High-efficiency Nitrogen Removal Research Articles

Mechanistic insight into assimilation capture: Implication for high-efficiency nitrogen removal from mature landfill leachate

The AO (Anoxic/oxic) process for treating high-strength ammonia in landfill leachate requires external carbon source and alkalinity. Alternatively, the processes of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) with less or no carbon source have been developed, but enabled modulation difficulty due to nitrogen valence transformation. Ammonia assimilation for nitrogen removal immobilize ammonia (NH4+-N) as organic nitrogen, without nitrogen valence conversion and reducing greenhouse gases emission. This study offers a novel approach for nitrogen removal from low chemical oxygen demand (COD) to nitrogen (C/N) ratio leachate. The nitrogen removal response of biomass to ammonia assimilation in landfill leachate was established. Results demonstrated that the nitrogen removal contribution of ammonia assimilation and organics utilization by microorganisms significantly increased with biomass. When the initial mixed liquor suspended solid (MLSS) was 11200 mg/L, the removal efficiency of total nitrogen (TN) and COD in the landfill leachate achieved 98.42 ± 0.12 % and 80.60 ± 0.35 % after 30 days of operation, respectively. The corresponding assimilation contributions for TN and COD removals were 82.00 ± 0.96 % and 52.24 ± 0.82 %, respectively. Cell protein analysis showed that higher biomass significantly increased the production of intracellular and extracellular proteins or amino acids. The enrichment of bacterial genera such as Defluviicoccus, Aequorivita, Truepera, and Proteiniphilum played a crucial role in organics removal and NH4+-N assimilation. Functional gene analysis further demonstrated that most NH4+-N and organics were removed through bacterial assimilation. This research offered a green, efficient, and economical solution for the treatment of low C/N ratio landfill leachate.

Feasibility of simultaneous optimization of Anammox start-up and nitrogen removal performance by intermittent dosing of nanoscale zero-valent iron

The long acclimation period and sensitivity to environmental conditions of Anammox are the bottlenecks for its promotion and application. An innovative strategy was adopted to accelerate functional microbial enhancement and improve nitrogen removal performance by inoculating cryopreserved Anammox sludge and activated sludge with intermittent dosing of nanoscale zero-valent iron (nZVI). The acclimation time was shortened by 76 days with nitrogen removal efficiency (NRE) reaching up to 91.07 %. Anammox, NDFO (nitrate/nitrite-dependent Fe(II) oxidation), Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) and abiotic reactions were coupled in the system with nZVI, contributing to 69.79 %, 15.14 %, 9.84 % and 0.25 % of nitrogen removal, respectively. Further microbial analysis demonstrated significant enrichment of functional microorganisms, such as Candidatus Jettenia, Acidovorax and Comamonas. High-efficient nitrogen removal was attribute to the increase of functional genes involved in Anammox, electronic transfer, heme C synthesis and iron metabolism. This work provides an inspiring idea for the mainstream Anammox application.

High-efficient nitrogen removal with low demand of Fe source and mechanism analysis driven by Fe(II)/Fe(III) cycle

Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) is less studied for nitrogen removal in wastewater treatment, and the limited studies show its low removal efficiency and need for continuous resupply of Fe(III) sources. In this study, sustainable and efficient nitrogen removal was obtained by the Fe redox cycle with only 1 g/L Fe2O3 dosage. The removal efficiencies of NH4+-N and TN were 100% and 92.45%, respectively, significantly higher than previous studies (∼50%). Fe(III) was reduced to Fe(II) by Feammox and subsequently regenerated by NDFO (NOx--N-dependent Fe(II) oxidation) and chemical oxidization. NOx--N produced by Feammox was also reduced to N2 by NDFO. The iron-reducing bacteria (Ferruginibacter and Dechloromonas) and the iron-oxidizing bacteria (Rhodanobacter and Thermomonas) were enriched by the addition of Fe2O3 and played important roles in Feammox and NDFO, respectively. Results of X-ray diffraction showed that Fe(OH)2 was produced from Feammox and then transformed to lepidocrocite by Fe(II) oxidation. Metagenomic analysis showed D/ANRA (dissimilatory/ assimilatory nitrate reduction to ammonia) were the potential nitrogen conversion pathways. N2O as an intermediate product of Feammox or NDFO was undetected. The genes associated with Fe transport were upregulated, accelerating the transfer of electrons between microorganisms and Fe(Hydr)oxide. The process for nitrogen removal by the Fe redox cycle requires no aeration and no organic carbon source, and can reduce the need for Fe(III) sources. It offers a promising method for nitrogen removal from wastewater.

Uncovering interactions among ternary electron donors of organic carbon source, thiosulfate and Fe0 in mixotrophic advanced denitrification: Proof of concept from simulated to authentic secondary effluent

To offset the imperfections of higher cost and emission of CO2 greenhouse gas in heterotrophic denitrification (HDN) as well as longer start-up time in autotrophic denitrification (ADN), we synergized the potential ternary electron donors of organic carbon source, thiosulfate and zero-valent iron (Fe0) to achieve efficient mixotrophic denitrification (MDN) of oligotrophic secondary effluent. When the influent chemical oxygen demand to nitrogen (COD/N) ratio ascended gradually in the batch operation with sufficient sulfur to nitrogen (S/N) ratio, the MDN with thiosulfate and Fe0 added achieved the highest TN removal for treating simulated and authentic secondary effluents. The external carbon is imperative for initiating MDN, while thiosulfate is indispensable for promoting TN removal efficiency. Although Fe0 hardly donated electrons for denitrification, the suitable circumneutral environment for denitrification was implemented by OH− released from Fe0 corrosion, which neutralized H+generated during thiosulfate-driven ADN. Meanwhile, Fe0 corrosion consumed the dissolved oxygen (DO) and created the low DO environment suitable for anoxic denitrification. This process was further confirmed by the continuous flow operation for treating authentic secondary effluent. The TN removal efficiency achieved its maximum under the combination condition of influent COD/N ratio of 3.1–3.5 and S/N ratio of 2.0–2.1. Whether in batch or continuous flow operation, the coordination of thiosulfate and Fe0 maintained the dominance of Thiobacillus for ADN, with the dominant heterotrophic denitrifiers (e.g., Plasticicumulans, Terrimonas, Rhodanobacter and KD4–96) coexisting in MDN system. The interaction insights of ternary electron donors in MDN established a pathway for realizing high-efficiency nitrogen removal of secondary effluent.

Performance and bacterial community analysis of multi-stage A/O biofilm system for nitrogen removal of rural domestic sewage

Rural domestic sewage was difficult to collect, and there was a lack of skilled professionals for its treatment. This study constructed a high-efficiency anaerobic- aerobic (A/O) biofilm reactor with multi-stage free combination, simple operation, and low consumption. The nitrogen removal capacity of the system was enhanced by changing the number of A/O stages, influent, and hydraulic retention times (HRT). The most economical system with the required total nitrogen (TN) removal loading is tertiary A/O with a step-feed ratio of 1:1:1 and HRT = 36 h. At this time, the TN removal rate could reach 71.29 %. Realizes high-efficiency nitrogen removal with low consumption and unattended operation. Increasing the influent carbon to nitrogen (C/N) ratio could effectively enhance the nitrogen removal capacity. In addition, chemical oxygen demand (COD) removal was better under various operating conditions. Pseudomonas was the dominant genera in the anaerobic zone, contributing to organic pollutant removal and denitrification. The aerobic zone was enriched with Nitrospira, related to the nitrification and denitrification process. The anoxic zone contained more heterotrophic denitrifying bacteria genera such as Denitratisoma. The system had excellent performance with the synergistic effect of the above microorganisms. The efficient and low-consumption biofilm system developed in this study suits engineering applications in poor rural areas.

Robust and high-efficient nitrogen removal from real sewage and waste activated sludge (WAS) reduction in zero-external carbon PN/A combined with in-situ fermentation-denitrification process under decreased temperatures

Despite the advantages of the combined anammox and fermentation-driven denitrification process in nitrogen removal and energy consumption, stable performance at decreased temperatures remains a challenge. In this study, a robust and high-efficient nitrogen removal efficiency (95.0–93.1 ∼ 86.8–93.4%) with desirable effluent quality (3.0–4.1 ∼ 7.9–4.9 mg/L) under long-term decreased temperatures (30 °C→25 °C→20 °C) was achieved in a zero-external carbon Partial Nitritation/Anammox combined with in-situ sludge Fermentation-Denitrification process treating sewage. Excellent sludge reduction averaged at 14.9% assuming no microbial growth. Increased hzsB mRNA (2.2-fold) and reduced Ea (80.9 kJ/mol) proved resilient anammox to lower temperature. RT-qPCR tests revealed increased NarG/NirK (5.1) and NarG/NirS (4.9) mRNA at 20 °C, suggesting higher NO3−→NO2− over NO2−→N2 pathway. Metagenomics unraveled dominant anammox bacteria (Candidatus_Brocadia, 2.27%), increased denitritation bacteria containing more NarG (Hyphomicrobium, 0.8%), fatty acid biosynthesis and CAZymes genes. Enhanced denitritation with recovered organics from sludge reserved nitrite for anammox and facilitated higher anammox contribution to N removal at 20 °C (42.4%) than 30 °C (39.5%). This study proposed an innovative low-temperature strategy for in-situ sludge fermentation, and demonstrated stability of advanced municipal wastewater treatment and sludge disposal through energy savings and carbon recovery under decreased temperatures.

Synergistic interactions between anammox and dissimilatory nitrate reducing bacteria sustains reactor performance across variable nitrogen loading ratios.

Anaerobic ammonium oxidizing (anammox) bacteria are utilized for high efficiency nitrogen removal from nitrogen-laden sidestreams in wastewater treatment plants. The anammox bacteria form a variety of competitive and mutualistic interactions with heterotrophic bacteria that often employ denitrification or dissimilatory nitrate reduction to ammonium (DNRA) for energy generation. These interactions can be heavily influenced by the influent ratio of ammonium to nitrite, NH4+:NO2-, where deviations from the widely acknowledged stoichiometric ratio (1:1.32) have been demonstrated to have deleterious effects on anammox efficiency. Thus, it is important to understand how variable NH4+:NO2- ratios impact the microbial ecology of anammox reactors. We observed the response of the microbial community in a lab scale anammox membrane bioreactor (MBR) to changes in the influent NH4+:NO2- ratio using both 16S rRNA gene and shotgun metagenomic sequencing. Ammonium removal efficiency decreased from 99.77 ± 0.04% when the ratio was 1:1.32 (prior to day 89) to 90.85 ± 0.29% when the ratio was decreased to 1:1.1 (day 89-202) and 90.14 ± 0.09% when the ratio was changed to 1:1.13 (day 169-200). Over this same timespan, the overall nitrogen removal efficiency (NRE) remained relatively unchanged (85.26 ± 0.01% from day 0-89, compared to 85.49 ± 0.01% from day 89-169, and 83.04 ± 0.01% from day 169-200). When the ratio was slightly increased to 1:1.17-1:1.2 (day 202-253), the ammonium removal efficiency increased to 97.28 ± 0.45% and the NRE increased to 88.21 ± 0.01%. Analysis of 16 S rRNA gene sequences demonstrated increased relative abundance of taxa belonging to Bacteroidetes, Chloroflexi, and Ignavibacteriae over the course of the experiment. The relative abundance of Planctomycetes, the phylum to which anammox bacteria belong, decreased from 77.19% at the beginning of the experiment to 12.24% by the end of the experiment. Analysis of metagenome assembled genomes (MAGs) indicated increased abundance of bacteria with nrfAH genes used for DNRA after the introduction of lower influent NH4+:NO2- ratios. The high relative abundance of DNRA bacteria coinciding with sustained bioreactor performance indicates a mutualistic relationship between the anammox and DNRA bacteria. Understanding these interactions could support more robust bioreactor operation at variable nitrogen loading ratios.

Promoting heterotrophic denitrification of Pseudomonas hunanensis strain PAD-1 using pyrite: A mechanistic study

Denitrification is critical for removing nitrate from wastewater, but it typically requires large amounts of organic carbon, which can lead to high operating costs and secondary environmental pollution. To address this issue, this study proposes a novel method to reduce the demand for organic carbon in denitrification. In this study, a new denitrifier, Pseudomonas hunanensis strain PAD-1, was obtained with properties for high efficiency nitrogen removal and trace N2O emission. It was also used to explore the feasibility of pyrite-enhanced denitrification to reduce organic carbon demand. The results showed that pyrite significantly improved the heterotrophic denitrification of strain PAD-1, and optimal addition amount was 0.8–1.6 g/L. The strengthening effect of pyrite was positively correlated with carbon to nitrogen ratio, and it could effectively reduce demand for organic carbon sources and enhance carbon metabolism of strain PAD-1. Meanwhile, the pyrite significantly up-regulated electron transport system activity (ETSA) of strain PAD-1 by 80%, nitrate reductase activity by 16%, Complex III activity by 28%, and napA expression by 5.21 times. Overall, the addition of pyrite presents a new avenue for reducing carbon source demand and improving the nitrate harmless rate in the nitrogen removal process.

Starting up anammox system with high efficiency nitrogen removal at low temperatures: Performance optimization, sludge characterization and microbial community analysis

Anaerobic ammonia oxidation (anammox) has potential advantages for nitrogen removal when operating at medium temperatures, but the increased operation costs of heating limit its application. It would be advantageous to start and operate anammox at low temperatures, the feasibility of which was studied here on a lab scale. Two identical expanded granular sludge bed (EGSB) reactors were inoculated at 35 ± 1 °C (Amed) and 15 ± 3 °C (Alow). Results showed that anammox was successful after 138 d for Alow, only 7 d longer than Amed. Stable operation to 194 d in Alow, the nitrogen loading rate (NLR) increased to 1.01 kg m−3·d−1, giving a high nitrogen removal efficiency (NRE) of 85%, which was only slightly lower than that of Amed (90%). More extracellular polymeric substance (EPS) was produced by the microbes of Alow compared to Amed, which prevented anaerobic ammonia oxidizing bacteria (AnAOB) against low temperature stress. Microbial community revealed presence of Candidatus Jettenia in Amed with relative abundance 7.4%, while the “cold-tolerant” Candidatus Kuenenia with 4% was the dominant anammox bacteria in Alow. The anammox granules adapted well to low temperatures and demonstrated high efficiency in anammox process without heating. Therefore, constructing an energy-saving and cost-effective anammox system in high latitudes or high altitudes can be considered.

Integration of Zeolite Membrane Bioreactor With Granular Sludge-Based Anammox in High-Efficiency Nitrogen Removal From Iron Oxide Red Wastewater.

Acquisition of stable nitritation and efficient anammox play a crucial role in partial nitritation (PN) combined with anammox for nitrogen removal from ammonium-rich wastewater. Due to the limitation of ammonia-oxidizing bacteria (AOB) enrichment and nitrite-oxidizing bacteria (NOB) control in traditional membrane biological reactor (MBR), it can result in a lower nitrite production rate (NPR) and unstable PN, eventually reducing the nitrogen removal rate (NRR) via PN-anammox. In this study, we developed a zeolite membrane biological reactor (ZMBR) to enhance the PN of iron oxide red wastewater (IORW), in which the biofilm derived from the zeolite surface can provide free ammonia (FA)-containing microenvironment for AOB enrichment and NOB inhibition. The results showed that ZMBR can tolerate a higher influent nitrogen loading rate (NLR) of 2.78 kg/(m3⋅day) in comparison to the traditional MBR [2.02 kg/(m3⋅day)] and the NPR in ZMBR and traditional MBR were 1.39 and 0.96 kg/(m3⋅day), respectively. The mass concentration ratio of -N/-N ranged from 1.05 to 1.33 in ZMBR, suggesting a suitable condition for nitrogen removal via anammox. Subsequently, the domesticated granular sludge obtained from a paper-making wastewater treatment was used as the carrier of anammox bacteria to remove nitrogen. After 93 days of operation, the NRR was observed to be 2.33 kg/(m3⋅day) and high-throughput sequencing indicated that the relatively higher abundance (45.0%) of Candidatus Kuenenia stuttgartiensis was detected in the granular sludge of the bottom part of the reactor, which can produce more proteins and lipids, suggesting a good settleability. Overall, this study provides a high-efficient method to control PN and domesticate anammox for nitrogen removal from IORW.

Byproducts of the anammox-hydroxyapatite coupling process — Characterization and its adsorption capacity for Cd(II)

The anammox-HAP coupling process can simultaneously achieve high-efficiency nitrogen removal and phosphorus recovery from sewage. The composition and physical properties of the byproducts (aHAP) collected in the anammox-HAP process were analyzed. In addition, the application potential and mechanisms for Cd(II) adsorption by aHAP in wastewater were investigated. The results show that aHAP is mainly composed of hydroxyapatite and calcium carbonate, having granular structure with honeycombs and pores. The aHAP shows an adsorption capacity of 21.10–34.80 mg/g for Cd(II) removal, and the adsorption behavior is consistent with pseudo-second-order and intra-particle diffusion models, showing that the rate-limiting step is controlled by the chemical reaction of surface complexation, ion exchange, and precipitation. In addition, the remaining anammox biomass in aHAP can bind Cd(II). The aHAP also shows a pH buffer capacity when the initial pH ranges between 4.10 and 8.46, and the final pH can be stabilized in the range of 6.3 to 8.3, which is suitable for anammox reactions. Collectively, the anammox-HAP coupling process can not only be used to achieve high-efficiency nitrogen and phosphorus removal, but its aHAP byproduct shows good adsorption properties and pH buffering capacity, which meets the requirements of green chemistry and has high economic and environmental benefits.

Synergistic Microbial Communities and Eps Analysis with High Efficiency Nitrogen Removal at Low Temperatures During Start-Up and Operation of Anammox Process

Synergistic Microbial Communities and Eps Analysis with High Efficiency Nitrogen Removal at Low Temperatures During Start-Up and Operation of Anammox Process

Application of electric fields to mitigate inhibition on anammox consortia under long-term tetracycline stress

The feasibility of applying electric fields to mitigate inhibition of tetracycline (TC) on anammox process and improve system stability was evaluated in this study. Three electric field intensities of 1, 3 and a variable intensity of 1–6 V (VEF) were used to optimize electric field intensity under gradually increasing addition of TC (0.5, 2 and 10 mg L−1). Results showed that the application of electric fields (3 V and VEF) could improve TC tolerance and keep relatively high-efficiency nitrogen removal performance, especially at TC ≥ 2 mg L−1. Furthermore, applying electric fields contributed to mitigate irreversible inhibition and improve the stability of community structure. Underlying mechanism analysis indicated that the main mechanism of applying electric fields to mitigate inhibition relies on sludge structure strengthening. This study explored a novel strategy to reduce the inhibition of antibiotics on microbial denitrification and broaden the application of anammox in industrial water treatment.

High nitrogen removal performance of anaerobically treated fish processing wastewater by one-stage partial nitritation and anammox process with hydroxyapatite (HAP)-based syntrophic granules and granule structure

The one-stage partial nitritation and anammox process with the hydroxyapatite (HAP)-based syntrophic granules was studied for the ammonium nitrogen removal from the effluents of a self-agitated anaerobic baffled reactor treating the fish processing wastewater. When the ammonium in the influent was 1140 mg N·L-1, a high nitrogen removal rate and nitrogen removal efficiency of 1.51 ± 0.10 kg N·m−3·d-1 and 88.2% were obtained, respectively. Anammox bacteria of Candidatus Kuenenia stuttgartiensis and ammonium oxidizing bacteria of Nitrosomonas were the two most predominant bacteria, while nitrite oxidizing bacteria activity was low and could be neglected during the treatment. The inorganic element properties of the sludge were analyzed by several methods to confirm the existence of HAP granules. Optical microscopic observation and scanning electron microscopy analysis revealed the structure of the granular sludge.This study supports the feasibility and potential of this process for high-efficiency nitrogen removal from fish processing wastewater.

Potential of anammox process towards high-efficient nitrogen removal in wastewater treatment: Theoretical analysis and practical case with a SBR

Anammox process has been widely applied in the wastewater nitrogen removal for its high rate and low cost. However, few researches reported the process potential in treating low-strength nitrogen wastewater. In this study, a sequencing batch reactor (SBR) was taken to explore the feasibility of low-strength nitrogen wastewater treatment by anammox process in theory and practice. The practical operation indicated that the effluent with satisfactory quality (1.90 ± 0.70 mg-TN·L−1) could be achieved, when the SBR was fed with low-strength nitrogen influent (6.20 ± 0.45 mg-NH4+-N·L−1 and 7.96 ± 0.59 mg-NO2--N·L−1). The hydraulic retention time (HRT), nitrogen removal efficiency, nitrogen removal rate (NRR) and hydraulic loading rate of SBR were 5.42 h, 86.5%, 0.054 kg-N·m−3·d−1 and 4.43 m3·m−3·d−1 during the 79-day operation, respectively. The theoretical analysis revealed the potential of anammox SBR. When SBR is stably operated, the maximum NRR would be 0.062 kg-N·m−3·d−1 if the effluent nitrogen was required to be as low as 3 mg·L−1. The NRR value is feasible for engineering. However, considering the lower specific substrates utilization rate in practice, the maximum stable NRR was calibrated and found inefficient afterwards. In order to improve the potential of anammox process, the reactors without back mixing and with periodic bioaugmentation should be taken in priority for the engineering applications. In particular, the bioaugmentation frequency and single addition amount were calculated as 7 d and 0.3 g-VSS·L−1, respectively. The results may provide guidance for the development of high-efficient and stable nitrogen removal process under low-strength condition.

High-efficient nitrogen removal and its microbiological mechanism of a novel carbon self-sufficient constructed wetland

The low denitrification efficiency in constructed wetlands (CWs) was a crucial problem for treating the carbon-deficient wastewater. To further improve the N removal from the tailwater of wastewater treatment plant, the plant fermentation liquid (PFL, derived from wetland plant litter in our CWs) as a supplementary carbon source was used in horizontal subsurface-flow CW amended with Fe-modified biochar (FeB-HSCW) to increase the influent C/N ratio and drive the denitrification. The N removal performance of FeB-HSCW was investigated under various influent C/N ratios for achieving high-efficient N removal. The excellent removal rates of COD (89.35%), NO3−-N (97.48%), TN (93.76%), NH4+-N (>16%) and NO2−-N (>98%) were obtained in FeB-HSCW at the C/N of 9.0. When the large amount of PFL was added into the systems, the amount of 16S rRNA genes from bacteria and anammox bacteria, as well as of denitrification and anammox functional genes (narG, napA, nirS, nirK, qnorB, cnorB, nosZ-I, nosZ-II and hzsA) were statistically greater in FeB-HSCW than those in other two systems (C-HSCW, without biochar and FeB; B-HSCW, amended with biochar). However, the abundances of nitrification genes (amoA of AOA, amoA of AOB and nxrA) were the lowest in FeB-HSCW after adding the PFL. High-throughput analysis for 16S rRNA gene revealed that the PFL coupled with FeB remarkably optimized the structure of bacterial community. The FeB-HSCW added with sufficient PFL was enriched with the highest abundances of norank_p_Saccharibacteria, Bacillus, Geobacter, Pseudolabrys, Mizugakiibacter, Bradyrhizobium and norank_f_ Planctomycetaceae which were capable of autotrophic and/or heterotrophic denitrification as well as anammox, whereas the distribution of nitrifiers (Nitrospira) was the lowest. Overall, this work illustrated that the PFL coupled with FeB-HSCWwas a feasible and effective carbon self-sufficient HSCW for the high-efficient N removal from wastewater with low C/N ratio mainly via the autotrophic and heterotrophic denitrification and anammox.

Metabolic insights into the enhanced nitrogen removal of anammox by montmorillonite at reduced temperature

Anammox is a low-cost and high-efficiency nitrogen removal technology. However, anammox bacteria are sensitive to realistic temperature variations of municipal wastewater, limiting their practical application in municipal wastewater treatment. In this study, to protect anammox bacteria against variable reduced temperatures, cheap and abundant clay montmorillonite (MMT) particles were used as anammox biomass carriers. Two 5-L sequencing batch reactors with MMT (RB) and without MMT (RA) were operated for 100 days. When the temperature decreased from 37 °C to 10 °C, under a nitrogen loading rate of 0.36 kg-N m−3 d−1, the total nitrogen removal rate was 0.21 kg-N m−3 d−1 in RB, but only 0.025 kg-N m−3 d−1 in RA, demonstrating the improvement of anammox performance at reduced temperatures by MMT. The 16S rRNA gene sequencing analysis verified that MMT promoted the growth of Candidatus Brocadia, resulting in 11% more abundance in RB than RA at 10 °C. Metabolomics analysis revealed MMT promoted the growth of anammox bacteria at reduced temperatures by stimulating metabolic pathways related to bacterial assimilation. In particular, MMT with excellent NH4+ adsorption capacity elevated L-Glutamine and L-Glutamate contents, subsequently stimulating the downstream metabolic pathways, including amino acid biosynthesis, purine and pyrimidine metabolism, and cryo-protectant synthesis. This study provides metabolic insights into how MMT was able to enhance nitrogen removal by anammox at reduced temperatures, which is meaningful towards overcoming the current limitations of the practical application of anammox in treating municipal wastewater.

Simultaneous biodegradability enhancement and high-efficient nitrogen removal in an innovative single stage anaerobic/anoxic/aerobic hybrid airlift bioreactor (HALBR) for composting leachate treatment: Process modeling and optimization

A novel hybrid airlift bioreactor (HALBR) for simultaneous carbon and nitrogen removal from composting leachate was studied. In contrast to conventional airlift bioreactors, an anaerobic chamber was mounted at the bottom part to improve biodegradability of composting leachate and optimize overall COD removal. Desired aerobic and anoxic conditions provided by airlift configuration and oxygen concentration gradients within the biofilm increased the capability of system for TN removal through SND. Three independent variables, hydraulic retention time (HRT) (18–30 h), air flow rate (AFR) (1–2 Lair/min), and aerobic volume ratio (AVR) (0.22–0.26) were evaluated as operating parameters. The optimum conditions were an HRT of 28.3–30 h and AFR of 1.7–2 Lair/min, giving 3600 mg/L (90%) of COD and 598.4 mg/L (80%) of TN removal, respectively with an effluent turbidity less than 70 NTU. The outcomes demonstrated that this innovative single HALBR is a feasible and reliable technology for treatment of composting leachate.

Autotrophic nitrogen removal by partial nitrification-anammox process in two-stage sequencing batch constructed wetlands for low-strength ammonium wastewater

In this study, partial nitrification-anammox process was established in two-stage sequencing batch constructed wetlands (SBCWs) to achieve autotrophic nitrogen removal for low-strength ammonium wastewater treatment. The operational parameters of the partial nitrification process were investigated and optimized, for the subsequent anammox process. The results indicated idle time and reaction time had significant influences to partial nitrification SBCW (WPN). In the WPN with optimal condition (idle time = 7.5 h, reaction time = 16 h), the effluent nitrite to ammonium ratio (NO2−-N/NH4+-N) remained stable at 1.24 ± 0.09, which favored the anammox process. The anammox SBCW (WAmx) was established rapidly within 61 d. The two-stage SBCWs showed high-efficient nitrogen removal capacity, with effluent total nitrogen (TN) concentration of 3.89 ± 0.62 mg/L and TN removal rate of 81.11 ± 2.92 %. Moreover, high-throughput sequencing revealed that Nitrosomonas (37.5 %) was dominant under optimal condition in WPN and responsible for partial nitrification process. Candidatus Brocadia (26.5 %) was enriched in WAmx, undertaking anammox process with synergism of flanking bacteria. This study provides a sustainable alternative for low-strength wastewater treatment.

A novel technology with precise oxygen-input control: Application of the partial nitritation-anammox process

Reliable and accurate oxygen-input control, which is critical to maintaining efficient nitrogen removal performance for partial nitritation-anammox (PN-A) process, remains one of the main operational difficulties. In this study, a novel, yet simple system (a simple process for autotrophic nitrogen-removal, SPAN) with precise oxygen-input control was developed to treat ammonium-rich wastewater via PN-A process. SPAN brings oxygen to biomass by circulating water and creating water spray (shower) at the water-air interface, and effectively balances the activities of core functional microorganisms through precise oxygen-input control. The oxygen-input rate is decided by the water circulation rate and shower rate and is measurable and predictable. Therefore, the required amount of oxygen for ammonium oxidation can be precisely delivered to the biomass by adjusting the circulation rate and shower rate. The results of two parallel SPAN reactors demonstrated that during long-term operation, the required oxygen input was precisely and reliably controlled. More than 99% of NH4+-N and 81% - 85% of total nitrogen were stably removed, with anammox bacteria contributing to more than 96% of total nitrogen removal. Anammox bacteria were efficiently enriched to the highest level among the key nitrogen-converting microbial groups, both in terms of abundance (8.17%) and nitrogen-conversion capacity, while ammonium oxidizing bacteria were well controlled to provide sufficient ammonium-oxidizing capacity. Nitrite oxidizing bacteria were maintained stable (relative abundance of 1.08%-1.88%) and their activity was effectively suppressed. This study provided a novel technology, SPAN, to precisely control oxygen input in PN-A system, and proved that SPAN was effective and reliable in achieving long-term high-efficiency nitrogen removal.