Total Nitrogen Removal Efficiency Research Articles

Improving nitrogen removal performance from rare earth wastewater via partial denitrification and anammox process with Fe(II) amendment

Treating rare earth wastewater which contains low concentration of nitrogen with little chemical oxygen demand (COD) is an increasing demand. In this study, a partial-denitrification/anammox (PD/A) process with Fe(II) amending for rare earth wastewater treatment was proposed and stably operated for 218 days. The total nitrogen removal efficiency (TNRE) reached up to 89.32 % for actual rare earth wastewater treatment. Continuously Fe(II) addition stimulated more secretion of extracellular polymeric substance (EPS), furthering enhancing the aggregation ability of microbial and adhesion of hydrophobic bacteria. The enrichment of denitrification genera Denitratisoma, Ignavibacterium, Thauera and Limnobacter provided sufficient nitrite substrate from nitrate reduction for subsequent anammox reaction, which was primarily carried out by Candidatus Brocadia (with relative abundance of 5.86 %). Metagenomic analysis indicated the relative abundance of genes hzo, hzsA/B/C and hdh responsible for anammox process increased by 12.84 %, 9.00 %, 9.25 %, 4.21 %, 1.32 %, respectively, which was significantly facilitated nitrogen removal performance of PD/A process.

Research on carbon and nitrogen removal of tetramethylammonium hydroxide containing wastewater by combined anaerobic/integrated fixed film activated sludge process

Tetramethylammonium hydroxide (TMAH) is widely used as a developer and etchant in the thin-film transistor liquid crystal display industry, which is the main component of developer wastewater with low C/N ratio. This study investigated TMAH degradation by combined anaerobic/integrated fixed film activated sludge (A/IFAS) process, especially for nitrogen removal. Effects of process condition on the TMAH degradation were studied, including dissolved oxygen concentration in IFAS reactor and the temperature of anaerobic reactor. Especially, the nitrogen removal was studied through the monitoring of intermediate products during TMAH biodegradation. The results indicated that lower the anaerobic treatment temperature can provide more available organic matters to enhance the denitrification in the subsequent IFAS reactor. Less oxygen supply in the IFAS reactor contributed to simultaneous nitrification and denitrification. Removal efficiency of total organic carbon and total nitrogen was up to 95.8% and 80.7%, when the temperature of anaerobic treatment was controlled at 30 °C with the DO kept at 0.7 mg/L. It indicated that A/IFAS process was efficient in carbon and nitrogen removal for TMAH degradation. The results also confirmed intermediate products of TMAH biodegradation can be used as the electron donor during denitrification, including trimethylamine, dimethylamine and methylamine. Illumina MiSeq sequencing showed that Proteobacteria was the dominant phylum contribute to nitrogen removal. Compared to sludge flocs in IFAS reactor, richer community and higher microbial diversity were observed in the biofilm.

Achieving advanced nitrogen removal from mature landfill leachate in continuous flow system involving partial nitrification-anammox and denitrification

Considering the challenges associated with nitrogen removal from mature landfill leachate, a novel combined continuous-flow process integrating denitrification and partial nitrification-Anammox (PN/A) was developed using an internal circulation (IC) system and a biological aerated filter (BAF) biofilm reactor (IBBR). In this study, IBBR successfully operated for 343 days, and when influent NH4+-N concentration of mature landfill leachate reached 1258.1 mg/L, an impressive total nitrogen removal efficiency (TNRE) of 93.3 % was achieved, along with a nitrogen removal rate (NRR) of 1.13 kg N/(m3·d). The analysis of the microbial community revealed that Candidatus Kuenenia, the dominant genus responsible for anammox, accounted for 1.7 % (day 265). Additionally, Nitrosomonas, Thauera and Truepera were identified as key contributors to the efficient removal of nitrogen from mature landfill. As a novel nitrogen removal strategy, the practical application of the IBBR system offers novel perspectives on addressing mature landfill leachate.

Temperature-resilient superior performances by coupling partial nitritation/anammox and iron-based denitrification with granular formation

Partial nitritation-anammox (PN/A), an energy-neutral process, is widely employed in the treatment of nitrogen-rich wastewater. However, the intrinsic nitrate accumulation limits the total nitrogen (TN) removal, and the practical application of PN/A continues to face a significant challenge at low temperatures (<15 °C). Here, an integrated partial nitritation-anammox and iron-based denitrification (PNAID) system was developed to address the concern. Two up-flow bioreactors were set up and operated for 400 days, with one as the control group and the other as the experiment group with the addition of Fe0. In comparison to the control group, the experiment group with the Fe0 supplement showed better nitrogen removal during the entire course of the experiment at different temperature levels. Specifically, the TN removal efficiency of the control group decreased from 82.9 % to 53.9 % when the temperature decreased from 30 to 12 °C, while in stark contrast, the experiment group consistently achieved 80 % of TN removal in the same condition. Apart from the enhanced nitrogen removal, the experiment group also exhibited better phosphorus removal (10.6 % versus 74.1 %) and organics removal (49.5 % versus 65.1 %). The enhanced and resilient nutrient removal performance of the proposed integrated process under low temperatures appeared to be attributed to the compact structure of granules and the increased microbial metabolism with Fe0 supplement, elucidated by a comprehensive analysis including microbial-specific activity, apparent activation energy, characteristics of granular sludge, and metagenomic sequencing. These results clearly confirmed that Fe0 supplement not only improved nitrogen removal of PN/A process, but also conferred a certain degree of robustness to the system in the face of temperature fluctuations.

Enhancement of nitrate reduction in microbial fuel cells by acclimating biocathode potential: Performance, microbial community, and mechanism

The enhancement of nitrate reduction in microbial fuel cells (MFCs) by acclimating biocathode potential was studied. An MFC system was started up, and measured by cyclic voltammetry to determine a suitable potential region for acclimating biocathode. The experimental results revealed that potential acclimation could efficiently improve denitrification performance by relieving the phenomenon of nitrite accumulation, and optimum performance was obtained at −0.4 V with a total nitrogen removal efficiency of 87.4 %. Subsequently, the characteristics of electron transfer behaviors were measured, suggesting that a positive correlation between nitrate reduction and the contribution of direct electron transfer emerged. Furthermore, a denitrification mechanism was proposed. The results indicated that potential acclimation was conducive to enhancing denitrifying enzyme activity and that the electron transport system activity could be increased by 5.8 times. This study provides insight into the electron transfer characteristics and denitrification mechanisms in MFCs for nitrate reduction at specific acclimatization potentials.

Effect of salinity on denitrification, membrane fouling and bacterial community in a fixed-bed biofilm membrane reactor.

In this study, a fixed-bed biofilm membrane bioreactor was used to assess denitrification and carbon removal performance, membrane fouling, composition, and the dynamics of microbial communities across 10 salinity levels. As salinity levels increased (from 0 to 30 g/L), the removal efficiency of total nitrogen and chemical oxygen demand decreased from 98 and 86% in Phase I to 25 and 45% in Phase X, respectively. Beyond a salinity level of 10 g/L, membrane fouling accelerated considerably. The analysis of fouling resistance distribution suggested that soluble microbial products (SMPs) were the primary cause of this phenomenon. The irregularity in microbial community succession reflected the varying adaptability of different bacteria to different salinity levels. The relative abundance of Sulfuritalea, Lentimircobium, Thauera, and Pseudomonas increased from 20.2 to 47.7% as the experiments progressed. Extracellular polymeric substances-related analysis suggested that Azospirillum plays a positive role in preserving the structural integrity of the biofilm carrier. The SMP-related analysis showed a positive correlation between Lentimircobium, Thauera, Pseudomonas, and the SMP content. These results suggested that these three bacterial genera significantly promoted the release of SMP under salt stress, which in turn led to severe membrane fouling.

Carbon Source in Tertiary Denitrification Regulates Dissolved Organic Nitrogen in Wastewater Effluent.

With global eutrophication and increasingly stringent nitrogen discharge restrictions, dissolved organic nitrogen (DON) holds considerable potential to upgrade advanced wastewater denitrification because of its large contribution to low-nitrogen effluents and stronger stimulation effect for algae. Here, we show that DON from the postdenitrification systems dominates effluent eutrophication potential under different carbon sources. Methanol resulted in significantly lower DON concentrations (0.84 ± 0.03 mg/L) compared with the total nitrogen removal-preferred acetate (1.11 ± 0.02 mg/L) (p < 0.05, ANOVA). With our well-developed mathematical model (R2 = 0.867-0.958), produced DON instead of shared (persist in both influent and effluent) and/or removed DON was identified as the key component for effluent DON variation (Pearson r = 0.992, p < 0.01). The partial least-squares path modeling analysis showed that it is the microbial community (r = 0.947, p < 0.01) rather than the predicted metabolic functions (r = 0.040, p > 0.1) that affected produced DON. Carbon sources rebuild the microorganism-DON interaction by affecting the structure of microbial communities with different abilities to generate and recapture produced DON to finally regulate effluent DON. This study revalues the importance of carbon source selection and overturns the current rationality of pursuing only the total nitrogen removal efficiency by emphasizing DON.

Effect of linear anionic surfactant (sodium dodecyl sulfate) dosage on nitrogen removal performance of an anammox reactor

AbstractThe impact of sodium dodecyl sulfate (SDS, as model linear anionic surfactant) dosage on overall nitrogen removal performance of anammox reactor alongside its microbial population and sludge properties was investigated. In this study (day 136), an anmmox sequencing batch biofilm reactor was subjected to gradual dosage of SDS from 0 to 20 mg L−1. Intriguingly, results revealed that SDS at ≥7.5 mg L−1 prompted sludge disintegration, evidenced by increased protein and polysaccharide content in the effluent. Nevertheless, reactor's average total nitrogen removal efficiency slightly improved from 83.12% (0 mg L−1) to 86.3% (20 mg L−1). The 16S rRNA gene sequencing revealed that SDS dosing significantly suppressed the unwanted and unavoidable nitrite oxidizing bacteria (NOBs) in the reactor as the abundance of genus Nitrospira declined from 40.68% (day 1) to 19.15% (day 136). The abundance of anammox genus Candidatus Kuenenia significantly improved from 1.86% (day 1) to 40.02% (day 136) as a result of NOB suppression. This study revealed that low concentration of surfactants in wastewater does not affect the anammox bacteria in a biofilm reactor. Furthermore, adding low concentrations of SDS (≥7.5 to 20 mg L−1) to wastewater may effectively suppress notorious NOBs in biofilm‐based anammox systems.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures.

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7±2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ±2 and 16 ±2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ±2 and 7±2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

NH2-MIL-101(Fe)-mediated photo-Fenton reaction enhanced simultaneous removal of nitrogen and refractory organics in anammox process through interfacial electron transfer

In this study, H2O2 (0.1 ‰) and NH2-MIL-101(Fe)-driven (150 mg/L) photo-Fenton-coupled anammox were proposed to simultaneously improve the removal efficiency of nitrogen and humic acid. Long-term experiments showed that the total nitrogen removal efficiency was increased by the photo-Fenton reaction to 91.9 ± 1.5 % by altering the bioavailability of refractory organics. Correspondingly, the total organic carbon removal efficiency was significantly increased. Microbial community analyses indicated that Candidatus_Brocadia maintained high activity during photo-Fenton reaction and was the most abundant genus in the reactor. Dissimilatory nitrate reduction to ammonium process and denitrification process were enhanced, resulting in reduced NO3–-N production. The establishment of electron transfer between microorganisms and NH2-MIL-101 (Fe) improved the charge separation efficiency of the quantum dots and increased the intracellular adenosine triphosphate content of anammox bacteria. These results indicated that photo-Fenton-anammox process promoted the removal of nitrogen and refractory organics in one reactor which had good economic value and application prospects.

The role of the combined nitrogen-sulfur-carbon cycles for efficient performance of anammox-based systems

The combined anammox/mixotrophic denitrification process was conducted in two granular sequencing batch reactors (SBRs) during a 200-day operation. Both reactors were fed with synthetic medium, but SBR2 was enriched with additional sulfate (SO42−) which influenced sulfate reduction ammonium oxidation (SRAO) and heterotrophic reduction of SO42− by sulfate reducing bacteria. It was hypothesized that the addition of SO42− could positively impact the removal rates of N-S-C compounds. A low C/N ratio (0.4–1.6) was maintained to prevent inhibition of anaerobic ammonium oxidizing bacteria (AnAOB), and alternating chemical oxygen demand (COD) on/off conditions were used to regenerate AnAOB during COD-off phases and heterotrophic denitrifiers during COD-on phases. Stoichiometric analysis showed that introducing SO42− in SBR2 enhanced the ammonium utilization rate, which was approximately 10 % higher compared to SBR1 in the final stage of the experiment (25.8 vs. 22.8 mg N/(g VSS·h)). The total nitrogen removal efficiencies ranged from 62 % to 99 % in both reactors, with SBR2 consistently exhibiting approximately 4 % higher efficiency than SBR1. In SBR2, the maximum overall SO42− utilization efficiency reached 27 % under COD-off conditions, while overall COD utilization was almost complete under COD-on conditions. A strong correlation (R2 = 0.98) was observed between SO42− production and COD utilization. The key players responsible for N and S transformations in response to SO42− addition were Candidatus Brocadia and Chloroflexi - Anaerolineae. This study highlights the potential to enhance the overall efficiency of N-S-C removal by implementing an integrated anammox/mixotrophic denitrification process. The combination of cycles emerges as a sustainable approach for treating wastewater rich in N-S-C compounds.

Performance of a Double-Filter-Medium Tandem Membrane Bioreactor with Low Operating Costs in Domestic Wastewater Treatment

To reduce the operating costs of conventional membrane bioreactors (MBRs) and improve the stability and quality of the dynamic membrane bioreactor (DMBR) effluent, a homemade inexpensive filter cloth assembly was connected to an up-flow ultra-lightweight-medium filter (UUF) in lieu of expensive membrane modules to form a double-filter-medium tandem (DT)-MBR. DT-MBR was used to treat domestic wastewater, and its removal efficiencies for chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus were similar to those of aerobic MBR, with average removal rates of 91.1%, 98.4%, 15.1%, and 50.7%, respectively. The average suspended solid (SS) of the final effluent was 5.6 mg∙L−1, and the filter cloth assembly played a leading role in SS removal, with an average removal rate of 86.0% and a relatively stable removal effect with little impact via backwashing. The activated sludge zeta potential, flocculation and sedimentation properties, particle size distribution, microbial compositions, extracellular polymeric substances (EPS), and filtration resistance of the cake layer were analyzed; it was found that the cake layer, which can also be called the dynamic membrane (DM), had an excellent filtration performance. However, the DM theory could not reasonably explain why the effluent quality of the filter cloth assembly maintained good stability even after backwashing. The real reason must be related to the sieving of cloth pores. Therefore, the concept of an in situ autogenous static membrane (ISASM) was proposed. With low operating costs and good and stable effluent quality, DT-MBR is a desirable alternative to the traditional MBR.

Simultaneous denitrification enhancement and sludge reduction based on novel suspended carrier modified using activated carbon and magnetite at low carbon/nitrogen ratio

A novel suspended carrier was prepared by sticking activated carbon (AC) and magnetite (Fe3O4) onto polypropylene slices. Although this carrier could not reverse the decreased denitrification capacity trends under anoxic conditions at an influent carbon/nitrogen (C/N) ratio of 2, it enhanced denitrification by stimulating sludge reduction and accelerating electron transfer to certain extent. The carrier stuck by mixed AC/Fe3O4 exhibited better performance in terms of sludge reduction, extracellular polymeric substances (EPS) secretion, and denitrification than that merely stuck by AC and Fe3O4 at an influent C/N ratio of 2. The carrier stuck by mixed AC/Fe3O4 increased the total nitrogen removal efficiency by 24.6 % ± 12.5 % in a 72-h denitrification batch experiment compared to the common polypropylene carrier. Moreover, the carrier improved EPS secretion and nitrogen metabolism and promoted the growth of Trichococcus and some denitrifying genera. This study provides a reference for the treatment of low C/N ratio sewage.

Intensified nitrogen and phosphorus removal and mechanism revelation in constructed wetlands amended with iron-carbon based substrate towards low C/N ratio wastewater

Constructed wetlands (CWs) show a promising capability of nutrient removal from the low C/N ratio characterized wastewater with the help of functional substrates, yet the mechanism remains unclear. In this study, sponge iron mixed with biochar was adopted as substrates to construct bench-scale CWs (CW-FeC) treating simulated urban tail water (C/N = 2). Over the experiment, it achieved a prominent performance with total nitrogen (TN) and total phosphorus (TP) removal efficiency of 89.8 and 92.1 %, respectively. Meanwhile, greenhouse gas emissions such as CO2 and N2O were extensively depressed. Mechanism analysis revealed that the deposition of ferrous ions on biochar would enlarge the micro-electrolysis interfaces and amplify the binding sites between P and Fe compared to CW systems with other substrates (gravel, biochar, and gravel mixed with sponge iron remarked as CW-G, CW-C, and CW-FeG). A significant difference regarding the mechanism of N removal was proposed based on the bacterial community analysis. The released ferrous (due to electrolysis and high abundance of iron-reduced bacteria) as electron donors could be easily captured by iron-based autotrophic denitrification bacteria as evidenced by 1.98 times higher the relative abundance of denitrifying bacteria and upregulated related genes expression. In contrast, the iron-oxidized bacteria have to be acclimatized in the CW-FeG to supply electrons for denitrification via interspecies extracellular electron transfer. The positive correlation between iron-redox bacteria and denitrification bacteria further demonstrated the integrity of the iron cycle in CWs for better nitrogen removal. These findings provide an elaborated insight into the nutrient transformation and removal processes interacting with substrates in CWs.

Distinct microbial characteristics of the robust single-stage coupling system during the conversion from anammox-denitritation to anammox-denitratation patterns

Simultaneous anammox-denitrification is effectively operated in two types, i.e., the anammox-denitritation (SAD pattern) and the anammox-denitratation (PDA pattern). The nitrate derived from inevitable nitrite oxidization likely determines the practical operational pattern of the coupling system, while little information is available regarding the microbial characteristics during the pattern conversion. Here, the single-stage bioreactor coupling anammox with denitrification was operated under conditions with a changed ratio of influent nitrite and nitrate. Results showed that the bioreactor exhibited a robust performance during the conversion from SAD to PDA patterns, corresponding with the total nitrogen removal efficiency ranging from 89.5% to 92.4%. Distinct community structures were observed in two patterns, while functional bacteria including the genera Denitratisoma, Thauera, Candidatus Brocadia, and Ca. Jettenia steadily co-existed. Meanwhile, the high transcription of hydrazine synthase genes demonstrated a stable anammox process, while the up-regulated transcription of nitrite and nitrous oxide reductase genes indicated that the complete denitrification process was enhanced for total nitrogen removal during the PDA pattern. Ecologically, stochastic processes dominantly governed the community assembly in two patterns. The PDA pattern improved the interconnectivity of communities, especially for the cooperative behaviors between dominant denitrifying bacteria and low-abundant species. These findings deepen our understanding of the microbial mechanism underlying the different patterns of the coupling system and potentially expand its engineering application.

Genomics and metabolic characteristics of simultaneous heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal by Acinetobacter indicus CZH-5

This study provides for the first time a systematic understanding of Acinetobacter indicus CZH-5 performance, metabolic pathway and genomic characteristics for aerobic nitrogen (N) and phosphorus (P) removal. Acinetobacter indicus CZH-5 showed promising performance in heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal. Under optimal conditions, the maximum ammonia-N, total nitrogen and orthophosphate-P removal efficiencies were 90.17%, 86.33%, and 99.89%, respectively. The wide tolerance range suggests the strong environmental adaptability of the bacteria. The complete genome of this strain was reconstructed. Whole genome annotation was used to re-construct the N and P metabolic pathways, and related intracellular substance metabolic pathways were proposed. The transcription levels of related functional genes and enzyme activities further confirmed these metabolic mechanisms. N removal was achieved via the nitrification–denitrification pathway. Furthermore, CZH-5 exhibited significant aerobic P uptake, with phosphate diesters as the main species of intracellular P.

Decrease in Oxygen Concentration for the Fast Start-Up of Partial Nitritation/Anammox without Inoculum Addition

Initiating the partial nitritation and anammox (PN/A) process without inoculation poses a significant challenge. Thus, there is a notable amount of interest in devising a straightforward strategy for the start-up of PN/A. This study demonstrates the feasibility of achieving the rapid start-up of a one-stage PN/A process within a moving-bed sequencing batch biofilm reactor (MBSBBR) by reducing the oxygen concentrations: 3.0 mg O2/L (Stage I), 2.0 mg O2/L (Stage II), and 1.0 mg O2/L (Stage III). The anammox activity was observed 15 days after a gradual decrease in the oxygen concentration and confirmed using a specific anammox activity test (5.9 mg N/gVSS∙h). During Stage III, the average total inorganic nitrogen (TIN) removal efficiency was 60.6%. The relative abundance of planctomycetes, a typical phylum representing anammox microorganisms, increased almost three times from Stage I (2.8%) to Stage III (7.1%). These results demonstrate the potential of a decrease in oxygen concentration for the fast start-up of the one-stage partial nitritation and anammox process without inoculation. The implementation of the studied DO strategy has practical implications for wastewater treatment plant operators, particularly in the start-up of the PN/A processes. Additionally, batch assays allow for the rapid assessment of treatment plant performance, providing real-time insights into its functionality and, thereby, optimizing wastewater treatment practices.

Enhanced total nitrogen removal and membrane fouling control by increasing biomass in MBR equipped with ceramic membrane

Simultaneous nitrification and denitrification (SND) is an efficient method to remove nitrogen in municipal wastewater treatment. However, low dissolved oxygen (DO) concentrations are generally required, leading to serious membrane fouling in membrane bioreactors (MBRs). This study aimed to clarify the synergistic effect of biomass and DO on nitrogen removal and membrane fouling. To achieve this goal, four submerged MBRs equipped with ceramic membranes were operated with different biomass (mixed liquor suspended solids (MLSS)) concentrations (3 000 mg/L, 5 000 mg/L, 7 500 mg/L, and 12 000 mg/L) under various DO concentrations (2.0 mg/L, 1.0 mg/L, and 0.5 mg/L). As a result, increasing biomass in the MBRs enhanced total nitrogen (TN) removal via SND, and excellent TN removal efficiencies of 60.7% and 75.8% were obtained using the MBR with an MLSS concentration of 12 000 mg/L and DO concentrations of 2.0 mg/L and 1.0 mg/L. However, a further decrease in DO deteriorated TN removal due to the inhibition of nitrification. Moreover, high MLSS concentrations were beneficial to membrane fouling control for ceramic membranes in MBRs. The lowest transmembrane pressure development rate was observed for the MBR with an MLSS concentration of 12 000 mg/L. High biomass offset the adverse effect of DO decrease on membrane fouling to some extent, and improved the stability of the reactor. Therefore, biomass might be an important parameter for membrane fouling reduction in ceramic MBRs. Overall, optimal biomass and DO concentrations for TN removal were identified, providing useful information for the successful operation of MBRs with efficient TN removal and membrane fouling control.

Efficient photocatalytic reduction of nitrate byproducts during anammox process by novel extracellular polymeric substances-embedded NH2-MIL-101(Fe) photocatalysts

Anaerobic ammonium oxidation (anammox) is an efficient nitrogen removal process; however, nitrate byproducts hampered its development. In this study, extracellular polymeric substances (EPS) were embedded into NH2-MIL-101(Fe), creating NH2-MIL-101(Fe)@EPS to reduce nitrate. Results revealed that chemical nitrate reduction efficiency of NH2-MIL-101(Fe)@EPS surpassed that of NH2-MIL-101(Fe) by 17.3 %. After adding 0.5 g/L NH2-MIL-101(Fe)@EPS within the anammox process, nitrate removal efficiency reached63.9 %, consequently elevating the total nitrogen removal efficiency to 92.4 %. 16S rRNA sequencing results elucidated the predominant role of Candidatus Brocadia within NH2-MIL-101(Fe)@EPS-anammox system. Concurrently, sufficient photogenerated electrons were transferred to microorganisms, promoting the growth of Desnitratisoma and OLB17. Additionally, photogenerated electrons activated flavin and Complex III, thereby up-regulating crucial genes involved in intra/extracellular electron transfer. Subsequently, denitrification and dissimilatory nitrate reduction to ammonium were activated to reduce nitrate. In summary, this study achieved a notable rate of photocatalytic nitrate reduction within anammox process through the NH2-MIL-101(Fe)@EPS photocatalysts.

Optimization of step-feed anoxic-oxic-membrane bioreactor (AO-MBR) with methanol addition for biological nitrogen removal in wastewater using BioWin and response surface methodology (RSM)

The study optimized a step-feed anoxic-oxic membrane bioreactor (AO-MBR) with methanol addition, an existing biological nitrogen removal (BNR) process, to improve total nitrogen (TN) removal and to reduce operating costs. Methanol, utilized as an external carbon source, was costly, which led to examining ways to reduce its usage by adjusting the operational parameters and modifying the configuration. The BioWin’s built-in activated sludge model underwent calibration through biokinetic batch experiments and numerical adjustments of stoichiometric and kinetic parameters to create the BNR process model. Dynamic simulations validated the calibrated model. Using the model, a modified configuration with a 20.8% increase in total anoxic volume was proposed. This increased the anoxic hydraulic retention time, improving the denitrification process. The response surface methodology (RSM) was then used to optimize the operating parameters of the modified configuration for maximum TN removal efficiency and minimum operating cost. The optimized parameters found were 0.5 mg/L dissolved oxygen, 45 days of solid retention time, 0:1 methanol distribution ratio, and 1,794.29 L/d methanol, which all enhanced the denitrification process. This resulted in a 16% increase in TN removal efficiency, a 4.12% decrease in operating costs, and an 8.96% reduction in methanol usage.