Showing papers on "Bioreactor published in 1997"

Performance of a sulfide-oxidizing expanded-bed reactor supplied with dissolved oxygen.

Abstract: The performance of a new sulfide-oxidizing, expanded-bed bioreactor is described. To stimulate the formation of well-settleable sulfur sludge, which comprises active sulfide-oxidizing bacterial biomass and elemental sulfur, the aeration of the liquid phase and the oxidation of sulfide to elemental sulfur are spatially separated. The liquid phase is aerated in a vessel and subsequently recirculated to the sulfide-oxidizing bioreactor. In this manner, turbulencies due to aeration of the liquid phase in the bioreactor are avoided. It appeared that, under autotrophic conditions, almost all biomass present in the reactor will be immobilized within the sulfur sludge which consists mainly of elemental sulfur (92%) and biomass (2.5%). The particles formed have a diameter of up to 3 mm and can easily be grinded down. Within time, the sulfur sludge obtained excellent settling properties; e.g., after 50 days of operation, 90% of the sludge settles down at a velocity above 25 m h-1 while 10% of the sludge had a sedimentation velocity higher than 108 m h-1. Because the biomass is retained in the reactor, higher sulfide loading rates may be applied than to a conventional “free-cell” suspension. The maximum sulfide-loading rate reached was 14 g HS- L-1 d-1, whereas for a free-cell suspension a maximum loading rate of 6 g HS- L-1 d-1 was found. At higher loading rates, the upward velocities of the aerated suspension became too high so that sulfur sludge accumulated in the settling zone on top of the reactor. When the influent was supplemented with volatile fatty acids, heterotrophic sulfur and sulfate reducing bacteria, and possibly also (facultatively) heterotrophic Thiobacilli, accumulated within the sludge. This led to a serious deterioration of the system; i.e., the sulfur formed was increasingly reduced to sulfide, and also the formation rate of sulfur sludge declined. © 1997 John Wiley & Sons, Inc.

Biodegradation of phenol at high initial concentrations in two-phase partitioning batch and fed-batch bioreactors

Abstract: A two-phase organic-aqueous system was used to degrade phenol in both batch and fed-batch culture. The solvent, which contained the phenol and partitioned it into the aqueous phase, was systematically selected based on volatility, solubility in the aqueous phase, partition coefficient for phenol, biocompatibility, and cost. The two-phase partitioning bioreactor used 500 mL of 2-undecanone loaded with high concentrations of phenol to deliver the xenobiotic to Pseudomonas putida ATCC 11172 in the 1-L aqueous phase, at subinhibitory levels. The initial concentrations of phenol selected for the aqueous phase were predicted using the experimentally determined partition coefficient for this ternary system of 47.6. This system was initially observed to degrade 4 g of phenol in just over 48 h in batch culture. Further loading of the organic phase in subsequent experiments demonstrated that the system was capable of degrading 10 g of phenol to completion in approximately 72 h. The higher levels of phenol in the system caused a modest increase in the duration of the lag phase, but did not lead to complete inhibition or cell death. The use of a fed-batch approach allowed the system to ultimately consume 28 g of phenol in approximately 165 h, without experiencing substrate toxicity. In this system, phenol delivery to the aqueous phase is demand based, and is directly related to the metabolic activity of the cells. This system permits high loading of phenol without the corresponding substrate inhibition commonly seen in conventional bioreactors.

Detoxification and partial mineralization of the azo dye mordant orange 1 in a continuous upflow anaerobic sludge-blanket reactor

Abstract: In batch toxicity assays, azo dye compounds were found to be many times more toxic than their cleavage products (aromatic amines) towards methanogenic activity in anaerobic granular sludge. Considering the ability of anaerobic microorganisms to reduce azo groups, detoxification of azo compounds towards methanogens can be expected to occur during anaerobic wastewater treatment. In order to test this hypothesis, the anaerobic degradation of one azo dye compound, Mordant orange 1 (MO1), by granular sludge was investigated in three separate continuous upflow anaerobic sludge-blanket reactors. One reactor, receiving no cosubstrate, failed after 50 days presumably because of a lack of reducing equivalents. However, the two reactors receiving either glucose or a volatile fatty acids (acetate, propionate, butyrate) mixture, could eliminate the dye during operation for 217 days. The azo dye was reductively cleaved to less toxic aromatic amines (1,4-phenylenediamine and 5-aminosalicylic acid) making the treatment of MO1 feasible at influent concentrations that were over 25 times higher than their 50% inhibitory concentrations. In the reactor receiving glucose as cosubstrate, 5-aminosalicylic acid could only be detected at trace levels in the effluent after day 189 of operation. Batch biodegradability assays with the sludge sampled from this reactor confirmed the mineralization of 5-aminosalicylic acid to methane.

Aerobic degradation of olive mill wastewaters.

Abstract: The degradation of olive mill wastewater by aerobic microorganisms has been investigated in a batch reactor, by conducting experiments where the initial concentration of organic matter, quantified by the chemical oxygen demand, and the initial biomass were varied. The evolution of the chemical oxygen demand, biomass and the total contents of phenolic and aromatic compounds were followed through each experiment. According to the Contois model, a kinetic expression for the substrate utilization rate is derived, and its biokinetic constants are evaluated. This final predicted equation agrees well with all the experimental data.

Ethanol production by Saccharomyces cerevisiae in biofilm reactors

Abstract: Biofilms are natural forms of cell immobilization in which microorganisms attach to solid supports. At ISU, we have developed plastic composite-supports (PCS) (agricultural material (soybean hulls or oat hulls), complex nutrients, and polypropylene) which stimulate biofilm formation and which supply nutrients to the attached microorganisms. Various PCS blends were initially evaluated in repeated-batch culture-tube fermentation with Saccharomyces cerevisiae (ATCC 24859) in low organic nitrogen medium. The selected PCS (40% soybean hull, 5% soybean flour, 5% yeast extract-salt and 50% polypropylene) was then used in continuous and repeated-batch fermentation in various media containing lowered nitrogen content with selected PCS. During continuous fermentation, S. cerevisiae demonstrated two to 10 times higher ethanol production in PCS bioreactors than polypropylene-alone support (PPS) control. S. cerevisiae produced 30 g L-1 ethanol on PCS with ammonium sulfate medium in repeated batch fermentation, whereas PPS-control produced 5 g L-1 ethanol. Overall, increased productivity in low cost medium can be achieved beyond conventional fermentations using this novel bioreactor design.

Membrane bioreactor for waste gas treatment.

Abstract: Summary This thesis describes the design and testing of a membrane bioreactor (MBR) for removal of organic pollutants from air. In such a bioreactor for biological gas treatment pollutants are degraded by micro-organisms. The membrane bioreactor is an alternative to other types of bioreactors for waste gas treatment, such as compost biofilters and bioscrubbers. Propene was used as a model pollutant to study the membrane bioreactor. A membrane bioreactor for waste gas treatment consists of a gas and a liquid compartment, separated by a membrane. Gaseous pollutants diffuse through the membrane and are consumed by microorganisms present in the liquid phase. The organisms are supplied with water and inorganic nutrients via this liquid phase. Various membrane bioreactors described in the literature are reviewed in Chapter 2. In the work presented in this thesis, microporous hydrophobic material was selected because of its low mass transfer resistance and the availability of both sheets and fibres. For the removal of propene from air the mass transfer resistance of this type of membrane was found to be negligible (Chapter 3). The propene-degrading bacterium Xanthobacter Py2 was shown to form biofilms in membrane bioreactors. Continuous propene removal by biofilms of Xanthobacter Py2 was demonstrated in both flat sheet reactors and hollow-fibre reactors. In both configurations the biofilms are situated on the membrane in the liquid phase. Propene consumption rates could be described quite accurately with the computer programme BIOSIM, that describes simultaneous diffusion and reaction in a biolayer (Chapter 3). During continuous operation of hollow-fibre reactors at inlet concentrations of 0.5 to 6 gram propene per m 3, the propene conversion decreased after several weeks (Chapter 4). Clogging of the fibres by excess biomass formation and acidification due to ammonium oxidation, were identified as possible causes. However, when both clogging and ammonium oxidation were prevented, the propene conversion still decreased in time. Apparently other factors than clogging and nitrification affect the long-term performance of biofilms of Xanthobacter Py2, growing In an MBR. These factors might be Identified with new methods for biofilm analysis, which allow the localization of activity within the biofilm. According to the Dutch emission standards, hydrocarbons such as propene, in offgas have to be reduced to less than 150 mg m -3. In Chapter 5, two propenedegrading strains were compared for their ability to degrade such low concentrations of propene and the faster growing strain, Xanthobacter Py2, was selected. At a concentration of 300 to 600 mg m -3in the gas phase, a 20 days startup period was required for biofilm formation. Once the biofilm had been established, the amount of active biomass adapted to the amount of propene available Within several days. Propene could be removed continuously from air at a concentration of 15 to 50 mg m -3in the gas phase without supplying other organic nutrients to the microbial population (Chapter 5). Besides the removal of poorly water soluble pollutants like propene, the membrane bioreactor is also suitable for the removal of pollutants that result in acidification, such as chlorinated hydrocarbons. Therefore, in Chapter 6 the biodegradation of trichloroethene (TCE) by Xanthobacter Py2 was tested during growth on propene in a stirred vessel. The aerobic biodegradation of TCE is difficult because of toxic intermediates that are formed. With Xanthobacter Py2 continuous cometabolic degradation of TCE was shown to be feasible with concentrations up to 206 μM in the liquid phase. The amount of TCE that could be degraded, depended on the TCE concentration and ranged from 0.03 to 0.34 grams of TCE per gram of biomass. Membrane bioreactors for gas-liquid contact have several potential applications. They are suitable for the removal of poorly soluble pollutants from air because of their large gas-liquid interface and small mass transfer resistance. Especially if biodegradation of a poorly soluble pollutant results in acidification, the membrane bioreactor might be a unique tool, since the acidic product can be removed via the liquid phase. Other applications might be the removal of highly chlorinated hydrocarbons from air by an aerobic or a combined anaerobic/aerobic: process, as was recently suggested in literature. Membrane bioreactors may also be useful tools in biofilm research, because of easy handling and processing of biofilm samples, excellent oxygen transfer properties and the possibility to apply counter gradients.

Temperature effects on physiology of biological phosphorus removal

Abstract: Phosphorus-removing sludge was enriched in an anaerobic-aerobic, acetate-fed, sequencing batch reactor at 20°C. Conversion of relevant compounds for biological phosphorus removal was studied at 5, 10, 20, and 30°C in separate batch tests. The stoichiometry of the anaerobic processes was insensitive to temperature changes. Some effect on aerobic stoichiometry was observed. In contrast, temperature had a strong influence on the kinetics of the processes under anaerobic as well as aerobic conditions. The anaerobic phosphorus-release (or acetate-uptake) rate showed a maximum at 20°C. However, a continuous increase was observed in the interval 5–30°C for the conversion rates under aerobic conditions. Based on these experiments, temperature coefficients for the different reactions were calculated. An overall anaerobic and aerobic temperature coefficient θ was found to be 1.078 (valid in the range 5°C

Bioremediation of pentachlorophenol-contaminated soil by bioaugmentation using activated soil

Abstract: The use of an indigenous microbial consortium, pollutant-acclimated and attached to soil particles (activated soil), was studied as a bioaugmentation method for the aerobic biodegradation of pentachlorophenol (PCP) in a contaminated soil. A 125-l completely mixed soil slurry (10% soil) bioreactor was used to produce the activated soil biomass. Results showed that the bioreactor was very effective in producing a PCP-acclimated biomass. Within 30 days, PCP-degrading bacteria increased from 105 cfu/g to 108 cfu/g soil. Mineralization of the PCP added to the reactor was demonstrated by chloride accumulation in solution. The soil-attached consortium produced in the reactor was inhibited by PCP concentrations exceeding 250 mg/l. This high level of tolerance was attributed to the beneficial effect of the soil particles. Once produced, the activated soil biomass remained active for 5 weeks at 20 °C and for up to 3 months when kept at 4 °C. The activated attached soil biomass produced in the completely mixed soil slurry bioreactor, as well as a PCP-acclimated flocculent biomass obtained from an air-lift immobilized-soil bioreactor, were used to stimulate the bioremediation of a PCP-impacted sandy soil, which had no indigenous PCP-degrading microorganisms. Bioaugmentation of this soil by the acclimated biomass resulted in a 99% reduction (from 400 mg/kg to 5 mg/kg in 130 days) in PCP concentration. The PCP degradation rates obtained with the activated soil biomass, produced either as a biomass attached to soil particles or as a flocculent biomass, were similar.

Toluene degradation kinetics for planktonic and biofilm-grown cells of Pseudomonas putida 54G.

Abstract: Toluene degradation kinetics by biofilm and planktonic cells of Pseudomonas putida 54G were compared in this study. Batch degradation of (14)C toluene was used to evaluate kinetic parameters for planktonic cells. The kinetic parameters determined for toluene degradation were: specific growth rate, micro(max) = 10.08 +/- 1.2/day; half-saturation constant, K(S) = 3.98 +/- 1.28 mg/L; substrate inhibition constant, K(I) = 42.78 +/- 3.87 mg/L. Biofilm cells, grown on ceramic rings in vapor phase bioreactors, were removed and suspended in batch cultures to calculate (14)C toluene degradation rates. Specific activities measured for planktonic and biofilm cells were similar based on toluene degrading cells and total biomass. Long-term toluene exposure reduced specific activities that were based on total biomass for both biofilm and planktonic cells. These results suggest that long-term toluene exposure caused a large portion of the biomass to become inactive, even though the biofilm was not substrate limited. Conversely, specific activities based on numbers of toluene-culturable cells were comparable for both biofilm and planktonically grown cultures. Planktonic cell kinetics are often used in bioreactor models to model substrate degradation and growth of bacteria in biofilms, a procedure we found to be appropriate for this organism. For superior bioreactor design, however, changes in cellular activity that occur during biofilm development should be investigated under conditions relevant to reactor operation before predictive models for bioreactor systems are developed.

Characterization and optimization of a two-phase partitioning bioreactor for the biodegradation of phenol

Abstract: A two-phase partitioning bioreactor containing Pseudomonas putida ATCC 11172 was used to degrade high concentrations of phenol in batch and fed-batch mode. The 2-l (nominal volume) partitioning bioreactor employs a 1-l cell-containing aqueous phase, and a 500-ml immiscible and biocompatible second organic phase (2-undecanone), which partitions the toxic substrate into the aqueous phase at a rate based on the metabolic activity of the microorganisms. Using this reactor configuration, operated in batch mode, 10-g phenol was degraded to completion within 84-h. The system was, however, oxygen-limited during the rapid growth phase of the fermentation. A second experiment, using enriched air to prevent oxygen limitation, resulted in the complete degradation of 10-g phenol within 72-h. The use of a sequential feeding strategy, in which a 10-g phenol load was added in sequential 5-g aliquots, resulted in a significant reduction in the lag phase, from 36-h to 12-h, and the consumption of 10-g phenol in 60 h. Finally, fed-batch fermentation was used to attempt to determine the ultimate capacity of the system to degrade phenol. The organic phase was loaded with 10-g phenol, the microorganisms were allowed to consume this aliquot almost to completion, and a second 10-g aliquot was then added. The organic phase was spiked in this manner a total of four times, resulting in the degradation of 46.55-g phenol within 12 days. The system was also monitored for nutrient depletion, and a nutrient-feeding schedule was formulated, in response to the mass of phenol consumed.

Improvement of the anaerobic biodegradation of olive mill wastewaters by prior ozonation pretreatment

Abstract: The purification of olive mill wastewaters (OMW) is investigated by a single anaerobic digestion in a batch reactor containing immobilized microorganisms, and by the combination of an ozonation pretreatment followed by an anaerobic digestion. In the single anaerobic digestion the removal of the COD is determined and the methane yield coefficient, which is the best measure of the extent of transformation of the biodegradable substrate, is also obtained, its value being 194 ml CH4/g COD. A kinetic study is performed by using the Monod model combined with the Levenspiel model, due to the presence of inhibition effects. Both models lead to the determination of the kinetic parameters of this anaerobic treatment: kinetic constants, critical substrate concentration of inhibition and inhibitory parameter. In the combined process, the ozonation pretreatment of OMW achieves a great reduction in the phenolic compounds, leading to a significant increase in the methane yield coefficient in the following anaerobic digestion, its value being 266 ml CH4/g COD.

Biological Treatment of Saline Wastewater by Fed‐Batch Operation

Abstract: The adverse effects of salt on biological treatment of saline wastewater inoculated by activated sludge culture were investigated. A synthetic wastewater composed of diluted molasses, urea, KH2PO4 and various concentrations of salt (1–5% w/v NaCl) was treated in an aerobic-biological reactor operating in fed-batch mode. An activated sludge culture obtained from a wastewater treatment plant was used as the seed. Variations of chemical oxygen demand (COD) removal rate and efficiency with salt concentration were determined. A rate expression including salt inhibition effect was proposed and kinetic constants were determined by using the experimental data. © 1997 SCI.

Tower reactors for bioconversion of lignocellulosic material

Abstract: An apparatus for enzymatic hydrolysis and fermentation of pretreated lignocellulosic material, in the form of a tower bioreactor, having mixers to achieve intermittent mixing of the material. Precise mixing of the material is important for effective heat and mass transfer requirements without damaging or denaturing the enzymes or fermenting microorganisms. The pretreated material, generally in the form of a slurry, is pumped through the bioreactor, either upwards or downwards, and is mixed periodically as it passes through the mixing zones where the mixers are located. For a thin slurry, alternate mixing can be achieved by a pumping loop which also serves as a heat transfer device. Additional heat transfer takes place through the reactor heat transfer jackets.

Membrane Bioreactor for Control of Volatile Organic Compound Emissions

Abstract: A membrane bioreactor system that overcomes many of the limitations of conventional compost biofilters is described. The system utilizes microporous hydrophobic hollow fiber membranes for mass transfer of volatile organic compounds (VOCs) from the gas phase to a microbially active liquid phase. The reactor design provides a high biomass concentration, a method for wasting biomass, and a method for addition of pH buffers, nutrients, cometabolites, and/or other amendments. A theoretical model is developed, describing mass transfer and biodegradation in the membrane bioreactor. Reactor performance was determined in a laboratory scale membrane bioreactor over a range of gas loading rates using toluene as a model VOC. Toluene removal efficiency was greater than 98% at an inlet concentration of 100 ppm\dv and a gas residence time of less than 2 s. Factors controlling bioreactor performance were determined through both experiments and theoretical modeling to include: compound Henry’s law constant, membrane specific surface area, gas and VOC loading rates, liquid phase turbulence, and biomass substrate utilization rate.

Two-phase anaerobic digestion of three different dairy effluents using a hybrid bioreactor

Abstract: The South African dairy industry is a major water user and as a result has to reconsider current effluent treatment and disposal methods The effluents from three dairy factories (cheese, fresh milk and milk powder/butter factories) were analysed and the chemical oxygen demand (COD), pH and effluent volumes were found to be highly variable over short time intervals during the daily production cycles The pH was found to vary between 22 and 118 units and the COD values ranged from 800 to 15 000 mgt 1 over a period of 2 h The average COD of the effluents emerging from the three factories varied between 1 908 and 5 340 mgt 1 Significant differences were also found in the composition of the effluents from the three factories In this study, a mesophilic laboratory-scale hybrid bioreactor was used in conjunction with a pre-acidification step to treat the three dairy factory effluents It was clear from the data obtained on the cheese, fresh milk and milk powder/butter waste waters that dairy effluents are suitable for treatment by means of the anaerobic digestion process and the use of a hybrid anaerobic bioreactor can be seen as a viable treatment option The COD values of the three pre-digested dairy waste waters were reduced by between 91 and 97% at organic loading rates of between 097 and 282 kgCODm 3 d -1 and subsequent methane yields varied from 0287 to 0359 m 3 CH 4 kg -1 COD removed (73 and 91% of the theoretical maximum yield) during anaerobic digestion The pH values of all the digester effluents were >75 units The data clearly indicated that anaerobic treatment of the different dairy effluents was successful and that this particular type of bioreactor would be suitable for the anaerobic treatment of dairy effluents An important consequence of the data from this study is that a two-phase set-up will be required to protect the methanogens in the bioreactor from prohibitively low pH values and high VFA concentrations produced during the acidogenic phase The two-phase system will allow pH control in the acidogenic phase should it be needed in a full-scale or pilot-scale treatment plant