Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 1. Experimental results

The influence of the organic loading rate on the performance of an innovative reactor, the periodic anaerobic baffled reactor (PABR) was examined. A laboratory-scale PABR of four compartments being fed with a glucose based synthetic medium performed with high stability while the feed organic load was doubled from 12.5 to 25 and then to 50 gCOD/l. Finally the feed concentration was increased to 75 gCOD/l. The successive step changes in the feed concentration lasted for 20, 15, and 7 d, respectively. The COD removal efficiency of the PABR was satisfactory in the first two transitions (approximately 97.5 and 96%). In the third transition (OLR=18.75 gCOD/l/d) the reactor failed as the pH dropped to 4. The concentrations of butyric and valeric acids increased as the organic loading was increased and eventually they became greater than the concentration of acetic and propionic acids.     

Performance of a glucose fed periodic anaerobic baffled reactor under increasing organic loading conditions: 2. Model prediction

A model was developed for the anaerobic digestion of a glucose-based medium in an innovative high-rate reactor, the periodic anaerobic baffled reactor (PABR). The model considers each PABR compartment as two variable volume interacting sections, of constant total volume, one with high solids and one with low solids concentration, with the gas and liquid flows influencing the material flows between the two sections. For the simulation of glucose degradation, the biomass was divided into acidogenic, acetogenic and methanogenic groups of microorganisms. The kinetic part of the model accounted for possible inhibition of acidogenesis, acetogenesis and methanogenesis by volatile fatty acids. The model succeeded in predicting the reactor performance upon step increases in the organic loading rate.     

Design and operation of pulsed anaerobic digesters

The development of a pulse-driven loop reactor (PDLR), a pulsed anaerobic filter (PAF) and a pulsed anaerobic baffled reactor (PABR) is described. In an anaerobic PDLR internal circulation is achieved by a specially designed pulse-nozzle. In a PAF and PABR an oscillation is superimposed onto the liquid content of the fermenters by means of a pulse pump without any moving devices in the reactors. Pulsed digesters faciliate degassing, avoid reactor clogging as well as short-circuiting and allow a variety of packed-bed to fluidized-bed operations. Anaerobic fermentation of acetic acid and distillery slops in pulsed digesters on a laboratory scale shows that hydrodynamic stress caused by pulsation is well compatible to degrading bacteria.List of Symbols PAF Pulsed Anaerobic Filter - PDLR Pulse-Driven Loop Reactor - PABR Pulsed Anaerobic Baffled Reactor     

Performance of a periodic anaerobic baffled reactor fed on Chinese traditional medicine industrial wastewater

A four-compartment periodic anaerobic baffled reactor (PABR) was run in a 'clockwise sequential' switching manner continuously fed on chinese traditional medicine industrial wastewater under an alkalinity concentration between 1000 and 1500 mg CaCO(3)/L of the feed with average organic load rate (OLR) at about 1, 2, 4 and 6 kg COD/(m(3)d) for 12, 24, 24 and 6d, respectively. Hydraulic residence time was 2d, while switching period was 4d. As the average OLR increased to 6 kg COD/(m(3)d), the time of the sharp fall in pH, chemical oxygen demand (COD) removal, gas production and methane percentage of the biogas of all the compartments and the time of rapid volatile fatty acids accumulation in effluent coincided, hence the PABR became sour. Denaturing gradient gel electrophoresis (DGGE) community fingerprints and their cluster analysis revealed that community structures of each compartment tended to be more closely related if the PABR was not overloaded.     

Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by co-immobilization of anaerobic and aerobic microbial communities in an upflow reactor under air-limited conditions

The co-immobilization and the culture of anaerobic and aerobic communities was tested for the mineralization of 2,4,6-trichlorophenol (2,4,6-TCP). At first, the anaerobic microorganisms (aggregated into granules) were cultivated in an upflow anaerobic sludge blanket (UASB) reactor, in a continuous mode, with glucose, propionate, acetate (COD loading rate = 0.5-2.0 g COD/l per day, ratio 1:1:1) and 2,4,6-TCP (2,4,6-TCP loading rate = 25-278 micromol/l per day) as substrates. 2,4,6-TCP was degraded into 2,4-DCP and 4-CP, but it was not mineralized because of the low degradation rates of 4-CP. Furthermore, the highest loading rates of 2,4,6-TCP (>126 micromol/l per day) caused the inhibition of the strains degrading the propionate. The granules were therefore tested in association with the aerobic community. They were immobilized in kappa-carrageenan/gelatin [2% (w/w) of each polymer] gel beads and cultivated in a reactor, on their own (to test the influence of the gel), and then with the aerobic community, under anaerobic and air-limited conditions, respectively. The results showed that (1) the gel did not influence the activity of the granules, (2) the anaerobic and aerobic communities could be easily co-immobilized in gel beads and cultivated in a reactor, (3) the mineralization of 2,4,6-TCP (2,4,6-TCP loading rate = 10-506 micromol/l per day), its intermediates of degradation and the other substrates [glucose + acetate + propionate (ratio 1:1:1) = COD loading rate = 500 mg COD/l per day] could be obtained under air-limited conditions if the culture parameters were strictly controlled [airflow = 36-48 vvd (volume of air/volume of liquid in the reactor per day), pH value at around 7.5]. Finally, the gel did not retain its structure during the whole culture (263 days) in the air-limited reactor, but the anaerobic and aerobic communities retained their activities and worked together for the mineralization.     

Development of a stable continuous flow immobilized enzyme reactor for the hydrolysis of inulin

A 23.5-fold purified exoinulinase with a specific activity of 413 IU/mg and covalently immobilized on Duolite A568 has been used for the development of a continuous flow immobilized enzyme reactor for the hydrolysis of inulin. In a packed bed reactor containing 72 IU of exoinulinase from Kluyveromyces marxianus YS-1, inulin solution (5%, pH 5.5) with a flow rate of 4 mL/h was completely hydrolyzed at 55 degrees C. The reactor was run continuously for 75 days and its experimental half-life was 72 days under the optimized operational conditions. The volumetric productivity and fructose yield of the reactor were 44.5 g reducing sugars/L/h and 53.3 g/L, respectively. The hydrolyzed product was a mixture of fructose (95.8%) and glucose (4.2%) having an average fructose/glucose ratio of 24. An attempt has also been made to substitute pure inulin with raw Asparagus racemosus inulin to determine the operational stability of the developed reactor. The system remained operational only for 11 days, where 85.9% hydrolysis of raw inulin was achieved.     

Development of a predictive description of an immobilized-cell, three-phase, fluidized-bed bioreactor

A Large bioreactor is an inhomogenous system with concentration gradients which depend on the fluid dynamics and the mass transfer of the reactor, the feeding strategy, the saturation constant, and the cell density. The responses of Escherichia coli cells to short-term oscillations of the carbon/energy substrate in glucose limited fed-batch cultivations were studied in a two-compartment reactor system consisting of a stirred tank reactor (STR) and an aerated plug flow reactor (PFR) as a recycle loop. Short-term glucose excess or starvation in the PFR was simulated by feeding of glucose to the PFR or to the STR alternatively. The cellular response to repeated short-term glucose excess was a transient increase of glucose consumption and acetate formation. But, there was no accumulation of acetate in the culture, because it was consumed in the STR part where the glucose concentration was growth limiting. However, acetate accumulated during the cultivation if the oxygen supply in the PFR was insufficient, causing higher acetate formation. The biomass yield was then negatively influenced, which was also the case if the PFR was used to simulate a glucose starvation zone. The results suggest that short-term heterogeneities influence the cellular physiology and growth, and can be of major importance for the process performance. (c) 1995 John Wiley & Sons, Inc.     

Simulation of a cross-flow shrinking-bed reactor for the hydrolysis of lignocellulosics.

An idealized model is developed for the case in which biomass slurry is conveyed through an annulus, with water or steam entering through an inner porous wall and liquid product leaving through an outer porous wall. It is assumed that the ratio of occluded liquid to solid in the slurry is a constant, Rws, and that non-occluded water is immediately removed from the reactor. The goal of > 90% sugar yield with > 10% sugar in the product is almost reached (88% glucose yield, 91% xylose yield, 47 g/l glucose and 45 g/l xylose) at 240 degrees C, 1% acid. Rws = 1 and a radial wash water flow of three times the initial mass flow of solids to the reactor per meter of reactor length per g/l of sugar concentration in the occluded water. If Rws is limited to 3, the yield falls to 85% and the total sugar concentration to 61 g/l. Even without cross-flow wash, the yields can be increased by about 16 percentage points, compared to plug flow, by extracting excess liquid through the outer wall as it is formed. At 200 degrees C, where one might prefer to operate for ease of control and concern about the possibility of making fermentation inhibitors at higher temperatures, the maximum glucose yield in a plug-flow reactor is low (12-13%) whereas in a cross-flow reactor, at a high cross-flow wash rate, it can still be quite high (60-83%) but at a very low concentration (0.57-1.47%). In these simulations it is assumed that one-half of the inerts is solubilized. The formation of oligomers is neglected.     

Acidogenic fermentation of protein/carbohydrate mixtures by bacterial populations adapted to one of the substrates in anaerobic chemostat cultures

Summary The influence of the adaptation procedure on the simultaneous fermentation of glucose and gelatin by putatively carbon-limited mixed anaerobic bacterial populations was investigated. In one series of experiments glucose, dissolved in a mineral salts solution, was fed to mixed populations of bacteria in anaerobic carbon-limited chemostat cultures maintained at different pH values and at 30°C. When, after reaching a steady state, the carbon substrate was switched to gelatin, growth ceased. However, when gelatin was added to the medium as a second carbon substrate, it was found in all cases that hydrolysis and fermentation of the protein proceeded to a limited extent (<30%) and that glucose continued to be completely metabolized. In a second series of experiments, bacterial populations were adapted to gelatin under comparable experimental conditions. After reaching a steady state, glucose was added to the medium as a second carbon substrate. Following establishment of the new steady state it was found that hydrolysis of gelatin was not inhibited but its fermentation was. It is concluded that anaerobic bacterial populations can loose their ability to degrade a protein substrate, depending on the adaptation procedure.     

The effect of vinyl acetate in acetoclastic methanogenesis

The influence of vinyl acetate (VA) in the methanogenesis was evaluated, by using an upflow anaerobic sludge blanket reactor of 1.5L. The reactor was operated at 33.5 g/L volatile suspended solids to 30±2 °C, a hydraulic residence time of 1 day, an organic loading rate of 1 kgCOD/m3/d of two different mixtures of VA and glucose. The VA was methanized to 81% when its proportion was of 10% into reactor loading rate, when VA proportion increased to 25%, the methane production rate decreased to 62% and the acetate production rate increased almost 8 times. These results indicated that VA was only hydrolyzed and glucose was not used as a co-substrate. The effect of glucose on VA methanogenic degradation was evaluated through batch reactors of 60 mL, concluding that the glucose supported the methanogenesis without favoring the VA elimination. On the other hand, the results of the sludge from the reactor in the presence of VA demonstrated that VA caused an irreversibly inhibition of acetoclastic methanogenesis when the anaerobic sludge was exposed to this compound.     

Scale down of recombinant protein production: a comparative study of scaling performance

A large bioreactor is heterogeneous with respect to concentration gradients of substrates fed to the reactor such as oxygen and growth limiting carbon source. Gradient formation will highly depend on the fluid dynamics and mass transfer capacity of the reactor, especially in the area in which the substrate is added. In this study, some production-scale (12 m³ bioreactor) conditions of a recombinant Escherichia coli process were imitated on a laboratory scale. From the large-scale cultivations, it was shown that locally high concentration of the limiting substrate fed to the process, in this case glucose, existed at the level of the feedpoint. The large-scale process was scaled down from: (i) mixing time experiments performed in the large-scale bioreactor in order to identify and describe the oscillating environment and (ii) identification of two distinct glucose concentration zones in the reactor. An important parameter obtained from mixing time experiments was the residence time in the feed zone of about 10 seconds. The size of the feed zone was estimated to 10%. Based on these observations the scale-down reactor with two compartments was designed. It was composed of one stirred tank reactor and an aerated plug flow reactor, in which the effect of oscillating glucose concentration on biomass yield and acetate formation was studied. Results from these experiments indicated that the lower biomass yield and higher acetate formation obtained on a large scale compared to homogeneous small-scale cultivations were not directly caused by the cell response to the glucose oscillation. This was concluded since no acetate was accumulated during scale-down experiments. An explanation for the differences in results between the two reactor scales may be a secondary effect of high glucose concentration resulting in an increased glucose metabolism causing an oxygen consumption rate locally exceeding the transfer rate. The results from pulse response experiments and glucose concentration measurements, at different locations in the reactor, showed a great consistency for the two feeding/pulse positions used in the large-scale bioreactor. Furthermore, measured periodicity from mixing data agrees well with expected circulation times for each impeller volume. Conclusions are drawn concerning the design of the scale-down reactor.     

Fed-batch culture of Bacillus thuringiensis for thuringiensin production in a tower type bioreactor

Fed-batch culture of Bacillus thuringiensis in a modified airlift reactor has been developed by using adaptive control of glucose concentration in the reactor. The glucose concentration was estimated via a correlation equation between carbon dioxide production rate and glucose consumption rate. The estimated glucose concentration as the output variable was fed back to computer for calculation of substrate addition. The modified reactor was an airlift reactor with a net draft tube. The airlift reactor had high oxygen transfer rate and low shear stress which were important factors for production of thuringiensin. Fed-batch culture of Bacillus thuringiensis in the modified airlift reactor provided significant improvement of thuringiensin production. (c) 1995 John Wiley & Sons, Inc.     

Influence of a supplemental carbon source on anaerobic dechlorination of pentachlorophenol in granular sludge.

Anaerobic dechlorination of pentachlorophenol (PCP) was studied in two upflow anaerobic sludge blanket reactors. One reactor received glucose (0.9 g liter-1) as an additional carbon source; the other one served as a control. The concentration of PCP in the medium was 4.5 and 3.0 mg liter-1 in the experimental and control reactors, respectively. The reactors were inoculated with granular sludge previously grown on sugar-containing wastewater. After 10 months of continuous operation, the removal of PCP was 99% in the glucose-amended reactor, whereas the removal in the control reactor varied between 32 and 77%. Furthermore, 94% of the PCP was completely dechlorinated in the glucose reactor compared with a maximum of 20% in the control reactor. In the same period, the amount of biomass in the glucose reactor had increased by approximately 150% compared with that in the control reactor, where no growth of the sludge bed occurred. Batch culture activity tests showed that the addition of glucose had a stimulatory effect on the dechlorination rate of PCP per gram of volatile solids. This indicated that the better performance of the glucose-amended reactor was due to a higher concentration of biomass and a direct stimulatory effect of glucose on the dechlorination rate. The pattern of dechlorination of PCP showed that an initial para cleavage was followed by two ortho cleavages.     

Influence of a supplemental carbon source on anaerobic dechlorination of pentachlorophenol in granular sludge.

Anaerobic dechlorination of pentachlorophenol (PCP) was studied in two upflow anaerobic sludge blanket reactors. One reactor received glucose (0.9 g liter-1) as an additional carbon source; the other one served as a control. The concentration of PCP in the medium was 4.5 and 3.0 mg liter-1 in the experimental and control reactors, respectively. The reactors were inoculated with granular sludge previously grown on sugar-containing wastewater. After 10 months of continuous operation, the removal of PCP was 99% in the glucose-amended reactor, whereas the removal in the control reactor varied between 32 and 77%. Furthermore, 94% of the PCP was completely dechlorinated in the glucose reactor compared with a maximum of 20% in the control reactor. In the same period, the amount of biomass in the glucose reactor had increased by approximately 150% compared with that in the control reactor, where no growth of the sludge bed occurred. Batch culture activity tests showed that the addition of glucose had a stimulatory effect on the dechlorination rate of PCP per gram of volatile solids. This indicated that the better performance of the glucose-amended reactor was due to a higher concentration of biomass and a direct stimulatory effect of glucose on the dechlorination rate. The pattern of dechlorination of PCP showed that an initial para cleavage was followed by two ortho cleavages.     

Stimulation of citric acid production in Aspergillus niger by addition of viscous substances in shake culture

When glucose (120mg/ml) was used as a carbon source, Aspergillus niger Yang no. 2. showed a markedly low citric acid productivity in shake culture (15.4 mg/ml) but a high productivity in semi-solid and surface cultures (72.3 mg/ml and 67.6 mg/ml, respectively). Since the viscosity of the medium was assumed to be one of the important factors for citric acid productivity in shake culture, the effects of the addition of viscous substances on citric acid productivity of strain Yang no. 2 were examined. The addition of 2.0–6.0 mg gelatin/ml as a viscous additive to the medium containing glucose as a carbon source increased slightly the medium viscosity but substantially increased the citric acid productivity in shake culture to levels of 52.0–53.3 mg/ml, about 3.4 times as much as that without gelatin. However, no influence of gelatin addition was observed in semi-solid and surface cultures, i.e. under static cultivation conditions. Different mycelial morphologies of the strain were observed when cultivations were done in shake culture with or without the addition of gelatin. Addition of 5.0 mg agar/ml, 5.0 mg carageenan/ml, 2.5 mg carboxymethylcellulose/ml and 2.5 mg polyethylene glycol 6000/ml, to the medium containing glucose as a carbon source also increased the citric acid productivity in shake culture to levels of 39.2–54.7 mg/ml. Since Yang no. 2 does not utilize these viscous substances, these results suggested that the viscous substances functioned as protectants for the mycelium from physiological stresses due to shaking and as a consequence resulted in a remarkably increased citric acid productivity in shake culture.     

Evaluation of anchorage-dependent cell propagation systems for production of human acetylcholinesterase by recombinant 293 cells

Production of recombinant human acetylcholinesterase (AChE) by a high producer human embryonic kidney cell line (293) was evaluated by three main cell propagation systems; surface propagator, fixed-bed reactor and stirred microcarrier cultures. The recombinant cell line expresses AChE levels as high as 10–20 mg/l/day. System productivities in either the surface propagator (multitray system), or in the fixed-bed reactor (polyurethane macroporous sponges) were 4–8 mg AChE/l/day during a production period of 8 days. Similar productive rates, yet longer production periods (up to 22 days), were obtained in microcarrier (MC) cultures using either polystyrene beads (Biosilon); collagen-coated dextran beads (Cytodex-3); or gelatin macroporous beads (Cultispher-G). Best results were obtained in an aggregate cculture using cellulose beads charged with diethylaminoethyl (DEAE) groups, (Servacel), as carriers. In this culture, a system productivity of 6–10 mg/l/day was maintained for 28 days.     

Glucose reactions within the heating period and the effect of heating rate on the reactions in hot compressed water

Glucose reactions were conducted in hot compressed water (473-773 K, 4-40 MPa) by means of a batch-type reactor. The reactions in the heating period (about for 60s) were observed. More than 80% of the glucose was consumed in the heating period above 573 K. Gasification of glucose was promoted with increasing temperature. The effect of heating rate (from 4.2 to 15.8K/s) on glucose conversion was also examined, and gasification of glucose was enhanced with increasing the heating rate.     

Beta-galactosidase monitoring by a biosensor based on Clark electrode: its optimization, characterization and application

beta-Galactosidase is an hydrolase enzyme that catalyzes the hydrolysis of beta-galactosides into monosaccharides. Substrates of different beta-galactosidases include ganglioside GM1, lactosylceramides, lactose, and various glycoproteins. A novel aspect of the activity determination of beta-galactosidase was presented. A glucose oxidase biosensor based on Clark electrode was utilized in order to monitor beta-galactosidase. Immobilization of glucose oxidase was made by gelatin and glutaraldehyde as cross-linker. Several parameters such as glucose oxidase activity, gelatin amount, and glutaraldehyde percentage for cross-linking were optimized. The most important parameter, lactose concentration in working buffer was studied in detail. Optimum temperature, thermal stability, optimum pH, buffer system and its concentration effect on the biosensor system, repeatability, reproducibility, and storage and operational stabilities of the biosensor were identified. A linear detection range for beta-galactosidase was observed between 9.4 x 10(-5) and 3.2 x 10(-2)U/ml. Finally, beta-galactosidase activity in artificial intestinal juice was investigated by the biosensor and the results obtained were compared with a reference spectrophotometric method.     

Anaerobic treatment of a chemical synthesis-based pharmaceutical wastewater in a hybrid upflow anaerobic sludge blanket reactor

In this study, performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor, treating a chemical synthesis-based pharmaceutical wastewater, was evaluated under different operating conditions. This study consisted of two experimental stages: first, acclimation to the pharmaceutical wastewater and second, determination of maximum loading capacity of the hybrid UASB reactor. Initially, the carbon source in the reactor feed came entirely from glucose, applied at an organic loading rate (OLR) 1 kg COD/m(3) d. The OLR was gradually step increased to 3 kg COD/m(3) d at which point the feed to the hybrid UASB reactor was progressively modified by introducing the pharmaceutical wastewater in blends with glucose, so that the wastewater contributed approximately 10%, 30%, 70%, and ultimately, 100% of the carbon (COD) to be treated. At the acclimation OLR of 3 kg COD/m(3) d the hydraulic retention time (HRT) was 2 days. During this period of feed modification, the COD removal efficiencies of the anaerobic reactor were 99%, 96%, 91% and 85%, and specific methanogenic activities (SMA) were measured as 240, 230, 205 and 231 ml CH(4)/g TVS d, respectively. Following the acclimation period, the hybrid UASB reactor was fed with 100% (w/v) pharmaceutical wastewater up to an OLR of 9 kg COD/m(3) d in order to determine the maximum loading capacity achievable before reactor failure. At this OLR, the COD removal efficiency was 28%, and the SMA was measured as 170 ml CH(4)/g TVS d. The hybrid UASB reactor was found to be far more effective at an OLR of 8 kg COD/m(3) d with a COD removal efficiency of 72%. At this point, SMA value was 200 ml CH(4)/g TVS d. It was concluded that the hybrid UASB reactor could be a suitable alternative for the treatment of chemical synthesis-based pharmaceutical wastewater.     

Enzymatic hydrolysis of gelatin layers on used lith film using thermostable alkaline protease for recovery of silver and PET film

To develop a new efficient and potential industrial enzymatic process for the recovery of silver and poly(ethylene terephthalate) (PET) from used lith film for printing, which has not been recycled at all, enzymatic hydrolysis of gelatin layers on lith film was investigated using the thermostabilized mutant enzyme of the alkaline protease from alkaliphilic Bacillus sp. B21-2. The rate of gelatin hydrolysis of lith film in a stirred-tank reactor increased with the temperature and enzyme concentration. The time required to complete the hydrolysis of gelatin on lith film was longer than that on X-ray film because of the tightly cross-linked structure of the gelatin layers of lith film. The time required to complete the hydrolysis by using the mutant enzyme was less than that using the wild-type enzyme. The gelatin hydrolysis of lith film was well explained by a model that took into consideration a number of physical processes in addition to the chemical process.