Endogenous Electron Donor Research Articles

Enhancing chain-elongating microbiomes: Sequential fungi-bacteria cooperation for efficient food waste upgrading using endogenous electron donors

The upgrading of organic waste such as food waste (FW) into medium-chain carboxylates (MCC) is within a bio-based circular economy concept. An efficient chain elongation (CE) microbiome is difficult to obtain, which normally requires long-term acclimatization and an exogenous supplement of electron donor (ED, especially ethanol). In this study, the CE microbiome was rapidly shaped within 18 days and an efficient endogenous ethanol-based CE was achieved through the amendment of distiller yeast (DY) during FW fermentation. Multiple FW feeding accumulated the caproate concentration to 5.76 ± 0.33 g COD/L, which also regulated the CE process from ethanol-dependent to lactate-dependent metabolism. During the lactate-based CE process, the caproate production increased linearly (R2 = 0.82) with the rising D-lactate content. Ethanol-producing fungi yeast mainly consisted of Wickerhamomyces (66.54 %), Saccharomycopsis (5.37 %), Issatchenkia (2.21 %), unclassified_f_Metschnikowiaceae (1.73 %), and Saccharomyces (1.33 %). These yeasts were eliminated by FW feeding, which was in line with the alteration of ED preference from ethanol to lactate. Metagenome analysis indicated that the total relative abundance of lactate-based chain elongators including Ruminococcaceae bacterium CPB6, Clostridium luticellarii, Caproiciproducens galactitolivorans, and Megasphaera elsdenii was increased by 28.6 %, while the ethanol-based chain elongator Clostridium kluyveri kept stable after FW feeding. In addition, the functional genes related to the oxidation of lactate to acetyl-CoA were enriched after FW feeding, which further enhanced the subsequent CE pathway of acetyl-CoA-based reverse β oxidation rather than the fatty acids synthesis. This study provides a new insight into upgrading FW into valuable MCC without exogenous ED addition.

The Pd (II) Reduction Mechanisms in Bacillus megaterium Y-4 Revealed by Proteomic Analysis.

Many studies have been conducted on the microbial reduction of Pd (II) to palladium nanoparticles (Pd-NPs) due to the environmental friendliness, low cost, and the decreased toxicity of Pd (II) ions. In this study, we investigate the reduction mechanism of Pd (II) by Bacillus megaterium Y-4 through proteomics. The data are available via ProteomeXchange with identifier PXD049711. Our results revealed that B. megaterium Y-4 may use the endogenous electron donor (NAD(P)H) generated by nirB, tdh, and fabG and reductase to reduce Pd (II) to Pd-NPs. The expression levels of fabG, tdh, gudB, and rocG that generate NAD(P)H were further increased, and the number of reduced Pd-NPs was further increased with the exogenous electron donor sodium formate. Endogenous electron mediators such as quinones and flavins in B. megaterium Y-4 can further enhance Pd (II) reduction. The findings provided invaluable information regarding the reduction mechanism of Pd (II) by B. megaterium Y-4 at the proteome level.

Pd (II) bioreduction by Bacillus wiedmannii MSM with energy storage compounds

In the present study, we found that nanoparticles (Pd-NPs) were biosynthesized by Bacillus wiedmannii MSM (B. wiedmannii MSM) with endogenous carbon under O2 condition, and more favorablity under N2 purging condition. XRD results indicated that crystal planes of Pd-NPs were attributed to Pd0 (111), Pd0 (200), Pd0 (220), and Pd0 (311), respectively. TEM and STEM-EDX results showed that the bio-reduction of Pd (II) (kpd,1=4.799 min−1) occurred predominately in periplasm space. FTIR results showed that the -COOH, -OH, and -NH2 were the main groups participating in the removal of Pd (II). The aerobic reduction of Pd (II) by B. wiedmannii MSM was proposed, including extracellular superoxide radicals produced by NAD(P)H oxidases, endogenous electron donors, and O2-insensitive hydrogenase. These studies provide new methods and insights for reduction of Pd (II).

From trash to treasure: Microbial conversion of palladium contaminants into valuable Pd nanoparticles by Bacillus thuringiensis Y9

Microbial reduction is a sustainable approach for both environmental remediation and recycling of precious metals from waste. Bacteria-mediated reduction of palladium ions (Pd2+) in wastewater under mild conditions is such a strategy. However, external electron donors are usually required for palladium bioreduction. Herein, a novel gram-positive bacterium, Bacillus thuringiensis Y9 (B. thuringiensis Y9), was found to reduce Pd2+ to palladium nanoparticles (Pd-NPs) with endogenous electron donors. Transcriptomic analyses revealed 443 and 439 differentially expressed genes response to palladium treatment under anaerobic and aerobic conditions, respectively. It was found the genes encoding NADH-quinone oxidoreductase, dehydrogenases, cytochrome c reductase, cytochrome c oxidase, quinone cycle and ribE in B. thuringiensis Y9 have strong positive relationship to palladium reduction. The removal efficiencies of palladium by B. thuringiensis Y9 are as high as 93 mg g−1 under anaerobic conditions and 60 mg g−1 under aerobic conditions. Hydrogenase also plays vital role in the bioreduction process. The maximum Pd removal ratio of 99.18% was obtained with the primary influencing factors using response surface methodology (RSM). Our study provides a novel and sustainable strategy for Pd recovery from wastewater. The transcriptome data are valuable for understanding the global bioreduction mechanism of the microbial conversion of palladium.

The role of oxygen and electron donors in indole biodegradation and mineralization

AbstractIndole is a recalcitrant compound whose aerobic biodegradation is triggered by a mono‐oxygenation process. Generally, the mono‐oxygenation process involves intracellular electron carriers and molecular oxygen as co‐substrates; the increase of concentrations for either one can accelerate the biotransformation of refractory substances. In this study, the initial biotransformation of indole proved to be a special mono‐oxygenation reaction, neither endogenous nor exogenous electron donors have influences on indole biodegradation. However, oxygen plays a significant role in indole mono‐oxygenation. Higher dissolved oxygen led to a faster rate of indole biodegradation. As the product of indole mono‐oxygenation, unstable indoxyl indirectly turned out to exist by its tautomer 2‐oxindole. Intermediates like isatin, N‐formylanthranilic acid, and anthranilic acid were confirmed. In addition, coupling biodegradation with UV photolysis accelerated indole mineralization, and longer photolysis time gave faster TOC removal. This is because the supplement of endogenous electron donors by photolysis could enhance the catabolism of isatin and anthranilic acid, thus promoting indole mineralization. The biodegradation of these two intermediates was further verified to be initiated by donor‐requiring steps, so the photolytic products which generated labile electron donors could accelerate their oxygenations. This study provides valuable information on further controlling the process of aerobic biodegradation for indole.

Nitrogen removal from poultry slaughterhouse wastewater in anaerobic-anoxic-aerobic combined reactor: Integrated effect of recirculation rate and hydraulic retention time

The aim of this work was to assess the nitrogen removal from slaughterhouse wastewater in an anaerobic-anoxic-aerobic combined reactor, evaluating the integrated effect of recirculation rate and hydraulic retention time. The recirculation of the liquid phase from the aerobic zone to the anoxic zone was applied to promote the denitrification through the use of endogenous electron donors. Three recirculation rates (R: 0.5, 1 and 2) and three hydraulic retention times (14, 11 and 8 h) were applied. The operation of the reactor was divided into 3 steps (I, II, and III) according to the factors evaluated (recirculation rate and HRT), to achieve operational conditions that would allow satisfactory performance in the different compartments of the reactor. During the experiment the reactor was fed with average total nitrogen (TN) and chemical oxygen demand (COD) of 65 mg L−1 and 580 mg L−1, respectively. The denitrification efficiency (theoretical) and kinetics parameters for COD decay were calculated. The highest performance was verified in the Step III (R = 2) and HRT of 11 h with NH4+ and TN removals of 84% and 65%, respectively. The TN removal efficiency (65%) was considered satisfactory, since the theoretical denitrification efficiency expected for this condition (R = 2) is 67%, without addition of an external carbon source. The lowest nitrification efficiency values were obtained in HRT of 8 h in the Step I and II (R = 0.5 and 1, respectively), indicating that the nitrification time (3 h - aerobic phase) may be the limiting factor in this HRT. The COD removal efficiency was high in all assays (>95%). The values of the kinetic degradation constants of organic matter were close for all recirculation rates, and the highest values were recorded for the HRT of 8 h and R = 1 and R = 2 (−0.48 and −0.43, respectively).

Magnetite drives self-dechlorination of 4-chlorophenol in anoxic aquatic sediments

The lack of available electron donors is well known as a major factor limiting the efficiency of microbial dechlorination of 4-chlorophenol (4-CP) in anoxic aquatic sediments. Considering that Fe(III) minerals largely contained in sediments can especially enrich Fe(III)-reducing bacteria and unlock the ring-like intermediates produced by dechlorination of 4-CP via dissimilatory Fe(III) reduction, a strategy of self-dechlorination of 4-CP utilizing its metabolism intermediates such as short-fatty acids (SCFAs) as the endogenous electron donors with magnetite was proposed in this study. The results showed that the removal efficiency of 4-CP increased by 156–203% in magnetite-supplemented biotic groups compared with the magnetite-free biotic group. Liquid chromatography-mass spectrometer (LC-MS) and gas chromatography (GC) revealed the possible metabolic pathway of anoxic 4-CP degradation with magnetite: 4-CP→phenol→cyclohexene-1-carboxylic acid→2-hydroxycyclohexanecarboxylic acid→hexanoic acid/valeric acid→butyric/propionic acids→CO2. High-throughput sequencing analysis showed that the abundance of functional bacteria, Desulfuromonas, Pseudomonas and Bacillus species, were increased by 1.38–1.97, 1.50–2.04, and 11.60–17.18 folds in magnetite-supplemented biotic groups, compared with the magnetite-free biotic groups. Analysis of Fe2+ concentration and cyclic voltammetry (CV) suggested that the potential Fe(III)/Fe(II) transformation occurred and proceeded the anoxic 4-CP degradation continuously.

Anoxic Microbial Community Robustness Under Variation of Hydraulic Retention Time and Availability of Endogenous Electron Donors.

The ADNMED (Anaerobic Digestion, Nitrification, and Mixotrophic Endogenous Denitrification) system comprises a triple chamber configuration that was shown to provide high-quality effluent regarding carbon, nitrogen, and sulfide. Hydraulic retention time (HRT) was 7h in the anaerobic and anoxic chambers, and 5h in the aerobic chamber (stage A). Sewage was directly added to the anoxic chamber to provide extra organic electron donors for denitrification (stage B) to improve the nitrogen removal efficiency (stage A 47 ± 19%). The addition of sewage at a flow rate equivalent to 10% of the feed flow increased nitrogen removal efficiency to 61 ± 12%. Illumina® sequencing revealed a restructuring of the microbial community in the anoxic chamber, according to the availability of the endogenous electron donors for denitrification. At stage A, denitrification was related to the decay of biomass, while the addition of sewage during stage B stimulated the establishment of fermentative bacteria.

Sulfide-driven denitrification: detecting active microorganisms in fed-batch enrichment cultures by DNA stable isotope probing.

A microbial community was enriched in the anoxic compartment of a pilot-scale bioreactor that was operated for 180days, fed with sewage and designed for organic matter, nitrogen and sulfide removal by coupling anaerobic digestion, nitrification and mixotrophic denitrification. Denitrification occurred with endogenous electron donors, mainly sulfide and residual organic matter, coming from the anaerobic compartment. The microorganisms involved in denitrification with sulfide as electron donor were identified by DNA-stable isotope probing with [U-13C]-labelled CO2 and NaHCO3. Complete denitrification occurred every two days, and the applied NO3-/S2- ratio was 1.6. Bacteria belonging to the Sulfurimonas denitrificans was identified as a chemoautotrophic denitrifier, and those related to Georgfuchisa toluolica, Geothrix fermentans and Ferritrophicum radicicola were most probably associated with heterotrophic denitrification using endogenous cells and/or intermediate metabolites. This study showed that DNA-SIP was a suitable technique to identify the active microbiota involved in sulfide-driven denitrification in a complex environment, which may contribute to improve design and operation of bioreactors aiming for carbon-nitrogen-sulfur removal.

Activity of Spore-Specific Respiratory Nitrate Reductase 1 of Streptomyces coelicolor A3(2) Requires a Functional Cytochrome bcc-aa3 Oxidase Supercomplex.

Spores have strongly reduced metabolic activity and are produced during the complex developmental cycle of the actinobacterium Streptomyces coelicolor Resting spores can remain viable for decades, yet little is known about how they conserve energy. It is known, however, that they can reduce either oxygen or nitrate using endogenous electron sources. S. coelicolor uses either a cytochrome bd oxidase or a cytochrome bcc-aa3 oxidase supercomplex to reduce oxygen, while nitrate is reduced by Nar-type nitrate reductases, which typically oxidize quinol directly. Here, we show that in resting spores the Nar1 nitrate reductase requires a functional bcc-aa3 supercomplex to reduce nitrate. Mutants lacking the complete qcr-cta genetic locus encoding the bcc-aa3 supercomplex showed no Nar1-dependent nitrate reduction. Recovery of Nar1 activity was achieved by genetic complementation but only when the complete qcr-cta locus was reintroduced to the mutant strain. We could exclude that the dependence on the supercomplex for nitrate reduction was via regulation of nitrate transport. Moreover, the catalytic subunit, NarG1, of Nar1 was synthesized in the qcr-cta mutant, ruling out transcriptional control. Constitutive synthesis of Nar1 in mycelium revealed that the enzyme was poorly active in this compartment, suggesting that the Nar1 enzyme cannot act as a typical quinol oxidase. Notably, nitrate reduction by the Nar2 enzyme, which is active in growing mycelium, was not wholly dependent on the bcc-aa3 supercomplex for activity. Together, our data suggest that Nar1 functions together with the proton-translocating bcc-aa3 supercomplex to increase the efficiency of energy conservation in resting spores.IMPORTANCEStreptomyces coelicolor forms spores that respire with either oxygen or nitrate, using only endogenous electron donors. This helps maintain a membrane potential and, thus, viability. Respiratory nitrate reductase (Nar) usually receives electrons directly from reduced quinone species; however, we show that nitrate respiration in spores requires a respiratory supercomplex comprising cytochrome bcc oxidoreductase and aa3 oxidase. Our findings suggest that the Nar1 enzyme in the S. coelicolor spore functions together with the proton-translocating bcc-aa3 supercomplex to help maintain the membrane potential more efficiently. Dissecting the mechanisms underlying this survival strategy is important for our general understanding of bacterial persistence during infection processes and of how bacteria might deal with nutrient limitation in the natural environment.

Proof of concept and improvement of a triple chamber biosystem coupling anaerobic digestion, nitrification and mixotrophic endogenous denitrification for organic matter, nitrogen and sulfide removal from domestic sewage.

In this study, two versions of a triple chamber biosystem, coupling anaerobic digestion, nitrification and mixotrophic endogenous denitrification (ADNMED), were evaluated and compared. They were designed to maximize the use of endogenous electron donors produced by anaerobic digestion (residual organic matter and sulfide) to abate a portion of the influent nitrogen contained in domestic sewage while removing the inconvenience of effluent sulfide. The first version was able to abate 40% of the influent nitrogen but presented operational and hydrodynamic problems, which resulted in sulfide emissions. A modified second version was proposed, improving the first approach and achieving a nitrogen abatement of more than 60% and a sulfide-free effluent, complying with local emission standards. The results demonstrated that endogenous electron donors produced by anaerobic digestion should not be neglected, and a significant cost reduction in nitrogen removal from domestic sewage could be achieved by exploiting their potential with novel reactor configurations.

Regulation of Ferredoxin-NADP+ Oxidoreductase to Cyclic Electron Transport in High Salinity Stressed Pyropia yezoensis.

Pyropia yezoensis can survive the severe water loss that occurs during low tide, making it an ideal species to investigate the acclimation mechanism of intertidal seaweed to special extreme environments. In this study, we determined the effects of high salinity on photosynthesis using increasing salinity around algal tissues. Both electron transport rates, ETR (I) and ETR (II), showed continuous decreases as the salinity increased. However, the difference between these factors remained relatively stable, similar to the control. Inhibitor experiments illustrated that there were at least three different cyclic electron transport pathways. Under conditions of severe salinity, NAD(P)H could be exploited as an endogenous electron donor to reduce the plastoquinone pool in Py. yezoensis. Based on these findings, we next examined how these different cyclic electron transport (CETs) pathways were coordinated by cloning the gene (HM370553) for ferredoxin-NADP+ oxidoreductase (FNR). A phylogenetic tree was constructed, and the evolutionary relationships among different FNRs were evaluated. The results indicated that the Py. yezoensis FNR showed a closer relationship with cyanobacterial FNR. The results of both real-time polymerase chain reaction and western blotting showed that the enzyme was upregulated under 90–120‰ salinity. Due to the structure-function correlations in organism, Py. yezoensis FNR was proposed to be involved in NAD(P)H-dependent Fd+ reduction under severe salinity conditions. Thus, through the connection between different donors bridged by FNR, electrons were channeled toward distinct routes according to the different metabolic demands. This was expected to make the electron transfer in the chloroplasts become more flexible and to contribute greatly to acclimation of Py. yezoensis to the extreme variable environments in the intertidal zone.

Accelerating biodegradation of a monoazo dye Acid Orange 7 by using its endogenous electron donors

Biodegradation of a monoazo dye – Acid Orange 7 (AO7) was investigated by using an internal circulation baffled biofilm reactor. For accelerating AO7 biodegradation, endogenous electron donors produced from AO7 by UV photolysis were added into the reactor. The result shows that AO7 removal rate can be accelerated by using its endogenous electron donors, such as sulfanilic and aniline. When initial AO7 concentration was 13.6mg/L, electron donors generated by 8h UV photolysis were added into the same system. The biodegradation rate 0.4mg0.05h−1 was enhanced 60% than that without adding electron donor. Furthermore, sulfanilic and aniline were found to be the main endogenous electron carriers, which could accelerate the steps of the azo dye biodegradation.

Microbial community in a pilot-scale bioreactor promoting anaerobic digestion and sulfur-driven denitrification for domestic sewage treatment.

A pilot-scale reactor treating domestic sewage was operated to promote anaerobic digestion and denitrification using endogenous electron donors. While 55 % of organic matter was removed, nitrogen and sulfur showed a different dynamics during the operation. Pyrosequencing analysis clarified this behavior revealing that specific microbial communities inhabited the anaerobic (47.05 % of OTUs) and anoxic (31.39 % of OTUs) chambers. Analysis of 16S rRNA gene partial sequences obtained through pyrosequencing revealed a total of 1727 OTUs clustered at a 3 % distance cutoff. In the anaerobic chamber, microbial community was comprised of fermentative, syntrophic and sulfate-reducing bacteria. The majority of sequences were related to Aminobacterium and Syntrophorhabdus. In the anoxic chamber, the majority of sequences were related to mixotrophic and strictly autotrophic denitrifiers Arcobacter and Sulfuricurvum, respectively, both involved in sulfur-driven denitrification. These results show that pyrosequencing was a powerful tool to investigate the microbial panorama of a complex system, providing new insights to the improvement of the system.

Accelerating Quinoline Biodegradation and Oxidation with Endogenous Electron Donors.

Quinoline, a recalcitrant heterocyclic compound, is biodegraded by a series of reactions that begin with mono-oxygenations, which require an intracellular electron donor. Photolysis of quinoline can generate readily biodegradable products, such as oxalate, whose bio-oxidation can generate endogenous electron donors that ought to accelerate quinoline biodegradation and, ultimately, mineralization. To test this hypothesis, we compared three protocols for the biodegradation of quinoline: direct biodegradation (B), biodegradation after photolysis of 1 h (P1h+B) or 2 h (P2h+B), and biodegradation by adding oxalate commensurate to the amount generated from photolysis of 1 h (O1+B) or 2 h (O2+B). The experimental results show that P1h+B and P2h+B accelerated quinoline biodegradation by 19% and 50%, respectively, compared to B. Protocols O1+B and O2+B also gave 19% and 50% increases, respectively. During quinoline biodegradation, its first intermediate, 2-hydroxyquinoline, accumulated gradually in parallel to quinoline loss but declined once quinoline was depleted. Mono-oxygenation of 2-hydroxyquinoline competed with mono-oxygenation of quinoline, but the inhibition was relieved when extra electrons donors were added from oxalate, whether formed by UV photolysis or added exogenously. Rapid oxalate oxidation stimulated both mono-oxygenations, which accelerated the overall quinoline oxidation that provided the bulk of the electron donor.

Shortcut Nitrification-Denitrification Coupled With Sulfide Oxidation In A Single Reactor

Nitrogen removal coupled with sulfide oxidation may be a suitable option for the post-treatment of anaerobic reactor effluents that contain ammoniacal nitrogen, which must be nitrified, and sulfide, which could be used as an endogenous electron donor for autotrophic denitrification. This research proposes the application of shortcut nitrification-denitrification coupled with sulfide oxidation in a single reactor to remove nitrogen from effluents of anaerobic reactors treating domestic sewage.A fixed-bed sequencing batch reactor (FBSBR) was used, operating in 8-hour cycles, subjected to intermittent aeration and employing autotrophic denitrification using the sulfide present in the effluent, pretreated anaerobically, as an electron donor.Nitrite accumulation was observed after application of the sulfide shock load, which inhibited the nitriteoxidizing bacteria.However, it was difficult to establish denitrification via nitrite due to the toxicity of this compound to denitrifying microorganisms in the reactor.The low overall efficiency of nitrogen removal and various operational constraints indicated that autotrophic denitrification using sulfide in the FBSBR was not satisfactory.

Catalytic activity of biomass-supported Pd nanoparticles: Influence of the biological component in catalytic efficacy and potential application in ‘green’ synthesis of fine chemicals and pharmaceuticals

Five gram negative and two gram positive bacterial strains known for their heavy metal tolerance or ability to reduce metal ions were coated with Pd(0) nanoparticles (NPs) via reduction of soluble Pd(II) ions under H2 following an initial uptake of PdCl42- without added electron donor ('biosorption'), where the gram negative strains had a ~5-fold greater capacity for Pd(II). Cupriavidis metallidurans accumulated Pd(II) exceptionally; the possibility of reduction to Pd(0) via an endogenous electron donor was not discounted. The initial rate of subsequent H2-mediated Pd(II) reduction correlated with the Pd(II) removed during biosorption (r2=0.9). TEM showed strain-specific variations of Pd-NPs. At a 1:3 loading of Pd:biomass the cell surfaces of Escherichia coli and Desulfovibrio desulfuricans showed uniform coverage with small NPs with the other strains showing larger aggregates. NPs made by the gram positive cells appeared larger than their gram negative counterparts. At a loading of 1:19 all were active catalysts in Cr(VI) reduction and in two Heck coupling reactions. BioPdE. coli and bioPdD. desulfuricans and bioPdA. oxydans were consistently the best and worst catalysts respectively. BioPdE. coli was further tested as a process catalyst according to industrial protocols in Heck and Suzuki coupling reactions. Laboratory and industrial tests (coupling of phenyl iodide and ethyl acrylate) gave 75% and 78% conversion to ethyl cinnamate, respectively. The biomaterial catalysed Heck and Suzuki reactions using bromoacetophenone and 4-bromoanisole (Heck) and 4-chloroanisole (Suzuki) but not 3-chlorotoluene. In accordance with known chemical catalysis the catalytic efficacy was related to electron-withdrawing substituents on the phenyl ring, with more than 90% conversion (Suzuki) using 4-bromobenzotrifluoride.

Nitrogen and sulfide removal from effluent of UASB reactor in a sequencing fed-batch biofilm reactor under intermittent aeration

Simultaneous nitrification/denitrification (SND) coupled with sulfide oxidation may be suitable for the post treatment of effluents from anaerobic reactors. These effluents contain ammonium, which must be nitrified, and sulfide, which could be used as an endogenous electron donor for autotrophic denitrification. The SND process occurred in a sequencing fed-batch biofilm reactor of 8h cycles, operated under intermittent aeration. The effect of the start-up period and the feeding strategy were evaluated. The previous establishment of nitrification process with subsequent application of sulfide in low concentrations was the best start-up strategy to enable the occurrence of SDN. The fed-batch mode with sulfide application in excess only in the anoxic periods was the best feeding strategy, providing average efficiencies of 85.7% and 53.0% for nitrification and denitrification, respectively. However, the low overall nitrogen removal efficiency and some operational constraints indicated that autotrophic denitrification using sulfide in a single SBR was not suitable for SND under the assayed conditions.

Effect of sulfide concentration on autotrophic denitrification from nitrate and nitrite in vertical fixed-bed reactors

Autotrophic denitrification coupled with sulfide oxidation represents an interesting alternative for the simultaneous removal of nitrate/nitrite and sulfide from wastewaters. The applicability of such bioprocess is especially advantageous for the post treatment of effluents from anaerobic reactors, since they usually produce sulfides, which can be used as endogenous electron donor for autotrophic denitrification. This study evaluated the effect of sulfide concentration on this bioprocess using nitrate and nitrite as electron acceptors in vertical fixed-bed reactors. The results showed that intermediary sulfur compounds were mainly produced when excess of electron donor was applied, which was more evident when nitrate was used. Visual evidences suggested that elemental sulfur was the intermediary compound produced. There was also evidence that the elemental sulfur previously formed was being used when sulfide was applied in stoichiometric concentration relative to nitrate/nitrite. Nitrite was more readily consumed than nitrate. For both electron acceptors and sulfide concentrations tested, autotrophic denitrification was not affected by residual heterotrophic denitrification via endogenic activity, occurring as a minor additional nitrogen removal process.

Determination of the intrinsic kinetic parameters of sulfide-oxidizing autotrophic denitrification in differential reactors containing immobilized biomass

Nitrogen removal coupled with sulfide oxidation has potential for the treatment of effluents from anaerobic reactors because they contain sulfide, which can be used as an endogenous electron donor for denitrification. This work evaluated the intrinsic kinetics of sulfide-oxidizing autotrophic denitrification via nitrate and nitrite in systems containing attached cells. Differential reactors were fed with nitrified synthetic domestic sewage and different sulfide concentrations. The intrinsic kinetic parameters of nitrogen removal were determined when the mass transfer resistance was negligible. This bioprocess could be described by a half-order kinetic model for biofilms. The half-order kinetic coefficients ranged from 0.425 to 0.658mgN1/2L−1/2h−1 for denitrification via nitrite and from 0.190 to 0.609mgN1/2L−1/2h−1 for denitrification via nitrate. In this latter, the lower value was due to the use of electrons donated from intermediary sulfur compounds whose formation and subsequent consumption were detected.