Simultaneous hydrogen utilization and in situ biogas upgrading in an anaerobic reactor

The possibility of converting hydrogen to methane and simultaneous upgrading of biogas was investigated in both batch tests and fully mixed biogas reactor, simultaneously fed with manure and hydrogen. Batch experiments showed that hydrogen could be converted to methane by hydrogenotrophic methanogenesis with conversion of more than 90% of the consumed hydrogen to methane. The hydrogen consumption rates were affected by both (hydrogen partial pressure) and mixing intensity. Inhibition of propionate and butyrate degradation by hydrogen (1 atm) was only observed under high mixing intensity (shaking speed 300 rpm). Continuous addition of hydrogen (flow rate of 28.6 mL/(L/h)) to an anaerobic reactor fed with manure, showed that more than 80% of the hydrogen was utilized. The propionate and butyrate level in the reactor was not significantly affected by the hydrogen addition. The methane production rate of the reactor with H₂ addition was 22% higher, compared to the control reactor only fed with manure. The CO₂ content in the produced biogas was only 15%, while it was 38% in the control reactor. However, the addition of hydrogen resulted in increase of pH (from 8.0 to 8.3) due to the consumption of bicarbonate, which subsequently caused slight inhibition of methanogenesis. Biotechnol. Bioeng. 2012; 109:1088–1094. © 2011 Wiley Periodicals, Inc.     

Integrated biogas upgrading and hydrogen utilization in an anaerobic reactor containing enriched hydrogenotrophic methanogenic culture

Biogas produced by anaerobic digestion, is mainly used in a gas motor for heat and electricity production. However, after removal of CO₂, biogas can be upgraded to natural gas quality, giving more utilization possibilities, such as utilization as autogas, or distant utilization by using the existing natural gas grid. The current study presents a new biological method for biogas upgrading in a separate biogas reactor, containing enriched hydrogenotrophic methanogens and fed with biogas and hydrogen. Both mesophilic‐ and thermophilic anaerobic cultures were enriched to convert CO₂ to CH₄ by addition of H₂. Enrichment at thermophilic temperature (55°C) resulted in CO₂ and H₂ bioconversion rate of 320 mL CH₄/(gVSS h), which was more than 60% higher than that under mesophilic temperature (37°C). Different dominant species were found at mesophilic‐ and thermophilic‐enriched cultures, as revealed by PCR–DGGE. Nonetheless, they all belonged to the order Methanobacteriales, which can mediate hydrogenotrophic methanogenesis. Biogas upgrading was then tested in a thermophilic anaerobic reactor under various operation conditions. By continuous addition of hydrogen in the biogas reactor, high degree of biogas upgrading was achieved. The produced biogas had a CH₄ content, around 95% at steady‐state, at gas (mixture of biogas and hydrogen) injection rate of 6 L/(L day). The increase of gas injection rate to 12 L/(L day) resulted in the decrease of CH₄ content to around 90%. Further study showed that by decreasing the gas–liquid mass transfer by increasing the stirring speed of the mixture the CH₄ content was increased to around 95%. Finally, the CH₄ content around 90% was achieved in this study with the gas injection rate as high as 24 L/(L day). Biotechnol. Bioeng. 2012; 109: 2729–2736. © 2012 Wiley Periodicals, Inc.     

Hollow fiber supported gas membrane for in situ removal of ammonium during an antibiotic fermentation

To study the influence of ammonium on an antibiotic cultivation, mass transfer measurements of ammonium through microporous hydrophobic membranes using different stripping methods were carried out and compared. The higher overall mass transfer coefficients for ammonium were obtained with an acid stripping solution compared to water, vacuum, or sweeping air. A hollow fiber module for in situ removal of ammonium during cultivation was designed and operated in an external bypass to a 10-L fermentor. Compared to a control fermentation, the cell dry mass could be increased 2.6 times and the antibiotic concentration 8 times, if the in situ ammonium removal was in operation.     

Co-digestion of manure and whey for in situ biogas upgrading by the addition of H2: process performance and microbial insights

In situ biogas upgrading was conducted by introducing H₂ directly to the anaerobic reactor. As H₂ addition is associated with consumption of the CO₂ in the biogas reactor, pH increased to higher than 8.0 when manure alone was used as substrate. By co-digestion of manure with acidic whey, the pH in the anaerobic reactor with the addition of hydrogen could be maintained below 8.0, which did not have inhibition to the anaerobic process. The H₂ distribution systems (diffusers with different pore sizes) and liquid mixing intensities were demonstrated to affect the gas-liquid mass transfer of H₂ and the biogas composition. The best biogas composition (75:6.6:18.4) was obtained at stirring speed 150 rpm and using ceramic diffuser, while the biogas in the control reactor consisted of CH₄ and CO₂ at a ratio of 55:45. The consumed hydrogen was almost completely converted to CH₄, and there was no significant accumulation of VFA in the effluent. The study showed that addition of hydrogen had positive effect on the methanogenesis, but had no obvious effect on the acetogenesis. Both hydrogenotrophic methanogenic activity and the concentration of coenzyme F₄₂₀ involved in methanogenesis were increased. The archaeal community was also altered with the addition of hydrogen, and a Methanothermobacter thermautotrophicus related band appeared in a denaturing gradient gel electrophoresis gel from the sample of the reactor with hydrogen addition. Though the addition of hydrogen increased the dissolved hydrogen concentration, the degradation of propionate was still thermodynamically feasible at the reactor conditions.     

Fermentative H2 production in an upflow anaerobic sludge blanket reactor at various pH values

Fermentative H(2) production in an upflow anaerobic sludge blanket reactor (UASB) at various pH values was investigated in this study. Experimental results show that the H(2) partial pressure in biogas, H(2) production rate and H(2) yield were all pH-dependent, in the range of 0.25-0.52 atm, 42-145 ml-H(2) l(-1) h(-1) and 0.47 to 1.61 mol-H(2)mol-glucose(-1), respectively. The maximum pH for the H(2) partial pressure was observed at pH 7.50. However, the optimum H(2) production rate and H(2) yield were observed at pH 6.50-7.50. In this UASB reactor, acetate, propionate, butyrate, i-butyrate, valerate, caporate and ethanol were present in the effluent as main aqueous products, and the dominant fermentation was butyrate-type at various pHs. The metabolic pathways and thermodynamics of H(2) production were also analyzed. Both H(2) production performance and fermentation pathways in this H(2)-producing UASB reactor were significantly affected by the pH value.     

Hollow fibre modules as membrane reactor in biocatalysis

As shown in the case of the enzymatic cleavage of Penicillin G by Penicillin acylase hollow fibre modules of the type MLW (molecular separation value of 10,000 Dalton) produced for blood dialysis are also suitable as membrane reactor. The enzymes physically bound in the hollow fibre allow a reproducible reaction rate and are characterized by an acceptable stability. The studies indicate an operating stability which makes possible low production costs of amino penicillin acid.     

Continuous H2 production by anaerobic mixed microflora in membrane bioreactor

The characteristics of H(2) production by anaerobic mixed microflora in a submerged membrane bioreactor (MBR) were investigated. For comparative purposes, a continuous stirred tank reactor (CSTR) was operated in parallel under the same conditions. The experimental results showed that 35-day stable and continuous H(2) fermentation was successfully achieved, the MBR revealing an H(2) content of 51% and the CSTR, 58%. No methane gas was detected during the experiments for the long solids retention time (SRT) of 90 days. The MBR's H(2) production rate was 2.43-2.56 l H(2) l(-1)d(-1), which was about 2.6 times higher than that (0.95-0.97 l H(2) l(-1)d(-1)) of the CSTR, reflecting the MBR's higher H(2) productivity.     

Support media for microbial adhesion in an anaerobic fluidized-bed reactor

The most significant variable in anaerobic digestion in an anaerobic fluidized-bed reactor (AFBR) is the selection of the support medium for microbial adhesion. Using eight kinds of media, cristobalite, zeolite, vermiculite, granular active carbon, granulated clay, pottery stone, volcanic ash, and slag, we examined the physical properties of each medium, microbial adhesion, loading rates of organic matter and removal efficiencies in an AFBR. It appeared that good performance as a support medium was associated with rougher surfaces rather than with larger surface areas, because, although cristobalite had a much smaller surface area (50 m²/g) than that of the granular active carbon (1,125 m²/g), it had a very rough surface with many tubercular processes, by which a maximum loading rate of TOC of 8 g/l·d could be achieved in a synthetic wastewater. Moreover, it appeared to be important that the surface of the medium has a positive charge judging from the difference in performance between cristobalite and zeolite. That is, the two media were charged positively and negatively at pH 7, respectively. As a result, microorganisms, charged negatively in general, could adhere more easily to cristobalite than to zeolite, which was confirmed under a scanning electron microscope (SEM) and by amounts of microbial cells adhering (85 mg cells/g). The upflow linear velocity to allow twice the expanded volume (defined as the ratio of the expanded height to the static height) was decreased to half (0.13 cm/s) by microbial adhesion. In conclusion, a suitable medium for adherence of microorganisms in AFBR should have a rough and positively charged surface rather than a large surface area.     

Changes in microbial ecology in an anaerobic reactor

This study examined the behaviour of the microbial population in an anaerobic reactor, in terms of changes in numbers of total bacterial community, autofluorescent methanogens, non-methanogens and morphology of the autofluorescent methanogens, using epifluorescence microscopy and microbiological enumeration techniques. A laboratory-scale, continuous flow-completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated at an HRT range between 24 and 12 h, using dairy wastewater as the substrate. The numbers of the total bacterial community and autofluorescent methanogens both decreased during start-up. Also, the proportion of the number of autofluorescent methanogens in the total bacterial community varied from 5% to 16% during operation. In particular, the activity of the methane-forming bacteria decreased significantly at HRTs of 16 and 12 h. A membrane module, instead of a conventional settling tank, would obviously have been a more effective method if recycling were required in the anaerobic treatment system.     

Continuous measurement of dissolved H2 in an anaerobic reactor using a new hydrogen/air fuel cell detector

A miniature fuel cell, using a hydrophobic Teflon(R) membrane, designed to continuously measure dissolved H(2) in nonbiological media, was tested for use in anaerobic digestion conditions. In water, this detector responds quickly and efficiently to variation of hydrogen concentration in the range from 80 to 770 nM The media used, and the metabolites or products found in anaerobic digestion media, i. e. inorganic carbon and phosphate buffers, formate, acetate, and dissolved methane, did not interfere with the signal of the detector cell. Dissolved hydrogen sulfide did not poison the cell but was detected. In spite of the detector's high sensitivity to hydrogen (about 21,000 times higher for hydrogen than for hydrogen sulfide), interferences can occur in media containing high sulfide levels.In a methanogenic reactor, the detector cell response to dissolved hydrogen was fast and reliable with time. The observed values ranged values ranged from 2 to 3.5muM. Dissolved hydrogen concentrations were 40 to 70 times higher than values calculated from measured hydrogen partial pressures and Henry's coefficient, suggesting a limitation of the process in the hydrogen transfer from the liquid to the gaseous phase.     

Polyurethane membrane as an efficient immobilization carrier for high-density culture of rat hepatocytes in the fixed-bed reactor

A fixed-bed bioreactor with a polyurethane membrane (PUM) as a cell-supporting material was developed for high-density culture of rat hepatocytes. The PUM has a heterogeneous porous structure of micropores (pore size <100 microm) and macropores (pore size >100 microm) with a porosity of 90%. One important feature of a PUM is that the macropores have finger-like structures and their diameters gradually decrease from the upper to the lower layer of the PUM. Most rat hepatocytes were readily immobilized in the micropores of PUM. Immobilized cell densities of 1-3 x 10(7) cells/cm(3) PUM were achieved within 5 min by natural downflow of cell suspension and their immobilization efficiencies were more than 99%. Using a syringe pump, a cell density of 5 x 10(7) cells/cm(3) PUM was achieved with more than 96% immobilization efficiency. Perfusion cultures using this reactor were performed for 7 days without cell leakage. The optimal cell density for albumin secretion was between 2 x 10(7) and 3 x 10(7) cells/cm(3) PUM. Albumin secretion in the perfusion culture was maintained for a relatively long period of time when compared to that in the monolayer culture. The rate of albumin secretion in the perfusion culture was about 50% of that in monolayer culture. Hepatocytes immobilized in PUM were slightly aggregated, but they maintained spherical form individually even after 7 days of cultivation. The above results show that PUM is a promising cell-supporting material for efficient immobilization of high cell density of hepatocytes.     

Enantioselective esterification of butanol-2 in an enzyme membrane reactor

The enzymatic esterification of octanoic acid with racemic butanol-2 was investigated. Esterifications of the acid were performed in a forced flow enzyme membrane reactor. The used membrane was prepared by a phase inversion process in polyamide-6 solution followed by the chemical immobilization of a lipase-catalyst. Influences of water content and pH were estimated. Their optimum values are equal to 0.5% w/w and pH 8. The reaction rate (at 303 K) of 5.1 × 10^?5 mol/h·cm² of the membrane area, and at least 85% enantiomeric excess in the produced ester mixture were obtained. The activity of immobilized lipase in the membrane process is about two times higher than that of the native lipase in the esterification performed in a tank reactor.     

Growth characteristic of anaerobic ammonium-oxidizing bacteria in an anaerobic biological filtrated reactor

The doubling time of anaerobic ammonium-oxidizing (anammox) bacteria in an anaerobic biological filtrated (ABF) reactor was determined. Fluorescence in situ hybridization analysis was used to detect and count anammox bacteria cells in anammox sludge. As a result, the populations of anammox bacteria at 14th and 21st days were 1.1×10⁶ and 1.7×10⁷ cells/ml reactor, respectively. From these results, the doubling time of anammox bacteria was calculated as 1.8 days, and the specific growth rate (μ) was 0.39 day⁻¹. This result indicated that the anammox bacteria have higher growth rate than the reported value (doubling time, 11 days). Furthermore, it was clearly demonstrated that nitrogen conversion rate was proportional to the population of anammox bacteria. Maintaining the ideal environment for the growth of anammox bacteria in the ABF reactor might lead to faster growth. This is the first report of the growth rate of anammox bacteria based on the direct counting of anammox bacteria.     

Treatment of food processing wastewater in a full-scale jet biogas internal loop anaerobic fluidized bed reactor

A full-scale jet biogas internal loop anaerobic fluidized bed (JBILAFB) reactor, which requires low energy input and allows enhanced mass transfer, was constructed for the treatment of food processing wastewater. This reactor has an active volume of 798 m³ and can treat 33.3 m³ wastewater per hour. After pre-treating the raw wastewater by settling, oil separating and coagulation-air floating processes, the reactor was operated with a relatively shorter start-up time (55 days). Samples for the influent and effluent of the JBILAFB reactor were taken and analyzed daily for the whole process including both the start-up and stable running periods. When the volumetric COD loading fluctuated in the range of 1.6–5.6 kg COD m⁻³ day⁻¹, the COD removal efficiency, the volatile fatty acid(VFA)/alkalinity ratio, the maximum biogas production and the content of CH₄ in total biogas of the reactor were found to be 80.1 ± 5%, 0.2–0.5, 348.5 m³ day⁻¹ and 94.5 ± 2.5%, respectively. Furthermore, the scanning electron microscope (SEM) results showed that anaerobic granular sludge and microorganism particles with biofilm coexisted in the reactor, and that the bacteria mainly in bacilli and cocci were observed as predominant species. All the data demonstrated that the enhanced mass transfer for gas, liquid and solid phases was achieved, and that the formation of microorganism granules and the removal of inhibitors increased the stability of the system.     

Low temperature pre-treatment of domestic sewage in an anaerobic hybrid or an anaerobic filter reactor

The ability of pigs to use nitrogen and energy in Bermuda grass was evaluated in order to assess whether Bermuda grass harvested from spray fields could be fed to pigs as a means to recycle nitrogen. Digestibility of Bermuda grass incorporated into corn-soybean meal diets was evaluated in heavy finishing pigs and gestating sows. Results suggest that Bermuda grass digestibility is negative in animals not adapted to a high-fiber diet. Enzymes improve this digestibility, but even with enzymes, nitrogen digestibility was poor. Pigs fed a diet containing 10% Bermuda grass required a one week adaptation period for maximal digestion; following adaptation, pigs can digest approximately 40% of the energy in Bermuda grass but none of the nitrogen. Feeding Bermuda grass to pigs as a means of recycling nitrogen is thus not recommended.     

Regeneration and retention of NADP (H) for xylitol production in an ionized membrane reactor

Summary A sulfonated polysulfone membrane reactor was used forin situ regeneration and retention of coenzymes NADP (H) using the xylose reductase ofCandida pelliculosa coupled with oxidoreductase system ofMethanobacterium sp. in the reduction of xylose to xylitol with hydrogen gas. The membrane could almost completely reject the permeation of NADP (H) (92 and 97%), F₄₂₀ (97%) and the required enzymes (100%), but not reject for the permeation of xylitol (product). After 4-h reaction for the production of xylitol from xylose (93% yield), although 25% NADP (H) initially added was lost its activity due to unavoidable degradation, the membrane could reject the permeation of the remaining NADP (H) and F₄₂₀ at the level of 90 and 95%, respectively.     

Methanogenic degradation of hydroquinone in an anaerobic fixed-bed reactor

Summary A 500-ml fixed-bed reactor filled with glass sinter spools was used to study the dynamics and potential of methanogenic hydroquinone degradation. The concentration of hydroquinone as sole energy and carbon source in the inflowing medium varied from 0.55 to 2.2 g/l. Degradation of hydroquinone to methane and CO₂ was complete at low flow rates (170 ml/h) and low hydroquinone concentrations (0.55 g/l). At higher hydroquinone concentrations and/or higher flow rates, acetate accumulated in the reactor, and traces of hydroquinone were detected in the outflowing medium. The maximum degradation rate was 0.3–0.4 hydroquinone/h per 500 ml reactor volume. The bacterial community that established in the reactor after several weeks of operation was fairly stable, and consisted primarily of three bacterial species: a rod-shaped bacterium responsible for the degradation of hydroquinone to acetate and hydrogen, and two species of methanogenic bacteria, Methanospirillum hungatei and Methanothix sp.     

Transformation of tetrachloroethene in an upflow anaerobic sludgeblanket reactor

  Reductive dechlorination of tetrachloroethene was studied in a mesophilic upflow anaerobic sludge blanket reactor. Operating the reactor in batch mode the dynamic transformation of tetrachloroethene, trichloroethene and dichloroethene (DCE) was monitored. Tetrachloroethene was reductively dechlorinated to trichloroethene, which again was dechlorinated at the same rate as DCE was produced. DCE showed a lag period of 40 h before transformation was observed. During normal reactor operation trans-1,2-DCE was the major DCE isomer, followed by cis-1,2-DCE. Small amounts of 1,1-DCE but no vinyl chloride were detected. When the influent tetrachloroethene concentration was increased from 4.6 μM to 27 μM, the transformation rate increased, indicating that the system was not saturated with tetrachloroethene. The main organic component in the effluent was acetate, indicating that the aceticlastic methane-producing bacteria were inhibited by the chlorinated ethenes. Received: 29 July 1996 / Received revision: 13 September 1996 / Accepted: 13 September 1996