Single-stage Autotrophic Nitrogen Removal Research Articles

Dual inner circulation and multi-partition driving single-stage autotrophic nitrogen removal in a bioreactor

The single-stage autotrophic nitrogen removal (ANR) process is impeded by a long start-up cycle and unstable operation performance. In this study, an airlift inner-circulation partition bioreactor (AIPBR) was operated continuously for 215 days to explore methods of strengthening the performance and stable operation of the single-stage ANR system. AIPBR start-up period took around 38 days, the total nitrogen removal efficiency was > 85% on day 35. With the decrease of hydraulic retention time and the increase of aeration rate, the nitrogen removal rate increased to 0.85 ± 0.02 kg-N/m3/day. The sludge morphology gradually changed into dark-red floc-coupled granular sludge. Nitrosomonas (9.95%) and Candidatus Brocadia (6.41%) were dominant in the sludge. During long-term operation, AIPBR achieved the dual inner circulation of sewage and sludge and then formed effective dissolved oxygen and sludge partitions to provide a suitable growth environment for various functional bacteria, promote synergy between them, and strengthen the ANR performance.

Integrated self-forming dynamic membrane (SFDM) and membrane-aerated biofilm reactor (MABR) system enhanced single-stage autotrophic nitrogen removal

The membrane aerated biofilm reactor (MABR) is a novel bioreactor technology, facilitating single-stage autotrophic nitrogen removal. Two laboratory-scale MABRs equipped with non-woven fabrics were operated simultaneously without and with a self-forming dynamic membrane (SFDM) filtration module. After 87 days of operation (system start-up), the reactor incorporated with SFDM filtration showed better performance in terms of total nitrogen removal (>80%) and effluent suspended solid (less than1 mg/L) than the MABR in the up flow anaerobic sludge blanket (UASB) configuration (i.e., without SFDM). The incorporation of SFDM has the ability to retain more slow growing biomass (anammox) inside the reactor. Microbial characterization by 16S rRNA-based amplicon sequencing shows that the abundance and composition of microbial communities in two MABR systems were different, i.e., the genusRhodanobacterwas abundant in UASB-MABR, while Calorithrixwas dominant in SFDM-MABR. PCA-based statistical analysis demonstrated a positive association between reactor performance, membrane characteristics and microbial communities.

Utilization of three-layered polyvinyl alcohol gel cubes for treating low-strength ammonium wastewater in a single-stage autotrophic nitrogen removal process

This study examined the feasibility of using a three-layered polyvinyl alcohol (PVA) gel cube for low-strength ammonium wastewater (<50 mg-NH4+-N/L) treatment in a single reactor. The outer layer of this three-layered PVA gel cube was composed of immobilized nitrifying bacteria, while the inner layers were composed of anaerobic ammonium oxidation (anammox) bacteria. A single-stage autotrophic nitrogen removal (SANR) reactor containing these three-layered PVA gel cubes was operated at 35 °C for 197 days, with intermittent aeration. Although the activity of nitrite-oxidizing bacteria (NOB) was incompletely inhibited under a narrow range of dissolved oxygen (DO) concentrations (0.1–1.1 mg-O2/L), a nitrogen removal efficiency (NRE) of 71.9% was achieved at 35 °C. At this temperature, the high NRE was achieved due to the coexistence of anammox and denitrifying bacteria. After decreasing the temperature to 20 °C, the NRE was maintained at a similar level (69.8%) for 53 days. The change in the structure of the bacterial community was insignificant with decreasing temperature. The 16S rRNA high-throughput sequencing analysis revealed that Planctomycetes (46.8–53.4%) was the most abundant phylum, wherein anammox bacteria accounted for 45.4–51.9% of the relative biodiversity abundance. Candidatus Jettenia asiatica disappeared for the operation of 187 days, while Candidatus Brocadia sinica was abundant. After 220 days, the relative abundances of ammonium-oxidizing bacteria (AOB) and NOB doubled and tripled, respectively. The abundant AOB were Nitrosomonas aestuarii and Nitrosomonas ureae, while the dominant NOB was Nitrospira moscoviensis. Nitrate produced by undesirable NOB activity was converted to nitrite by Denitratisoma oestradiolicum, which led to the abundance of anammox bacteria.

Intelligent Control System Based on Artificial Neural Network Applied research in autotrophic nitrogen removal process

In view of the difficulty in controlling the stable operation of autotrophic nitrogen removal system, this study plans to design a DO intelligent control system based on artificial neural network control, which can intelligently and accurately control dissolved oxygen in liquid phase according to the water inflow and operation state of the system. Firstly, the autotrophic nitrogen removal system was constructed step by step, and the influence of dissolved oxygen with different concentrations was explored by using the characteristics of system microbes sensitive to dissolved oxygen. Then, the dissolved oxygen intelligent control system based on artificial neural network was developed. Finally, the operation mode of autotrophic nitrogen removal process optimized by the dissolved oxygen intelligent control system based on artificial neural network was explored and the key parameters of system operation were put forward. The single-stage autotrophic nitrogen removal system equipped with DO precise control system was tested by artificial simulated wastewater. Under various load conditions, the total nitrogen removal rate of the system was more than 86%, and the system was efficient and stable.

Achieving single-stage autotrophic nitrogen removal by composite membrane aerated biofilm with gel under two microbial entrapping patterns: experimental and modeling aspects.

Single-stage autotrophic nitrogen removal offers advantages of low energy and carbon consumptions. Based on previous work about a novel composite membrane aerated biofilm (CMAB), two microbial entrapping patterns (mixed and stratified patterns) were evaluated for their applicability to artificially regulate the spatial distribution of distinct microbial aggregates for single-stage autotrophic nitrogen removal. Experimental results showed that the stratified pattern caused little accumulation of NO2- and NO3-, which leads to a superior nitrogen removal performance compared with the mixed pattern. Candidatus Kuenenia was found to be the major anammox bacterium in the gel film of the mixed pattern and the outer film of the stratified pattern. In contrast, Nitrosomonas, as a representative genus of ammonia-oxidizing bacteria, was substantially enriched in the inner film of the stratified pattern and the gel film of the mixed pattern. Finally, modeling results further confirmed the advantages of the stratified pattern with respect to the formation of rational microbial and nutrient profiles in gel films. The ratio of partial nitrification and anammox film thicknesses should remain below 3:2 to obtain a high fraction of anammox bacteria and to avoid NO2- accumulation. Increasing O2 surface loading does not affect microbial profiles, but can greatly promote the TN removal performance only in the stratified pattern. Overall, the stratified pattern should be employed to achieve optimal microbial profiles and nitrogen removal efficiency.

Start-up Performance and Sludge Characteristics of Single-stage Autotrophic Nitrogen Removal System with Granular Sludge at Low Ammonia Nitrogen Concentration at Room Temperature

The start-up and stable operation of single-stage autotrophic nitrogen removal process under low ammonia nitrogen substrate at room temperature appears as the premise and basis for the application in municipal wastewater treatment. In this study, the PN/A (partial nitritation and ANAMMOX) granular sludge for long-term storage was inoculated into an air-lift bioreactor to investigate the nitrogen removal performance during the start-up of single-stage partial nitritation and ANAMMOX process under the following conditions:temperature at (23±2)℃, pH at 7.7-8.0. Synthetic wastewater with ammonia nitrogen concentration of 70 mg·L-1 was used as influent. By stepwise shortening hydraulic retention time (HRT) (1.1 h→0.9 h→0.7 h→0.5 h) and increasing ammonia nitrogen loading rate[1.53 kg·(m3·d)-1→1.87 kg·(m3·d)-1→2.40 kg·(m3·d)-1→3.36 kg·(m3·d)-1], the bioactivity as the synergy between the ammonia oxidizing bacteria (AOB) and anaerobic oxidizing bacteria (AMX) were gradually restored. After 95 d operation and regulation, the process was successfully established and the removal rate of NH4+-N and TN were 85% and 69%, respectively. According to the performance of sludge at each stage, the nitrite oxidizing bacteria (NOB) were selectively inhibited by controlling dissolved oxygen strictly. The average particle size gradually increased and finally was reached to 1.30 mm after the sludge was adapted to the environment. The profile of the mature autotrophic granular sludge was smooth and clear, SEM showed that the center of granular sludge formed a cavity with porous structure on the surface, the sludge morphology consisted mainly of cocci, with a small amount of bacilli and short bacilli. The major component of EPS in granular sludge was protein (81.48%) indicating that it had a good settling performance.

A novel method to treat old landfill leachate combining multi-stage biological contact oxidation (MBCO) and single-stage autotrophic nitrogen removal using anammox and partial nitrification (SNAP)

In this paper, combination of multi-stage biological contact oxidation (MBCO) and single-stage autotrophic nitrogen removal using anammox and partial nitrification (SNAP) was used to treat high concentration of chemical oxygen demand (COD) and ammonia nitrogen in landfill leachate. MBCO was optimized using response surface methodology (RSM), achieving 91.3% COD removal efficiency. For ammonium nitrogen, nitrogen removal rate (NRR) of 1.68 kg N/m3/d was obtained in 140 days. Since MBCO effluent contained 350 mg/L COD, bio-oxidized humic acid was used as the stimulant COD source in SNAP influent. As a result, refractory COD almost had no impact on nitrogen removal ability of SNAP reactor and 20% COD was removed. Besides, the bacteria community structure analysis also demonstrated that the bio-oxidized humic acid didn’t change the bacterium proportion obviously. This new combination provided landfill leachate treatment with an effective alternative.

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 172days of operation, a superior total nitrogen (TN) removal rate over 3.9kg N/(m3/day) was stable implemented at a fixed dissolved oxygen concentration of 1.9mg/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.

Core-shell structured poly(vinyl alcohol)/sodium alginate bead for single-stage autotrophic nitrogen removal

A core-shell structured poly(vinyl alcohol)/sodium alginate gel bead was fabricated and the thickness of the outer layer was controlled. Immobilized ammonia-oxidizing bacteria (AOB) and ANAMMOX bacteria in outer and inner parts of the beads, respectively, cooperate to perform single-stage autotrophic nitrogen removal (SANR). As a critical designing factor, oxygen penetration depth according to the oxygen concentration in bulk phase and nitrifying biomass concentration in the outer layer were examined to protect strictly anaerobic ANAMMOX bacteria from oxygen inhibition. Oxygen penetrated up to a depth of 2350±360μm with the lowest nitrifying biomass of 703mg-VSS/L at a dissolved oxygen concentration of 8mg/L. However, a thick shell layer of more than 3mm effectively protected the ANAMMOX bacteria from oxygen inhibition. The applicability of the core-shell structured gel bead for single-stage autotrophic nitrogen removal was validated in batch and continuous modes. A continuous bioreactor with a synthetic ammonia wastewater showed a maximum nitrogen removal efficiency of 80.4±1.20% with a total nitrogen loading rate of 590±12.1g-N/m3-d. Findings of this study suggest that start-up strategy of SANR using the core-shell structured gel bead can minimize the adaptation period without scarifying the ANAMMOX activity.

Effects of HRT on biological nitrogen removal in single-stage autotrophic process

An external circulation Sequencing Batch Reactor (ecSBR) was used to study the efficiency of nitrogen removal by autotrophic microbe. With gradually reducing the dissolved oxygen (DO) concentration from 1.2 mg/L to 0.04 mg/L, the single-stage autotrophic biological nitrogen removal (sABNR) process could be operated stably. After removing the aeration, the process could still stay sABNR stably, and the concentration of NH4+-N was 0.9 mg/L in effluent, the rate of nitrate (produced)/NH4+-N (removed) was in the range of 0.12–0.40. The results showed that the concentration of NH4+-N in effluent was 0.8, 0.8 and 9.9 mg/L with the hydraulic retention time (HRT) at 8 h, 6 h and 4 h respectively, the removal efficiency of ammonia were 98.2%, 98.1% and 73.6% respectively. The rate of nitrate (produced)/NH4+-N (consumed) was 0.05 at HRT 6 h, and the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were 169.7 and 129.7 g/m3/d, the removal efficiency of total nitrogen (TN) was 77.5%. In conclusion the optimal HRT was 6 h instead of 8 h or 4 h enough for ammonia removal without causing energy wastage.

Effects of HRT on biological nitrogen removal in single-stage autotrophic process

An external circulation Sequencing Batch Reactor (ecSBR) was used to study the efficiency of nitrogen removal by autotrophic microbe. With gradually reducing the dissolved oxygen (DO) concentration from 1.2 mg/L to 0.04 mg/L, the single-stage autotrophic biological nitrogen removal (sABNR) process could be operated stably. After removing the aeration, the process could still stay sABNR stably, and the concentration of NH4+-N was 0.9 mg/L in effluent, the rate of nitrate (produced)/NH4+-N (removed) was in the range of 0.12–0.40. The results showed that the concentration of NH4+-N in effluent was 0.8, 0.8 and 9.9 mg/L with the hydraulic retention time (HRT) at 8 h, 6 h and 4 h respectively, the removal efficiency of ammonia were 98.2%, 98.1% and 73.6% respectively. The rate of nitrate (produced)/NH4+-N (consumed) was 0.05 at HRT 6 h, and the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were 169.7 and 129.7 g/m3/d, the removal efficiency of total nitrogen (TN) was 77.5%. In conclusion the optimal HRT was 6 h instead of 8 h or 4 h enough for ammonia removal without causing energy wastage.

Effects of dissolved oxygen on microbial community of single-stage autotrophic nitrogen removal system treating simulating mature landfill leachate

The performance of four identical sequencing biofilm batch reactors (SBBR) for autotrophic nitrogen removal was investigated with 2000mg/L ammonia-containing mature landfill leachate at 30°C. The main objective of this study was to evaluate the effects of dissolved oxygen (DO) on the performance and microbial community of single-stage nitrogen removal using anammox and partial nitritation (SNAP) system. At an applied load of 0.5kgNm−3d−1, average total nitrogen removal efficiency (TNRE) above 90% was long-term achieved with an optimal DO concentration of 2.7mg/L. The microelectrode-measured profiles showed the microenvironments inside the biofilms. 16S ribosomal Ribonucleic Acid (rRNA) amplicon pyrosequencing and denaturing gradient gel electrophoresis (DGGE) were used to analyze the microbial variations of different DO concentrations and different positions inside one reactor.

A novel control strategy for single-stage autotrophic nitrogen removal in SBR

A novel feedforward–feedback control strategy was developed for complete autotrophic nitrogen removal in a sequencing batch reactor. The aim of the control system was to carry out the regulation of the process while keeping the system close to the optimal operation. The controller was designed based on a process model and then tested experimentally. The resulting batch-to-batch control strategy had the total nitrogen removal efficiency as controlled variable and the setting of the aeration mass flow controller as manipulated variable. Compared to manual operation mode (constant air supply), the controller resulted in a significant performance improvement: removal efficiency was kept at a stable high level in the presence of influent ammonium concentration disturbances, and the absolute deviation on removal efficiency was reduced by 40%. The successful validation of the controller in a lab-scale reactor is a promising result, which brings this control strategy one step closer to full-scale implementation.

Development of novel control strategies for single-stage autotrophic nitrogen removal: A process oriented approach

The autotrophic nitrogen removing granular sludge process is a novel and intensified process. However, its stable operation and control remain a challenging issue. In this contribution, a process oriented approach was used to develop, evaluate and benchmark novel control strategies to ensure stable operation and rejection of disturbances. Three novel control strategies were developed, evaluated, and benchmarked against each other: a feedforward control (control structure 1 – CS#1), a rule-based feedback control (CS#2), and a feedforward–feedback controller, in which the feedback loop updates the set point of the feedforward loop (CS#3). The CS#1 gave the best performance against disturbances in the ammonium concentration, whereas the CS#2 provided the best performance against disturbances in the organic carbon concentration and dynamic influent conditions. The CS#3 rejected both disturbances satisfactorily. Thus, the appropriate design will depend on the specific disturbances in the influent generated in the upstream units of the wastewater treatment plant.

Microbial community and population dynamics of single-stage autotrophic nitrogen removal for dilute wastewater at the benchmark oxygen rate supply

Microbial communities and their kinetic performance in a single-stage autotrophic nitrogen-removal filter at an optimal oxygen supply were examined to determine the presence and activity of denitrifiers, anaerobic ammonia-oxidizing (anammox), ammonia-oxidizing, and nitrite-oxidizing bacteria. To this end, different molecular biology techniques such as real-time quantitative polymerase chain reaction (qPCR) and biomarkers such as 16S rRNA revealed a diverse microbial community along the filter. It was important to survey the specific species of anammox bacteria using a newly designed Candidatus Brocadiafulgida (BF) specific primer, as well as Candidatus Brocadia anammoxidans (BA) and Candidatus Kuenenia stuttgartiensis (KS) specific primers. An unexpected finding was that the predominant anammox species switched from KS in concentrated wastewater to BA in dilute wastewaters. The Eckenfelder model of the NH3-N transformation along the filter was Se=S0 exp(-0.192D/L(2.3217)). These results provide a foundational understanding of the microbial structure and reaction kinetics in such systems.

Novel single-stage autotrophic nitrogen removal via co-immobilizing partial nitrifying and anammox biomass

In this study, we developed an effective strategy to achieve single-stage autotrophic nitrogen removal by co-immobilizing partial nitrifying and anaerobic ammonia oxidation (anammox) biomass. Batch experiments were carried out to determine the optimum dissolved oxygen concentration of 1.5mg/L, and the optimum biomass ratio of partial nitrifying biomass versus anammox biomass of 1:2. In continuous experiment, the total nitrogen removal rate reached 1.69gN/L/d (nitrogen loading rate up to 2.2gN/L/d). At the stable running stage, the TN average removal efficiency reached 77%. Scanning electron microscopy observations showed microorganisms greatly increased after 80days cultivating. FISH analysis indicated that most anammox cells agglomerated in groups and ammonia oxidizing bacteria formed a thick layer around anammox cells.

Efficient single-stage autotrophic nitrogen removal with dilute wastewater through oxygen supply control

Autotrophic nitrogen removal via ammonia oxidizing (AOB) and anaerobic ammonium oxidizing (anammox) bacteria was evaluated for treatment of a dilute 50mg/L ammonia-containing solution in a single-stage nitrogen-removal filter at 25°C. Important was an external oxygenation system that permitted close control and measurement of oxygen supply, a difficulty with the generally used diffused air systems. Hydraulic retention time (HRT) was reduced in steps from 15 to 1h. At 1h HRT, total nitrogen (TN) removals varied between 73% and 94%, the maximum being obtained with a benchmark oxygenation ratio of 0.75mol O2/mol ammonia fed. At higher ratios, nitrate was formed causing TN removal efficiency to decrease. With lower ratios, TN and ammonia removals decreased in proportion to the decrease in BOR. When operating at or below the BOR, nitrate formation equaled no more than 2% of the ammonia removed, a value much less than has previously been reported.

Rapid startup and high rate nitrogen removal from anaerobic sludge digester liquor using a SNAP process

In this study, a single-stage autotrophic nitrogen removal reactor, packed with a novel acrylic fiber biomass carrier material (Biofix), was applied for nitrogen removal from sludge digester liquor. For rapid start-up, conventional activated sludge was added to the reactor soon after the attachment of anammox biomass on the Biofix carriers, which allowed conventional activated sludge to form a protective layer of biofilm around the anammox biomass. The Nitrogen removal efficiency reached 75% within 1week at a nitrogen loading rate of 0.46 kg-N/m(3)/day for synthetic wastewater treatment. By the end of the synthetic wastewater treatment period, the maximum nitrogen removal rate had increased to 0.92 kg-N/m(3)/day at a nitrogen loading rate of 1.0 kg-N/m(3)/day. High nitrogen removal rate was also achieved during the actual raw digester liquor treatment with the highest nitrogen removal rate being 0.83 kg-N/m(3)/day at a nitrogen loading rate of 0.93 kg-N/m(3)/day. The thick biofilm on Biofix carriers allowed anammox bacteria to survive under high DO concentration of 5-6 mg/l resulting in stable and high nitrogen removal performance. FISH and CLSM analysis demonstrated that anammox bacteria coexisted and surrounded by ammonium oxidizing bacteria.

Feasibility of a membrane-aerated biofilm reactor to achieve single-stage autotrophic nitrogen removal based on Anammox

A laboratory-scale membrane-aerated biofilm bioreactor (MABR) equipped with non-woven fabrics support around the gas-permeable carbon tube was developed for single-stage autotrophic nitrogen removal based on partial nitrification and anaerobic ammonium oxidization. This reactor allowed air to be supplied through the microporous carbon tube wall to the biofilm that was supported by non-woven fabrics. The partial nitrification and consumption of dissolved oxygen occurred in the inner layer and Anammox in the anoxic outer layer of the non-woven fabrics, thus realizing autotrophic nitrogen removal in a single reactor. After 116 d of operation, the maximal nitrogen removal of 0.77 kg N m −3 d −1 at a volumetric ammonium loading rate of 0.87 kg N m −3 d −1 was achieved. The spatial profiles of the ammonia-oxidizing bacteria and Anammox bacteria were evaluated by fluorescence in situ hybridization. This study demonstrated that MABR was a very suitable experimental set-up for the operation of the single-stage autotrophic nitrogen removal process.