摘要:

AbstractThe kinetics of anaerobic degradation of a molasses wastewater were measured under constant pH conditions in a laboratory scale packed bed reactor. In continuous and batch experiments the formation and degradation rates of the organic acids (butyric, propionic and acetic) have been followed. The influence of hydrogen gas on the acid degradation rates has been measured and, contrary to the literature and the thermo‐dynamic calculations, no inhibition was detected, biofilm diffusional effects may be the reason. Two dynamic simulation models were tested, a heterogeneous model, which considered the biofilm diffusion–reaction phenomena and a quasihomogeneous model with the same kinetics. Except for hydrogen, the diffusion effects were found to be negligible. Otherwise both models gave essentially the same results and the time profiles of acids, hydrogen, carbon dioxide and methane agreed relatively well with dynamic startup experiments. Batch experiments showed the acid concentrations to be highly sensitive to the initial molasses concentration. This aspect was not included in the model but is being investigated furt

ISSN:0006-3592    

DOI:10.1002/bit.260310102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe use of immobilized hepatocytes represents a promising approach for the problem of detoxification in acute hepatic failure. Hepatocyte viability and detoxification function of a number of complex enzyme systems were examined before and after immobilization in alginate droplets. Detoxification function was assessed quantitatively by measuring the kinetics of several specific detoxification systems: the cytochrome P450 system, the urea cycle, and two conjugation systems. Reaction rates for all enzyme systems were similar in immobilized and nonimmobilized cells, and were in good agreement with previously published literature values. These results indicate that transport limitations do not occur in these gels and that the intrinsic reaction rate is the limiting step. Feasibility of detoxification replacement by immobilized cells is discussed using measured reaction rates.

ISSN:0006-3592    

DOI:10.1002/bit.260310103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIn an attempt to resolve the difficult problem of on‐line determination of the viscosity of non‐Newtonian fermentation media, the authors have used a vibrating rod sensor mounted on a bioreactor. The sensor signal decreases nonlinearly with increased apparent viscosity. Electronic filtering of the signal damps the interfering effect of aeration and mechanical agitation. Sensor drift is very low (0.03% of measured value per hour).On the rheological level the sensor is primarily an empirical tool that must be specifically calibarated for each fermentation process. Once this is accomplished, it becomes possible to establish linear or second‐degree correlations between the electrical signal from the sensor and the essential parameters of the ferementation process in question (pH of a feremented milk during acidification, concentration of extra cellular polysaccharide). In addition, by applying the power law to describe the rheological behavior of fermentation media, we observe a second‐order polynomial correlation between the sensor signal and the behavior in

ISSN:0006-3592    

DOI:10.1002/bit.260310104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractConcentration multiplicity in a two‐phase or three‐phase draft tube fluidized‐bed bioreactor containing biofloc particles is studied. The kinetics of biological reactions considered involve two limiting substrates. The necessary and sufficient conditions for concentration multiplicity in both the biofilm and bioreactor are examined in terms of effectiveness factor, inlet and bulk concentration of substrates, and liquid flow rate. Hysteresis behavior in both the biofilm and bioreactor and multiplicity of concentration profiles in the biofilm are also disc

ISSN:0006-3592    

DOI:10.1002/bit.260310105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe attrition bioreactor (ABR) combines wet ball milling and enzymatic hydrolysis in one process step. It was found that the ABR did not accelerate enzyme deacti‐vation. Interfacial forces, not shear forces, caused the most deactivation. Elimination of the air–liquid interface by covering the reactor substantially increased enzyme stability. A simple exponential kinetic model was tested to predict the cellulose conversion in an ABR. Kinetic parameters were estimated from batch runs performed at various enzyme and substrate concentrati

ISSN:0006-3592    

DOI:10.1002/bit.260310106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA revised enzyme synthesis rate expression for cybernetic models of bacterial growth is presented. The rate expression, which is comprised of inducible and constitutive contributions, provides for a basal enzyme level that is necessary to predict certain types of commonly observed continuous culture transients. The response of a continuous culture to a step change in feed stream composition is simulated using both the old and new formulations, and the ramifications for the “matching‐law” formulation are disc

ISSN:0006-3592    

DOI:10.1002/bit.260310107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractPichia pastorisis a methylotrophic yeast that makes use bf the enzyme alcohol oxidase to catalyze the first step of the dissimilatory pathway that enables it to grow on methanol. Because of its stability and low substrate specificity, alcohol oxidase is of considerable interest for a range of biotechnological processes. Various feeding regimes were evaluated in an effort to increase the biomass concentration and productivity that could be achieved from fermentations using this organism. Through continuous or semicontinuous feeding, biomass concentrations were increased 10‐fold over those achieved in batch fermentations. In subsequent trials, nongrowing whole cells were applied successfully to convert ethanol to acetaldehyde. Quantitative conversions of 20‐g/L solutions of ethanol have been achieved in 2 h, and acetaldehyde concentrations of up to 35 g/L have been achieved using extended reaction times of 5 h. The conversion reaction was limited by end product inhibition and by acetaldehyde holdup within the yeast ce

ISSN:0006-3592    

DOI:10.1002/bit.260310108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractOver a pH range 1–4 and temperatures from 170 to 230°C, the decomposition rates of xylose, gaiactose, mannose, glucose, 2‐furfural, and 5‐hydroxymethyl‐2‐furfural (5‐HMF) were pseudo first order. The effect of temperature and pH on the pseudo first‐order decomposition rate constants was modeled using the Arrhenius equation and acid‐base catalysis, respectively. Decomposition rates of the monosaccharides were minimum at a pH 2–2.5. Above pH 2.5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid catalysis at below ca. pH 3.5. The hydrothermal conversion of glucose to its decomposition products during thermochemical Pretreatment can be modeled as a combination of series and parallel reactions. The formation rates of identified soluble products from glucose decomposition, 5‐HMF and levulinic acid, were also functions of temperature and pH. The rate of 5‐HMF formation relative to glucose decomposition decreased as the pH increased from 2.0 to 4.0, with levulinic acid formation only detected when the pH was 2.5 or less. For glucose decomposition, humic solids accounted for ca. 20% of the

ISSN:0006-3592    

DOI:10.1002/bit.260310109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA model was developed and evaluated as a tool for predicting the formation of soluble products from staged thermochemical treatment of lignocellulosic materials under acidic conditions typical of autohydrolysis. The model was used to predict the general trend of hemi‐cellulose and cellulose hydrolysis between pH 2 and 4 and temperatures of 170–230°C, and results were compared with experimental data. When the model was evaluated for this range of temperatures and pH values, results indicated: (1) a relatively low temperature (175°C) during the first stage allows hydrolysis of the hemi‐cellulose polysaccharides without significant mono‐saccharide decomposition, (2) subsequent stages at higher temperatures (equal or greater than 200°C) are needed for significant cellulose hydrolysis, but glucose decomposition will also occur, and, (3) a pH in the range of 2–2.5 will enhance polysaccharide hydrolysis while limiting monosaccharide decomposition. The model's predictions, indicating that the formation of biodegradable products could be optimized using Pretreatments at pH 2–2.5 for the pH range evaluated, were confirmed in experiments with white fir as a representative l

ISSN:0006-3592    

DOI:10.1002/bit.260310110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThis study investigated the relationship between sludge loading rate, COD‐to‐nitrogen ratio of influent waste, and maximum difference in specific resistance as a result of chemical conditioning (ΔZ). It also related ΔZto sludge carbohydrate content, protein content, and surface charge. This research also explored the necessity of chemical conditioning when an activated sludge exhibits excellent bioflocculation characteri

ISSN:0006-3592    

DOI:10.1002/bit.260310111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY