Partial Nitritation Reactor Research Articles

Shortcut nitrification/partial nitritation start-up for reject water treatment in a SBR

For many wastewater treatment plants (WWTPs), side-stream treatment of reject water from digested sludge dewatering is a feasible opportunity to improve N-removal efficiency without costly plant expansion. Biological nitrogen removal over nitrite or combined partial nitritation (PN)-Anammox process has recently become a popular treatment method for such ammonium-rich streams. Shortcut nitrification and PN start-ups were successfully performed in a pilot-scale SBR treating real reject water. In all performed experiments, effective nitrate production inhibition occurred in less than 20 days due to operational conditions selection and without advanced control system. pH adjustment in the PN reactor allowed to achieve NO 2 -N /NH 4 -N ratio suitable for Anammox process (1.24±0.07).

Effect of short term external perturbations on bacterial ecology and activities in a partial nitritation and anammox reactor

This research investigated the short term effects of temperature changes (lasting 2–4weeks each) from 35±2°C to 21±2°C and 13±2°C and sulfide toxicity on partial nitrification-anammox (PN/A) system. Temperatures below 20°C and sulfide content as low as 5mgSL−1 affected both aerobic and anaerobic catabolic activities of ammonia oxidation and the expression of related functional gene markers. The activity of AOB was inversely correlated with ammonium monooxygenase (amoA) gene expression. In contrast, the activity of AMX bacteria was positively correlated with the expression of their hydrazine synthase (hzsA) gene. Although the overall activities of AMX bacteria decreased at lower temperatures, the AMX bacteria were still active at the low temperatures. The inverse correlation between amoA gene expressions and the corresponding AOB activities was surprising. 16S rDNA based high throughput amplicon sequencing revealed the dominance of Chloroflexi, Planctomycetes and Proteobacteria phyla the distribution of which changed with temperature changes.

Effect of the dissolved oxygen concentration on the N2O emission from an autotrophic partial nitritation reactor treating high-ammonium wastewater

A laboratory-scale sequencing batch reactor (SBR) fed with synthetic high-ammonium wastewater was operated for partial nitritation, and the effect of the dissolved oxygen (DO) concentration on the N2O emission was investigated. From a macroscopic viewpoint, as the DO concentration increased from 0.35 to 0.60 and 0.85 mg l−1, the N2O emission factor (the ratio between N2O nitrogen emitted and the influent total nitrogen) decreased from 2.35% ± 0.32% to 1.81% ± 0.16% and 0.57% ± 0.08%, respectively. When air was replaced with N2 for blowing, N2O emission was also observed, demonstrating the N2O production pathway of denitrification. A higher ammonia oxidation rate (AOR) led to a lower N2O emission rate, and the concentration of free nitrous acid (FNA) had no obviously effect on the N2O emission. From a microscopic viewpoint, nitrogen transformation inside sludge aggregates under different DO concentrations was investigated by using microelectrodes. It demonstrated that N2O production increased with decreasing DO concentration, and at lower DO concentrations (0.35 and 0.60 mg l−1) N2O production enhanced from denitrification pathway.

Optimized operational strategies based on maximum nitritation, stability, and nitrite accumulation potential in a continuous partial nitritation reactor

The relative nitritation rate (qAOB*), nitratation rate (qNOB*), and nitrite accumulation potential (NAP,qAOB*/qNOB*) were investigated to assess the operational conditions for stable and maximized nitritation in a continuous-stirred tank reactor (CSTR) with activated (flocculent) sludge. Novel stability ridge and pH optima curves were identified on a STAN-pH plane. The stability ridge divides the stable and unstable reaction regions, while the pH optima curve identifies optimal pH values for fastest nitritation at any desired STAN. Thus, the best operational pH for a desired STAN is found on the pH optima curve when it resides in the stable region; otherwise, the stability ridge itself indicates the best operational pH value. The locations of the stability ridge and pH optima are subject to the structure of the kinetic equation and parameter values. While the NAP decreases with an increase in DO, a necessary NAP for sufficient nitrite accumulation (e.g., NAP≥2) is still ensured unless STAN becomes very low (e.g., ≤40mgN/L). Consequently, desired nitritation performance can be achieved by optimizing both the sludge retention time and pH; a lower pH is essential to generate an anammox-suited feed. Modelling results were verified by treating a semi-synthetic sewage sludge digester effluent having ∼600mgTAN/L at 30°C and varying pH.

Effect of pH on nitrous oxide production and emissions from a partial nitritation reactor under oxygen-limited conditions

The effect of pH on nitrous oxide (N2O) emissions from a laboratory-scale partial nitritation sequencing batch reactor under oxygen-limited conditions was investigated from both macro- and microscopic viewpoints. During the aeration period of a single cycle, N2O emissions decreased when the initial pH increased from 7.5 to 8.5. By application of microelectrodes, N2O production was observed inside entire sludge aggregates, and it increased with decreasing pH from 8.5 to 7.0. At pH 8.0 and 8.5, N2O was mainly produced in the outer layer (<1000μm) of sludge aggregates, where nitritation mainly occurred. At pH 7.0 and 7.5, N2O production was mainly observed in the inner layer (>1000μm), where the dissolved oxygen was almost depleted, revealing that the dominant pathway here was denitrification. Under oxygen-limited conditions, a decrease in pH led to increased N2O emissions from denitrification pathway.

Non-Linear Data Reconciliation for a Partial Nitritation (SHARON) Reactor

This work demonstrates the usefulness of non-linear data reconciliation to evaluate available measurements and estimate unmeasured variables for a full-scale partial nitritation (SHARON) reactor for the treatment of wastewater with high ammonium concentrations. Despite a lack of measured data, the bilinear approach of formulating system constraints allowed to satisfy the requirements for data reconciliation and gross error detection, leading to a balanced data set and the estimation of unmeasured variables.

Identifying N2O formation and emissions from a full-scale partial nitritation reactor

In this study, N2O formation and emissions from a full-scale partial nitritation (SHARON) reactor were identified through a three-weeks monitoring campaign during which the off-gas was analysed for N2O, O2, CO2 and NO. The overall N2O emission was 3.7% of the incoming ammonium load. By fitting the N2O emission to a theoretical gas stripping profile, the N2O emissions could be assigned to aerobically formed N2O and N2O formed under anoxic conditions. This was further substantiated by liquid N2O measurements. Under standard operation, 70% of the N2O emission was attributed to anoxic N2O formation. Dedicated experiments revealed that low dissolved oxygen concentrations (<1.0 g O2·m−3) and longer anoxic periods resulted in an increased N2O emission. Minimising or avoiding anoxic conditions has the highest effect in lowering the N2O emissions. As an additional result, the use of the off-gas N2O concentration measurements to monitor the gas–liquid mass transfer rate coefficient (kLa) during dynamic reactor operation was demonstrated.

Two-step partial nitritation/Anammox process in granulation reactors: Start-up operation and microbial characterization

A two-stage Partial Nitritation (PN)/Anammox process was carried out at lab-scale conditions to treat reject water from a municipal WWTP. PN was achieved in a granular SBR obtaining an effluent with a NH4+–N/NO2−–N molar ratio around 1.0. The microbial characterization of this reactor revealed a predominance of Betaproteobacteria, with a member of Nitrosomonas as the main autotrophic ammonium oxidizing bacterium (AOB). Nitrite oxidizing bacteria (NOB) were under the detection limit of 16S rRNA gene pyrosequencing, indicating their effective inhibition. The effluent of the PN reactor was fed to an Anammox SBR where stable operation was achieved with a NH4+–N:NO2−–N:NO3−–N stoichiometry of 1:1.25:0.14. The deviation to the theoretical stoichiometry could be attributed to the presence of heterotrophic biomass in the Anammox reactor (mainly members of Chlorobi and Chloroflexi). Planctomycetes accounted for 7% of the global community, being members of Brocadia (1.4% of the total abundance) the main anaerobic ammonium oxidizer detected.

SHARON process as preliminary treatment of refinery wastewater with high organic carbon-to-nitrogen ratio

In this study, a partial nitritation reactor (SHARON, Single reactor for High activity Ammonium Removal Over Nitrite) was used to treat ammonium-rich (up to 620 mg N/L) petrochemical wastewater produced by the integrated gasification combined cycle (IGCC) and characterized also by a high organic carbon-to-nitrogen ratio (C/N, up to 1.1 gC/gN). The reactor was initially fed with a synthetic influent containing only NH4-N as substrate, then a preliminary acute toxicity test was used to assess the potential inhibiting effect of IGCC wastewater on SHARON biomass: the observed IC10, IC50, and IC90 (14.9, 54.5, and 200 mL/L, respectively) suggested a prudential operating strategy based on the gradual replacement of the synthetic medium with the IGCC wastewater. As the synthetic influent was replaced by the IGCC wastewater, the resulting influent alkalinity-to-NH4-N ratio (expressed as inorganic carbon-to-nitrogen molar ratio, Cinorg/N) influenced process performance in terms of NH4-N removal efficiency. Despite the high influent C/N ratio, when the reactor was fed only with the IGCC wastewater, the ammonium removal efficiency was as high as 53 ± 10%, the corresponding effluent NO2-N/NH4-N ratio was 1.14 ± 0.42 and nitrate production was low. The presence of the organic substrate allowed the development of heterotrophic bacteria, as indicated by the high dissolved organic carbon removal efficiency (80 ± 8%) and the low effluent C/N ratio (0.20 ± 0.04). Such reactor performance made the effluent suitable for its subsequent treatment by anammox (ANaerobic AMMonium OXidation), providing useful information about the applicability of the SHARON process for the preliminary treatment of IGCC wastewater and similar ammonium-rich industrial wastewaters with high C/N ratio.

Would a two-stage N-removal be a suitable technology to implement at full scale the use of anammox for sewage treatment?

Sewage treatment with anammox could be implemented through a two-step reactor system, where the first reactor would be devoted to partial nitritation. A process design was sketched including control loops. The control strategy regulates the flow-rate of the rich ammonium sidestream produced after dewatering the digested sludge, to keep the ammonium concentration at a set point in the partial nitritation reactor by DOsing the SIde Stream (DOSIS). A second control loop manages the ammonium concentration set point based on the measurement of the total nitrogen in the partial nitritation reactor. A mathematical model was developed to assess the amount of sidestream required. Even in the case of a strong diurnal variability, simulations show how the control strategy is correctly performing, demonstrating the potential of the proposed technology.

The Effect of Influent Characteristics and Operational Conditions over the Performance and Microbial Community Structure of Partial Nitritation Reactors

Nitrogen is a main contaminant of wastewater worldwide. Novel processes for nitrogen removal have been developed over the last several decades. One of these is the partial nitritation process. This process includes the oxidation of ammonium to nitrite without the generation of nitrate. The partial nitritation process has several advantages over traditional nitrification-denitrification processes for nitrogen removal from wastewaters. In addition, partial nitritation is required for anammox elimination of nitrogen from wastewater. Partial nitritation is affected by operational conditions and substances present in the influent, such as quinolone antibiotics. In this review, the impact that several operational conditions, such as temperature, pH, dissolved oxygen concentration, hydraulic retention time and solids retention time, have over the partial nitritation process is covered. The effect of quinolone antibiotics and other emerging contaminants are discussed. Finally, future perspectives for the partial nitritation process are commented upon.

Anoxic phases are the main N2O contributor in partial nitritation reactors treating high nitrogen loads with alternate aeration.

Partial nitritation (PN) reactors treating complex industrial wastewater can be operated by alternating anoxic-aerobic phases to promote heterotrophic denitrification via NO2(-). However, denitrification under stringent conditions can lead to high N2O production. In this study, the suitability of including anoxic phases in a PN-SBR treating real industrial wastewater was assessed in terms of process performance and N2O production. The PN-SBR was operated successfully and, when the HCO3(-):NH4(+) molar ratio was adjusted, produced a suitable effluent for a subsequent anammox reactor. 10-20% of the total influent nitrogen was removed. N2O production accounted for 3.6% of the NLR and took place mainly during the anoxic phases (60%). Specific denitrification batch tests demonstrated that, despite the availability of biodegradable COD, NO2(-) denitrification advanced at a faster rate than N2O denitrification, causing high N2O accumulation. Thus, the inclusion of anoxic phases should be avoided in PN reactors treating industrial wastewaters with high nitrogen loads.

Comparative performance of air-lift partial nitritation processes with attached growth and suspended growth without biomass retention

Partial nitritation is an essential first step in anaerobic ammonium oxidation. This study compared the performance of air-lift partial nitritation reactors with attached growth (AG) and suspended growth (SG) without biomass retention using ammonium-rich recirculated liquor produced from the dewatering of anaerobically digested sludge. The steady-state results showed that the AG can effectively retain ammonium-oxidizing bacteria (AOB) with high activity and allow minimizing biomass discharge (∼10 mg volatile suspended solids/L) in the effluent. The nitrogen loading (based on the total reactor volume) satisfying the effluent characteristics could be suggested to be 0.42 g N/L/d for the SG, and 0.76 g N/L/d for the AG, respectively. Compared with the SG, the AG achieved a higher ammonium loading rate (∼1.8 times), maximal ammonium oxidation activity (48 mg N/L-h based on liquid-phase volume) under a short hydraulic retention time (HRT) and a long solids retention time (SRT>80 d). The overall performance confirmed that AG is a promising configuration for partial nitritation in terms of the process stability, maximization of the AOB activity and minimization of the effluent biomass under a short HRT and high nitrogen loading rate.

Effect of pH and HNO2 concentration on the activity of ammonia-oxidizing bacteria in a partial nitritation reactor

Ammonia-oxidizing bacteria (AOB) are very sensitive to environmental conditions and wastewater treatment plant operational parameters. One of the most important factors affecting their activity is pH. Its effect is associated with: NH3/NH4(+) and HNO2/NO2(-) chemical equilibriums and biological reaction rates. The aim of this study was to quantify and model the effect of pH and free nitrous acid (FNA) concentration on the activity of AOB present in a lab-scale partial nitritation reactor. For this purpose, two sets of batch experiments were carried out using biomass from this reactor. Fluorescent in situ hybridization analysis showed that Nitrosomona eutropha and Nitrosomona europaea species were dominant in the partial nitritation reactor (>94%). The experimental results showed that FNA inhibits the AOB activity. This inhibition was properly modelled by the non-competitive inhibition function and the half inhibition constant value was determined as 1.32 mg HNO2-N L(-1). The optimal pH for these AOB was found to be in the range 7.4-7.8. The pH inhibitory effect was stronger at high pH values than at low pH values. Therefore, an asymmetric inhibition function was proposed to represent the pH effect on these bacteria. A combination of two sigmoidal functions was able to reproduce the experimental results obtained.

Modelling nitrous and nitric oxide emissions by autotrophic ammonia-oxidizing bacteria

The emission of greenhouse gases, such as N2O, from wastewater treatment plants is a matter of growing concern. Denitrification by ammonia-oxidizing bacteria (AOB) has been identified as the main N2O producing pathway. To estimate N2O emissions during biological nitrogen removal, reliable mathematical models are essential. In this work, a mathematical model for NO (a precursor for N2O formation) and N2O formation by AOB is presented. Based on mechanistic grounds, two possible reaction mechanisms for NO and N2O formation are distinguished, which differ in the origin of the reducing equivalents needed for denitrification by AOB. These two scenarios have been compared in a simulation study, assessing the influence of the aeration/stripping rate and the resulting dissolved oxygen (DO) concentration on the NO and N2O emission from a SHARON partial nitritation reactor. The study of the simulated model behaviour and its comparison with previously published experimental data serves in elucidating the true NO and N2O formation mechanism.

Simultaneous removal of TOC and TSS in swine wastewater using the partial nitritation process

AbstractBACKGROUND: Considering biological nitrogen removal, the partial nitritation connected with the anaerobic ammonium oxidation (anammox) process is a promising alternative for nitrogen elimination at high loading rates. The objective of the present study was to evaluate the establishment and operation of a partial nitritation process in an airlift reactor with simultaneous removal of total organic carbon and suspended solids using swine wastewater.RESULTS: The partial nitritation reactor was inoculated with a nitrifying sludge at 2.1 gTSS L−1 and fed with an UASB reactor effluent. High organic carbon loading rates, above 2 kgTOC m−3 d−1 have been shown to be potential inhibitors of the partial nitritation process due to competition between autotrophic and heterotrophic bacteria. In this study, the partial nitritation process was established using undiluted swine wastewater, with HRT of 24 h, 1.84 mgO2 L−1 (SD = 0.41) DO, loading rate of 1.14 gTOC L−1 d−1 and 0.91 gN‐NH3 L−1 d−1 for more than 100 consecutive days. At the same time, the system proved to be an effective tool in TOC and TSS removal, reaching 84.9% (SD = 9.3) and 83.1% (SD = 0.1), respectively.CONCLUSION: This result enhances partial nitritation application as a technology for high load nitrogen converting, and allows the possibility of connection with anammox reactors. Copyright © 2012 Society of Chemical Industry

Fast start-up of ANAMMOX reactor: Operational strategy and some characteristics as indicators of reactor performance

Fast start-up of anaerobic ammonium oxidation (ANAMMOX) reactor was investigated by inoculating the mixed sludge from a partial nitritation reactor and a low loaded ANAMMOX reactor. At room temperatures (24–30 °C) and without taking deoxygenated measures for preparing the influent, nitrogen removal rate (NRR) up to 2.0 kg/m 3/d on day 35 and 6.2 kg/m 3/d on day 91 was achieved, indicating successful rapid start-up of ANAMMOX reactor. Dissolved oxygen (DO) concentration of 0.30 mg/L inside the reactor did not impair the ANAMMOX performance, suggesting that there is no need to take deoxygenated measures for preparing the ANAMMOX influent. The pH, conductivity, effluent nitrate nitrogen concentration and sludge color were simple indicators of ANAMMOX performance.

Influence of the feeding regime on the start-up and operation of the autotrophic nitrogen removal process

The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a sustainable nitrogen removal technique for nitrogen-rich streams. A modelling and experimental study was performed to define optimal process conditions for the autotrophic nitrogen removal process. Special attention was given to the influence of feeding characteristicson the performance of both the partial nitritation reactor and the Anammox reactor. It was revealed that the feeding regime is an important factor in the successful start-up of the Anammox process. Nitrite concentration peaks at the beginning of a feeding period will lead to an unsuccessful start-up, while a slow input of nitrogen speeds up the process. Feeding regimes are less important in partial nitritation reactors since laboratory results show that slow or fast supply of influent does not influence the growth of ammonium oxidisers.

Performance analysis and optimization of autotrophic nitrogen removal in different reactor configurations: a modelling study

The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a new and sustainable nitrogen removal technique for nitrogen‐rich streams. A modelling study has been performed to define optimal process conditions (temperature, oxygen supply, pH and biomass retention) and to investigate the influence of chemical oxygen demand, nitrogen loading rate and hydraulic retention time on three alternative reactor configurations: a single oxygen‐limited partial nitritation reactor, a single Anammox reactor, and a combination of partial nitritation and Anammox in a single reactor. The model applied was compared to experimental data from the literature and gave good agreement for all three reactor configurations. The simulations revealed that a system with separated partial nitritation and Anammox offered a wider range of optimal process conditions than a one‐reactor system. The key factors in the successful operation of partial nitritation were found to be control of aeration, ammonium loading rate and temperature. Heterotrophs remained present in all three reactor systems and it was confirmed that interaction between heterotrophs and Anammox and between heterotrophs and ammonium oxidizers was possible.

Partial nitritation and anammox of a livestock manure digester liquor and analysis of its microbial community

A swim-bed reactor for partial nitritation with polymeric coagulant treatment and an UASB reactor for anammox were applied to the treatment of livestock manure digester liquor. The partial nitritation was maintained for 32 days under a 1.6 kg N/m(3)/d nitrogen loading rate (NLR) with an average conversion efficiency of 51%, and achieved 1.65 kg N/m(3)/d of the maximum nitrite production rate under 2.58 kg N/m(3)/d of NLR. Although 200 mg/L of TOC remained in the effluent of the partial nitritation reactor, the anammox nitrogen removal rate was not significantly decreased and a relatively high rate of 2.0 kg N/m(3)/d was obtained under a NLR of 2.2 kg N/m(3)/d. 16S rRNA gene analysis showed that Nitrosomonas and KSU-1 were dominant in the partial nitritation and anammox reactor, respectively. The results of this study demonstrated that the partial nitritation-anammox process has possibility of applying to the nitrogen removal of livestock manure digester liquor.