency, with turbidity, chromaticity, and UV254 average values of the effluent being 0.470 NTU, 0.011 A, and 0.057 cm-1, respectively, and the average CODCr removal rate was 80%. The nitrogen and phosphorus recoveries were significantly higher than the nitrogen and phosphorus removal rates of conventional AnMBR at 23.20 ± 1.17% and 43.34 ± 1.54%, respectively. Microscopic analysis revealed the formation of magnesium ammonium phosphate (MAP) crystals on the carrier's surface, and friction between the carrier and the membrane surface could delay membrane fouling while allowing the contaminated membrane surface to retain significant roughness. Membrane fouling was mostly brought on by amides and saturated hydrocarbons, and inorganic metal ions also played a role to some extent.

Carrier with cyclodextrin and quorum sensing synergy: An efficient method for selective enrichment of anammox bacteria

High-efficiency enrichment of functional bacteria is one of the biggest technical barriers to the application of anaerobic ammonium oxidation (anammox). This study combined biofilm carriers and quorum sensing to achieve rapid biomass accumulation. A biofilm carrier with biomass adsorption and quorum sensing regulation functions was developed for the rapid start-up of the reactor and enrichment of anammox bacteria (AnAOB). The nitrogen removal rates of the three reactors were further tested, and the carrier mechanism was explored. The start-up time of the reactor with the modified carriers was 28 days, which was ∼44 % shorter than that of the reactor without carriers. After 90 days of operation, the absolute abundance of total AnAOB was 3.2 times that in the control group. The modified carrier promoted the rapid adhesion of biomass through the hydrophobic cavity of cyclodextrin and induced rapid proliferation, enhancement of activity, and extracellular protein secretion of AnAOB through quorum sensing signaling molecules. Finally, a special hydrophobic biofilm with granular sludge characteristics was formed on the modified carrier through the self-assembly of hydrophobic biomass particles. Overall, we propose a novel approach to enrich anammox bacteria involving a combination of quorum sensing and biofilm carriers.

Nitrogen removal and performance deterioration in digested effluent treatment by partial nitrification-anammox (PNA) process based on aeration sedimentation integrated microaerobic reactor (ASIMR)

The existing microaerobic reactors for PN/A process have the drawbacks of complex structure and hard to scale-up in full scale application. Aiming at these problems, we have designed new aeration sedimentation integrated microaerobic reactor (ASIMR). The feasibility of ASIMR for PN/A processes and the optimal HRT were explored by gradually reducing the hydraulic retention time (HRT). When the HRT was 4.45 h and the NLR was 3.98 kg·(m3·d)-1, ASIMR achieved the highest nitrogen removal performance, with the ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (NRE) of 90.5 % and 79.2 %, respectively, and the total nitrogen removal rate (NRR) could reach 3.15 kg·(m3·d)-1. When HRT decreased to 3.60 h with the NLR of 4.76 kg·(m3·d)-1, the performance deterioration was observed, with ARE and NRE decreasing to 35.9 % and 12.4 %, and NRR decreasing to 0.59 kg·(m3·d)-1. The main reasons for the decrease in nitrogen removal performance were overhigh hydraulic load in the sedimentation zone which led to the loss of nitrifying sludge. The loss of nitrifying sludge in turn reduced the efficiency of ammonia nitrogen removal resulting in the accumulation of free ammonia (FA) which inhibited the activity of nitrogen removal functional bacteria. Although reactor performance deteriorated at too low HRT, when the HRT was much than 4.45 h, ASIMR could achieve a good performance for nitrogen removal owe to the combined action of reactor design, enriched nitrified and anammox sludge as inoculum, and dissolved oxygen control. Except good nitrogen removal performance, ASIMR has another advantage, such as simple structure, low cost for manufacture, and more suitable for engineering scale-up in full scale application.

Resource-efficient nitrogen and salinity removal in a synergistic partial nitritation-anammox bioelectrochemical system

We investigated the performance of a two-stage partial-nitritation-anammox biocathode integrated microbial desalination cell (TNiAmoxMDC) for concurrent nitrogen removal, desalination, and bioelectricity generation at different aeration rates in the nitritation chamber. The TNiAmoxMDC system achieved a maximum total nitrogen removal rate of 50.4 ± 8.2 g-TN/m3/d with 300 mW/m2 of maximum power production utilizing 500 mg/L of glucose chemical oxygen demand (COD) in the anode. The organic removal in the anode chamber showed a good fit to first order reaction model with a rate constant of 0.036 h−1. The biocatalytic activity of anammox bacteria in the biocathode produced a current density of 0.7 A/m2 in the absence of oxygen. More than 98% of the salinity was removed at a rate of 1.48 mg/h. The energy consumption values for nitrogen removal at aeration rates of 0.7, 2.2, and 10 ml/min were 0.022, 0.55, and 0.20 kWh/kg-N, respectively. The maximum energy produced by the TNiAmoxMDC was 0.0157 kWh/m3. Excluding the energy consumption by the system, the net energy recovery was 0.0023 kWh/m3 at an airflow rate of 10 ml/min. Thus, the integration of the partial nitritation-anammox process with microbial desalination cell (MDC) provides energy-and resource-efficient synergy for bioelectrochemical wastewater treatment.

Experiments with indigenous green algae under varying N and P regimes for revealing their potential in phycoremediation and biomass yield

ABSTRACT Three series of experimental treatments were carried out to assess five indigenous green algae for biomass quality, productivity, and phycoremediation potential under varying N, P, NP, and N:P in Bold’s Basal Medium. Algae showed species-specific responses to particular concentrations of N, P, NP, and N:P ratio in the medium. Most species showed their highest yield and productivity in N-varied treatments (2–3 × N with N:P = 3.42–5.13), whereas the lowest yield occurred in P-varied treatments (3–4 × P with N:P = 0.68–0.53). A low N:P from a decrease in N was favourable to Chlamydopodium starrii, whereas a low N:P from an increase of P was favourable to Chlorococcum humicola. A high N:P from an increase of N was favourable to Scenedesmus javanensis. An increase of N:P by adding more N increased the nitrogen removal rate (NRR) of C. humicola and S. javanensis. However, S. javanensis showed the highest phosphorus removal rate (PRR) at low N:P (0.68) from 3 × P in the medium. Algal protein content was directly proportional to the amount of nitrogen in all species except S. javanensis. Chlamydopodium starrii showed the highest protein content at 4 × N in the medium. N starvation stimulated an increase of lipid content in all five microalgae, and the lipid content of C. starrii and Parachlorella kessleri was significantly higher than that of others. Overall, the experiment constitutes a model to identify the optimum nutrient requirements for maximum phycoremediation potential and quality biomass productivity of particular algal species.

Liquid-phase adsorption of nitrogen compounds from model diesel fuel on activated carbons

One of the great challenges in deep hydrodesulfurization (HDS) to produce ultra-low-sulfur diesel (ULSD) is the coexisting heterocyclic nitrogen-containing compounds in middle distillates, which significantly inhibit the HDS reactions. This study investigates various activated carbon (AC) samples for selectively removing nitrogen compounds from a model diesel fuel through adsorption. The physical and chemical properties of the AC samples were characterized using low-temperature N2 adsorption–desorption, SEM–EDS, and FT-IR to explore their impact on the adsorption performance. The results indicate that the adsorption performance is influenced not only by the surface area and by the number of oxygen-containing functional groups on the surface but also by the pore diameter distribution. Among all AC samples tested, AC-W exhibited the highest adsorption capacity, achieving a nitrogen removal rate of 97.8% with the addition of 10 wt.% of AC-W. The adsorption capacity was approximately 24.0 mg-N/g-A at a nitrogen equilibrium concentration of 200 ppmw. The adsorption isotherms for total nitrogen and individual nitrogen compounds in the fuel over AC can be described well by the Freundlich isotherm model. An approach for improving the ADN performance of AC is discussed based on the findings in this study.

Improved performance of single-stage partial nitritation-anammox membrane bioreactor (PN/A MBR) by adding biofilm carriers: start-up, membrane operation and microbial structure

Serious sludge washout is a bottleneck in the partial nitritation-anammox (PN/A) process that needs to be addressed urgently. A membrane bioreactor (MBR) is suitable for the PN/A process because of its 100 % biomass retention ability. Therefore, this study establishes a single-stage PN/A MBR and a PN/A moving bed membrane reactor (PN/A MB-MBR) for investigating the operation performance, membrane fouling behavior, and effect of biofilm carrier addition. The results demonstrate that the PN/A MB-MBR achieves a significantly shorter start-up time and substantially higher maximum nitrogen removal rate (NRR) of 17 days and 1.02 g N/L/d, respectively, compared to that of PN/A MBR (61 days and 0.19 g N/L/d, respectively). Further, the PN/A MB-MBR exhibits a lower membrane fouling of 0.023 kPa/L compared to that of 0.050 kPa/L in PN/A MBR because of the integration of the biofilm carrier. The biofilm in PN/A MB-MBR shows a higher relative abundance of Candidatus Kuenenia (18.90–25.10 %), which is a major AnAOB, compared to that observed in the suspended sludge of PN/A MB-MBR (10.30–14.32 %). Furthermore, the relative abundance of Candidatus Kuenenia absorbed on the membrane surface of PN/A MB-MBR (8.6 %) was lower than that on PN/A MBR (15.5 %). This study presented a promising method for enhancing the performance of PN/A MBR, which can serve as a valuable reference for its extensive implementation.

RETRACTED: Enhanced biofiltration coupled with ultrafiltration process in marine recirculating aquaculture system: Fast start-up of nitrification and long-term performance

In marine recirculating aquaculture systems (RAS), the biological nitrification system usually suffers from long time start-up and proliferation of potential pathogenic bacteria under the high salinity stress. This study aims to develop a strategy for fast start- up and long-term biosecurity of marine RAS by using a combined biofiltration system (ceramic rings (CR) - granular activated carbon (GAC) - ultrafiltration (UF) process) in an actual marine RAS for selenotoca multifasciata. The ammonia nitrogen and dissolved organic matter (DOM) removal performance, membrane fouling characteristics and microbial communities during long-term operation (200 days) were investigated. The CR-GAC-UF process minimized the start-up time of the nitrification system to 14 days under low ammonia concentrations (below 2 mg/L). Long-term operation of the marine RAS with ammonia and nitrite nitrogen stabilized below 0.1 mg/L with a daily ammonia nitrogen removal rate of 91.7 %. The UF membranes were operated at fluxes at 15 LHM and the protein/polysaccharide ratios of soluble microbial products (SMP) and extracellular polymeric substances (EPS) on the membranes were stable below 0.5 with low fouling levels. A number of bacterial genera that have the potential to degrade protein and humic-like substances were recognized, which was related to the long-term DOM removal. Candidatus_Nitrosopumilus, Nitrosomonas_sp. and Nitrospira sp. ENR4 were detected as the core nitrifiers in CR-GAC-UF process, which were closely related to the amoABC, hao and nxrA genes (p < 0.05). With the multi-stage barrier of CR-GAC-UF, the heterotrophic plate count in therecirculating water was kept at 3 ± 1 CFU/mL and the relative abundance of potential pathogens declined gradually below 0.81 %. Taken together, this study provides a theoretical basis for the wider application of marine RAS.

Characteristics of nutrient element migration in electrodeionization process

In this work, a constructed five-compartment electrodeionization (EDI) device was used to treat simulated wastewater with ammonium and phosphate ions. The voltage and influent concentration in the EDI system were examined. Meanwhile, the ion migration characteristics in the EDI were studied. Results showed that at optimal conditions, operating at 15 V, with an ammonia nitrogen concentration of 1500 mg/L, and a phosphate concentration of 300 mg/L, the removal rates of ammonia nitrogen and phosphate were 98.50 % and 73.85 %, respectively. The energy consumption of ammonia and phosphorus was 1.347 kWh/mol and 43.629 kWh/mol. The ion migration characteristic experiments revealed that adsorption and desorption rates of the resin do not impose limitations on ion migration in EDI; the ion migration in EDI device is mainly through the resin phase and the rate of ion migration is intricately influenced by the concentration of nutrient ions present on the resin.

A novel pure biofilm system based on aerobic denitrification for nitrate wastewater treatment: Exploring the feasibility of high total nitrogen removal under low-carbon condition

To improve the poor denitrification efficiency of traditional biological treatment for low-carbon wastewater, a novel pure biofilm moving bed biofilm reactor (PH-MBBR) based on heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was proposed. The start-up of PH-MBBR inoculated with HN-AD bacteria and the operating performances and microbial community composition under various C/N ratios were studied. The results showed that at C/N ratio of only 4, the total nitrogen (TN) removal rate of 10.02 mg/(L·h) was achieved under aerobic conditions. Microbial analysis indicates that the synergistic effect of oligotrophic bacteria Thauera and Azoarcus was the main reason for the high pollutant removal at C/N ratio of 4. Furthermore, the analysis of functional genes and enzymes reveals that NorB and NosZ played important roles in nitrate metabolism in PH-MBBR, and aerobic denitrification pathway was NO3–-N → NO → N2O → N2. This study provides a practical and theoretical basis for low-carbon nitrate wastewater treatment.

The influence of electric current density on specific denitrification rate of and nitrogen removal rate in electrochemical and electrobiological rotating contactor

The influence of electric current density on specific denitrification rate of and nitrogen removal rate in electrochemical and electrobiological rotating contactor

Multipathway of Nitrogen Metabolism Revealed by Genome-Centered Metatranscriptomics from Pyrite-Guided Mixotrophic Partial Denitrification/Anammox Installations.

Further reducing the organic requirements is essential for the sustainable development of partial denitrification/anammox technology. Here, an innovative mixotrophic partial denitrification/anammox (MPD/A) installation fed with pyrite and few organics was realized, and the average nitrogen and phosphorus removal rates were as high as 96.24 ± 0.11% and 79.23 ± 2.06%, respectively, with a C/N ratio of 0.5. To understand the nature by which MPD/A achieves efficient nitrogen removal and organic conservation, the electron transfer-dependent nitrogen escape and energy metabolism were first elucidated using multiomics analysis. Apart from heterotrophic denitrification and anammox, the results revealed some unexpected metabolic couplings of MPD/A systems, in particular, putative nitrate-dependent organic and pyrite oxidation among nominally heterotrophic Denitratisoma (PRO3) strains, which accelerated nitrate gasification with a low-carbon supply. Additionally, Candidatus Brocadia (AMX) employed extracellular solid-state electron acceptors as terminal electron sinks for high-rate ammonium removal. AMX transported ammonium electrons to extracellular γFeO(OH) (generated from pyrite oxidation) through the transient storage of menaquinoline pools, cytoplasmic migration via multiheme cytochrome(s), and OmpA protein/nanowires-mediated electron hopping on cell surfaces. Further investigation observed that extracellular electron flux resulted in the transfer of more energy from the increased oxidation of the electron donor to the ATP, supporting nitrite-independent ammonium removal.

Deciphering performance and microbial characterization of marine anammox bacteria-based consortia treating nitrogen-laden hypersaline wastewater: Inhibiting threshold of salinity

Hypersaline wastewater posed a challenge to microbial nitrogen removal processes. Herein, halophilic marine anammox bacteria (MAB) were applied to treat nitrogen-rich wastewater with 35–90 g/L salts for the first time. It was found that MAB, with low relative abundance (2.3–6.9 %), still exhibited good nitrogen removal efficiency (>90 %) under 35–70 g/L salts. The specific anammox activity peaked at 180.16 mg N/(g·VSS·d) at 65 g/L salts. MAB secreted more extracellular polymeric substances to resist the adverse effects of hypersaline stress. Nevertheless, the nitrogen removal deteriorated at 75 g/L salts, and further collapsed as the salinity increased. At 90 g/L salts, total nitrogen removal rate decreased by 74 % compared with that of 35 g/L salts. Besides, SBR1031 increased from 12.0 % (35 g/L salts) to 17.4 % (90 g/L salts) and became the dominant bacterial genus in the reactor. This work shed light on the treatment of hypersaline wastewater through MAB.

Efficient reactivation of anammox sludge after prolonged storage using a combination of batch and continuous reactors.

Due to the slow growth rate of anammox bacteria, enriched sludge is required for the rapid start-up of anammox-based reactors. However, it is still unclear if long-term stored anammox sludge (SAS) is an effective source of inoculum to accelerate reactor start-up. This study explored the reactivation of long-term SAS and developed an efficient protocol to reduce the start-up period of an anammox reactor. Although stored for 13months, a low level of the specific anammox activity of 28mg N/g VSS/d was still detected. Experimental Phase 1 involved the direct application of SAS to an upflow sludge bed reactor (USB) operated for 90 d under varying conditions of hydraulic retention time and nitrogen concentrations. In Phase 2, batch runs were executed prior to the continuous operation of the USB reactor. The biomass reactivation in the continuous flow reactor was unsuccessful. However, the SAS was effectively reactivated through a combination of batch runs and continuous flow feed. Within 75days, the anammox process achieved a stable rate of nitrogen removal of 1.3g N/L/day and a high nitrogen removal efficiency of 84.1 ± 0.2%. Anammox bacteria (Ca. Brocadia) abundance was 37.8% after reactivation. These overall results indicate that SAS is a feasible seed sludge for faster start-up of high-rate mainstream anammox reactors.

Waste iron scraps promote anammox bacteria to resist inorganic carbon limitation

The anaerobic ammonium oxidation (anammox) process is adversely affected by the limitation of inorganic carbon (IC). In this research, a new technique was introduced to assist anammox biomass in counteracting the adverse effects of IC limitation by incorporating waste iron scraps (WIS), a cheap and easily accessible byproduct of lathe cutting. Results demonstrated that reducing the influent IC/TN ratio from 0.08–0.09 to 0.04 resulted in a 20 % decrease in the nitrogen removal rate (NRR) for the control reactor, with an average specific anammox activity (SAA) of 0.65 g N/g VSS/day. Nevertheless, the performance of the WIS-assisted anammox reactor remained robust despite the reduction in IC supply. In fact, the NRR and SAA of the WIS-assisted reactor exhibited substantial improvements, reaching approximately 1.86 kg/(m3·day) and 0.98 g N/g VSS/day, respectively. These values surpassed those achieved by the control reactor by approximately 39 % and 51 %, respectively. The microbial analysis confirmed that the WIS addition significantly stimulated the proliferation of anammox bacteria (dominated by Candidatus Kuenenia) under IC limitation. The anammox gene abundances in the WIS-assisted anammox reactor were 3–4 times higher than those in the control reactor. Functional genes prediction based on the KEGG database revealed that the addition of WIS significantly enhanced the relative abundances of genes associated with nitrogen metabolism, IC fixation, and central carbon metabolism. Together, the results suggested that WIS promoted carbon dioxide fixation of anammox species to resist IC limitation. This study provided a promising approach for effectively treating high ammonium-strength wastewater using anammox under IC limitation.