Nitrification Reactor Research Articles

Effect of lime-nitrogen application on N2O emission from an Andosol vegetable field

Lime-nitrogen (calcium cyanamide, CaCN2) is used as a nitrogenous fertilizer, pesticide, and herbicide. During the process of decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed. Therefore, lime-nitrogen application may mitigate nitrous oxide (N2O) emission from the soil. We conducted a field experiment to investigate the effect of lime-nitrogen on nitrification and N2O emission in fertilized soils, and a soil incubation experiment for further analysis of the effect of the lime-nitrogen. In a field experiment we compared four nitrogen (N) fertilizer treatments: CF (chemical fertilizer), LN100 (application of all N fertilizer as lime-nitrogen), LN50 (application of 50% of N as lime nitrogen and the remainder as chemical fertilizer), and CFD (chemical fertilizer with DCD). In a soil incubation experiment, we also studied two nitrogen treatments: CF and lime-nitrogen. Soil nitrification activity was lower in the LN100, LN50, and CFD plots than in the CF plot. The duration of this reduction in soil nitrification activity was longer in the LN100 plot than in the other plots. We found an apparent decrease in the N2O emission rate between 7 and 14 days after fertilization in the LN100, LN50, and CFD plots compared with that in the CF plot. This period of decreased N2O emission paralleled that when DCD was detected in the topsoil layers of the former three plots. Moreover, in the soil incubation experiment, cumulative N2O emission was significantly lower in the lime-nitrogen treatment than in the CF treatment, although the difference in cumulative N2O emission among the plots was not significant in the field experiment. Correlation analysis suggested that application of lime-nitrogen affects N2O emission by controlling both the first (ammonium to nitrite) and the second (nitrite to nitrate) soil nitrification reactions, whereas DCD blocks only the first nitrification reaction.

Improving Nutrient Removal While Reducing Energy Use at Three Swiss WWTPs Using Advanced Control

Aeration consumes about 60% of the total energy use of a wastewater treatment plant (WWTP) and therefore is a major contributor to its carbon footprint. Introducing advanced process control can help plants to reduce their carbon footprint and at the same time improve effluent quality through making available unused capacity for denitrification, if the ammonia concentration is below a certain set-point. Monitoring and control concepts are cost-saving alternatives to the extension of reactor volume. However, they also involve the risk of violation of the effluent limits due to measuring errors, unsuitable control concepts or inadequate implementation of the monitoring and control system. Dynamic simulation is a suitable tool to analyze the plant and to design tailored measuring and control systems. During this work, extensive data collection, modeling and full-scale implementation of aeration control algorithms were carried out at three conventional activated sludge plants with fixed pre-denitrification and nitrification reactor zones. Full-scale energy savings in the range of 16-20% could be achieved together with an increase of total nitrogen removal of 40%.

Molecular indicators of Nitrobacter spp. population and growth activity during an induced inhibition event in a bench scale nitrification reactor

The Nitrobacter spp. ribosomal RNA gene (rDNA) and transcript (rRNAt) abundance were quantified in a bench scale nitrification reactor during baseline periods of high nitrification efficiency and an intervening staged inhibition event. The transcript to gene ratio (rRNAt/rDNA) was highly sensitive to changes in the reactor nitrite oxidation rate. During high nitrification efficiency, the rRNAt/rDNA metric displayed a range from 0.68 to 2.01 with one-sided (α=0.10) lower and upper prediction intervals of 0.70 and 1.78, respectively. When nitrification was inhibited by disabling the reactor pH control system, this activity metric declined an order of magnitude to ∼0.05, well below the lower prediction interval reflecting high nitrification efficiency. The decline was rapid (2h) and preceded a significant drop in reactor nitrification performance, which occurred as ammonia accumulated. The rRNAt/rDNA ratio remained low (∼0.05) for several days after the pH control system was re-enabled at a setpoint of 8.0, which otherwise induced rapid oxidation of accumulated ammonia and produced high free ammonia concentrations. The timing of a subsequent increase in the rRNAt/rDNA ratio, which transiently exceeded the upper prediction interval established during the baseline period of high nitrification efficiency, was not coincidental with resumption of pH control at 7.2 that lowered free ammonia concentrations to non-inhibitory levels. Rather, nitrite oxidation resumed and the rRNAt/rDNA ratio increased only after oxidation of accumulated ammonia was complete, which was coincidental with reduced reactor oxygen demand. In summary, the Nitrobacter rRNAt/rDNA activity metric reflected timely and easily recognizable changes in nitrite oxidation activity, illustrating that molecular data can be used to diagnose poor biological wastewater treatment performance.

Monitoring the nitrification and identifying the endpoint of ammonium oxidation by using a novel system of titrimetry

Based on the structure of the hybrid respirometer previously developed in our group, a novel implementation for titrimetry was developed, in which two pH electrodes were installed at the inlet and outlet of the measuring cell. The software capable of digital filtering and titration time delay correction was developed in LabVIEW. The hardware and software of the titrimeter and the respirometer were integrated to construct a novel system of respirometry-titrimetry. The system was applied to monitor a batch nitrification process. The obtained profiles of oxygen uptake rate (OUR) and hydrogen ion production rate (HPR) are consistent with each other and agree with the principle of the biological nitrification reaction. According to the OUR and HPR measurements, the oxidized ammonium concentrations were estimated accurately. Furthermore, the endpoint of ammonium oxidation was identified with much higher sensitivity by the HPR measurement. The system could be potentially used for on-line monitoring of biochemical reactions occurring in any kind of bioreactors because its measuring cell is completely independent of the bioreactor.

Partial nitrification of sludge reject water using suspended and granular biomass

AbstractBACKGROUND: Partial nitrification–Anammox is a combined promising advanced biological process for the removal of nitrogen from wastewater, which allows important savings in energy consumption, sludge production, and organic carbon. Granular biomass appears to be an interesting alternative to conventional activated sludge, mainly because of its better settling properties. This study deals with the experimental results of a comparison between a conventional and a granular sequencing batch reactor (SBR) for the partial nitrification of reject water.RESULTS: After some days of operation, 30 days in the conventional SBR (system A) and 100 days in the granular SBR (system B), partial nitrification was achieved. Granular sludge showed much better settling properties than suspended biomass, with values of sludge volumetric index (SVI10) of 130 mL g−1 in system A and 38 mL g−1 in system B. Consequently, the solids concentration within the granular reactor was three times higher than for the conventional system while the concentration of solids in the effluent was 10 times higher in the conventional SBR. Morphology, microstructure and microbial populations in both systems were also studied.CONCLUSION: A partial nitrification process was successfully achieved in both systems, obtaining an effluent with a NO2−‐N/NH4+‐N ratio near 1, suitable for a following Anammox process. Granular biomass, mostly formed by round particles, showed better settling properties, leading to better sludge–effluent separation as well as higher biomass retention in the reactor. The granulation process does not affect bacterial populations, since they were the same in both systems. Copyright © 2011 Society of Chemical Industry

Nitrous Oxide Emissions from Wastewater Treatment and Water Reclamation Plants in Southern California

Nitrous oxide (N₂O) is a long-lived and potent greenhouse gas produced during microbial nitrification and denitrification. In developed countries, centralized water reclamation plants often use these processes for N removal before effluent is used for irrigation or discharged to surface water, thus making this treatment a potentially large source of N₂O in urban areas. In the arid but densely populated southwestern United States, water reclamation for irrigation is an important alternative to long-distance water importation. We measured N₂O concentrations and fluxes from several wastewater treatment processes in urban southern California. We found that N removal during water reclamation may lead to in situ N₂O emission rates that are three or more times greater than traditional treatment processes (C oxidation only). In the water reclamation plants tested, N₂O production was a greater percentage of total N removed (1.2%) than traditional treatment processes (C oxidation only) (0.4%). We also measured stable isotope ratios (δN and δO) of emitted N₂O and found distinct δN signatures of N₂O from denitrification (0.0 ± 4.0 ‰) and nitrification reactors (-24.5 ± 2.2 ‰), respectively. These isotope data confirm that both nitrification and denitrification contribute to N₂O emissions within the same treatment plant. Our estimates indicate that N₂O emissions from biological N removal for water reclamation may be several orders of magnitude greater than N₂O emissions from agricultural activities in highly urbanized southern California. Our results suggest that wastewater treatment that includes biological nitrogen removal can significantly increase urban N₂O emissions.

Modeling Nitrous Oxide Production during Biological Nitrogen Removal via Nitrification and Denitrification: Extensions to the General ASM Models

Nitrous oxide (N(2)O) can be formed during biological nitrogen (N) removal processes. In this work, a mathematical model is developed that describes N(2)O production and consumption during activated sludge nitrification and denitrification. The well-known ASM process models are extended to capture N(2)O dynamics during both nitrification and denitrification in biological N removal. Six additional processes and three additional reactants, all involved in known biochemical reactions, have been added. The validity and applicability of the model is demonstrated by comparing simulations with experimental data on N(2)O production from four different mixed culture nitrification and denitrification reactor study reports. Modeling results confirm that hydroxylamine oxidation by ammonium oxidizers (AOB) occurs 10 times slower when NO(2)(-) participates as final electron acceptor compared to the oxic pathway. Among the four denitrification steps, the last one (N(2)O reduction to N(2)) seems to be inhibited first when O(2) is present. Overall, N(2)O production can account for 0.1-25% of the consumed N in different nitrification and denitrification systems, which can be well simulated by the proposed model. In conclusion, we provide a modeling structure, which adequately captures N(2)O dynamics in autotrophic nitrification and heterotrophic denitrification driven biological N removal processes and which can form the basis for ongoing refinements.

A model to predict the effects of soil structure on denitrification and N 2O emission

► Dual porous model of soil that closely reproduces experimental water retention. ► Simplified to critical percolation path with hotspots positioned 10 μm or 100 μm away. ► Denitrification and nitrification assumed to occur in micro-porous hot-spot zones. ► A priori diffusion and kinetics reproduce experimental CO 2 , N 2 O and N 2 emissions. ► Model shows sensitivity of O 2 thresholds, rate coefficients and hotspot positions. A model of the void space of soil is presented, and used for the a priori biophysical simulation of denitrification. The model comprises a single critical percolation channel through a 5 cm stack of four unit cells of a dual-porous void structure. Together, the micro- and macro-porous structures closely replicate the full water retention characteristic of a sandy clay loam soil from the Woburn Experimental Farm operated by Rothamsted Research, UK. Between 1 and 10 micro-porous hot-spot zones of biological activity were positioned at equally spaced distances within 5 cm from the surface, and at either 10 μm or 100 μm from the critical percolation channel. Nitrification and denitrification reactions within the hotspots were assumed to follow Michaelis–Menten kinetics, with estimated values of rate coefficients. Estimates were also made of the threshold values of oxygen concentration below which the anaerobic processes would commence. The pore network was fully saturated following addition of an aqueous ‘amendment’ of nitrate and glucose which started the reactions, and which mirrored an established laboratory protocol. Diffusion coefficients for Fickian and Crank-Nicolson calculations were taken from the literature, and were corrected for the tortuosity of the micro-porosity. The model was used to show the amount of carbon dioxide, nitrous oxide and molecular nitrogen emerging from the simulated soil with time. Adjustment of the rate coefficient and oxygen threshold concentrations, within the context of a sensitivity analysis, gave emission curves in good agreement with previous experimental measurements. Positioning of the hot-spot zones away from the critical percolation path slowed the increase and decline in emission of the gases. The model and its parameters can now be used for modelling the effect of soil compaction and saturation on the emission of nitrous oxide.

Comparative study of free cyanide inhibition on nitrification and denitrification in batch and continuous flow systems

The differences of free cyanide inhibition on nitrification and denitrification responsible for nitrogen removal in an activated sludge process were investigated in both batch and continuous flow systems. In a batch system, free cyanide of 0.2 mg/L caused a distinct lag phase on nitrification in activated sludge, while denitrification was almost completely inhibited at 5.0 mg/L of free cyanide. However, the continuous exposure to the toxicity of free cyanide in a successive batch system progressively increased its toxicity, resulting in lowering the threshold level necessary to inhibit both nitrification and denitrification over time. Compared to the batch systems, the threshold level of nitrification and denitrification of the continuous flow systems were 100 and 20 times higher than that of the batch systems, and the threshold level of denitrification of the continuous flow system was 2 times higher than that of nitrification. Contrary to CN - removal efficiency of the continuous nitrification reactor being gradually decreased under higher CN - loading, the denitrification reactor provided a continuous CN - removal.

Sequencing batch biofilm reactor: from support design to reactor operation

The aim of this work was to improve the overall understanding of sequencing batch biofilm reactors (SBBRs) from support selection (biofilm formation) to reactor operation (carbon and nitrogen removal). Supports manufactured with different materials and geometries were tested in 2.5 L SBBRs and it was observed that biofilm accumulation was favoured on the supports that presented a higher internal surface area. The geometry of the supports and the hydrodynamic conditions established in the SBBRs seemed to play a more important role in biofilm formation than the thermodynamic interaction, expressed as free energy of adhesion (ΔG), between the support material and the biomass. The support that presented the highest biofilm accumulation per unit of surface area (DupUM) was used in a 28 L SBBR and it was observed that, along a typical SBBR cycle, time profiles of nitrogen compounds showed the typical behaviour of nitrification and denitrification reactions. During the fill phase (without aeration) acetate was simultaneously consumed in biomass growth and denitrification. Immediately after the beginning of the aeration phase (without influent addition), acetate was depleted from the liquid phase and stored as poly‐β‐hydroxybutyrate that was later on used in the growth of biomass, owing to the high oxygen concentration in the reactor.

Regime Shift and Microbial Dynamics in a Sequencing Batch Reactor for Nitrification and Anammox Treatment of Urine

The microbial population and physicochemical process parameters of a sequencing batch reactor for nitrogen removal from urine were monitored over a 1.5-year period. Microbial community fingerprinting (automated ribosomal intergenic spacer analysis), 16S rRNA gene sequencing, and quantitative PCR on nitrogen cycle functional groups were used to characterize the microbial population. The reactor combined nitrification (ammonium oxidation)/anammox with organoheterotrophic denitrification. The nitrogen elimination rate initially increased by 400%, followed by an extended period of performance degradation. This phase was characterized by accumulation of nitrite and nitrous oxide, reduced anammox activity, and a different but stable microbial community. Outwashing of anammox bacteria or their inhibition by oxygen or nitrite was insufficient to explain reactor behavior. Multiple lines of evidence, e.g., regime-shift analysis of chemical and physical parameters and cluster and ordination analysis of the microbial community, indicated that the system had experienced a rapid transition to a new stable state that led to the observed inferior process rates. The events in the reactor can thus be interpreted to be an ecological regime shift. Constrained ordination indicated that the pH set point controlling cycle duration, temperature, airflow rate, and the release of nitric and nitrous oxides controlled the primarily heterotrophic microbial community. We show that by combining chemical and physical measurements, microbial community analysis and ecological theory allowed extraction of useful information about the causes and dynamics of the observed process instability.

Ammonia‐oxidizing bacteria dominates over ammonia‐oxidizing archaea in a saline nitrification reactor under low DO and high nitrogen loading

A continuous nitrification reactor treating saline wastewater was operated for almost 1 year under low dissolved oxygen (DO) levels (0.15-0.5 mg/L) and high nitrogen loadings (0.26-0.52 kg-N/(m(3) day)) in four phases. The diversity and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were analyzed by cloning, terminal restriction fragment length polymorphism (T-RFLP) and quantitative polymerase chain reaction (qPCR). The results showed that there were only one dominant AOA species and one dominant AOB species in the reactor in all of the four experimental phases. The amoA gene of the dominant AOA only had a similarity of 89.3% with the cultured AOA species Nitrosopumilus maritimus SCM1. All of the AOB species detected in the reactor belong to Nitrosomonas genus and it was found that the AOB populations changed with the ammonium loadings and DO levels. The abundance of AOB in the reactor was ∼40 times larger than that of AOA, and the ratio of AOB to AOA increased significantly up to ∼2,000 to ∼4,000 with the increase of ammonium loading, indicating that AOB are much more competitive than AOA in high ammonium environments and probably AOA play a less important role than AOB in the nitrification reactors.

Analysis of the bacterial community in a laboratory-scale nitrification reactor and a wastewater treatment plant by 454-pyrosequencing

For full understanding of the microbial community in the wastewater treatment bioreactors, one of the feasible and effective ways is to investigate the massive genetic information contained in the activated sludge. In this study, high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in a laboratory-scale nitrification reactor and a full-scale wastewater treatment plant. In total, 27,458 and 26,906 effective sequence reads of the 16S rRNA gene were obtained from the Reactor and the wastewater treatment plant activated sludge samples respectively. The taxonomic complexities in the two samples were compared at phylum and genus levels. According to the pyrosequencing results, even for a laboratory-scale reactor as simple as that in this study, a small size clone library is far from enough to reflect the whole profile of the bacterial community. In addition, it was found that the commonly used informatics tool “RDP classifier” may drastically assign Nitrosomonas sequences into a wrong taxonomic unit resulting in underestimation of ammonia-oxidizing bacteria in the bioreactors. In this paper the reasons for this mistakenly assignment were analyzed and correction methods were proposed.

Energy efficiency in waste water treatments plants: Optimization of activated sludge process coupled with anaerobic digestion

This paper presents a study concerning the optimization of a Waste Water Treatment process. The process deals with carbon and nitrogen removal and includes activated sludge reactors coupled with an anaerobic digestion reactor. Nitrification and de-nitrification biochemical reactions are due to the biological activity of heterotrophic and autotrophic micro-organisms occurring inside the reactors. Rigorous Plant-Wide models that represent the main biochemical transformations have been constructed as per the CEIT approach [1]. The energy consumption for each Physical Unit Operation (P.U.O.) involved in the flow-sheet is evaluated and a full link is made between the biological activity and the electrical demand or production. Steady-state mathematical optimizations are then computed and the influence of primary settling efficiency on electrical autonomy is quantified and demonstrated. The ammonium recycling from digestion to activated sludge reactors is also demonstrated to be a limiting factor for the overall energy efficiency, as well as the C-substrate availability for denitrifying. Some conclusions are then drawn to improve the global electrical efficiency of the system.

Importance of the operating pH in maintaining the stability of anoxic ammonium oxidation (anammox) activity in moving bed biofilm reactors

Two bench-scale parallel moving bed biofilm reactors (MBBR) were operated to assess pH-associated anammox activity changes during long term treatment of anaerobically digested sludge centrate pre-treated in a suspended growth partial nitrification reactor. The pH was maintained at 6.5 in reactor R1, while it was allowed to vary naturally between 7.5 and 8.1 in reactor R2. At high nitrogen loads reactor R2 had a 61% lower volumetric specific nitrogen removal rate than reactor R1. The low pH and the associated low free ammonia (FA) concentrations were found to be critical to stable anammox activity in the MBBR. Nitrite enhanced the nitrogen removal rate in the conditions of low pH, all the way up to the investigated level of 50mg NO2-N/L. At low FA levels nitrite concentrations up to 250mg NO2-N/L did not cause inactivation of anammox consortia over a 2-days exposure time.

Development of long-term stable partial nitrification and subsequent anammox process

The partial nitrification reactor was successfully started up and operated stably for more than 250 days with a maximum nitrite production rate of 1.12 kg-N m −3 day −1. The important factors for successful partial nitrification were high ammonium loading rate (>1.0 kg-N m −3 day −1) and relatively high pH (ca. 8.0), giving high free ammonia concentrations (>10 mg NH 3-N L −1). In addition, the air flow rate must be controlled at the ratio of air flow rate to ammonium loading rate below 0.1 ( m air 3 day - 1 ) /(kg-N m −3 day −1). After the establishment of stable partial nitrification, the effluent NO 2 - -N / NH 4 + -N ratio and effluent NO 3 - -N concentration were 1.20 ± 0.33 and 1.2 ± 1.0 mg-N L −1, respectively, which was then fed into an granular-sludge anammox reactor. Consistent nitrogen removal was achieved for more than 250 days with a maximum nitrogen removal rate of 15.0 kg-TN m −3 day −1.

Impact of the addition of a compound fertilizer on the dissolution of carbonate rock tablets: A column experiment

Abstract The chemical weathering dynamics of carbonate and the C cycle are strongly influenced by anthropogenic perturbations such as agricultural fertilization. In this study, two columns (a control column and a fertilizer column) with carbonate rock tablets in the bottom of each were established to explore the impact of the addition of a compound fertilizer on the dissolution of carbonate rock tablets. The impacts were assessed from hydro-chemical analyses of the leachates from the two columns and comparison of the amount of dissolution of the carbonate rock tablets. The results showed that NH 4 + , free CO2, HCO 3 - , HPO 4 2 - and COD increased in the leachate after addition of the compound fertilizer, whereas the pH decreased. The pH decrease was attributed to the release of protons from the nitrification reaction. The amount of dissolution of limestone and dolomite tablets decreased as a result of the compound fertilizer application. Furthermore, the calculated results using Phreeqci software showed that the compound fertilizer reduced the saturation index of calcite and dolomite. Thus, the impact of a compound fertilizer, especially an ammonium fertilizer, on the budget of the CO2 sink cannot be disregarded on either a regional or a global scale.

Redistribution of wastewater alkalinity with a microbial fuel cell to support nitrification of reject water

In wastewater treatment plants, the reject water from the sludge treatment processes typically contains high ammonium concentrations, which constitute a significant internal nitrogen load in the plant. Often, a separate nitrification reactor is used to treat the reject water before it is fed back into the plant. The nitrification reaction consumes alkalinity, which has to be replenished by dosing e.g. NaOH or Ca(OH) 2. In this study, we investigated the use of a two-compartment microbial fuel cell (MFC) to redistribute alkalinity from influent wastewater to support nitrification of reject water. In an MFC, alkalinity is consumed in the anode compartment and produced in the cathode compartment. We use this phenomenon and the fact that the influent wastewater flow is many times larger than the reject water flow to transfer alkalinity from the influent wastewater to the reject water. In a laboratory-scale system, ammonium oxidation of synthetic reject water passed through the cathode chamber of an MFC, increased from 73.8 ± 8.9 mgN/L under open-circuit conditions to 160.1 ± 4.8 mgN/L when a current of 1.96 ± 0.37 mA (15.1 mA/L total MFC liquid volume) was flowing through the MFC. These results demonstrated the positive effect of an MFC on ammonium oxidation of alkalinity-limited reject water.

Factors affecting the treatment of reject water by the anammox process

Reject water from a municipal wastewater treatment plant was treated using a stirred tank anammox reactor after being treated by a partial nitrification reactor. The results indicated the variations in the influent NO 2 - -N to NH 4 + -N ratio had a negative effect on reactor performance, especially when the T–N concentrations were high. Influent total organic carbon concentrations greater than 50 mg/L were proven to have a serious effect on the nitrogen removal efficiencies of the anammox reactor. Observations by scanning electron microscope showed that the surface of the anammox granular sludge was covered by some materials, possibly the effluent SS contained in the partial nitrified reject water. Furthermore, the study of the bacterial composition of the anammox granular sludge showed that the anammox bacterium, Planctomycete KSU-1, was dominant, even during the inhibition phase.

High-rate partial nitrification treatment of reject water as a pretreatment for anaerobic ammonium oxidation (anammox)

In this study, a lab-scale swim-bed partial nitrification reactor was developed to treat ammonium-rich reject water to achieve an appropriate NO2--N/NH4+-N mixture that could serve as a pretreatment for anaerobic ammonium oxidation (anammox). Strictly controlling the DO concentration was adopted as the main operational strategy. In addition, the influent concentrations of inorganic carbon/ammonium (IC/NH4+) and alkalinity/ammonium (Alk/NH4+) that were approximately 0.8 and 4.8, respectively, were regarded as the suitable ratios for the steady and high-rate operation of the reactor in this study. When reject water that was not diluted was introduced to this system, the maximum nitrogen loading rate was 5.9kg-N/m3/day, the ammonium conversion rate was 3.1kg-N/m3/day, and the effluent NO2-N/(NO2-N+NO3-N) percentage ratio was over 99.9%. Furthermore, DNA analysis confirmed the existence of AOB, which was responsible for the stable performance that was achieved in the PN reactor.