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Development of denitrifying and methanogenic activities in USB reactors for the treatment of wastewater: Effect of COD/N ratio
Abstract
Nitrification–denitrification is the traditional biological process for nitrogen removal from wastewaters. During its second step, denitrification, nitrate formed during nitrification is reduced to gaseous nitrogen under anoxic conditions. Under the presence of organic matter and nitrogen, also methanogenesis and dissimilatory nitrate reduction to ammonia (DRNA) may also take place. COD/N has been referred to be a key factor in the expression of these metabolic pathways. During this research, five upflow sludge bled (USB) reactors were operated at different COD/N ratios, in order to study the evolution of the methanogenic and denitrifying activities in the sludge. The use of nitrogen and organic matter through denitrification, DNRA and methanization was also studied through mass balances, as well as its granule structure. COD/N ratio showed a strong influence on biomass activity, and therefore on the metabolic pathways of nitrate and organic matter utilization. Low values generated high denitrifying activities, and high value, elevated methanogenic activities. Even though it was possible to perform methanization and denitrification in one single reactor, feasible loading rates will be limited by the available activities, so in many cases separated reactors will be more suitable. Granular structure could not be maintained in denitrifying reactors at low COD/N ratio (COD/N 5 and lower): granules disappeared and were replaced by flocculent sludge, with low settling velocities.
... C/N ratio is an important parameter for optimal operation of denitrification systems, from a technical and economic standpoint. Simultaneous denitrification and anaerobic digestion are possible when the carbon source is easily assimilated and when there is a C/N ratio appropriate to prevent methanogenic inhibitions (Ruiz et al., 2006). Investigations have shown that was possible to maintain both processes in a single reactor at low organic loading rates, such as Mosquera et al. (2001), who reported 100 % denitrification and 80 % methanogenic activity in an upflow biofilter treating fish cannery wastewater. ...
... Investigations have shown that was possible to maintain both processes in a single reactor at low organic loading rates, such as Mosquera et al. (2001), who reported 100 % denitrification and 80 % methanogenic activity in an upflow biofilter treating fish cannery wastewater. Ruiz et al. (2006) investigated the removal of nitrate and carbon in upflow sludge blanket (UASB) reactor with nitrate and peptone as nitrogen source and acetate as the carbon source. ...
... It is observed that when the substrate concentration increases, the maximum consumption rate of nitrate increases as well, and their values are presented in Table 3. The rates values obtained in this study are higher than those reported by Zhang (2003) and Rustrian (1997) who worked with C/N ratios of 4.9 to 61 and obtained consumption rates from 0.03 to 1 gNO 3 /L·d, while Ruiz et al. (2006) mentioned that after a strategy of acclimatization in gradual increases in nitrate concentrations, with loading rates from 0.075 to 7.5 gNO 3 /L·d and C/N ratios from 1.7 to 170, higher removals are achieved (more than 80%) in an UASB reactor, in addition, it has been observed that the type of reactor influences the consumption rates of nitrate as Chen et al. (1997) in a CSTR fixed reactor obtained velocities from 0.58 to 4.7 gNO 3 /L·d with C/N ratios from 1.7 to 5.8. ...
Wastewaters from some industries contain high levels of nitrate but an insufficient amount of electron donor to sustain biological denitrification. An option of treatment is combining anaerobic digestion and denitrification process in a single unit. During this research, an anaerobic expanded bed reactor was operated at different C/N ratios (10, 7, 4, 3, 2 and 1) in order to study nitrogen and organic matter removal. A 3 L reactor was used with a flow feed of 3 L/d, upflow velocity of 7 m/h and temperature between 30-35°C. Organic matter removal remained above 90% throughout the 177 days of experimentation. Nitrogen removal was over 90%, when C/N ratios were greater than the stoichiometric (C/N>1), however, with a ratio C/N=1, nitrogen removal was 60%, causing the accumulation of nitrite. The high removal of nitrate and organic matter reached in this study demonstrate the viability to use this type of reactors for the treatment of such efluents, in spite of the fact that the increase of nitrate concentration changed the biomass distribution, which caused a decrease in the size of anaerobic granules. © 2017, Universidad Autonoma Metropolitana Iztapalapa. All rights reserved.
... al., 2009). Eiroa et al. (2004) described successful granulation at the ratio of 3.5, but according to Ruiz et al. (2006), values under 5 resulted in the disintegration of granules. Some biologically degradable substrates (e.g. ...
... Moreover, higher concentrations of N-NO 3 encouraged the growth of larger granules (Cuervo-Lopez et al., 1999; Ruiz et al., 2006). Hulshoff Pol, (1989) reported that with a little deterioration of granular structure under anoxic storage conditions, unfed granulated biomass retains its morphology and activity for several years at 15-20 °C. ...
ABSTRACT
The experiment was conducted to testify to the
effectiveness of granular biomass (49.5 tonnes) transferred
and stored in the 24 Isotainers each having a capacity of
1.2 tonnes and 2 storage tanks each having a capacity of
10.2 tonnes. The biomass was stored for a p eriod of 22
weeks after the decommissioning of the EGSB reactor.
The intention was to re-use the same biomass during the
recommissioning of the EGSB reactor, after the completion
of its repair. The biomass was stored under natural anoxic
environmental conditions. During the anoxic storage period,
neither of the parameters, such as temperature and pH were
adjusted, nor were any nutrients added.
During the whole anoxic storage period, the pH was in
the neutral range (7.09) whereas the temperature was in the
mesophilic range (25 °C). The granular biomass activity was
reduced to 0.21 g/gVSS.d. Granular colour and morphology
(round) remained unchanged. However, the granular size
showed the characteristics of shrinkage. Granular size
reduced from 4.5-5.0 mm to 2.0-3.0 mm after 22 weeks
of anoxic storage. Elevated NH4-N nitrogen (948 ppm) and
orthophosphate (162.7 ppm) levels were also observed
during the stressed storage period. Cannibalism and cell
lysis hypothesis were proved positive based on increased
available phosphorus and ammonium-N concentrations in
the storage tank. Redox potential decreased by 97 % by the
end of the study.
The same anoxic granulated biomass was then reused to
restart the EGSB reactor. After 4 weeks of EGSB operations,
the biomass activity increased to 0.51 g/gVSS.d and the
granular size increased its size to 5.0 mm. The sCOD
concentration of the stored biomass also showed a gradual
reduction during the storage time. The reuse of stored
biomass is not in the scope of this paper.
... al., 2009). Eiroa et al. (2004) described successful granulation at the ratio of 3.5, but according to Ruiz et al. (2006), values under 5 resulted in the disintegration of granules. Some biologically degradable substrates (e.g. ...
... Moreover, higher concentrations of N-NO 3 encouraged the growth of larger granules (Cuervo-Lopez et al., 1999; Ruiz et al., 2006). Hulshoff Pol, (1989) reported that with a little deterioration of granular structure under anoxic storage conditions, unfed granulated biomass retains its morphology and activity for several years at 15-20 °C. ...
The experiment was conducted to testify to the effectiveness of granular biomass (49.5 tonnes) transferred and stored in the 24 Isotainers each having a capacity of 1.2 tonnes and 2 storage tanks each having a capacity of 10.2 tonnes. The biomass was stored for a period of 22 weeks after the decommissioning of the EGSB reactor. The intention was to re-use the same biomass during the recommissioning of the EGSB reactor, after the completion of its repair. The biomass was stored under natural anoxic environmental conditions. During the anoxic storage period, neither of the parameters, such as temperature and pH were adjusted, nor were any nutrients added. During the whole anoxic storage period, the pH was in the neutral range (7.09) whereas the temperature was in the mesophilic range (25 °C). The granular biomass activity was reduced to 0.21 g/gVSS.d. Granular colour and morphology (round) remained unchanged. However, the granular size showed the characteristics of shrinkage. Granular size reduced from 4.5-5.0 mm to 2.0-3.0 mm after 22 weeks of anoxic storage. Elevated NH 4-N nitrogen (948 ppm) and orthophosphate (162.7 ppm) levels were also observed during the stressed storage period. Cannibalism and cell lysis hypothesis were proved positive based on increased available phosphorus and ammonium-N concentrations in the storage tank. Redox potential decreased by 97 % by the end of the study. The same anoxic granulated biomass was then reused to restart the EGSB reactor. After 4 weeks of EGSB operations, the biomass activity increased to 0.51 g/gVSS.d and the granular size increased its size to 5.0 mm. The sCOD concentration of the stored biomass also showed a gradual reduction during the storage time. The reuse of stored biomass is not in the scope of this paper.
... Especially, the chemical oxygen demand (COD)/N ratio seems to influence the co-occurrence of these two metabolic pathways. Ruiz et al. (2006) investigated several ratios of these parameter and if they either inhibit or promote denitrification or methanogenesis. Low COD/N ratios (but >1) improved the activity of denitrifying organisms and inhibited methanogens, whereas higher ratios (e.g., 100) resulted in higher activity of methanogenic microorganisms. ...
... Nevertheless, the ratio around 10 appeared to be appropriate for both metabolic activities, because neither the methanogens nor the denitrifiers were completely inhibited. But at this stage, their general activity was lower than in separately operated denitrification or methanogenetic bioreactors (Ruiz et al., 2006). Also, Grießmeier et al. (2017) observed a simultaneous methanogenesis and denitrification in their laboratory reactors. ...
Nitrate pollution is a growing environmental threat that affects both ground‐ and surface‐water. The typically used technique for nitrate elimination in wastewater treatment plants cannot be applied for all water streams as it necessitates a highly developed technical infrastructure. Field denitrification beds comprise one strategy to treat surface water containing high nitrate loads, which typically is due to the increasing agricultural land use. Here, the water passes through a basin containing a cheap carbon material as electron donor that provides the environmental niche for a complex microbial biocenosis. The microorganisms catalyze the hydrolysis of the polymeric organic carbon substrate and a variety of fermentative and respiratory pathways that are in the end supposed to lead to an efficient denitrification process. This review article integrates our current knowledge on environmental and operating parameters of and within denitrification beds including biotic and abiotic factors influencing the nitrate removal efficiency. Steering of these two factors can allow to minimize pollution swapping and the formation of greenhouse gases.
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... This behavior can be attributed to the preferential development of organic carbon degrading microorganisms. TOC/N ratio had a strong effect on biomass activity: lower values of this ratio generate high heterotrophic denitrifying activity, while high organic carbon matter concentrations promote organic carbon removal [46]. ...
... During denitritation, the OCV values were detected only in tests D5 and D6, though they were This behavior can be attributed to the preferential development of organic carbon degrading microorganisms. TOC/N ratio had a strong effect on biomass activity: lower values of this ratio generate high heterotrophic denitrifying activity, while high organic carbon matter concentrations promote organic carbon removal [46]. ...
In this work, the feasibility of the Shortcut Biological Nitrogen Removal (SBNR) in the anodic chamber of a Microbial Fuel Cell (MFC) was investigated. Thirty day experiments were carried out using synthetic wastewaters with a Total Organic Carbon vs. nitrogen ratio (TOC/N) ranging from 0.1 to 1. Ammonium, nitrite, nitrate, pH, and TOC were daily monitored. Results showed that microaerobic conditions in the anodic chamber favored the development of nitritation reaction, due to oxygen transfer from the cathodic chamber through the membrane. Nitritation was found to depend on TOC/N ratio: at TOC/N equal to 0.1 an ammonium removal efficiency of up to 76% was observed. Once the oxygen supply to the cathodic chamber was stopped, denitritation occurred, favored by an increase of the TOC/N ratio: a nitrite removal of 80.3% was achieved at TOC/N equal to 0.75. The presence of nitrogen species strongly affected the potential of the electrochemical system: in the nitritation step, the Open Circuit Voltage (OCV) decreased from 180 mV to 21 mV with the decrease of the TOC/N ratio in the investigated range. Lower OCV values were observed in the denitritation steps since the organic carbon acted as the energy source for the conversion of nitrite to nitrogen gas. A kinetic analysis was also performed. Monod and Blackman models described the ammonium and the organic carbon removal processes well during the nitritation step, respectively, while Blackman-Blackman fitted experimental results of the denitritation step better.
... During period IV the sludge concentration increased to 2.8 g VSS/L and SDA decreased to 19 mg N/gVSS·h. SDA values were in the same range of previously reported values for up flow sludge bed reactors (Ruiz et al., 2006). ...
... Similar amounts of CH 4 can be generated from septic tanks that are often used as wastewater pretreatment in CW systems. No methane generation was explained because at COD/N ratios around 5 or lower, denitrification effectively competes for COD utilization over methanogenesis (Ruiz et al., 2006). Thus, recirculation of the nitrified effluent effectively suppresses CH 4 generation in the pre-treatment step. ...
The aim of this work was to study the operational characteristics and the efficiency of a compact constructed wetland system for municipal wastewater treatment that integrates denitrification in the pre-treatment unit. The proposed system was simulated by two units in series with effluent recirculation, the first one being an anoxic digester, conceived as a hydrolytic up flow sludge bed for solids hydrolysis and denitrification, and the second one a sand column that simulated the operation of a vertical flow constructed wetland. The hybrid system consisted of two small columns of 4 and 10.2cm in diameter (anoxic digester and vertical flow unit, respectively). The unplanted system was operated successively with synthetic and real municipal wastewater over a period of 136days. Hydraulic loading rate ranged from 212 to 318mm/day and surface loading rate from 122 to 145g/m(2)·day of chemical oxygen demand and 10-15g/m(2)·day of total nitrogen for the overall system. The overall system reached removals of 91% to 99% for total suspended solids, chemical oxygen demand and biochemical oxygen demand whilst total nitrogen removal ranged from 43% to 61%. In addition to suspended solids removal (up to 78%), the anoxic digester provided high denitrification rates (3-12gN/m(2)·day) whilst the vertical flow unit provided high nitrification rates (8-15gN/m(2)·day). Organic matter was mainly removed in the anoxic digester (63-82% chemical oxygen demand) and used for denitrification. Final effluent concentration was lower for ammonia (7.4±2.4mgN/L on average) than for nitrate (19.8±4.4mgN/L), denitrification appearing as the limiting step in nitrogen removal in the system. CH4 or N2O emissions were not detected in any of the units of the system indicating very low greenhouse gas emissions.
... This might lead to dominance of heterotrophs other than DNPAOs which in turn might have a negative impact on the overall denitrification process 2 . A similar impact on the metabolism of denitrifying bacteria can also be contemplated from the current observation and analogous results have been reported elsewhere 16,17 . With suspension of sludge (collected in fasting condition from the parent SBR during aerobic cycle) in fresh media, microorganisms switch to feasting condition and assimilate PO 4 rapidly. ...
... COD/N ratio was <10 (0.36-6.37) to uphold denitrification as the only route of organic matter consumption 17 . ...
Simultaneous nitrate-N, phosphate and COD removal was evaluated from synthetic waste water using mixed microbial consortia in an anoxic environment under various initial carbon load (ICL) in a batch scale reactor system. Within 6 hours of incubation, enriched DNPAOs (Denitrifying Polyphosphate Accumulating Microorganisms) were able to remove maximum COD (87%) at 2g/L of ICL whereas maximum nitrate-N (97%) and phosphate (87%) removal along with PHB accumulation (49 mg/L) was achieved at 8 g/L of ICL. Exhaustion of nitrate-N, beyond 6 hours of incubation, had a detrimental effect on COD and phosphate removal rate. Fresh supply of nitrate-N to the reaction medium, beyond 6 hours, helped revive the removal rates of both COD and phosphate. Therefore, it was apparent that in spite of a high carbon load, maximum COD and nutrient removal can be maintained, with adequate nitrate-N availability. Denitrifying condition in the medium was evident from an increasing pH trend. PHB accumulation by the mixed culture was directly proportional to ICL; however the time taken for accumulation at higher ICL was more. Unlike conventional EBPR, PHB depletion did not support phosphate accumulation in this case. The unique aspect of all the batch studies were PHB accumulation was observed along with phosphate uptake and nitrate reduction under anoxic conditions. Bioinformatics analysis followed by pyrosequencing of the mixed culture DNA from the seed sludge revealed the dominance of denitrifying population, such as Corynebacterium, Rhodocyclus and Paraccocus (Alphaproteobacteria and Betaproteobacteria). Rarefaction curve indicated complete bacterial population and corresponding number of OTUs through sequence analysis. Chao1 and Shannon index (H') was used to study the diversity of sampling. "UCI95" and "LCI95" indicated 95% confidence level of upper and lower values of Chao1 for each distance. Values of Chao1 index supported the results of rarefaction curve.
... When naturally the nitrification process affects the concentration of dissolved oxygen (DO) in water bodies and can cause eutrophication. When the nitrification process takes place oxic process, it will form nitrate (NO3¯) and nitrite then in anoxic conditions is reduced to nitrogen gas (Ruiz et al., 2006). Because the wastewater from the tofu industry contains a high organic and protein load, it must be treated technically before being discharged into water bodies. ...
It is necessary to design a nitrification bioreactor process so that further processing takes place optimally. Performance studies are carried out by evaluating the kinetic parameters that apply specifically to the applied process. The Monod model was applied to determine the value of kinetic parameters in designing and operating a bioreactor. This study aims to determine the value of the kinetic parameters to variations in feed concentration (50, 75, and 100%). The mechanism of the reactor process for the decomposition of pollutants, the influent is fed into the reactor with an up-flow pristaltic pump. The decomposition process provides contact time between organic matter and microorganisms, resulting in a good separation from the reactor outlet. The most optimum kinetic parameter value at 100% wastewater concentration with a value of (k) 1.1086 (dayˉ 1), (Ks) 1.0564 g l-1, (Y) 5.4862 mg MLVSS/mg, (kd) 1.7944 (dayˉ 1), (µm) 6.8372 (dayˉ 1).
... Three possible routes can occur in oxygen limiting environment for the treatment of nitrate and organic matter rich wastewater including denitrification, methanization, and dissimilatory nitrate reduction to ammonia (DNRA). DNRA is considered as an undesired route since it results in the production of ammonia which denotes a step back in the treatment procedure (Ruiz et al., 2006). While, on the other hand, the additional intermingling e.g., co-digestion of food waste with municipal wastewater can also result in the undesirable increase of sulphate load to AnMBR (Meng et al., 2009;Zhang et al., 2014). ...
The application of Anaerobic Membrane Bioreactors (AnMBRs) for municipal wastewater treatment has been made sufficiently sustainable for practical implementations. The potential benefits are significant as AnMBRs effectively remove a broad range of contaminants from wastewater for water reuse, degrade organics in wastewater to yield methane-rich biogas for resultant energy production, and concentrate nutrients for subsequent recovery for fertilizer production. However, there still exist some concerns requiring vigilant considerations to make AnMBRs economically and technically viable. This review paper briefly describes process fundamentals and the basic AnMBR configurations and highlights six major factors which obstruct the way to AnMBRs installations affecting their performance for municipal wastewater treatment: (i) organic strength, (ii) membrane fouling, (iii) salinity build-up, (iv) inhibitory substances, (v) temperature, and (vi) membrane stability. This review also covers the energy utilization and energy potential in AnMBRs aiming energy neutrality or positivity of the systems which entails the requirement to further determine the economics of AnMBRs. The implications and related discussions have also been made on future perspectives of the concurrent challenges being faced in AnMBRs operation.
... Some factors that interfere in the denitrification process in anaerobic reactors include concentration of dissolved oxygen (DO), pH, alkalinity, temperature, presence of toxic substances, hydraulic retention time (HRT), solids retention time (SRT), source of organic carbon, carbon to nitrogen ratio, and recirculation ratio (Jimenez et al. 1987;Dinçer and Kargi 2000;Ruiz et al. 2006;Chen et al. 2009;Han et al. 2015). However, to date, all research carried out has sought to evaluate the recirculation to anoxic tanks, which precede the reactors in the activated sludge system. ...
Anaerobic reactors have been spreading in places with tropical climate and in developing countries. Their association with aerobic reactors provides great removal of carbonaceous matter with lower energy consumption and sludge production, although it does not allow the reduction in the concentration of total nitrogen. An alternative that could provide nitrogen removal without the construction of new reactors would be the nitrified effluent recirculation to the anaerobic reactor, in which denitrification would take place. Therefore, in this study, we sought to perform the nitrified effluent recirculation to the packed bed reactor (PBR) and UASB and concluded the following: (a) due to the presence of filling material, PBR tended to present a better performance in denitrification and removal of organic matter and suspended solids than the UASB reactor; (b) when performing the nitrified effluent recirculation to anaerobic reactors, the COD/NO3−-N ratio must not be less than 6; (c) the concentration of N2O in the biogas of both reactors remained below the detection limit, minimizing the production of greenhouse gases; and (d) the limitation of organic matter promoted partial denitrification, creating conditions for the emergence of anammox bacteria in the sludge.
... While the COD/NO3 --N ratio is between 1.5 and 2.5, the nitrite concentration reaches 1.98 mgL -1 to 1.02 mgL -1 in 2.5 h, and then rapidly decreasing almost 0 mgL -1 within 8h. But, at the COD/NO3 --N ratios of 1.0 and 2.5, the nitrite concentration increased to a highest at 1.5 h and then gradually declined, causing a definite amount of nitrite to accumulate in 5 h [27]. Simultaneously, when the COD/NO3 --N ratio was 0.5 and 1.0, the corresponding denitrification efficiency was low. ...
In this study, a three-dimensional bioelectrochemical reactor system (3D-BERs) with granular activated carbon (GAC) epitomizes a novel treatment technology for treating nitrate-polluted water. The conventional denitrification process faces many challenges, including the huge demand for organic carbon, long-term accumulation of intermediate products, and the adaptation period. Results shown that under the optimal conditions of the COD/NO3--N ratio was 1.5, the denitrification efficiency reached 98.62%, when compared to 81.12% at COD/ NO3--N ratio of 3.5, and the initial pH of 7.5 ± 0.5, NO3--N was entirely removed at 2.2 h without accumulation of nitrite. The high initial ratio of NO2--N/NO3--N is mainly to accelerate the denitrification rate by accelerating the reduction of nitrite. Denitrification process followed by zero-order kinetics linear model for at different concentrations of inlet NO3--N, and achieved higher denitrification rate at greater inlet NO3--N concentration. High-throughput sequencing shows that the community structure and relative abundance of bacteria changed significantly, especially at the genes and the phyla level in immobilized GAC particles. Microbial composition enhanced the removal of nitrogen at the inner surface (IS) and bottom surface (BS) of immobilized GAC carriers. Therefore, this system is expected to be a more efficient and useful supplement or a cost-effective alternative compared to the traditional low carbon to nitrogen wastewater treatment system.
... DRNA dominates the NO 3 − and NO 2 − reduction in reductant-rich anoxic environments, such as highly organic marine sediments. This process is competitive with denitrification process, especially with a higher C/N ratio (Ruiz et al. 2006). It is assumed in earlier studies that nitrate-reducing bacteria exploit this pathway primarily when NO 3 − is limited because DRNA consumes 8 electrons compared with the 4 and 5 consumed when NO 3 − is reduced only as far as N 2 O or N 2 , respectively (Madigan et al. 2010). ...
Bioretention cell (BRC), bioretention cell with microbial fuel cell (BRC-MFC), and an enhanced combined BRC-MFC system with bimetallic zero-valent iron (BRC-MFC-BZVI) were implemented in current study to treat the domestic wastewater. Nitrogen removal characteristics of three systems were investigated by adjusting influent carbon/nitrogen ratio (C/N ratio of 2.54–19.36). Results revealed that the nitrification and denitrification performances were mainly influenced by organic matter and system combination, which further affected nitrogen removal. When the influent C/N ratio was between 2 to 3, compared with BRC system, in BRC-MFC and BRC-MFC-BZVI system, chemical oxygen demand (COD), total nitrogen (TN), and ammonical nitrogen (NH4+-N) removal efficiencies were still reached to 83.04%, 61.06%, and 42.26% and 86.53%, 43.61%, and 50.99% respectively, which simultaneously achieved high-efficiency of organic matter and nitrogen removal. The efficient supply of electrons in the BRC-MFC and BRC-MFC-BZVI processes was the main reason to achieve profound denitrification removal under the condition of low C/N. Removal rates of nitrate (NO3−−N) and nitrite (NO2−−N) were relatively higher due to microbial-driven redox reactions caused by driving electrons to flow in the closed circuit of metal wire connection. Moreover, phylogenetic diversity of bacterial communities mainly induced the catalytic iron, which further enhanced biological nitrogen reduction. The maximum efficient removal of organic matter (OM), TN, and NH4 + −N were obtained in the BRC-MFC-BZVI system, which were 98.42% (C/N = 10.42), 55.61% (C/N = 4.16), and 61.13% (C/N = 4.16), respectively.
... Besides, nitrate being directly reduced to ammonia via DNRA, frequently happened in SDM systems fed with glucose. 5,25 That could explain a bit of ammonia left in the final effluent. Given these factors, we forecast that methanogenesis, aerobic methane oxidation, and denitrification should be concurrently developed in a single methane-producing system through integrating SMD and AME-D. ...
BACKGROUND
Improved denitrification with methane as alternative electron donor is regarded as a promising low‐cost approach for organic nitrate‐containing wastewater treatment. However, in situ capture of methane released from a methanogenic system for enhancing nitrogen removal seems to be scarcely reported. The applications of simultaneous denitrification, methanogenesis, and aerobic methane oxidation coupled to denitrification provide the possibility for solving the challenging issue.
RESULTS
In this study, simultaneous methanogenesis, aerobic methane oxidation, and denitrification (SMAMOD) was firstly established in a microaerobic up‐flow sludge bed biofilm reactor (MUSBBR) treating high‐strength synthetic wastewater with 2000 mg L ⁻¹ Chemical oxygen demand (COD) and 400 mg L ⁻¹ nitrate. The operation demonstrated 98.8% COD, 98.8% NO 3 ⁻ ‐N, and 93.5% TN removals were stably obtained. Microbial community found the coexistence and cooperation of Methanothrix as methanogens, Methylogaea as aerobic methanotrophs, as well as facultative denitrification genera in SMAMOD system. Gene profiling demonstrated key functional genes involved in aerobic and anaerobic fermentation, methanogenesis and aerobic methane oxidation, as well as nitrate reduction induced by nitrate reductase systems. In organic oxygen‐limited biotransformation, glucose was degraded mainly through aerobic respiration, anaerobic fermentation into methane by decarboxylation of acetic acid, and further methane aerobic oxidation pathways, while acetate‐ and methanol‐denitrification and dissimilatory nitrate reduction to ammonium pathways participated in the nitrogen bioconversion. Further, the metabolic mechanism of SMAMOD might be unraveled by spatial interactions of key metagenomes in core microbial consortiums in the MUSBBR reactor.
CONCLUSION
The study offers valuable metagenomic insights into SMAMOD as a potentially compact process for sustainable treatment of high‐strength organic nitrate‐containing wastewater. © 2020 Society of Chemical Industry
... In recent years, fixed film reactors, such as fluidized bed reactor (Xu et al. 2019), biofilm reactor (Swain et al. 2018), and UASB (Ruiz et al. 2006), have been successfully developed for the wastewater treatment. Among them, the fluidized bed bioreactor (FBBR) has attracted considerable concern as an alternative to the conventional activated sludge process due to its higher biomass concentration, lower hydraulic retention time (HRT), and high performance efficiency. ...
Partial nitrification combined with anaerobic ammonium oxidation (Anammox) process has been recognized as a promising technology for the nitrogen removal in wastewater treatment. This research aimed to focus on how to successfully achieve the partial nitrification in a fluidized bed bioreactor (PNFBR) for the treatment of synthetic wastewater with high ammonia concentration. The influence factors, including dissolved oxygen (DO) levels, free ammonia (FA)/free nitrous acid (FNA) concentration, ambient temperature, influent ammonia concentration, and alkalinity, were investigated to achieve the goal of high nitrite accumulation. Results exhibit that the optimal conditions for the PNFBR was 30 °C with the 7:1 of ratio of alkalinity to influent nitrogen, 1 mg/L of DO concentration, 28 day of SRT, 16.6 day of hydraulic retention time (HRT), and 400 mg/L of influent ammonia concentration. Additionally, at the lower temperature (20 °C), high nitrite accumulation was also attained by increasing the alkalinity (8:1 of ratio of alkalinity to influent nitrogen) in system. Compared with other biofilm system, the PNFBR with the new media mixture of acrylonitrile butadiene styrene (ABS) plastic and its modified one could achieve the effluent requirements for anammox, with the PNFBR effluent NO2⁻-N:NH4⁺-N ratio appropriately at 1:1.
... Sugar industries generate molasses as waste, which is used as raw material for the alcohol production by the distilleries (Nandy et al., 2002). Distillery generates an average of 15 L of wastewater (spent wash) per liter of alcohol produced from molasses (Ruiz et al., 2006). Distillery effluent is one of the most complicated wastes to handle due to its acidic pH, high temperature, dark brown color, high ash content, chloride, sulfate, nutrient, and high percentage of dissolved inorganic and organic matter (Aiorella et al., 1983;Beltran et al., 2001). ...
Corrosion affects the usefulness of metallic materials used in the construction of an effluent treatment plant (ETP). The present report investigates the corrosive and inhibitive properties of the chemicals present in the effluent of paper mill and distillery industries. Chemicals such as chloride, chlorophenols, phosphate, calcium, nitrite, and nitrate enhance corrosion, whereas the presence of sulfate, potassium, organic matter, and melanoidins (color) inhibits corrosion at an acidic pH level in distillery and paper mill effluents. A finding shows that pH level has an important role in increasing or decreasing the effect on corrosivity of effluents.
... Although no operational problems occurred during this experiment, the structure degradation trend observed would likely produce sludge buoyancy or significant biomass washout during long-term operations. Granular structure degradation that leads to sludge with low settling velocities is a severe problem for the operation of upflow reactors under low COD/N ratios as pointed out by Ruiz et al. (2006) who, studying the effect of different COD/N ratios on denitrifying and methanogenic activities in upflow sludge blanket reactors, observed that under COD/N ratios of 5 and lower, granules disappeared and were replaced by flocculent sludge with high sludge volumetric index that caused an increment in the height of the sludge bed inside the reactors. The poor settling velocities of low-density sludge could make the overall reactor operation difficult by increasing sludge washout and overall treatment capacity (Yoda and Nishimura 1997;Lee et al. 2004). ...
Effluents from petroleum refineries contain a toxic mixture of sulfide, nitrogen, and phenolic compounds that require adequate treatment for their removal. Biological denitrification processes are a cost-effective option for the treatment of these effluents, but the knowledge on the microbial interactions in simultaneous sulfide and phenol oxidation in denitrifying reactors is still very limited. In this work, microbial community structure and macrostructure of granular biomass were studied in three denitrifying reactors treating a mixture of inorganic (sulfide) and organic (p-cresol) electron donors for their simultaneous removal. The differences in the available substrates resulted in different community assemblies that supported high removal efficiencies, indicating the community adaptation capacity to the fluctuating compositions of industrial effluents. The three reactors were dominated by nitrate reducing and denitrifying bacteria where Thiobacillus spp. were the prevalent denitrifying organisms. The toxicity and lack of adequate substrates caused the endogenous decay of the biomass, leading to release of organic matter that maintained a diverse although not very abundant group of heterotrophs. The endogenous digestion of the granules caused the degradation of its macrostructure, which should be considered to further develop the denitrification process in sulfur-based granular reactors for treatment of industrial wastewater with toxic compounds.
... Based on this, the performance of denitrifying reactor is closely related with the amount and activities of the denitrifiers in the reactor (Tang et al. 2011;Chen et al. 2010). Compared to activated sludge and biofilm reactors, denitrifying granular sludge reactor holds higher amount of dominant microorganisms that appeared as granular sludge, which was normally reported to be more excellent for denitrification because of higher cell concentrations in the reactors (Nancharaiah and Venugopalan 2011;Ruiz et al. 2006). ...
Denitrifying granular sludge reactor holds better nitrogen removal efficiency than other kinds of denitrifying reactors, while this reactor commonly needs seeding anaerobic granular sludge and longer period for start-up in practice, which restricted the application of denitrifying granular sludge reactor. This study presented a rapid and stable start-up method for denitrifying granular sludge. An upflow sludge blanket (USB) reactor with packings was established with flocculent activated sludge for treatment of high concentration nitrite wastewater. Results showed mature denitrifying granular sludge appeared only after 15 days with highest nitrogen removal rate of 5.844 kg N/(m³ day), which was much higher than that of compared anoxic sequencing batch reactor (ASBR). No significant nitrite inhibition occurred in USB and denitrification performance was mainly influenced by hydraulic retention time, influent C/N ratio and internal reflux ratio. Hydraulic shear force created by upflow fluid, shearing of gaseous products and stable microorganisms adhesion on the packings might be the reasons for rapid achievement of granular sludge. Compared to inoculated sludge and ASBR, remarkable microbial communitiy variations were detected in USB. The dominance of Proteobacteria and Bacteroidetes and enrichment of species Pseudomonas_stutzeri should be responsible for the excellent denitrification performance, which further verified the feasibility of start-up method.
... This indicates that the biodegradation was significantly dependent upon available DO (> 1 mg/L). In the biodegradation of organic matter, metabolism may be dependent upon the COD/TN ratio [28]. The ratio of COD Cr /TN in this study decreased a little, from 9.7 to 7.9, implying a stable metabolism of organic matter degradation [18]. ...
To examine the feasibility of reuse of raw fishmeal wastewater, it was biodegraded by a microbial consortium in a 1-m³ reactor, and the final culture broth including mixed microbes was applied as biofertilizer to field cultivation of lettuce and Chinese cabbage. Moreover, economic analysis of the entire process was performed. A stable metabolism of organic matter degradation for 80 h with sufficient dissolved oxygen produced an amino acid content of 14.66 g per 100 g sample, along with increased cation and anion concentrations. The concentrations of N, P and K in the final culture broth were 2.26, 0.87 and 0.65%, respectively, while those of heavy metals were very low. In field cultivation of the two leafy vegetables, the biodegraded fishmeal wastewater showed better fertilizing ability than commercial fertilizers because of its high amino acid content. In addition, no external damage to leaves by the fertilization was observed. In economic analysis, the expected profitability from the practical reuse of raw fishmeal wastewater was estimated to be $491.68 per a single biodegradation, which corresponds to $25,567.36 per year. As a result, the complete reuse of fishmeal wastewater could be feasible and provide essential benefits.
... Influent chemical oxygen demand (COD)/NO x − -N ratio is one of the most critical parameters for the realization of the SDM process and succession of the functional microbes (Akunna et al. 1993;Chen et al. 2009). Suitable COD/NO x − -N ratios with different carbon sources for the SDM process have been well discussed in literatures (Akunna et al. 1992;Del Pozo and Diez 2003;Ruiz et al. 2006), and with glucose as the carbon source, a COD/NO 3 − -N ratio around 8.0 could be treated as the minimum threshold for the SDM process from the aforementioned reports and used in the experiment. ...
Batch experiment at COD/NO3⁻-N ratio of 8.0 was conducted to investigate the initial performance of the simultaneous denitrification and methanogenesis (SDM) process and corresponding granular sludge (SDMGS). The results showed a high level of inhibition of methanogenesis activity with nitrate addition, and the particle size, settling performance, and morphologies of the SDMGS were also different from conventional methanogenesis granular sludge. The structure and succession of bacterial communities of the granular sludge during the initial stage of the SDM process were determined using the high-throughput sequencing method. Sequence analysis indicated that diversity of bacterial communities was significantly decreased due to nitrate addition. Proteobacteria, Bacteroidetes, Firmicutes, and Spirochaetes were identified to be the dominant bacterial communities (96.06%) of the SDMGS samples, and microbes associated with anaerobic fermentation were reorganized. Alpha-, Beta- and Gamma-proteobacteria, and Bacteroides might be the sources of denitrificans. Lastly, species associated with animal and human infections, such as Enterobacteriaceae, Bacteroides, and other common human enteric pathogens, were found to be recovered during the initial stage. Short-term assessment of bacterial communities of the SDMGS would strengthen understandings of the effects of nitrate contamination in water bodies and provide vital guidance for operation of nitrate-containing wastewater treatment.
... The high value of SMA in DN cultures was unexpected because it is generally recognized that denitrification negatively affects methanogenesis in the context of simultaneous denitrification-methanogenic systems (Akizuki et al., 2015;Garibay-Orijel et al., 2005, 2006aTutgas et al., 2010). Also, the negative effect has been related to competition for organic substrate (Garibay-Orijel et al., 2006b), high oxidation-reduction potential imposed by denitrifying conditions that could have a negatively effect on methanogenic archaea (Ruiz et al., 2006), the inhibitory effects of intermediate N species in nitrate reduction (such as NO) on methanogenic archaea (Akizuki et al., 2015;Tutgas et al., 2010), inter alia. Thus, methanogenesis inhibition by denitrification seems to be a multifactorial issue. ...
The objective of this work was to evaluate the degradation of the nonionic surfactant Tween 80 by a PCE-degrading consortium anchored in bioparticles of fluidized bed bioreactors used in onsite remediation. Batch lab-scale bioreactors were set with dominant denitrifying (DN), methanogenic (M), and aerobic (Ab) metabolisms. Tween 80 at 100 mg/L was the sole source of carbon and energy. Denitrifying bioreactors had the highest surfactant removal (70%). Tween removals in M and Ab bioreactors were 53 and 37%, respectively. Removals of organic matter (COD) closely followed the efficiencies reported for Tween. This strongly suggested that degradation of Tween 80 occurred. Positive consequences of Tween degradation in remediation are first, the surfactant will not become an environmental/health liability by remaining as a recalcitrant or toxic substance in aquifers or in treated effluents; and second, savings on aeration could be achieved by conducting Tween 80 degradation in anaerobic conditions, either DN or M.
... However, as shown in Fig. 4, a 13% decrease in the nitrate/nitrite reduction efficiency was observed when the recirculation ratio was increased from 0.25 to 0.5. This finding was attributed to the corresponding decrease in the COD/NO 3 À eN ratio of compartment 3 from 7.8 to 4.5, leading to insufficient carbon source for denitrification (19,27). When the recirculation ratio was further increased to 2, only less than 70% of nitrate was removed because of the low COD/NO 3 À eN ratio of 2.5 in compartment 3. To supplement the carbon source for denitrification, the influent leachate was step fed into compartments 1 and 2 with equal flux (Fig. 1, dashed line). ...
The application of an anaerobic baffled reactor (ABR) with four compartments was investigated for the simultaneous removal of carbon and nitrogen from leachate. The nitrified effluent was recycled to compartment 3 of the ABR, thereby avoiding the adverse influence of nitrogen oxides on anaerobic methanogenesis in compartment 1. Nitrified effluent recirculation not only enhanced chemical oxygen demand removal (>95.6%) but also improved the total nitrogen removal efficiency from 12.7% to 67.4% with increasing recirculation ratio from 0.25 to 2. The challenge of insufficient carbon sources for heterotrophic denitrification in compartment 3 with a high recirculation ratio could be overcome by step feeding of leachate. Moreover, various reduced sulfurs (e.g., sulfide, elemental sulfur, and organic sulfur) were involved in nitrate reduction via sulfur-based autotrophic denitrification. The addition of sulfide to compartment 3 further confirmed nitrate reduction using reduced sulfur as an electron donor. The interaction of organic carbon, reduced sulfur, and nitrate in leachate treatment needs further study.
... It was also determined that as long as the COD/NO 3 − -N ratio is lower in the cathode (<12) and higher in the anode (≥100), the OCV in positive, denitrification is favored and high rates of NO 3 − -N removal are achieved. Lower COD/NO 3 − -N ratio tested in anaerobic digesters have been shown to promote denitrification activity (Akunna et al. 1992;Ruiz et al. 2006). ...
Microbial fuel cells (MFCs) are emerging wastewater treatment systems with a proven potential for denitrification. In this study, we have developed a high-rate denitrifying MFC. The anode consisted of cow manure and fruit waste and the cathode consisted of cow manure and soil. The initial chemical oxygen demand (COD)/nitrate nitrogen (NO3 (-)-N) was varied from 2 to 40 at the cathode while keeping the anode ratio fixed at 100. NO3 (-)-N removal rate of 7.1 ± 0.9 kg NO3 (-)-N/m(3) net cathodic compartment (NCC)/day was achieved at cathode COD/NO3 (-)-N ratio 7.31 with the current density of 190 ± 9.1 mA/m(2) and power density of 31.92 ± 4 mW/m(2) of electrode surface area. We achieved an open-circuit voltage (OCV) of 410 ± 20 mV at initial cathodic NO3 (-)-N of 0.345 g/l. The cathode COD/NO3 (-)-N ratio had a significant influence on MFC's OCV and nitrate removal rate. Lower OCV (<150 mV) and NO3 (-)-N removal rates were observed at COD/NO3 (-)-N ratio >12 and <7. Experiments done at different cathode pH values indicated that the optimum pH for denitrification was 7. Under optimized biochemical conditions, nitrate removal rate of 6.5 kg NO3 (-)-N/m(3) net cathodic compartment (NCC)/day and power density of 210 mW/m(2) were achieved in a low resistance MFC. The present study thus demonstrates the utility of MFCs for the treatment of high nitrate wastes.
... The resulting CODCr/TN ratio decreased from 8.6 (at the beginning) to 2.0 (at the end). It is known that the C/N ratio may influence the metabolic pathway of organic matter utilization [26]. Accordingly, the decrease in the C/N ratio in a later stage of aerobic denitrification implies that external carbon may be necessary for high efficiency of N removal. ...
To treat leather industry wastewater (LIW) containing high nitrogen concentration, eight aerobic denitrifiers were isolated from sludge existing in an LIW-treatment aeration tank. Among them, one strain named as KH8 had showed the great ability in denitrification under an aerobic condition, and it was identified as Pseudomonas aeruginosa R12. The aerobic denitrification ability of the strain KH8 was almost comparable to its anaerobic denitrification ability. In lab-scale aerobic denitrifications performed in 1-L five-neck flasks for 48 hr, denitrification efficiency was found to be much improved as the strain KH8 held a great majority in the seeded cells. From the nitrogen balance at the cell-combination ratio of 10:1 (the strain KH8 to the other seven isolates) within the seeded cells, the percentage of nitrogen loss during the aerobic denitrification process was estimated to be 58.4, which was presumed to be converted to N2 gas. When these seeded cells with lactose were applied to plant-scale aeration tank for 56 day to treat high-strength nitrogen in LIW, the removal efficiencies of CODCr and TN were achieved to be 97.0% and 89.8%, respectively. Under this treatment, the final water quality of the effluent leaving the treatment plant was good enough to meet the water-quality standards. Consequently, the isolated aerobic denitrifiers could be suitable for the additional requirement of nitrogen removal in a limited aeration-tank capacity. To the best of our knowledge, this is the first report of aerobic denitrifiers applied to plant-scale LIW treatment.
... This implies that the transfer of lab-scale data to a large-scale production will be successful without transport limitation. It is known that the COD/TN ratio may influence the metabolic pathway of the organic matter utilization [35]. Accordingly, control of the COD/TN ratio may be necessary for better bioconversion. ...
A scaled-up bioconversion of fishmeal wastewater (FMW) into liquid fertilizer was performed five times in a 1 m 3 reactor in order to examine the feasibility of commercialization. The importance of aeration was marked. Analyses indicated that dissolved oxygen (DO) level was closely related to the value of oxidation-reduction potential (ORP) and it was crucial to achieve high-quality liquid fertilizer. When pure oxygen was supplied through four diffusers into the reactor, DO levels and ORP values were maintained over 1.2 mg/L and 0.2 mV, respectively all the time during 52 hr of bioconversion. The pH changed from 6.8 to 5.9. The average removal percentages of chemical oxygen demand (COD Cr) and total nitrogen (TN) were 75.0% and 71.6%, respectively. Compared to the result acquired in a 5-L reactor, bioconversion of FMW into liquid fertilizer was achieved in a shorter time under the same removal percentages of COD Cr and TN. The 52-hr culture of inoculated FMW was phytotoxic-free and it possessed comparable fertilizing ability to a liquid fertilizer made from the fish waste in hydroponic culture with amino acid contents of 5.93 g/ 100 g sample. From all the above results, transferring lab-scale data to large-scale production appeared to be successful. As a result, the commercialization of a liquid fertilizer made from FMW was feasible.
Amidst rapid urbanization, municipal wastewater treatment plants remain a significant source of nitrogen compounds, which stems from their effluents. Constructed wetlands, employing denitrification processes, have been proven effective at nitrogen removal. Variations in influent nutrient concentrations are often seen as limiting factors affecting nitrogen removal and influencing microbial communities. This study evaluates the impact of nutrient limitation on nitrogen removal by analyzing changes in microbial communities within constructed wetlands under different influent water C/N ratios. The findings indicate that both excessively high and low C/N ratios constrain nitrogen decomposition, with optimal nitrogen removal observed at C/N ratios of 6 or 7. Moderate C/N values (6–7) support diverse and stable microbial networks, ensuring treatment system stability. Microorganisms play a pivotal role in nitrogen transformation, with the nirk gene being crucial for NH4+−N conversion, while the AOA gene dominates NO2−−N and TN conversion. This study offers practical guidance for identifying a suitable C/N ratio for wastewater treatment and establishes a theoretical foundation for regulating nitrogen removal by microbial communities in constructed wetlands within nitrogen removal systems.
In this study, a heterotrophic/biofilm‐electrode autotrophic denitrification reactor (HAD‐BER) was constructed and nano‐ɑ‐Fe2O3 was coated on granular activated carbon (GAC) as a third electrode to enhance the nitrate removal performance. The introduction of nano‐ɑ‐Fe2O3 could stimulate microorganisms to secrete more extracellular polymeric substances (EPS), accelerating the electron transfer. Moreover, more denitrification bacteria were enriched on the particle electrodes, especially Pseudomonas and Thermomonas, which played a significant role in denitrification. The denitrification performance at different COD/N ratios (0.65‐3.23) and current intensities (0‐150 mA) was investigated in depth. When the nitrate concentration of the influent was 60 mg/L, nitrate was almost completely removed at the optimal current intensity (60 mA) and COD/N ratio (1.29). At the same time, there was almost no nitrite (< 0.10 mg/L) and ammonia nitrogen (0 mg/L) accumulation in the effluent. This study provided a new direction for the advancement of HAD‐BER and accelerated its implementation.
A recirculação de efluente nitrificado para reatores desnitrificantes em sistemas anaeróbios-aeróbios pode implicar na melhora do tratamento de esgotos. Nesse sentido, este estudo avaliou experimentalmente o efeito da razão DQO/N-NO3- na desnitrificação em reator UASB e, a partir dos resultados e com cálculos teóricos de balanço de massa, foi estimado o efeito de diferentes razões de recirculação (R) na concentração final de nitrogênio total em um sistema teórico. Para razões DQO/N-NO3- entre 1,6 - 5,7, a eficiência de desnitrificação varia linearmente entre 31,7 ± 4,3% e 98,6 ± 0,1%, com remoção completa para razões superiores a 5,7. Com a simulação teórica, estimaram-se concentrações finais de nitrogênio total próximas a 30, 20, 15 e 10 mgL-1 utilizando razões de recirculação iguais a 1,5; 2,5; 4,0 e 6,0. Embora não avaliado, o aumento de R deve levar em consideração consequências como a possibilidade de arraste de sólidos, a redução da produção de biogás e a entrada de OD no reator anaeróbio. Palavras-chave: Desnitrificação. Anaeróbio. UASB. Empacotado. Nitrato. Nutriente.
In this work, a three-dimensional bioelectrochemical reactor system (3D-BERs) with granular activated carbon (GAC) was utilized to study the feasibility of simultaneous removal of nitrates by autotrophic-heterotrophic denitrification process under different pH levels. In this present study, it was found that when the influent COD/ NO3--N ratio ranged between 1.5 and 3.5, both autotrophic and heterotrophic denitrifying microorganisms played an important role in denitrification. The experimental results demonstrated that the highest removal efficiency of nitrates under the optimum COD/NO3--N ratio of 1.5 (98.62%) was achieved with an initial pH of 7.5 ± 0.4. Likewise, when the COD/NO3--N ratio of 3.5, the nitrates removal efficiency (81.12%) was achieved with an initial pH of 8.2 ± 0.3, respectively. Batch denitrification processes followed zero-order kinetics at various NO3--N concentrations obtained. The bacterial community structure and relative abundance of bacteria changed at the level of genes and the phylum of immobilized GAC particles. Moreover, the diversity of bacterial composition enhanced the removal of NO3--N at the inner surface (IS), and bottom surface (BS) of immobilized GAC carriers were Gammaproteobacteria, Bacilli, Proteobacteria, and Thauera. In general, this technique is more effective for enhancing the denitrification process in the 3D-BER system.
The issue of enhancing nitrogen removal and managing dissolved methane emission in anaerobic treatment systems is a major bottleneck in its wider application to treat high-strength organic wastewater with nitrate. Herein, a novel aerobic methane oxidation, denitrification coupled to methanogenesis (AMODM) process was developed in a glucose-fed microaerobic expanded granular sludge blanket biofilm reactor (EGSBBR) through in-situ utilization of produced methane for nitrogen removal. The 162-day operation demonstrated that long-term treatment performance under the decreased COD/NO3−-N (C/N) ratio from 66.7 to 10 and the optimal C/N ratio for completing AMODM was found to be 16.7. Microbial community analysis further evidenced that Methanothrix as key methanogen predominated in the sludge bed, while Methlogaea as aerobic methane oxidizer was mainly detected in the packing bed of the hybrid system. Meanwhile, some facultative heterotrophic and dissimilated nitrate-reduction (DNRA) genera also co-existed. The profiling of key functional genes further proved concurrent occurrence of methanogenesis, aerobic methane oxidation and denitrification. Furthermore, possible microbial mechanism on AMODM process was elucidated from the prospective of targeted species interaction within the reactor. This research provides a robust and environment-friendly alternative process treating nitrate-containing organic wastewater towards efficient nitrogen removal, low resource consumption, bioenergy recovery and greenhouse gas reduction.
Two upflow anaerobic sludge blanket reactors were used to investigate the effects of carbon source and COD/N ratio on simultaneous denitrification and methanogenesis (SDM). One reactor (R1) used sucrose as the carbon source, whereas another reactor (R2) was fed with acetate. The formation of SDM granules occurred by increasing the nitrate concentration of wastewater and thus decreasing the COD/N ratio. The analysis of scanning electron microscopy showed that the R1-granule-predominant microbial community was strikingly different with the stepwise increase of nitrate. Indeed, the gas production, soluble metabolites, granular-sludge formation, and nitrogen- and COD-removal efficiency for SDM in the two reactors are dependent on carbon source and COD/N ratio. The average nitrogen- and COD-removal rates for R1 reached 89.1% and 91.8%, respectively at a COD/N ratio higher than four, On the other hand, the average nitrogen- and COD-removal rates for R2 reached 81.8% and 83.4%, respectively, with a COD/N ratio higher than 10. The results of soluble metabolites production in R1 demonstrated that propionate and butyrate were utilized by the denitrifiers. Sucrose should be used as an electron donor at high nitrogen-loading rates. Moreover, if the dissimilatory-nitrate-reduction-to-ammonia process is suppressed, then the buffer-agent dosage could be decreased.
To investigate the advantages of mixed carbon source over a single one in deep denitrification, sodium acetate, glucose and their mixture were used as carbon sources in present study. Denitrification performance, effluent pH, microbial community and carbon source cost were taken into account. With the same influent NO3–-N concentration of 50 mg/L and the same C/N ratio of 1.5, the NO3–-N removal rate with the mixed carbon source (96.53%) was slightly lower than that with sodium acetate (98.15%), but significantly higher than that with glucose (74.69%). The specific denitrification rates of the sodium acetate, glucose and sodium acetate/glucose reactor were 47.7, 29.7 and 45.4 mg N/g VSS d, respectively. The effluent pH with sodium acetate varied in the range of 9.13–9.60, exceeding the discharge standard limit of 9.0, whereas the sodium acetate/glucose reactor could keep pH in the range of 7.80–8.23. The 16 s rRNA gene based high-throughput sequencing revealed that carbon sources determined the microbial community structure and the sludge Shannon index with the mixed carbon source was the highest. Furthermore, cost estimation indicated that the mixed carbon source was the cheapest. This study is significant to reasonable selection of carbon sources for deep denitrification in practice.
Coupling of methanogenesis and denitrification with elevated nitrate shows potential advantages for (N-) heterocyclic compounds removal and methane recovery simultaneously. However, methane production, sludge characteristics and microbial evolution response to elevated nitrate were seldom reported. Here, an experiment lasing about 300 days under the methanogenic condition with sequential influent nitrate addition as COD/NO3⁻-N ratio from 486.03 to 8.00 was carried out. More than 50% decline of removal rate was observed when the COD/NO3⁻-N ratio varied from 19.97 to 8.00 (232 d). At last, the removal rate recovered to around 94% at the COD/NO3⁻-N ratio of 8.00. About 90% of nitrate was removed through denitrification, and a lower content of methane (40–45%) and effluent acetate and propionate (<10 mg/L) were observed with elevated nitrate. Damage of the granule-shaped and multi-layer structure of the sludge with the lift of nitrate addition was studied. Results of high-throughput sequencing hinted that bacteria accounted for about 70% of total microbes and Proteobacteria, Bacteroidetes, Firmicute and Chloroflexi were the dominant phyla shared with sludge at different COD/NO3⁻-N ratio. Pseudomonas genus and Enterobacteriaceae family (Gammaproteobacteria class, Proteobacteria phylum), Brachymonas genus and Rhodocyclaceae family (Betaproteobacteria class, Proteobacteria phylum) might be vital for the denitrification process. An increase of Smithella and Syntrophobacterale genus with elevated nitrate could be partly contributed to denitrification from the transformation of intermediates as propionate and butyrate. Methanosaeta and Methanobacterium genus were two major methanogenic microorganisms, and Methanosaeta seemed to be less adaptable for elevated nitrate than Methanobacterium. A suitable nitrate addition as influent COD/NO3⁻-N ratio ranged from 121.43 to 15.18 was recommended. The results of this work would enhance the understanding of the effects and adaptive mechanism with elevated nitrate under the methanogenic condition and instruct engineering practice for low COD/NO3⁻-N wastewater treatment and methane recovery.
Up-flow anaerobic sludge bed (UASB) reactor originally inoculated by methanogenic granules was operated for nine months for total ammonia nitrogen (TAN) removal through anaerobic ammonium oxidation (Anammox) route with external nitrite source (NH4:NO2 = 0.99 ± 0.19). However, bioreactor was operated at elevated TAN (330 ± 48 mg/L) and total chemical oxygen demand (tCOD) (2868 ± 378 mg/L) in diluted chicken waste digestate between 120 and 274 d with respective removals up to 57 ± 7% and 80 ± 4%. The response of microbial cultures, especially Planctomycetes (Anammox bacteria) to such influent TAN and tCOD was also investigated by high-throughput sequencing analyses. Results indicated the co-existence of denitrifying bacteria playing significant role in nitrogen removal with Anammox bacteria. Firmicutes and Bacteroidetes phyla doubled their relative abundances; however, a sharp decrease in Planctomycetes was observed. Moreover, predominant phylum changed from Proteobacteria to Firmicutes while dominance of Euryarchaeota remained constant indicating nitrogenous and organic matter contents were the most important factors dominating the bacterial community structure.
Many wastewater treatment plants in the world do not remove reactive nitrogen from wastewater prior to release into the environment. Excess reactive nitrogen not only has a negative impact on human health, it also contributes to air and water pollution, and can cause complex ecosystems to collapse. In order to avoid the deleterious effects of excess reactive nitrogen in the environment, tertiary wastewater treatment practices that ensure the removal of reactive nitrogen species need to be implemented. Many wastewater treatment facilities rely on chemicals for tertiary treatment, however, biological nitrogen removal practices are much more environmentally friendly and cost effective. Therefore, interest in biological treatment is increasing. Biological approaches take advantage of specific groups of microorganisms involved in nitrogen cycling to remove reactive nitrogen from reactor systems by converting ammonia to nitrogen gas. Organisms known to be involved in this process include autotrophic ammonia-oxidizing bacteria, heterotrophic ammonia-oxidizing bacteria, ammonia-oxidizing archaea, anaerobic ammonia oxidizing bacteria (anammox), nitrite-oxidizing bacteria, complete ammonia oxidizers, and dissimilatory nitrate reducing microorganisms. For example, in nitrifying–denitrifying reactors, ammonia- and nitrite-oxidizing bacteria convert ammonia to nitrate and then denitrifying microorganisms reduce nitrate to nonreactive dinitrogen gas. Other nitrogen removal systems (anammox reactors) take advantage of anammox bacteria to convert ammonia to nitrogen gas using NO as an oxidant. A number of promising new biological treatment technologies are emerging and it is hoped that as the cost of these practices goes down more wastewater treatment plants will start to include a tertiary treatment step.
The objective of this work was to analyze organic matter removal, nitrification, biomass growth and membrane fouling in a submerged flat-sheet membrane bioreactor, fed with synthetic wastewater, of similar composition to the effluents generated in a fish meal industry. After biomass acclimatization with saline conditions of 12 gNaCl/L and COD/N ratio of 15 in the bioreactor, results showed that the organic matter removal was higher than 90%, for all organic loading rates (0.8, 1, 1.33 and 2 gCOD/L·d) and nitrogen loading rates (0.053, 0.067, 0.089 and 0.133 gN/L·d) tested during the study. However, nitrification was only carried out with the lowest OLR (0.8 gCOD/L·d) and NLR (0.053 gN/L·d). An excessive concentration of organic matter in the wastewater appears as a limiting factor to this process' operating conditions, where nitrification values of 65% were reached, including nitrogen assimilation to produce biomass. The analysis of membrane fouling showed that the bio-cake formation at the membrane surface is the most impacting mechanism responsible of this phenomenon and it was demonstrated that organic and nitrogen loading rates variations affected membrane fouling rate.
In this study, simultaneous denitrification and methanogenesis (SDM) granules were formed for the first time from dispersed digested and denitrifying sludges. The successful formation of the SDM granules occurred through an increase in substrate concentration of wastewater. Comparatively, formation of conventional methanogenic granules requires an increase in upflow velocity as well as substrate concentration. Nitrate, which is known to inhibit methanogenesis, was key in increasing extracellular polymeric substances (EPS) production because of the protection mechanism of methanogens. The produced EPS clearly enhanced the formation of the SDM granules. The formed SDM granules showed high simultaneous removal efficiencies above 90% for the chemical oxygen demand (COD) and nitrate under high organic and nitrate loading rates (10 g-COD L⁻¹ d⁻¹ and 0.67 g-NO3-N L⁻¹ d⁻¹, respectively). Although the methane concentration in biogas from the SDM granules were relatively low (60%) compare to the conventional methanogenic granules, it remains feasible for energy recovery.
Using prepared nitrifying sludge, anaerobic ammonia oxidization (anammox) sludge and two heterotrophic ammonia oxidization bacterial (AOB) species as inocula, this study elucidated the effect of oxygen conditions, assay media, and selective metabolic inhibitors on various microbial nitrogen (N)-transformation activities including aerobic chemolithotrophic ammonia and nitrite oxidization, aerobic heterotrophic ammonia oxidization, anammox, and aerobic and anoxic denitrification. The oxygen conditions and assay media effectively differentiated among almost all ammonia removal pathways except for separating aerobic chemolithotrophic ammonia oxidization from aerobic heterotrophic ammonia oxidization. A final allylthiourea concentration of 10 mg · L–1 was optimal for accurate determination of aerobic heterotrophic ammonia oxidization activity in the presence of aerobic chemolithotrophic AOB. Finally, this study developed a simple and reliable method to individually determine and compare the comprehensive N-transformation activity characteristics of several activated sludge samples from different origins, and to elucidate the major microbial N-transformation mechanisms for ammonia removal and N2 production.
An anaerobic-aerobic sequential batch system using simultaneous organic and nitrogen removal was investigated to treat intermittently discharged organic solid wastes. Two different recirculation ratios of 10% and 20% day−1 of liquid volume of the anaerobic reactor were examined. In both conditions, methanogenesis occurred during the first 5 days of the process, whereas only denitrification occurred during the subsequent 10 days. At the end of the experiment, high COD removal efficiencies of 97.7% and 96.4% were achieved for the 10% and 20% day−1 recirculation ratios, respectively. A relatively large amount of COD consumed by denitrification was achieved for the 20% day−1 condition, indicating that an increase in the recirculation ratio enhances denitrification. Consequently, the final nitrogen removal efficiencies were 69.0% and 81.9% for the 10% and 20% day−1 recirculation ratios, respectively. To optimize the recirculation ratio, model equations were developed for the scale of this study. The modelling results demonstrated that high recirculation during the active solubilization period enhances the nitrogen removal efficiency. Recirculating 35% day−1 during the first 5 days and 10% day−1 during the subsequent 10 days is recommended as optimal for achieving high organic and nitrogen removal efficiencies.
Batch experiments under different COD/NO3--N ratios were carried out to investigate physicochemical characteristics and microbial community structure of granular sludge under the simultaneous denitrification and methanogenesis (SDM) process. COD/NO3--N ratio of 8.0 was proved to be a critical point of the SDM process and sludge at this ratio was selected for analysis. BET, SEM, FTIR and zeta potential measurement were used to characterize the micro-structure, functional groups and surface charge of the granular sludge related to nitrate addition. SEM observation showed that rod-shaped bacteria were predominant at the surface of granules and FTIR spectrum (1745cm-1) presented an evidence for the carboxyl group protonation upon reduction of the cytochrome c oxidase. Furthermore, high-throughput sequencing technology was used to analyze the microbial structure and diversity. Archaea was found to be accounted for 3.33% of the total microbial communities and Methanosaeta and Methanobacterium were the dominant archaeas. Otherwise, Proteobacteria (63.00%), Bacteroidetes (21.79%) and Firmicutes (9.73%) phyla were identified to be the three dominant bacterial communities. Enterobacteriaceae was detected with a content of 50.24% of the total bacterial sequences and might be the core bacterium contributed to the SDM process. The results would provide vital guidances for the design and stable operation of nitrate-containing wastewater treatment.
To improve the technique efficiency of removing chemical oxygen demand (COD) and nitrogen of livestock wastewater in simultaneous methanogenesis and denitrification, the effects of different concentration ratio associated with COD and nitrite nitrogen were analyzed. The experiment was conducted through livestock wastewater reacting in anaerobic mixing reactor which has seeded with granular sludge. Experimental results obtained by real time monitoring. The criteria are as follows: COD, total kjeldahl nitrogen (TKN), coenzyme F420, β-glucosidase, gas production rate, pH and oxidation-reduction potential (ORP). The results show that the removal rate of COD, concentration of coenzyme F420 and β-glucosidase would be consistent with no nitrite nitrogen, when COD/NO2-N reaches to 30/1 and 40/1. It is indicated that nitrite nitrogen would have few inhibition on the activity of carbohydrate hydrolysis bacteria and methanogens. Otherwise, when COD/NO2-N equals 10/1 and 20/1, the removal rate of COD, concentration of coenzyme F420 and β-glucosidase would be low, which implies high inhibition on the activity of carbohydrate hydrolysis bacteria and methanogens.
The landfill leachate treatment test of denitrification/methanogenesis was done on the anaerobic composite bed reactor. Test results show that, denitrification/methanogenesis can simultaneously occur in anaerobic composite bed reactor if there is high concentration of organic matter. The lower sludge bed contributed to the denitrifying progress mainly. When COD/NO3-N is higher than 9, removal rate of NO3-N can reach 99 percent in the lower sludge bed. When the inflow COD reaches 4 000 mg/L, COD removal capacities of upper biofilm and lower sludge bed remain stable, which of the bottom sludge bed is at 6.0~7.0 g COD/(L·d), and upper biofilm 5.0~6.0 g COD/(L·d).
The title biomass with excellent sedimentatuion properties can be obtained from activated or anaerobic granular sludge in high-load upflow sludge bed (USB) reactors. The article deals with the anoxic granulation process, granular biomass cultivation and growth, loading of the reactors and application of the biomass in water and wastewater treatment.
This review summarises research efforts and case studies in the treatment of wine distillery wastewaters. Experiences in treating wine distillery wastewaters can contribute to the field of oenology, as many oenologists are concerned with the selection, efficiency and economy of their wastewaters. Characteristics of wastewaters from different distilleries and various methods for treating these wastes are discussed. Wine distillery wastewaters are strongly acidic, have a high chemical oxygen demand, high polyphenol content and are highly variable. Primary attention is focused on the sustainable biological treatment of wine distillery wastewaters, mainly by energyefficient anaerobic digestion in different reactor configurations from bench to pilot and full-scale treatment. Finally, areas where further research and attention are required are identified.
To provide an option for the reutilization of high-salinity anchovy fishmeal wastewater (FMW), generated during the anchovy fishmeal manufacturing processes, its potential for biodegradation was assessed in 1-l five-neck flasks using a halotolerant and proteolytic microbial consortium. During the first 41 h of biodegradation, the pH, DO, ORP, and dry-sludge weight decreased as the total cell number of the microbial consortium increased steadily; the CODCr/TN ratios remained between 4.0 and 5.5, respectively, indicating the stable metabolic degradation of organic matter. The ORP tended to increase after 41 h, and the unpleasant fishy smell disappeared once positive ORP values were achieved. The removal percentages of CODCr and TN were 59.0 and 54.4 %, respectively, and the dry-sludge weight decreased from 115.5 to 68.0 g, with a degradation rate of 0.59 g h(-1), during the 80 h experiment. The supernatant from the culture of the anchovy FMW at 70 h (culture supernatant) was phytotoxin-free, and the level of total amino acids was 8.04 g 100 g(-1), comparable to that of commercial fertilizers. In hydroponic cultures containing red bean and barley, the culture supernatant demonstrated a good fertilizing ability. The culture supernatant also exhibited a high degree of antioxidant activity, with a 52.3 % hydroxyl radical-scavenging activity and 0.16 reducing power (at OD 700 nm). Moreover, the culture supernatant inhibited DNA damage from hydroxyl radicals, enhancing the reutilization value of anchovy FMW. This report presents the first description of high-salinity anchovy FMW possessing a high reutilization value potential both for agriculture and medicine.
The effects of sulfide on the integration of denitrification with anaerobic digestion using anaerobic effluents of cassava stillage as carbon source were investigated. Batch tests indicated that nitrate reduction efficiencies decreased from 96.5% to 15.8% as sulfide/nitrate (S/NO3(-)-N) ratios increased from 0.27 to 1.60. At low S/NO3(-)-N ratios (0.27-1.08) anaerobic acidogenesis was accelerated. Nitrate was reduced to nitrite via sulfur-based autotrophic denitrification, after which the formed nitrite and residual nitrate were converted to N2 via heterotrophic denitrification. Increases in the S/NO3(-)-N ratio (1.60) caused a shift (76.3%) in the nitrate reduction pathway from denitrification to dissimilatory nitrate reduction to ammonia (DNRA). Sulfide concentrations (S/NO3(-)-N ratio of 1.60) suppressed not only heterotrophic denitrification but also acidogenesis. The potentially toxic effect of sulfide on acid production was mitigated by its rapid oxidation to sulfur, allowing the recovery of acidogenesis.
Copyright © 2015 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.
Simultaneous methanogenesis and short-cut denitrification processes have attracted attention because it enables the removal of organic matter and nitrogen in a same reactor. In this study, these processes were applied to the treatment of blue mussels, which are discharged worldwide intermittently and in vast quantities as organic solid waste. The effects of substrate COD/NO2⁻-N ratios on denitrifying and methanogenic performances were evaluated in batch experiments. NO2⁻ acclimated sludge was used as a part of seed sludge to enhance the tolerance to NO2⁻. Two acclimated sludges were obtained by two-different acclimating conditions which exposed to influent COD/NO2⁻-N ratios of 25 with high COD loading rate and 5 with low COD loading rate during acclimation periods (referred to as AS25 and AS5). AS25 added reactors showed the relatively high methanogenic and denitrifying performances compared to AS5 added reactors. The results obtained in AS25 added reactors showed comparable results to different studies which used liquid substrates. High COD and NO2⁻ removal efficiencies were achieved under substrate COD/NO2⁻-N ratio ranging from 8.6 to 123, representing the successful performance for the treatment of blue mussels which contains COD/N ratio of 16.3 in their tissue.
In order to ensure the stable and standard discharge of mixed nitrogen sewage, Guangzhou Datansha Wastewater Treatment Plant has made a test using an inverted A2 / O process, with the actual Wastewater as entry water. When the ratio of mixed fecal sewage is 0.33%, the results showed that, extending the HRT(Hydraulic Retention Time) can help to enhance the effect of removing nitrogen, and HRT should be ensured at least 8 hours under the test conditions. And the increase of the concentration of dissolved oxygen can promote the effect of removing nitrogen ranging from 1.0 to 1.5 mg/L. And the sludge reflux ratio should be remained at 60%. Besides, the growth of sludge age has positive effect on nitrification, so the sludge age should be controlled in more than 20 days under the experimental conditions.
This study investigated the performance of a reactor in which denitrification was integrated into the anaerobic acidogenic process. Industrial wastewater cassava stillage was used as the carbon source, and the nitrate reduction pathway and its effects on acid fermentation were examined. Results from batch and semi-continuous tests showed that the presence of nitrate did not inhibit anaerobic acidification but altered the distribution of volatile fatty acid (VFA) species. Nitrate reduction was attributable to denitrification and to dissimilatory nitrate reduction to ammonia (DNRA). The ratio of DNRA to denitrification was proportional to the ratio of [Formula: see text] . After 130 days of semi-continuous operation, denitrification removal efficiency accounted for about 60% at a [Formula: see text] of 50. The proportional distribution of VFAs was acetate, followed by propionate and then butyrate. The polymerase chain reaction-denaturing gradient gel electrophoresis results confirmed the contributions of denitrification and DNRA in the nitrate-amended reactor and showed that the addition of nitrate enriched the structure of the bacterial community, but did not suppress the activity of acid-producing bacteria.
Design criteria for nitrification and denitrification of high-strength wastewaters are presented in two upflow submerged filters in series. Oxygen was a very important parameter effecting the ammonia removal rate in nitrification. The half-order and zero-order rate constants for nitrification were determined for the dissolved oxygen ranges of 2 to 3 mg/L and 4 to 5 mg/L, respectively. The transition from ammonia to oxygen rate limitation occurred at a bulk oxygen:bulk ammonia ratio of approximately 2.5 to 4, showing that nitrification was oxygen limited for practical purposes. In nitrification nitrite accumulation reached a considerable degree at bulk oxygen:bulk ammonia ratios lower than 5. Also, in denitrification the half- and zero-order rate constants were determined. The nitrite produced in the nitrification stage could be successfully reduced in denitrification without causing any inhibitory effect.
Internal recycle ratio is an important parameter in anaerobic/anoxic/oxic (A2/O) wastewater treatment plant (WWTP) operation. An increase in this ratio decreases nitrate and nitrite concentration in the effluent and hence improves the nitrogen removal efficiency, even though the economical cost increases simultaneously. Determining the most favourable recycle ratio taking into account both considerations is an important item in A2/O WWTP operational optimisation. In this work, the effect of recycle ratio on nitrogen removal when using different influent nitrogen loads was tested in a pilot A2/O WWTP. Experimental results obtained show how increasing the internal recycle ratio from 0 to 5 produced a 12% increase in nitrogen removal. This increase was achieved by improving N–NOx removal by 9% with an increase in N–NH4+ removal of 3%.
Laboratory-scale completely-stirred anaerobic digesters were fed with synthetic wastewaters containing nitrate and nitrite and with glucose as the only source of organic carbon in order to investigate and compare the denitrification potentials of anaerobic digesters in the presence of nitrate and nitrite. Varying the input nitrate and nitrite concentration at fixed COD and HRT, methane production without denitrification occurred at COD/N-NOX > 53; denitrification and methane production at 8.86 ≤ COD/N-NOX≤ 53 and only denitrification at COD/N-NOX < 8.86. At COD/N-NOX > 53, ammonification appeared to be the main nitrate and nitrite reduction pathway. The successful competition of ammonia formers over the true denitrifiers at high ratios was attributed to the low initial nitrate and nitrite concentrations.
A new nutrient removal plant configuration was designed and tested in pilot-scale for the treatment of piggery wastewater. The core of the process is represented by a Hybrid Upflow Anaerobic Filter where both anaerobic digestion and denitrification takes place. The pre-screened piggery wastewater is fed to the mesophilic anaerobic reactor. In the bottom of the sludge bed, anaerobic digestion and sulfate reduction are the prevalent processes. In the upper filter zone, a stream of nitrified clarified effluent is recycled and nitrates are dentrified utilizing the remaining available carbon and sulfides as electron donors. The anaerobic reactor should be slightly overloaded in order to provide VFAs for dentrification. The effluent of the anaerobic reactor is fed to the following P-release step, and aerobic nitrification tank and a final settler. The pilot-plant treated 5 m3 d-1 of pre-screened piggery wastewater. The anaerobic digester (volume 15 m3) demonstrated it was to couple anaerobic digestion and dentrification. The overall plant removal efficiency was around 96% for COD, 92% for nitrogen and 92% for phosphorus. The anaerobic digester contributed 80% to the overall dentrification capacity.
Two sets of fixed-film biological processes were operated separately for nitritification of ammonium and for denitritification of nitrite associated with organic compounds. High strength ammonium wastewater (50-1000 mg NH4+-N/l) could be effectively nitritified by a draft-tube fluidized bed which was operated at an extremely high loading of 1.0 kg NH4+-N/m3·day with 95% ammonium conversion and 60 to 95% nitrite formation. Additionally, a biofilm fixed-bed was employed to denitritify the high strength nitrite (200 to 1000 mg NO2--N/l) associated with organic compounds of glucose, acetate and benzoic acid. Complete nitrite removal could be achieved with sufficient HRT and COD/NO2--N ratio. The conversion ratios were estimated experimentally at 2.5 for glucose and acetate, and 2.0 g ΔCOD/g ΔNO2--N for benzoic acid. A proposed process of an aerobic nitritifying biofilm reactor combined with an anoxic denitritifying biofilm reactor in series could be employed for complete nitrogen removal.
Warm concentrated industrial wastewaters are preferably treated in an anaerobic reactor for reasons of energy generation and low surplus sludge production. Problems to be solved in the practical application concern a low growth rate of the micro-organisms, their low settling rate, process instability and the need for after treatment of the noxious anaerobic effluent which often contains NH and HS−. The use of biomass immobilized on small suspended carriers (< 0.5 mm) has proven to be a suitable means to overcome most of these problems. Results are presented on pilot and full-scale pretreatment of industrial wastewater in an anaerobic 2-state fluidized bed reactor for CH4-production and laboratory and pilot scale post-treatment of the anaerobic effluent, which contains NH and HS− in an aerobic air-lift suspension reactor for the production of NO and SO.
Nitrogen removal via nitrite allows operational cost reduction in wastewater treatment of effluents with a low COD/N-NH4+ ratio, due to lower oxygen requirements for partial nitrification and a further diminishing in requirements of the external carbon source for the denitrification step. Two nitrifying systems - a suspended activated sludge (AS) reactor, and an airlift biofilm (AB) reactor-were compared to determine the best alternative for obtaining a maximum nitrite buildup. Both systems were operated under similar operational conditions; synthetic feed of ammonia nitrogen was applied to both reactors, at an ammonia loading rate (ALR) of 3.3 kg N-NH4+/m(3) and an hydraulic retention time of 4.3 h. Nitrite accumulation was studied by means of controlling dissolved oxygen (DO) concentration, keeping both pH and temperature constant. Similar results were obtained in both systems. In the activated sludge reactor maximum nitrite accumulation was achieved at 0.7 and at 3.5 mg DO/L in the airlift reactor. The obtained results showed that at a similar percentage of nitrite accumulation, the K(L)a value of the airlift reactor was always 3.6 times higher than the value obtained in the activated sludge reactor; however, the airflows required were similar in both reactors. The operation of nitrifying systems (biofilm and suspended biomass reactors) with low oxygen concentration to obtain nitrite accumulation make possible a decrease of required airflow, even at small nitrite accumulation. Airflow savings of 38 and 58% were obtained for the activated sludge reactor and the airlift reactor, respectively, at 15% of nitrite accumulation. When 40% of nitrite accumulation was detected in the activated sludge reactor and the airlift reactor, a savings of 80% and 65% were obtained, respectively.
Biological nitrification-denitrification is the most common process for nitrogen removal from wastewaters. During the first step, ammonia is aerobically oxidized to nitrite and then to nitrate. Subsequently, this nitrate is reduced to gaseous nitrogen by denitrifying microorganisms that use it as final electron acceptor. Shortcut biological nitrogen removal is based on the fact that nitrite is an intermediary compound in both steps: a partial nitrification up to nitrite is performed followed by nitrite denitrification. This will produce savings in aeration during the nitrification step. This research studies the effect of dissolved oxygen concentration in nitrite accumulation. An activated sludge reactor is operated under different DO levels, analyzing nitrite accumulation and ammonia removal. Results show that at 1.4 mg DO/L, 75% of nitrite accumulation takes place, with 95% of ammonia removal. Moreover, nitrite accumulation showed to be stable over more than 170 days of operation. Under these conditions, a reduction of 40% in the value of the required mass transfer coefficient K(L)a is achieved. (c) 2004 Elsevier Ltd. All rights reserved.
Piggery wastewater contains high organic carbon and nitrogen concentrations. These compounds can be removed by anaerobic digestion associated with biological nitrification-denitrification. Anaerobic digestion and denitrification can be carried out in the same reactor. Dissimilatory nitrate or nitrite reduction by anaerobic sludge in swine wastewater was studied in flasks with different available carbon/nitric or nitrous nitrogen ratios. In all cases, the nitrate reduction pathway was denitrification, no ammonium appeared in the media. When the TOC/NO3-N ratio was lower than 1.56, nitrate reduction was not completed. When the ratio was between 1.56 and 2.38, nitrate was totally reduced but there was nitrous oxide in the gas produced. Finally, when the TOC/NO3-N ratio was higher than 2.38 and up to 18.04, nitrate was completely reduced to molecular nitrogen. Nitrite reduction was studied at initial TOC/NO3-N ratios of 6.24, 3.34 and 1.57; in all cases, nitrite was completely reduced to molecular nitrogen.
A methanogenic sludge showed denitrifying activity for acetate, glucose and effluents from methanogenic treatments as substrates; denitrifiers were present in a relatively high number. When glucose was used as substrate dissimilatory reduction of nitrate to ammonium occurred. Methane production from acetate was inhibited by denitrification and resumed after nitrite and nitrous oxide depletion.
A denitrifying bacterial biofilm population established on a polypropylene substratum of a fixed-film reactor was characterized by microscopy, scanning electron microscopy and immunofluorescence after 120 days of operation. The reactor, operated at pH 7.0, 22°C, and - 180 mV with synthetic wastewater containing methanol/nitrate, achieved a denitrification rate of 0.24 mol NO3- l-1 day-1 with a removal efficiency for nitrate of 95%-99% at an organic loading rate of 0.325 mol methanol l-1 day-1. The gas produced contained 2%-3% (v/v) methane and 3%-4% (v/v) carbon dioxide in addition to nitrogen. The biofilm contained mainly cells of Methanobrevibacter arboriphilus antigenically related to strain DC, short, flagellated, gram-negatively staining rods of Pseudomonas sp. antigenically related to Pseudomonas stutzeri strain AN11, non-identified pink-pigmented rods and small lemon-shaped cells with mono- and bipolar appendages resembling prosthecate Hyphomicrobium sp. The biofilm analysis provided evidence for a syntrophy between the denitrifying, methylotrophic, bacterial consortium and hydrogenotrophic methanogens, which were identified by antigenic fingerprinting with 17 antibody probes.
Ammonium oxidation to nitrite nitratation and nitrite oxidation to nitrate (nitratation) were studied in a suspended biomass system (SBS) and an immobilised biomass system (IBS). Nitritation and nitratation rates at several substrate concentrations were obtained through respirometry. Process kinetics were evaluated by comparing different substrate inhibition models. The applied statistical criteria prove that the Aiba equation is the best model to describe nitritation inhibition by ammonium in the SBS and the IBS whereas the Haldane equation is the best model to describe nitratation inhibition by nitrite in both systems. The ratios between the kinetic coefficients in both systems suggest that the IBS coefficients are influenced by internal mass transfer in the biofilm. Moreover, the small difference in these coefficient ratios in the nitritation and the nitratation processes suggests that the distribution of the ammonium-oxidising and the nitrite-oxidising biomasses in the biofilm is homogeneous.
The effect of influent COD/N ratio on biological nitrogen removal (BNR) from high-strength ammonium industrial wastewater was investigated. Experiments were conducted in a modified Ludzack–Ettinger pilot-plant configuration for 365 days. Total nitrification of an influent concentration of 1200 mg NH4+–N l−1 was obtained in this period. Influent COD/N ratios between 0.71 and 3.4 g COD g N−1 were tested by varying the nitrogen loading rate (NLR) supplied to the pilot plant. An exponential decrease of nitrification rate was observed when the influent COD/N ratio increased.The experimental COD/N ratio for denitrification was 7.1±0.8 g COD g N−1 while the stoichiometric ratio was 4.2 g COD g N−1. This difference is attributable to the oxidation of organic matter in the anoxic reactor with the oxygen of the internal recycle. The influence of influent COD/N ratio on the treatment of high-strength ammonium industrial wastewater can be quantified with these results. The influence of COD/N ratio should be one of the main parameters in the design of biological nitrogen removal processes in industrial wastewater treatment.
The aim of this work was to achieve rapid nitrate removal from synthetic wastewater (SW) without nitrite accumulation and to improve the economic effectiveness of the process. For that purpose, experiments were carried out to determine the influence of methanol on denitrification rate in batch assays and in the continuous-flow stirred cultures. Nitrate–N (200 mgNO3−–N/l) was reduced under anoxic conditions during approximately 4–6 h for the MeOH/NO3−–N ratio above 2.5. Nitrite concentration was elevated to the maximum of 1.2 mgNO2−–N/l and at the end of the tests nitrite concentrations were 0.06–0.1 mgNO2−–N/l. At lower MeOH/NO3−–N ratios the denitrification process stopped after exhaustion of methanol. The analysis of experimental results showed that denitrification was a zero-order reaction with respect to nitrate and a first-order reaction with respect to the biomass concentration (the first-order overall reaction). In the continuous denitrification process during 45 days the hydraulic retention time (HRT) was decreased from 62 to 28 h. Dissolved oxygen concentration fell from 5.50 to 0.40 mgO2/l during the first 4 h, but over 3 days of continuous flow it increased to 2.5 mgO2/l and remained at that level. Accumulation of nitrite ions in SW was similar to that in batch tests, but at an HRT of 28 h the nitrite concentration increased to 6 mgNO2−–N/l. Complete denitrification at 25 °C was achieved at nitrate and methanol loading rates of 4.35 mgNO3−–N/l h and 23 mgO2/l h, respectively.
Batch-tests were used to determine the potentials of digested sludge to reduce nitrate and nitrite in the presence of five different carbon sources: glucose, glycerol, acetic acid, lactic acid and methanol. Ammonium accumulation was found in glucose and glycerol media. Dissimilatory reduction to ammonium accounted for up to 50% of reduced nitrate and nitrite. The rest were denitrified. In the media containing these carbon substrates volatile fatty acids, particularly acetic acid, were produced and ammonification was higher than denitrification activities only when glucose and glycerol were still present in the media. Ammonium production was higher in nitrite cultures than in nitrate cultures. In the culture media with acetic and lactic acids and methanol, ammonium was not detected. Nitrate/nitrite reduction in acetic and lactic acids media was essentially denitrification activity. Up to 100% of reduced nitrate and nitrite in the culture media with these acids were denitrified at average rates between 27 and 23 mg N-NOx/g MLVSSh, nitrite reduction rate being about 14% lower than total nitrate reduction rate. COD requirements for nitrate and nitrite reductions were generally lower in cultures with acetic and lactic acids than in glucose and glycerol cultures. Methanol culture media showed a very small reduction rate for the N-NOx indicating the absence (or presence in very small quantity) of the bacteria capable of denitrifying with this substrate.
The biological treatment of some industrial wastewaters with high strength ammonium can be affected by the presence of inhibiting compounds. In the case of industries that frost bottles, this inhibitor can be fluoride. In this study, the effect of fluoride on nitrification in an activated sludge system was quantified. Working continuously in steady state, the maximum nitrification rate (MNR) was determined for different fluoride concentrations without substrate limitation. The kinetic equations for noncompetitive, Aiba and Luong inhibition models were adjusted with experimental MNR values. The non-competitive inhibition constant (K-I) was found to be 520 mgF(-) l(-1) at 20 degreesC. The only published values for this inhibition constant are for systems with immobilised biomass. The results of this work indicate that nitrification inhibition by fluoride in this suspended biomass system is higher than that observed in immobilised biomass systems in the literature.
A synthetic wastewater containing glucose as the sole source of carbon was used to assay glucose-acclimatized anaerobic digester sludge in batch-tests for its potential to carry out ammonification (nitrate- -> ammonium), denitrification (nitrate —>nitrogen gas) and to continue anaerobic digestion processes at various nitrate loads. Nitrate—>ammonium reduction activity was found to increase with decrease in the initial nitrate load. This activity appeared to take place principally during the acidogenesis of the glucose. Nitrate/nitrite loss after the fermentation process was essentially through denitrification. The denitrification capacity of the anaerobic sludge used was very high. Up to 80% of added nitrate was denitrified. The presence of nitrate or nitrite enhanced the fermentation of glucose to acetic acid but inhibited the production of propionic acid and methane. This inhibition was not observed after the complete reduction of nitrate and nitrite.
Substrate competition between methanogenic and facultative bacteria under highly aerobic conditions was investigated in batch experiments. Natural mixed cultures of anaerobic bacteria immobilized in granular sludge were able to concurrently utilize oxygen and produce methane when supplied with ethanol as substrate. The most oxygen tolerant sludge converted 3 to 25% of substrate chemical oxygen demand to methane after 3 days while 23 to 2 mg 1−1 of dissolved oxygen were present in the media. The tolerance of methanogens to oxygen and their coexistence with facultative bacteria were evident even after long periods of oxygen exposure. Eventually, methane oxidizing bacteria developed in the co-culture. The consumption of oxygen by facultative bacteria, creating anaerobic microniches inside the granules, is hypothesized to protect the methanogens.
Granular sludge from an upflow anaerobic sludge blanket reactor treating synthetic waste water containing a mixture of volatile fatty acids and nitrate showed a removal efficiency of nearly 100% for both nitrogen and carbon. This activity was achieved by a combined process of denitrification and methanogenesis under conditions of surplus carbon. Under batch conditions the two processes proceeded clearly separated in time with first denitrification dominating and excluding methanogenesis. However, as soon as nitrate was depleted, methane production was initiated, showing that the inhibition of methanogenesis by nitrate was reversible. Of the volatile fatty acids supplied to the reactor, i.e. acetate, propionate, and butyrate, the denitrifying population clearly preferred butyrate and propionate even though acetate could also be metabolized. Consequently, growth of syntrophic volatile fatty acid degraders was suppressed by the denitrifiers in cases of low C:N ratios in the medium, leaving acetate as the major substrate for methanogenesis.
A lab-scale hybrid upflow sludge bed-filter (USBF) reactor was employed to carry out methanogenesis and denitrification of the effluent from an anaerobic industrial reactor (EAIR) in a fish canning industry. The reactor was initially inoculated with methanogenic sludge and there were two different operational steps. During the first step (Step I: days 1-61), the methanogenic process was carried out at organic loading rates (OLR) of 1.0-1.25 g COD l-1 d-1 reaching COD removal percentages of 80%. During the second step (Step II: days 62-109) nitrate was added as KNO3 to the industrial effluent and the OLR was varied between 1.0 and 1.25 g COD l-1 d-1. Two different nitrogen loads of 0.10 and 0.22 g NO3(-)-N l-1 d-1 were applied and these led to nitrogen removal percentages of around 100% in both cases and COD removal percentages of around 80%. Carbon to nitrogen ratio (C:N) in the influent was maintained at 2.0 and eventually it was increased to 3.0, by means of glucose addition, to control the denitrification process. From these results it is possible to establish that wastewater produced in a fish canning industry can be used as a carbon source for denitrification and that denitrifying microorganisms were present in the initially methanogenic sludge. Biomass productions of 0.23 and 0.61 g VSS:g TOC fed for Steps I and II, respectively, were calculated from carbon global balances, showing an increase in biomass growth due to denitrification.
The objective of this paper was to determine the best conditions for partial nitrification with nitrite accumulation of simulated industrial wastewater with high ammonia concentration, lowering the total oxygen needed in the nitrification step, which may mean great saving in aeration. Dissolved oxygen (DO) concentration and pH were selected as operational parameters to study the possibility of nitrite accumulation not affecting overall ammonia removal. A 2.5 L activated sludge reactor was operated in nitrification mode, feeding a synthetic wastewater simulating an industrial wastewater with high ammonia concentration. During the start-up a pH of 7.85 and a DO of 5.5 mg/L were used. The reactor was operated until stable operation was achieved at final nitrogen loading rate (NLR) of 3.3 kg N– NH4⁺/m³ d with an influent ammonia concentration of 610 mg N–NH4⁺/L.
The biological nitrification-denitrification process is used extensively for removal of ammonia nitrogen from wastewaters. Saves in aeration, organic matter (for denitrification) and surplus sludge are achievable if nitrite accumulation is possible in the nitrification step. In this paper, operational parameters were studied for each process for maximum nitrite accumulation in the nitrification step and nitrite adaptation in the denitrification step. Nitrite accumulation during nitrification can be controlled by the dissolved oxygen (DO) concentration, presenting a maximum of 65% at around 0.7 mg DO/L. Denitrification can be adapted to nitrite and the process is stable if nitrite in the reactor is keep low. The performance of a continuous stirred tank reactor (CSTR) and an up flow sludge blanket reactor (USB) were compared. Once the operational parameters were established, a CSTR for nitrification and an USB reactor for denitrification were operated in series for 25 days. The process was stable and a steady state was maintained for 20 days, and 93.5% of overall nitrogen removal was achieved in the nitrification-denitrification via the nitrite process.
Criteria for nitrification and denitrification of high-strength waste water in two upflow submerged filters
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