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The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh . Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Heterotrophic-sulfur autotrophic denitrification (HAD) has been proposed to be a prospective nitrogen removal process. In this work, the potential of fermentation liquid (FL) from waste-activated sludge (WAS) as the electron donor for denitrification in the HAD system was explored and compared with other conventional carbon sources. Results showed that when FL was used as a carbon source, over 99% of NO 3 - -N was removed and its removal rate exceeded 14.00 mg N/g MLSS/h, which was significantly higher than that of methanol and propionic acid. The produced sulfate was below the limit value and the emission of N 2 O was low (1.38% of the NO 3 - -N). Microbial community analysis showed that autotrophic denitrifiers were predominated in the HAD system, in which Thiobacillus (16.4%) was the dominant genus. The economic analysis showed the cost of the FL was 0.062 €/m 3 , which was 30% lower than that in the group dosed with methanol. Our results demonstrated the FL was a promising carbon source for the HAD system, which could reduce carbon emission and cost, and offer a creative approach for waste-activated sludge resource reuse., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Elemental sulfur autotrophic denitrification (S 0 AD) processes are temperature-sensitive, presenting a substantial challenge for the practical implementation of S 0 AD bioreactors. In this study, a comprehensive methodology for designing and operating S 0 AD bioreactors was developed, effectively managing fluctuations in nitrogen removal efficiency caused by seasonal temperature variations. Initially, the nitrate removal rate was correlated with simulated on-site temperature and nitrate loading, revealing correlation coefficients of k 1 , k 2 , k 3 , and A as 5.42×10 -4 , -0.41, 0.04, and 0.13, respectively, to establish a mathematical model for predicting S 0 AD efficiency. Subsequently, by considering influence factors such as dissolved oxygen and dynamic sulfur consumption, the model was employed to accurately design a pilot-scale S 0 AD bioreactor for a case study. By utilizing an alternative multi-subunit operation, a stable effluent nitrate concentration of less than 8 mg-N/L was maintained throughout the year. Importantly, this approach resulted in a substantial reduction of 76.8% in excessive nitrate removal, sulfur consumption, and sulfate production. This study aims to provide an optimal design and operation strategy for the practical application of S 0 AD bioreactors, thereby enhancing reliability and cost-effectiveness in the face of seasonal temperature changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Sulfur-packed beds (SPBs) have been increasingly incorporated into constructed wetland systems to overcome limitations in achieving satisfactory nitrate removal efficiency. However, the underlying impact of hydraulic regimes on SPB performance remains understudied. This study investigated the performance of a pilot-scale SPB, encompassing sulfur autotrophic denitrification (SAD) and sulfur disproportionation (SDP) processes, under various horizontal flow (HF) and vertical flow (VF) regimes. The HF regime exhibited superior SAD efficiency, achieving 3.1-4.4 mg-N/L of nitrate removal compared to 0.9-2.8 mg-N/L under VF regimes. However, greater sulfide production of 3.8-5.6 mg/L was observed, in contrast to only 1.5-2.3 mg/L under VF regimes when SDP occurred. Employing current computational fluid dynamics simulations could predict general regimes but lacked precision in detailing sulfur layer dynamics. In contrast, determining the spatial distribution of SAD substrates and SDP products offered a viable solution, revealing stagnate, short-circuit, and back flows. Moreover, the feasibility of an aeration approach to reduce sulfide emissions below 0.5 mg/L in case of accidental SDP occurrence was confirmed. This study offers a method for assessing detailed hydraulic regimes within SPBs. Additionally, it provides guidance on optimizing the packing of sulfur-based materials when implementing SPBs in constructed wetland systems and presents a strategy for mitigating excessive sulfide emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Efficient recovery of nitrous oxide (N 2 O) through heterotrophic denitrification with the help of Fe(II)EDTA-NO as a chelating agent has been regarded as an ideal technology to treat nitric oxide (NO)-rich flue gas. In this study, an integrated NO-based biological denitrification model was developed to describe the sequential reduction of the NO fixed in Fe(II)EDTA-NO with organic carbon as the electron donor. With the inclusion of only the key pathways contributing to nitrogen transformation, the model was firstly developed and then calibrated/validated and evaluated using the data of batch tests mediated by the identified functional heterotrophic bacteria at various substrates concentrations and then used to explore the possibility of enhancing N 2 O recovery by altering the substrates condition and reactor setup. The results demonstrated that the optimal COD/N ratio decreased consistently from 1.5 g-COD/g-N at the initial NO concentration of 40 g-N/m 3 to 1.0 g-COD/g-N at the initial NO concentration of 420 g-N/m 3 . Furthermore, sufficiently increasing the headspace volume of the reactor was considered an ideal strategy to obtain ideal N 2 O production of 86.6 % under the studied conditions. The production of high-purity N 2 O (98 %) confirmed the practical application potential of this integrated treatment technology to recover a valuable energy resource from NO-rich flue gas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Microbial denitrification is a crucial biological process for the treatment of nitrogen-polluted water. Traditional denitrification process consumes external organic carbon leading to an increase in treatment costs. We developed a novel sulfide-driven denitrification methane oxidation (SDMO) system that integrates autotrophic denitrification (AD) and denitrification anaerobic methane oxidation (DAMO) for cost-effective denitrification and biogas utilization in situ. Two SDMO systems were operated for 735 days, with nitrate and nitrite serving as electron acceptors, to explore the performance of sewage denitrification and characterize metabolic mechanisms. Results showed SDMO system could reach as high as 100% efficiency of nitrogen removal and biogas desulfurization without an external carbon source when HRT was 10 days and inflow nitrogen concentrations were 50-100 mgN·L -1 . Besides, nitrate was a preferable electron acceptor for SDMO system. Biogas not only enhanced nitrogen removal but also intensified the DAMO, nitrogen removed through DAMO contribution doubled as original period from 2.9 mgN·(L·d) -1 to 6.2 mgN·(L·d) -1 , and the ratio of nitrate removal through AD to DAMO was 1.2:1 with nitrate as electron acceptor. While nitrogen removed almost all through AD contribution and DAMO was weaken as before, the ratio of nitrate removal through AD to DAMO was 21.2:1 with nitrite as electron acceptor. Biogas introduced into SDMO system with nitrate inspired the growth of DAMO bacteria Candidatus Methylomirabilis from 0.3% to 19.6% and motivated its potentiality to remove nitrate without ANME archaea participation accompanying with gene mfnE upregulating ∼100 times. According to the reconstructed genome from binning analysis, the dramatically upregulated gene mfnE was derived from Candidatus Methylomirabilis, which may represent a novel metabolism pathway for DAMO bacteria to replace the role of archaea for nitrate reduction., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This work studied the impacts of key granule properties on the granular reactor performing partial nitritation/anammox from the modeling perspective. The results could guide not only future reliable modeling but also practical startup/operation of the reactor. To achieve high total nitrogen (TN) removal whilst avoiding significant N 2 O production, inoculated granules should be big and anammox-enriched. The optimum boundary layer thickness for maximum TN removal increased with the decreasing diffusivity of soluble components in the granule structure. Even though a thick boundary layer could protect anammox bacteria from elevated dissolved oxygen (DO) (e.g., 0.5 g-O 2 /m 3 ) and obtain high TN removal (>90.0%) and low N 2 O production (<1.8%), even complete removal of the boundary layer would fail to provide sufficient substrate for anammox and therefore couldn't increase TN removal to 90.0% and decrease N 2 O production to <2.4% at insufficient DO (e.g., 0.3 g-O 2 /m 3 in the presence of lifted influent NH 4 + concentration)., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

While sulfur-driven autotrophic denitrification (SDAD) occurring in the anoxic reactor of the sulfate reduction, autotrophic denitrification and nitrification integrated (SANI) system has been regarded as the main nitrogen removal bioprocess, little is known about the accompanying Anammox bacteria whose presence is made possible by the co-existence of NH 4 + and NO 2 - . Therefore, this work firstly developed an integrated SDAD-Anammox model to describe the interactions between sulfur-oxidizing bacteria and Anammox bacteria. The model was subsequently used to explore the impacts of influent conditions on the reactor performance and microbial community structure of the anoxic reactor. The results revealed that at a relatively low ratio of <1.5 mg S/mg N, Anammox bacteria could survive and even take a dominant position (up to 58.9%). Finally, a modified SANI system configuration based on the effective collaboration between SDAD and Anammox processes was proposed to improve the efficiency of the treatment of sulfate-rich saline sewage., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

To reclaim nitrous oxide (N 2 O) as an energy resource economically, this study developed an autotrophic denitrification-based system with thiosulfate (S 2 O 3 2- O production profile and NO conversion efficiency from thiosulfate-based denitrification under varied Fe (II)EDTA-NO conditions (5-20 mM). Up to 39% of NO was converted to gaseous N 2 O production profile and NO conversion efficiency from thiosulfate-based denitrification under varied Fe (II)EDTA-NO conditions (5-20 mM). Up to 39% of NO was converted to gaseous N 2 OR being suppressed harder than NOR. Microbial diversity was reduced in the continuous thiosulfate-driven Fe(II)EDTA-NO-based denitrification system. NO-resistant bacteria and sulfide-tolerant denitrifiers were enriched, facilitating NO conversion to N 2 OR being suppressed harder than NOR. Microbial diversity was reduced in the continuous thiosulfate-driven Fe(II)EDTA-NO-based denitrification system. NO-resistant bacteria and sulfide-tolerant denitrifiers were enriched, facilitating NO conversion to N 2 O thereafter., (Copyright © 2022. Published by Elsevier Ltd.)

Nitrous oxide (N 2 O) was previously deemed as a potent greenhouse gas but is actually an untapped energy source, which can accumulate during the microbial denitrification of nitric oxide (NO). Compared with the organic electron donor required in heterotrophic denitrification, elemental sulfur (S 0 ) is a promising electron donor alternative due to its cheap cost and low biomass yield in sulfur-driven autotrophic denitrification. However, no effort has been made to test N 2 O recovery from sulfur-driven denitrification of NO so far. Therefore, in this study, batch and continuous experiments were carried out to investigate the NO removal performance and N 2 O recovery potential via sulfur-driven NO-based denitrification under various Fe(II)EDTA-NO concentrations. Efficient energy recovery was achieved, as up to 35.5%-40.9% of NO was converted to N 2 O under various NO concentrations. N 2 O recovery from Fe(II)EDTA-NO could be enhanced by the low bioavailability of sulfur and the acid environment caused by sulfur oxidation. The NO reductase (NOR) and N 2 O reductase (N 2 OR) were inhibited distinctively at relatively low NO levels, leading to efficient N 2 O accumulation, but were suppressed irreversibly at NO level beyond 15 mM in continuous experiments. Such results indicated that the regulation of NO at a relatively low level would benefit the system stability and NO removal capacity during long-term system operation. The continuous operation of the sulfur-driven Fe(II)EDTA-NO-based denitrification reduced the overall microbial diversity but enriched several key microbial community. Thauera, Thermomonas, and Arenimonas that are able to carry out sulfur-driven autotrophic denitrification became the dominant organisms with their relative abundance increased from 25.8% to 68.3%, collectively., (© 2021 Wiley Periodicals LLC.)

[Display omitted] • Low concentrations (less than 5 mM) of EDTA improved nitrate removal rate. • High concentrations of EDTA hindered TN removal, leading to N 2 O accumulation. • EDTA increased the redox potential of pyrite, resulting in the improvement of pyrite oxidation. • Ferric iron as product of denitrification could facilitate the conversion of solid pyrite into S0. • Fe(II)/Fe(III) cycle was a critical biological process driving the bioleaching of pyrite. Pyrite autotrophic denitrification (PAD) is crucial for removing nitrate in groundwater and advanced wastewater treatment. While disulfide is typically seen as the electron donor, the role of iron in pyrite oxidation is often ignored. In this study, Ethylene Diamine Tetraacetic Acid (EDTA) had been proven to have the potential to facilitate pyrite oxidation by promoting the solubility of iron in solution, thereby enhancing the kinetics of pyrite autotrophic denitrification. Firstly, EDTA could improve PAD performance, i.e. the nitrate removal rate at EDTA addition of 5 mM was 0.69 mg N/L•h and twice that of the control. However, high concentrations of EDTA inhibited the activity of the nitrous oxide reductase, resulting in the maximum accumulation of N 2 O reaching 13.26 mg N/L with an EDTA concentration of 15 mM. Furthermore, the X-ray Photoelectron Spectroscopy (XPS) result indicated that the EDTA addition promoted the production of bioavailable sulfur, with the concentration of S0 at 15 mM EDTA being more than twice higher than that of the control. Transmission electron microscopy (TEM) analysis indicated that EDTA could relieve the damage of iron encrustation on cell activity because it was difficult for EDTA-chelated ferrous iron to penetrate the cell membrane. Microbial community analyses showed an increase abundance of iron oxidizing bacteria, suggesting that EDTA addition promoted the bioavailability of iron for Fe(II) autotrophic denitrification. Overall, this study will provide insights into the understanding of oxidation mechanism of PAD process and the practical application for efficient nitrogen removal and N 2 O mitigation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various nitrogen removal pathways are exhibited by different species of GAOs. • The denitrification capacity of GAOs enables their potential synergy with anammox. • EPD offers a dependable and effective alternative for a nitrite supply. • EPDA process extends anammox-based application combined with PN and DPR processes. • Control strategies and functional microbial interaction mechanisms are imperative. The recently proposed glycogen accumulating organisms (GAOs)-driven anammox process, which terminates nitrate (NO 3 –) reduction to nitrite (NO 2 –) without external carbon source addition, has emerged as a promising alternative for supplying NO 2 – to anammox bacteria. The endogenous partial denitrification anammox (EPDA) process demonstrates superior nitrogen elimination efficiency, cost-effectiveness, and operational stability in low C/N wastewater treatment, concurrently mitigating greenhouse gas releases. This comprehensive review presents and discusses an in-depth analysis of the notable progress in EPDA, covering the physiology and biochemistry of diverse GAO-lineages under specified conditions, intricate microbial interactions and metabolic pathways shared between GAOs and anammox bacteria, and appropriate process modifications. Strategies for sludge morphology, carbon content, and spatial distribution of functional bacteria are discussed in detail to regulate the metabolic activity of EPDA. Future research needs to focus on balancing the competitiveness between functional consortia such as GAOs, phosphorus accumulating organisms (PAOs) and anammox bacteria in the synergetic system, and countermeasures to deal with the effects of adverse conditions on nutrient removal performance of the EPDA-based processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Impacts of NH 2 OH and N 2 H 4 on the SDAD process were studied. • NH 2 OH and N 2 H 4 showed different potential for NO 2 − and N 2 O accumulation. • NIR/N 2 OR were sensitive to NH 2 OH inhibition, while N 2 H 4 primarily suppressed N 2 OR. Hydroxylamine (NH 2 OH) and hydrazine (N 2 H 4) are crucial intermediates in biological nitrogen removal processes, but their potential effects on the nitrogen-related metabolic pathway during the sulfur-driven autotrophic denitrification (SDAD) process remain unclear and were thus explored in this work. The results of dedicated batch tests indicated that the accumulation ratio of NO 2 − was positively correlated with the NH 2 OH concentration, reaching 86.2 ± 2.6% at the NH 2 OH concentration of 2.0 mg-N/L, while it was barely affected by the N 2 H 4 concentration. Furthermore, the joint inhibition of NH 2 OH and free nitrous acid led to the substantial accumulation of N 2 O (up to 32.9 ± 1.3%) during the NO 2 − reduction phase. In contrast, N 2 H 4 exhibited great potential for facilitating N 2 O accumulation in both the NO 3 − reduction and NO 2 − reduction phases with an accumulation ratio of 13.0 ± 0.3% and 27.5 ± 1.5%, respectively, at the N 2 H 4 concentration of 2.0 mg-N/L. Total enzyme activity analyses revealed that the presence of NH 2 OH inhibited the activity expression of all denitrifying enzymes, with the downstream enzymes (such as NO 2 − reductase and N 2 O reductase) being more susceptible to NH 2 OH. The addition of N 2 H 4 did not cause a significant decrease in the activity of NO 3 − reductase and NO 2 − reductase, but notably curbed the activity of N 2 O reductase. Based on the responses of the SDAD-related nitrogen metabolic pathway to NH 2 OH/N 2 H 4 , this work provided effective technical means for i) the promotion of NO 2 − accumulation which might enable the coupling of SDAD with Anammox and ii) the efficient recovery of N 2 O via the SDAD process. [ABSTRACT FROM AUTHOR]

[Display omitted] • A SNAD model aimed to recover N 2 O from Fe(II)EDTA-NO was developed and evaluated. • Impacts of key operational conditions on N 2 O recovery were studied. • S/N mass ratio of ∼ 1.0 and high gas/liquid volumetric ratios favoured N 2 O recovery. • N 2 O recovery efficiency of up to 80.2%−84.9% was reached within 3.1 h–3.5 h. Instead of the conventional perception of nitrous oxide (N 2 O) as a potent greenhouse gas whose production should be minimized, this work aimed to assess N 2 O recovery as a potential energy source from nitric oxide (NO) in the form of Fe(II)EDTA-NO through element sulfur (S0) or thiosulfate (S 2 O 3 2−)-driven NO-based autotrophic denitrification (SNAD S0 or SNAD S2O3). A mathematical model was proposed to describe substrate dynamics related to N 2 O production and reduction and was successfully calibrated and validated using batch experimental data from lab-scale SNAD S0 and SNAD S2O3 systems under different substrates conditions. The model was subsequently employed to assess the potential of N 2 O accumulation and recovery by altering the S/N mass ratio and the ratio of gas volume to liquid volume of the system. The simulation results suggested that with a S/N mass ratio of nearly 1.0, high-purity N 2 O could be more rapidly and efficiently recovered from Fe(II)EDTA-NO in the SNAD S0 and SNAD S2O3 systems with a higher ratio of gas volume to liquid volume (i.e., a N 2 O recovery efficiency of up to 80.2%−84.9% reached within 3.1 h−3.5 h under the studied conditions). Comparatively, the SNAD S0 process showed an economic and viable advantage for practical applications to the efficient treatment and resource utilization of NO-containing flue gas. [ABSTRACT FROM AUTHOR]

• A novel iGB-A/PD reactor was developed for treating mainstream wastewaters. • An effluent TN of ∼3 mg•L−1 was achieved at a NRR of 0.8 ± 0.1 kg-N•m−3•d−1. • Multilevel A/PD is responsible for the exceptional performance in the single reactor. • PD and DNRA were responsible for 50% and 25% of nitrate reduction, respectively. This study describes an integrated granular sludge and fixed-biofilm (iGB) reactor innovatively designed to carry out the anammox/partial-denitrification (A/PD) process for nitrogen removal with mainstream municipal wastewater. The iGB-A/PD reactor consists of anammox granules inoculated in the lower region of reactor and an acclimated fixed-biofilm positioned in the upper region. Compared to the other reported A/PD systems for mainstream wastewater treatment, this iGB-A/PD reactor is notable due to its higher quality effluent with a total inorganic nitrogen (TIN) of ∼3 mg•L−1 and operation at a high nitrogen removal rate (NRR) of 0.8 ± 0.1 kg-N•m−3•d−1. Reads-based metatranscriptomic analysis found that the expression values of hzsA and hdh , key genes associated with anammox, were much higher than other functional genes on nitrogen conversion, confirming the major roles of the anammox bacteria in nitrogen bio-removal. In both regions of the reactor, the nitrate reduction genes (napA / narG) had expression values of 56–99 RPM, which were similar to that of the nitrite reduction genes (nirS / nirK). The expression reads from genes for dissimilatory nitrate reduction to ammonium (DNRA), nrfA and nirB , were unexpectedly high, and were over the half of the levels of reads from genes required for nitrate reduction. Kinetic assays confirmed that the granules had an anammox activity of 16.2 g-NH 4 +-N•kg−1-VSS•d−1 and a nitrate reduction activity of 4.1 g-N•kg−1-VSS•d−1. While these values were changed to be 4.9 g- NH 4 +-N•kg−1-VSS•d−1and 4.3 g-N•kg−1-VSS•d−1 respectively in the fixed-biofilm. Mass flux determination found that PD and DNRA was responsible for ∼50% and ∼25% of nitrate reduction, respectively, in the whole reactor, consistent with high effluent quality and treatment efficiency via a nitrite loop. Metagenomic binning analysis revealed that new and unidentified anammox species, affiliated with Candidatus Brocadia, were the dominant anammox organisms. Myxococcota and Planctomycetota were the principal organisms associated with the PD and DNRA processes, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

Using solar energy to catalytically convert nitrate into ammonia is attractive for waste recycling and sustainable development. However, the rapid recombination of electron-hole pairs and the poor selectivity are obstructing photocatalytic nitrate reduction to ammonia to be mass applied currently. In this work, we reported a facile synthesis of carbon/bismuth/bismuth oxide photocatalyst via a one-pot hydrothermal reaction without using reducing reagent. Compared with α-bismuth oxide (α-Bi 2 O 3), the photocatalytic ammonia yield of the optimum sample increased 3.65 times. In addition, the ammonia selectivity increased from 65.21% to 95.00%. The highly enhanced photocatalytic performance was attributed to the surface plasmon resonance of metallic bismuth. Meanwhile, the formation of carbon enables to boost the transfer of electrons significantly. Under light irradiation, electrons can be accumulated on metallic bismuth, effectively boosting the reduction of nitrate. The findings of this work will contribute to the recycling of nitrate for ammonia synthesis and sustainable environmental development. [Display omitted] • A carbon/bismuth/Bi 2 O 3 photocatalyst prepared via a one-pot hydrothermal reaction. • The composites exhibited efficient NO 3 − reduction to NH 3 with high selectivity. • The mechanism for the enhanced photocatalytic activity was studied. [ABSTRACT FROM AUTHOR]