A continuous reactor system for production of lactulose

A continuous reactor process was developed to produce lactulose from lactose. A system of two CSTRs in series with a tubular finishing reactor gave conversion to lactulose of about 76%. The reactors ran at 71–75°C with a volumetric hold-up in the CSTRs of 22·7 dm³ and in the tubular reactor of 2·6 dm³. Each CSTR had a nominal residence time of 44 min. The flow rate was 0·53 dm³ min^?1.     

Effect of aeration and pH on gramicidin S production by Bacillus brevis

Although the biosynthesis of the antibiotic gramicidin S (GS) by Bacillus brevis ATCC 9999 has been studied extensively, almost no attention has been given to environmental control of its fermentation process. In this respect, GS fermentations conducted in a 7.5 dm³ fermentor in complex (YP) medium revealed that a high aeration rate resulted in a high biomass yield (12 g DCW dm^?3) with very low GS levels (170 mg GS dm^?3). Lowering the aeration rate (5 dm³ air min^?1 at 300 rev min^?1) caused a dramatic increase in GS formation (2100 mg GS dm^?3) and comparable but slower biomass formation. In chemically-defined (F3/6) medium fermentations, an aeration rate of 5 dm³ air min^?1 at 300 rev min^?1 was apparently too high as only 0.104 mg GS mg^?1 DCW was produced. A much lower aeration rate (2 dm³ air min^?1 at 250 rev min^?1) was needed to arrive at a higher specific antibiotic level: 0.130 mg GS mg^?1 DCW. These data seem compatible with the finding that oxygen is known to inactivate the GS-synthetases. Furthermore, keeping the pH constant at 7.3 under low aeration conditions increased specific GS production up to 0.220 mg GS mg^?1 DCW in YP, as well as in F3/6 fermentations. Both environmental pH and dissolved oxygen tension clearly affect growth pattern, growth extent and GS production in these high yielding media. These data stress the importance of controlling pH and aeration rate during GS fermentations.     

The production of propionic acid from sugars by fermentation through lactic acid as an intermediate

As an alternative to propionic acid production from sugars by species of propionibacteria, propionic acid may be produced from sugars through lactate as an intermediate. Propionibacteria are actually able to utilize lactate as a substrate much more rapidly than glucose. In this study, Lactobacillus xylosus and Propionibacterium shermanii were utilized to convert glucose and xylose to propionate through lactate as an intermediate. Pure culture batch studies were carried out to obtain fermentation parameters for the two cultures. The pure cultures were then combined in a mixed culture series arrangement designed to prevent nutrient limitation. Finally, propionic acid production from lactate was demonstrated in a cross-linked immobilized cell reactor using lactate added to the medium and produced by L. xylosus in a continuous stirred tank reactor. Productivities of 14 g dm^?3 h^?1 at a 9 min residence time (2·1 g dm^?3 propionate) and 2 g dm^?3 h^?1 at a 9·9 h residence time (19·7 g dm^?3 propionate) were obtained without pH control.     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

Oxidation of ethanol vapors in a spiral bioreactor

A fixed film spiral bioreactor containing immobilized activated sludge microorganisms has been used to degrade ethanol vapors. The effect of air flow rate, and ethanol feed concentration on elimination capacity has been investigated. Air flow rate is varied in the range from 2?34 to 40?0 dm³ min^?1. Ethanol feed concentration is varied in the range from 600 to 7000 ppmv. In the concentration range studied, the elimination capacity increased proportionately with an increase in feed concentration. However, the elimination capacity decreased significantly at flow rates greater than 20 dm³ min^?1 owing to insulfficient residence time. The maximum elimination capacity observed was 185 g ethanol h^?1 m^?3 of reactor volume. Critical ethanol loading, defined as the maximum loading to achieve greater than 99% elimination at various residence times have been determined. These data are extremely useful in designing bioreactor for large scale applications.     

Photocatalytic degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO₂ layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0·8–8·0×10⁻⁵ mol dm⁻³) and on the light intensity (0·8–2·7×10⁻⁹ einstein cm⁻² s⁻¹) but independence on the flow rate (2·5–3·6 dm³ min⁻¹) were found. A reaction scheme was proposed following the main identified primary [3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methylurea] and secondary [3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichlorophenylurea] products. © 1998 SCI     

Interaction of transport resistances with biochemical reaction in packed bed solid state fermenters: The effect of gaseous concentration gradients

Mass transfer plays an important role in solid state fermentation (SSF) systems. Earlier work on SSF in tray bioreactors⁷ indicated that steep gaseous concentration gradients developed within the substrate bed, owing to mass transfer resistances, which may adversely affect the bioreactor performance. For all practical purposes these gradients have been eliminated using a packed bed column bioreactor with forced aeration. Gaseous concentrations (oxygen and carbon dioxide) and enzyme activities were measured at various bed heights for various air flow rates during the course of fermentation. The results indicated that concentration gradients were decreased effectively by increasing air flow rate. For example, the actual oxygen and carbon dioxide concentration gradients reduced from 0.07% (v/v) cm^?1 and 0.023% (v/v) cm^?1 to 0.007% (v/v) cm^?1 and 0.0032% (v/v) cm^?1 respectively when the air flow rate was increased from 5 dm³ min^?1 to 25 dm³ min^?1. This resulted in an overall improvement in the performance of the bioreactor in terms of enzyme production.     

Anaerobic biodegradation of phenol in sulfide‐rich media

In the refinery industry, the washing processes of middle‐distillates using caustic solutions generate phenol‐ and sulfide‐containing waste streams. The spent caustic liquors generated contain phenols at concentrations higher than 60 g dm^?3(638.3 mmol dm^?3). For sulfur compounds, the average sulfide concentration was 48 g dm^?3(1500 mmol dm^?3) in these streams. The goal of this study was to evaluate the specific impact of phenol and sulfide concentrations towards the phenol‐biodegradation activity of a phenol‐acclimated anaerobic granular sludge. An inhibition model was used to calculate the phenol and sulfide inhibitory concentrations that completely stopped the phenol‐biodegradation activity (IC100). A maximum phenol‐biodegradation activity of 83 µmol g^?1 VSS h^?1 was assessed and the IC100 values were 21.8 mmol dm^?3 and 13.4 mmol dm^?3 for phenol and sulfide respectively. The limitation of the phenol biodegradation flow by phenol inhibition seemed to be related to the more important sensitivity of phenol‐degrading bacteria. The up‐flow anaerobic sludge bed reactor operating in a non‐phenol‐dependent inhibition condition did not present any sensitivity to sulfide concentrations below 9.6 mmol dm^?3. At this residual concentration, the pH and bisulfide ions' concentration might be responsible for the general collapsing of the reactor activity. Copyright © 2004 Society of Chemical Industry     

Production of L‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor

Production of L ‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor was investigated. Based on the determination of relative enzymatic activity in the immobilized pellets, the optimum pH and temperature for the resolution reaction were 8.0 and 60 °C, respectively. The effects of substrate concentration on the resolution reaction were also investigated and the kinetic constants (K_m and V_m) of immobilized pellets were found to be 7.99 mmol dm^?3 and 1.38 mmol dm^?3 h^?1, respectively. The maximum substrate concentration for the resolution reaction without inhibition was 0.2 mol dm^?3. The L ‐methionine conversion rate reached 94% and 78% when substrate concentrations were 0.2 and 0.4 mol dm^?3, respectively, at a flow rate of 7.5 cm³ h^?1 using the small‐scale packed bed reactor developed. The half‐life of the L ‐aminoacylase in immobilized pellets was 70 days in continuous operation. All the results obtained in this paper exhibit a practical potential of using immobilized pellets of Aspergillus oryzae in the production of L ‐methionine. © 2002 Society of Chemical Industry     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Reclamation of wastewater from a steel-making plant using an airlift submerged biofilm reactor

A bench-scale airlift submerged biofilm reactor was developed to test the possibility of nitrification of the final effluent discharged from a wastewater treatment process of a steel-making plant with an aim of reusing it as irrigation water. Despite the fluctuation of ammonia concentration in the wastewater (55–90 mg NH₃-N dm⁻³), the ammonia was completely converted to nitrate in the hydraulic retention time of 8 h. When decreasing the hydraulic retention time further down to 4 h, the nitrification efficiency decreased to 67·9%. However, the nitrification efficiency could be significantly enhanced by increasing the airflow rate due to an increase in both of the oxygen transfer rate and liquid circulation rate. At the aeration rate of 4 dm³ min⁻¹ and the hydraulic retention time of 4 h, the nitrification efficiency was as high as 92·6% and the nitrification rate was 34·6 mg NH₃-N dm⁻³ bed h⁻¹. © 1998 Society of Chemical Industry     

ENZYME-MEDIATED PRODUCTION OF SUGARS FROM SAGO STARCH: STATISTICAL PROCESS OPTIMIZATION

Glucoamylase (γ-amylase, EC 3.2.1.3) from Aspergillus niger was used to hydrolyze the soluble sago starch to reducing sugars without any major pretreatment of the substrate. A 2 L stirred tank reactor was used for the hydrolysis. The effects of pH, temperature, agitation speed, substrate concentration, and enzyme concentration on the reaction were investigated in order to maximize both the initial reaction velocity v and the final product yield Y_p/s. A response surface methodology central composite design was used for the optimization. A maximum Y_p/s of 0.58 g · g^?1 and a high v of 0.50 mmoles · L^?1 · min^?1 were predicted by the response surface at the identified optimal conditions (61°C, a substrate concentration of 0.1% (w/v, g/100 mL), an enzyme concentration of 0.2 U · mL^?1). The pH and agitation speed did not significantly affect the production of sugars. The subsequent validation experiments under the above-specified optimal conditions confirmed a maximum conversion rate and yield combination of 0.51 ± 0.07 mmoles · L^?1 · min^?1 and 0.60 ± 0.08 g · g^?1.     

Production of optically pure L-alanine by immobilized Pseudomonas sp. BA2 cells

The conditions for immobilizing the new L -aminoacylase-producing bacterial strain, Pseudomonas sp. BA2, by entrapment in κ-carrageenan gel, were investigated. The optimal gel concentration and cell load were determined. The addition of CoCl₂ and N-acetyl-L -alanine to the immobilizing matrix enhanced L -aminoacylase activity. The enzymatic properties of immobilized Pseudomonas sp. BA2 were investigated. Enzyme activity in immobilized cells was optimal at a pH of 6·5 using 0·15 mol dm⁻³ Tris–maleate buffer at 45°C. The presence of 0·7 mmol dm⁻³ CoCl₂ in the enzymatic reaction mixture improved L -aminoacylase activity. The immobilized cell preparation was used for the production of L -alanine from N-acetyl-DL -alanine in a batch reactor. Conversions of 100% were obtained using substrate concentrations ranging from 20 to 200 mmol dm⁻³. The reactor production was 0·74 mol h⁻¹ g cell⁻¹ dm⁻³ which is noticeably higher than that previously reported in the literature. © 1998 Society of Chemical Industry     

The application of reticulated vitreous carbon rotating cylinder electrodes to the removal of cadmium and copper ions from solution

The removal of cadmium and cupric ions from 0.50 mol dm^?3 Na₂SO₄ at pH 2 and 298 K was studied using a reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The cathode was a 100 pores per linear inch porosity grade with a radius of 0.5 cm, a height of 1.2 cm and a volume of 0.94 cm 3 . The cathode was rotated a constant speed of 1500 rev min^?1. A rate enhancement of approximately three times is reported for the removal of cupric ions from a chloride solution (0.05 mol dm^?3 cupric ions in 0.1 mol dm^?3 NaCl at pH 7) when compared with the analogous reaction in acid sulfate solutions (0.50 mol dm^?3 Na₂SO₄ at pH 2). SEM images of the metal deposit morphology allow the morphology of the metal deposits to be characterised. The deposits showed incomplete coverage of the RVC surface and appreciable roughness developed with time due to dendritic growths. Copyright © 2004 Society of Chemical Industry     

Determination of potential methane production capacity of a granular sludge from a pilot‐scale upflow anaerobic sludge blanket reactor using a specific methanogenic activity test

A 450 dm³ pilot‐scale upflow anaerobic sludge blanket (UASB) reactor was used for the treatment of a fermentation‐based pharmaceutical wastewater. The UASB reactor performed well up to an organic loading rate (OLR) of 10.7 kg COD m^?3 d^?1 at which point 94% COD removal efficiency was achieved. This high treatment efficiency did not continue, however and the UASB reactor was then operated at lower OLRs for the remainder of the study. Specific methanogenic activity (SMA) tests were, therefore, carried out to determine the potential loading capacity of the UASB reactor. For this purpose, the SMA tests were carried out at four different initial acetate concentrations, namely 500 mg dm^?3, 1000 mg dm^?3, 1500 mg dm^?3 and 2000 mg dm^?3 so that substrate limitation could not occur. The results showed that the sludge sample taken from the UASB reactor (OLR of 6.1 kg COD m^?3 d^?1) had a potential acetoclastic methane production (PMP) rate of 72 cm³ CH₄ g^?1 VSS d^?1. When the PMP rate was compared with the actual methane production rate (AMP) of 67 cm³ CH₄ g^?1 VSS d^?1 obtained from the UASB reactor, the AMP/PMP ratio was found to be 0.94 which ensured that the UASB reactor was operated using its maximum potential acetoclastic methanogenic capacity. In order to achieve higher OLRs with desired COD removal efficiencies it was recommended that the UASB reactor should be loaded with suitable OLRs pre‐determined by SMA tests. © 2001 Society of Chemical Industry     

Photoelectrocatalytic humic acid degradation kinetics and effect of pH,applied potential and inorganic ions

This study addresses the removal of humic acid (HA) dissolved in an aqueous medium by a photoelectrocatalytic process. UV₂₅₄ removal and the degradation of color (Vis₄₀₀) followed pseudo‐first order kinetics. Rate constants were 1.1 × 10^?1 min^?1, 8.3 × 10^?2 min^?1 and 2.49 × 10^?2 min^?1 (R² > 0.97) for UV₂₅₄ degradation and 1.7 × 10^?1 min^?1, 6.5 × 10^?2 min^?1 and 2.0 × 10^?2 min^?1 for color removal from 5 mg dm^?3, 10 mg dm^?3 and 25 mg dm^?3 HA respectively. Following a 2 h irradiation time, 96% of the color, 98% of the humic acid and 85% of the total organic carbon (TOC) was removed from an initial 25 mg dm^?3 HA solution in the photoanode cell. Photocatalytic removal on the same photoanode was also studied in order to compare the two methods of degradation. Results showed that the photoelectrocatalytic method was much more effective than the photocatalytic method especially at high pH values and with respect to UV₂₅₄ removal. The effect of other important reaction variables, eg pH, external potential and electrolyte concentration, on the photoelectrocatalytic HA degradation was also studied. Copyright © 2003 Society of Chemical Industry     

Production of L-aminoacylase by fermentation of Pseudomonas sp. BA2

The growth and enzymatic production of Pseudomonas sp. BA2 a new L -aminoacylase-producing microorganism, were studied in a bench-top fermenter. Multiple fermentations were carried out in order to determine the optical pH and temperature values. The influence of the substrate concentration on both growth and L aminoacylase activity was also investigated. The maximum growth rate and the greatest yield of enzyme were obtained when the fermentation was carried out at pH 7·5, 25°C and DOT ≥ 50%. N-Acetyl-DL -alanine, at a concentration 20 g dm^?3, was used as the sole carbon and nitrogen source. The fermentation process provided a maximum biomass concentration of 3·36 g dry weight dm^?3. The highest L -aminoacylase production (11429 U g^?1 dry weight) was obtained after 39 h of cultivation. The results were a significant improvement over those previously reported.     

Batch production of L(+) lactic acid from whey by Lactobacillus casei (NRRL B‐441)

The effects of temperature, pH, and medium composition on lactic acid production by Lactobacillus casei were investigated. The highest lactic acid productivity values were obtained at 37 °C and pH 5.5. The productivity was 1.87 g dm^?3 h^?1 at 37 °C in shake flasks. In the fermenter, a productivity of 3.97 g dm^?3 h^?1 was obtained at pH 5.5. The most appropriate yeast extract concentration was 5.0 g dm^?3. Whey yielded a higher productivity value than the analytical lactose and glucose. Initial whey lactose concentration did not affect lactic acid productivity. MnSO₄ ·H₂O was necessary for lactic acid production by L casei from whey. Product yields were approximately 0.93 g lactic acid g lactose^?1. Copyright © 2004 Society of Chemical Industry     

DECOMPOSITION OF 4-NITROPHENOL BY OZONATION IN A HOLLOW FIBER MEMBRANE REACTOR

The effect of initial pH, liquid flow rate, gas flow rate, and gaseous ozone concentration on the ozonation of 4-nitrophenol in a membrane reactor was investigated. The results showed that the disappearance of 4-nitrophenol increased with the increase of liquid flow rate, gas flow rate, and gaseous ozone concentration. The rise of the initial pH value led to an increase in 4-nitrophenol removal rate, but the increase became negligible after initial pH exceeded 9.5. The highest removal efficiency of 4-nitrophenol achieved was 94% after 100 min reaction when gaseous ozone concentration was 0.51 mmol L^?1, gas flow rate was 57 mL min^?1, liquid recirculation rate was 72 mL min^?1, and initial pH was 10.3. The membrane reaction system could be modeled based on the lumped kinetics of 4-nitrophenol removal, and the corresponding rate constant of 4-nitrophenol removal was determined from the model.     

Anaerobic acidogenesis of dairy wastewater: the effects of variations in hydraulic retention time with no pH control

The performance of a laboratory‐scale mesophilic acidogenic reactor was evaluated in this study, in terms of volatile fatty acid production and distribution, with respect to variations in hydraulic retention time (HRT). The continuous flow‐completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated in a hydraulic retention time ranging between 24 and 12 h, and up to an organic loading rate of about 9.3 kg COD m^?3 d^?1, without pH control. The acid production gradually increased proportionally to the organic loading rate, with decrease in hydraulic retention time. The highest degree of acidification and the rate of acid production were 56% and 3.1 g dm^?3 d^?1 at 12 h of HRT. Variations in hydraulic retention time affected volatile fatty acid production and distribution substantially, for the range investigated. Acetic, propionic, butyric and valeric acids were commonly produced during acidogenesis of dairy wastewater. Copyright © 2004 Society of Chemical Industry