Single-stage Nitrogen Removal Research Articles

Intensifying single-stage denitrogen by a dissolved oxygen-differentiated airlift internal circulation reactor under organic matter stress: Nitrogen removal pathways and microbial interactions

Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH4+–N. During the operation, the COD/NH4+–N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1–2 and AR = 1.4–1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.

Effect of humic acid on the single-stage nitrogen removal using anammox and partial nitritation (SNAP) process: performance and bacterial communities

The present research investigated the effect of humic acid on nitrogen removal performance and microbial community structure in a single-stage nitrogen removal using anammox and partial nitrification (SNAP) reactor. The results showed that 576 mg·L−1 humic acid enhanced nitrogen removal efficiency maximally to 96% and nitrogen removal rate to 1.61 kgN·m−3·d−1. COD concentration (provided by humic acid) of 120–233 mg·L−1, the nitrogen removal rate (NRR) was 1.27 kgN·m−3·d−1. COD concentration (provided by humic acid) of 259–658 mg·L−1 enhanced the NRR above 1.5 kgN·m−3·d−1, and COD concentration increased to 691–1637 mg·L−1, the average NRR decreased to 1.45 kgN·m−3·d−1. The results indicated COD concentration of 691–1637 mg·L−1 has the strongest positive effect on the anammox reaction. The analysis of high throughput sequencing presented COD concentration of 500 mg·L−1 promoted the growth of Candidatus_brocadia, and 1500 mg·L−1 COD concentration improved Candidatus kuenenia growth. Functional genes from KEGG and COG database showed that the expressions of nitrate reductase and nitrite reductase were highly promoted with the increase of humic acid concentration, which proved the nitrification enhanced by humic acid. All findings in this study were inferred that humic acid enhanced nitrogen removal in SNAP reactor. This result will improve the practical and effective use of the SNAP process to treat landfill leachate in engineering application.

Startup of pilot-scale single-stage nitrogen removal using anammox and partial nitritation (SNAP) reactor for waste brine treatment using marine anammox bacteria

This study is the first to demonstrate the startup of a pilot-scale single-stage nitrogen removal using anammox and partial nitritation (SNAP) reactor utilizing marine anammox bacteria. A complete mixing type reactor, continuously fed with waste brine obtained from a natural gas plant (salinity 3%, NH4+-N 130-180mg/L) and having an effective volume of 2m3, achieved stable operation at temperatures of 20-30°C with a maximum nitrogen removal rate of 1.43kg-N/m3/day. During the startup process, along with a small amount of seed sludge, granular sludge was additionally inoculated as a biomass carrier for the enrichment of ammonia oxidizing bacteria (AOB), followed by the enrichment of anammox bacteria. A mesh screen equipped at the outlet of the reactor facilitated the successful sludge retention in the reactor. Analysis of bacterial community composition indicated that Candidatus Scalindua was successfully enriched in the pilot SNAP reactor. These methods for stable sludge retention in the reactor greatly contributed to the startup of the first pilot-scale SNAP reactor using marine anammox bacteria.

Nitrogen removal from landfill leachate by single-stage anammox and partial-nitritation process: effects of microaerobic condition on performance and microbial activities

Nitrogen levels in landfill leachate (LL) could potentially pollute water bodies and surrounding groundwater, when discharged untreated. Against this backdrop, pollutant removal from leachate generated at landfill sites is essential. However, a cost-efficient approach, which could concurrently remove various pollutants within LL via single-stage approach, and under microaerobic conditions, has not been fully explored. In this study, single-stage nitrogen removal using anammox and partial-nitritation (SNAP) process was proposed and employed to treat LL under microaerobic condition in an upflow sludge blanket. When reactor dissolved oxygen-(DO) of 0.2 mg/L was implemented along with nitrogen loading rate-(NLR) ranging 0.31-1.84 kg/m3·d, 99.5% NH4+-N, 94.3% TN and 31.04% chemical oxygen demand (COD) removals was concurrently achieved. Conversely, when DO was elevated to 0.6 mg/L, nitrogen removal was curtailed to <20%, NO2--N accumulation reached 98.68%, indicating inhibition of anammox bacterial (AmxB) activities. 16S-rRNA-high-throughput gene sequencing revealed ammonium oxidizing bacteria-[AOB] (Nitrosomonas and Sphingomonas), AmxB (Candidatus Kuenenia), heterotrophic denitrifiers-[HDB] (Comamonas, Dechloromonas), and COD degrading bacteria (Bellilinea, Ignavibacterium) as the dominant genera which coordinated synergistic activities to establish the SNAP process and led to the single-stage pollutants removal from the LL. Sludge morphological revealed by SEM and energy-dispersive X-ray spectroscopy indicated that reactor sludge comprised of granulated sludge, and was noticeably embedded in extracellular polymeric substances (EPS), an indication of a defense mechanism initiated by microbes against heavy metals toxicity. The SNAP process demonstrated a promising cost-efficient simultaneous nitrogen and carbon removal from LL.

Rapid start-up of single-stage nitrogen removal using anammox and partial nitritation (SNAP) process in a sequencing batch biofilm reactor (SBBR) inoculated with conventional activated sludge

The long initiation period of the single-stage nitrogen removal using the anammox and partial nitritation (SNAP) process is a major hindrance to its practical application. In this study, the SNAP process was initiated in a sequencing batch biofilm reactor (SBBR) inoculated with conventional activated sludge within 46 days when the ammonium removal efficiency (ARE) and total nitrogen removal efficiency (TNRE) reached 86.9% and 76.8%, respectively. After the 46 days, ARE of 93.7 ± 2.8% and TNRE 77.5 ± 2.3% were achieved. The rapid initiation of the SNAP process could be attributed to biomass retention provided by biofilm and regulation of parameters including dissolved oxygen (DO), pH, temperature, organic matter, inorganic carbon (IC), free ammonium (FA), and free nitrite acid (FNA). The microbial analysis suggested that microbial richness of biomass increased while the microbial diversity reduced during the initiation of the SNAP process. Nitrosomonas and Candidatus Brocadia were the main ammonium oxidizing bacteria (AOB) and anammox bacteria (AnAOB), respectively, and were found to be enriched. Nitrospira was the main nitrite oxidizing bacteria (NOB) and relative abundance of it was decreased. The heterotrophic denitrification established rapidly and then gradually declined during the start-up of the SNAP process.

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

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

Non-aerated single-stage nitrogen removal using a down-flow hanging sponge reactor as post-treatment for nitrogen-rich wastewater treatment

A laboratory-scale experiment is conducted to remove nitrogen from nitrogen-rich wastewater using a down-flow hanging sponge (DHS) reactor. Effluent from an anaerobic–aerobic system for treating synthetic natural rubber wastewater, which still contains high levels of ammonia, was used as nitrogen-rich wastewater. Experimental period was divided into four phases based whether a carbon source was fed to the DHS reactor. The highest nitrogen removal efficiency (59.5 ± 5.4%) was achieved during phase 4, when a sodium acetate solution was fed into bottom section of the DHS reactor. In the DHS reactor, the nitrification occurred in the upper and middle sections. Then, after adding the sodium acetate solution, denitrification occurred. The final chemical oxygen demand, ammonia, and total inorganic nitrogen concentrations in the DHS reactor effluent were 37 ± 24 mg/L, 34 ± 5 mgN/L, and 42 ± 8 mgN/L, respectively. These concentrations were sufficient to meet the effluent standards of the Vietnamese natural rubber industry, which are the strictest in South-East Asia. The dominant bacteria in the sludge retained by the reactor's sponge media were the nitrifying bacteria Nitrosovibrio (0.2%) and Nitrospira (0.2–0.3%), the denitrifying bacteria Hylemonella (1.0–13.7%), Pseudoxanthomonas (1.2–2.1%), and Amaricoccus (2.4–3.5%), and the anammox bacterium Candidatus Brocadia (0.1–0.2%). Significant amounts of the nitrogen-fixing bacterium Xanthobacter (11.2–14.8%) and the rubber-degrading bacterium Gordonia (11.0–28.6%) were also found in the DHS reactor. These bacteria were thus considered to be the key microbes for nitrogen removal in a DHS reactor fed with a carbon source for denitrification.

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

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

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

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

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

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

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.

Nitrogen removal from old landfill leachate with SNAP technology using biofix as a biomass carrier

Single-stage nitrogen removal using Anammox and partial nitritation (SNAP) is a novel technology developed in recent years for removing nitrogen. To evaluate the ability of SNAP technology to remove nitrogen in old landfill leachate under the conditions in Vietnam, we conducted a survey with 7 different nitrogen loading rates of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4kg-N/m(3)day and a concentration from 100 to 700mg-N/L. The operating conditions were as follows: DO at 1.0-5.3mg/L, HRT at 12h, and pH at 7.5-7.8. The biomass carrier was a biofix made from acrylic fiber. The maximum ammonium conversion and nitrogen removal efficiency were approximately 98% and 85%, respectively, at 1.2kg-N/m(3)day. In general, the nitrogen removal efficiency increased and stabilized at the end of each loading rate. The first step showed that SNAP could potentially be applied in real life for removing nitrogen from old landfill leachate.

Outcompeting nitrite-oxidizing bacteria in single-stage nitrogen removal in sewage treatment plants: A model-based study

This model-based study investigated the mechanisms and operational window for efficient repression of nitrite oxidizing bacteria (NOB) in an autotrophic nitrogen removal process. The operation of a continuous single-stage granular sludge process was simulated for nitrogen removal from pretreated sewage at 10 °C. The effects of the residual ammonium concentration were explicitly analyzed with the model. Competition for oxygen between ammonia-oxidizing bacteria (AOB) and NOB was found to be essential for NOB repression even when the suppression of nitrite oxidation is assisted by nitrite reduction by anammox (AMX). The nitrite half-saturation coefficient of NOB and AMX proved non-sensitive for the model output. The maximum specific growth rate of AMX bacteria proved a sensitive process parameter, because higher rates would provide a competitive advantage for AMX.

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

In this study, a lab-scale sequencing batch biofilm reactor (SBBR) was used to start up the single-stage nitrogen removal system using anammox and partial nitritation (SNAP) process seeding from surplus activated sludge. The volumetric nitrogen loading rate (vNLR) was firstly 0.075kgNm−3d−1 and then gradually increased to 0.60kgNm−3d−1. A maximal total nitrogen (TN) removal rate of 0.54kgNm−3d−1 was achieved by the SNAP process after 132days operation with NH4+-N and TN removal efficiency of 99.4% and 90.5%, respectively. This reactor may have applications for the SNAP process treating high strength ammonia wastewater. And dewatered surplus activated sludge was recommended as the seed sludge for engineering applications. The dominant bacterial strains were Xanthomonas campestris, Nitrosomonas europaea and Ignavibacterium album, corresponding to the percentage of 24%, 22% and 20%, respectively, based on the 16S rDNA amplicon pyrosequencing of the SNAP sludge.

Effects of Operational Conditions on Treatment Performances of Single-Stage Nitrogen Removal using Anammox and Partial Nitritation (SNAP) Process

Effects of Operational Conditions on Treatment Performances of Single-Stage Nitrogen Removal using Anammox and Partial Nitritation (SNAP) Process

Development of single-stage nitrogen removal using anammox and partial nitritation (SNAP) and its treatment performances

Single-stage Nitrogen removal using Anammox and Partial nitritation (SNAP) process was newly developed as an economical nitrogen removal process for ammonium rich wastewaters. The experimental studies for the evaluation of SNAP process were carried out using a novel biofilm reactor, in which hydrophilic net-type acryl fiber biomass carrier was applied. This SNAP reactor was operated under operational conditions of pH 7.5-7.7, 35 degrees C and DO 2-3 mg/L, and 60 to 80% of influent NH4-N was removed under loading rate of 0.48 kg-N/m3/d. Through the DNA analysis of the attached sludge, it was made clear that ammonium oxidizing bacteria (AOB) and anammox bacteria coexisted in the attach-immobilized sludge on the acryl fiber biomass carrier. Favorable conditions for the growth of anammox bacteria were created inside attach-immobilized nitrifying sludge. Two kinds of anammox bacteria and two kinds of AOB were detected in the SNAP sludge. Existence ratios of anammox and AOB were estimated to be 15% and 8.7%, respectively, based on the obtained clone numbers. This coexisting condition was confirmed by the FISH image of SNAP sludge and its confocal laser scanning microscope.

Characterization of Sludge from Single-Stage Nitrogen Removal Using Anammox and Partial Nitritation (SNAP)

Characterization of Sludge from Single-Stage Nitrogen Removal Using Anammox and Partial Nitritation (SNAP)

Single-Stage Nitrogen Removal Using Anammox and Partial Nitritation (SNAP) for Treatment of Synthetic Landfill Leachate

In the process named SNAP (Single-stage Nitrogen removal using Anammox and Partial Nitritation), influent ammonium was removed as nitrogen gas by the combination of two autotrophic steps, partial nitritation and anammox, in one unit process. The reactors were packed with acryl-resin fiber biomass carriers and gently aerated. The synthetic influent, simulating secondary-treated landfill leachate, contained ammonium concentrations of 240 mg-N/l and 500 mg-N/l for reactors named SN-2 and SN-3, respectively. Data from 300 days of SNAP operation using reactor SN-2 showed ammonium conversions of 47.7∼88.1% with nitrogen removal rates of 0.31∼0.45 kg-N/m3/d under various operational conditions. The best performance with loading rate of 0.6 kg-N/m3/d was obtained at 35°C, pH 7.8, and aeration rate of 0.10 vvm (volume per volume per minute), with 88.1% ammonium conversion and 78.5% nitrogen removal. The results of about 100 days of operation for reactor SN-3 confirmed the treatment capability of SNAP process, with about 80% nitrogen removal with loading rates up to 1.0 kg-N/m3/d. Some important characteristics of the SNAP process are discussed.

Combined nitrification-denitrification processes

Nitrification and denitrification have traditionally been regarded as essentially separate phenomena, carried out by different bacteria in segregated areas of soil, sediments, water or reactors. However, research in the 1980s and 1990s has established that nitrifiers and denitrifiers are not as metabolically fastidious as previously thought, and strict segregation is not necessary. Moreover, some bacteria are able to convert NH44 and other reduced nitrogen compounds to nitrogen gas and the gaseous nitrogen oxides in combined nitrification/denitrification processes. Such organisms are of interest for wastewater treatment for two opposing reasons. Firstly, the idea of single-stage nitrogen removal has obvious attractions for system design. Secondly, N2O is a serious pollutant, implicated in virtually all current environmental problems (e.g. acid rain, greenhouse effect, ozone depletion).