Showing papers on "Bioreactor published in 2007"

Influence of the pH on (open) mixed culture fermentation of glucose: A chemostat study

Abstract: Catabolic products from anaerobic fermentation processes are potentially of industrial interest. The volatile fatty acids and alcohols produced can be used as building blocks in chemical processes or applied directly as substrates in a mixed culture process to produce bioplastics. Development of such applications requires a predictable and controllable product spectrum of the fermentation process. The aim of the research described in this paper was (i) to investigate the product spectrum of an open mixed culture fermentation (MCF) process as a function of the pH, using glucose as substrate, and (ii) to relate the product spectrum obtained to generalized biochemical and thermodynamic considerations. A chemostat was operated under carbon and energy limitation in order to investigate the pH effect on the product spectrum in a MCF process. A transition from CO 2 / H 2 production at lower pH values to formate production at higher pH values was observed. The ratio of CO 2 /H 2 versus formate production was found to be related to the thermodynamics of formate dehydrogenation to CO 2 /H 2 . This transition was associated with a shift in the catabolic products, from butyrate and acetate to ethanol and acetate, likely due to a decrease in the oxidation state of the electron carriers in the cell. The product spectrum of the MCF process as a function of the pH could largely be explained using general biochemical considerations.

Operation of a two-stage fermentation process producing hydrogen and methane from organic waste

Abstract: A pilot-scale experimental plant for the production of hydrogen and methane by a two-stage fermentation process was constructed and operated using a mixture of pulverized garbage and shredded paper wastes. Thermophilic hydrogen fermentation was established at 60 degrees C in the first bioreactor by inoculating with seed microflora. Following the hydrogenogenic process, methanogenesis in the second bioreactor was conducted at 55 degrees C using an internal recirculation packed-bed reactor (IRPR). After conducting steady-state operations under a few selected conditions, the overall hydraulic retention time was optimized at 8 d (hydrogenogenesis, 1.2 d; methanogenesis, 6.8 d), producing 5.4 m3/m3/d of hydrogen and 6.1 m3/m3/d of methane with chemical oxygen demand and volatile suspended solid removal efficiencies of 79.3% and 87.8%, respectively. Maximum hydrogen production yield was calculated to be 2.4 mol/mol hexose and 56 L/kg COD loaded. The methanogenic performance of the IRPR was stable, although the organic loading rate and the composition of the effluent from the hydrogenogenic process fluctuated substantially. A clone library analysis of the microflora in the hydrogenogenic reactor indicated that hydrogen-producing Thermoanaerobacterium-related organisms in the inoculum were active in the hydrogen fermentation of garbage and paper wastes, although no aseptic operations were applied. We speculate that the operation at high temperature and the inoculation of thermophiles enabled the selective growth of the introduced microorganisms and gave hydrogen fermentation efficiencies comparable to laboratory experiments. This is the first report on fermentative production of hydrogen and methane from organic waste at an actual level.

An immobilized cell bioprocess for the removal of heavy metals from aqueous flows.

Abstract: Microorganisms can be used to remove toxic heavy metals from liquid industrial wastes. In addition to the chemical toxicity of many of the latter, the production of long-lived nuclides from nuclear power programmes has introduced additional radiotoxicological hazards. Associated problems of the presence of contaminating, non-metal co-pollutants and the presentation of dilute, high-volume wastes have received little attention. Traditional biotechnological waste treatments have relied either on the use of non-living biomass ('biosorption') or on the accumulation of metals by living cells with the associated problems of metal toxicity effects and the requirements for cell viability or growth. Identification of an enzymically-mediated metal accumulation step can permit decoupling of cell growth from metal accumulation. Using pre-grown biomass immobilized in a flow-through filter ('bioreactor') the metal-accumulative bioprocess can be described accurately applying traditional Michaelis-Menten kinetics. The effect of co-pollutants can be then quantified in order to run the bioreactor in the most efficient way.

Multi-Scale Individual-Based Model of Microbial and Bioconversion Dynamics in Aerobic Granular Sludge

Abstract: Aerobic granular sludge is a novel compact biological wastewater treatment technology for integrated removal of COD (chemical oxygen demand), nitrogen, and phosphate charges. We present here a multiscale model of aerobic granular sludge sequencing batch reactors (GSBR) describing the complex dynamics of populations and nutrient removal. The macro scale describes bulk concentrations and effluent composition in six solutes (oxygen, acetate, ammonium, nitrite, nitrate, and phosphate). A finer scale, the scale of one granule (1.1 mm of diameter), describes the two-dimensional spatial arrangement of four bacterial groupsheterotrophs, ammonium oxidizers, nitrite oxidizers, and phosphate accumulating organisms (PAO)using individual based modeling (IbM) with species-specific kinetic models. The model for PAO includes three internal storage compounds: polyhydroxyalkanoates (PHA), poly phosphate, and glycogen. Simulations of long-term reactor operation show how the microbial population and activity depends on the o...

Twenty-four-well plate miniature bioreactor high-throughput system : Assessment for microbial cultivations

Abstract: High-throughput (HT) miniature bioreactor (MBR) systems are becoming increasingly important to rapidly perform clonal selection, strain improvement screening, and culture media and process optimization. This study documents the initial assessment of a 24-well plate MBR system, Micro (micro)-24, for Saccharomyces cerevisiae, Escherichia coli, and Pichia pastoris cultivations. MBR batch cultivations for S. cerevisiae demonstrated comparable growth to a 20-L stirred tank bioreactor fermentation by off-line metabolite and biomass analyses. High inter-well reproducibility was observed for process parameters such as on-line temperature, pH and dissolved oxygen. E. coli and P. pastoris strains were also tested in this MBR system under conditions of rapidly increasing oxygen uptake rates (OUR) and at high cell densities, thus requiring the utilization of gas blending for dissolved oxygen and pH control. The E. coli batch fermentations challenged the dissolved oxygen and pH control loop as demonstrated by process excursions below the control set-point during the exponential growth phase on dextrose. For P. pastoris fermentations, the micro-24 was capable of controlling dissolved oxygen, pH, and temperature under batch and fed-batch conditions with subsequent substrate shot feeds and supported biomass levels of 278 g/L wet cell weight (wcw). The average oxygen mass transfer coefficient per non-sparged well were measured at 32.6 +/- 2.4, 46.5 +/- 4.6, 51.6 +/- 3.7, and 56.1 +/- 1.6 h(-1) at the operating conditions of 500, 600, 700, and 800 rpm shaking speed, respectively. The mixing times measured for the agitation settings 500 and 800 rpm were below 5 and 1 s, respectively.

Hydrogen production by anaerobic microbial communities exposed to repeated heat treatments.

Abstract: Biological hydrogen production by anaerobic mixed communities was studied in laboratory-scale bioreactors using sucrose as the substrate. A bioreactor in which a fraction of the return sludge was exposed to repeated heat treatments performed better than a control bioreactor without repeated heat treatment of return sludge and produced a yield of 2.15 moles of hydrogen per mole of sucrose, with 50% hydrogen in the biogas. Terminal restriction fragment length polymorphism analysis showed that two different Clostridium groups (comprised of one or more species) were dominant during hydrogen production. The relative abundance of two other non-Clostridium groups increased during periods of decreased hydrogen production. The first group consisted of Bifidobacterium thermophilum, and the second group included one or more of Bacillus, Melissococcus, Spirochaeta, and Spiroplasma spp.

Activated Carbon Addition to a Submerged Anaerobic Membrane Bioreactor: Effect on Performance, Transmembrane Pressure, and Flux

Abstract: This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors SAMBRs in terms of chemical oxygen demand COD removal, flux, and transmembrane pressure TMP. The feed was a synthetic substrate with a COD of 460 mg L 1 , with one reactor run as a control, one with 1.7 g L 1 of powdered activated carbon PAC, and the third with 1.7 g L 1 of granular activated carbon GAC. While COD removal was high in all reactors 90%, in comparison to the control SAMBR1, the average COD removal in SAMBR2 PAC increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low 18 mg L 1 , even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage.

Sulfide oxidation at halo-alkaline conditions in a fed-batch bioreactor

Abstract: A biotechnological process is described to remove hydrogen sulfide (H2S) from high-pressure natural gas and sour gases produced in the petrochemical industry. The process operates at halo-alkaline conditions and combines an aerobic sulfide-oxidizing reactor with an anaerobic sulfate (SO) and thiosulfate (S2O) reducing reactor. The feasibility of biological H2S oxidation at pH around 10 and total sodium concentration of 2 mol L-1 was studied in gas-lift bioreactors, using halo-alkaliphilic sulfur-oxidizing bacteria (HA-SOB). Reactor operation at different oxygen to sulfide (O2:H2S) supply ratios resulted in a stable low redox potential that was directly related with the polysulfide (S) and total sulfide concentration in the bioreactor. Selectivity for SO formation decreased with increasing S and total sulfide concentrations. At total sulfide concentrations above 0.25 mmol L-1, selectivity for SO formation approached zero and the end products of H2S oxidation were elemental sulfur (S0) and S2O. Maximum selectivity for S0 formation (83.3±0.7%) during stable reactor operation was obtained at a molar O2:H2S supply ratio of 0.65. Under these conditions, intermediary S plays a major role in the process. Instead of dissolved sulfide (HS-), S seemed to be the most important electron donor for HA-SOB under S0 producing conditions. In addition, abiotic oxidation of S was the main cause of undesirable formation of S2O. The observed biomass growth yield under SO producing conditions was 0.86 g N mol-1 H2S. When selectivity for SO formation was below 5%, almost no biomass growth was observed

Ecology of the Microbial Community Removing Phosphate from Wastewater under Continuously Aerobic Conditions in a Sequencing Batch Reactor

Abstract: All activated sludge systems for removing phosphate microbiologically are configured so the biomass is cycled continuously through alternating anaerobic and aerobic zones. This paper describes a novel aerobic process capable of decreasing the amount of phosphate from 10 to 12 mg P liter(-1) to less than 0.1 mg P liter(-1) (when expressed as phosphorus) over an extended period from two wastewaters with low chemical oxygen demand. One wastewater was synthetic, and the other was a clarified effluent from a conventional activated sludge system. Unlike anaerobic/aerobic enhanced biological phosphate removal (EBPR) processes where the organic substrates and the phosphate are supplied simultaneously to the biomass under anaerobic conditions, in this aerobic process, the addition of acetate, which begins the feed stage, is temporally separated from the addition of phosphate, which begins the famine stage. Conditions for establishing this process in a sequencing batch reactor are detailed, together with a description of the changes in poly-beta-hydroxyalkanoate (PHA) and poly(P) levels in the biomass occurring under the feed and famine regimes, which closely resemble those reported in anaerobic/aerobic EBPR processes. Profiles obtained with denaturing gradient gel electrophoresis were very similar for communities fed both wastewaters, and once established, these communities remained stable over prolonged periods of time. 16S rRNA-based clone libraries generated from the two communities were also very similar. Fluorescence in situ hybridization (FISH)/microautoradiography and histochemical staining revealed that "Candidatus Accumulibacter phosphatis" bacteria were the dominant poly(P)-accumulating organisms (PAO) in both communities, with the phenotype expected for PAO. FISH also identified large numbers of betaproteobacterial Dechloromonas and alphaproteobacterial tetrad-forming organisms related to Defluviicoccus in both communities, but while these organisms assimilated acetate and contained intracellular PHA during the feed stages, they never accumulated poly(P) during the cycles, consistent with the phenotype of glycogen-accumulating organisms.

Two new disposable bioreactors for plant cell culture: The wave and undertow bioreactor and the slug bubble bioreactor.

Abstract: The present article describes two novel flexible plastic-based disposable bioreactors. The first one, the WU bioreactor, is based on the principle of a wave and undertow mechanism that provides agitation while offering convenient mixing and aeration to the plant cell culture contained within the bioreactor. The second one is a high aspect ratio bubble column bioreactor, where agitation and aeration are achieved through the intermittent generation of large diameter bubbles, "Taylor-like" or "slug bubbles" (SB bioreactor). It allows an easy volume increase from a few liters to larger volumes up to several hundred liters with the use of multiple units. The cultivation of tobacco and soya cells producing isoflavones is described up to 70 and 100 L working volume for the SB bioreactor and WU bioreactor, respectively. The bioreactors being disposable and pre-sterilized before use, cleaning, sterilization, and maintenance operations are strongly reduced or eliminated. Both bioreactors represent efficient and low cost cell culture systems, applicable to various cell cultures at small and medium scale, complementary to traditional stainless-steel bioreactors.

High Density Bioreactor System, Devices, and Methods

Abstract: A bioreactor and bioreactor system are suitable for the growth of materials from algae. More specifically, the system preferred embodiments use concentrated sunlight in a solo- or co-generation system to produce algae and products therefrom as well as solar thermal energy.

Quantitative analysis of a high-rate hydrogen-producing microbial community in anaerobic agitated granular sludge bed bioreactors using glucose as substrate

Abstract: Fermentative H(2) production microbial structure in an agitated granular sludge bed bioreactor was analyzed using fluorescence in situ hybridization (FISH) and polymerase chain reaction-denatured gradient gel electrophoresis (PCR-DGGE). This hydrogen-producing system was operated at four different hydraulic retention times (HRTs) of 4, 2, 1, and 0.5 h and with an influent glucose concentration of 20 g chemical oxygen demand/l. According to the PCR-DGGE analysis, bacterial community structures were mainly composed of Clostridium sp. (possibly Clostridium pasteurianum), Klebsiella oxytoca, and Streptococcus sp. Significant increase of Clostridium/total cell ratio (68%) was observed when the reactor was operated under higher influent flow rate. The existence of Streptococcus sp. in the reactor became more important when operated under a short HRT as indicated by the ratio of Streptococcus probe-positive cells to Clostridium probe-positive cells changing from 21% (HRT 4 h) to 38% (HRT 0.5 h). FISH images suggested that Streptococcus cells probably acted as seeds for self-flocculated granule formation. Furthermore, combining the inspections with hydrogen production under different HRTs and their corresponding FISH analysis indicated that K. oxytoca did not directly contribute to H(2) production but possibly played a role in consuming O(2) to create an anaerobic environment for the hydrogen-producing Clostridium.

Fed-batch bioreactor process scale-up from 3-L to 2,500-L scale for monoclonal antibody production from cell culture.

Abstract: This case study focuses on the scale-up of a Sp2/0 mouse myeloma cell line based fed-batch bioreactor process, from the initial 3-L bench scale to the 2,500-L scale. A stepwise scale-up strategy that involved several intermediate steps in increasing the bioreactor volume was adopted to minimize the risks associated with scale-up processes. Careful selection of several available mixing models from literature, and appropriately applying the calculated results to our settings, resulted in successful scale-up of agitation speed for the large bioreactors. Consideration was also given to scale-up of the nutrient feeding, inoculation, and the set-points of operational parameters such as temperature, pH, dissolved oxygen, dissolved carbon dioxide, and aeration in an integrated manner. It has been demonstrated through the qualitative and the quantitative side-by-side comparison of bioreactor performance as well as through a panel of biochemical characterization tests that the comparability of the process and the product was well controlled and maintained during the process scale-up. The 2,500-L process is currently in use for the routine clinical production of Epratuzumab in support of two global Phase III clinical trials in patients with lupus. Today, the 2,500 L, fed-batch production process for Epratuzumab has met all scheduled batch releases, and the quality of the antibody is consistent and reproducible, meeting all specifications, thus confirming the robustness of the process.