Nitrogen Removal Pathway Research Articles

Efficient nitrogen removal of a novel Pseudomonas chengduensis strain BF6 mainly through assimilation in the recirculating aquaculture systems

Biological nitrogen removal has received increasing attention in wastewater treatment. A bacterium with excellent nitrogen removal performance was isolated from biofilters of recirculating aquaculture systems (RAS) and identified as Pseudomonas chengduensis BF6. It was indicated that inorganic nitrogen is transformed into gaseous and biological nitrogen by the metabolic pathways of denitrification, anammox, and assimilation, which is the main nitrogen removal pathway of strain BF6. The strain BF6 could effectively remove nitrogen within 24 h under the conditions of ammonia, nitrate, nitrite, and mixed nitrogen sources with maximum total nitrogen removal efficiencies reaching 97.00 %, 61.40 %, 79.10 %, and 84.98 %, respectively. The strain BF6 exhibited total nitrogen removal efficiency of 91.14 %, altered the microbial diversity and enhanced the relative abundance of Pseudomonas in the RAS biofilter. These findings demonstrate that Pseudomonas sp. BF6 is a highly efficient nitrogen-removing bacterium with great potential for application in aquaculture wastewater remediation.

Performance of simultaneous carbon and nitrogen removal of high-salinity wastewater in heterotrophic nitrification-aerobic denitrification mode

In this work, heterotrophic nitrification-aerobic denitrification (HN-AD) mode was successfully established after a 105-day acclimation in a sequencing batch reactor (SBR) system using mustard tuber wastewater (MTWW) as substrate. The performance of simultaneous carbon and nitrogen removal (SCNR) was investigated using manual wastewater within the salinity from 1% to 6%. Results indicate that high salinity caused little effect on carbon removal, while it brought a significant influence on nitrogen removal. At the salinity of 1% and 3%, the heterotrophic nitrification rates were 2.83 and 3.96-fold of those of the autotrophic nitrification, respectively. As the salinity was up to 6%, the autotrophic nitrification was significantly inhibited, while the anoxic denitrification was slightly affected and the aerobic denitrification became dominant. The analysis on microbial community structure of the acclimated wastewater sludge reveals that the genera with autotrophic nitrification were gradually eliminated with an increasing salinity during the acclimation. Paracoccus, Pseudomonas, Alcaligenes and Bacillus were the dominant genera related to HN-AD process. The optimal operation parameters for SCNR were investigated, including C/N ratio (25), DO concentration (6 mg/L) and temperature (35 °C). This work provides an insight into the migration of nitrogen removal pathway and the succession of HN-AD microbial community in the process of high-salt wastewater biotreatment.

Metagenomic analysis revealed the mechanism of extracellular polymeric substances on enhanced nitrogen removal in coupled MABR systems with low C/N ratio containing salinity

A combined membrane-aerated biofilm reactor (MABR) was conducted to treat various C/N ratios with saline wastewater. The influence of C/N on nitrogen removal property, extracellular polymeric substances (EPS) features, bacterial community and relevant functional genes were investigated. Fourier-transform infrared spectrum (FTIR), three-dimensional exaction and emission matrix (3D-EEM) fluorescence spectra and metagenomics analysis were conducted to study the mechanism of EPS for enhanced nitrogen removal at low C/N ratio. The results showed that TN removal rate of the whole MABR system were 73.21%, 69.51% and 67.04%, respectively, with the C/N ratio of 6, 4.5 and 3. MABR-2 biofilms secreted more EPS under low C/N and high-salinity conditions to maintain intracellular and extracellular osmotic pressure balance and to participate in cellular metabolic processes. Meanwhile, under the stimulation of low C/N, MABR-2 system with low influent loading was in a “starvation state”, thus EPS could be utilized by the biofilm of MABR-2 system as carbon source to enhance nitrogen removal. Besides, metagenomics analysis showed that aerobic denitrification and dissimilatory nitrite reduction to ammonia (DNRA) were dominant nitrogen removal pathways in MABR-2 system at low C/N ratio. EPS might participate in related metabolic processes in the electron donors and energy production processes as well as the electron transfer pathways in denitrification system. This work provided a feasible practical application scheme for the enhanced TN removal of low C/N ratio containing salinity.

Simultaneous removal of typical antibiotics and nitrogen by SWIS assisted by iron carbon micro-electrolysis

In this study, a combination of subsurface wastewater infiltration system (SWIS) with iron carbon micro-electrolysis (namely ICMESWIS) was used to enhance the simultaneous removal of nitrogen and typical antibiotics (SMX, OTC and HCl-Lev was selected). The results indicated that assisted by 10 % dopant amount of ICME, SMX, OTC, Lev-HCl, NH4+-N, NO3--N and NO2--N removal rates increased by 26.6 %, 19.7 %, 10.2 %, 33.7 %, 28.5 % and 19.3 %, respectively via ICMESWIS than SWIS. The higher TFe release rate, organic matter content and richer microbial populations encouraged ICMESWIS to resist the impact of antibiotics. High-throughput sequencing revealed that electrochemical effect enhanced the microbial community structure, which was the main pathway for nitrogen and antibiotics removal. The total proportions of nitrogen and antibiotics removal relating bacteria were 18.38 % and 46.67 %, 5.49 % and 4.72 % higher than those of SWIS, respectively. Anammox became an additional N removal way in ICMESWIS.

Reactive and microbial inhibitory mechanisms depicting the panoramic view of pH stress effect on common biological nitrification

pH is a crucial factor of microbial nitrification, which often combines with high-strength ammonium to influence nitrogen removal pathway in wastewater treatment. However, the detailed inhibitory mechanisms of pH stress are not sufficiently disclosed yet. In this study, the pH stress effect on nitrification was comprehensively studied by a set of experiments which identified the reactivity of nitrification processes and activity of nitrifiers, the time dependence of inhibition effect and the hybrid pH stress effect with ammonium. The results revealed two distinct inhibitory mechanisms dominating in alkaline and acid ranges. In alkaline range (pH > 8), pH stress causes physiological damages on microorganisms which is named as microbial inhibition. It has the features of less recoverability of nitrifiers, time-dependent inhibition effect and low pH-tolerance of nitrite oxidation bacteria. Free ammonia enhanced microbial inhibition and greatly promoted nitrite accumulation. A novel reactive inhibition mechanism dominated in acid range (pH < 7) was disclosed. It only impedes ammonia oxidation process (AOP) but not impair microbial activity obviously and the effect is time-independent. The mechanism was clarified from H+ transport because AOP involved H+ production. The H+ transport was impeded under acid stress owing to the decrease of pH gradient across cell membrane. The two mechanisms formed a panoramic view of pH stress effect on nitrification advancing the understanding of nitrifier adaptability and nitritation regulation in wastewater treatment processes.

Quantification of enhanced nitrogen removal pathways of pyrite interaction with anammox sludge system

Fe and S could improve the anammox performance by coupling with the N cycle. However, the coexistence of Fe and S complicates the metabolic process, troubling the quantification of nitrogen removal pathways. Herein, the nitrogen removal pathways were quantificationally analyzed by 15N stable isotope tracing and elaborate batch tests, and the enhancing mechanism was illuminated by physiological and metatranscriptome analyses in pyrite (FeS2)-amended anammox system. We found that anammox, denitrification and Feammox (NH4+ oxidation coupled with Fe(III) reduction) contributed to 80.22 %, 19.53 % and 0.25 % nitrogen removal in this process. With pyrite addition, Fe, S release and the extracellular polymeric substances secretion were responsible for the enhancement of nitrite and nitrate removal via chemical, autotrophic and heterotrophic denitrification, improving nitrogen removal by 14 % and 19 %. The network analyses further confirmed that the multiple nitrogen removal pathways (i.e., anammox, Feammox and denitrification) contribute to pyrite-induced nitrogen removal enhancement in the anammox system. This work enables the in-depth understanding, future design and optimization of the pyrite-amended anammox system, providing a fundamental basis for developing Fe- and S-based anammox enhancement technologies.

Biofilm stratification and autotrophic-heterotrophic interactions in a structured bed reactor (SBRIA) for carbon and nitrogen removal

The structured-bed reactor with intermittent aeration (SBRIA) is a promising technology for simultaneous carbon and nitrogen removal from wastewater. An in depth understanding of the microbiological in the reactor is crucial for its optimization. In this research, biofilm samples from the aerobic and anoxic zones of an SBRIA were analyzed through 16S rRNA sequencing to evaluate the bacterial community shift with variations in the airflow and aeration time. The control of the airflow and aeration time were essential to guarantee reactor performances to nitrogen removal close to 80%, as it interfered in nitrifying and denitrifying communities. The aeration time of 1.75 h led to establishment of different nitrogen removal pathways by syntrophic relationships between nitrifier, denitrifier and anammox species. Additionally, the predominance of these different species in the internal and external parts of the biofilm varied according to the airflow.

Metagenomics reveals the microbial community and functional metabolism variation in the partial nitritation-anammox process: From collapse to recovery

Mainstream partial nitritation-anammox (PNA) process easily suffers from performance instability and even reactor collapse in application. Thus, it is of great significance to unveil the characteristic of performance recovery, understand the intrinsic mechanism and then propose operational strategy. In this study, we combined long-term reactor operation, batch tests, and metagenomics to reveal the succession of microbial community and functional metabolism variation from system collapse to recovery. Proper aeration control (0.10-0.25 mg O2/L) was critical for performance recovery. It was also found that Candidatus Brocadia became the dominant flora and its abundance increased from 3.5% to 11.0%. Significant enhancements in carbon metabolism and phospholipid biosynthesis were observed during system recovery, and the genes abundance related to signal transduction was dramatically increased. The up-regulation of sdh and suc genes showed the processes of succinate dehydrogenation and succinyl-CoA synthesis might stimulate the production of amino acids and the synthesis of proteins, thereby possibly improving the activity and abundance of AnAOB, which was conducive to the performance recovery. Moreover, the increase in abundance of hzs and hdh genes suggested the enhancement of the anammox process. Changes in the abundance of key genes involved in nitrogen metabolism indicated that nitrogen removal pathway was more diverse after system recovery. The achievement of performance recovery was driven by anammox, nitrification and denitrification coupled with dissimilatory nitrate reduction to ammonium. These results provide deeper insights into the recovery mechanism of PNA system and also provide a potential regulation strategy for the stable operation of the mainstream PNA process.

Isolation and characteristics of two heterotrophic nitrifying and aerobic denitrifying bacteria, Achromobacter sp. strain HNDS-1 and Enterobacter sp. strain HNDS-6

In order to solve nitrogen pollution in environmental water, two heterotrophic nitrifying and aerobic denitrifying strains isolated from acid paddy soil were identified as Achromobacter sp. strain HNDS-1 and Enterobacter sp. strain HNDS-6 respectively. Strain HNDS-1 and strain HNDS-6 exhibited amazing ability to nitrogen removal. When (NH4)2SO4, KNO3, NaNO2 were used as nitrogen resource respectively, the NH4+-N, NO3−-N, NO2−-N removal efficiencies of strain HNDS-1 were 93.31%, 89.47%, and 100% respectively, while those of strain HNDS-6 were 82.39%, 96.92%, and 100%. And both of them could remove mixed nitrogen effectively in low C/N (C/N = 5). Strain HNDS-1 could remove 76.86% NH4+-N and 75.13% NO3−-N. And strain HNDS-6 can remove 65.07% NH4+-N and 78.21% NO3−-N. A putative ammonia monooxygenase, nitrite reductase, nitrate reductase, assimilatory nitrate reductase, nitrate/nitrite transport protein and nitric oxide reductase of strain HNDS-1, while hydroxylamine reductase, nitrite reductase, nitrate reductase, assimilatory nitrate reductase, nitrate/nitrite transport protein, and nitric oxide reductase of strain HNDS-6 were identified by genomic analysis. DNA-SIP analysis showed that genes Nxr, narG, nirK, norB, nosZ were involved in nitrogen removal pathway, which indicates that the denitrification pathway of strain HNDS-1 and strain HNDS-6 was NO3−→NO2−→NO→N2O→N2 during NH4+-N removal process. And the nitrification pathway of strain HNDS-1 and strain HNDS-6 was NO2−→NO3−, but the nitrification pathway of NH4+→ NO2− needs further studies.

Start-up phase optimization of pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR): Mixotrophic denitrification performance and mechanism

Pyrite-based autotrophic denitrification (PAD) is an emerging biological process to diminish nitrate pollution, but the relatively low NO3−-N removal rate limits its practical application. In this research, a pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR) was designed to treat low C/N ratio domestic wastewater. The results showed that PIHSBBR could achieve optimal removal of COD, NH4+-N, and TN under the aeration rate of 1.0 L/L∙min and the hydraulic retention time (HRT) of 8 h, with removal rates of 69.67 ± 4.37%, 77.04 ± 4.84%, and 63.92 ± 6.66%, respectively. The PAD efficiency in PIHSBBR during the stable operation was not high (13.05–31.01%), and the main nitrogen removal pathway in PIHSBBR, especially in the aerobic zone, was simultaneous nitrification and denitrification (SND). High-throughput sequencing analysis unraveled that Planctomycetota (3.65%) had a high abundance in the anoxic zone of PIHSBBR, implying that anaerobic ammonium oxidation (anammox) might have occurred in the anoxic zone. In addition, the nitrogen cycle function gene with the highest abundance was nirBD, indicating the possible presence of dissimilatory nitrate reduction to ammonium (DNRA) within the system (aerobic and anoxic zones). Our research can provide useful information for the improvement and future application of PIHSBBR.

Impact of aeration frequency on performance of mixotrophic sequencing batch biofilm reactor (SBBR) treating real domestic wastewater: Removal efficiency, pathways, and mechanisms

Real domestic wastewater usually contains multiple pollutants including nitrogen, phosphorus and organics, which are not easy to be polished by a single process due to the lack of electron donors for denitrification, especially for low carbon to nitrogen (C/N) ratio wastewater. Autotrophic denitrification with inorganic substances as electron donors is a potent pathway for nitrogen removal and can be coupled with the heterotrophic process to achieve high performance. In this study, three double-layered mixotrophic sequencing batch biofilm reactors (SBBRs) involving pyrite-based autotrophic denitrification (PAD) were constructed to treat real domestic wastewater under different aeration frequencies. By adjusting the frequency of intermittent aeration to 16 times per operating cycle, the mean percent removals of ammonium-nitrogen (NH4+-N), total nitrogen (TN), and orthophosphate (PO43--P) reached 83.74 ± 6.95%, 54.41 ± 4.42%, and 90.45 ± 9.70%, respectively. Meanwhile, the increase of aeration frequency enhanced the removal of NH4+-N and PO43--P from the system, but high aeration frequency had an inhibitory effect on both heterotrophic denitrification and the PAD process. The 16S rRNA sequencing analysis revealed that the dominant taxa appeared in the system were Microscillaceae_unclassified, Nitrospira, Thiobacillus, and Candidatus_Competibacter, etc., which were contributable to the multiple nitrogen metabolism. The relative abundance of genes involved in complete nitrification, denitrification, assimilatory nitrate reduction to ammonium (ANRA), and dissimilatory nitrate reduction to ammonium (DNRA) was predicted based on PICRUSt2. In addition, two sulfur metabolic pathways, i.e. the sulfur oxidation (Sox) and sulfide:quinone oxidoreductase (SQR) pathways were found in the system. These findings might provide new insight into the mechanism of nutrient removal in PAD-based mixotrophic denitrification systems treating real domestic wastewater in an intermittent aeration mode.

Evaluation of the stability of shortcut nitrification-denitrification process based on online specific oxygen uptake rate monitoring

Shortcut nitrification-denitrification (SCND) is widely concerned because of its low energy consumption and high nitrogen removal efficiency. However, the current difficulty lies in the stable maintenance of SCND performance, which leads to the challenge of large-scale application of this new denitrification technology. In this study, the nitrogen removal pathway from complete nitrification-denitrification (CND) to SCND was rapidly realized under high free ammonia (FA), high pH and low dissolved oxygen (DO) conditions. The variations of specific oxygen uptake rate (SOUR) of activated sludge in both processes were investigated by an online SOUR monitoring device. Different curves of SOUR from CND to SCND process were observed, and the ammonia peak obtained based on SOUR monitoring could be used to control aeration time accurately in SCND process. Accordingly, the SOUR ratio of ammonia oxidizing bacteria (AOB) to nitrite oxidizing bacteria (NOB) (SOURAOB/SOURNOB) was increased from 1.40 to 2.93. 16S rRNA Miseq high throughput sequencing revealed the dynamics of AOB and NOB, and the ratio of relative abundance (AOB/NOB) was increased from 1.03 to 3.12. Besides, SOURAOB/SOURNOB displayed significant correlations to ammonia removal rate (P < 0.05), ammonia oxidation rate / nitrite oxidation rate (P < 0.05), nitrite accumulation rate (P < 0.05) and the relative abundance of AOB/NOB (P < 0.05). Thus, a strategy for evaluation the SCND process stability based on online SOUR monitoring is proposed, which provides a theoretical basis for optimizing the SCND performance.

Overlooked pathways of endogenous simultaneous nitrification and denitrification in anaerobic/aerobic/anoxic sequencing batch reactors with organic supplementation

The anaerobic/aerobic/anoxic (A/O/A) process is a promising biotechnology to intensify denitrification in low carbon/nitrogen (C/N) wastewater treatment, but the neglected typical rate-limiting step—nitrification—would hinder its wider application. Heterotrophic nitrification driven by intracellular carbon (PHAs) could enhance nitrification and achieve endogenous simultaneous nitrification and denitrification (ESND) in the A/O/A process, but its feasibility remains unexamined. Here we established four A/O/A-SBRs at different C/N ratios (3, 7.5, 12, and 16.5) to address the above-mentioned knowledge gaps. The results showed that organic supplementation promoted both nitrification and denitrification (performance and relevant enzymatic activities) until organic overdose (C/N = 16.5) exacerbated niche competitions from other non-functional heterotrophs. qPCR and batch tests indicated that high C/N ratios inhibited autotrophic nitrifiers, and heterotrophic nitrifiers (HNB) dominated in the enhanced nitrification. Given the high HNB contribution (43.7%) and low COD variation (< 10 mg L−1) in the SND (76.4%) of CN12, we proposed a potential SND pathway based on heterotrophic nitrification and denitrification driven by PHAs and verified it with batch tests. Microbial and functional analyses suggested that CN12 favored the intracellular carbon transformation and harbored the minimum autotrophic nitrifiers, supporting the dominance of ESND in the enhanced SND. Our findings expand the understanding of the relationships between intracellular carbon transformation and SND and provide a novel nitrogen removal pathway for the practical application of the A/O/A process.

Nitrogen removal and metabolic pathways of nitrifying coal ash propelled by temperature change under high nitrogen loading

Coal ash, owing to its cost-effectiveness and greater adhesion with nitrifiers, has been used as a carrier for immobilizing nitrifiers when treating wastewater with a low C/N ratio and high nitrogen loading. Various environmental conditions significantly affect the nitrogen metabolic pathways of nitrifying coal ash. In this study, the nitrogen metabolic pathways of nitrifying coal ash propelled at different temperatures were investigated to evaluate the impact of seasonal variation on nitrifying coal ash. Results showed average NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;-N effluent concentrations increased with temperature, and reached 3.37, 5.16, and 76.06 mg N/L with 1158 mg N/L influent under 15 ℃, 25 ℃, and 35 ℃ systems. The total nitrogen removal rate at a cooling temperature of 15 ℃ was higher than that at 25 ℃ and 35 ℃. Further analysis showed &lt;i&gt;Nitrosomonas&lt;/i&gt; and &lt;i&gt;Nitrobacter&lt;/i&gt; were enhanced, whereas a significant evolution of autotrophic denitrifiers, &lt;i&gt;Acidovorax&lt;/i&gt;, was enriched at 15 ℃. An in-depth investigation of N-metabolism pathways suggested higher temperatures of 25 ℃ and 35 ℃ reduced the abundance of key genes involved in ammonia oxidation (amoABC, &lt;i&gt;hao&lt;/i&gt;) and nitrite oxidation (&lt;i&gt;nar&lt;/i&gt;GH). Network analysis between N-metabolic functional genes and genera presented stronger relevance and richer sources between nitrifiers/denitrifiers and nitrification/denitrification-associated genes under cooler temperatures.

Differential responding patterns of the nirK-type and nirS-type denitrifying bacterial communities to an Ulva prolifera green tide in coastal Qingdao areas

Coastal eutrophication may be a vital inducement of green tide. Denitrification is an important nitrogen removal pathway that involves a series of enzymatic reactions. The rate-limiting step in the conversion of nitrite to nitric oxide is encoded by two functionally equivalent but structurally distinct genes, copper-containing nitrite reductase gene (nirK) and cytochrome cd1-containing nitrite reductase gene (nirS). Here, we used Illumina Miseq sequencing approach to examine the variations in denitrifying bacterial community characteristics and interactions during an Ulva prolifera green tide in coastal Qingdao areas. Our findings suggested that the variations in the denitrifying bacterial community structure during the green tide were closely related to the changes of chlorophyll a content, salinity and dissolved oxygen content. The nirK-type denitrifying bacteria were more sensitive to green tide than the nirS-type denitrifying bacteria. Additionally, the nirK-type denitrifying bacterial interactions were more stable and complex during the outbreak phase, while the nirS-type denitrifying bacterial interactions were more stable and complex during the decline phase. All of these characters demonstrated that the nirK-type and nirS-type denitrifying bacteria respond differently to the green tide, implying that they may occupy different niches during the green tide in coastal Qingdao areas.

Diversity, structure, and distribution of bacterioplankton and diazotroph communities in the Bay of Bengal during the winter monsoon.

The Bay of Bengal (BoB) is conventionally believed to be a low productive, oligotrophic marine ecosystem, where the diazotroph communities presumed to play a vital role in adding "new" nitrogen through the nitrogen fixation process. However, the diazotroph communities in the oceanic region of the BoB are still poorly understood though it represents most of the seawater volume. The present study investigated a detailed account of the bacterioplankton community structure and distribution in the oceanic BoB during the winter monsoon using high throughput sequencing targeting the 16S rRNA and nifH genes. Our study observed diverse groups of bacterioplankton communities in the BoB including both cyanobacterial and non-cyanobacterial phylotypes. Cyanobacteria (Prochlorococcus spp. and Synechococcus spp.) and Proteobacteria (mainly α-, γ-, and δ-Proteobacteria) were the most abundant groups within the bacterial communities, possessing differential vertical distribution patterns. Cyanobacteria were more abundant in the surface waters, whereas Proteobacteria dominated the deeper layers (75 m). However, within the diazotroph communities, Proteobacteria (mainly γ-Proteobacteria) were the most dominant groups than Cyanobacteria. Function prediction based on PICRUSt revealed that nitrogen fixation might more active to add fixed nitrogen in the surface waters, while nitrogen removal pathways (denitrification and anammox) might stronger in deeper layers. Canonical correspondence analysis (CCA) indicated that temperature, salinity, and silicate were major environmental factors driving the distribution of bacterial communities. Additionally, phosphate was also an important factor in regulating the diazotroph communities in the surface water. Overall, this study provided detailed information on bacterial communities and their vital role in the nitrogen cycles in oligotrophic ecosystems.

A three-year study on the treatment of domestic-industrial mixed wastewater using a full-scale hybrid constructed wetland.

Three full-scale constructed wetlands (CWs), namely vertical flow (VFCW), surface flow (SFCW), and horizontal flow (HFCW) systems, were combined in a series process to form a hybrid CW, which was used for the treatment performance of domestic-industrial mixed wastewater and investigated over a three-year period. The hybrid CW demonstrated that it is effective and stable during the long-term treatment of high-loading mixed wastewater under different operation years, season changes, and technology processes, with the average removal efficiencies of suspended solids, chemical oxygen demand, biological oxygen demand, total nitrogen, ammonia nitrogen, nitrate nitrogen, and total phosphorous being 84, 40, 54, 54, 70, 40, and 46%, respectively. The effluent quality of the hybrid CW reached the highest discharge standard for wastewater treatment plants. First, a variety of pollutants from the mixed wastewater were effectively removed in the subsurface processes (VFCW and HFCW) via substrate adsorption and degradation of the attached biofilm. The higher dissolved oxygen content and oxygen transfer capacity values in the VFCW were favourable for the occurrence of aerobic pathways (such as nitrification and inorganic phosphorus oxidation). In addition, with the large consumption of oxygen in the previous process, the oxygen-enriching capacity of the SFCW processes, provided aerobic potential for the next stage. In particular, the plant debris in the SFCW temporarily increased the organics and suspended solids, further increasing the C/N ratio, which was beneficial for denitrification as the main nitrogen removal pathway in the HFCW.

Effects of sulfamethoxazole on nitrogen transformation and antibiotic resistance genes in short-cut nitrification and denitrification process treating mariculture wastewater

The influential mechanism of sulfamethoxazole (SMX) on short-cut nitrification and denitrification (SCND) and antibiotic resistance genes (ARGs) was evaluated in a sequencing batch reactor (SBR). Excellent removal for NH4+-N and total inorganic nitrogen (TIN) was realized with above 95.7 and 93.0 % under 0.0–1.2 mg/L SMX, while 2.0 mg/L SMX induced the deterioration of their removal to 53.5 and 55.2 %, respectively. SMX altered the microbial composition by showing positive correlation to microbes, resulting in the dominant microorganisms changing from Denitromonas to Vibrio and occurrence of more antibiotic resistance bacteria (ARB). SMX dosage suppressed significantly ammonia oxidizing bacteria (AOB) Nitrosomonas, but enriched and diversified the denitrifying bacteria (DNB). 2.0 mg/L SMX led to the emergence of heterotrophic nitrification-aerobic denitrification (HNAD) as a nitrogen removal pathway and strengthened the sulfide-oxidizing autotrophic denitrification (SOAD) process by enrichment of SOAD bacteria (Candidatus_Thiobios, Sedimenticola). Metagenomic analysis revealed that 2.0 mg/L SMX decreased the NH4+-N removal by reducing nitrification related genes (amoABC, hao) at genetic level. Compared with 0.0 mg/L SMX, 2.0 mg/L SMX significantly inhibited the electron supply for heterotrophic denitrifying process by restraining the carbon source metabolism related genes (such as ACSS, sucC, mdh), but stimulated the electron generation for autotrophic denitrification by enhancing sulfide oxidation related genes aprA and aprB. Moreover, 2.0 mg/L SMX induced higher diversity and relative percentage of antibiotic resistance genes (ARGs) but barely affected the potential ability of dissemination of ARGs, revealing SCND was a promising system for controlling transmission of ARGs under SMX treating mariculture wastewater.

Extracellular polymeric substances trigger microbial immigration from partial denitrification (PD) to anammox biofilms in a long-term operated PD/anammox process in low-strength wastewater

The immigration of microbial communities in a synergistic partial denitrification/anammox (SPDA) system was investigated in a moving bed biofilm reactor (MBBR) inoculated with partial denitrification (PD) and anaerobic ammonium oxidation (anammox) biofilms. The SPDA system was operated at 25 ± 1 °C over 260 days. The total nitrogen (TN) of the effluent was only 3.71 ± 0.92 mg·L−1 in the stable phase with a TN removal efficiency of 95.23%. The anammox process was the dominant nitrogen removal pathway with an average contribution of 74.31% to TN removal. The results of the in situ activity and key enzymatic activity revealed that the nitrate-reducing bacteria tended to immigrate to anammox biofilms. Correspondingly, the abundance of the genus Thauera, the second most dominant bacteria in anammox biofilms, quickly increased from 0.78 to 10.69% on day 50 and eventually to 16.45% on day 221 according to the Illumina MiSeq sequencing data. The microbial immigration might be caused by different extracellular polymeric substance (EPS)-mediated mechanisms in PD and anammox biofilms. For fast-growing denitrifiers, PD biofilms tend to increase the ability of mass transfer by excreting more polysaccharides to form loosely-bound EPS at the expense of the ability to harbor the nitrate-reducing bacteria. However, for the slow-growing anaerobic ammonium oxidizing bacteria (AnAOB), the anammox biofilms tend to increase the retention of AnAOB by excreting more proteins to form enhanced tightly-bound EPS at the expense of the mass transfer ability, thereby causing the detached nitrate-reducing bacteria to immigrate into anammox biofilms.

Integrated treatment of suburb diffuse pollution using large-scale multistage constructed wetlands based on novel solid carbon: Nutrients removal and microbial interactions

In this study, an integrated treatment system was proposed and applied in situ, including detention tank, multistage constructed wetlands (CWs) and wastewater treatment plants (WWTPs), preventing nutrients flowing into Dianchi Lake, in which the treatment performance of multistage CWs were evaluated principally. Results skillfully realized the bypass purification of upstream river at dry reasons, as well as the effective management and treatment of the collected diffuse pollution at rainy reasons. The purified water flowing into water bodies could satisfy the Grade III of environmental quality standards for surface water in China with the average effluent concentrations of COD, NH4+-N, TN and TP decreased to 10 (51.2–72.7%), 0.5 (67.2–83.0%), 1.0 (71.2–79.6%) and 0.15 (72.3–89.4%) mg L−1, respectively. High-throughput sequencing results indicated that the application of poly-3-hydroxybutyrate-cohyroxyvelate-sawdust (PS) blends could enrich norank_f_Anaerolineaceae (7.95%) and Bradyrhizobium (10.2%), which were distinct from the dominant genera of Pleurocapsa (13.0%) in gravel-based CWs. Functional genes and metabolism analysis uncovered that the heterotrophic denitrification was the main pathway of nitrogen removal with the abundance of genes encoding TCA cycle, glycolysis and denitrification process up-regulated. In addition, molecular ecological network (MEN) analysis suggested the denitrification genes were positively correlated with the predominant microbes in PS-based CWs, favorable for denitrifiers to transfer and utilize electron donors during denitrification process. This study proved that the developed PS blends as carbon supplies in CWs and the proposed integrated treatment system are effective methods for watershed management, providing valuable reference to low-pollution wastewater treatment in practical engineering projects.