Effluent Nitrite Concentrations Research Articles

A novel coupling process to replace the traditional multi-stage anammox process-sulfur autotrophic denitrification coupled anammox system.

A novel coupling process to replace the traditional multi-stage anammox process-sulfur autotrophic denitrification (SAD) coupled anaerobic ammonium oxidation (anammox) system was designed, which solved problems of nitrate produced in anammox process and low nitrate conversion rate caused by nitrite accumulation in SAD process. Different filter structures (SAD filter and anammox granular sludge) were investigated to further explore the excellent performance of the novel integrated reactor. The results of sequential batch experiments indicated that nitrite accumulation occurred during SAD, which inhibited the conversion of nitrate to dinitrogen gas. When SAD filter and anammox granular sludge were added to packed bed reactor simultaneously, the nitrate removal rate increased by 37.21% and effluent nitrite concentration decreased by 100% compared to that achieved using SAD. The stratified filter structure solved groove flow. Different proportion influence of SAD filter and anammox granular sludge on the stratified filter structure was evaluated. More suitable ratio of SAD filter to anammox granular sludge was 2:1. Proteobacteria (57.26%), Bacteroidetes (20.12%) and Chloroflexi (9.95%) were the main phyla. The dominant genera of denitrification functional bacteria were Thiobacillus (39.80%), Chlorobaculum (3.99%), norank_f_PHOs-HE36 (2.90%) and Ignavibacterium (2.64%). The dominant genus of anammox bacterium was Candidatus_Kuenenia (3.05%).

Stable nitrogen removal by anammox process after rapid temperature drops: Insights from metagenomics and metaproteomics

This study investigated the impacts of rapid temperature drops on anammox process performance and the metabolism of its core microbial populations through proteomic analysis. Over a 50-day period, the temperature of an up-flow granular bed anammox reactor was stepwise decreased from 35 °C to 15 °C and resulted in repeated transient increases in effluent nitrite concentrations. At 15 °C, a nitrogen removal rate of 2.71 ± 0.23 gN/(L·d) was maintained over 100 days operation. Total AnAOB population abundance (20.9%±4.9%) and AnAOB protein abundances (75.7% ± 3.3%) remained stable with decreased temperature. Key proteins of Ca. Brocadia for nitrogen metabolism, as well as for carbohydrate metabolism and primary metabolite biosynthesis were less expressed at 15 °C than 35 °C, while several proteins of heterotrophic Chloroflexi spp. involved in carbohydrate and metabolites metabolisms were expressed to a higher degree at 15 °C. Overall, metabolism of AnAOB responded at a higher degree to low temperatures than that of heterotrophs.

Return-Sludge Treatment with Endogenous Free Nitrous Acid Limits Nitrate Production and N2O Emission for Mainstream Partial Nitritation/Anammox.

Nitrite oxidizing bacteria (NOB) and nitrous oxide (N2O) hinder the development of mainstream partial nitritation/anammox. To overcome these, endogenous free ammonia (FA) and free nitrous acid (FNA), which can be produced in the sidestream, were used for return-sludge treatment for two integrated-film activated sludge reactors containing biomass in flocs and on carriers. The repeated exposure of biomass from one reactor to FA shocks had a limited impact on NOB suppression but inhibited anammox bacteria (AnAOB). In the other reactor, repeated FNA shocks to the separated flocs failed to limit the system's nitrate production since NOB activity was still high on the biofilms attached to the unexposed carriers. In contrast, the repeated FNA treatment of flocs and carriers favored aerobic ammonium-oxidizing bacteria (AerAOB) over NOB activity with AnAOB negligibly affected. It was further revealed that return-sludge treatment with higher FNA levels led to lower N2O emissions under similar effluent nitrite concentrations. On this basis, weekly 4 h FNA shocks of 2.0 mg of HNO2-N/L were identified as an optimal and realistic treatment, which not only enabled nitrogen removal efficiencies of ∼65% at nitrogen removal rates of ∼130 mg of N/L/d (20 °C) but also yielded the lowest cost and carbon footprint.

Achieving stable two-stage mainstream partial-nitrification/anammox (PN/A) operation via intermittent aeration.

The mainstream anammox process has attracted extensive attention recently. Compared to single-stage partial-nitrification/anammox (PN/A) system, two-stage PN/A process was more advantageous for achieving mainstream anammox. However, complex control strategy in partial-nitrification reactor (N-SBR) might not be feasible in practical application. The aim of this study was to provide an easy operation strategy to achieve two-stage PN/A process. Firstly, intermittent aeration was investigated to achieve 100% conversion of ammonium to nitrite in N-SBR. The effluent nitrite concentrations increased from 19.96 to 38.62mg/L when intermittent aeration ratio (IAC) varied from 30min/30min-30min/15min. During 125d's operation of N-SBR, stable partial nitrification performance was obtained through intermittent aeration, without coupling with low dissolve oxygen or short sludge retention time. Then, raw municipal wastewater was directly mixed with N-SBR effluent to provide suitable feed to anaerobic sequencing batch reactor (A-SBR).When the mixture ratio between the raw wastewater and the N-SBR effluent was 2.5, the effluent ammonium and total inorganic nitrogen (TIN) was only 0.97 and 2.52mgN/L, respectively. Additionally, carbon-based pollutants was also removed in the proposed system without any pretreatment, which made the process easier to operate in practice.

Long-term operation and autotrophic nitrogen conversion process analysis in a biofilter that simultaneously removes Fe, Mn and ammonia from low-temperature groundwater

One lab-scale biofilter that simultaneously removes Fe, Mn and ammonia from 4 °C groundwater was established to investigate the nitrogen conversion process. The results showed that 333 days were needed to achieve the required standards for Fe, Mn and ammonia under a filtration rate of 3 m/h. Effluent nitrite concentration was the key factor determining the final operation parameters. Both nitrification and anaerobic ammonium oxidation (ANAMMOX) contributed to nitrogen conversion. The calculation results demonstrated that autotrophic nitrogen removal proportion was about 15.92% in steady operation period. Meanwhile, 7 genera of Mn oxidizing bacteria (MnOB) were detected; Candidatus Brocadia was the only detected ANAMMOX genera. The corresponding functional oxidizing bacteria could be acclimated sufficiently in biofilter treating low-temperature groundwater.

Nitrate and phosphate removal from agricultural subsurface drainage using laboratory woodchip bioreactors and recycled steel byproduct filters

Woodchip bioreactors have been increasingly used as an edge-of-field treatment technology to reduce the nitrate loadings to surface waters from agricultural subsurface drainage. Recent studies have shown that subsurface drainage can also contribute substantially to the loss of phosphate from agricultural soils. The objective of this study was to investigate nitrate and phosphate removal in subsurface drainage using laboratory woodchip bioreactors and recycled steel byproduct filters. The woodchip bioreactor demonstrated average nitrate removal efficiencies of 53.5–100% and removal rates of 10.1–21.6 g N/m3/d for an influent concentration of 20 mg N/L and hydraulic retention times (HRTs) of 6–24 h. When the influent nitrate concentration increased to 50 mg N/L, the bioreactor nitrate removal efficiency and rate averaged 75% and 18.9 g N/m3/d at an HRT of 24 h. Nitrate removal by the woodchips followed zero-order kinetics with rate constants of 1.42–1.80 mg N/L/h when nitrate was non-limiting. The steel byproduct filter effectively removed phosphate in the bioreactor effluent and the total phosphate adsorption capacity was 3.70 mg P/g under continuous flow conditions. Nitrite accumulation occurred in the woodchip bioreactor and the effluent nitrite concentrations increased with decreasing HRTs and increasing influent nitrate concentrations. The steel byproduct filter efficiently reduced the level of nitrite in the bioreactor effluent. Overall, the results of this study suggest that woodchip denitrification followed by steel byproduct filtration is an effective treatment technology for nitrate and phosphate removal in subsurface drainage.

N2O emissions from full-scale nitrifying biofilters

A full-scale nitrifying biofilter was continuously monitored during two measurement periods (September 2014; February 2015) during which both gaseous and liquid N2O fluxes were monitored on-line. The results showed diurnal and seasonal variations of N2O emissions. A statistical model was run to determine the main operational parameters governing N2O emissions. Modification of the distribution between the gas phase and the liquid phase was observed related to the effects of temperature and aeration flow on the volumetric mass transfer coefficient (kLa). With similar nitrification performance values, the N2O emission factor was twice as high during the winter campaign. The increase in N2O emissions in winter was correlated to higher effluent nitrite concentrations and suspected increased biofilm thickness.

Role of Solids Retention Time on Complete Nitrification: Mechanistic Understanding and Modeling

Effects of solids retention time (SRT) on both steps of the nitrification process (e.g., ammonia oxidation and nitrite oxidation) and the nitrifier community in a complete-mix activated sludge process were studied. At a SRT less than or equal to 20 days, the effluent ammonia concentration was lower than the effluent nitrite concentration. At the 40-day SRT, however, the effluent nitrite concentration became equal to or less than the effluent ammonia concentration. Quantitative Polymerase Chain Reaction (QPCR) assays indicated that increasing SRT significantly increased nitrite-oxidizing bacteria/ammonia-oxidizing bacteria (NOB/AOB) ratio. Further investigation indicated that Nitrosomonas europaea/eutropha were the dominant AOB for ammonia oxidation under all SRTs. However, for nitrite oxidation, Nitrobacter-like NOB played the key role at low SRTs, while Nitrospira-like NOB played the key role at high SRTs. Modeling results indicated that, for AOB and NOB, the values of maximum specific growth rate (μ) were 0.24 and 0.18/day, respectively, while the values of decay coefficient (Kd) were 0.066 and 0.045/day, respectively. The half-velocity constants (KS) for both AOB and NOB were approximately 0.02 mg/L, and the maximum specific substrate utilization rate (k) for AOB and NOB were 1.3 and 3.0 g-N/g-VSS-day, respectively. These values suggest that AOB had an advantage over NOB at a lower SRT, mainly because AOB grew faster than NOB did. On the contrary, the increased NOB/AOB ratio at a longer SRT was likely due to NOB having a smaller kd. The very low KS values for both AOB and NOB imply that a plug-flow reactor may not have much kinetic advantage over a complete-mixed reactor for a complete nitrification process. The mass concentrations of AOB and NOB in the activated sludge can also be calculated based on the measured nitrification capacity and their k value.

Nitritation versus full nitrification of ammonium-rich wastewater: Comparison in terms of nitrous and nitric oxides emissions

The processes of nitritation and full nitrification of synthetic reject wastewater were compared in terms of N2O and NO emissions. Two lab-scale sequencing batch reactors (SBR1 and SBR2) were enriched with Nitrosomonas (ammonia-oxidizing bacteria) and Nitrobacter (nitrite-oxidizing bacteria), as shown by fluorescence in situ hybridization (FISH) and high-resolution 16S rRNA tag pyrosequencing. Stable conversion of ammonium to nitrite and nitrite to nitrate was achieved in SBR1 and SBR2 respectively. Biomass from SBR2 was added in SBR1 in order to achieve full nitrification. Under nitritation, 1.22% of the converted-N was emitted as N2O, and 0.066% as NO. During the transition from nitritation to full nitrification, effluent nitrite concentrations decreased but nitrogen oxides were emitted at levels similar to the nitritation period. Gas emissions decreased sharply under full nitrification conditions (0.54% N2O-N/converted-N; 0.021% NO-N/converted-N), probably as a result of the combined effect of lower nitrite and ammonium concentrations in the bioreactor.

Using carrier surface loading to design heterotrophic denitrification reactors

This article tests the theory of using nitrate carrier surface loading (SL) as the primary design criterion for heterotrophic denitrification of drinking water. Two load‐increase tests (flow rate and nitrate concentration) with a pilot‐scale heterotrophic biofilm reactor identified that the maximum SL was approximately 6 g nitrogen/m2/d and was controlled by the effluent nitrite concentration. A comparison of SL values obtained from the literature also showed that the maximum SLs were similar for a wide range of heterotrophic denitrification processes. All of the SL values are consistent, even though the empty bed contact time and the nitrate volumetric loading varied widely. The experimental results confirm that the electron donor should be supplied at the stoichiometric requirement to achieve simultaneously low concentrations of nitrate, nitrite, and organic carbon.

塩分によるDHSリアクター内の硝化細菌群の菌叢変化と亜硝酸化の促進

The effect of salinity on nitritation in a Down-flow Hanging Sponge (DHS) reactor was evaluated through a long-term continuous experiment for 700 days. The DHS reactor was fed with artificial wastewater containing 100 mg-N·L-1 ammonium nitrogen (HRT = 2 h, 20-25°C). The salinity of the influent was controlled by adding NaCl at concentrations of 5 to 18 g-Cl-·L-1. The effluent nitrite concentration increased with increasing of salinity, i.e., the nitrite concentration increased up to approximately 60% of the total nitrogen in the effluent at 18 g-Cl-·L-1. The nitrifying bacterial community in the DHS markedly changed at the species level. For example, the dominant nitrite-oxidizing bacteria changed from Nitrospira-sublineage I at 0 g-Cl-·L-1 to Nitrobacter spp. at 18 g-Cl-·L-1.

Performance of two combined anaerobic–aerobic biofilters packed with clay or plastic media for the treatment of highly concentrated effluent

Biological treatment of high-strength carbon and nitrogen synthetic wastewater by two combined anaerobic–aerobic biofiltration systems packed with clay (system 1) or plastic media (system 2) has been studied for 143 days. Four phases of operating conditions were carried out with an influent COD and TKN concentrations varied from 2595 to 5969 mg/L and 510 to 1866 mg/L, respectively. Both systems exhibited excellent COD removal performance and the average removal efficiencies were superior to 90% for a loading of 2 to 4 kg COD/m 3/d. The BOD 5 average removal during the four operating phases varied from 91 to 98%. Total nitrogen removal occurred in the aerobic stage showing 60% and 77% of elimination obtained for aerobic filters of systems 1 and 2, respectively. Nitrogen removal was related to many factors such as nitrification/denitrification, bacterial assimilation and NH 3-stripping. The aerobic filter packed with plastic media produced less nitrates than the other filter. This may due to an enhancement of the denitrification or to the inhibition of nitrobacter by free NH 3. Effluent nitrite concentrations confirmed the possibility of NH 3-inhibition. Phosphorus removal was also at acceptable level for both systems with yields varied from 50% (system 1) to 70% (system 2).

Denitrification of drinking water sources by advanced biological treatment using a membrane bioreactor

Nitrate often contaminates groundwater resources due to excessive use of fertilizers and uncontrolled on-land discharges of raw and treated wastewater and can therefore limit the direct use of groundwater for drinking water purposes. In order to investigate the possible application of a membrane bioreactor (MBR) for denitrification of groundwater, the performance of a pilot-scale MBR was tested as a function of hydraulic and biological parameters. For this purpose synthetic groundwater was prepared by taking lake water (Lago Maggiore, Italy) and adding known amounts of ethanol and sodium nitrate to study the nitrate removal capacity of the sludge, to search for an optimum C/N ratio and to measure filtering ability for micro-organisms through the membrane. The optimum C/N ratio was found at 2.2 gC/gN, resulting in an effluent nitrate concentration within the limits stated in EU Directive 98/83 and the US EPA for drinking water use. The effluent nitrite concentration was one order under the EU limit. The membrane module, Zenon ZW-10, was monitored and performed well except for a short stress episode due to low airflow, afterwards rapidly corrected and thus putting the membrane back to its previous stable behavior. Total bacterial count for the treated effluent was lower than influent water, and 100% removal was observed for both total coliforms and E. coli. Calorimetric thermograms related to heat dissipation due to biological denitrification (nitrate and nitrite consumption) and to substrate adaptation are discussed. A maximum nitrate removal rate close to 20 mgN-NO − 3 gVSS −1h −1 was measured in the calorimetric tests.

Feasibility of biological aerated filters (bafs) for treating landfill leachate

Ammonia can be removed from landfill leachate using aerobic biological treatment processes. The biological aerated filter (BAF) combines biological treatment and subsequent biomass separation in one reactor providing a small footprint alternative to conventional systems. Leachate from an operational landfill was found to be aerobically treatable using the OECD recommended Modified Zahn‐Wellens test. This leachate was used as feed to a pilot‐scale BAF at influent chemical oxygen demand (COD) and ammoniacal‐nitrogen concentrations of 765 mg 1‐1 and 568 mg 1‐1 respectively. During an initial period of stable operation without pH control, 33 %w/w of influent ammonia was removed. The reactor pH was 9.2 with little conversion to total oxidized nitrogen (<45 mg 1‐1), this removal was accounted for primarily by air stripping. In a second period of stable operation, the reactor pH was reduced to pH 72 and ammonia removal increased to 97 %w/w with a concomitant increase in effluent nitrite concentration to an average of 524 mg 1‐1. Biological aerated filters (BAFs) can be used to nitrify landfill leachates though onward denitrification of nitrite‐nitrogen and COD polishing is required to reach typical discharge consent standards.

Use of autotrophic sulfur-oxidizers to remove nitrate from bank filtrate in a permeable reactive barrier system

This study was conducted to evaluate the potential applicability of an in situ biological reactive barrier system to treat nitrate-contaminated bank filtrate. The reactive barrier consisted of sulfur granules as an electron donor and autotrophic sulfur-oxidizing bacteria as a biological component. Limestone was also used to provide alkalinity. The results showed that the autotrophic sulfur oxidizers were successfully colonized on the surfaces of the sulfur particles and removed nitrate from synthetic bank filtrate. The sulfur-oxidizing activity continuously increased with time and then was maintained or slightly decreased after five days of column operation. Maximum nitrate removal efficiency and sulfur oxidation rate were observed at near neutral pH. Over 90% of the initial nitrate dissolved in synthetic bank filtrate was removed in all columns tested with some nitrite accumulation. However, nitrite accumulation was observed mainly during the initial operation period, and the concentration markedly diminished with time. The nitrite concentration in effluent was less than 2 mg-N/l after 12 days of column operation. When influent nitrate concentrations were 30, 40, and 60 mg-N/l and sulfur content in column was 75%, half-order autotrophic denitrification reaction rate constants were 31.73×10 −3, 33.3×10 −3, and 36.4×10 −3 mg 1/2/l 1/2min, respectively. Our data on the nitrate distribution profile along the column suggest that an appropriate wall thickness of a reactive barrier for autotrophic denitrification may be 30 cm when influent nitrate concentration is less than 60 mg-N/l.

Nitrate Removal in Sulfur: Limestone Pond Reactors

The feasibility of using sulfur:limestone autotrophic denitrification (SLAD) pond reactors to treat nitrate-contaminated water or wastewater after secondary treatment was investigated with four lab-scale continuously fed SLAD ponds. The start-up period, temperature effects, and effects of different feed solutions were evaluated. With an influent concentration of 30 mg NO3--N/L at an HRT of 30 days, the pond reactors had an overall nitrate removal efficiency of 85–100%. Effluent nitrite concentrations were <0.2 mg N/L in all tests. Aerobic conditions could result in a decrease of the SLAD pH of the pond by 2 to 3 units and a large increase in sulfate production (∼1600-1800 mg-SO42-/L). Under unmixed (anoxic) conditions, the pH and sulfate produced were maintained at approximately 5.5 to 5.6 and 400-600 mg-SO42-/L, respectively, in all the SLAD ponds. Temperature affected the pond reactors adversely. By assuming that a first-order reaction occurred in a SLAD pond reactor, the temperature-activity coefficient, θ was found to be 1.068. Treatment of nitrate-contaminated surface water and wastewater using SLAD pond systems is feasible only if (1) the chemical oxygen demand (COD)/nitrate–N (COD/N) ratio is low (<1.2 with an initial NO3- concentration of 30 mg-N/L), (2) sulfur:limestone granules are not covered by sediment, and (3) sulfur-utilizing but nondenitrifying bacteria (SUNDB) are greatly inhibited due to the lack of DO in the pond systems. The SLAD ponds are not feasible for the treatment of raw wastewater or surface water if they contain high concentrations of organic matters due to the possible inhibition of sulfur-based autotrophic denitrifiers by heterotrophs (including heterotrophic denitrifiers). In addition, a high sulfate and low DO concentration as well as a low pH in the SLAD effluent of the pond (even when the pond is operated in an unmixed mode) also will limit the application of SLAD pond processes.

Nitrate Removal with Sulfur-Limestone Autotrophic Denitrification Processes

Nitrate removal using sulfur and limestone autotrophic denitrification (SLAD) processes was evaluated with four laboratory-scale fixed-bed column reactors. The research objectives were (1) to determine the optimum design criteria of the fixed-bed SLAD columns; and (2) to evaluate the effects of biofouling on the SLAD column performance. A maximum denitrification rate of 384 g NO3--N/(m3⋅day) was achieved at a loading rate between 600 and 700 g NO3--N/(m3⋅day). The effluent nitrite concentration started to rise gradually once the loading rate was above 600 g NO3--N/(m3⋅day). A loading rate between 175 and 225 g NO3--N/(m3⋅day) achieved the maximum nitrate-N removal efficiency (∼95%). Biofouling was evaluated based on tracer studies, the measured biofilm thickness, and modeling. The porosities of the columns fluctuated with time, and the elongation of the filter media was observed. Biofouling caused short-circuiting and decreased nitrate removal efficiency. A SLAD column will require backwashing after 6 months of operation when the influent is synthetic ground water but will foul and require backwashing within 1–2 months when the influent is real ground water.

Membrane bioreactor for drinking water denitrification

The aim of this study is to evaluate the performance of a membrane bioreactor with cell recycle to be used for drinking water denitrification, when operated with a high nitrate load (up to 7.68 kgNO3−/m3 day) and low hydraulic retention time (down to 0.625 h). Nitrate and nitrite were always completely removed for all the operational conditions used. The effluent's nitrite concentration kept below 0.1 mg NO2−/l with exception of a short period, during the reactor start-up, when it accumulates. The performance of the membrane bioreactor was also evaluated using a groundwater containing 148 mg NO3−/l. Nitrate and nitrite concentration in the effluent were below the recommended values for drinking water when the reactor was controlled at pH 7.0. The membrane flux decreases during operation as a consequence of membrane fouling. The flux decrease was more severe during operation with synthetic medium than with contaminated groundwater due to the existence of molecular complexes in the synthetic broth. A backshock technique was used to reduce the surface fouling of the membrane. Combining this technique with the use of a reserve asymmetric structured membrane it was found that the membrane flux remains nearly unchanged.

Ammonia oxidation at low pH by attached populations of nitrifying bacteria

Biofilm populations of Nitrosomonas europaea were formed in continuous flow sand columns supplied with defined inorganic medium containing 50 μg NH 4 +-N ml −1. Steady-state nitrite concentrations in effluent from the columns decreased as the pH of the inflowing medium was reduced but ammonia oxidation occurred at a pH value of 6, even though the pH minimum for growth of the organism in liquid batch culture was 7. No evidence was obtained for NH 3 limitation at low pH values, resulting from ionization to NH 4 +. The pH minimum for ammonia-oxidizing activity was also reduced in continuous flow vermiculite columns supplied with medium of pH 5.4, with an effluent pH of 6.3, but detailed assessment of the effects of low pH on activity was prevented by the strong buffering capacity of vermiculite. A multispecies, nitrifying biofilm, formed as wall growth in an ammonia-limited chemostat, was capable of ammonia-oxidizing activity, but not growth, at pH 5 while growth was possible at pH 5.5. The data provide evidence of the potential for autotrophic nitrification in acid soils.