Effect of COD/N ratio on nitrogen removal and microbial communities of CANON process in membrane bioreactors

Biological treatment of N-methylpyrrolidone, cyclopentanone, and diethylene glycol monobutyl ether distilled residues and their effects on nitrogen removal in a full-scale wastewater treatment plant

Manufacturing processes in semiconductor and photonics industries involve the use of a significant amount of organic solvents. Recycle and reuse of these solvents produce distillate residues and require treatment before being discharged. This study aimed to evaluate the performance of the biological treatment system in a full-scale wastewater treatment plant that treats wastewater containing distillate residues from the recycling of electronic chemicals. Batch experiments were conducted to investigate the optimal operational conditions for the full-scale wastewater treatment plant. To achieve good nitrogen removal efficiency with effluent ammonia and nitrate concentrations below 20 mg N/L and 50 mg N/L, respectively, it was suggested to control the ammonia concentration and pH of the influent below 500 mg N/L and 8.0, respectively. In addition, the biodegradability of N-methylpyrrolidone, diethylene glycol monobutyl ether, and cyclopentanone distillate residues from the electronic chemicals manufacturing process were evaluated under aerobic, anoxic, and anaerobic conditions. N-methylpyrrolidone and cyclopentanone distillate residues were suggested to be treated under anoxic condition. However, substrate inhibition occurred when using cyclopentanone distillate residue as a carbon source with chemical oxygen demand (COD) levels higher than 866 mg/L and nitrate levels higher than 415 mg N/L. Under aerobic condition, the COD from both N-methylpyrrolidone and cyclopentanone distillate residues could be easily degraded. Nevertheless, a negative effect on nitrification was observed, with a prolonged lag time for ammonia oxidation as the initial COD concentration increased. The specific ammonia oxidation rate and nitrate production rate decreased under high COD concentration contributed by N-methylpyrrolidone and cyclopentanone distillate residues. Furthermore, the biodegradability of diethylene glycol monobutyl ether distillate residue was found to be low under aerobic, anoxic, and anaerobic conditions. With respect to the abundance of nitrogen removal microorganisms in the wastewater treatment plant, results showed that Comammox may have an advantage over ammonia oxidizing bacteria under high pH conditions. In addition, Comammox may have higher resistance to environmental changes. Dominance of Comammox over ammonia oxidizing bacteria under high ammonia condition was first reported in this study.

Shift in microorganism and functional gene abundance during completely autotrophic nitrogen removal over nitrite (CANON) process

Nitrification-denitrification process has failed to meet wastewater treatment standards. The completely autotrophic nitrite removal (CANON) process has a huge advantage in the field of low carbon/nitrogen wastewater nitrogen removal. However, slow start-up and system instability limit its applications. In this study, the time of the start-up CANON process was reduced by using bio-rope as loading materials. The establishing of graded dissolved oxygen improved the stability of the CANON process and enhanced the stratification effect between functional microorganisms. Microbial community structure and the abundance of nitrogen removal functional genes are also analyzed. The results showed that the CANON process was initiated within 75 days in the complete absence of anaerobic ammonium oxidizing bacteria (AnAOB) inoculation. The ammonium and nitrogen removal efficiencies of CANON process reached to 94.45% and 80.76% respectively. The results also showed that the relative abundance of nitrogen removal bacterial in the biofilm gradually increases with the dissolved oxygen content in the solution decreases. In contrast, the relative abundance of ammonia oxidizing bacteria was positively correlated with the dissolved oxygen content in the solution. The relative abundance of g__Candidatus_Brocadia in biofilm was 15.56%, and while g__Nitrosomonas was just 0.6613%. Metagenomic analysis showed that g__Candidatus_Brocadia also contributes 66.37% to the partial-nitrification functional gene Hao (K10535). This study presented a new idea for the cooperation between partial-nitrification and anammox, which improved the nitrogen removal system stability.

Long-term performance and biofilms of the novel nano manganese dioxide coupling carbon source pre-loaded biological activated carbon filters for drinking water

In order to accelerate the start-up of biological activated carbon (BAC) filters and enhance ammonium (NH4+-N) removal performance, three substrates (sucrose and/or nano manganese dioxide (nMnO2)) pre-loaded BAC filters were set up to investigate the pollutants removals and microbiological characteristics for a long-term operation of 197 days. The average NH4+-N removal performance treated by the sucrose coupled with nMnO2 loaded BAC filter was the highest (71.18 %), which was 3.83 times of that by the control filter (18.58 %). 29 % of NH4+-N treated by the sucrose coupled with nMnO2 loaded BAC removed through the traditional nitrification and denitrification, or simultaneous nitrification and denitrification (SND) pathways according to the calculation of the alkalinity consumption (6.12 mmol/L). There was no leakage of carbon source and Mn, and no accumulation of nitrite from the substrates loaded BAC. The dominant bacteria in the sucrose coupled with nMnO2 loaded BAC were Dechloromona (accounting for 8.02% of the total bacterial) and Acidaminobacter (accounting for 15.16% of total bacterial) on the Day 180, which had the capacity of nitrification or denitrification. NH4+-N and micropollutants removals treated by the combined process of peracetic acid (PAA) pre-oxidation and substrates loaded BAC were significant due to the generation of assimilable organic carbon (AOC) (5.98 ± 1.93 μg-C/mL) by PAA (100 μM)/Fe2+ pre-oxidation and the higher biomass ((4.57 ± 3.07) × 107 cells/g DW BAC) in the sucrose coupled with nMnO2 loaded BAC filter. Therefore, nMnO2 coupling carbon source pre-loading strategy could not only enhance initial colonization, but also promote pollutants removals for long-term operation.

Microbial activity along the depth of biofilm in the simultaneous partial nitrification, anammox and denitrification (SNAD) system

Simultaneous partial nitrification, anammox and denitrification (SNAD) is a sustainable and cost-effective technology for nitrogen removal from low-strength wastewater. However, knowledge of the biofilm microenvironment of the SNAD system is currently unsatisfactory. The purpose of this study was to evaluate organic carbon effects on the microenvironment and microbial growth in the SNAD biofilm system. Microelectrodes were used to investigate microbial activity in-depth within biofilms. ORP distribution of the SNAD system was positively related to anammox activity(R2 = 0.9), and had some influence on microbial community structure. The synergistic effect of anammox bacteria and denitrifiers could be achieved when the abundance ratio of anammox bacteria to denitrifying bacteria is greater than 1.2.

Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox

Anaerobic ammonium oxidation (anammox) is a potential process to achieve the neutralization of energy and carbon. Due to the low temperature and variation of municipal sewage, the application of mainstream anammox is hard to be implemented. For spreading mainstream anammox in practice, several key issues and bottlenecks including the start-up, stable NO₂^--N supply, maintenance and dominance of AnAOB with high activity, prevention of NO₃^--N buildup, reduction of sludge loss, adaption to the seasonal temperature and alleviation of COD impacts on AnAOB are discussed and summarized in this review in order to improve its startup, stable operation and resilience of mainstream anammox. Hence a combined biological nitrogen removal (CBNR) system based on conventional denitrification, shortcut nitrification-denitrification, Partial Nitritation and partial Denitrification combined Anammox (PANDA) process through the management of organic matter and nitrate is proposed correspondingly aiming at adaptation to the variations of seasonal temperature and pollutants in influent.

Increasing nitrogen and organic matter removal from swine manure digestate by including pre-denitrification and recirculation in single-stage partial nitritation/anammox

A novel two-stage process comprising pre-denitrification and single-stage partial nitritation/anammox was developed to treat swine manure digestate with a constant nitrogen loading rate of 1.0 gN/L/d. As the influent NH₄⁺-N concentration increased from 500 to 1500 mg/L, a nitrogen removal efficiency of 88 %-96 % and 5-day biochemical oxygen demand removal efficiency of 93 %-97 % were achieved. Owing to the high influent chemical oxygen demand (COD)/nitrates and nitrites (NO_X) ratio of 8.2-9.2 and high COD utilization of denitrifying bacteria (DB), the NO₂^--N and NO₃^--N removal efficiencies in the denitrification reactor reached 96 %-99 % and 97 %-99 %, respectively. The contribution of anammox bacteria to nitrogen removal was 70.9 %-84.3 %, whereas that of DB was 11.7 %-18.3 %. The contributions of DB and ordinary heterotrophic organisms to COD removal were 19.5 %-49.3 % and 17.9 %-39 %, respectively. This study will help guide the anammox process in swine wastewater treatment.

Concept development of a mainstream deammonification and comparison with conventional process in terms of energy, performance and economical construction perspectives

Deammonification for nitrogen removal in municipal wastewater in temperate and cold climate zones is currently limited to the side stream of municipal wastewater treatment plants (MWWTP). This study developed a conceptual model of a mainstream deammonification plant, designed for 30,000 P.E., considering possible solutions corresponding to the challenging mainstream conditions in Germany. In addition, the energy-saving potential, nitrogen elimination performance and construction-related costs of mainstream deammonification were compared to a conventional plant model, having a single-stage activated sludge process with upstream denitrification. The results revealed that an additional treatment step by combining chemical precipitation and ultra-fine screening is advantageous prior the mainstream deammonification. Hereby chemical oxygen demand (COD) can be reduced by 80% so that the COD:N ratio can be reduced from 12 to 2.5. Laboratory experiments testing mainstream conditions of temperature (8-20°C), pH (6-9) and COD:N ratio (1-6) showed an achievable volumetric nitrogen removal rate (VNRR) of at least 50 gN/(m³∙d) for various deammonifying sludges from side stream deammonification systems in the state of North Rhine-Westphalia, Germany, where m³ denotes reactor volume. Assuming a retained N_organic content of 0.0035 kgN_org./(P.E.∙d) from the daily loads of N at carbon removal stage and a VNRR of 50 gN/(m³∙d) under mainstream conditions, a resident-specific reactor volume of 0.115 m³/(P.E.) is required for mainstream deammonification. This is in the same order of magnitude as the conventional activated sludge process, i.e., 0.173 m³/(P.E.) for an MWWTP of size class of 4. The conventional plant model yielded a total specific electricity demand of 35 kWh/(P.E.∙a) for the operation of the whole MWWTP and an energy recovery potential of 15.8 kWh/(P.E.∙a) through anaerobic digestion. In contrast, the developed mainstream deammonification model plant would require only a 21.5 kWh/(P.E.∙a) energy demand and result in 24 kWh/(P.E.∙a) energy recovery potential, enabling the mainstream deammonification model plant to be self-sufficient. The retrofitting costs for the implementation of mainstream deammonification in existing conventional MWWTPs are nearly negligible as the existing units like activated sludge reactors, aerators and monitoring technology are reusable. However, the mainstream deammonification must meet the performance requirement of VNRR of about 50 gN/(m³∙d) in this case.

Successful Application of Anammox Using the Hybrid Autotrophic-Heterotrophic Denitrification Process for Low-Strength Wastewater Treatment

Directly integrating anammox into sewage treatment is attractive, but anammox bacteria (AnAOB) enrichment is complex due to vicious competition from heterotrophic bacteria (HB). A novel strategy of optimal organics management using a preanaerobic stage and subsequent limited-oxygen conditions (0.32 ± 0.15 mg-O₂/L) is applied, and a hybrid autotrophic-heterotrophic denitrification process is developed to treat sewage-like wastewater with a COD/N ratio of 3.1 for 420 days. The stable process was achieved, and a high total nitrogen removal rate of 0.53 kg-N/(m³·d) was obtained compared to conventional nitrification/denitrification. The 16S rRNA high-throughput sequencing analysis suggested that the relative abundance of the nonendogenous HB (Denitratisoma and Thauera) was drastically reduced (P ≤ 0.001), whereas the endogenous denitrifying HB (Candidatus (Ca.) Competibacter) was significantly enriched in the anammox granules (9.98%, P ≤ 0.001). Moreover, Ca. Competibacter as an inner core and Nitrospira and Ca. Brocadia as an outside coating of the anammox granules indicated the cooperation of AnAOB with HB as revealed by laser-scanning confocal microscopy and qPCR. In situ tests further confirmed nitrite from two pathways (partial nitritation and endogenous partial denitritation) that favored AnAOB enrichment. Optimal organics management can mitigate the competition of HB with AnAOB by redirecting the metabolic pathways and microbial community, which is critical to directly integrating anammox into sewage treatment.

Integrated moving bed biofilm reactor with partial denitrification-anammox for promoted nitrogen removal: Layered biofilm structure formation and symbiotic functional microbes

Partial denitrification/anaerobic ammonia oxidation (anammox) (PD/A) is currently an advanced nitrogen removal process. This study developed a PD/A system in a moving bed biofilm reactor. Results showed that the nitrogen removal efficiency reached 76.60% with a COD/NO₃-N of 2.0, and the contribution of anammox was 88.01%. Further analysis showed that the biocarriers could form layered pH and dissolved oxygen structures to promote the aggregation of different functional bacteria at various depths, thus stabilizing the coupled process. Microbial structure analysis showed that the abundance of Saccharimonadales, responsible for denitrification, increased from 0% to 36.27% between day 0 and day 120, while the abundance of Candidatus Jettenia, responsible for anammox, decreased from 10.41% to 2.20%. The synergistic effect of Saccharimonadales and Candidatus Jettenia enabled stable and efficient removal of nitrogen. This study proposed a novel configuration of the PD/A process and provided a theoretical basis for its promotion and application.

A divided flow aerobic-anoxic baffled reactor for simultaneous nitrification-denitrification of domestic wastewater

A novel aerobic-anoxic baffled reactor is designed for the effective denitrification of real domestic wastewater without an external carbon source. The flow is divided between two inlets at the beginning of each zone to provide a carbon source for the denitrifying bacteria. The effects of operating parameters such as the ratio of chemical oxygen demand to nitrogen (COD/N), flow division ratio, and hydraulic retention time (HRT) on the nitrogen removal were investigated. The optimum values of COD/N and HRT were estimated using response surface methodology (RSM) coupled with a central composite experimental design. The addition of porous biomass support media considerably improved the denitrification and removal of COD. Furthermore, the aerobic-anoxic system showed high stability against sudden HRT and COD/N ratio changes. The microbial analysis showed that Alcaligenes, Achromobacter, and Bordetella were the dominant denitrifying bacteria in the anoxic zone, whereas other species coexisted in the aerobic zone.

Control strategy and performance of simultaneous removal of nitrogen and organic matter in treating swine manure digestate using one reactor with airlift and micro-granule

A simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) process was used to evaluate the nitrogen and biodegradable organic matter removal of swine manure digestate based on a nitrite limitation and ammonium surplus strategy. As influent ammonium concentration increased from 500 mg/L to 2100 mg/L, the 5 day biochemical oxygen demand (BOD₅) maintained at a high removal efficiency of 95.4%. However, nitrogen removal efficiency (NRE) decreased from 90.9% to 68.2% due to the inhibition of AnAOB caused by an ammonium concentration of 2100 mg/L. The contribution of AnAOB to nitrogen removal was 75.6-86.5%, while that of denitrifying bacteria was 4.6-7.0%. In the case of COD removal, the contributions were from ordinary heterotrophic organisms and denitrifying bacteria, at 27.1-64.9% and 11.2-22.1%, respectively. The results of specific bacteria activity tests and microbial analysis showed that a highly efficient synergism between functional microorganisms is essential for the stability of the SNADCO process.

Partition of Anammox and Nitrifiers Through Bio-Carriers for Full-Scale Sidestream Partial Nitrification–Anammox Plant

This study assessed the activity and community structure in different types of sludge to reveal the partition mechanism of anammox and nitrifiers in a full-scale partial nitrification–anammox plant. Batch experiments confirmed that suspended sludge had higher partial nitrification capacity, and biofilm sludge had higher anammox activity, 16.9 times higher than suspended sludge. qPCR analysis confirmed that the amoA gene was mainly present in suspended sludge, and the highest abundance of the Amx gene was observed in biofilm sludge, reaching 1.01 × 107 copies/ng DNA. High-throughput results revealed that Nitrosomonas was the main ammonia-oxidizing bacteria with high activity in suspended sludge, and Candidatus Brocadia had the highest abundance of 13.4% in biofilm sludge. This is the exploration of the microbial community of three different sludge types in the full-scale sidestream PN/A system for the first time, which can guide the construction and replication of full-scale PN/A plants.

Comparison of three anaerobic digestion reactors for low-carbon wastewater treatment

In this study, three anaerobic digestion reactors using up-flow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (AnSBR), and anaerobic membrane bioreactor (AnMBR) were studied. The chemical oxygen demand (COD), gas production, sludge performance, and microbial characteristics of the anaerobic digestion process were assessed. The results showed that the average COD removal efficiencies reached 86%, 83%, and 85%, with corresponding removed rates of 2.49, 0.48, and 0.79 kg COD m-3  d-1 in UASB, AnSBR, and AnMBR, respectively. After the reactors attained stable operation, both extracellular polymeric substances and soluble microbial products decreased in all the reactors compared with the seed sludge. Methanothrix was the dominant archaea for methane production in the UASB, the relative abundance of which increased from 58.3% to 83.4%. These results identify UASB as the most suitable reactor for anaerobic digestion when treating wastewater with low carbon. Such reactors are important for the application and development of the energy self-sufficiency in sewage treatment. PRACTITIONER POINTS: UASB, SBR, and MBR were adopted to treat low-carbon wastewater using anaerobic digestion process. UASB performed the highest COD removal from low-carbon wastewater. The main microorganisms in UASB were Methanothrix, Methanomassiliicoccus, and Methanobacterium.

The performance of simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) method in the treatment of digested effluent of fish processing wastewater

The simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) method was successfully carried out in an air-lift moving bed biofilm reactor (AL-MBBR) with cylinders carriers for the treatment of digested fish processing wastewater (FPW). Synthetic wastewater was used as substrate at stage 1. It changed into the digested FPW with dilution variation in order to increase the nitrogen and COD loading rates. With influent concentration of NH₄⁺-N of 909 ± 101 mg-N/L and COD of 731 ± 26 mg/L, the nitrogen removal efficiency was 86.8% (nitrogen loading rate of 1.21 g-TN/L/d) and the COD removal efficiency was 50.5% (COD loading rate at 0.98 g-COD/L/d). This study showed that the process has the advantages in treating the real high ammonia concentration of digested wastewater containing organic compounds. The nitritation and anammox route was predominant in nitrogen removal, while COD oxidation and microbe proliferation played the main role in COD removal.

A novel simultaneous partial nitritation, denitratation and anammox (SPNDA) process in sequencing batch reactor for advanced nitrogen removal from ammonium and nitrate wastewater

This study presented a novel simultaneous partial nitritation (PN), denitratation and anammox (SPNDA) process for treating ammonium and nitrate wastewater. Results indicated that SPNDA could achieve a great total nitrogen (TN) removal of 97.6 ± 0.5%, leading to effluent TN concentration of only 3.4 mg/L. Mass balance indicated that nitrogen removal rates via anammox, simultaneous nitrification and denitrification were 96.7% and 3.3%, respectively. Extended aerobic duration (12 h) and low dissolved oxygen (DO) concentration (0.15 mg/L) could improve ammonia-oxidizing bacteria (AOB) activity and maintain PN stability. The stable suppression of nitrite-oxidizing bacteria activity was attributed to the low DO (0.15 mg/L) and high free ammonia (3.63 mg/L) in SPND. Besides, the nitrogen conversion mechanisms for SPNDA were revealed based on a typical operational cycle. Microbial analysis showed that AOB (Nitrosomonas) and partial denitrifying bacteria (Thauera and Denitratisoma) coexisted with anammox bacteria (Candidatus Brocadia and Candidatus Anammoxoglobus) in the mixotrophic bio-community.

Kitchen waste hydrolysate enhances sewage treatment efficiency with different biological process compared with glucose

Insufficient carbon source is the primary factor that limits biological nitrogen and phosphorus removal during sewage treatment. This study investigates the feasibility and biological process of kitchen waste hydrolysate (KWH) replacing glucose to improve pollutant removal efficiency. It was found that using KWH as carbon source achieved better removal effect than glucose during sewage treatment. And more than 96% of total nitrogen (TN), total phosphorus (TP), and the chemical oxygen demand were removed after 48 h of acclimation. Nitrogen and phosphorus introduced by adding KHW had no negative effect on the effluent quality. Compared with glucose, KWH decreased the diversity of bacteria and significantly promoted the accumulation of acid-producing bacteria (Propionibacterium) and denitrifying bacteria (Rhodobacteraceae). Moreover, KWH significantly improved the relative abundance of the amo A, nap A, and nos Z genes. This result further indicated that KWH was beneficial for denitrification and was a favorable external carbon source.

Exploring the role of heterotrophs in partial nitritation-anammox process treating thermal hydrolysis process - anaerobic digestion reject water

Heterotrophic bacteria (HB) are generally prevalent in anammox-based processes, but their functional and ecological roles in partial nitritation-anammox (PN/A) process treating high-organics wastewater remained unclear. This study aimed to elucidate HB activities and microbial interactions in a one-stage PN/A treating thermal hydrolysis process (THP) - anaerobic digestion (AD) reject water. The PN/A reactor achieved a satisfactory nitrogen removal rate of 0.58 ± 0.06 g N/(L·d), and around 12% of COD in the THP-AD reject water was removed. N₂O emission factors of the PN/A reactor were 1.15% ± 0.18% treating synthetic wastewater, and 0.95% ± 0.06% treating reject water. A balanced symbiotic relationship was maintained between HB and functional groups (i.e., anammox bacteria and aerobic-ammonia-oxidizing bacteria) over the reactor operation. The relative abundances of Anaerolineae spp. clearly increased, while Denitratisoma, capable of denitrification, slightly decreased when treating THP-AD reject water. The preference for electron donors of heterotrophs explained discrepant growth trends.

Advanced nitrogen removal from low C/N municipal wastewater by combining partial nitrification-anammox and endogenous partial denitrification-anammox (PN/A-EPD/A) process in a single-stage reactor

In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.

Improving the outcomes from electroactive constructed wetlands by mixing wastewaters from different beverage-processing industries

Denitrification in electroactive constructed wetland (EW) systems is constrained by the carbon source and the carbon/nitrogen (C/N) ratio (the COD/TN ratio). In this study, wastewater with a high C/N from a brewery was added to wastewater with a low C/N (dairy wastewater) in an EW system, and the pollutant removal, bioelectricity generation, transformations of dissolved organic matter, and microbial community structures were evaluated. The results showed that the average removal rates of ammonium nitrogen, total nitrogen, and chemical oxygen demand from the wastewater mixture were 6.40%, 46.44%, and 23.85% higher than those from the wastewater with a low C/N, respectively. Dissimilatory nitrate reduction to ammonium was effectively inhibited, and the NH₄⁺-N removal was 25.52% higher, when the wastewater mixture was used instead of the high C/N wastewater. Similarly, the output voltage was significantly increased, and the internal resistance of the device was reduced, for the wastewater mixture. The structure of the microbial community improved, the relative abundance of electrochemically active bacteria was higher, and the protein-like and humic-like components were lower, in the mixture treatment than in the individual treatment. The results show that the nitrogen removal and biopower generation improved in an EW system when high C/N wastewater was used as the carbon source.

Insights into two stable mainstream deammonification process and different microbial community dynamics at ambient temperature

How to achieve stable mainstream deammonification is still a huge challenge. In this work, satisfactory nitrogen removal were achieved in a deammonification granular sludge reactor (R1, 0.42 ± 0.03 kg N / (m³·d)) and a mixed flocculent with granular sludge reactor (R2, 0.39 ± 0.04 kg N / (m³·d)) at ambient temperature (21-28 ℃) . The good adaptability of anammox bacteria (Candidatus Jettenia) to ambient temperature ensured its efficient activity (0.84-1.54 mg N/(g VSS·h)). The overexpression ammonia monooxygenase gene abundances in ammonia oxidizing bacteria (Nitrosomonas) was also predicted. The inhibition of hydrazine and the competition of denitrifying bacteria (Denitratisoma) to nitrite nitrogen, leading to a low Nitrospira relative abundances (0.2%-2.1%) . It was also found that R1 was more resistant to the unfavorable condition. For R2, higher Denitratisoma abundances (9.2%-18.5%) and predicted metabolic pathway abundances related to carbon metabolism were observed.

Research progress on enhancing the performance of autotrophic nitrogen removal systems using microbial immobilization technology

The autotrophic nitrogen removal process has great potential to be applied to the biological removal of nitrogen from wastewater, but its application is hindered by its unstable operation under adverse environmental conditions, such as those presented by low temperatures, high organic matter concentrations, or the presence of toxic substances. Granules and microbial entrapment technology can effectively retain and enrich microbial assemblages in reactors to improve operating efficiency and reactor stability. The carriers can also protect the reactor's internal microorganisms from interference from the external environment. This article critically reviews the existing literature on autotrophic nitrogen removal systems using immobilization technology. We focus our discussion on the natural aggregation process (granulation) and entrapment technology. The selection of carrier materials and entrapment methods are identified and described in detail and the mechanisms through which entrapment technology protects microorganisms are analyzed. This review will provide a better understanding of the mechanisms through which immobilization operates and the prospects for immobilization technology to be applied in autotrophic nitrogen removal systems.

An Analysis of Operation Conditions and Microbial Characteristics in Swine Wastewater Treatment Plants with Spontaneously Enriched Anammox Bacteria

The spontaneous enrichment of anammox bacteria has been reported in swine wastewater treatment facilities. However, their causative conditions and microbial characteristics, which this study aims to explain, are poorly understood. We discovered eight treatment facilities where the collected red biofilms exhibited high anammox activity levels at 57–843 µmol-N2/g-ignition loss (IL)/h and anammox DNA concentrations of 4.3 × 108–1.6 × 1012 copies/g-IL. The facilities used various wastewater treatment methods—six of them employed a multi-stage continuous reactor, whereas aeration tanks were continuously aerated at another combination of six facilities. Levels of dissolved oxygen (DO) in these tanks were fairly low at ≤1 mg/L. Pyrosequencing of the biofilms indicated the presence of 3–62.5% Planctomycetes, and the dominant anammox in each biofilm comprised three operational taxonomic units (OTUs) similar to Candidatus Jettenia asiatica, Ca. Brocadia fulgida, and Ca. B. caroliniensis. This suggested that some particular species of anammox bacteria naturally thrive when operating a swine wastewater treatment facility at low DO levels. The frequent enrichment of anammox biofilms at the sampled sites indicated that these treatment facilities were good seed sources of anammox; therefore, anammox treatment would be a viable method for the removal of nitrogen from swine wastewater.

Deammonification process in municipal wastewater treatment: Challenges and perspectives

The deammonification process has been proved to be an efficient nitrogen removal process in treating high NH₄⁺-N concentration wastewater (sidestream deammonification). It is very hopeful to bring WWTP close to energy autarky. However, the feasibility of applying mainstream deammonification to sewage treatment need to be further explored. Therefore, this review attempts to give an overview of challenges in applying mainstream deammonification and to discuss the impacts of unfavorable conditions on main functional species. In addition, some novel control strategies to maintain the dominant position of desired species were summarized. Efficient solution to the conflict between AnAOB (Anaerobic ammonium-oxidizing bacteria) biomass retention and NOB (Nitrite oxidizing bacteria) wash out was also reviewed. Ultimately, we suggested further studies including effective improved process that achieve combination of autotrophy and organotrophy species based on the metabolic diversity of AnAOB.

Comprehensive performance, bacterial community structure of single-chamber microbial fuel cell affected by COD/N ratio and physiological stratifications in cathode biofilm

This study compares the effects and bacterial community structure of single-chamber microbial fuel cells (MFCs) in the treatment of NH₄⁺-containing wastewater with different chemical oxygen demand (COD)/N ratios, whilst simultaneously conducting stratification research on the cathode biofilm. To this end, five nitrifier pre-enriched single-chamber MFC reactors are established to treat five different COD/N wastewaters, respectively. The results show that MFCs with low COD/N have better NH₄⁺-N removal, electrochemical performance, but the removal stability and COD removal effect are lower than MFCs with high COD/N. High-throughput sequencing reveals that the anode community structure is weakly affected by the COD/N and is dominated by Geobacter; however, the cathode community is complex and susceptible to the COD/N. Furthermore, the pH profile in the cathode biofilm is characterized by a pH microelectrode and fluorescence in situ hybridization (FISH) is used to confirm that the distribution trend of nitrifiers and denitrifiers in cathode biofilm.

Achieving stable mainstream deammonification process by a novel combinatorial control strategy

In this study, a novel combinatorial control strategy was developed to guarantee a stable mainstream deammonification process, with three critical steps including (a) upflow airwater washing, (b) short-term increased nitrogen loading rate (NLR), and (c) low oxygen supply. Results showed that two upflow double-blanket filter (UDBF) reactors effectively performed the mainstream deammonification process with the nitrogen removal efficiency (NRE) 84.5 ± 2.2% and 84.6 ± 1.6%, respectively and nitrogen removal rate (NRR) 123.8 ± 2.9 and 125.5 ± 6.2 g N·(m³·d)^-1, respectively. Statistically, temperature and C/N were considered as two vital factors affecting the nitrogen removal pathways, which co-explained 80.9% and 78.4% of the maximum possible contribution of heterotrophic denitrification in both reactors. The deammonification process accounted for more than 59.8% of TN removal in R2 and 54.8% in R1, which cooperated well with heterotrophic denitrification for efficient performance in treating municipal sewage.

Optimization of nitrogen and carbon removal with simultaneous partial nitrification, anammox and denitrification in membrane bioreactor

In this study, a membrane bioreactor (MBR) was used to achieve both nitrogen and carbon removal by a simultaneous partial nitrification, anammox and denitrification (SNAD) process. During the entire experiment, the intermittent aeration (non-aerobic time : aeration time, min min^-1) cycle was controlled by a time-controlled switch, and the aeration rate was controlled by a gas flowmeter, and the optimal operating parameters as determined by response surface methodology (RSM) were a C/N value of 1.16, a DO value of 0.84 mg l^-1 and an aerobic time (T _ae) of 15.75 min. Under these conditions, the SNAD process achieved efficient and stable nitrogen and carbon removal; the total inorganic nitrogen removal efficiency and chemical oxygen demand removal efficiency were 92.31% and 95.67%, respectively. With the formation of granular sludge, the membrane fouling rate decreased significantly from 35.0 Pa h^-1 at SNAD start-up to 19.9 Pa h^-1 during stable operation. Fluorescence in situ hybrid analyses confirmed the structural characteristics and the relative ratio of aerobic ammonia-oxidizing bacteria, anaerobic ammonia-oxidizing bacteria and denitrifying bacteria in the SNAD system.

Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review

Integrated fixed-film activated sludge (IFAS) process is considered as one of the leading-edge processes that provides a sustainable solution for wastewater treatment. IFAS was introduced as an advancement of the moving bed biofilm reactor by integrating the attached and the suspended growth systems. IFAS offers advantages over the conventional activated sludge process such as reduced footprint, enhanced nutrient removal, complete nitrification, longer solids retention time and better removal of anthropogenic composites. IFAS has been recognized as an attractive option as stated from the results of many pilot and full scales studies. Generally, IFAS achieves >90% removals for combined chemical oxygen demand and ammonia, improves sludge settling properties and enhances operational stability. Recently developed IFAS reactors incorporate frameworks for either methane production, energy generation through algae, or microbial fuel cells. This review details the recent development in IFAS with the focus on the pilot and full-scale applications. The microbial community analyses of IFAS biofilm and floc are underlined along with the special emphasis on organics and nitrogen removals, as well as the future research perspectives.

New insights on biological nutrient removal by coupling biofilm-based CANON and denitrifying phosphorus removal (CANDPR) process: Long-term stability assessment and microbial community evolution

It was difficult to obtain a stable and efficient biological nutrient removal for high-strength wastewater treatment, the possibility of exploiting innovative CANDPR process, integrating biofilm-based completely autotrophic nitrogen removal over nitrite (CANON) with denitrifying phosphorus removal (DPR) was evaluated to resolve the difficulty. Results revealed that the excellent NH₄⁺-N, PO₄^3--P and COD removal efficiencies of 96%, 96% and 91%, were achieved respectively under a high nitrogen loading rate (0.79 kg·m^-3·d^-1) without adding organic matters during 320 days operation. Promoting NO_x^--N recirculation demonstrated as an efficient strategy for further nutrient depletion, facilitating the enhanced NO₃^--N removal to 100% with the considerably high P-uptake performance. Batch tests confirmed that denitrifying phosphorus accumulating organisms (DPAOs) using NO₃^--N as electron acceptors accounting for 68% in total PAOs. Dechloromonas was identified as dominating genus in DPR, while Nitrosomonas (1.31%), Candidatus_Kuenenia (5.53%) and Candidatus_Brocadia (1.77%) contributed to the desirable nitrogen removal, indicating that cooperative consortia of DPAOs, AOB and AnAOB were harvested during long-term operation. The CANDPR process was verified to be energy-saving and treatment-reliable for renovating of existing plants.

Using pH as a single indicator for evaluating/controlling nitritation systems under influence of major operational parameters

This study focused on using pH as a single indicator to evaluate/control the performance of the nitritation system under the influence of three major operational parameters, and a total of fifteen batch tests were conducted. Results indicated that there were important interactions among different operational parameters and pH in the nitritation system; it was possible to propose the optimal nitritation operation scheme to compensate for negative changes in operational parameters. The optimal carbon to nitrogen (C/N) ratio was kept at 2.0 to ensure efficient removal of ammonium. The reaction time was the lowest (150 min) with the temperature = 20 °C, C/N = 0, and sludge/water ratio = 1:1. However, the C/N ratio could be adjusted to close to zero by reducing the temperature to about 10 °C, weakening the heterotrophic bacteria, and supplying sufficient biomass. The C/N ratio and sludge/water ratio could also be set at 4.0 and 1:3 respectively to deal with the impact of low temperature and organic matter. Results of this study might be useful to explain the optimal conditions and process control schemes with pH as a single indicator.

Biodegradable organic matter-containing ammonium wastewater treatment through simultaneous partial nitritation, anammox, denitrification and COD oxidization process

For both nitrogen and COD removal from biodegradable organic matter (BOM)-containing ammonium wastewater, the simultaneous partial nitritation, anammox, denitrification and COD oxidization (SNADCO) process is a promising solution. In this study, with the stable influent ammonium concentration of 250.0 mg/L (nitrogen loading rate of 0.5 kg/m³/d) and the variation of influent COD/NH₄⁺-N (C/N) ratio from 0.0 to 1.6, the performance of the SNADCO process in a one-stage carrier-packing airlift reactor with continuous mode was investigated for the first time. The results showed that until the C/N ratio of 0.8, both the well nitrogen and COD removal targets could be reached. Mass balance calculations indicated that the average nitrogen removal efficiency (NRE) of 80.9% achieved at the C/N ratio of 0.8 were due to both the anammox and denitrification pathways. Correspondingly, the achieved average COD removal efficiency of 94.6% was attributed to both the denitrification and COD oxidization pathways. Based on the specific sludge activity tests and Fluorescence in Situ Hybridization observation, anammox and denitrification bacteria were mainly distributed in the biofilm sludge, while ammonium oxidizing bacteria and ordinary heterotrophic organisms were mainly in the suspended sludge. At the C/N ratio of 1.6, the washout of suspended sludge became serious while the biofilm sludge was well retained, resulting in inefficient nitritation and a subsequent decrease in NRE. The microbial interaction analysis provided a clear explanation of the performance change of the SNADCO process under different C/N ratios. This research enriches the knowledge of the SNADCO process in BOM-containing ammonium wastewater treatment.

Insight into the impacts of organics on anammox and their potential linking to system performance of sewage partial nitrification-anammox (PN/A): A critical review

Partial nitrification-anammox (PN/A) is an energy-efficient process for nitrogen removal from sewage. The influent organics of sewage is usually pre-removed, reducing the risk for enriching anammox bacteria (AnAOB). However, recent studies demonstrate that optimum influent organics could improve nitrogen removal and operational stability of PN/A. Thus, the impact of organics on PN/A-based process should not be overlooked. In this review, the complicated impacts of organics-containing influent on anammox and their linking to apply PN/A are discussed. Firstly, the effect of organics on AnAOB metabolism and the competition relationship between AnAOB and heterotrophic bacteria are summarized. Secondly, the combined effects of influent organics and operational strategies on PN/A-based process were reviewed. Thirdly, how to control influent organics in the real application of PN/A were discussed. Lastly, recent development of the PN/A-based process combined with denitrification were reviewed. Overall, influent organics could be an essential factor for successful application of sewage PN/A.

Integrated leachate management approach incorporating nutrient recovery and removal

This manuscript presents an integrated management scheme for leachate which employed struvite precipitation to recover ammonia nitrogen and phosphorus, aerobic granular sludge process for carbon oxidation (in the form of BOD and sCOD) and single stage anaerobic ammonia oxidation (ANAMMOX) for nitrogen management. The influent fed to the integrated treatment scheme was a mixture of anaerobic digester centrate and real leachate in 4:1 ratio. Almost 77% recovery of phosphorus and 25% removal of NH₄⁺-N were accomplished through struvite precipitation at an optimum pH of 9. High pH contributed to free ammonia loss during struvite precipitation experiments. In the aerobic granular sludge reactor overall, BOD₅, COD and NH₄⁺-N removal percentages were 74%, 45% and 35% and in the PN/A reactor, overall 35% removal of total inorganic nitrogen (TIN) was observed. More than 80% BOD removal was recorded in the granular reactor with soluble COD (sCOD) removal fluctuating between 28 and 57% depending on the operational phase. High-throughput amplicon sequencing of 16S rRNA gene targeting V4 region revealed a dominance of phylum Planctomycetes, in the PN/A reactor system. Presence of Rhodobacteraceae, Xanthomonadaceae, Flavobacteriaceae in the granular biomass confirmed the defined redox zones inside mature granules indicating simultaneous removal of nitrogen (N) and organics in aerobic granular sludge technology. Exposing the synthetically cultured aerobic granules directly to the mixture of leachate and centrate unveiled an alteration in physical characteristics of granules; however, reactor operational data and microbial community analysis ascertain the effectiveness of the treatment scheme treating two urban waste-streams.

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.

Evaluation of anammox pathway recovery after high COD loading using water quality, molecular biology and isotope labelling analysis

Anaerobic ammonium oxidation (anammox) pathway is sensitive to organic matter, and its recovery requires reliable evidence regarding the dominance of anammox in N-removal. This study showed that the anammox process deteriorated, with N-removal efficiencies rapidly decreasing from 87.2 to 45.7% when reactors were exposed to COD shocks of 1.12, 2.24 and 3.36 g L^-1 (COD/N ratio 2, 4 and 6). Comprehensive assessments of water quality, microbial characteristics and isotope analysis were adopted to investigate anammox recovery. Operational performance took 8-20 days to recover; anammox relative abundance recovered after 20 days, based on the results of fluorescence in situ hybridisation and quantitative PCR; and the anammox pathway contributed to 80.0-91.5% of N-loss 40 days after COD shock terminated, based on the results of the isotope labelling experiment. Therefore, a complete recovery required 40 days. The isotope labelling method supplied a reliable reference for recovery assessment of anammox system in real-world applications.

Evaluation of Partial Nitritation/Anammox (PN/A) Process Performance and Microorganisms Community Composition under Different C/N Ratio

A one-stage partial nitritation/anammox (PN/A) process with intermittent aeration is possible under sidestream conditions, but implementation in a mainstream is a challenge due to increased Carbon/Nitrogen (C/N) ratios in domestic wastewater. This study investigated the effect of C/N ratios on process efficiency and the effect of narrowing non-aeration time on process improvement at high chemical oxygen demand (COD) load. An increase in TN removal efficiency was achieved in both series with gradual change of C/N ratio from 1 to 3, from 65.1% to 83.4% and 63.5% to 78% in 1st and 2nd series, respectively. However, at the same time, the ammonium utilization rate (AUR) value decreased with the increase in C/N ratio. At a high COD (C/N = 3) concentration, the process broke down and regained productivity after narrowing the non-aeration time in both series. Shifts in the system performance were also connected to adaptive changes in microbial community revealed by data obtained from 16S rRNA NGS (next-generation sequencing), which showed intensive growth of the bacteria with dominant heterotrophic metabolism and the decreasing ratio of autotrophic bacteria. The study shows that deammonification is applicable to the mainstream provided that the C/N ratio and the aeration/non-aeration time are optimized.

Effect of chemical oxygen demand load on the nitrification and microbial communities in activated sludge from an aerobic nitrifying reactor

In this study, we explored the effect of chemical oxygen demand (COD) load on the nitrification and microbial communities in activated sludge isolated from an aerobic nitrifying tank. The activated sludge was cultured in three different COD groups: L-COD, 200 mg/L; M-COD, 1200 mg/L; H-COD, 4200 mg/L. The results indicated that the COD exerts a negligible effect on the nitrogen removal ability within the first 24 h. However, the nitrification rate decreased with culture time; the ammonium degradation rates were found to be 80.26%, 57.56%, and 43.43% at 72 h in the three COD groups, respectively. These values correspond to decreases of 19.40%, 41.83%, and 51.48%, respectively, in relation to those observed at 24 h. The activated sludge in the different COD groups exhibited similar community compositions after 24 h, as assessed by Illumina high-throughput sequencing, while a significant difference in the relative abundances of some organisms occurred after 48 and 72 h. Proteobacteria was the main phylum, with a relative abundance of >51.45%. The genera Aridibacter, Paracoccus, Nitrospira, and Nitrosomonas were suppressed by COD load over time. This study may contribute to our knowledge about the nitrification ability and microbial communities in activated sludge at different COD load levels.

Partial denitrification providing nitrite: Opportunities of extending application for anammox

Anaerobic ammonium oxidation (anammox) has been extensively investigated for cost-efficient nitrogen removal from wastewater. However, the major issues of nitrate (NO₃^--N) residue and instability in the current combination of nitritation and anammox process necessitates being addressed efficiently. The recently proposed partial-denitrification (PD), terminating NO₃^--N reduction to nitrite (NO₂^--N), has been regarded as a promising alternative of NO₂^--N supplying for anammox bacteria. Given the engineering practices, the steadily high NO₂^--N production, alleviating organic inhibition, and reducing greenhouse gas of PD process offers a viable and efficient approach for anammox implementation. Moreover, it allows for the extending applications of anammox process due to the NO₃^--N removal availability. Here we comprehensively review the important new outcomes and discuss the emerging applications of PD-based anammox including the process development, mechanism understanding, and future trends. Significant greater stability and enhanced nitrogen removal efficiency have been demonstrated in the novel integrations of PD and anammox process, indicating a broad perspective in dealing with the mainstream municipal sewage, ammonia-rich streams, and industrial NO₃^--N contained wastewater. Furthermore, researches are still needed for the predictable and controllable strategies, along with the detailed microbiological information in future study. Overall, the achievement of PD process provides unique opportunity catalyzing the engineering applications of energy-efficient and environmental-friendly wastewater treatment via anammox technology.

Autotrophic nitrogen removal in an integrated fixed-biofilm activated sludge (IFAS) reactor: Anammox bacteria enriched in the flocs have been overlooked

In this study, an autotrophic nitrogen removal process was established using an integrated fixed-biofilm activated sludge (IFAS) reactor treated with high ammonium wastewater. A nitrogen removal rate (NRR) of 2.78 kg N/(m³·d) was obtained during the 206-day operation. Moreover, during the stable period, the large flocs (D > 0.2 mm) had a significantly higher abundance of anammox bacteria than the small flocs (D < 0.2 mm) and biofilm, resulting in 51% of the anammox bacteria being located in the flocs. The result indicates that anammox bacteria can be enriched in the flocs and in the biofilm, which has been rarely reported for IFAS reactors. In addition, the large flocs are likely formed through biofilm detachment since the microbial community was similar for the two kinds of biomass. Overall, the role of flocs in IFAS reactors are complicated and their contribution to the anammox reaction have been overlooked thus far.

A critical review of one-stage anammox processes for treating industrial wastewater: Optimization strategies based on key functional microorganisms

The one-stage nitritation/anammox (anaerobic ammonium oxidation) process is an energy-saving technology, which has been successfully developed and widely applied to treat industrial wastewaters. For the one-stage nitritation/anammox process, key functional microbes generally include anaerobic ammonia oxidation bacteria (AnAOB), ammonia-oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and heterotrophic bacteria (HB). Cooperation and competition among the key functional microbes are critical to the stability and performance of anammox process. Based upon key functional microorganisms, this review summarizes and discusses the optimized strategies that promote the operation of one-stage nitritation/anammox process. In particular, the review focuses on strategies related to: (1) the retention of anammox biomass through granular sludge or biofilm, (2) the balanced relationship between AOB and AnAOB, (3) the NOB suppression and (4) the HB management by controlling the influent organic matter. In addition, the review proposes further research to address the existing challenges.

The role of COD/N ratio on the start-up performance and microbial mechanism of an upflow microaerobic reactor treating piggery wastewater

This study investigated the role of COD/N ratio on the start-up and performance of an upflow microaerobic sludge reactor (UMSR) treating piggery wastewater at 0.5 mgO₂/L. At high COD/N ratio (6.24 and 4.52), results showed that the competition for oxygen between ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and heterotrophic bacteria limited the removal of nitrogen. Nitrogen removal efficiency was below 40% in both scenarios. Decreasing the influent COD/N ratio to 0.88 allowed achieving high removal efficiencies for COD (∼75%) and nitrogen (∼85%) due to the lower oxygen consumption for COD mineralization. Molecular biology techniques showed that nitrogen conversion at a COD/N ratio 0.88 was dominated by the anammox pathway and that Candidatus Brocadia sp. was the most important anammox bacteria in the reactor with a relative abundance of 58.5% among the anammox bacteria. Molecular techniques also showed that Nitrosomonas spp. was the major ammonia-oxidiser bacteria (relative abundance of 86.3%) and that denitrification via NO₃^- and NO₂^- also contributed to remove nitrogen from the system.

Achieving mainstream nitrogen removal through simultaneous partial nitrification, anammox and denitrification process in an integrated fixed film activated sludge reactor

The anaerobic ammonium oxidation (anammox) is becoming a critical technology for energy neutral in mainstream wastewater treatment. However, the presence of chemical oxygen demanding in influent would result in a poor nitrogen removal efficiency during the deammonification process. In this study, the simultaneous partial nitrification, anammox and denitrification process (SNAD) for mainstream nitrogen removal was investigated in an integrated fixed film activated sludge (IFAS) reactor. SNAD-IFAS process achieved a total nitrogen (TN) removal efficiency of 72 ± 2% and an average COD removal efficiency was 88%. The optimum COD/N ratio for mainstream wastewater treatment was 1.2 ± 0.2. Illumina sequencing analysis and activity tests showed that anammox and denitrifying bacteria were the dominant nitrogen removal microorganism in the biofilm and the high COD/N ratios (≥2.0) leaded to the proliferation of heterotrophic bacteria (Hydrogenophaga) and nitrite-oxidizing bacteria (Nitrospira) in the suspended sludge. Network analysis confirmed that anammox bacteria (Candidatus Kuenenia) could survive in organic matter environment due to that anammox bacteria displayed significant co-occurrence through positive correlations with some heterotrophic bacteria (Limnobacter) which could protect anammox bacteria from hostile environments. Overall, the results of this study provided more comprehensive information regarding the community composition and assemblies in SNAD-IFAS process for mainstream nitrogen removal.

Start-up of the completely autotrophic nitrogen removal over nitrite process with a submerged aerated biological filter and the effect of inorganic carbon on nitrogen removal and microbial activity

Good start-up and performance are essential for the completely autotrophic nitrogen removal over nitrite (CANON) process, and inorganic carbon (IC) is also important for this process. In this study, a lab-scale submerged aerated biological filter (SABF) was adopted for the CANON process. A 16S rRNA gene high-throughput sequencing analysis showed that the phyla Proteobacteria and Planctomycetes were the dominant microorganisms and that the genus Candidatus Brocadia functioned as the nitrogen remover. The effect of IC on the nitrogen removal was analyzed. The results showed that the optimum concentration ratio of IC to nitrogen (IC/N) was 1.2, which produced the highest average ammonium nitrogen removal rate (ANR) and total nitrogen removal rate (TNR) values of 95.5% and 80.3%, respectively. The average AOB and AnAOB activities were 2.45 mg·L^-1·h^-1 and 3.57 mg·L^-1·h^-1, respectively. This research could promote the nitrogen removal ability of the CANON process with a SABF in the future.

Effect of inorganic carbon concentration on the stability and nitrite-oxidizing bacteria community structure of the CANON process in a membrane bioreactor

In the completely autotrophic nitrogen removal over nitrite (CANON) process, the nitrite-oxidizing bacteria (NOB) should be effectively suppressed or thoroughly washed out. In this study, the nitrate production and the structure of NOB community under different inorganic carbon (IC) concentrations were investigated using denaturing gradient gel electrophoresis (DGGE) in a membrane bioreactor (MBR). Results showed that IC decrease correspondingly lowered the nitrogen removal, and simultaneously induced the nitrate production by NOB. DGGE results indicated the IC deficit led to the biodiversity increasing of both Nitrobacter-like NOB and Nitrospira-like NOB. An equation fitted between the ratio of nitrate production to ammonia consumption ([Formula: see text]) and the ratio of influent IC to ammonia concentration ([Formula: see text]) indicated the influent [Formula: see text] should be controlled between 1.6 and 2.3 to ensure the stable operation of the CANON process. A small amount addition of organic material could be used as an effective strategy to suppress NOB when the [Formula: see text] ratio was not appropriate.

Nitrogen removal capacity and bacterial community dynamics of a Canon biofilter system at different organic matter concentrations

Three Canon bench-scale bioreactors with a volume of 2 L operating in parallel were configured as submerged biofilters. In the present study we investigated the effects of a high ammonium concentration (320 mgNH₄⁺· L^-1) and different concentrations of organic matter (0, 100 and 400 mgCOD·L^-1) on the nitrogen removal capacity and the bacterial community structure. After 60 days, the Canon biofilters operated properly under concentrations of 0 and 100 mgCOD·L^-1 of organic matter, with nitrogen removal efficiencies up to 85%. However, a higher concentration of organic matter (400 mgCOD·L^-1) produced a partial inhibition of nitrogen removal (68.1% efficiency). The addition of higher concentrations of organic matter a modified the bacterial community structure in the Canon biofilter, increasing the proliferation of heterotrophic bacteria related to the genera of Thauera, Longilinea, Ornatilinea, Thermomarinilinea, unclassified Chlorobiales and Denitratisoma. However, heterotrophic bacteria co-exist with Nitrosomonas and Candidatus Scalindua. Thus, our study confirms the co-existence of different microbial activities (AOB, Anammox and denitrification) and the adaptation of a fixed-biofilm system to different concentrations of organic matter.

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.

Efficient simultaneous partial nitrification, anammox and denitrification (SNAD) system equipped with a real-time dissolved oxygen (DO) intelligent control system and microbial community shifts of different substrate concentrations

Simultaneous partial nitrification, anammox and denitrification (SNAD) process was studied in a sequencing batch biofilm reactor (SBBR) fed with synthetic wastewater in a range of 2200 mgN/L ∼ 50 mgN/L. Important was an external real-time precision dissolved oxygen (DO) intelligent control system that consisted of feed forward control system and feedback control system. This DO control system permitted close control of oxygen supply according to influent concentration, effluent quality and other environmental factors in the reactor. In this study the operation was divided into six phases according to influent nitrogen applied. SNAD system was successfully set up after adding COD into a CANON system. And the presence of COD enabled the survival of denitrifiers, and made Thauera and Pseudomonas predominant as functional denitrifiers in this system. Denaturing gradient gel electrophoresis (DGGE), fluorescence in situ hybridization (FISH) and 16S rRNA amplicon pyrosequencing were used to analyze the microbial variations of different substrate concentrations. Results indicated that the relative population of ammonia oxidizing bacteria (AOB) members decreased when influent ammonia concentration decreased from 2200 mg/L to 50 mg/L, while no dramatic drop of the percent of anammox bacteria was seen. And Nitrosomonas europaea was the predominant AOB in SNAD system treating sewage, while Candidatus Brocadia was the dominant anammox bacteria.

Applying fermentation liquid of food waste as carbon source to a pilot-scale anoxic/oxic-membrane bioreactor for enhancing nitrogen removal: Microbial communities and membrane fouling behaviour

Fermentation liquid of food waste (FLFW) was applied as an external carbon source in a pilot-scale anoxic/oxic-membrane bioreactor (A/O-MBR) system to enhance nitrogen removal for treating low COD/TN ratio domestic wastewater. Results showed that, with the FLFW addition, total nitrogen removal increased from lower than 20% to 44-67% during the 150days of operation. The bacterial metabolic activities were obviously enhanced, and the significant change in microbial community structure promoted pollutants removal and favored membrane fouling mitigation. By monitoring transmembrane pressure and characterizing typical membrane foulants, such as extracellular polymeric substances (EPS), dissolved organic matter (DOM), and inorganics and biopolymers in the cake layer, it was confirmed that FLFW addition did not bring about any additional accumulation of membrane foulants, acceleration of fouling rate, or obvious irreversible membrane fouling in the whole operation period. Therefore, FLFW is a promising alternative carbon source to enhance nitrogen removal for the A/O-MBR system.

Ammonia nitrogen removal and recovery from acetylene purification wastewater by air stripping

Ammonia nitrogen (NH₄-N) contaminated wastewater has posed a great threat to the safety of water resources. In this study, air stripping was employed to remove and recover NH₄-N from acetylene purification wastewater (APW) in a polyvinylchloride manufacturing plant. Investigated parameters were initial APW pH, air flow rate, APW temperature and stripping time. The NH₄-N removal by air stripping has been modeled and the overall volumetric mass transfer coefficient (K_La) of the stripping process has been calculated from the model equation obtained. In addition, the ability of H₂SO₄ solution to absorb the NH₃ stripped was also investigated. The results indicated that under the experimental conditions, the APW temperature and its initial pH had significant effects on the NH₄-N removal efficiency and the K_La, while the effects of other factors were relatively minor. The removal efficiency and residual concentration of NH₄-N were about 91% and 12 mg/L, respectively, at the optimal operating conditions of initial APW pH of 12.0, air flow rate of 0.500 m³/(h·L), APW temperature of 60 °C and stripping time of 120 min. One volume of H₂SO₄ solution (0.2 mol/L) could absorb about 93% of the NH₃ stripped from 54 volumes of the APW.