Evaluation and modeling of biochemical methane potential (BMP) of landfilled solid waste: A pilot scale study

The main goal of this study was to present a comparison of landfill performance with respect to solids decomposition. Biochemical methane potential (BMP) test was used to determine the initial and the remaining CH₄ potentials of solid wastes during 27 months of landfilling operation in two pilot scale landfill reactors. The initial methane potential of solid wastes filled to the reactors was around 0.347 L/CH₄/g dry waste, which decreased with operational time of landfill reactors to values of 0.117 and 0.154 L/CH₄/g dry waste for leachate recirculated (R1) and non-recirculated (R2) reactors, respectively. Results indicated that the average rate constant increased by 32% with leachate recirculation. Also, the performance of the system was modeled using the BMP data for the samples taken from reactors at varying operational times by MATLAB program. The first-order rate constants for R1 and R2 reactors were 0.01571 and 0.01195 1/d, respectively. The correlation between the model and the experimental parameters was more than 95%, showing the good fit of the model.     

Kinetic modeling of the enzymatic hydrolysis of pretreated cellulose

The production of sugars by the enzymatic hydrolysis of cellulose is a two-step process that includes conversion of the intermediate cellobiose to glucose by beta-glucosidase. The hydrolysis was followed by analyzing the two sugar products (cellobiose and glucose). The enzyme showed maximum activity at pH 4.8. Thermal deactivation was significant at temperatures above 45 degrees C. At 50 degrees C (optimum temperature) thermal deactivation was found to follow first-order kinetics. Several models were tested by modeling the kinetics of the reaction. Their parameter values were determined by numerical optimization, including temperature dependence. The best fitting model was a competitive product inhibition for the two reactions in the operational range.     

Development of effective modified cellulase for cellulose hydrolysis process

Cellulase was modified with amphilic copolymers made of alpha-allyl-omega-methoxy polyoxyalkylene (POA) and maleic acid anhydride (MAA) to improve the cellulose hydrolytic reactivity and cellulase separation. Amino groups of the cellulase molecule are covalently coupled with the MAA functional groups of the copolymer. At the maximum degree of modification (DM) of 55%, the modified cellulase activity retained more than 80% of the unmodified native cellulase activity. The modified cellulase shows greater stability against temperature, pH, and organic solvents, and demonstrated greater conversion of substrate than native cellulase does. Cellulase modification is also useful for controlling strong adsorption of cellulase onto substrate. Moreover, cellulase modified with the amphiphilic copolymer displays different separation characteristics which are new. One is a reactive two-phase partition and another is solubility in organic solvents. It appears that these characteristics of modified cellulase work very effectively in the hydrolysis of cellulose as a total system, which constitutes the purification of cellulase from culture broth, hydrolysis of cellulose, and recovery of cellulase from the reaction mixture. (c) 1995 John Wiley & Sons, Inc.     

Kinetics of enzymatic hydrolysis of cellulose: analytical description of a mechanistic model.

A generalized mechanistic model for the enzymatic hydrolysis of cellulose is developed and expressed mathematically. The model is based on Michaelis--Menten-type kinetics for concurrent random and endwise attack of the substrate involving end-product inhibitions and three types of enzymes: an endo-beta-1,4-glucanase, an exo-beta-1,4-glucanase, and beta-glucosidase. Basic parameters of the model which can explain synergistic and other effects observed experimentally are quantified and discussed. It is shown that cellulose degradation kinetics are expected to be strongly affected by the ratio of endo- to exocellulases in the reaction mixture as indicated by previous experimental data, and the substrate degree of polymerization, a factor not fully appreciated in previous studies, which appear to be overridingly important in many practical cases.     

Kinetic studies of enzymatic hydrolysis of insoluble cellulose: Derivation of a mechanistic kinetic model

A comprehensive mechanistic kinetic model for enzymatic hydrolysis of insoluble cellulose has been synthesized by combining models for several key aspects which have been derived independent of each other. The model takes into account the major contributing factors: the nature of the enzyme system, the structure of cellulose, and the mode of interaction between the enzyme and cellulose molecules. It consists of a set of simultaneously occurring ordinary differential equations with ten kinetic constants. All of the kinetic constants have been determined independently by carrying out critically designed experiments, and they appear in the comprehensive model without any arbitrary manipulations. The governing equations of the model have been numerically simulated by means of the computer subroutine CSMP III. The model predicts the progress of hydrolysis of cellulose over a wide range of experimental conditions and hydrolysis times reasonably well. The model can even be applied to predict the progress of hydrolysis for intensively pretreated cellulose with a minor adjustment. The applicability of the model for the actual process development is also discussed.     

Kinetic modeling of cellulose hydrolysis with first order inactivation of adsorbed cellulase

Enzymatic hydrolysis involves complex interaction between enzyme, substrate, and the reaction environment, and the complete mechanism is still unknown. Further, glucose release slows significantly as the reaction proceeds. A model based on Langmuir binding kinetics that incorporates inactivation of adsorbed cellulase was developed that predicts product formation within 10% of experimental results for two substrates. A key premise of the model, with experimental validation, suggests that V(max) decreases as a function of time due to loss of total available enzyme as adsorbed cellulases become inactivated. Rate constants for product formation and enzyme inactivation were comparable to values reported elsewhere. A value of k(2)/K(m) that is several orders of magnitude lower than the rate constant for the diffusion-controlled encounter of enzyme and substrate, along with similar parameter values between substrates, implies a common but undefined rate-limiting step associated with loss of enzyme activity likely exists in the pathway of cellulose hydrolysis.     

Kinetic modeling of enzymatic hydrolysis of cellulose in differently pretreated fibers from dairy manure

A kinetic model incorporating dynamic adsorption, enzymatic hydrolysis, and product inhibition was developed for enzymatic hydrolysis of differently pretreated fibers from a nitrogen-rich lignocellulosic material-dairy manure. The effects of manure proteins on the enzyme adsorption profile during hydrolysis have been discussed. Enzyme activity, instead of protein concentration, was used to describe the enzymatic hydrolysis in order to avoid the effect of manure protein on enzyme protein analysis. Dynamic enzyme adsorption was modeled based on a Langmiur-type isotherm. A first-order reaction was applied to model the hydrolysis with consideration being given for the product inhibition. The model satisfactorily predicted the behaviors of enzyme adsorption, hydrolysis, and product inhibition for all five sample manure fibers. The reaction conditions were the substrate concentrations of 10-50 g/L, enzyme loadings of 7-150 FPU/g total substrate, and the reaction temperature of 50 degrees C.     

Kinetic modeling of rapid enzymatic hydrolysis of crystalline cellulose after pretreatment by NMMO

Pretreatment of cellulose with an industrial cellulosic solvent, N-methylmorpholine-N-oxide, showed promising results in increasing the rate of subsequent enzymatic hydrolysis. Cotton linter was used as high crystalline cellulose. After the pretreatment, the cellulose was almost completely hydrolyzed in less than 12 h, using low enzyme loading (15 FPU/g cellulose). The pretreatment significantly decreased the total crystallinity of cellulose from 7.1 to 3.3, and drastically increased the enzyme adsorption capacity of cellulose by approximately 42 times. A semi-mechanistic model was used to describe the relationship between the cellulose concentration and the enzyme loading. In this model, two reactions for heterogeneous reaction of cellulose to glucose and cellobiose, and a homogenous reaction for cellobiose conversion to glucose was incorporated. The Langmuir model was applied to model the adsorption of cellulase onto the treated cellulose. The competitive inhibition was also considered for the effects of sugar inhibition on the rate of enzymatic hydrolysis. The kinetic parameters of the model were estimated by experimental results and evaluated.     

Solute exclusion from cellulose in packed columns: process modeling and analysis

In this investigation, process modeling and analysis were used to explore the behavior of solute exclusion from cellulose in packed columns. The study focused on modeling the effects of dispersion, mass transport, and pore diffusion. Three mathematical models were used to predict the behavior of the columns: an equilibrium model, a mass transfer model, and a combined mass transfer and pore diffusion model. Computer implementations of these models were tested against experimental conditions where cellulose particle size and solution velocity were used to either amplify or minimize dispersion or skewness in the elution curves. For small cellulose particles (200-300 mesh), all three models accurately predicted the shape of the elution curve and the particle porosity. For larger particles (45-60 mesh), the mass transfer model and the combined mass and pore diffusion model best represented the behavior of the column. At high solution velocities (0.63 cm(3) min(-1)) and large particles, only the combined mass transfer and pore diffusion model accurately represent the column behavior. Sensitivity analysis revealed that the mass transfer coefficient had little effect on the elution curves for the range of values (10(-6)-10(-3) cm s(-1)) calculated from the experimental data. The combined mass transfer and pore diffusion model presented in this article can be used to design solute exclusion measurement experiments for the larger cellulose particles found in a commercial cellulose-to-ethanol plant.     

Ultrasound mediated enzymatic hydrolysis of cellulose and carboxymethyl cellulose

A recombinant Trichoderma reesei cellulase was used for the ultrasound‐mediated hydrolysis of soluble carboxymethyl cellulose (CMC) and insoluble cellulose of various particle sizes. The hydrolysis was carried out at low intensity sonication (2.4–11.8 W cm^?2 sonication power at the tip of the sonotrode) using 10, 20, and 40% duty cycles. [A duty cycle of 10%, for example, was obtained by sonicating for 1 s followed by a rest period (no sonication) of 9 s.] The reaction pH and temperature were always 4.8 and 50°C, respectively. In all cases, sonication enhanced the rate of hydrolysis relative to nonsonicated controls. The hydrolysis of CMC was characterized by Michaelis‐Menten kinetics. The Michaelis‐Menten parameter of the maximum reaction rate V_max was enhanced by sonication relative to controls, but the value of the saturation constant K_m was reduced. The optimal sonication conditions were found to be a 10% duty cycle and a power intensity of 11.8 W cm^?2. Under these conditions, the maximum rate of hydrolysis of soluble CMC was nearly double relative to control. In the hydrolysis of cellulose, an increasing particle size reduced the rate of hydrolysis. At any fixed particle size, sonication at a 10% duty cycle and 11.8 W cm^?2 power intensity improved the rate of hydrolysis relative to control. Under the above mentioned optimal sonication conditions, the enzyme lost about 20% of its initial activity in 20 min. Sonication was useful in accelerating the enzyme catalyzed saccharification of cellulose. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1448–1457, 2013     

A hyperefficient process for enzymatic cellulose hydrolysis in the intensive mass transfer reactor

Summary A new type of bioreactor, the intensive mass transfer reactor (IMTR), has been developed for enzymatic hydrolysis of cellulose. Using T. reesei cellulases (2 FPU/ml), 3.5–6% of sugars were obtained in the IMTR after 0.5–2 h of cellulose hydrolysis with a productivity of 30–73 g/l.h.     

Recognition and hydrolysis of noncrystalline cellulose

Cellulase Cel5A from alkalophilic Bacillus sp. 1139 contains a family 17 carbohydrate-binding module (BspCBM17) and a family 28 CBM (BspCBM28) in tandem. The two modules have significantly similar amino acid sequences, but amino acid residues essential for binding are not conserved. BspCBM28 was obtained as a discrete polypeptide by engineering the cel5A gene. BspCBM17 could not be obtained as a discrete polypeptide, so a family 17 CBM from endoglucanase Cel5A of Clostridium cellulovorans, CcCBM17, was used to compare the binding characteristics of the two families of CBM. Both CcCBM17 and BspCBM28 recognized two classes of binding sites on amorphous cellulose: a high affinity site (K(a) approximately 1 x 10(6) M(-1)) and a low affinity site (K(a) approximately 2 x 10(4) M(-1)). They did not compete for binding to the high affinity sites, suggesting that they bound at different sites on the cellulose. A polypeptide, BspCBM17/CBM28, comprising the tandem CBMs from Cel5A, bound to amorphous cellulose with a significantly higher affinity than the sum of the affinities of CcCBM17 and BspCBM28, indicating cooperativity between the linked CBMs. Cel5A mutants were constructed that were defective in one or both of the CBMs. The mutants differed from the wild-type enzyme in the amounts and sizes of the soluble products produced from amorphous cellulose. This suggests that either the CBMs can modify the action of the catalytic module of Cel5A or that they target the enzyme to areas of the cellulose that differ in susceptibility to hydrolysis.     

Enzymatic hydrolysis of waste cellulose

Interstitial flow (IF) modulates both the biochemical and biophysical cues surrounding cells. It represents a very important regulating mechanism for cell/tissue function and has been commonly utilized in tissue engineering (TE). This article discusses the possible regulating mechanisms of IF on fibroblasts, the various fibroblast responses to IF, the current challenges in understanding the IF–fibroblast relationship and the application of IF for fibroblast involved TE. In particular, IF can affect fibroblast growth at both intracellular (e.g., calcium signaling, protein/proteinase secretion) and cellular (e.g., autocrine/paracrine signaling, proliferation, differentiation, alignment, adhesion, migration) levels. One major challenge for understanding IF–fibroblast interaction has been the determination of the flow and cell growth condition at microlevel especially in a three‐dimensional environment. To utilize IF and optimize the fluidic environment for TE, several influencing factors in the system including perfusate composition, flow profile, nutrient supply, signaling molecule effect, scaffold property, and fibroblast type should be considered. Biotechnol. Bioeng. 2010;107: 1–10. © 2010 Wiley Periodicals, Inc.     

Role of fragmentation activity in cellulose hydrolysis

Most studies of cellulose hydrolysis have been carried out on three components of the cellulolytic systems, viz, endoglucanases, exoglucanases, and cellobiases. Little attention has been paid to the fragmentation activity of certain cellulolytic systems. We have noticed that despite being a more powerful degrader of modified cellulose (CMC), the 7-day grown culture filtrate of Myrothecium verrucaria was less effective than that of Trichoderma reesei at degrading pure unmodified cellulose. Scanning electron microscopy imaging showed that one distinguishing feature of the latter is its ability to fragment (macerate) the cellulose. Cellulose particle size decreased with time as it was incubated in the culture filtrate of T. reesei at 37 °C. This was used as a pre-treatment. Pre-treated cellulose was then washed and incubated with fresh T. reesei or M. verrucaria culture filtrates. Pre-treatment increased liberation of reducing sugars during subsequent incubation of cellulose in T. reesei culture filtrate but not in subsequent incubation in M. verrucaria culture filtrate. It was hypothesized that fragmentation activity of the pre-treatment opened up attack sites for further hydrolysis, but these were not available for attack by other enzyme systems.     

Cellulase adsorption-desorption and cellulose saccharification during enzymatic hydrolysis of cellulose materials

Treatment of different cellulose materials with cellulase from Penicillium funiculosum showed a cellulase adsorption-desorption pattern on all materials. The relative rate of adsorption and saccharification (enzyme activity) increases with increasing temperature. At 60° cellulase adsorption increased while the enzyme activity decreased.     

Role of fragmentation activity in cellulose hydrolysis

Most studies of cellulose hydrolysis have been carried out on three components of the cellulolytic systems, viz, endoglucanases, exoglucanases, and cellobiases. Little attention has been paid to the fragmentation activity of certain cellulolytic systems. We have noticed that despite being a more powerful degrader of modified cellulose (CMC), the 7-day grown culture filtrate of Myrothecium verrucaria was less effective than that of Trichoderma reesei at degrading pure unmodified cellulose. Scanning electron microscopy imaging showed that one distinguishing feature of the latter is its ability to fragment (macerate) the cellulose. Cellulose particle size decreased with time as it was incubated in the culture filtrate of T. reesei at 37 °C. This was used as a pre-treatment. Pre-treated cellulose was then washed and incubated with fresh T. reesei or M. verrucaria culture filtrates. Pre-treatment increased liberation of reducing sugars during subsequent incubation of cellulose in T. reesei culture filtrate but not in subsequent incubation in M. verrucaria culture filtrate. It was hypothesized that fragmentation activity of the pre-treatment opened up attack sites for further hydrolysis, but these were not available for attack by other enzyme systems.