Measurement of dissolved hydrogen in an anaerobic digestion process by a membrane-covered electrode

Dissolved hydrogen in an anaerobic digestion process was continuously measured by a voltammetric membrane electrode which consisted of a Pt-Pt black and Ag-AgCl covered FEP membrane with 0.1 M KCl and 0.1 M HCl. This sensor showed high reliability and sensitivity (i.e., detection limit: 50 nM) in distilled water. The sensor was not affected by several compounds in the anaerobic digestion media (e.g., inorganic salts, acetate, and propionate) except for sulfide. The indication in a sample containing 1.56 mM sulfide corresponded to that of 0.26 μM dissolved hydrogen. The sensor was also applied to measure the dissolved hydrogen in a laboratory-scale anaerobic reactor, and the dissolved hydrogen was continuously monitored for 565-h. The sensor was calibrated every 120-h, and the output signal was very stable during this period. The dissolved hydrogen concentration ranged from 0.5 to 3 μM, and H₂ partial pressure from 2 to 7 Pa in the gas phase. A good correlation (r = 0.85) between theoretical values calculated with H₂ partial pressure and the output signals was recognized. The actual dissolved hydrogen concentration was about 60-fold higher than the theoretical values calculated with H₂ partial pressure.     

Phosphorus forms and extractability in dairy manure: a case study for Wisconsin on-farm anaerobic digesters

The effect of anaerobic digestion on phosphorus (P) forms and water P extractability was investigated using dairy manure samples from six full-scale on-farm anaerobic digesters in Wisconsin, USA. On an average, total dissolved P (TDP) constituted 12 +/- 4% of total P (TP) in the influent to the anaerobic digesters. Only 7 +/- 2% of the effluent was in a dissolved form. Dissolved unreactive P (DUP), comprising polyphosphates and organic P, dominated the dissolved P component in both the influent and effluent. In most cases, it appeared that the fraction of DUP mineralized during anaerobic digestion became subsequently associated with particulate-bound solids. Geochemical equilibrium modeling with Mineql+ indicated that dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, octacalcium phosphate, newberyite, and struvite were the probable solid phases in both the digester influent and effluent samples. The water-extractable P (WEP) fraction in undigested manure ranged from 45% to 70% of TP, which reduced substantially after anaerobic digestion to 25% to 45% of TP. Anaerobic digestion of dairy manure appears capable of reducing the fraction of P that is immediately available by increasing the stability of the solid phases controlling P solubility.     

Measurement of H2S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography,Deans Switching and Sulfur-selective Detection

A method for the analysis of dissolved hydrogen sulfide in crude oil samples is demonstrated using gas chromatography. In order to effectively eliminate interferences, a two dimensional column configuration is used, with a Deans switch employed to transfer hydrogen sulfide from the first to the second column (heart-cutting). Liquid crude samples are first separated on a dimethylpolysiloxane column, and light gases are heart-cut and further separated on a bonded porous layer open tubular (PLOT) column that is able to separate hydrogen sulfide from other light sulfur species. Hydrogen sulfide is then detected with a sulfur chemiluminescence detector, adding an additional layer of selectivity. Following separation and detection of hydrogen sulfide, the system is backflushed to remove the high-boiling hydrocarbons present in the crude samples and to preserve chromatographic integrity. Dissolved hydrogen sulfide has been quantified in liquid samples from 1.1 to 500 ppm, demonstrating wide applicability to a range of samples. The method has also been successfully applied for the analysis of gas samples from crude oil headspace and process gas bags, with measurement from 0.7 to 9,700 ppm hydrogen sulfide.     

Cooccurrence of aerobic and anaerobic methane oxidation in the water column of Lake Plusssee

Dissolved methane was investigated in the water column of eutrophic Lake Plusssee and compared to temperature, oxygen, and sulfide profiles. Methane concentrations and delta-13C signatures indicated a zone of aerobic methane oxidation and additionally a zone of anaerobic methane oxidation in the anoxic water body. The latter coincided with a peak in hydrogen sulfide concentration. High cell numbers of aerobic and anaerobic methane-oxidizing microorganisms were detected by fluorescence in situ hybridization (FISH) or the more sensitive catalyst-amplified reporter deposition-FISH, respectively, in these layers.     

Mass spectrometric control of the thermophilic anaerobic digestion process based on levels of dissolved hydrogen

Summary The continuous and simultaneous monitoring of dissolved CH₄ and H₂ in samples from a laboratory scale thermophilic anaerobic digester contents by use of a silicone rubber-covered probe has enabled control of methanogenesis: regulation of the hydrogen signal in a closed feedback loop was by controlled addition of the carbon source. Dissolved hydrogen became apparent in this system at a lower loading rate than was obtained for a mesophilic anaerobic digestion system (Whitmoreet al., 1986). Controlling the supply of glucose (25 mM) at a dilution rate of 0.02 h^–1 and at progressively lower preset hydrogen levels allowed methanogenesis to be significantly prolonged before inhibition of the process occurred.     

A new method for the determination of dissolved sulfide in strongly colored anaerobically treated effluents

A simple method for dissolved sulfide determination in colored complex media was developed using ion exchange chromatography. Its principle is based on the complete oxidation of an unstable compound (sulfide) into its stable form (sulfate) through a strong oxidant: hydrogen peroxide. The difference between sample analyzed before and after this treatment gives the total dissolved sulfide. In order to avoid H₂S exhaust, this oxidation has to be performed immediately after sampling, without cell separation. In that way, standard solutions were prepared using raw anaerobic effluents from an industrial plant. It was shown in the calibration curve that no bacterial interaction was present. Finally, sulfide from continuous and discontinuous digestions of these sulfate rich wastewaters were successfully assayed by this technique. A theoretical evaluation based on Henry's law and the sulfide dissociation equilibrium led to a very good agreement with the analytical results. This study was supported by a research grant from the “Agence de l'Environement et de la Maitrise de l'Energie”, (ADEME) Paris, France. The authors would like to express their gratitude to A. Bories for his valuable advice.     

Cooccurrence of Aerobic and Anaerobic Methane Oxidation in the Water Column of Lake Plußsee

Dissolved methane was investigated in the water column of eutrophic Lake Plußsee and compared to temperature, oxygen, and sulfide profiles. Methane concentrations and δ-¹³C signatures indicated a zone of aerobic methane oxidation and additionally a zone of anaerobic methane oxidation in the anoxic water body. The latter coincided with a peak in hydrogen sulfide concentration. High cell numbers of aerobic and anaerobic methane-oxidizing microorganisms were detected by fluorescence in situ hybridization (FISH) or the more sensitive catalyst-amplified reporter deposition-FISH, respectively, in these layers.     

Simulation of constituent processes of anaerobic degradation of organic matter by the 〈methane〉 model

The model of anaerobic digestion described earlier by the authors was used for analysis of the different phases of the process. It was shown that at the glucose conversion a coexistence of hydrogen-producing acidogenic bacteria and hydrogen-utilizing non-methanogenic bacteria causes a hydrogen partial pressure decrease at an increase of solids retention time (i), the intensity of the negative feed-back effect in sulfate-reduction through hydrogen sulfide formation is regulated by the pH level during an oscillation dynamics in acetate/sulfate system (ii), under the toxicity influence the processes of methanogenesis and acetogenesis together with hydrolysis may be rate-limiting steps in the anaerobic system with particulate substrate degradation (iii).Abbreviations B1, B2 two groups of acidogens - DS total dissolved sulfide concentration - HRT hydraulic retention time - MPB methane-producing bacteria - SRB sulfate-reducing bacteria - SRT solids retention time - VFA's volatile fatty acids     

Effect of sulfide on growth of marine bacteria

Severe hypoxia leads to excess production of hydrogen sulfide in marine environments. In this study, we examined the effect of sulfide on growth of four facultative anaerobic marine bacteria in minimal media under anaerobic conditions. The Gram-negative chemolithoautotrophic Marinobacter sp. tolerated sulfide concentrations up to 0.60 mM, with doubling and lag times increasing as a function of increasing sulfide concentration but with no change in maximum culture yields; growth did not occur at 1.2 mM sulfide. Similar results were obtained for the metabolically diverse Gram-negative denitrifying Pseudomonas stutzeri, except that growth occurred at 1.2 mM and culture yields at 0.60 and 1.2 mM sulfide were approximately 10-fold lower than at sulfide concentrations between 0 and 0.30 mM. Increases in doubling and lag times accompanied by an overall 10-fold decrease in maximum culture yields were found for the Gram-negative chemoheterotrophic Vibrio sp. at all sulfide concentrations tested. In contrast, growth of a Gram-positive chemoheterotrophic Bacillus sp. was resistant to all sulfide concentrations tested (0.15–1.2 mM). Our results highlight the variable responses of marine bacteria to sulfide and provide some insight into shifts that may occur in microbial community structure and diversity as a consequence of changes in sulfide levels that are the result of hypoxia.     

Kinetic parameters and relative turnovers of some important catabolic reactions in digesting sludge.

The kinetics of propionate degradation, acetate splitting, and hydrogen consumption in digesting sludge were investigated in a lab-scale digester. At natural steady-state conditions, the acetate-splitting systems in well-digested sludge were about half saturated. Propionate-degrading systems were saturated to only 10 to 15%, and hydrogen removal was less than 1% of the maximum possible rate. It was concluded that acetate splitting rather than "methanogenesis from fatty acids" is the rate-limiting reaction in the anaerobic degradation of dissolved organic matter and that a methoanogenic anaerobic ecosystem is stabilized by its large unused capacity of hydrogen consumption which is "buffering" the partial pressure of dissolved hydrogen in the system at sufficiently low values to permit rapid fatty acid oxidation. A tentative scheme of the substrate flow in sludge digestion is presented. It suggests that acid formation coupled with hydrogen formation via pyridine dinucleotide oxidation yields the immediate substrates, namely acetate and hydrogen, for about 54% of the total methanogenesis.     

The roles of acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of biomass to methane: a review

Among different conversion processes for biomass, biological anaerobic digestion is one of the most economic ways to produce biogas from various biomass substrates. In addition to hydrolysis of polymeric substances, the activity and performance of the methanogenic bacteria is of paramount importance during methanogenesis. The aim of this paper is primarily to review the recent literature about the occurrence of both acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of particulate biomass to methane (not wastewater treatment), while this review does not cover the activity of the acetate oxidizing bacteria. Both acetotrophic and hydrogenotrophic methanogens are essential for the last step of methanogenesis, but the reports about their roles during this phase of the process are very limited. Despite, some conclusions can still be drawn. At low concentrations of acetate, normally filamentous Methanosaeta species dominate, e.g., often observed in sewage sludge. Apparently, high concentrations of toxic ionic agents, like ammonia, hydrogen sulfide (H₂S) and volatile fatty acids (VFA), inhibit preferably Methanosaetaceae and especially allow the growth of Methanosarcina species consisting of irregular cell clumps, e.g., in cattle manure. Thermophilic conditions can favour rod like or coccoid hydrogenotrophic methanogens. Thermophilic Methanosarcina species were also observed, but not thermophilic Methanosaetae. Other environmental factors could favour hydrogentrophic bacteria, e.g., short or low retention times in a biomass reactor. However, no general rules regarding process parameters could be derivated at the moment, which favours hydrogenotrophic methanogens. Presumably, it depends only on the hydrogen concentration, which is generally not mentioned in the literature.     

Effect of microorganisms and seasonal factors on the isotope composition of organic carbon from Black Sea suspensions

The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the 12C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO2 fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC delta 13C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.     

Influence of pH on microbial hydrogen metabolism in diverse sedimentary ecosystems.

Hydrogen transformation kinetic parameters were measured in sediments from anaerobic systems covering a wide range of environmental pH values to assess the influence of pH on hydrogen metabolism. The concentrations of dissolved hydrogen were measured and hydrogen transformation kinetics of the sediments were monitored in the laboratory by monitoring hydrogen consumption progress curves. The hydrogen turnover rate constants (kt) decreased directly as a function of decreasing sediment pH, and the maximum hydrogen uptake velocities (Vmax) varied as a function of pH within each of the trophic states. Conversely, the half-saturation concentrations (Km) were independent of pH. The steady-state hydrogen concentrations were at least 2 orders of magnitude lower than the half-saturation constants for hydrogen uptake. Dissolved hydrogen concentrations were at least fivefold higher in sediments from eutrophic systems than from oligotrophic and dystrophic systems. The rates of hydrogen production determined from the assumption of steady state decreased with sediment pH. These data indicate that progressively lower pH values inhibit microbial hydrogen-producing and -consuming processes within sedimentary ecosystems.     

Influence of pH on microbial hydrogen metabolism in diverse sedimentary ecosystems

Hydrogen transformation kinetic parameters were measured in sediments from anaerobic systems covering a wide range of environmental pH values to assess the influence of pH on hydrogen metabolism. The concentrations of dissolved hydrogen were measured and hydrogen transformation kinetics of the sediments were monitored in the laboratory by monitoring hydrogen consumption progress curves. The hydrogen turnover rate constants (kt) decreased directly as a function of decreasing sediment pH, and the maximum hydrogen uptake velocities (Vmax) varied as a function of pH within each of the trophic states. Conversely, the half-saturation concentrations (Km) were independent of pH. The steady-state hydrogen concentrations were at least 2 orders of magnitude lower than the half-saturation constants for hydrogen uptake. Dissolved hydrogen concentrations were at least fivefold higher in sediments from eutrophic systems than from oligotrophic and dystrophic systems. The rates of hydrogen production determined from the assumption of steady state decreased with sediment pH. These data indicate that progressively lower pH values inhibit microbial hydrogen-producing and -consuming processes within sedimentary ecosystems.     

Continuous culture of Methanococcus maripaludis under defined nutrient conditions

To study global regulation in the methanogenic archaeon Methanococcus maripaludis, we devised a system for steady-state growth in chemostats. New Brunswick Bioflo 110 bioreactors were equipped with controlled delivery of hydrogen, nitrogen, carbon dioxide, hydrogen sulfide, and anaerobic medium. We determined conditions and media compositions for growth with three different limiting nutrients, hydrogen, phosphate, and leucine. To investigate leucine limitation we constructed and characterized a mutant in the leuA gene for 2-isopropylmalate synthase, demonstrating for the first time the function of this gene in the Archaea. Steady state specific growth rates in these studies ranged from 0.042 to 0.24 h(-1). Plots of culture density vs. growth rate for each condition showed the behavior predicted by growth modeling. The results show that growth behavior is normal and reproducible and validate the use of the chemostat system for metabolic and global regulation studies in M. maripaludis.     

Novel mechanism for conditional aerobic growth of the anaerobic bacterium Treponema denticola

Treponema denticola, a periodontal pathogen, has recently been shown to exhibit properties of a facultative anaerobic spirochete, in contrast to its previous recognition as an obligate anaerobic bacterium. In this study, the capacity and possible mechanism of T. denticola survival and growth under aerobic conditions were investigated. Factors detrimental to the growth of T. denticola ATCC 33405, such as oxygen concentration and hydrogen sulfide (H(2)S) levels as well as the enzyme activities of gamma-glutamyltransferase, cysteinylglycinase, and cystalysin associated with the cells were monitored. The results demonstrated that T. denticola grew only at deeper levels of broth (>or=3 ml in a 10-ml tube), high inoculation ratios (>or=20% of culture in medium), and short cultivation times (相似文献   

In situ rumen hydrogen concentrations in steers fed eight times daily, measured using a mercury reduction detector

Abstract Dissolved hydrogen was measured in the bovine rumen using an in situ hydrogen probe coupled to a mercury reduction detector. The probe can quantitate dissolved hydrogen from low nM concentrations to saturation. In the rumen of steers fed every 3 h, basal hydrogen concentrations averaged 1.38 μ M ± 0.26, and the basal level remained stable throughout an 18–25 h period. In contrast, a steer fed once a day had a basal hydrogen concentration of 1.40 μM, but the level was not stable between feedings. For the steers fed every 3 h, the reticulum displayed the most dramatic fluctuations in the hydrogen concentration after the feeding event. Hydrogen spikes (10–20 μM) in the reticulum were detected 2 min after feed ingestion, and lasted for 30 min. In the center of the rumen the feeding response was observed 30 min after feeding and typically lasted 1 h. The magnitude of hydrogen spikes in the center of the rumen was reduced in comparison to the reticulum. The magnitude of the hydrogen spikes indicates that feeding steers as frequently as eight times a day does not establish a steady-state with respect to hydrogen concentration. However, frequent feedings do minimize drift from the basal hydrogen level. Assuming Michaelis-Menten kinetics our data predict that methane production from hydrogen proceeds at 22% of its maximal velocity.     

Physiological and morphological observations on Thiovulum sp.

Cell suspensions of Thiovulum sp., collected from enrichment cultures, were grown, maintained, and harvested for periods up to 7 months. In open-flow cultures run with aerated seawater, a continuous supply of hydrogen sulfide was provided by diffusion through a semipermeable membrane from either a live culture of Desulfovibrio esturaii, neutralized sodium sulfide, or a N2-H2S gas mixture. Attempts to grow Thiovulum in pure culture failed despite variation in concentrations of dissolved oxygen and hydrogen sulfide in stratified as well as in completely mixed systems. Uptake of 14CO2 and some organic compounds by purified cell suspensions was measured, and values were corrected for the activity of heterotrophic as well as autotrophic contaminants as determined in control experiments. Cell populations exhibited maximum uptake activities during formation of the characteristic veils. Substantial uptake of CO2 in air-saturated seawater was coincident with an optimal concentration of hydrogen sulfide of about 1 mM. Glutamate and a selection of vitamins (B12M biotin, and thiamine) did not significantly affect the uptake of CO2. No substantial uptake of carbon from acetate, glutamate, mannitol, and Casamino Acids was found. Within the range of error indicated, the data are consistent with acceptance of a chemolithotrophic nature of Thiovulum.     

Toxicants inhibiting anaerobic digestion: A review

Anaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.     

Continuous glucose fermentation by an immobilized saccharolytic sulfate-reducer

A technique for the immobilization of a novel, strictly anaerobic saccharolytic sulfate-reducer, in alginate gel, was developed. Metabolites formed from glucose, both in the presence and in the absence of exogenous sulfate, in a continuously fed upflow-reactor at hydraulic retention times of between 12 hours and 1.3 hours included acetate, ethanol, lactate and hydrogen sulfide. Comparison of the data obtained during continuous fermentation of glucose and by free cells in batch cultures showed that this method of immobilizing strict anaerobic cells did not alter metabolite compositions meaningfully.