Biological Denitrification Process Research Articles

Iron shavings supported biological denitrification in sequencing batch reactor

Iron shavings, as the main substrate, were applied to support biological denitrification process in a sequencing batch biological reactor. Operation performances of 248 days were evaluated. The results indicate that stable nitrate removal process can be achieved with a denitrification rate of 15.49–52.32g NO3-–N m-3 d-1 in different operation conditions. Hydrogen generated from iron corrosion contributed 66.5% of total needed electron and other 33.5% may be provided by both ferrous iron and endogenous carbon. Nitrate removal was accompanied by increase of iron concentration in suspended solid in reactor and average ratio of total removed N to consumed iron was 1:7.52. Effluent total iron concentration was as low as 2–4 mg L-1 and the consumed iron were mainly adsorbed over the microorganism's surface or in the form of settleable small particles. The sludge activity was seriously repressed when the percentage of iron in suspended solid was over 70% and can be recovered by highly reducing iron concentration in reactor.

Interpretation of redox potential variation during biological denitrification using linear non-equilibrium thermodynamic model

In this study, the oxidation reduction potential (ORP) of biological denitrification processes is interpreted based on the MIRROR model No. 1, a linear non-equilibrium thermodynamic model developed in an earlier study. The model interconnects the affinities of catabolism and anabolism, the driving forces of microbial metabolism, with the system ORP and reaction rates of biological processes. Experimental results reported in the literature were used for calibrating the MIRROR model No. 1 to determine the optimal values of model stoichiometric, kinetic, and phenomenological parameters; the calibrated model was then used to simulate laboratory data. The simulation results agree well with the experimental observations. There is a close relationship between the affinities of catabolism and the system ORP of the biological denitrification process, but the ORP variation per unit affinity of catabolism is not a constant but proportional to the molarity of electrons transferred catabolically. The linear relationship between redox potential and reaction rate, which is derived based on MIRROR model No. 1, is subsequently verified by the experimental results reported in the literature. This linear relationship enables evaluation of the biological denitrification rate based on the real-time monitoring of the system ORP.

N2O production in anaerobic/anoxic denitrifying phosphorus removal process: The effects of carbon sources shock

Nitrous oxide (N2O) emissions from biological denitrification processes are one of the major sources of N2O emissions during the biological nutrient removal process in wastewater treatment. In this study, the effects of carbon source shocks on N2O production during denitrifying phosphorus removal were investigated using biomass that was initially acclimated with acetate. The shock tests were conducted in three laboratory-scale anaerobic/anoxic (An/A) reactors using acetate, acetate/propionate or propionate as the carbon sources. After switching the carbon source from acetate to acetate/propionate and propionate, the ratios of N2O–N production to total nitrogen (TN) removal increased by 1.72 or 0.77 times, respectively, and the total nitrogen (TN) removal efficiency decreased from 80% to 52% or 38%, respectively; also, the PO43−–P removal efficiency declined from 75% to 63% or 47%, respectively.

Evaluation of N2O Production from Anaerobic Ammonium Oxidation (Anammox) at Different Influent Ammonia to Nitrite Ratios

Abstract Nitrogen discharged to aquatic system can effect in eutrophication. The improper treatment design to remove nitrogen could also cause negative effect to atmospheric environment by emission of nitrous oxide (N 2 O). The conventional biological denitrification process under the condition of a low influent COD/N ratio or electron donor to electron acceptor ratio, N 2 O could be detected. However, recently, autotrophic denitrificaiton process named ANAMMOX has been applied for nitrogen removal from wastewater containing high NH 4 + but low carbon content, for example the anaerobically treated swine wastewater in which carbon content was only half of that recommended for conventional biological nitrogen removal process. Anammox bacteria were able to use ammonia as electron donor and nitrite as electron acceptor under anaerobic condition. This study investigated the N 2 O production by Anammox process operated in SBR reactors with HRT of 4 days by varying influent ammonia to nitrite ratios or electron donor to electron acceptor ratios at 0.75:1, and 1:1. The results showed that the substrate consumption mole ratios (ΔNO 2 -N/ΔNH 4 -N) at the influent ratio of 0.75:1 and 1:1were 2.2:1 and 1.7:1, respectively. Moreover the average N2O of 1.05 ppm was detected even at the higher influent ratio of 1:1.

Denitrification of a landfill leachate with high nitrate concentration in an anoxic rotating biological contactor

The denitrification performance of a lab-scale anoxic rotating biological contactor (RBC) using landfill leachate with high nitrate concentration was evaluated. Under a carbon to nitrogen ratio (C/N) of 2, the reactor achieved N-NO(3)(-) removal efficiencies above 95% for concentrations up to 100 mg N-NO(3)(-) l(-1). The highest observed denitrification rate was 55 mg N-NO(3)(-) l(-1) h(-1) (15 g N-NO(3)(-) m(-2) d(-1)) at a nitrate concentration of 560 mg N-NO(3)(-) l(-1). Although the reactor has revealed a very good performance in terms of denitrification, effluent chemical oxygen demand (COD) concentrations were still high for direct discharge. The results obtained in a subsequent experiment at constant nitrate concentration (220 mg N-NO(3)(-) l(-1)) and lower C/N ratios (1.2 and 1.5) evidenced that the organic matter present in the leachate was non-biodegradable. A phosphorus concentration of 10 mg P-PO(4)(3-) l(-1) promoted autotrophic denitrification, revealing the importance of phosphorus concentration on biological denitrification processes.

Heterotrophic Biological Denitrification Using Microbial Cellulose as Carbon Source

The objective of this study was to investigate the feasibility of using a microbial biopolymer produced by Acetobacter xylinum as a carbon source for heterotrophic biological denitrification. The denitrification rate, COD availability and nitrite concentration were response param- eters. Under the experimental conditions, a denitrification rate of about 0.74 kg NO3 - N/m 3 d at 6 h retention time was achieved with microbial cellulose (MC). The reactor efflu- ent contained significantly COD concentrations (20-86 mg/ L) so it was not carbon limited, and was receiving enough carbon to facilitate the denitrification process. The maxi- mum nitrite concentration in the effluent was found to be 0.4 mg/L. However, decreasing the retention time to 3 h significantly reduced the efficiency. It can be concluded that the MC is a suitable carbon source for nitrate removal in a heterotrophic biological denitrification process.

Effect of pine bark and compost on the biological denitrification process of non-hazardous landfill leachate: Focus on the microbiology

In an attempt to optimize the cost-efficiency of landfill leachate treatment by biological denitrification process, our study focused on finding low-cost alternatives to traditional expensive chemicals such as composted garden refuse and pine bark, which are both available in large amount in South African landfill sites. The overall objective was to assess the behaviour of the bacterial community in relation to each substrate while treating high strength landfill leachates. Denitrification processes in fixed bed reactors were simulated at laboratory scale using anaerobic batch tests with immature compost and pine bark. High strength leachate was simulated using a solution of water and nitrate at a concentration of 500 mg l −1. Results suggest that pine bark released large amounts of phenolic compounds and hydroxylated benzene rings, which both can delay the acclimatization time and inhibit the biological denitrification (only 30% efficiency). Furthermore, presence of potential pathogens like Enterobacter and Pantoea agglomerans prevents the applicability of the pine bark in full-scale operations. On the other hand, lightly composted garden refuse (CGR) offered an adequate substrate for the formation of a biofilm necessary to complete the denitrification process (total nitrate removal observed within 7 days). CGR further contributed to a rapid establishment of an active consortium of denitrifiers including Acinetobacter, Rhizobium, Thermomonas, Rheinheimera, Phaeospirillum and Flavobacterium. Clearly the original composition, nature, carbon to nitrogen ratio (C/N) and degree of maturity and stability of the substrates play a key role in the denitrification process, impacting directly on the development of the bacterial population and, therefore, on the long-term removal efficiency.

Nitrogen transformation in acid soils subjected to pH value changes

The aim of this investigation was to determine which application of fertilizer and lime material does not form toxic quantities of nitrite nitrogen and when the losses by denitrification are the lowest in the examined acid soils. Investigations were performed on pseudogley soils of different acidity. Changes of available nitrogen forms were examined by the method of short-term incubation experiments. Experimental treatments were without the use of mineral fertilizers and with application of (NH4)2SO4 (100 ppm of NO3-N) and KNO3 (100 ppm of NO3-N); with and without addition of Ca(OH)2 (50% of full neutralization and full neutralization). When (NH4)2SO4 was used, nitrites occurred in both examined soils as a result of decelerated nitrification and when KNO3 was added as a result of chemical denitrification. Application of Ca(OH)2 caused the intensification of mineralization, nitrification and biological denitrification processes. When a higher dose of lime material was used (full neutralization), nitrites occurred in larger quantities as a result of the strengthening of nitrification and denitrification processes. Application of a lower lime dose caused nitrite occurrence in smaller quantities. Therefore, in these soils as well as in soils of similar chemical properties, application of lower doses of lime material can be recommended (<50% of full neutralization) as well as the application of ammonium fertilizer, bearing in mind that in such conditions losses of added fertilizer in the denitrification process are reduced and the occurrence of nitrites as an intermediate product of this process is prevented.

Enhanced biological denitrification of high concentration of nitrite with supplementary carbon source

Nitrite accumulates during biological denitrification processes when carbon sources are insufficient. Acetate, methanol, and ethanol were investigated as supplementary carbon sources in the nitrite denitrification process using biogranules. Without supplementary external electron donors (control), the biogranules degraded 200 mg l(-1) nitrite at a rate of 0.27 mg NO(2)-N g(-1) VSS h(-1). Notably, 1,500 mg l(-1) acetate and 700 mg l(-1) methanol or ethanol enhanced denitrification rates for 200 mg l(-1) nitrite at 2.07, 1.20, and 1.60 mg NO(2)-N g(-1) VSS h(-1), respectively; these rates were significantly higher than that of the control. The sodium dodecyl sulfate polyacrylamide gel electrophoresis of the nitrite reductase (NiR) enzyme identified three prominent bands with molecular weights of 37-41 kDa. A linear correlation existed between incremental denitrification rates and incremental activity of the NiR enzyme. The NiR enzyme activity was enhanced by the supplementary carbon sources, thereby increasing the nitrite denitrification rate. The capacity of supplementary carbon source on enhancing NiR enzyme activity follows: methanol > acetate > ethanol on molar basis or acetate > ethanol > methanol on an added weight basis.

Long‐term stability of biological denitrification process for high strength nitrate removal from wastewater of uranium industry

AbstractThe aim of the present study was to biologically denitrify uranium nitrate raffinate (UNR) from nuclear industry, which is a principle source of high strength nitrate waste. To denitrify the high nitrate waste, a pilot‐scale continuous stirred tank reactor was designed with two inbuilt settlers. Acclimatization of mixed culture with synthetic waste was carried out prior to the inoculation of the acclimatized sludge into the reactor. Initial concentration of nitrate in uranium raffinate was 77,000 mg/L NO3. It was diluted and used as a feed to the reactor. Concentration of nitrate in feed was increased gradually from 10,000 mg/L NO3 to 40,000 mg/L NO3 with hydraulic retention time (HRT) maintained at 34.4 h. Complete denitrification of 40,000 mg/L NO3 was achieved in a specified HRT.To facilitate understanding of the treatablity and long‐term stability of biological denitrification of UNR, study was carried out for 211 days by periodical perturbation of the system. Furthermore, to find the volume ratio of reactor to settler required for the full‐scale design of the denitrification plant, settling of acclimatized sludge was carried out. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Application of photocatalysis as a post treatment method of a heterotrophic–autotrophic denitrification reactor effluent

The aim of this study is the application of photocatalysis as an effective post treatment scheme for the removal of the organic matter and bacteria released by an innovative biological denitrification process referred to as heterotrophic–autotrophic denitrification, which combines heterotrophic and autotrophic denitrification processes. Photocatalytic treatment was applied using TiO 2 as a photocatalyst in the loading range of 0.25–2.00 g l −1 for irradiation periods up to 60 min using a black light fluorescent lamp with an intensity of I 0 = 1309 μW cm −2. The photocatalytic inactivation data were modelled to pseudo first order kinetics as well as by the areal rates to evaluate the photocatalyst loading effect. Chlorination was used as a final disinfection step to attain an overall inactivation of total coliforms as well as to the formation of very low level of trihalomethanes.

Biological denitrification by Pseudomonas stutzeri immobilized on microbial cellulose

This study demonstrated the feasibility of a biological denitrification process using immobilized Pseudomonas stutzeri. The microbial cellulose (MC) from Acetobacter xylinum was used as the support material for immobilization of the bacterium. Nitrate removal took place mainly in the anoxic system. The effects of various operating conditions such as the initial nitrate concentration, pH, and carbon source on biological denitrification were demonstrated experimentally. The system demonstrated a high capacity for reducing nitrate concentrations under optimum conditions. The denitrification rate increased up to a maximal value of 1.6 kg NO3-N m−3 day−1 with increasing nitrate loading rate. Because of its porosity and purity, MC may be considered as appropriate supports for adsorbed immobilized cells. The simplicity of immobilization and high efficiency in operation are the main advantages of such systems. To date, the immobilization of microorganisms onto MC has not been carried out. The results of this research shows that a pilot bioreactor containing P. stutzeri immobilized on MC exhibited efficient denitrification with a relatively low retention time.

Cotton-supported heterotrophic denitrification of nitrate-rich drinking water with a sand filtration post-treatment

The biological denitrification (BD) process represents an interesting solution to remove nitrate from water and as well as to close the natural nitrogen cycle. Potential applications are related to both groundwater denitrification and treatment of nitraterich effluents from reverse osmosis and ion-exchange processes. This paper presents the results obtained from a pilot-scale cotton-supported heterotrophic denitrification reactor (HDR) where cotton acts as both organic carbon source and supporting material for the growth of a denitrifier biofilm. A trickling sand filter (TSF) was inserted as post-treatment to remove TOC released by the HDR and to re-oxygenate the treated water. The system is evaluated for drinking water treatment. Nitrate removal efficiency of the HDR was over 90% for 85 mg/ℓ of inlet nitrate concentration which is a mean groundwater value in many EU countries. The process maintained its high performance up to 358 mg of daily nitrate inlet with a maximum specific volumetric ratio of 24.5 gN/m3·d. A first-order kinetic value was shown for sequential nitrate-nitrite and nitrite-nitrogen gas transformations. For that, the kinetic constants of 2.6 ℓ/d (K1) and 15.9 ℓ/d (K2) were assumed. The TSF provided additional nitrification-aerobic denitrification at a rate of 20.7gN/m3·d. Although both reactors showed high performances in terms of nitrogen removal, this plant configuration cannot assure an adequate TOC outlet concentration (>3 mg/ℓ).. Water SA Vol. 31 (2) 2005: pp.229-236

Control of carbon and ammonium ratio for simultaneous nitrification and denitrification in a sequencing batch bioreactor

This study shows how the carbon and nitrogen (C/N) ratio controls the simultaneous occurrence of nitrification and denitrification in a sequencing batch reactor (SBR). Data demonstrated that a low C/N ratio resulted in a rapid carbon deficit, causing an unbalanced simultaneous nitrification–denitrification (SND) process in SBR. When the initial COD/NH 4 + -N ratio was adjusted to 11.1, the SND-based SBR achieved complete removal of NH 4 -N and COD without leaving any NO 2 − -N in the effluent. The nitrogen removal efficiency decreases gradually with increasing ammonium-loading rate to the SND–SBR system. Altogether, data showed that appropriate controls of carbon and nitrogen input are required to achieve an efficient SND–SBR. An established SND technology can save operation time and energy, and might replace the traditional two-stage biological nitrification and denitrification process.

Optimal operations for groundwater denitrification of drinking water using heterotrophic biological denitrification process

Due to the extensive application of artificial nitrogen-based fertilizers on land, groundwater from the central part of Taiwan faces problems of increasing concentrations of nitrate, which were measured to be well above 30 mg/L all year round. For meeting the 10 mg/L nitrate standard, optimal operations for a heterotrophic denitrification pilot plant designed for drinking water treatment was investigated. Ethanol and phosphate were added for bacteria growing on anthracite to convert nitrate to nitrogen gas. Results showed that presence of high dissolved oxygen (around 4 mg/L) in the source water did not have a significantly negative effect on nitrogen removal. When operated under a C/N ratio of 1.88, which was recommended in the literature, nitrate removal efficiency was measured to be around 70%, sometimes up to 90%. However, the reactor often underwent severe clogging problems. When operated under C/N ratio of 1.0, denitrification efficiency decreased significantly to 30%. Finally, when operated under C/N ratio of 1.5, the nitrate content of the influent was almost completely reduced at the first one-third part of the bioreactor with an overall removal efficiency of 89–91%. Another advantage for operating with a C/N ratio of 1.5 is that only one-third of the biosolids was produced compared to a C/N value of 1.88.

NOx removal from flue gas by an integrated physicochemical absorption and biological denitrification process

An integrated physicochemical and biological technique for NO(x) removal from flue gas, the so-called BioDeNO(x) process, combines the principles of wet absorption of NO in an aqueous Fe(II)EDTA(2-) solution with biological reduction of the sorbed NO in a bioreactor. The biological reduction of NO to di-nitrogen gas (N(2)) takes place under thermophilic conditions (55 degrees C). This study demonstrates the technical feasibility of this BioDeNO(x) concept in a bench-scale installation with a continuous flue gas flow of 650 l.h(-1) (70-500 ppm NO; 0.8-3.3% O(2)). Stable NO removal with an efficiency of at least 70% was obtained in case the artificial flue gas contained 300 ppm NO and 1% O(2) when the bioreactor was inoculated with a denitrifying sludge. An increase of the O(2) concentration of only 0.3% resulted in a rapid elevation of the redox potential (ORP) in the bioreactor, accompanied by a drastic decline of the NO removal efficiency. This was not due to a limitation or inhibition of the NO reduction, but to a limited biological iron reduction capacity. The latter leads to a depletion of the NO absorption capacity of the scrubber liquor, and thus to a poor NO removal efficiency. Bio-augmentation of the reactor mixed liquor with an anaerobic granular sludge with a high Fe(III) reduction capacity successfully improved the bioreactor efficiency and enabled to treat a flue gas containing at least 3.3% O(2) and 500 ppm NO with an NO removal efficiency of over 80%. The ORP in the bioreactor was found to be a proper parameter for the control of the ethanol supply, needed as electron donor for the biological regeneration process. The NO removal efficiency as well as the Fe(III)EDTA(-) reduction rate were found to decline at ORP values higher than -140 mV (pH 7.0). For stable BioDeNO(x) operation, the supply of electron donor (ethanol) can be used to control the ORP below that critical value.

Integrated real-time control strategy for nitrogen removal in swine wastewater treatment using sequencing batch reactors

A new integrated real-time control system was designed and operated with fluctuating influent loads for swine wastewater treatment. The system was operated with automatic addition control of an external carbon source, using real-time control technology, which utilized the oxidation–reduction potential (ORP) and the pH as parameters to control the anoxic phase and oxic phase, respectively. The fluctuations in swine wastewater concentration are extreme; an influent with a low C/ N ratio is deficient in organic carbon, and a low carbon source level can limit the overall biological denitrification process. Consequently, a sufficient organic source must be provided for proper denitrification. The feasibility of using swine waste as an external carbon source for enhanced biological nitrogen removal was investigated. The real-time control made it possible to optimize the quantity of swine waste added as the load fluctuated from cycle to cycle. The average removal efficiencies achieved for TOC and nitrogen were over 94% and 96%, respectively, using the integrated real-time control strategy.

Treatment of spent brine from a nitrate exchange process using combined biological denitrification and sulfate precipitation

A combined biological denitrification and sulfate precipitation process was developed to treat and reuse the spent brine produced by a nitrate exchange system. Although the spent brine contained a relatively high salt concentration, more than 80% of NO3(-)-N fed into the denitrification reactors was removed at a nitrate-N loading rate of 2.2 g NO3(-)-N/l x day, regardless of the presence or absence of sulfate up to 8,000 mg/l. Sulfate present in the spent brine was successfully removed by the addition of BaCl2 and the settling velocity of BaSO4 suspension was remarkably enhanced by FeCl3 coagulation. Since most of the chloride consumed in regenerating the exhausted resins was replaced during chemical treatment with BaCl2 and FeCl3, it was possible to reuse the treated spent brine as a regenerant after compensating for the small amount of unreplaced NaCl.

Applying the Nernst equation to simulate redox potential variations for biological nitrification and denitrification processes.

In this paper, various forms of Nernst equations have been developed based on the real stoichiometric relationship of biological nitrification and denitrification reactions. Instead of using the Nernst equation based on a one-to-one stoichiometric relation for the oxidizing and the reducing species, the basic Nernst equation is modified into slightly different forms. Each is suitable for simulating the redox potential (ORP) variation of a specific biological nitrification or denitrification process. Using the data published in the literature, the validity of these developed Nernst equations has been verified by close fits of the measured ORP data with the calculated ORP curve. The simulation results also indicate that if the biological process is simulated using an incorrect form of Nernst equation, the calculated ORP curve will not fit the measured data. Using these Nernst equations, the ORP value that corresponds to a predetermined degree of completion for the biochemical reaction can be calculated. Thus, these Nernst equations will enable a more efficient on-line control of the biological process.

Complete Digestion of Sewage Sludge Using Wet-Oxidation and Subsequently Simultaneous Removal of Residual NH4+ and Volatile Fatty Acids by Biological Treatment

Thickened sewage sludge consisting of primary and surplus sludges with a total solids of 4% was treated by wet-oxidation without catalysts. The digestion efficiency of VSS was 94 to 96% at 80 kgf (cm2G) -1 and 250°C for holding times ranging from 30 to 120min. However, TOC and NH4+ in the liquid generated by the wet-oxidation pmcess was as high as 3, 845 mg l-1 and 1, 410 mg l-1, respectively, even at a holding time of 120 min.The organic matter containing in the wet-oxidized wastewater could be removed in the biological denitrification with the supplement of NaNO3.The TOC and VFA removal efficiencies in the biological denitrification were 65% and 100%, respectively, at a TOC loading rate of 5.0g l-1 d-1.The NH4+ remained in the denitrified wastewater was treated in the biological nitrification after two-times dilution and the NH4+ was oxidized to NO3- completely, at the same time the TOC removal efficiency was 36 to 50%.On the basis of these results, NH4+ and organic matter in the two-times diluted wet-oxidized wastewater could be removed simultaneously in a biological denitrification and nitrification process with a recirculation, resulted in reduction of the supplementation amount of NO3- and HCO3- necessary for denitrification and nitrification, respectively. Moreover, the supplementation of NO3- and HCO3- could be reduced to zero by an improved process, namely, installing an activated sludge tank between the denitrification and the nitrification reactors.