Start-up and bacterial communities of single-stage nitrogen removal using anammox and partial nitritation (SNAP) for treatment of high strength ammonia wastewater

Revealing the functional potential of microbial community of activated sludge for treating tuna processing wastewater through metagenomic analysis

Reports regarding the composition and functions of microorganisms in activated sludge from wastewater treatment plants for treating tuna processing wastewater remains scarce, with prevailing studies focusing on municipal and industrial wastewater. This study delves into the efficiency and biological dynamics of activated sludge from tuna processing wastewater, particularly under conditions of high lipid content, for pollutant removal. Through metagenomic analysis, we dissected the structure of microbial community, and its relevant biological functions as well as pathways of nitrogen and lipid metabolism in activated sludge. The findings revealed the presence of 19 phyla, 1,880 genera, and 7,974 species, with Proteobacteria emerging as the predominant phylum. The study assessed the relative abundance of the core microorganisms involved in nitrogen removal, including Thauera sp. MZ1T and Alicycliphilus denitrificans K601, among others. Moreover, the results also suggested that a diverse array of fatty acid-degrading microbes, such as Thauera aminoaromatica and Cupriavidus necator H16, could thrive under lipid-rich conditions. This research can provide some referable information for insights into optimizing the operations of wastewater treatment and identify some potential microbial agents for nitrogen and fatty acid degradation.

Influence of aeration modes and DO on simultaneous nitrification and denitrification in treatment of hypersaline high-strength nitrogen wastewater using sequencing batch biofilm reactor (SBBR)

Sequencing batch biofilm reactor (SBBR) has the potential to treat hypersaline high-strength nitrogen wastewater by simultaneous nitrification-denitrification (SND). Dissolved oxygen (DO) and aeration modes are major factors affecting pollutant removal. Low DO (0.35-3.5 mg/L) and alternative anoxic/aerobic (A/O) mode are commonly used for municipal wastewater treatment, however, the appropriate DO concentration and operation mode are still unknown under hypersaline environment because of the restricted oxygen transfer in denser extracellular polymeric substances (EPS) barrier and the decreased carbon source consumption during the anoxic phase. Herein, two SBBRs (R1, fully aerobic mode; R2, A/O mode) were used for the treatment of hypersaline high-strength nitrogen wastewater (200 mg/L NH4+-N, COD/N of 3 and 3% salinity). The results showed that the relatively low DO (2 mg/L) could not realize effective nitrification, while high DO (4.5 mg/L) evidently increased nitrification efficiency by enhancing oxygen transfer in denser biofilm that was stimulated by high salinity. A stable SND was reached 16 days faster with a ∼10% increase of TN removal under A/O mode. Mechanism analysis found that denser biofilm with coccus and bacillus were present in A/O mode instead of filamentous microorganisms, with the secretion of more EPS. Corynebacterium and Halomonas were the dominant genera in both SBBRs, and HN-AD process might assist partial nitrification-denitrification (PND) for highly efficient TN removal in biofilm systems. By using the appropriate operation mode and parameters, the average NH4+-N and TN removal efficiency could respectively reach 100% and 70.8% under the NLR of 0.2 kg N·m-3·d-1 (COD/N of 3), which was the highest among the published works using SND-based SBBRs in treatment of saline high-strength ammonia nitrogen (low COD/N) wastewater. This study provided new insights in biofilm under hypersaline stress and provided a solution for the treatment of hypersaline high-strength nitrogen (low COD/N) water.

Influence of C/N ratio and ammonia on nitrogen removal and N2O emissions from one-stage partial denitrification coupled with anammox

The development of low carbon treatment processes is an important issue worldwide. Partial denitrification coupled with anammox (PD/A) is a novel strategy to remove nitrogen and reduce N2O emissions. The influence of C/N ratio and NH4+ concentration on nitrogen removal and N2O emissions was investigated in batch reactors filled with PD/A coupled sludge. A C/N ratio of 2.1 was effective for nitrogen removal and N2O reduction; higher ammonia concentration might make anammox more active and indirectly reduce N2O emissions. Long-term operation further confirmed that a C/N ratio of 2.1 resulted in a minimum effluent N2O concentration (mean value of 0.94 μmol L-1); as the influent NH4+ concentration decreased to 50 mg L-1 (NH4+-N/NO3--N: 1), the nitrogen removal rate increased to 82.41%. Microbial analysis showed that anammox bacteria (Candidatus Jettenia and Ca. Brocadia) were enriched in the PD/A system and Ca. Brocadia gradually dominated the anammox community, with the relative abundance increasing from 1.69% to 18.44% between days 97 and 141. Finally, functional gene analysis indicated that the abundance of nirS/K and hao involved in partial denitrification and anammox, respectively, increased during long-term operation of the reactor; this change benefitted nitrogen metabolism in anammox, which could indirectly reduce N2O emissions.

Bacterial Communication Coordinated Behaviors of Whole Communities to Cope with Environmental Changes

Bacterial communication plays an important role in coordinating microbial behaviors in a community. However, how bacterial communication organizes the entire community for anaerobes to cope with varied anaerobic-aerobic conditions remains unclear. We constructed a local bacterial communication gene (BCG) database comprising 19 BCG subtypes and 20279 protein sequences. BCGs in anammox-partial nitrification consortia coping with intermittent aerobic and anaerobic conditions as well as gene expressions of 19 species were inspected. We found that when suffering oxygen changes, intra- and interspecific communication by a diffusible signal factor (DSF) and bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) changed first, which in turn induced changes of autoinducer-2 (AI-2)-based interspecific and acyl homoserine lactone (AHLs)-based intraspecific communication. DSF and c-di-GMP-based communication regulated 455 genes, which covered 13.64% of the genomes and were mainly involved in antioxidation and metabolite residue degradation. For anammox bacteria, oxygen influenced DSF and c-di-GMP-based communication through RpfR to upregulate antioxidant proteins, oxidative damage-repairing proteins, peptidases, and carbohydrate-active enzymes, which benefited their adaptation to oxygen changes. Meanwhile, other bacteria also enhanced DSF and c-di-GMP-based communication by synthesizing DSF, which helped anammox bacteria survive at aerobic conditions. This study evidences the role of bacterial communication as an "organizer" within consortia to cope with environmental changes and sheds light on understanding bacterial behaviors from the perspective of sociomicrobiology.

Start-up and optimization of a one-stage partial nitrification-anammox (PN-A) process treating low ammonium concentration wastewater: experimental results and modeling investigation

Although the partial nitrification-anammox process (PN-A) has achieved great success in nitrogen removal for the high ammonium concentration wastewater, its application is still limited in low ammonium concentration wastewater treatment due to its instability and low nitrogen removal efficiency. In this study, a sequencing batch reactor (SBR) with continuous aeration was employed to enrich ammonia oxidation bacteria (AOB) and suppress nitrite oxidation bacteria (NOB) first; then, the SBR was operated intermittently aerated SBR (IASBR), to which the anammox granular sludge (AMX) was added to achieve complete autotrophic nitrogen removal under low influent ammonium concentration of 100 mg/L. A mathematical model was used to optimize the IASBR aeration strategy to achieve sub-optimal nitrogen removal. The experimental results showed that high nitrite accumulation efficiency (above 80%) in the SBR and a fast start-up within 100 days and a stable TN (total nitrogen) removal efficiency of 70% were achieved in the IASBR. Meanwhile, the simulation results indicated that keeping aeration duration at 4 h, k_La (oxygen transfer coefficient) at 50 day^-1, or aeration duration at 2.5 h, k_La at 80 day^-1 could obtain a higher total nitrogen removal efficiency (TNR) (TNR > 80%), and the TN removal could also be improved by increasing hydraulic retention time (HRT) under the optimal oxygen supply rate.

Microbial dynamics reveal the adaptation strategies of ecological niche in distinct anammox consortia under mainstream conditions

The feasibility of anammox-based processes for nitrogen-contained wastewater treatment has been verified with different anammox bacteria, however, the ecological niche of anammox bacteria under mainstream conditions is still elusive. In this study, six sludge samples collected from different habitats were utilized to culture anammox bacteria under mainstream conditions, and two distinct anammox genera (Ca. Kuenenia and Ca. Brocadia) with a relative abundance of 6.31% (C1) and 3.09% (C3), respectively, were identified. Notably, the microbial dynamics revealed that anammox bacteria (AMX), ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), Chloroflexi bacteria (CFX), and heterotrophic denitrification bacteria (HDB) were the core members in anammox consortia. However, Ca. Kuenenia and Ca. Brocadia occupied different ecological niches in anammox consortia. The dissolved oxygen and microbial structures of the anammox-continuous stirred tank reactor systems were the main factors to affect their niche differentiation. Meanwhile, comammox might exist in the systems and occupy the ecological niche of AOB in nitrogen cycling. The network analysis suggested that Ignavibacterium could be the associated bacteria in Ca. Kuenenia-dominated consortia, while Ca. Nitrotoga was that in the Ca. Brocadia-dominated consortia. Our findings reveal a valuable reference for the observation of distinct anammox genera under mainstream conditions, which provides theoretical guidance for the engineering application of mainstream anammox-based processes.

Biochar enhances partial denitrification/anammox by sustaining high rates of nitrate to nitrite reduction

To examine the short-term effects of biochar on the partial-denitrification anammox (PD/A) process, the adsorption kinetics, nitrogen degradation, electron transfer properties, and microbial community succession of wastewater treatment systems with and without biochar added were monitored and characterized. The results showed that biochar increased nitrate reduction rates, which enhanced total nitrogen (TN) removal of the system by about 10%. The findings attributed improved TN removal to biochar's influence in accelerating electron transfer rather than its adsorption properties. Analysis of the nitrogen transfer pathway showed that when sufficient substrate was available, the anammox and denitrification reactions simultaneously removed nitrogen. When the nitrite supply was insufficient, the anammox reaction outcompeted the denitrification reaction for regenerated nitrite. Integrated microbial community and functional protein analyses indicated that biochar addition increased the abundance of Ca. Kuenenia and Pseudomonas. Meanwhile, biochar modulates denitrifying cellular metabolism by inducing protein changes.

Effect of inorganic carbon limitation on the nitrogen removal performance of the single-stage reactor containing anammox and nitritation gel carriers

Herein, the effect of inorganic carbon (IC) limitation on the nitrogen removal performance of the single-stage reactor containing nitritation and anammox gel carriers was investigated. As a result of a continuous feeding test, the effluent ammonium concentration increased as the IC concentration decreased, indicating the deterioration of nitritation activity, not anammox. Furthermore, the sensitivity of IC to anammox and nitritation activity was investigated in anammox and nitritation reactors, respectively. Consequently, the relationship between the effluent IC concentration and nitritation rate was well described using the Michaelis-Menten equation. The apparent K_m value of nitritation was calculated as 4.4 mg-C L^-1. In anammox reactor, it was calculated as 1.7 mg-C L^-1. These results revealed that the affinity of nitritation gel carriers to IC was lower than that of anammox, supporting that nitritation activity was easily deactivated by decrease in the IC concentration rather than anammox. Microbial community analysis revealed that Nitrosomonas europaea and Candidatus Jettenia asiatica were the dominant species of ammonium-oxidizing and anammox bacteria.

Coupled biodegradation of p-nitrophenol and p-aminophenol in bioelectrochemical system: Mechanism and microbial functional diversity

Biodegradation mechanisms and microbial functional diversity during coupled p-nitrophenol (PNP) and p-aminophenol (PAP) degradation were studied in a bioelectrochemical system. PNP in the biocathode and PAP in the bioanode were almost completely removed within 28hr and 68hr respectively. The degradation followed the steps including hydrating hydroxyalkylation, dehydrogenating carbonylation, and hydrolating ring cleavage, etc. Metagemomic analysis based on the KEGG and eggNOG database annotations revealed the microbial composition and functional genes/enzymes related to phenol degradation in the system. The predominant bacteria genera were Lautropia, Pandoraea, Thiobacillus, Ignavibacterium, Truepera and Hyphomicrobium. The recognized biodegradation genes/enzymes related to pollutant degradation were as follows: pmo, hbd, & ppo for phenol degradation, nzba, amie, & badh for aromatic degradation, and CYP & p450 for xenobiotics degradation, etc. The co-occurrence of ARGs (antibiotic resistant genes), such as adeF, MexJ, ErmF, PDC-93 and Escherichia_coli_mdfA, etc., were annotated in CARD database during the biodegradation process. The Proteobacteria & Actinobacteria phylum was the primary host of both the biodegradation genes & ARGs in this system. The microbial functional diversity ensured the effective biodegradation of the phenol pollutants in the bioelectrochemical system.

Simultaneous nitrogen and phosphorus removal from simulated digested piggery wastewater in a single-stage biofilm process coupling anammox and intracellular carbon metabolism

A Single-stage biofilm process coupling Anammox and Intracellular Carbon metabolism (SAIC) was constructed for treating simulated digested piggery wastewater with low carbon/nitrogen ratio (C/N) in this study. TN removal in SAIC system increased by more than 12.77% compared to the reference, and the maximum total phosphorus (TP) removal efficiency reached to 83.70% (C/N = 1.5). Denitrification driven by intracellular carbon, mainly poly-β-hydroxybutyrate (PHB, 78.57%), contributed 32.60% of TN elimination at most, and at least 67.40% should be attributed to anammox. Phosphorus was thought to be mainly removed through biological route, while chemical precipitation also explained around 10% of removed TP. Furthermore, commensalism of glycogen accumulating organisms (GAOs), phosphate accumulating organisms (PAOs), nitrifiers and anammox bacteria was revealed by combining 16S rRNA amplicon sequencing and metagenomics. As a result, multiple metabolic pathways including anammox, (partial) nitrification, endogenous (partial) denitrification and biological P-removal played synergistic effect in SAIC system.

Electrode-dependent ammonium oxidation with different low C/N ratios in single-chambered microbial electrolysis cells

Alternative method should be found to solve the ammonia accumulation in anaerobic digestion. Herein, electrode-dependent ammonium oxidation was successfully achieved in anaerobic single-chambered microbial electrolysis cells (MECs)under different low C/N ratios (0, 1, and 1.5), with an applied voltage of 0.6 V as well as an initial NH₄⁺-N and NO₃^--N concentration of 500 and 300 mg/L. The nitrogen removal performance of MECs and the controls indicated that applying a voltage stimulated nitrogen removal under low C/N ratios of 0, 1, and 1.5. However, the remaining organic carbon in MEC with a relatively higher C/N ratio of 3 inhibited the ammonium oxidation. Current changes and cyclic voltammetry demonstrated that the bioanode with several bioelectrochemical activities could promote ammonium oxidation. The dominant genera Truepera, Aquamicrobium, Nitrosomonas, Arenimonas, Comamonas, and Cryobacterium enriched on both electrodes could be the key functional taxa in MECs with C/N ratios of 0, 1, and 1.5. The remaining sodium acetate in MEC with C/N ratio of 3 inhibits microbial community structure and relative abundance, which may adversely affected nitrogen removal. Further caculation showed that nitrogen balance was essentially achieved, while electron balance was disrupted since electrons may be consumed through NO₃^--N recycle and cell synthesis, and finally caused low coulombic efficiency.

One-step start-up and subsequent operation of CANON process in a fixed-bed reactor by inoculating mixture of partial nitrification and Anammox sludge

The feasibility of one-step start-up of CANON process in a FBR by inoculating mixture of partial nitrification and Anammox sludge as well as its subsequent operation performances were investigated in the present study. The FBR was operated for around 3 months. The CANON process was quickly started up within 21 days. The max total nitrogen (TN) removal rate reached 183.61 g m^-3 d^-1 with the TN removal efficiency of 91.81% on day 95. The CANON process exhibited a good capability for resistance to loading shock and restoration from the unstable state. The mature CANON biofilms displayed a morphology of aggregates and had porous and microporous structure. The structural characteristics of the biofilms were conducive to improve the transferring of substrates and products. AOB and Anammox bacteria absolutely predominated in the mature biofilms and furthermore established a balanced interaction relationship. The microbial community structure contributed to the relatively stable operation performances.

Production of bioelectricity may play an important role for the survival of Xanthomonas campestris pv. campestris (Xcc) under anaerobic conditions

The plant pathogen Xanthomonas is commonly found in biocontaminated bioreactors; however, few studies have evaluated the growth and impacts of this microorganism on bioreactors. In this study, we examined the characteristics of Xanthomonas campestris pv. campestris (Xcc). Our results showed that Xcc could reduce metal Fe (III) and decolorise methyl orange in vitro. Moreover, I-t and cyclic voltammetry curves showed that Xcc could generate bioelectricity and had two extracellular electron transfer pathways, similar to that of Shewanella. Based on the spectral analysis of intact cells and scanning electron microscopy analysis, one pathway was speculated to involve cytochrome C by direct contact with the pili or cell surface. The other pathway may involve indirect mediators, such as redox substrates, among extracellular polymeric substances. For the direct extracellular electron transfer process, the charge transfer coefficient α, electron number n, and the electron transfer rate constant k_s were determined to be 0.49, 2.6, and 2.2 × 10^-3 s^-1, respectively. In the indirect extracellular electron transfer processes, the values of α, n, and k_s were 0.52, 4, and 1.21 s^-1, respectively. Of these two transfer methods, indirect electron transfer is dominant and faster than direct electron transfer. Moreover, after mutation of the dsbD gene, which is important for indirect electron transfer, the electrochemical parameters α, n, and k_s decreased. Our findings reveal a new anaerobic mechanism mediating the survival of Xcc during wastewater treatment, and may help develop new strategies for preventing Xcc growth during wastewater treatment.

Microbial diversity reveals the partial denitrification-anammox process serves as a new pathway in the first mainstream anammox plant

A full-scale sewage treatment plant in Xi'an city is discovered as the first mainstream anaerobic ammonia oxidation (anammox) treatment process in China. Whether its biological mechanism is the nitritation-anammox or partial denitrification (PD)-anammox brought violent controversy between two groups. As a third party, here we uncovered the mystery of the moving-bed biofilm reactor (MBBR) as a PD-anammox process by analyzing the diversity and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) of microbes in anoxic pond. Anammox bacteria was found in the MBBR anoxic tank, which abundance is 8.9 times of that in the common anaerobic-anoxic-oxic process, confirming the existence of anammox process. The denitrifying bacteria (DNB) content in the anoxic tank is 5.9 times of the content of ammonia oxidizing bacteria (AOB), thus the DNB-anammox system is proved at the microbial composition level. The PICRUSt analysis found that ammonium nitrogen is mainly derived from the deamination of urea. The functional genes NAR and AMO of DNB and AOB are 910.84 and 5.80 rpms, respectively. The NAR gene content is 157.0 times of the AMO gene content and it is proved at the genetic level that the nitrite in the anoxic pool is mainly derived from denitrification. This study demonstrated the feasibility and advantages of the PD-anammox in the anammox process, which is different from the traditional nitritation-anammox demonstrated in Strass Wastewater Treatment Plant, Austria and Changi Water Reclamation Plant, Singapore and provided an alternative option for the mainstream application of anammox.

Development of Strategies for AOB and NOB Competition Supported by Mathematical Modeling in Terms of Successful Deammonification Implementation for Energy-Efficient WWTPs

Novel technologies such as partial nitritation (PN) and partial denitritation (PDN) could be combined with the anammox-based process in order to alleviate energy input. The former combination, also noted as deammonification, has been intensively studied in a frame of lab and full-scale wastewater treatment in order to optimize operational costs and process efficiency. For the deammonification process, key functional microbes include ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidation bacteria (AnAOB), which coexisting and interact with heterotrophs and nitrite oxidizing bacteria (NOB). The aim of the presented review was to summarize current knowledge about deammonification process principles, related to microbial interactions responsible for the process maintenance under varying operational conditions. Particular attention was paid to the factors influencing the targeted selection of AOB/AnAOB over the NOB and application of the mathematical modeling as a powerful tool enabling accelerated process optimization and characterization. Another reviewed aspect was the potential energetic and resources savings connected with deammonification application in relation to the technologies based on the conventional nitrification/denitrification processes.

Selective stress of antibiotics on microbial denitrification: Inhibitory effects, dynamics of microbial community structure and function

Antibiotics commonly exist in municipal, livestock and industrial wastewaters. However, the response of key microbiota performance in wastewater treatment plants to antibiotic exposure lacks systematic research. In this study, the short-term acute stress of four commonly used antibiotics (sulfamethoxazole, chlortetracycline, ciprofloxacin, and amoxicillin) on microbial denitrification performance was systematically investigated. All tested antibiotics exhibited the inhibitory effects in varying degrees by repeated addition for six cycles. The nitrate removal efficiencies (NrE) decreased to 7.98-26.80%, accompanied by the significant decrease of the expressed narG gene, by exposure to sulfamethoxazole, chlortetracycline or amoxicillin. Nitrite reduction was inhibited more severely than nitrate reduction, which was further verified by the low- or non-expressed nirS and nosZ genes. Furthermore, a higher antibiotic concentration made stronger inhibitory effect. Except for chlortetracycline, 2.09-6.80 times decrease of k value was commonly observed as concentration increased from 10 to 50 or 100 mg L^-1. Even in a short period (24 h), antibiotics largely decreased the abundance of the dominant denitrifying bacterial genera (Thauera, Comamonas, etc.), while, some unclassified populations (Labrenzia, Longilinea, etc.) were enriched. This study provides theoretical researches on the microbial denitrification behaviors influenced by exposure to different antibiotics.

Ammonia oxidation and denitrification in a bio-anode single-chambered microbial electrolysis cell

In this study, anodic ammonia oxidation and denitrification were performed in single-chamber bioelectrochemical systems at a wide range of anodic potentials (-400 to +400 mV) versus Ag/AgCl. The low coulombic efficiencies (~30.84%) in reactors were mainly due to electrons being transferred to atmospheric oxygen through the electrode and reversal of the electrode. The removal efficiencies of acetate, ammonia, and total nitrogen were 100%, 100%, and 40.44% at +200 mV and 100%, 100%, and 50.24% at -200 mV, respectively. The nitrogen-removal mechanisms were nitrogen respiration/nitrate reduction at +200 mV and denitrification at -200 mV, and ammonia oxidation occurred by coupling with sulfate-reducing at -300 and -400 mV. Thauera, Comamonas, Alicycliphilus, Nitrosomonas, Desulforhabdus, Dethiosulfatibacter, and Desulfomicrobium were the dominant genera at the anode which participated in the nitrification/denitrification or sulfate-reducing processes. In summary, ammonia oxidation and denitrification could be coupled with carbon-removal or sulfur-reduction using a bio-anode with a suitable anodic potential.

Efficient transition from partial nitritation to partial nitritation/Anammox in a membrane bioreactor with activated sludge as the sole seed source

A lab-scale membrane bioreactor (MBR) was employed to carry out the partial nitritation/Anammox (PN/A) process from conventional activated sludge. Seed sludge was cultivated under microaerobic conditions for 10 days before seeding into the MBR. The bacterial community was analyzed on the basis of cloning and sequencing of 16S rRNA gene. Relative slow ammonia oxidation rates (3.2-13.0 mgN/L/d) were established in the microaerobic cultivation period. In the continuous MBR operation, the nitritation was achieved in the first 16 days and the reactor produced a balanced ratio between ammonia and nitrite which favored the proliferation of Anammox bacteria. Efficient transition from PN to PN/A was achieved in two months which was supported by appearance of reddish spots on the reactor inner wall and the concurrent consumption of ammonium and nitrite. The PN/A performed a robust and high-rate nitrogen removal capability and achieved a peak nitrogen removal of 1.81 kg N/m³/d. 16S rRNA gene-based analysis indicated that "Nitrosomonas sp." and "Candidatus Jettenia sp." accounted for ammonia oxidation and nitrogen depletion, respectively. Denitratisoma facilitated denitrification in the reactor. The present study suggested that a pre-cultivation of seed sludge under microaerobic conditions assists fast realization of PN and further convoyed efficient transition from PN to PN/A. Knowledge gleaned from this study is of significance to initiation, operation, and control of MBR-PN/As.

The Co-occurrence of DNRA and Anammox during the anaerobic degradation of benzene under denitrification

It was revealed that Anammox process promotes the anaerobic degradation of benzene under denitrification. This study investigates the effect of dissimilatory nitrate reduction to ammonium (DNRA) and exogenous ammonium on anaerobic ammonium oxidation bacteria (AnAOB) during the anaerobic degradation of benzene under denitrification. The results indicate that anammox occurs synergistically with organisms using the DNRA pathway, such as Draconibacterium and Ignavibacterium. Phylogenetic analysis showed 64% (16/25) and 36% (5/25) hzsB gene sequences, a specific biomarker of AnAOB, belonged to Candidatus 'Brocadia fuldiga' and Candidatus 'Kuenenia', respectively. Exogenous ammonium addition enhanced the anammox process and accelerated benzene degradation at a 1.89-fold higher average rate compared to that in the absence of exogenous ammonium and AnAOB belonged to Ca. 'Kuenenia' (84%) and Ca. 'Brocadia fuldiga' (16%). These results indicate that Ca. 'Brocadia fuldiga' could also play a role in DNRA. However, the diversity of abcA and bamA, the key anaerobic benzene metabolism biomarkers, remained unchanged. These findings suggest that anammox occurrence may be coupled with DNRA or exogenous ammonium and that anammox promotes anaerobic benzene degradation under denitrifying conditions. The results of this study contribute to understanding the co-occurrence of DNRA and Anammox and help explore their involvement in degradation of benzene, which will be crucial for directing remediation strategies of benzene-contaminated anoxic environment.

An improved start-up strategy for mainstream anammox process through inoculating ordinary nitrification sludge and a small amount of anammox sludge

The difficulties in enriching anammox bacteria and maintaining stable partial nitrification during start-up phase limit the application of mainstream anammox process. In this study, the feasibility of starting up simultaneous partial nitrification, anammox and denitrification (SNAD) reactor treating municipal wastewater by inoculating ordinary nitrification sludge (96.2%) and a small amount of anammox sludge (3.8%) was investigated. A sequencing batch reactor with intermittent aeration was used for the SNAD process. The SNAD reactor was started up in 75 days with a nitrogen removal efficiency of 85.4% at ambient temperature. The nitrogen removal performance maintained stable despite the fluctuating inflow. Anammox bacterial activity exponentially increased although nitrite oxidizing bacteria (NOB) activity in seeding sludge was high. The enhanced ammonium oxidizing bacterial activity and partial denitrification provided sufficient nitrite for anammox bacteria. Moreover, NOB was inhibited by intermittent aeration, anammox bacteria had competitive advantage on nitrite. The improved particle size and settleability of activated sludge also favored the anammox bacterial enrichment. This study provided an improved and easily-implemented start-up strategy for mainstream anammox. The seeding sludge was easily obtained and the operation strategy was simple. These findings were meaningful to the engineering application of mainstream anammox.

Treatment of anaerobically digested effluent from kitchen waste using combined processes of anaerobic digestion-complete nitritation-ANAMMOX based on reflux dilution

In this study, an anaerobically digested effluent from kitchen waste with high concentrations of chemical oxygen demand (COD) and ammonia nitrogen was treated using combined processes of anaerobic digestion (AD), complete nitritation (CN), and anaerobic ammonium oxidation (ANAMMOX). The COD and nitrogen removal efficiency of each treatment unit were investigated. The feasibility of using the final treatment effluent to dilute the original wastewater was also discussed. Findings showed that as a pretreatment step, AD resulted in the decline in biodegradability and increase in NH 4 + - N concentration. CN was successfully and stably achieved for 106 days with an average nitritation rate of 95% by maintaining the dissolved oxygen at 2-3 mg/L and hydraulic retention time of 24 hr under 30 ± 1°C. High NH 4 + - N and NO 2 - - N . removal efficiencies of over 88% and 96% were attained in the following ANAMMOX reactor. The reflux of ANAMMOX-treated effluent for the dilution of raw wastewater or an influent of CN and ANAMMOX ensured the stable operation of the combined system. PRACTITIONER POINTS: Anaerobic digestion effluent of kitchen waste had low COD/ NH 4 + - N ratio and poor biodegradability. Stable and efficient nitritation was realized by controlling DO, HRT and TEMP. High NH 4 + - N and NO 2 - -N removal efficiency were obtained by ANAMMOX process. Average nitrogen removal rate of 0.94 kg N/m³ /day were obtained by ANAMMOX. Reflux dilution with the effluent guaranteed the system's successful operation.

Performance and microbial community of the CANON process in a sequencing batch membrane bioreactor with elevated COD/N ratios

In this study, the effects of elevated chemical oxygen demand/nitrogen (COD/N) ratios on nitrogen removal, production and composition of the extracellular polymer substances (EPS) and microbial community of a completely autotrophic nitrogen removal via nitrite (CANON) process were studied in a sequencing batch membrane bioreactor (SBMBR). The whole experiment was divided into two stages: the CANON stage (without organic matter in influent) and the simultaneous partial nitrification, anaerobic ammonia oxidation and denitrification (SNAD) stage (with organic matter in influent). When the inflow ammonia nitrogen was 420 mg/L and the COD/N ratio was no higher than 0.8, the addition of COD was helpful to the CANON process; the total nitrogen removal efficiency (TNE) was improved from approximately 65% to more than 75%, and the nitrogen removal rate (NRR) was improved from approximately 0.255 kgN/(m³·d) to approximately 0.278 kgN/(m³•d), while the TNE decreased to 60%, and the NRR decreased to 0.236 kgN/(m³•d) when the COD/N ratio was elevated to 1.0. For the EPS, the amounts of soluble EPS (SEPS) and loosely bound EPS (LB-EPS) were both higher in the CANON stage than in the SNAD stage, while the amount of tightly bound EPS (TB-EPS) in the SNAD stage was significantly higher due to the proliferation of heterotrophic bacteria. The metagenome sequencing technique was used to analyse the microbial community in the SBMBR. The results showed that the addition of COD altered the structure of the bacterial community in the SBMBR. The amounts of Candidatus 'Anammoxoglobus' of anaerobic ammonia oxidation bacteria (AAOB) and Nitrosomonas of ammonia oxidizing bacteria (AOB) both decreased significantly, and Nitrospira of nitrite oxidizing bacteria (NOB) was always in the reactor, although the amount changed slightly. A proliferation of denitrifiers related to the genera of Thauera, Dokdonella and Azospira was found in the SBMBR.

Nitrogen removal from food waste digestate using partial nitritation-anammox process: Effect of different aeration strategies on performance and microbial community dynamics

The feasibility of employing anammox and partial nitritation-anammox (PN/A) processes for nitrogen removal from food waste (FW) digestate was investigated in this study. The effects of different aeration strategies on the microbial community were also investigated. To achieve this, after anammox enrichment (Phase 1), the reactor was fed with digestate supplemented with nitrite (Phase 2), and subsequently different aeration strategies were evaluated to establish PN/A. Aeration strategies with high anoxic periods (30 and 45 min) in relation to aerobic periods (15 min) coupled with low air flow rates (0.026 L  min^-1. L_reator^-1) were found to be better for establishing PN/A, as coefficients of produced nitrate/removed ammonium were closer to those reported previously (0.17 and 0.21). Aeration conditions considerably altered the microbial community. Candidatus Brocadia was replaced by Candidatus Jettenia, after the first aeration strategies. These results support the feasibility of FW digestate treatment using anammox and PN/A processes and provide a better understanding of the effect of aeration on microbial dynamics in PN/A reactors.

Simultaneous partial nitrification, anammox and denitrification (SNAD) process for nitrogen and refractory organic compounds removal from mature landfill leachate: Performance and metagenome-based microbial ecology

In this study, a simultaneous partial nitrification, Anammox and denitrification (SNAD) bioreactor was constructed for mature landfill leachate treatment, which exhibited favorable NH₄⁺-N (98.9-99.9%), TN (90.7-94.9%) and bio-refractory organic compounds (46.2-67.7%) removal efficiencies. Stoichiometric analysis demonstrated that the synergy of ammonium-oxidizing bacteria and Anammox bacteria dominated TN removal (96.1-97.2%). NO₃^--N produced in Anammox could be further reduced through (partial) denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The results highlighted that humic-like and their intermediates might serve as the electron donor for these (partial) denitrifiers and DNRA bacteria to remove NO₃^--N, and could be effectively removed from mature landfill leachate in SNAD bioreactor. Metagenomic characterization further demonstrated that phyla Chloroflexi, Chlorobi and genera Nitrosomonas, Ignavibacterium and Aminiphilus might be responsible for such humic-like degradation. Overall, this work offers new insights into the metagenome-based bioinformatic roles for the previously understudied microorganisms in SNAD bioreactor for mature landfill leachate treatment.

High-rate partial-nitritation and efficient nitrifying bacteria enrichment/out-selection via pH-DO controls: Efficiency, kinetics, and microbial community dynamics

Conventional nitrification/denitrification process is gradually being replaced with partial-nitritation/anammox (PN/A) processes due to its installation and running cost. However, high ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing (anammox) bacteria activity as well as optimum out-selection of nitrite-oxidizing bacteria (NOB) are necessary to achieving efficient PN/A process. Consequently, to enhance PN process via nitrifying bacteria enrichment/out-selection within psychrophilic environment, a novel pH-DO (dissolved oxygen) control strategy was proposed and the response of PN, kinetics, AOB enrichment, and NOB out-selection efficiency was investigated during start-up and long-term operation. With DO of 0.7 mg/L and pH of 7.5-7.9, quick start-up of the PN process was established within 34d as NO₂^--N accumulation ratio (NAR) reached 90.08 ± 1.4%. Again, when NLR was elevated to 0.8 kg/m³·d (400mgNH₄⁺-N/L), DO curtailed to 0.2 mg/L, pH maintained at 7.7 and free ammonium at 6.5 mg/L, NAR and NH₄⁺-N removal rate could still reach 97.04 ± 2.4% and 97.84 ± 1.5%, respectively. After optimum control factors had been established, real nitrogen-rich-mine-wastewater was fed (DO, 0.2 mg/L, pH, 8.9, and free ammonia, 6.5 mg/L) and NAR and NH₄⁺-N removal rate reached was 97.33 ± 0.5% and 97.76 ± 1.1%, respectively. Estimated kinetic parameters including maximum degradation rate (Vmax = 1.58/d), half-rate constant (Km = 33.8 mg/L), and inhibition constant (Ki = 201.6 mg/L) suggested that inhibition on NH₄⁺-N oxidation was most feasible at higher concentration of NH₄⁺-N. To elucidate biological mechanisms, 16S rRNA high-throughput revealed that AOB (Nitrosomonas) enrichment had increased from 0.08% to 49% whereas NOB (Nitrospira) abundance reduced from 1% to 0.034%, indicating pH-DO control efficiently enriched AOB and out-selected NOB. Conversely, when influent NH₄⁺-N was curtailed to about 200 mg/L and free ammonia concentration maintained at 6.5 mg/L, the population of AOB was observably reduced by 6% within a period of 14 days, indicating control strategies including pH-DO control and substrate availability were the key factors which substantially influenced and promoted the activities and growth of AOBs in the present SBR.

Modeling the performance of Single-stage Nitrogen removal using Anammox and Partial nitritation (SNAP) process with backpropagation neural network and response surface methodology

Two novel feedforward backpropagation Artificial Neural Networks (ANN)-based-models (8:N_H:1 and 7:N_H:1) combined with Box-Behnken design of experiments methodology was proposed and developed to model NH₄⁺ and Total Nitrogen (TN) removal within an upflow-sludge-bed (USB) reactor treating nitrogen-rich wastewater via Single-stage Nitrogen removal using Anammox and Partial nitritation (SNAP) process. ANN were developed by optimizing network architecture parameters via response surface methodology. Based on the goodness-of-fit standards, the proposed three-layered NH₄⁺ and TN removal ANN-based-models trained with Levenberg-Marquardt-algorithm demonstrated high-performance as computations exhibited smaller deviations-(±2.1%) as well as satisfactory coefficient of determination (R²), fractional variance-(FV), and index of agreement-(IA) ranging 0.989-0.997, 0.003-0.031 and 0.993-0.998, respectively. The computational results affirmed that the ANN architecture which was optimized with response surface methodology enhanced the efficiency of the ANN-based-models. Furthermore, the overall performance of the developed ANN-based models revealed that modeling intricate biological systems (such as SNAP) using ANN-based models with the view to improve removal efficiencies, establish process control strategies and optimize performance is highly feasible. Microbial community analysis conducted with 16S rRNA high-throughput approach revealed that Candidatus Kuenenia was the most pronounced genera which accounted for 13.11% followed by Nitrosomonas-(6.23%) and Proteocatella-(3.1%), an indication that nitrogen removal pathway within the USB was mainly via partial-nitritation/anammox process.

Identification and nitrogen removal characteristics of Thauera sp. FDN-01 and application in sequencing batch biofilm reactor

A strain FDN-01 was isolated from the sequencing batch biofilm reactor (SBBR) which was seeded with wasted activated sludge from a municipal wastewater treatment plant in Shanghai. Bacterium FDN-01 was identified as Thauera sp., and Genbank Sequence_ID was KY393097. By comparing inorganic total nitrogen (TN) removal efficiency by strain FDN-01 under different conditions, the optimal initial pH, carbon source and the ratio of carbon to nitrogen were 7.5, sodium succinate and 4.0, respectively. Inorganic TN removal efficiency was 93% within 3 d while the concentration of nitrate was 100 mg/L, and the type of substrates affected extracellular polymeric substances (EPS) production and the ratio of protein to polysaccharide in the EPS. Further investigation for the application of strain FDN-01 in the SBBRs showed that anoxic ammonia oxidation occurred at room temperature, and the removal efficiencies of inorganic TN were noticeably enhanced by the augmentation of bacterium FDN-01 back into the SBBR. This study provided a promising method of TN removal requiring less carbon source in the wastewater.

Sustainable Approach to Eradicate the Inhibitory Effect of Free-Cyanide on Simultaneous Nitrification and Aerobic Denitrification during Wastewater Treatment

Simultaneous nitrification and aerobic denitrification (SNaD) is a preferred method for single stage total nitrogen (TN) removal, which was recently proposed to improve wastewater treatment plant design. However, SNaD processes are prone to inhibition by toxicant loading with free cyanide (FCN) possessing the highest inhibitory effect on such processes, rendering these processes ineffective. Despite the best efforts of regulators to limit toxicant disposal into municipal wastewater sewage systems (MWSSs), FCN still enters MWSSs through various pathways; hence, it has been suggested that FCN resistant or tolerant microorganisms be utilized for processes such as SNaD. To mitigate toxicant loading, organisms in SNaD have been observed to adopt a diauxic growth strategy to sequentially degrade FCN during primary growth and subsequently degrade TN during the secondary growth phase. However, FCN degrading microorganisms are not widely used for SNaD in MWSSs due to inadequate application of suitable microorganisms (Chromobacterium violaceum, Pseudomonas aeruginosa, Thiobacillus denitrificans, Rhodospirillum palustris, Klebsiella pneumoniae, and Alcaligenes faecalis) commonly used in single-stage SNaD. This review expatiates the biological remedial strategy to limit the inhibition of SNaD by FCN through the use of FCN degrading or resistant microorganisms. The use of FCN degrading or resistant microorganisms for SNaD is a cost-effective method compared to the use of other methods of FCN removal prior to TN removal, as they involve multi-stage systems (as currently observed in MWSSs). The use of FCN degrading microorganisms, particularly when used as a consortium, presents a promising and sustainable resolution to mitigate inhibitory effects of FCN in SNaD.

Improving Wastewater Nitrogen Removal and Reducing Effluent NOx - -N by an Oxygen-Limited Process Consisting of a Sequencing Batch Reactor and a Sequencing Batch Biofilm Reactor

A series of reactors including a sequencing batch reactor (SBR) and a sequencing batch biofilm reactor (SBBR) were used for nitrogen removal. The aim of this study was simultaneous removal of NH4+-N and NOx–-N from synthetic wastewater. In the novel proposed method, the effluent from SBR was sequentially introduced into SBBR, which contained 0.030 m3 biofilm carriers, so the system operated under a paired sequence of aerobic-anoxic conditions. The effects of different carbon sources and aeration conditions were investigated. A low dissolved oxygen (DO) level in the biofilm depth of the fixed-bed process (SBBR) simulated the anoxic phase conditions. Accordingly, a portion of NH4+-N that was not converted to NO3–-N by the SBR process was converted to NO3–-N in the outer layer of the biofilm in the SBBR process. Further, simultaneous nitrification and denitrification (SND) was achieved in the SBBR where NO2–-N was converted to N2 directly, before NO3–-N conversion (partial nitrification). The level of mixed liquid suspended solids (MLSS) was 2740 mg/l at the start of the experiments. The required carbon source (C: N ratio of 4) was provided by adding an internal carbon source (through step feeding) or ethanol. Firstly, as part of the system (SBR and SBBR), SBR operated at a DO level of 1 mg/l while SBBR operated at a DO concentration of 0.3 mg/l during Run-1. During Run-2, the system operated at the low DO concentration of 0.3 mg/l. When the source of carbon was ethanol, the nitrogen removal rate (RN) was higher than the operation with an internal carbon source. When the reactors were operated at the same DO concentration of 0.3 mg/l, 99.1 % of the ammonium was removed. The NO3–-N produced during the aerobic SBR operation of the novel method was removed in SBBR reactor by 8.3 %. The concentrations of NO3--N and NO2–-N in the SBBR effluent were reduced to 2.5 and 5.5 mg/l, respectively. Also, the total nitrogen (TN) removal efficiency was 97.5 % by adding ethanol at the DO level of 0.3 mg/l.

When C:N adjustment was carried out SND efficiency at C:N ratio of 6.5 reached to 99 %. The increasing nitrogen loading rate (NLR) to 0.554 kg N/m3 d decreased SND efficiency to 80.7 %.

Performance, microbial community evolution and neural network modeling of single-stage nitrogen removal by partial-nitritation/anammox process

Single-stage nitrogen removal by anammox/partial-nitritation (SNAP) process was proposed and explored in a packed-bed-EGSB reactor to treat nitrogen-rich wastewater. With dissolved oxygen (DO) maintained within 0.2-0.5 mg/L, reactor performance and microbial community dynamics were evaluated and reported. To ascertain whether control/prediction of the SNAP process was feasible with mathematical modeling, a novel 3-layered backpropagation-artificial-neural-network-(BANN) was also developed to model nitrogen removal efficiencies. When NLR of 300 gN/m³·d and DO of <0.3 mg/L was employed, the SNAP-process demonstrated autotrophic nitrogen removal pathways with NH₄⁺-N and TN removal of 91.1% and 81.9%, respectively. Microbial community succession revealed by 16S rRNA high-throughput gene-sequencing indicated that Candidatus-Kuenenia-(33.83%), Nitrosomonas-(3.4%) Armatimonadetes_gp5-(1.39%), Ignavibacterium-(1.80%), Thiobacillus-(1.33%), and Nitrospira-(1.17%) were the most pronounced genera at steady-state. The proposed BANN-model demonstrated high-performance as computational results revealed smaller deviations (±3%) and satisfactory coefficient of determination-(R² = 0.989), fractional variance-(FV = 0.0107), and index of agreement-(IA = 0.997). Thus, forecasting the efficiency of a SNAP-process with neural-network modeling was highly feasible.

A pilot-scale deep bed denitrification filter for secondary effluent treatment using sodium acetate as external carbon

A pilot-scale quartz sand deep bed denitrification filter (DBDF) using sodium acetate as the additional carbon source was implemented to treat secondary effluent, with a high nitrate nitrogen (NO₃ -N) concentration and low C/N ratio, from an urban municipal water resource recovery facility. By the 18th day, results showed that the removal efficiency of NO₃ -N and the chemical oxygen demand (COD) were stable at above 85% and 70%, respectively. When the filter layer depth was set to 1,600 mm and the concentration of additional sodium acetate was maintained at 51 mg/L, the total nitrogen and COD concentrations of the DBDF effluent were stabilized below 5 and 30 mg/L, respectively. The quartz sand DBDF had a good effect on the removal of dissolved organic matter, especially for aromatic protein-like and tryptophan protein-like substances. Bacteria with denitrification function, such as Cloacibacterium and Zoogloea, became increasingly dominant with increasing filling layer depth. PRACTITIONER POINTS: The denitrification filter had a good effect on the removal of aromatic protein-like and tryptophan protein-like substances. Cloacibacterium and Zoogloea became increasingly dominant with increasing filling layer depth.

Efficient step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD) equipped with real-time control parameters treating raw mature landfill leachate

An innovative step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD), equipped with real-time control parameters, achieved efficient nitrogen removal from raw mature landfill leachate. The variables pH and ORP served as real time on-line parameters to flexibly control the durations of aerobic and anoxic. A nitrogen removal efficiency (NRE) of 98.7% and nitrogen removal rate (NRR) of 0.23 kg m^-3d^-1 were obtained at the influent NH₄⁺ -N, SCOD and total nitrogen (TN) of 1000 ± 250 mg L^-1, 1100 ± 200 mg L^-1, and 1300 ± 75 mg L^-1, respectively. Mass balance research demonstrated that Anammox contributed 69.3% to nitrogen removal and denitrification contributed 15.7%. A significant change in the Anammox community structure occurred (ca. Brocadia from 0.26% to 2.13%, ca. Kuenenia from 0.29% to 0.02%). This change is mainly attributed to different kinetic strategies (R-strategist of ca. Brocadia and K-strategist of ca. Kuenenia). Further study revealed the co-existence of functional microorganisms Nitrosomonas (3.0%), Cadidatus-Brocadia (2.13%), and Thauera (25.3%).

Start up of partial nitritation-anammox process using intermittently aerated sequencing batch reactor: Performance and microbial community dynamics

This study investigated the performance and microbial community dynamics of a start-up method for the partial nitritation-anammox (PN-A) process: start-up from return sludge in an intermittently aerated sequencing batch reactor (IASBR). The robustness of this PN-A IASBR system in achieving long-term efficient nitrogen removal was also investigated. Stable partial nitritation with nitrite accumulation ratio of about 80% was firstly achieved in the IASBR. Then, PN-A process with total nitrogen removal of up to 81.5% was established due to the thriving of anammox bacteria Candidatus Kuenenia resulting from the reduction of the aeration rate. Molecular analysis showed that both bacterial and archaeal communities shifted greatly throughout the start-up stage and the PN-A stage. Besides bacterial genus Nitrosomonas, ammonium-oxidizing archaea (AOA) Candidatus Nitrososphaera with a high abundance of 3.44% also contributed to partial nitritation. Nitrospira was effectively restrained (abundance <1.6%) while methanogens co-existed with the aerobic and anaerobic nitrogen-conversion microorganisms. This study showed that IASBR configuration was efficient in starting up the PN-A process from return sludge, maintaining long-term efficient nitrogen removal and triggering the thrive of AOA.

Approaches and processes for ammonia removal from side-streams of municipal effluent treatment plants

The main objective of this review article is to provide a comprehensive view on various conventional and emerging side-stream ammonia removal treatment options for municipal wastewater treatment plants (WWTPs). Optimization of wastewater treatment facilities from an energy and emissions stand-point necessitates consideration of the impact of the various internal side-streams. Side-streams from anaerobic sludge digesters in particular have the potential to be a significant ammonium load to the mainstream treatment process. However, the literature suggests that managing side-streams through their treatment in the mainstream process is not the most energy efficient approach, nor does it allow for practical recovery of nutrients. Furthermore, as effluent criteria become more stringent in some jurisdictions and sludge hydrolysis pre-treatment for digesters more common, an understanding of treatment options for ammonia in digester supernatant becomes more important. Given these considerations, a variety of side-stream treatment processes described in the literature are reviewed.

Negligible seeding source effect on the final ANAMMOX community under steady and high nitrogen loading rate after enrichment using poly(vinyl alcohol) gel carriers

This study investigated the effect of seeding source on the mature anaerobic ammonia oxidation (ANAMMOX) bacterial community niche in continuous poly(vinyl alcohol) (PVA) gel systems operated under high nitrogen loading rate (NLR) condition. Four identical column reactors packed with PVA gels were operated for 182 d using different seeding sources which had distinct community structures. The ANAMMOX reaction was achieved in all the bioreactors with comparable total and ANAMMOX bacterial 16S rRNA gene quantities. The bacterial community structure of the bioreactors became similar during operation; some major bacteria were commonly found. Interestingly, one ANAMMOX species, "Candidatus Brocadia sinica", was conclusively predominant in all the bioreactors, even though different seeding sludges were used as inoculum source, possibly due to the unique physiological characteristics of "Ca. Brocadia sinica" and the operating conditions (i.e., PVA gel-based continuous system and 1.0 kg-N/(m³·d) of NLR). The results clearly suggest that high NLR condition is a more significant factor determining the final ANAMMOX community niche than is the type of seeding source.

Impacts of different morphologies of anammox bacteria on nitrogen removal performance of a hybrid bioreactor: Suspended sludge, biofilm and gel beads

The difficulties in the anaerobic ammonium oxidation (anammox) process mainly consist of low microbial growth rates and long start-up times of bioreactors. The morphologies of anammox bacteria might affect nitrogen removal performance and microbial community. In this study, three morphologies of anammox bacteria, namely, suspended sludge, biofilm and suspended sludge embedded in gel beads, were compared in a hybrid bioreactor under anoxic conditions (DO concentration < 0.1 mg L^-1). The results show that the average total inorganic nitrogen removal efficiency of a hybrid bioreactor reached 67 ± 15% with a maximum value of 80% for continuous synthetic wastewater feeding, and that the specific total inorganic nitrogen removal rate reached 15.75 mg·(gVSS·h)^-1 regardless of the organic matter stress. Batch tests indicate that mainly suspended sludge (67%) and biofilm (26%) contributed to the anammox process, with the specific total inorganic nitrogen removal rate reaching 10.55 and 4.05 mg·(gVSS·h)^-1, respectively. However, the embedding of sludge in gel resulted in nitrification instead of anammox with a nitrification rate of 0.20 ± 0.01 mg·(L·h)^-1 due to the expansion of gel beads floating on the water surface. Therefore, a pore-forming technique was developed to produce more channels for gas dispersion inside the gel beads. In terms of microbial community, Candidatus Kuenenia involved in the anammox group was the most abundant genus in biofilm (43.4%) and suspended sludge (15.7%), while Nitrospira occupied the largest proportion in gel beads (25.6%). This study offers useful information for the selection of anammox bacteria morphology.

Fast start-up of the single-stage nitrogen removal using anammox and partial nitritation (SNAP) from conventional activated sludge in a membrane-aerated biofilm reactor

The single-stage nitrogen removal using anammox and partial nitritation (SNAP) is a promising alternative for low-cost ammonium removal from wastewaters. This study aimed to evaluate the anammox biomass enrichment and SNAP process start-up in a laboratory-scale membrane-aerated biofilm reactor (MABR) at nitrogen loading rates of 50 g N.m^-3.d^-1 (period 1) and 100 g N.m^-3.d^-1 (period 2). Anammox activity was observed after 48 days, and the SNAP process was stable after 80 days. In period 1, the average total nitrogen (TN) removal was 78 ± 6%, and the maximum removal was 84%. In period 2, the average TN removal was 61 ± 5%, and the maximum was 69%. Higher dissolved oxygen levels may have caused imbalances in the microbial community in period 2, decreasing the reactor performance. These results demonstrated the potential of the MABR for the fast implementation of the single-stage partial nitritation and anammox processes.

Resuscitation of starved anaerobic ammonium oxidation sludge system: Impacts of repeated short-term starvation

Starvation of biomass is common during underloading of bioreactors or sludge storage in biological wastewater treatment industries. The aim of this work was to study the impact of starvation modes on the nitrogen removal capacity of anaerobic ammonium oxidation (anammox) process in sequencing batch reactor (SBR). The repeated short-term starvation and reactivation experiments were performed to evaluate the response of anammox sludge system in the condition of 27 ± 1.5 °C and 320 min HRT. Moreover, the nitrogen removal ability of the anammox process was reactivated rapidly in the low substrate condition, then the total nitrogen (TN) removal efficiency reached 82.5%, with the effluent TN of around 14.6 mgNL^-1. The repeated short-term starvation (1 day-4 days) and recovery mode could improve the tolerance and apparent activity of anammox sludge system. The dominant species of general anaerobic ammonium oxidation bacteria (AnAOB) was Candidatus Brocadia, which had better self-adaption to repeated starvation.

State of the art on granular sludge by using bibliometric analysis

With rapid industrialization and urbanization in the nineteenth century, the activated sludge process (ASP) has experienced significant steps forward in the face of greater awareness of and sensitivity toward water-related environmental problems. Compared with conventional flocculent ASP, the major advantages of granular sludge are characterized by space saving and resource recovery, where the methane and hydrogen recovery in anaerobic granular and 50% more space saving, 30-50% of energy consumption reduction, 75% of footprint cutting, and even alginate recovery in aerobic granular. Numerous engineers and scientists have made great efforts to explore the superiority over the last 40 years. Therefore, a bibliometric analysis was desired to trace the global trends of granular sludge research from 1992 to 2016 indexed in the SCI-EXPANDED. Articles were published in 276 journals across 44 subject categories spanning 1420 institutes across 68 countries. Bioresource Technology (293, 11.9%), Water Research (235, 9.6%), and Applied Microbiology and Biotechnology (127, 5.2%) dominated in top three journals. The Engineering (991, 40.3%), China (906, 36.9%), and Harbin Inst Technol, China (114, 4.6%) were the most productive subject category, country, and institution, respectively. The hotspot is the emerging techniques depended on granular reactors in response to the desired removal requirements and bio-energy production (primarily in anaerobic granular sludge). In view of advanced and novel bio-analytical methods, the characteristics, functions, and mechanisms for microbial granular were further revealed in improving and innovating the granulation techniques. Therefore, a promising technique armed with strengthened treatment efficiency and efficient resource and bio-energy recovery can be achieved.

Single-stage autotrophic nitrogen removal process at high loading rate: granular reactor performance, kinetics, and microbial characterization

For the possible highest performance of single-stage combined partial nitritation/anammox (PNA) process, a continuous complete-mix granular reactor was operated at progressively higher nitrogen loading rate. The variations in bacterial community structure of granules were also characterized using high-throughput pyrosequencing, to give a detail insight to the relationship between reactor performance and functional organism abundance within completely autotrophic nitrogen removal system. In 172 days of operation, a superior total nitrogen (TN) removal rate over 3.9 kg N/(m³/day) was stable implemented at a fixed dissolved oxygen concentration of 1.9 mg/L, corresponding to the maximum specific substrate utilization rate of 0.36/day for TN based on the related kinetics modeling. Pyrosequencing results revealed that the genus Nitrosomonas responsible for aerobic ammonium oxidation was dominated on the granule surface, which was essential to offer the required niche for the selective enrichment of anammox bacteria (genus Candidatus Kuenenia) in the inner layer. And the present of various heterotrophic organisms with general functions, known as fermentation and denitrification, could not be overlooked. In addition, it was believed that an adequate excess of ammonium in the bulk liquid played a key role in maintaining process stability, by suppressing the growth of nitrite-oxidizing bacteria through dual-substrate competitions.

Comparison of inoculum sources for long-term process performance and fate of ANAMMOX bacteria niche in poly(vinyl alcohol)/sodium alginate gel beads

The process performance and microbial niche of anaerobic ammonia oxidation (ANAMMOX) bacteria were compared in two identical bioreactors inoculated with different inoculum sources (i.e., pre-cultured ANAMMOX bacteria: PAB and activated sludge: AS) entrapped in poly(vinyl alcohol)/sodium alginate (PVA/SA) gel beads for a long-term period (i.e., 1.5 years). The start-up period with AS was longer than that with PAB; however, both bioreactors were successfully operated over the long-term with stable ANAMMOX activity. After long-term operation, the 16S rRNA gene concentration of ANAMMOX bacteria in both bioreactors was significantly increased, and thereby became comparable. In addition, Candidatus Jettenia sp. became the dominant ANAMMOX species in both bioreactors. Our results suggested that the ANAMMOX performance and microbial niche of ANAMMOX bacteria became nearly identical during long-term operation despite the use of different inoculum sources. Therefore, the use of PVA/SA gel beads entrapping AS appears to be a relevant option for constructing an ANAMMOX process in places where a full-scale ANAMMOX process has never been done previously.

Realization of microbial community stratification for single-stage nitrogen removal in a sequencing batch biofilter granular reactor

A permanent microbial stratified nitrogen removal system coupling anammox with partial nitrification (SNAP) in a sequencing batch biofilter granular reactor (SBBGR) was successfully constructed for the treatment of ammonia-rich wastewater. With a nitrogen loading rate of 0.1kgNm^-3·d^-1, the maximal ammonia and total nitrogen removal efficiencies could reach up to 96.08% and 84.86% on day 108, respectively. The pH, DO profiles revealed a switch of functional species (AOB and anammox) at a typical intermittent aeration cycle. qPCR and high throughput analyses certified a stable spatial microbial stratified community structure. Although, anammox preferred strict anaerobic environment while AOB needed oxygen, a special stratified community structure contributed to conquer this obstacle. Moreover, Bacteroidet, Chlorobi, OD1, Planctomycetes, and Proteobacteria were the dominant species in the SBBGR. Although we have predicted the possible pathways of nitrogen transformation, further studies are needed to validate the pathways in enzymology.

Is denitrifying anaerobic methane oxidation-centered technologies a solution for the sustainable operation of wastewater treatment Plants?

With the world's increasing energy crisis, society is growingly considered that the operation of wastewater treatment plants (WWTPs) should be shifted in sustainable paradigms with low energy input, or energy-neutral, or even energy output. There is a lack of critical thinking on whether and how new paradigms can be implemented in WWTPs based on the conventional process. The denitrifying anaerobic methane oxidation (DAMO) process, which uses methane and nitrate (or nitrite) as electron donor and acceptor, respectively, has recently been discovered. Based on critical analyses of this process, DAMO-centered technologies can be considered as a solution for sustainable operation of WWTPs. In this review, a possible strategy with DAMO-centered technologies was outlined and illustrated how this applies for the existing WWTPs energy-saving and newly designed WWTPs energy-neutral (or even energy-producing) towards sustainable operations.

N2O micro-profiles in biofilm from a one-stage autotrophic nitrogen removal system by microelectrode

Emission of nitrous oxide (N₂O), a greenhouse gas, is of growing concern in biological wastewater treatment. N₂O emission from biofilm in a one-stage completely autotrophic nitrogen removal system was investigated using microelectrodes in this study. It is indicated that the pathways of nitrogen transformation in biofilm mainly included partial nitrification and anaerobic ammonium oxidation (anammox), also included nitrification and heterotrophic denitrification (HD). Ammonium-oxidizing bacteria (AOB) denitrification and HD were the main pathways resulting in N₂O production in the biofilm, and hydroxylamine (NH₂OH) oxidation was a subordinate pathway. In addition, the amount of N₂O emission in test in which both NH₄⁺ and NO₂^- were added (NH₄⁺-N: NO₂^--N = 1:1) was about 2 times greater than that in test with NH₄⁺ addition only. This result expressed that NO₂^- is an important factor affecting N₂O production in the biofilm. In conclusion, the present study provides a theoretical support for reducing N₂O production in one-stage completely autotrophic nitrogen removal system.

Achieving nitritation in a continuous moving bed biofilm reactor at different temperatures through ratio control

A ratio control strategy was implemented in a continuous moving bed biofilm reactor (MBBR) to investigate the response to different temperatures. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and total ammonia nitrogen (TAN) concentrations. The results revealed that a stable nitritation in a biofilm reactor could be achieved via ratio control, which compensated the negative influence of low temperatures by stronger oxygen-limiting conditions. Even with a temperature as low as 6°C, stable nitritation could be achieved when the controlling ratio did not exceed 0.17. Oxygen-limiting conditions in the biofilm reactor were determined by the DO/TAN concentrations ratio, instead of the mere DO concentration. This ratio control strategy allowed the achievement of stable nitritation without complete wash-out of NOB from the reactor. Through the ratio control strategy full nitritation of sidestream wastewater was allowed; however, for mainstream wastewater, only partial nitritation was recommended.

A novel process combining simultaneous partial nitrification, anammox and denitrification (SNAD) with denitrifying phosphorus removal (DPR) to treat sewage

In this study, a novel process combined simultaneous partial nitrification, anammox and denitrification (SNAD) with denitrifying phosphorus removal (DPR) was proposed for advanced nitrogen removal. Firstly simulating sewage was introduced to a sequencing batch reactor (SBR) for organic matter removal and anaerobic phosphorus release (stage 1). Then effluent of stage 1 with low COD was discharged to a sequencing biofilm batch reactor (SBBR) for partial nitrification, anammox and partial denitrification (stage 2). The nitrate produced in SBBR was fed into SBR again, in which the nitrate was removed by DPR process (stage 3). The performance of the SNAD-DPR process was investigated. And effects of carbon source addition during start-up period on microbial community were discussed based on 16S rRNA amplicon pyrosequencing.