Effects Of Different Electron Acceptors Research Articles

Performance comparison of photocatalysts for degradation of organic pollutants using experimental studies supported with DFT and fundamental characterization

The effect of different metal supported TiO2 catalysts on the photocatalytic degradation of p-Nitrophenol (PNP) was investigated experimentally and supported by Density Functional Theory (DFT) approach. Process optimization studies were carried out using the best performing catalyst and the effect of different electron acceptors was also investigated. Degradation was strongly influenced by operating parameters and oxidants with efficacy as H2O2 > K2S2O8 > air. DFT simulations confirmed higher electrostatic potential in presence of hydroxyl radicals explaining the higher degradation. Overall, this work clearly establishes the effectiveness of electron acceptors in maximizing PNP degradation and explains the interaction of organic pollutants with different radicals.

Mechanism of Electron Acceptor Promoting Propionic Acid Transformation in Anaerobic Fermentation

To improve the conversion efficiency of propionic acid in the post-anaerobic fermentation of biogas slurry, the anaerobic fermentation process using biogas slurry with a high acid content was simulated in an anaerobic reactor at 35 ± 0.5 °C using sodium propionate as the sole substrate. The effects of different electron acceptors (NO3−, SO42− and Fe3+) on propionic acid conversion and the succession of microbial community structures were investigated. The results showed that the experimental group with the electron acceptor NO3− exhibited the best anaerobic fermentation effect, with a maximum propionate removal rate of 94%, which was 36% higher than the control group without an electron acceptor. The maximum methane production rate was 307.6 mL/g COD, an increase of 30% compared with the control group. Thauera, Aquabacterium, Desulfomicrobium, Clostridium_sensu_stricto_1, and other functional microorganisms were all enriched. The dominant functional genes related to redox reactions, such as K03711, K00384, and K03406, were highly enriched in the reactor when Fe3+ and NO3− were added. The study shows that adding an electron acceptor can enhance interactions between microorganisms, achieve efficient propionate conversion, and improve methane production in the system.

Metagenomic analysis of denitrifying phosphorus removal in SBR system: Comparison of nitrate and nitrite as electron acceptors

Denitrifying phosphorus removal (DPR) is a novel technology for removing phosphorus and nitrogen with low energy requirements. Still, the metagenomic analysis comparing the effect of different electron acceptors on DPR has not been studied clearly. In this study, Nitrate-DPR and Nitrite-DPR were established using different concentrations of nitrate and nitrite as electron acceptors. The results showed that the nitrogen and phosphorus removal efficiency of Nitrite-DPR could reach 99%, which was significantly higher than that of Nitrate-DPR. The sludge settling ability of Nitrite-DPR was also enhanced. The high-throughput sequencing analysis indicated that unclassified_g_Thauera, Chloroflexi_bacterium, Betaproteobacteria_bacterium, and Gammaproteobacteria_bacterium were the main functional bacteria in Nitrate-DPR, while in the Nitrite-DPR, Candidatus_Contendobacter_sp., unclassified_g_Thauera, Candidatus_Competibacteraceae_bacterium, Rhodocyclaceae_bacterium, and Xanthomonadaceae_bacterium were the main ones. Metagenome sequencing analysis further revealed the superior performance of Nitrite-DPR. A series of functional genes, for example, ActP, ACK, PTA and ACS (dominated the synthesis and decomposition of intracellular carbon source), Nir, Nor and Nos (dominated nitrogen metabolism), along with ppk, adk and ppx (dominated phosphorus cycle), were all significantly increased in nitrite-electron acceptor system. It is noted that T6SS functional genes, related to the resistance of microorganisms to environmental stress, were also increased in Nitrite-DPR significantly, which accounted for the significant increase in tightly bound extracellular polymeric substances (TB-EPS) protein in Nitrite-DPR to some extent. The DPR mechanism was deeply explored in this study, and a theoretical basis for the practical application was established.

Effects of electron acceptor and light on the abundance of microbial function gene related to soil CH4 emission

To explore the effects of different electron acceptors on soil methane emission and responses of soil microorganisms to different light conditions, a strict anaerobic 20-day incubation experiment was conducted with eight treatments: darkness + Fe3+ (DF); darkness + NO3- (DN); darkness +SO42- (DS); darkness + distilled water (DCK); light + Fe3+ (LF); light + NO3- (LN); light +SO42- (LS); light + distilled water (LCK). The changes of methane concentration in the anaerobic incubation flask and the variation of the abundance of bacteria, archaea, fungi and six soil functional genes were analyzed. Results showed that soil methane emission under NO3-, SO42- addition and control (CK) was significantly lower under light conditions than dark, except the Fe3+ treatment. DN, DCK and LF treatments had the highest abundance of bacteria, fungi and archaea genes, respectively. The gene abundance of methanogenic mcrA, sulfate-reducing bacteria Dsr, and carbon-fixing CbbL were significantly up-regulated in the LF, while that of methanotrophs pmoA, iron-reducing bacteria Geo, and denitrifying bacteria nosZ were significantly up-regulated in the LN, DCK and LCK, respectively. Results of Pearson correlation and RDA analysis showed that CH4 emission was significantly positively correlated with CO2 concentration, pH, ammonium-nitrogen, and total N contents, and negatively correlated with N2O concentration, Eh, nitrate, and total C contents. Under dark condition, methane emission was positively correlated with archaea and pmoA genes abundance, and negatively correlated with other genes abundance. Under light condition, methane emission was negatively correlated with the abundance of soil microbe and functional genes. In general, methane emission under light condition was significantly lower than that under dark condition (except for the Fe3+ treatment). These results showed that it was helpful to reduce methane emission under light condition, but the increase or decrease of methane emission was closely related to the type of electron acceptors and the functional responses of soil micro-organisms.

Chlorine (Cl) - Substituted Carbazole Based A-π-D-π-a Push-Pull Chromophores as Aggregation Enhanced Emission (AEE) Active Viscosity Sensors: Synthesis, DFT and NLO Approach.

Three new carbazole functionalized A-π-D-π-A extended chromophores 4a, 4b and 4c comprising of different chemical functional groups on C=C bond with the assistance of chlorovinylene group in π-conjugation are synthesized and investigated spectroscopically. We have investigated the effect of different electron acceptors - carboxycyanomethylene, dicyanomethylene and 2-(benzothiazol-2-yl) cyanomethylene, the effect of the insertion of chlorine in π-conjugation on photophysical properties and the effect of double acceptors. The chromophores 4a, 4b and 4c exhibited positive solvatochromism with large Stokes shifts and bright orange to red solid-state fluorescence. Amongst all the three compounds 4c exhibited maximum emission wavelength at 615nm in DMSO. They presented characteristic twisted intramolecular charge transfer (TICT) emission. Observations exhibited that 4c containing long hexyl group in donor unit and 2-(benzothiazol-2-yl) cyanomethylene as an acceptor group formed an aggregate in the mixture of solvents and exhibited better aggregation enhanced emission (AEE) compared to the other two derivatives. Amongst the three styryls, 4c showed the highest emission intensity 299a.u. at 90% water:DMF fraction (fw). Chromophores 4a-4c also exhibited good fluorescence response towards viscosity. Among the three fluorescent molecular rotors (FMR), 4c exhibited excellent viscosity sensitivity with x value = 0.687. The Non-linear (NLO) characters are estimated with the help of solvatochromic and computational methods using the functionals, B3LYP and CAM-B3LYP. The dyes showed large "linear polarizability (αCT)", "first order hyperpolarizability" (β) and "second order hyperpolarizability" (γ) values which show that synthesized styryls can be used as a "NLO" material. The αCT, β and γ for 4c are found to be the maximum amongst the all three dyes which can be ascribed to the smaller band gap apparent from experimental as well as DFT method.

Improvement of n-caproic acid production with Ruminococcaceae bacterium CPB6: selection of electron acceptors and carbon sources and optimization of the culture medium

BackgroundGlobal energy and resource shortages make it necessary to quest for renewable resources. n-Caproic acid (CA) production based on carboxylate platform by anaerobic fermentation is booming. Recently, a novel Ruminococcaceae bacterium CPB6 is shown to be a potential biotransformation factory for CA production from lactate-containing wastewater. However, little is known about the effects of different electron acceptors (EAs) on the fermentative products of strain CPB6, as well as the optimum medium for CA production.ResultsIn this study, batch experiments were performed to investigate the fermentative products of strain CPB6 in a lactate medium supplemented with different EAs and sugars. Supplementation of acetate, butyrate and sucrose dramatically increased cell growth and CA production. The addition of propionate or pentanoate resulted in the production of C5 or C7 carboxylic acid, respectively. Further, a Box–Behnken experiment was conducted to optimize the culture medium for CA production. The result indicated that a medium containing 13.30 g/L sucrose, 22.35 g/L lactate and 16.48 g/L butyrate supported high-titer CA production (16.73 g/L) with a maximum productivity of 6.50 g/L/day.ConclusionsThis study demonstrated that strain CPB6 could produce C6–C7 carboxylic acids from lactate (as electron donor) with C2–C5 short-chain carboxylic acids (as EAs), but CA (C6 carboxylic acid) was the most major and potential product. Butyrate and sucrose were the most significant EA and carbon source respectively for CA production from lactate by strain CPB6. High titer of CA can be produced from a synthetic substrate containing sucrose, lactate and butyrate. The work provided significant implications for improving CA production in industry-scale.

Effects of different electron acceptors on the methanogenesis of hydrolyzed polyacrylamide biodegradation in anaerobic activated sludge systems

The type of electron acceptor was a crucial factor in regulating the methanogenic process of anaerobic hydrolyzed polyacrylamide (HPAM) degradation. The combined methods of biodegradation experiments and thermodynamic calculations were applied to explore the effects of different electron acceptors on methanogenic HPAM degradation. Under the conditions of without electron acceptor, SO42−, Fe3+, SO42− and Fe3+ as electron acceptors, HPAM biodegradation ratio reached 31.56%, 41.48%, 49.4% and 61.1%, acetate production reached 0.0532, 28.28, 112.7 and 141.95mg·L−1, CH4 production reached 0.024, 0.3015, 9.446 and 11.78mg·L−1, respectively. The synergistic effect of SO42− and Fe3+ further promoted methanogenic HPAM biotransformation. Archaeal community analysis revealed that Methanobacteriales, Methanomicrobiales and Methanosarcinales were dominant. Thermodynamic opportunity windows of methanogenesis with Fe3+ as electron acceptor are 35 times larger than that with SO42− as electron acceptor. It indicated that acetoclastic methanogenesis was dominant and hydrogenotrophic methanogenesis was inhibited in the methane-producing process of anaerobic HPAM degradation.

Physiological and electrochemical effects of different electron acceptors on bacterial anode respiration in bioelectrochemical systems.

To understand the interactions between bacterial electrode respiration and the other ambient bacterial electron acceptor reductions, alternative electron acceptors (nitrate, Fe2O3, fumarate, azo dye MB17) were added singly or multiply into Shewanella decolorationis microbial fuel cells (MFCs). All the added electron acceptors were reduced simultaneously with current generation. Adding nitrate or MB17 resulted in more rapid cell growth, higher flavin concentration and higher biofilm metabolic viability, but lower columbic efficiency (CE) and normalized energy recovery (NER) while the CE and NER were enhanced by Fe2O3 or fumarate. The added electron acceptors also significantly influenced the cyclic voltammetry profile of anode biofilm probably via altering the cytochrome c expression. The highest power density was observed in MFCs added with MB17 due to the electron shuttle role of the naphthols from MB17 reduction. The results provided important information for MFCs applied in practical environments where contains various electron acceptors.

Solar-Fenton catalytic degradation of phenolic compounds by impure bismuth ferrite nanoparticles synthesized via ultrasound

In this work, a heterogeneous oxidation of phenolic compounds was examined by impure bismuth ferrite (BiFeO3) nanoparticles synthesized by ultrasound. The nanoparticles were characterized by different techniques. The impure nanoparticles were more effective than pure one. The heterogeneous solar-Fenton catalytic degradation of phenolic compounds was used for the first time. A complete degradation of the phenolic compounds was achieved along with easy separation of the catalyst from the solution by an external magnetic field. The limitations of Fenton reaction such as iron sludge and slow regeneration of Fe(II) ions improved in this work. In the present work, a multivariate analysis has been used to assess the conditions for obtaining complete degradation in terms of the oxidant and catalyst concentrations. The response surface methodology (RSM) was performed to evaluate the effects of the two major factors (amount of impure BiFeO3 magnetic nanoparticles (BFO MNPS) and concentration of H2O2) during the process. The effect of other variables such as initial concentration of phenol and initial pH was also examined. Partial oxidation of phenol took place at dark and a complete degradation was achieved at light in 60 min. The Fenton catalytic degradation mechanism was determined in dark and light. New reaction sites can be generated on the solid surface by the conversion of Fe(III) to Fe(II) for the generation of hydroxyl radical (OH). The effect of different electron acceptors on the heterogeneous solar-Fenton catalytic degradation of phenol was examined too. In addition, the solar-Fenton catalytic degradation of derivatives of phenol such as 4-chlorophenol (4-CP), 2,4,6-trichlorophenol (2,4,6-TCP), biphenyl (BP), 4-nitrorophenol (4-NP), 2,4 dinitrophenol (2,4 DNP) and 2,4,6-trinitrophenol (2,4,6-TNP) was evaluated for the first time. Phenol and its derivatives completely degraded under solar light irradiation by the solar-Fenton catalyst in a short time with low concentration of H2O2.

The Nitrogen and Phosphorus Removal and Sludge Yield Comparative Study under Anaerobic/Aerobic and Anaerobic/Anoxic Conditions

The nitrogen and phosphorus removal efficiency and effect of different electron acceptors (O2 and NO3-) on the sludge yield were studied through experiments in two SBRs (Sequencing Batch Reactors ) in this paper. The results showed that two systems both had good decontamination effect; the theory value of sludge yield (It was 0.435gVSS/gCOD and 0.402gVSS/gCOD for anaerobic /aerobic and anaerobic/anoxic condition, respectively) was higher than the actual value (It was 0.335gVSS/gCOD and 0.321g VSS/gCOD for anaerobic/aerobic and anaerobic/anoxic condition, respectively); There was no significant difference for the sludge yield under anaerobic/aerobic and anaerobic/anoxic conditions, because the endogenesis respiration of sludge under anaerobic/aerobic condition was stronger consequently more sludge being attenuated (Attenuation coefficient was 0.0081 and 0.0026 for anaerobic/aerobic and anaerobic/anoxic condition, respectively).

Effects of electron donor and acceptor conditions on reductive dehalogenation of tetrachloromethane by Shewanella putrefaciens 200

Shewanella putrefaciens 200 is a nonfermentative bacterium that is capable of dehalogenating tetrachloromethane to chloroform and other, unidentified products under anaerobic conditions. Since S. putrefaciens 200 can respire anaerobically by using a variety of terminal electron acceptors, including NO3-, NO2-, and Fe(III), it provides a unique opportunity to study the competitive effects of different electron acceptors on dehalogenation in a single organism. The results of batch studies showed that dehalogenation of CT by S. putrefaciens 200 was inhibited by O2, 10 mM NO3-, and 3 mM NO2-, but not by 15 mM Fe(III), 15 mM fumarate, or 15 mM trimethylamine oxide. Using measured O2, Fe(III), NO2-, and NO3- reduction rates, we developed a speculative model of electron transport to explain inhibition patterns on the basis of (i) the kinetics of electron transfer at branch points in the electron transport chain, and (ii) possible direct inhibition by nitrogen oxides. In additional experiments in which we used 20 mM lactate, 20 mM glucose, 20 mM glycerol, 20 mM pyruvate, or 20 mM formate as the electron donor, dehalogenation rates were independent of the electron donor used. The results of other experiments suggested that sufficient quantities of endogenous substrates were present to support transformation of tetrachloromethane even in the absence of an exogenous electron donor. Our results should be significant for evaluating (i) the bioremediation potential at sites contaminated with both halogenated organic compounds and nitrogen oxides, and (ii) the bioremediation potential of iron-reducing bacteria at contaminated locations containing significant amounts of iron-bearing minerals.

The capacity of hydrogenotrophic anaerobic bacteria to compete for traces of hydrogen depends on the redox potential of the terminal electron acceptor

The effect of different electron acceptors on substrate degradation was studied in pure and mixed cultures of various hydrogenotrophic homoacetogenic, methanogenic, sulfate-reducing, fumarate-reducing and nitrate-ammonifying bacteria. Two different species of these bacteria which during organic substrate degradation produce and consume hydrogen, were cocultured on a substrate which was utilized only by one of them. Hydrogen, which was excreted as intermediate by the first strain (and reoxidized in pure culture), could, depending on the hydrogen acceptor present, also be used by the second organism, resulting in interspecies hydrogen transfer. The efficiency of H2 transfer was similar when methanol, lactate or fructose were used as organic substrate, although the free energy changes of fermentative H2 formation of these substrates are considerably different. In coculture experiments nitrate or fumarate>sulfate> CO2/CH4>sulfur or CO2/acetate were the preferred electron acceptors, and an increasing percentage of H2 was transferred to that bacterium which was able to utilize the preferred electron acceptor. In pure culture the threshold values for hydrogen oxidation decreased in the same order from ≤1,100 ppm for homoacetogenic bacteria to about 0.03 ppm for nitrate or fumarate reducing bacteria. The determined H2-threshold values as well as the percentage of H2 transfer in cocultures were related to the Gibbs free energy change of the respective hydrogen oxidizing reaction.