Total Nitrogen Removal Efficiency Research Articles

Deciphering the influence of salinity stress on the biological aniline degradation system: pollutants degradation performance and microbial response.

In order to evaluate the impact of salinity gradients on the aniline biodegradation system, six reactors at salinity concentrations (0%-5%) were established. The results presented the salinity except for 5% imposed negligible effects on aniline degradation performance. Nitrification had prominent resistance to salinity (0%-1.5%) while were significantly restrained when salinity increased. The total nitrogen (TN) removal efficiency of Z4 (1.5%) was 20.5% higher than Z1 (0%) during the stable operation phase. Moreover, high throughput sequencing analysis showed that halophilic bacterium,such as Halomonas, Rhodococcus, remained greater survival advantages in high salinity system. The substantial enrichment of Flavobacterium, Dokdonella, Paracoccus observed in Z4 ensured its excellent nitrogen removal performance. The close cooperation among dominant functional bacteria was strengthened when salt content was below 1.5% while exceeding 1.5% led to the collapse of metabolic capacity through integrating the toxicity of aniline and high osmotic pressure.

Tailoring Ni 3d orbitals in Ni-Fe/Ni foam heterostructures for enhanced H* adsorption and boosted electrocatalytic nitrate reduction performance

The electrochemical nitrate (NO3−) reduction (ENR) in wastewater, a promising remediation strategy, is often impeded by the essential use of costly noble metals. This study introduces an innovative non-noble Ni-Fe/Ni foam cathode fabricated via one-step electrodeposition technique. Efficient nitrate removal (99.4 %) was achieved with the selectivity of 83.6 % to NH3. The exceptional performance can be ascribed to the augmented active sites and the synergistic interaction between Ni and Fe. The leftward shift of the 3d orbitals density of Ni and the elevation of density at the Fermi level on Ni foam heterostructures, consequent to Fe doping, enhance the adsorption of H*. The addition of reactive chlorine species, generated through anodizing in Cl− mediated system, further improves N2 selectivity by oxidizing intermediate NH4+ product. The coupled anodic oxidation method employed herein achieves nearly 100 % removal efficiency of total nitrogen (TN) for initial concentration of 100 mg/L within 180 min, under the conditions of 1.5 g/L Cl− concentration and a current density of 25 mA cm−2. The findings underscore the potential of the Ni-Fe/Ni foam cathode within a Cl− mediated electrocatalytic framework for nitrate wastewater treatment, providing novel insights into the design of cathode catalysts and anodic coupling strategies for efficient TN removal.

Enhanced degradation of enrofloxacin in mariculture wastewater based on marine bacteria and microbial carrier

This study aimed to isolate marine bacteria to investigate their stress response, inhibition mechanisms, and degradation processes under high-load conditions of salinity and enrofloxacin (ENR). The results demonstrated that marine bacteria exhibited efficient pollutant removal efficiency even under high ENR stress (up to 10 mg/L), with chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ENR removal efficiencies reaching approximately 88%, 83%, 61%, and 73%, respectively. The predominant families of marine bacteria were Bacillaceae (50.46%), Alcanivoracaceae (32.30%), and Rhodobacteraceae (13.36%). They responded to ENR removal by altering cell membrane properties, stimulating the activity of xenobiotic-metabolizing enzymes and antioxidant systems, and mitigating ENR stress through the secretion of extracellular polymeric substance (EPS). The marine bacteria exhibited robust adaptability to environmental factors and effective detoxification of ENR, simultaneously removing carbon, nitrogen, phosphorus, and antibiotics from the wastewater. The attapulgite carrier enhanced the bacteria's resistance to the environment. When treating actual mariculture wastewater, the removal efficiencies of COD and TN exceeded 80%, TP removal efficiency exceeded 90%, and ENR removal efficiency approached 100%, significantly higher than reported values in similar salinity reactors. Combining the constructed physical and mathematical models of tolerant bacterial, this study will promote the practical implementation of marine bacterial-based biotechnologies in high-loading saline wastewater treatment.

The growth and nutrient removal properties of heterotrophic microalgae Chlorella sorokiniana in simulated wastewater containing volatile fatty acids

To reduce the high cost of organic carbon sources in waste resource utilization in the cultivation of microalgae, volatile fatty acids (VFAs) derived from activated sludge were used as the sole carbon source to culture Chlorella sorokiniana under the heterotrophic cultivation. The addition of VFAs in the heterotrophic condition enhanced the total nitrogen (TN) and phosphorus (TP) removal of C. sorokiniana, which proved the advantageous microalgae in using VFAs in the heterotrophic culture after screening in the previous study. To discover the possible mechanism of nitrogen and phosphorus adsorption in heterotrophic conditions by microalgae, the effect of different ratios of VFAs (acetic acid (AA): propionic acid (PA): butyric acid (BA)) on the nutrient removal and growth properties of C. sorokiniana was studied. In the 8:1:1 group, the highest efficiency (77.19%) of VFAs assimilation, the highest biomass (0.80 g L−1) and lipid content (31.35%) were achieved, with the highest TN and TP removal efficiencies of 97.44 % and 91.02 %, respectively. Moreover, an aerobic denitrifying bacterium, Pseudomonas, was determined to be the dominant genus under this heterotrophic condition. This suggested that besides nitrate uptake and utilization by C. sorokiniana under the heterotrophy, the conduct of the denitrification process was also the main reason for obtaining high nitrogen removal efficiency.

Iron particle-integrated anammox granules in baffled reactor: Enhanced settling property and nitrogen removal performance

This study evaluates iron particle-integrated anammox granules (IP-IAGs) to enhance wastewater treatment efficiency. The IP-IAGs resulted in notable improvements in settleability and nitrogen removal. The settling velocity of IP-IAGs increased by 17.91 % to 2.92 ± 0.20 cm/s, and the total nitrogen removal efficiency in batch mode improved by 6.82 %. These changes indicate enhanced biological activity for effective treatment. In continuous operation, the IP-IAGs reactor showed no accumulation of nitrite until 40 d, reaching a peak nitrogen removal rate (NRR) of 1.54 kg-N/m3·d and a nitrogen removal efficiency of 82.61 %. Furthermore, a partial nitritation-anammox reactor that treated anaerobic digestion effluent achieved a NRR of 1.41 ± 0.09 kg-N/m3·d, proving the applicability of IP-IAGs in real wastewater conditions. These results underscore the potential of IP-IAGs to enhance the efficiency and stability of anammox-based processes, marking a significant advancement in environmental engineering for wastewater treatment.

Irons differently modulate bacterial guilds for leading to varied efficiencies in simultaneous nitrification and denitrification (SND) within four aerobic bioreactors

As a novel biological wastewater nitrogen removal technology, simultaneous nitrification and denitrification (SND) has gained increasing attention. Iron, serving as a viable material, has been shown to influence nitrogen removal. However, the precise impact of iron on the SND process and microbiome remains unclear. In this study, bioreactors amended with iron of varying valences were evaluated for total nitrogen (TN) removal efficiencies under aerobic conditions. The acclimated control reactor without iron addition (NCR) exhibited high ammonia nitrogen (AN) removal efficiency (98.9%), but relatively low TN removal (78.6%) due to limited denitrification. The reactor containing zero-valent iron (Fe0R) demonstrated the highest SND rate of 92.3% with enhanced aerobic denitrification, albeit with lower AN removal (84.1%). Significantly lower SND efficiencies were observed in reactors with ferrous (Fe2R, 66.3%) and ferric (Fe3R, 58.2%) iron. Distinct bacterial communities involved in nitrogen metabolisms were detected in these bioreactors. The presence of complete ammonium oxidation (comammox) genus Nitrospira and anammox bacteria Candidatus Brocadia characterized efficient AN removal in NCR. The relatively low abundance of aerobic denitrifiers in NCR hindered denitrification. Fe0R exhibited highly abundant but low-efficiency methanotrophic ammonium oxidizers, Methylomonas and Methyloparacoccus, along with diverse aerobic denitrifiers, resulting in lower AN removal but an efficient SND process. Conversely, the presence of Fe2+/Fe3+ constrained the denitrifying community, contributing to lower TN removal efficiency via inefficient denitrification. Therefore, different valent irons modulated the strength of nitrification and denitrification through the assembly of key microbial communities, providing insight for microbiome modulation in nitrogen-rich wastewater treatment.

Towards in-site carbon utilization and highly efficient nutrients removal: Effects of ammonium on the phosphorus recovery performance in a biofilm-based system

An alternatively anaerobic–aerobic biofilm system was operated for treating synthetic municipal wastewater for 150 days, and the effect of ammonium concentration in range of 15 mg∙L−1 - 50 mg∙L−1 on the phosphorus recovery performance was discussed. The ammonium concentration was confirmed as an important factor for balancing phosphorus accumulating organisms (PAOs) and denitrifying phosphorus-accumulating organisms (DPAOs) to affect nutrients removal and phosphorus recovery. The PAOs dominated in phosphorus removal with the ammonium less than 30 mg∙L−1, the ortho-P concentration in recovery steam was plateaued at 52 mg∙L−1. The increase in ammonium to 40 mg∙L−1 caused the seriously deterioration in PAOs activity; however, the phosphorus removal and recovery performance was decreased slightly which attributed to the vital contribution of DPAOs in phosphorus removal. The adverse effect of ammonium can be eliminated by decreasing the volume exchange ratio (VER) from 3.0 to 1.5, leading to the phosphorus concentration in recovery steam of 72.21 mg∙L−1. Meanwhile, the phosphorus removal efficiency (PRE) and total nitrogen removal efficiency (NRE) were stable at 97.8 % and 99.2 %, respectively, indicating highly efficient phosphorus recovery and nutrients removal in the biofilm system. The outcome of the present study could facilitate the establishment of an integrative technology to realize in-site carbon utilization, highly efficient nutrients removal and phosphorus recovery simultaneously in the mainstream treatment of sewage wastewater, and the study reveals the transformation pathways of P and N in the BPRR system, as well as the complex interactions between functional microorganisms.

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Effects of carbon to nitrogen ratio on nitrogen removal in a single-stage microaerobic system: A model-based evaluation

Single-stage microaerobic systems have been proven to be effective for concurrent removal of ammonium and organic carbon from sewage. While mechanistic models derived from activated sludge models (ASMs) have simulated nutrients removal under microaerobic conditions, classic ASMs exhibit limitations in capturing the intricate effects of carbon to nitrogen (C/N) ratio on nitrogen removal performance. To address this issue, a mechanistic model modified from the classic ASMs was proposed to capture the combined inhibitory effects of carbon and ammonium on microaerobic systems. This modified model was established based on experimental data from a single-stage microaerobic reactor encompassing simultaneous nitrification-denitrification and anammox processes. The inhibition coefficient of C/N ratio was integrated into the process rate equations, and its effectiveness was validated through model performance evaluation. Compared to the classic models, the modified one achieved superior predictions for nitrite and nitrate nitrogen concentrations. Simulations revealed that under optimized conditions with a C/N of 4.57 and a dissolved oxygen (DO) of 0.41 mg/L, the system could achieve up to 95.5% of total nitrogen (TN) removal efficiency. Based on the simulation of substrate uptake/production rate, increasing the nitrogen loading rate (NLR) rather than organic loading rate (OLR) was crucial for efficient nitrogen removal. The proposed modified model served as a valuable tool for designing and optimizing similar biological wastewater treatment systems.

Promoting mechanism of nitrogen removal by Fe3O4 magnetic particles during the start-up phase in sequencing batch reactor.

In this paper, a magnetic sequencing batch reactor (SBR) was constructed, and the influence rule of magnetic particle dosing performance of denitrification was investigated. The diversity, structure, and potential functions of the microbial community were comprehensively explored. The results showed that the particle size and the dosage of Fe3O4 magnetic particles were the main parameters affecting the sedimentation performance of activated sludge. The start-up phase of the SBR reactor with Fe3O4 magnetic particles was 5days less than the control. Moreover, total nitrogen removal efficiency during the start-up phase was improved, with the maximum value reaching 91.93%, surpassing the control by 9.7% with the Fe3O4 dosage of 1.2g L-1. In addition, the activated sludge concentration and dehydrogenase activity were improved, compared to the control. High-throughput sequencing showed that the denitrifying bacterium Saccharimonadales dominated the reactor and was enriched by magnetic particles. According to predicted functions, the abundance of genes for denitrification increased with the addition of magnetic particles, suggesting the capacity of nitrogen removal was enhanced in the microbial community. Overall, the Fe3O4 magnetic particles provide great potential for enhanced wastewater nitrogen removal.

Optimization of pollutants removal from anaerobically digested dairy wastewater by electro-oxidation process: a response surface methodology modeling and validation

AbstractThe release of anaerobically digested dairy wastewater (ANDDW) without a treatment can lead to severe environmental pollution, prompting the exploration of effective and sustainable treatment methods. Amidst various wastewater treatment approaches, the electro-oxidation (EO) process is considered as a promising, clean, and adaptable solution. In this study, the major operational parameters viz. current density, electrolyte concentration, treatment time, and mixing speed of an EO comprising Ti/PbO2 anode and stainless-steel cathode, were optimized using response surface methodology (RSM) for efficient removal of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP), orthophosphate (OP), total nitrogen (TN), and total Kjeldahl nitrogen (TKN) from ANDDW. Optimal conditions were identified as a current density of 90 mA cm−2, 0.08% electrolyte concentration, 180 min treatment time, and 400 rpm mixing speed. Under the optimum conditions, the COD, NH3-N, TP, OP, TN, and TKN removal efficiencies were 78.36, 63.93, 87.41, 92.39, 67.01, and 81.42%, respectively. Furthermore, the reaction rate followed the first-order kinetic model for the pollutants removal with correlation coefficients (R2) close to 1. The findings highlight the potential of using the EO process to treat high pollutant-laden ANDDW and encourage further studies to confirm the corresponding outcomes on a pilot scale. Graphical abstract

Impacts of polymethyl methacrylate nanoplastics on nutrient removal, microbial community and antibiotic resistant genes in bioretention systems amended with biochar and pyrolusite

Increasing release of nanoplastics (NPs) into wastewater may pose a potential threat to nitrogen and phosphorous removals in ecological wastewater treatment systems. To better understand the responses of bioretention system (BRS) by NPs, a Conventional Sand BRS (CB-BRS) and two modified BRSs, Microbial Fuel Cell (MFC)-Biochar BRS (MB-BRS) and Pyrolusite-MFC-Biochar BRS (PMB-BRS) were established and the effects of 0.5 mg/L polymethyl methacrylate (PMMA) NPs on nutrient removal, microbial community structures, as well as key enzyme activities, functional genes, antibiotic resistance genes (ARGs) were comprehensively investigated within a 120-day exposure. We observed a significant decrease in total nitrogen (TN) and total phosphorous (TP) removals in BRSs. TN removal efficiencies gradually declined from 93.56 % to 54.23 % and the TP removal efficiencies declined from 88.29 % to 74.47 % in CB-BRS. By contrast, MB-BRS (TN:72.28 %; TP:81.58 %) and PMB-BRS (TN:80.76 %; TP:96.69 %) apparently overperformed CB-BRS. In conjunction with ecological-relevant functional prediction based on the FAPROTAX database, the Illumina high-throughput sequencing unveiled substantial selective pressure imposed by PMMA NPs, particularly leading to diminished denitrifying microbes. PMMA NPs adversely affected key nitrogen-transformation enzyme activities (URE, AMO, and NIR) and denitrification functional genes (nirK, nirS, and nosZ). Alarmingly, PMMA NPs stimulated ARGs (sulI and tetC) propagation in all BRSs. Notably, the introduction of pyrolusite and biochar mitigated the adverse effects through the formation of manganese cycle and prosperous electron transfer process and effectively retained ARGs after 120-day exposure. The findings provide unprecedented insights into the potential ecological threat posed by PMMA NPs and viable strategies to control this hidden danger.

Nitrogen removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions by simultaneous partial nitrification anammox and denitrification

In this study, a SNAD-SBBR process was implemented to achieve ammonia removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions (0.051 mg/L) for a continuous operation of 266 days. The process demonstrated excellent removal performance, with ammonia nitrogen removal efficiency reaching 100 %, total nitrogen removal efficiency reaching 87.56 %, and an average removal rate of 0.180 kg/(m3·d). The recalcitrant organic compound removal efficiency reached 34.96 %. Nitrogen mass balance analysis revealed that the Anammox process contributed to approximately 98.1 % of the nitrogen removal. Candidatus Kuenenia achieved a relative abundance of 1.49 % in the inner layer of the carrier. In the SNAD-SBBR system, the extremely low DO environment created by the highly efficient partial nitrification stage enabled the coexistence of AnAOB, denitrifying bacteria, and Nitrosomonas, synergistically achieving ammonia removal and carbon reduction. Overall, the SNAD-SBBR process exhibits low-cost and high-efficiency characteristics, holding tremendous potential for landfill leachate treatment.

The superiority of citrate as denitrification carbon source in an activated sludge system: Substrate metabolism, electron transfer and microbial characteristics

Citrate, a low-molecular-weight organic substance, was rich in citric acid production wastewater with the potential for reuse. Although citrate has been extensively used as a denitrification carbon source, previous studies mainly focus on its application by pure cultures of denitrifying bacteria. The information about denitrification performance and mechanisms using citrates as carbon source in an activated sludge system is still very limited. This study investigated the denitrification efficiency and mechanisms using citrate as carbon source through a long-term operation of continuous reactor. Under the C/N ratio of 5, the total nitrogen (TN) removal efficiency using citrate as carbon source was 93.21 ± 4.24 %, which was comparable to that of acetate (99.84 ± 0.44 %), and much higher than glucose (65.64 ± 3.86 %). Higher denitrification rate was achieved using citrate as carbon source, which was slightly higher than acetate and >4 times of that using glucose. Due to the high activities of denitrifying enzymes including nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (N2OR), there was almost no NO2‐-N and N2O accumulation in the reactor fed with citrate, which was superior to the reactors fed with acetate or glucose. Azoarcus (48.2 %) with the ability of complete denitrification was the most dominant bacteria in the reactor fed with citrate. Considering denitrification kinetics, activities of key enzymes and microbial community characteristics, citrate had a superiority as an effective denitrification carbon source.

Rapid establishment of municipal sewage partial denitrification-anammox for nitrogen removal through inoculation with side-stream anammox biofilm without domestication

Mainstream partial denitrification anammox was achieved through inoculation of side-stream mature partial nitritation anammox biofilm without domestication. The contribution of anammox to nitrogen removal was 29.4 %. Moreover, prolonging anoxic hydraulic retention time and introducing side-stream nitrite under different carbon/nitrogen ratios enriched anammox bacteria. The abundance of anammox bacteria increased by ∼ 10 times ((2.19 ± 0.17) × 1012 copies gene / g dry sludge) with a total relative abundance of 18.51 %. During 258 days of operation, the contribution of anammox to nitrogen removal gradually increased to 68.8 %. The total nitrogen in the effluent decreased to 8.84 mg/L with a total nitrogen removal efficiency of 76.4 % under a carbon/nitrogen ratio of 3. This paper proposes a novel way to rapidly achieve mainstream partial denitrification anammox via inoculation with side-stream mature partial nitritation anammox biofilm. This method achieves advanced nitrogen removal from municipal wastewater, even under low carbon/nitrogen ratios.

Pilot–scale vertical continuous–flow reactors applied to treat rural domestic wastewater at low temperature via aerobic granular sludge

A pilot–scale vertical–flow continuous flow reactors (VF–CFR) was investigated for the treatment of rural domestic wastewater in the cold areas of Northeast China. VF–CFR helps in the creating of aerobic granular sludge (AGS), which improves the sludge concentration and removal efficiency of pollutants. VF–CFR achieved a high removal efficiency of Chemical Oxygen Demand (COD), Ammonia Nitrogen (NH3−N), Total Nitrogen (TN) and Total Phosphorus (TP) with 90 %, 94 %, 75 % and 93 % under the condition of sharp fluctuation of influent quality and temperature. The high–throughput sequencing analysis of the AGS revealed that Flavobacterium was a functional bacterium in the AGS process that had the function of heterotrophic nitrification and denitrification. The field–scale experiment confirmed the superiority of VF–CFR in wastewater treatment efficacy and stability. During the experiment, the concentrations of COD, TP and NH3–N in effluent at different temperatures were well met with the first–class A discharge standard of China (GB 18596–2001). However, there was a risk of exceedance exists in the reduction of TN removal under low temperature conditions.

Kinetics of ammonium removal from domestic wastewater by partial nitrification and anammox process

The research was conducted for 210 days on a partial nitrification/Anammox system (PN/A) using fixed bed biomass carrier to remove nitrogen in domestic wastewater. Total nitrogen and ammonium removal efficiency reached 69.8 % and 91.4 %, respectivety. In this study, we investigated three kinetic models (the first-order, Grau second-order and Stover Kincannon model) to determine which model is most suitable to describe the kinetics of the partial nitrification and anammox process. The results have shown that the Stover-Kincannon model is the most suitable and applicable for prediction the substrate concentration in the wastewater and the optimal volume of the reactor. The values of saturation constant (KB) and the max ultilizaion rate (Umax) were calculated for partial nitrification process as 15.489 and 8.038 (mg L−1 d−1). respectively. The research has also determined the values of KB and Umax for anammox process as 1.738 and 1.241 (mg L−1 d−1), respectively.

Nitrogen removal from urea effluent in an anammox sequencing batch biofilm reactor with valorised dishwashing scrubber as biocarrier

BackgroundThis study aimed for efficient nitrogen removal from urea wastewater in an anammox SBBR with valorised dishwashing scrubber as biocarrier. MethodsThe study (225 d) comprised three discrete phases: Phase I [1 – 26 d; Inf. NH4+-N (Simulated ww)], Phase II [27 – 131 d; Inf. NH4+-N (Real ww) + Inf. NH4+-N (Simulated ww)] and Phase III [132 – 225 d; Inf. NH4+-N (Real ww)] in which the reactor was supplemented with varied ratios (0 – 7) of influent NH4+-N reflecting varying combinations of real and simulated wastewater. Significant findingsThe reactor exhibited average total nitrogen removal efficiency of approximately 83 %, 81 %, and 80 % in the subsequent phases I, II, and III, respectively at varied nitrogen loading rates (100 – 232 g N m−3 d−1). The 16S rRNA gene sequencing revealed significant enrichment of Candidatus Kuenenia (from 41.69 % to 48.11 %) on the 225th day which was primarily attributed to significant decline in Nitrospira from 23.9 % to 1.24 % (due to nitrite oxidizing bacteria inhibition on account of high free ammonia concentrations in the reactor) and Nitrosomonas from 4.32 % to 0.01 %. Additionally, genera that were not initially present (on the 1st day) including Stenotrophobacter (17.34 %), Sphingobium (8.41 %), Rhodococcus (5.88%) and Ohtaekwangia (5.84 %) were observed to emerge by the end of the experiment (225 d).

Nitrogen removal and nitrous oxide emission from moving bed biofilm reactor (MBBR) under different loads and airflow

Total nitrogen (TN) removal by sewage treatment required the development of nitrifying and denitrifying activities; however, these metabolite activities can produce and emit nitrous oxide (N2O), one of the greenhouse gases (GHG). With the expansion of sewage treatment in the world, compact systems such as moving bed biofilm reactor (MBBR) may be promising, mainly in more populated cities. However, little is known about N2O emission by the MBBR. This work investigated the N-NHx and TN removal, N2O production and emission and nitrogen mass balance in a MBBR under organic load and airflow variation. The highest TN removal (47%) was observed under higher load and higher aeration rate. Meanwhile, the MBBR under lower load and lower airflow had the lowest efficiency of TN and N-NHx removal probably due to a lower nitrifying activity. The N2O emission factors were lower than 1.6% (value estimated by the IPCC for sewage aerobic treatment systems). In addition, in the essay with higher load and lower airflow, half of removed TN was released by settled sludge and there is little research about this subject. Therefore, the MBBR showed to be a promising process for nitrogen removal with little emission of N2O even under different operational conditions that normally can occur in sanitary sewage system in cities around the world.

Interspecies cooperation-driven photogenerated electron transfer processes and efficient multi-pathway nitrogen removal in the g-C3N4-anammox consortia biohybrid system

Photocatalytic materials-microbial biohybrid systems pave the way for solar-driven wastewater nitrogen removal. In this study, interspecies cooperation in photogenerated electron transfer and efficient nitrogen removal mechanism in the g-C3N4-anammox consortia biohybrid system were first deciphered. The results indicated that the essential extracellular electron carriers (cytochrome c and flavin) for anammox genomes were provided by associated bacteria (BACT3 and CHLO2). This cooperation, regulated by the ArcAB system and electron transfer flavoprotein, made anammox bacteria the primary photogenerated electron sink. Furthermore, an efficient photogenerated electron harness was used to construct a reductive glycine pathway (rGlyP) in anammox bacteria inventively, which coexisted with the Wood–Ljungdahl pathway (WLP), constituting a dual-pathway carbon fixation model, rGlyP-WLP. Carbon fixation products efficiently contributed to the tricarboxylic acid cycle, while inhibiting electron diversion in anabolism. Photogenerated electrons were targeted channeled into nitrogen metabolism-available electron carriers, enhancing anammox and dissimilatory nitrate reduction to ammonium (DNRA) processes. Moreover, ammonia assimilation by the glycine cleavage system in rGlyP established an alternative ammonia removal route. Ultimately, multi-pathway nitrogen removal involving anammox, DNRA, and rGlyP achieved 100 % ammonia removal and 94.25 % total nitrogen removal efficiency. This study has expanded understanding of anammox metabolic diversity, enhancing its potential application in carbon-neutral wastewater treatment.