Nitrogen Removal Mechanism Research Articles

Mechanism of stable autotrophic nitrogen removal and NOB inhibition in low-sludge PN-Anammox system under non-temperature control and low ammonia environment

PN/Anammox, as an economical and effective nitrogen removal process, is of great significance for reducing carbon emission in municipal wastewater treatment. However, municipal wastewater has mainstream characterized of low temperature and low NH4+-N concentration, and NOB activity is difficult to inhibit, so achieving a stable PN process is the biggest challenge in the application of PN/Anammox to mainstream wastewater. This study developed a method for stable and efficient PN/Anammox based on very low sludge volume (MLVSS = 65 mg/L). Even when the temperature dropped to 15℃ or there was exogenous nitrite-oxidizing bacteria (NOB) interference, the system still had good inhibition of NOB activity. The total stable operation time was 386 days, and the NO2–-N accumulation efficiency could reach more than 90 %. Ellin6067, Nitrosomonas and Candidatus_Brocadia were the dominant functional microorganisms in the system. Nitrospira was the dominant genera of NOB with very low relative abundance (<0.04 %). The mechanism of the long-term stable mainstream PN/Anammox system showed that low sludge content was beneficial to light irradiation on microorganisms in the reactor, while nxrA, the functional gene of NOB, had weak light resistance and oxidation resistance, which makes the system had strong inhibition effect on NOB. The construction of this new system which does not depend on activated sludge volume and complex NOB activity inhibition strategy can better promote the practical application of PN/Anammox under mainstream conditions.

Influence of hydraulic retention time on advanced synergistic nitrogen removal using internal carbon source

Hydraulic retention time (HRT) is a significant operational eter of denitrifying filter (DF). The influence of HRT on the performance and mechanism of advanced synergistic nitrogen removal (ASNR) of partial-denitrification anammox (PDA) and denitrification was investigated, consuming the hydrolytic and oxidation products of refractory organics in the secondary effluent (SE) as carbon source. When the HRT was 8, 6, 4 and 2 h, the filtered effluent total nitrogen (TN) was 1.47, 3.47, 4.17 and 4.49 mg/L, and the effluent CODcr was 8.12, 9.95, 9.40 and 9.87 mg/L, respectively. Removing 1 mg of TN actually consumed 0.87–0.96 mg CODcr, and the contribution rate of PDA to TN removal was 62.10–70.02 %. A variety of manganese oxidizing (MnOB), hydrolytic, anammox and denitrifying bacteria were identified, and their abundance was obviously affected by the HRT. The lack of carbon source was the main factor limiting the ASNR efficiency, rather than the HRT.

Effects of microorganisms on nitrogen and phosphorus removal from wastewater

Nitrogen and phosphorus are key to plant growth. The balance of nitrogen and phosphorus is crucial in nature. Excessive nitrogen and phosphorus content in wastewater has caused great harm to the environment. Traditional nitrogen and phosphorus removal methods can no longer meet the treatment standards for nitrogen and phosphorus. This article introduces the hazards of nitrogen and phosphorus, and points out the harm to nature and human beings if they are not up to standard in wastewater treatment plants. Through the analysis and discussion of several methods, the advantages of microbial nitrogen and phosphorus removal are explained. This article further summarizes several representative new microorganisms and microbial processes through the types and mechanisms of microbial nitrogen and phosphorus removal. Anammox bacteria can accept other electron pools to increase nitrogen removal efficiency. Denitrifying phosphorus-removing bacteria can achieve energy saving and carbon reducing effects through endogenous denitrification. Besides, the enhanced biological phosphorus removal process can allow denitrifying phosphorus accumulating bacteria to absorb phosphorus in an anaerobic, anoxic, aerobic alternating environment. The moving bed biofilm reactor (MBBR) abandons the disadvantages of the traditional biofilm method, while retaining the advantages of the traditional biofilm method such as shock load resistance and low sludge production. These new microorganisms and new microbial processes have become important applications in future nitrogen and phosphorus removal processes due to their advantages of high efficiency, low energy, and no secondary pollution. This article is conducive to the promotion of microbial-based wastewater treatment and can provide suggestions for the sustainable development of wastewater treatment.

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.

Interactions between bacteria and microalgae in microalgal-bacterial symbiotic wastewater treatment systems: mechanisms and influencing factors

Microalgal-bacterial symbiotic wastewater treatment systems (MBSWTSs) have received widespread attention due to their capacity to achieve high pollutant removal efficiency during wastewater treatment, with low energy consumption requirements, efficient carbon sequestration, and wastewater resource utilization. This paper provides an overview of the treatment performance and current research status of MBSWTSs, including a detailed summary of the mechanisms of nitrogen, phosphorus, and carbon removal by MBSWTSs and the interactions between bacteria and microalgae. In particular, this review focuses on the influence of operational parameters on the regulation of the symbiotic system, such as the microalgal:bacterial ratio, N:P ratio, external carbon source, dissolved oxygen concentration, aeration mode, and light availability. Among these factors, the microalgal:bacterial ratio, carbon source, and light availability have an important influence on microalgal-bacterial competition, as well as the trophic mode of the system, biomass production, and the capacity for the process to be practically applied on a large scale. MBSWTSs still have some challenging aspects that have hindered their development and application, such as the unknown mechanism of microalgal-bacterial co-metabolism, limited previous practical applications, algal contamination, and harvesting difficulties. To overcome these challenges, future research requires a multidisciplinary approach, incorporating life sciences, material science, and other disciplines. Comprehensive research should be conducted on the metabolic mechanisms of MBSWTSs, the optimization of process performance and waste resource utilization, providing a theoretical and practical foundation for the practical application of MBSWTSs.

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.

Promoting Aquatic Health in Constructed Wetlands: Removal of Pathogens and Nitrogen

Due to urbanization and population growth, freshwater resources have become a long-term concern for most developing countries. With the growth of population, the demand for fresh water is increasing and the requirement for sewage treatment is also increasing. In recent years, the demand for sewage recycling has increased sharply. Constructed wetlands (CWs) are an effective sewage treatment system with low energy consumption, minimal maintenance requirements, and a low operation cost, which will meet the current demand for the removal of nutrients and pathogens. The application of CWs in sewage treatment has attracted more and more attention because it is also a nature-based solution (NbS). These systems are capable of removing not only nitrogen (N) and phosphorus (P), but also pathogen indicators, such as fecal coliform and Escherichia coli. The presence of these indicators also suggests the influx of other pathogens into aquatic systems, thereby threatening aquatic ecological health. However, research on the removal of pathogens in CWs is relatively scare and their removal mechanisms are not fully understood. Despite their widespread application, the role of plants in CWs, particularly in the specific mechanism of pathogens and nitrogen removal, remains largely unknown. This article will help us to better understand this technology and provide help for our further research. In this paper, the coupled denitrification mechanism between microorganisms and plants in the process of nitrogen transformation was discussed. Plants affect nitrogen transformation microorganisms by releasing oxygen and secretions from their roots and provide substrates for bioremediation. The removal effects of different types of CWs on pathogen and nitrogen species were also summarized. Overall, the removal effect of subsurface flow wetlands outperforms that of surface flow wetlands, with multi-stage wetland systems being the most effective. The main factors affecting the removal of pathogens and nitrogen species in CWs include plants, substrates, operating parameters, UV radiation, temperature, water composition, and pH. Finally, the research frontiers on the removal of pathogens in CWs were prospected.

Simultaneous removal of manganese and ammonium nitrogen from mine water using sodium hexametaphosphate modified natural zeolite loaded by 3D MnOx

Manganese and ammonia nitrogen pollution are widespread in the water of northern Chinese mines, exacerbating regional water scarcity and potential ecological issues. This study aimed to remova dissolved manganese(II) and ammonia nitrogen from mine water using a natural zeolite (NZ) modified with sodium hexametaphosphate impregnation (SHMP-NZ) and loaded with 3D manganese(III)/(IV) oxide nanosheets (SHMP-NZ/MnOx). The influence of factors such as pH value, dissolved oxygen, and coexisting ions on adsorption was investigated. The capacity of NZ to removing ammonium was determined by SHMP impregnation, while the capability to remove manganese was determined by 3D manganese(III)/(IV) oxide nanosheets. Compared to NZ, SHMP-NZ/MnOx exhibited an increased efficiency of 39.93% and 41.54% in the simultaneously removing low-concentration manganese(II) and ammonia nitrogen, respectively. Adsorption processes of manganese and ammonia nitrogen onto NZ and SHMP-NZ/MnOx followed the Elovich and pseudo second order kinetic models, respectively. Both materials exhibited stages of external diffusion, internal diffusion, and reaction equilibrium during adsorption. The maximum adsorption capacities of SHMP-NZ/MnOx for manganese(II) and ammonia nitrogen were 10.12 mg/g and 26.24 mg/g, representing improvements of 72.7% and 113.2%, respectively, compared to NZ. The primary mechanism for ammonia nitrogen removal by SHMP-NZ/MnOx was based on ion exchange, while manganese(II) removal was mediated by Mn3+/Mn4+ species. A regeneration study over five cycles indicated that SHMP-NZ/MnOx possessed promising reusability potential.

Revealing the differences in metabolisms and nitrogen removal mechanisms of the full and shortcut nitrification-denitrification processes for the treatment of livestock wastewater

The full nitrification-denitrification process (FN) and shortcut nitrification-denitrification process (SN) are both important approaches for treating livestock wastewater. However, most existing studies focus on pollutant removal performance in wastewater treatment, while the differences between the two processes in terms of bacterial communities, metabolic pathways, nitrogen removal mechanisms, and potential pathogen threats have been poorly investigated. In this study, the SN process exhibited lower oxygen demand, reduced sludge production, higher nitrogen removal rate, and lower pathogen threat for treating livestock wastewater. The bacterial communities, the primary participants of pollutant removal in wastewater treatment, were significantly different between the two processes. In the FN process, 15 genera were significantly enriched, including Saccharimonadales, Micropruina, Ferruginibacter, etc. On the other hand, the SN process showed enrichment of 10 genera, including Brachymonas, Tessaracoccus, Ottowia, etc. These enriched genera, such as Brachymonas, Tessaracoccus, and Ottowia in the SN process, were positively correlated with the denitrification genes, facilitating a higher nitrogen removal rate. Moreover, the FN process exhibited significantly higher amino acid metabolism and reproduction-related pathways, contributing to its higher alpha-diversity of the bacterial community. The significantly enriched genes involved in assimilatory nitrate reduction and nitrogen assimilation pathway suggested that nitrogen assimilation played a crucial role in ammonia nitrogen removal, but it also increased sludge production in the FN process. Additionally, the FN process had a higher number and abundance of potential pathogens, indicating a greater pathogen threat. In conclusion, this study provides valuable insights into the differences between the FN and SN processes in terms of bacterial communities, nitrogen removal mechanisms, and potential pathogen threats. It also offers theoretical guidance for adopting appropriate strategies in wastewater treatment.

Biological nitrogen removal characteristics and mechanisms of a novel salt-tolerant strain Vibrio sp. LV-Q1 and its application capacity for high-salinity nitrogen-containing wastewater treatment

High concentration of salts in wastewater can adversely affects the metabolic activities and growth of microorganisms, resulting in reduced efficiency of biological nitrogen removal. Screening high-efficiency heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria with salt tolerance is important for the wastewater treatment. In this study, a novel salt-tolerant strain LV-Q1 capable of HN-AD was isolated and identified as Vibrio sp. This strain demonstrates a salinity tolerance range of 0–8 %. Notably, strain LV-Q1 exhibited exceptional nitrogen removal efficiencies (at initial concentrations of 100 mg/L), achieving 97.97 % for NH4+-N, 100 % for NO3--N, and approximately 100 % for mixed nitrogen (NH4+-N and NO3--N) at a salinity of 5 %. Optimal ammonium removal parameters for LV-Q1 were established. The nitrogen removal pathway of LV-Q1 primarily involves direct assimilation of ammonium and its conversion into N2 through HN-AD. Analysis of the salt tolerance mechanism revealed LV-Q1's ability to equilibrate osmotic pressure through the accumulation of amino acids and betaine, production of antioxidative enzymes or extracellular protein, and utilization of its quorum sensing (QS) properties to withstand high-salinity environments. The strain LV-Q1 exhibited strong resistance to salinity shock in bioaugmentation within a moving bed biofilm reactor (MBBR), markedly enhancing nitrogen and carbon removal performance with an improved removal efficiency of 26.74 % and 10.15 % averagely at the end of the reaction at a salinity of 5 %. Moreover, Vibrio sp. LV-Q1 successfully proliferated and dominated, and its relative abundance gradually increased to 59.81 %. This study contributes new insights and resources for the treatment of nitrogen in saline effluents.

Study on the impact of hydraulic loading rate (HLR) on removal of nitrogen under low C/N condition by modular moving bed constructed wetland (MMB-CW) system

Traditional constructed wetlands often exhibit low nitrogen removal efficiency when treating low C/N wastewater, prompting the need for targeted technological innovation. Modular moving bed constructed wetlands (MMB-CWs) have demonstrated superior performance, achieving over 15% higher TN removal compared to traditional subsurface flow wetlands, even without the addition of carbon, further research is required to fully understand the operational effects of different hydraulic loads and the underlying nitrogen removal mechanisms. To address this gap, the contrast performance of MMB-CWs with three different substrate addition ratios 90% (unit A), 60% (unit B), 30% (unit C) was studied under low C/N conditions and different hydraulic loading rates (HLRs). Results show that there are no significant differences in TN removal among the three systems at 250 mm/d and 500 mm/d. NH4+-N and NO3--N removal rates don't significantly decrease (p>0.05). High HLR leads to significantly lower effluent NO2--N concentrations. HLR minimally affects CODCr removal, with unit C exhibiting better resistance. Functional gene analysis reveals a minor role of nitrification, emphasizing the crucial role of anaerobic ammonium oxidation. The copy number of the Anammox gene is 1.2–4.0 times that of the NIR gene, with a larger ratio in the secondary unit, indicating that denitrification is mainly driven by Anammox. The dominant genera in the first unit are Azospira, Thauera, and Denitratisoma, while Defluviicoccus, Mycobacterium, and Nocardioides dominate the ceramsite and biochar of the second unit. The addition of biochar enhances the composition and abundance of microbial communities in the system, and as biochar addition increases, the removal rates of NH4+-N and TN gradually increase, ensuring effective denitrification under varying loads.

Optimization of nitrogen removal and microbial mechanism of a hydrogen-based membrane biofilm reactor

ABSTRACT The hydrogen-based membrane biofilm reactor (H2-MBfR) is an emerging biological nitrogen removal technology characterized by high efficiency, energy-saving capability, and environmental friendliness. The technology achieves denitrification and denitrogenation of microorganisms by passing hydrogen as an electron donor from inside to outside through the hollow fibre membrane module, and eventually the hydrogen reachs the biofilm attached to the surface of the fibre membrane. H2-MBfR has obtained favourable outcomes in the treatment of secondary biochemical effluent and low concentration nitrogen polluted water source. The experiment was optimized by s single-factor testing and response surface methodology-based optimization (RSM), and the optimal operational conditions were obtained as follows: an influent flow rate of 2 mL/min, hydrogen pressure of 0.04 MPa, and influent nitrate concentration of 24.29 mg/L. Under these conditions, a high nitrate removal rate of 98.25% was achieved. In addition, Proteobacteria and Bacteroidetes were the dominant bacteria in all stages, and the genus Hydrogenophaga was sufficiently enriched, occurring at 13.0%–49.0% throughout the reactor operation. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for nitrate reduction and inorganic carbon utilization by microorganisms in the H2-MBfR was explored through comparison with the KEGG database. The results provided a mechanistic explanation for the denitrification and carbon sequestration capacity of the H2-MBfR.

Synergistic denitrification mechanism of domesticated aerobic denitrifying bacteria in low-temperature municipal wastewater treatment

To address the problems of low efficacy and low microbial activity in low-temperature municipal wastewater treatment, this study utilized an air-lift micro-pressure internal circulation integrated reactor (AMICIR). Through controlling the amount of aeration and dissolved oxygen (DO) in the reactor, AMICIR creates alternating aerobic and anaerobic environments, explores the enrichment conditions of aerobic denitrifying bacteria, examines the changes in pollutant removal efficiency and the characteristics of bacterial colony structure during the process of enrichment of aerobic denitrifying bacteria in the system, and reveals the mechanism of nitrogen removal by aerobic denitrifying bacteria cooperating with anaerobic denitrifying bacteria in the low-temperature municipal wastewater treatment system. Experimental results showed average removal rates of NH4+-N, chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) reaching 93.85%, 89.30%, 92.75%, and 75.4%, respectively. The microorganisms secreted large amounts of proteins and polysaccharides, forming zoogloea and anaerobic microenvironments conducive to traditional denitrification reactions. IlluminaMiSeq sequencing analysis revealed the presence of anaerobic phyla. The system was enriched with a large number of microorganisms, and aerobic denitrifying bacteria (Flavobacterium, Rhodoferax, and Pseudomonas) were successfully cultured. Flavobacterium emerged as the dominant species, with relative abundance ranging from 18.56% to 22.60%. Functional gene prediction indicated high abundance of aerobic denitrification genes, such as napA. Aerobic denitrifying bacteria were successfully enriched in the system to improve nitrogen removal from municipal wastewater at low temperatures.

Insight into the C/N Effect on Treating Domestic Wastewater by the Electrical Gradual Deammonification Reactor (EGDR): Removal Performance, Microbial Communities, and the Nitrogen Removal Mechanism

Insight into the C/N Effect on Treating Domestic Wastewater by the Electrical Gradual Deammonification Reactor (EGDR): Removal Performance, Microbial Communities, and the Nitrogen Removal Mechanism

Nitrogen removal performance and mechanisms of three aquatic plants for farmland tail water purification

Constructed wetlands (CWs) are commonly used to control excessive nitrogen from farmlands; however, the interactions between vegetation and microorganisms, nitrogen removal performance, and the mechanisms involved remain unclear in subtropical areas. This study aimed to investigate the nitrogen removal performance and mechanism of CWs containing Canna indica, Acorus calamus, and Thalia dealbata. The results show that CWs with plants had significantly higher nitrogen removal efficiencies than those without, with those planted with T. dealbata having the highest efficiency. T. dealbata performed better than the other two plants due to its high biomass and excellent nitrogen uptake capacity; more importantly, CWs with it had the highest abundance of nitrogen functional genes. Microbial nitrification-denitrification, the primary process of nitrogen removal in CWs, contributed to 88 %, 91 %, and 84 % of the TN removal in the CWs with C. indica, A. calamus, and T. dealbata, respectively, 29 %–158 % higher than that in CWs without plants. Microorganisms played a crucial role in nitrogen removal in the CWs, while plants significantly stimulated microbial activity by enhancing microbial abundance and creating a suitable environment for growth and metabolism. These results can help in understanding the contribution of plants in cleaning farmland tailwater and further optimization of plant configuration and management strategies in wetland ecosystems to improve nitrogen removal efficiency.

Sulfadiazine and Nitrogen Removal Performance and Mechanisms of a Saline-Resistant Strain of Acinetobacter sp. RT-6

The main goal of this article is to elucidate the SDZ and TN removal characteristics and mechanisms of a saline-resistant strain of Acinetobacter sp. RT-6. The SDZ and TN removal characteristics indicated that SDZ and TN removal were significantly affected by SDZ concentration and salinity. The removal curves and kinetics of different typical amounts of nitrogen showed the shortcut nitrification and denitrification present in the ammonia-N removal process; the nitrogen-containing compound was mainly transformed into N2, and approximately 19.05 ± 0.83 mM of the electrons was transferred to the nitrate respiratory chain. The intermediates of SDZ degradation were identified, and it was speculated that the main reaction sites for SDZ transformation were the N–C bond, N–S bond, pyrimidine ring, and benzene ring.

Enhanced adaptability of pyrite-based constructed wetlands for low carbon to nitrogen ratio wastewater treatments: Modulation of nitrogen removal mechanisms and reduction of carbon emissions

Pyrite-based constructed wetlands (CWs) stimulated nitrate removal performance at low carbon to nitrogen (C/N) ratio has been gaining widely attention. However, the combined effects of pyrite and C/N on the nitrate removal mechanisms and greenhouse gases (GHGs) reduction were ignored. This study found that pyrite-based CWs significantly enhanced nitrate removal in C/N of 0, 1.5 and 3 by effectively driving autotrophic denitrification with high abundance of autotrophs denitrifiers (Rhodanobacter) and nitrate reductase (EC 1.7.7.2), while the enhancement was weakened in C/N of 6 by combined effect of mixotrophic denitrification and dissimilatory nitrate reduction to ammonium (DNRA) with high abundance of organic carbon-degrading bacteria (Stenotrophobacter) and DNRA-related nitrite reductase genes (nrf). Moreover, pyrite addition significantly reduced GHGs emissions from CWs in all stages with the occurrence of iron-coupled autotrophic denitrification. The study shed light on the potential mechanism for pyrite-based CWs for treating low C/N ratio wastewater.

Simulation assisted process simplification and energy recovery from a cryptic biological nutrient removal plant

In this study, simulation-based analysis is conducted for nitrogen removal mechanism in a biological nutrient removal plant designed in an encrypted manner. In the first phase, the simulation study elucidates how nitrogen removal occurs in a complex design using a series of 4 carousel bioreactors with additional nitrate recycle. It is demonstrated that pre-anoxic volume fed with limited internal recirculation only would not be sufficient to meet the discharge Total Nitrogen (TN) limit of 10 mg N/L. However, the addition of simultaneous nitrification-denitrification (SND) processes in aerobic reactors enables compliance with TN discharge limits. In the second phase, the configuration is simplified by means of process simulation, where the complex design is streamlined by eliminating internal recycle while achieving nitrogen removal through the SND process. Plant data confirmed that the simplified configuration can achieve nitrogen removal providing the same discharge quality. The simulations resulted that TN concentration achieved at the plant effluent is comparable, while effluent total phosphorus concentration is decreased by approximately 50 % due to increased activity of Phosphorus Accumulating Organisms (PAOs) under reduced sludge retention time (SRT). In the third phase, the application of the SND process in the field using a simplified and new activated sludge configuration yields similar results to the simulation. According to plant records, 28 % energy savings and an equivalent chemical cost reduction of €945,000 per year were achieved with the new process configuration.

Lumen air pressure regulated multifunctional microbiotas in membrane-aerated biofilm reactors for simultaneous nitrogen removal and antibiotic elimination from aquaculture wastewater

In this study, two membrane-aerated biofilm reactors (MABRs) were constructed: one solely utilizing biofilm and another hybrid MABR (HMABR) incorporating both suspended-sludge and biofilm to treat low C/N aquaculture wastewater under varying lumen air pressure (LAP). Both HMABR and MABR demonstrated superior nitrogen removal than conventional aeration reactors. Reducing LAP from 10 kPa to 2 kPa could enhance denitrification processes without severely compromising nitrification, resulting in an increase in total inorganic nitrogen (TIN) removal from 50.2±3.1 % to 71.6±1.0 %. The HMABR exhibited better denitrification efficacy than MABR, underscoring its potential for advanced nitrogen removal applications. A decline in LAP led to decreased extracellular polymeric substance (EPS) production, which could potentially augment reactor performance by minimizing mass transfer resistance while maintaining microbial matrix stability and function. Gene-centric metagenomics analysis revealed decreasing LAP impacted nitrogen metabolic potentials and electron flow pathways. The enrichment of napAB at higher LAP and the presence of complete ammonia oxidation (Comammox) Nitrospira at lower LAP indicated aerobic denitrification and Comammox processes in nitrogen removal. Multifunctional microbial communities developed under LAP regulation, diversifying the mechanisms for simultaneous nitrification-denitrification. Increased denitrifying gene pool (narGHI, nirK, norB) and enzymatic activity at a low LAP can amplify denitrification by promoting denitrifying genes and electron flow towards denitrifying enzymes. Sulfamethoxazole (SMX) was simultaneously removed with efficiency up to 80.2 ± 3.7 %, mainly via biodegradation, while antibiotic resistome and mobilome were propagated. Collectively, these findings could improve our understanding of nitrogen and antibiotic removal mechanisms under LAP regulation, offering valuable insights for the effective design and operation of MABR systems in aquaculture wastewater treatment.

A novel method for enhancing nitrogen removal from wastewater treatment plant tailwater by zeolite-supported nano zero-valent iron substrate constructed wetland

The discharge of tailwater from wastewater treatment plants can cause pollution to receiving water bodies. Constructed wetlands (CWs) provide an economical approach to tailwater treatment. However, biological denitrification is limited due to the low bioavailability of carbon (C) relative to nitrogen (N) for denitrification in tailwater. Zeolite-supported nano zero-valent iron (Z-nZVI) and montmorillonite-supported nano zero-valent iron (Mt-nZVI) were prepared and used as substrates in CWs to evaluate their efficiency and mechanism of nitrogen removal from low C:N ratio tailwater. The results suggest that Z-nZVI can convert different forms of inorganic nitrogen to ammonium nitrogen (NH4+–N),which can be subsequently removed by the adsorption via zeolite or montmorillonite. The conversion rate for nitrate (NO3−–N) reached a maximum of 76.5%, electron transfer occurred during the reduction of NO3−–N by Z-nZVI. The removal rates of NO3−–N, NH4+–N, and total nitrogen by the Z-nZVI-substrate CW were 66.42 ± 1.33%, 86.56 ± 0.93%, and 69.92 ± 0.56%, which were, on average, 40.77%, 18.34%, and 35.73% higher than those observed in the CW with traditional gravel substrate. This presents a practical method for improving nitrogen reduction in CWs.