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G Lettinga - One of the best experts on this subject based on the ideXlab platform.
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sulfidogenic volatile Fatty Acid Degradation in a baffled reactor
Water Science and Technology, 2003Co-Authors: M V G Vallero, Piet N L Lens, C Bakker, G LettingaAbstract:The effect of staging the sludge bed on volatile Fatty Acid Degradation by sulfidogenic reactors was evaluated in a baffled reactor. In a 5.4 l baffled reactor, containing three equal compartments, a volatile Fatty Acid (VFA) mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) was treated under mesophilic (30°C) and sulfidogenic (COD:SO42- ratio: 0.5) conditions for 38 days. At a specific sludge loading rate of 0.50 g COD.gVSS-1.d-1, a COD and sulfate removal of 85% and 30%, respectively, was obtained. In the baffled reactor, staging of the sulfidogenic VFA Degradation occurred. Propionate and butyrate were mainly degraded in the first compartment. Their Degradation was incomplete, resulting in elevated acetate concentrations in compartment I. In the second and third compartment of the baffled reactor, a net Degradation of acetate took place. Acetate was the sole substrate present in compartment III and residual acetate concentrations of about 200 mg/l were present in the effluent at a specific sludge loading of 0.50 g COD.gVSS-1.d-1. Sludges with different maximum specific VFA and acetate degrading activities developed in the first and second compartment. These maximal specific activities were almost equal for sludge present in compartment II and III.
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kinetics of Fatty Acid Degradation by psychrophilically grown anaerobic granular sludge
Bioresource Technology, 1999Co-Authors: Salih Rebac, Piet N L Lens, Sybren Gerbens, Jules B Van Lier, Alfons J M Stams, K J Keesman, G LettingaAbstract:The kinetic parameters of anaerobic granular sludge, grown at 10–12°C in an expanded granular sludge bed (EGSB) reactor and fed with volatile Fatty Acid (VFA) mixtures, were determined in batch assays. The homoacetogenic, hydrogenotrophic and acetoclastic specific activities of the sludge at 10°C, measured after 306 days exposure to psychrophilic conditions were 1.744, and 0.296 and 0.331 g COD g−1 volatile suspended solids (VSS) day−1, respectively. At 30°C these values were 18.024, 2.732 and 2.204 g COD g−1 VSS day−1, respectively. The temperature characteristics of the granular sludge and the homoacetogenic enrichment culture from cultivated sludge showed that the temperature optima were still in the mesophilic range (30–40°C) even after long term (306 days) operation at low temperature (10–12°C). In the overall conversion rate for acetate and propionate, evidence for the temperature compensation effect was found. In contrast, no temperature compensation effect was present for butyrate Degradation. The results of EGSB batch reactor experiments revealed apparent Km of the acetate and propionate degraders in the ranges of 39–58 mg COD l−1 and 7–14 mg COD l−1, respectively. For butyrate degraders, higher Km values were found, i.e., 142–243 mg COD l−1. The observed low Km values could be attributed to prevailing mixing conditions in the EGSB reactor system.
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effect of staging on volatile Fatty Acid Degradation in a sulfidogenic granular sludge reactor
Water Research, 1998Co-Authors: Piet N L Lens, M C Van Den Bosch, G LettingaAbstract:Abstract The use of an upflow staged sludge bed (USSB) reactor for the optimization of acetate removal during treatment of sulfate rich wastewaters was investigated. The USSB treated a VFA mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) under mesophilic (30°C) and sulfidogenic (COD:SO42− ratio 0.5) conditions. Its performance was compared to that of an upflow anaerobic sludge bed (UASB) reactor operating at the same operational conditions. The hydrodynamic conditions were clearly different in both reactor types. The USSB reactor (number of ideal mixed reactors Nth=10) had a more plug-flow pattern than the UASB reactor (Nth=3). Both reactors reached a specific sludge loading rate of 1.20 gCOD gVSS−1 d−1, corresponding to a volumetric loading rate of 20 and 30 gCOD l−1 d−1 for the UASB and USSB reactor, respectively. At these loading rates, a maximum COD removal of 80% was obtained by both reactors and the average %COD used by sulfate reducing bacteria was 74(±7)% and 80(±9)% for the UASB and USSB reactor, respectively. The UASB and USSB reactor reached a sulfate loading rate of 40 and 60 g SO42− l−1 d−1, respectively, with an average sulfate removal of 45(±19)% and 35(±24)%, respectively. The USSB reactor showed more oscillations in its performance than the UASB reactor, already at lower loading rates. Staging of sulfidogenic treatment in the USSB reactor resulted in development of sludges with different maximum specific microbial activities, but with similar physico-chemical sludge characteristics. Activity of the USSB sludge on a VFA mixture or with acetate as the sole substrate increased from the bottom to the top compartments. Sludge in the top compartments adapted only slowly to acetate, as indicated by the minor increase (13.5% in 138 days) of the activity on acetate and sulfate in those compartments.
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effect of upward velocity and sulphide concentration on volatile Fatty Acid Degradation in a sulphidogenic granular sludge reactor
Process Biochemistry, 1996Co-Authors: F Omil, Piet N L Lens, G LettingaAbstract:During anaerobic treatment of sulphate-containing wastewaters, sulphate-reducing bacteria (SRB) compete with methane-producing bacteria (MPB) for the available electron-donors. In this work, the anaerobic treatment of a synthetic wastewater, consisting of a mixture of acetate, propionate and butyrate and high concentrations of sulphate (COD: sulphate ratio 0·5) was studied in an upflow anaerobic granular sludge bed reactor. The influence of the superficial upward liquid velocity (vup), the influent composition and reactor pH on the competition between SRB and MPB was investigated. At a vup of 2 m h−1 and pH 8, 93–97% of the COD was degraded by SRB. With increasing vup-values, COD removal efficiencies decreased, while at a vup of 6 m h−1 the fraction of COD removed by MPB rose to 23%. Elevation of the influent acetate concentrations, by decreasing the vup (lower recirculation) or by the use of an influent volatile Fatty Acid mixture with a higher acetate content, resulted in an increase of methanogenesis up to 41% of the total COD removal. In contrast, elevated levels of propionate and butyrate in the influent favoured the sulphate reducing process. A decrease of pH from 8 to 7 resulted in free hydrogen sulphide concentrations higher than 200 mg litre−1. This strongly inhibited methanogenesis while SRB were hardly affected, with a subsequent decrease of the COD removed by MPB from 41 to 7% as a result.
Piet N L Lens - One of the best experts on this subject based on the ideXlab platform.
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sulfidogenic volatile Fatty Acid Degradation in a baffled reactor
Water Science and Technology, 2003Co-Authors: M V G Vallero, Piet N L Lens, C Bakker, G LettingaAbstract:The effect of staging the sludge bed on volatile Fatty Acid Degradation by sulfidogenic reactors was evaluated in a baffled reactor. In a 5.4 l baffled reactor, containing three equal compartments, a volatile Fatty Acid (VFA) mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) was treated under mesophilic (30°C) and sulfidogenic (COD:SO42- ratio: 0.5) conditions for 38 days. At a specific sludge loading rate of 0.50 g COD.gVSS-1.d-1, a COD and sulfate removal of 85% and 30%, respectively, was obtained. In the baffled reactor, staging of the sulfidogenic VFA Degradation occurred. Propionate and butyrate were mainly degraded in the first compartment. Their Degradation was incomplete, resulting in elevated acetate concentrations in compartment I. In the second and third compartment of the baffled reactor, a net Degradation of acetate took place. Acetate was the sole substrate present in compartment III and residual acetate concentrations of about 200 mg/l were present in the effluent at a specific sludge loading of 0.50 g COD.gVSS-1.d-1. Sludges with different maximum specific VFA and acetate degrading activities developed in the first and second compartment. These maximal specific activities were almost equal for sludge present in compartment II and III.
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kinetics of Fatty Acid Degradation by psychrophilically grown anaerobic granular sludge
Bioresource Technology, 1999Co-Authors: Salih Rebac, Piet N L Lens, Sybren Gerbens, Jules B Van Lier, Alfons J M Stams, K J Keesman, G LettingaAbstract:The kinetic parameters of anaerobic granular sludge, grown at 10–12°C in an expanded granular sludge bed (EGSB) reactor and fed with volatile Fatty Acid (VFA) mixtures, were determined in batch assays. The homoacetogenic, hydrogenotrophic and acetoclastic specific activities of the sludge at 10°C, measured after 306 days exposure to psychrophilic conditions were 1.744, and 0.296 and 0.331 g COD g−1 volatile suspended solids (VSS) day−1, respectively. At 30°C these values were 18.024, 2.732 and 2.204 g COD g−1 VSS day−1, respectively. The temperature characteristics of the granular sludge and the homoacetogenic enrichment culture from cultivated sludge showed that the temperature optima were still in the mesophilic range (30–40°C) even after long term (306 days) operation at low temperature (10–12°C). In the overall conversion rate for acetate and propionate, evidence for the temperature compensation effect was found. In contrast, no temperature compensation effect was present for butyrate Degradation. The results of EGSB batch reactor experiments revealed apparent Km of the acetate and propionate degraders in the ranges of 39–58 mg COD l−1 and 7–14 mg COD l−1, respectively. For butyrate degraders, higher Km values were found, i.e., 142–243 mg COD l−1. The observed low Km values could be attributed to prevailing mixing conditions in the EGSB reactor system.
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effect of staging on volatile Fatty Acid Degradation in a sulfidogenic granular sludge reactor
Water Research, 1998Co-Authors: Piet N L Lens, M C Van Den Bosch, G LettingaAbstract:Abstract The use of an upflow staged sludge bed (USSB) reactor for the optimization of acetate removal during treatment of sulfate rich wastewaters was investigated. The USSB treated a VFA mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) under mesophilic (30°C) and sulfidogenic (COD:SO42− ratio 0.5) conditions. Its performance was compared to that of an upflow anaerobic sludge bed (UASB) reactor operating at the same operational conditions. The hydrodynamic conditions were clearly different in both reactor types. The USSB reactor (number of ideal mixed reactors Nth=10) had a more plug-flow pattern than the UASB reactor (Nth=3). Both reactors reached a specific sludge loading rate of 1.20 gCOD gVSS−1 d−1, corresponding to a volumetric loading rate of 20 and 30 gCOD l−1 d−1 for the UASB and USSB reactor, respectively. At these loading rates, a maximum COD removal of 80% was obtained by both reactors and the average %COD used by sulfate reducing bacteria was 74(±7)% and 80(±9)% for the UASB and USSB reactor, respectively. The UASB and USSB reactor reached a sulfate loading rate of 40 and 60 g SO42− l−1 d−1, respectively, with an average sulfate removal of 45(±19)% and 35(±24)%, respectively. The USSB reactor showed more oscillations in its performance than the UASB reactor, already at lower loading rates. Staging of sulfidogenic treatment in the USSB reactor resulted in development of sludges with different maximum specific microbial activities, but with similar physico-chemical sludge characteristics. Activity of the USSB sludge on a VFA mixture or with acetate as the sole substrate increased from the bottom to the top compartments. Sludge in the top compartments adapted only slowly to acetate, as indicated by the minor increase (13.5% in 138 days) of the activity on acetate and sulfate in those compartments.
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effect of upward velocity and sulphide concentration on volatile Fatty Acid Degradation in a sulphidogenic granular sludge reactor
Process Biochemistry, 1996Co-Authors: F Omil, Piet N L Lens, G LettingaAbstract:During anaerobic treatment of sulphate-containing wastewaters, sulphate-reducing bacteria (SRB) compete with methane-producing bacteria (MPB) for the available electron-donors. In this work, the anaerobic treatment of a synthetic wastewater, consisting of a mixture of acetate, propionate and butyrate and high concentrations of sulphate (COD: sulphate ratio 0·5) was studied in an upflow anaerobic granular sludge bed reactor. The influence of the superficial upward liquid velocity (vup), the influent composition and reactor pH on the competition between SRB and MPB was investigated. At a vup of 2 m h−1 and pH 8, 93–97% of the COD was degraded by SRB. With increasing vup-values, COD removal efficiencies decreased, while at a vup of 6 m h−1 the fraction of COD removed by MPB rose to 23%. Elevation of the influent acetate concentrations, by decreasing the vup (lower recirculation) or by the use of an influent volatile Fatty Acid mixture with a higher acetate content, resulted in an increase of methanogenesis up to 41% of the total COD removal. In contrast, elevated levels of propionate and butyrate in the influent favoured the sulphate reducing process. A decrease of pH from 8 to 7 resulted in free hydrogen sulphide concentrations higher than 200 mg litre−1. This strongly inhibited methanogenesis while SRB were hardly affected, with a subsequent decrease of the COD removed by MPB from 41 to 7% as a result.
John E Cronan - One of the best experts on this subject based on the ideXlab platform.
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The enigmatic Escherichia coli fadE gene is yafH
Journal of Bacteriology, 2002Co-Authors: John W. Campbell, John E CronanAbstract:The identity of the gene encoding acyl coenzyme A dehydrogenase is a major remaining mystery of the Escherichia coli Fatty Acid Degradation (fad) regulon. Our prior genome array analyses showed that transcription of the yafH gene is controlled by the FadR regulatory protein. We now report direct experimental proof that yafH and fadE are the same gene.
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FadR, transcriptional co‐ordination of metabolic expediency
Molecular Microbiology, 1998Co-Authors: John E Cronan, Satyanarayana SubrahmanyamAbstract:FadR is an Escherichia coli transcriptional regulator that optimizes Fatty Acid metabolism in response to exogenously added Fatty Acids. Many bacteria grow well on long-chain Fatty Acids as sole carbon source, but at the expense of consuming a useful structural material. Exogenous Fatty Acids are readily incorporated into membrane phospholipids in place of the acyl chains synthesized by the organism, and phospholipids composed of any of a large variety of exogenously derived acyl chains make biologically functional membranes. It would be wasteful for bacteria to degrade Fatty Acids to acetyl-CoA and then use this acetyl-CoA to synthesize the same (or functionally equivalent) Fatty Acids for phospholipid synthesis. This line of reasoning suggests that bacteria might shut down endogenous Fatty Acid synthesis on the addition of long-chain Fatty Acids to the growth medium. Moreover, this shutdown could be closely coupled to Fatty Acid Degradation, such that a bacterial cell would use a portion of the exogenous Fatty Acid for phospholipid synthesis while degrading the remainder to acetyl-CoA. To a degree, the bacterium could both have its cake (the acyl chains for phospholipid synthesis) and eat it (to form acetyl-CoA). This scenario turns out to be true in E. coli. The key player in this regulatory gambit is FadR, a transcription factor that acts both as a repressor of the Fatty Acid Degradation and as an activator of Fatty Acid biosynthesis.
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In Vivo Evidence that S-Adenosylmethionine and Fatty Acid Synthesis Intermediates Are the Substrates for the LuxI Family of Autoinducer Synthases
Journal of Bacteriology, 1998Co-Authors: John E CronanAbstract:Many gram-negative bacteria synthesize N-acyl homoserine lactone autoinducer molecules as quorum-sensing signals which act as cell density-dependent regulators of gene expression. We have investigated the in vivo source of the acyl chain and homoserine lactone components of the autoinducer synthesized by the LuxI homolog, TraI. In Escherichia coli, synthesis of N-(3-oxooctanoyl)homoserine lactone by TraI was unaffected in a fadD mutant blocked in β-oxidative Fatty Acid Degradation. Also, conditions known to induce the fad regulon did not increase autoinducer synthesis. In contrast, cerulenin and diazoborine, specific inhibitors of Fatty Acid synthesis, both blocked autoinducer synthesis even in a strain dependent on β-oxidative Fatty Acid Degradation for growth. These data provide the first in vivo evidence that the acyl chains in autoinducers synthesized by LuxI-family synthases are derived from acyl-acyl carrier protein substrates rather than acyl coenzyme A substrates. Also, we show that decreased levels of intracellular S-adenosylmethionine caused by expression of bacteriophage T3 S-adenosylmethionine hydrolase result in a marked reduction in autoinducer synthesis, thus providing direct in vivo evidence that the homoserine lactone ring of LuxI-family autoinducers is derived from S-adenosylmethionine.
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escherichia coli transcription factor that both activates Fatty Acid synthesis and represses Fatty Acid Degradation
Journal of Molecular Biology, 1991Co-Authors: Michael F Henry, John E CronanAbstract:Abstract The fadR gene of Escherichia coli encodes a protein that acts as a negative regulator (repressor) of the inducible β-oxidation pathway. We report that the FadR protein also functions as a positive transcriptional activator of the fabA gene, which encodes the enzyme introducing the double bond of the unsaturated Fatty Acids of E. coli .
Paul Illmer - One of the best experts on this subject based on the ideXlab platform.
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impact of several antibiotics and 2 bromoethanesulfonate on the volatile Fatty Acid Degradation methanogenesis and community structure during thermophilic anaerobic digestion
Bioresource Technology, 2015Co-Authors: Philipp Lins, Christoph Reitschuler, Paul IllmerAbstract:The main aim of the present study was to gain insight into the stability of an anaerobic digestion process suffering from exposure to antibiotics and the methanogenic inhibitor 2-bromoethanesulfonate (BES). For this purpose, eleven antibiotics and BES were investigated with regard to the Degradation of volatile Fatty Acids (VFAs), methanogenesis, and impact on the microbial community structure. Only neomycin, gentamicin, rifampicin, and BES showed complete inhibitions of VFA Degradations. This points to distinct interferences with important trophic Degradation cascades. Based upon DGGE and sequencing approaches, Methanosarcina spp. were severely influenced by the treatments while hydrogenotrophic methanogens were less affected. Interestingly, BES and neomycin inhibited the Degradation of acetate while only BES inhibited methanogenesis completely. It seems that Methanosarcina spp. were mandatory for the Degradation of acetate at high rates. The present results highly emphasize the detrimental effects of antimicrobial compounds with the potential to significantly inhibit the anaerobic digestion.
Philipp Lins - One of the best experts on this subject based on the ideXlab platform.
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impact of several antibiotics and 2 bromoethanesulfonate on the volatile Fatty Acid Degradation methanogenesis and community structure during thermophilic anaerobic digestion
Bioresource Technology, 2015Co-Authors: Philipp Lins, Christoph Reitschuler, Paul IllmerAbstract:The main aim of the present study was to gain insight into the stability of an anaerobic digestion process suffering from exposure to antibiotics and the methanogenic inhibitor 2-bromoethanesulfonate (BES). For this purpose, eleven antibiotics and BES were investigated with regard to the Degradation of volatile Fatty Acids (VFAs), methanogenesis, and impact on the microbial community structure. Only neomycin, gentamicin, rifampicin, and BES showed complete inhibitions of VFA Degradations. This points to distinct interferences with important trophic Degradation cascades. Based upon DGGE and sequencing approaches, Methanosarcina spp. were severely influenced by the treatments while hydrogenotrophic methanogens were less affected. Interestingly, BES and neomycin inhibited the Degradation of acetate while only BES inhibited methanogenesis completely. It seems that Methanosarcina spp. were mandatory for the Degradation of acetate at high rates. The present results highly emphasize the detrimental effects of antimicrobial compounds with the potential to significantly inhibit the anaerobic digestion.
