Study On The Technology And Mechanism Of Cellulase Enzymatic Hydrolysis Of Paper Sludge And Its Efficiency-Improving

Paper sludge is a major solid waste from pulp and paper industry. Because it contains 40% ~ 60% cellulose in the dry components, paper sludge could be used as a raw material for cellulose ethanol industry. Comparing with the traditional lignocellulosic materials, such as wood, crop residues and straws, paper sludge has its own advantages: low price and loose structure. Paper sludge as a material for ethanol product through enzymatic hydrolysis and fermentation, will expand the material resource of ethanol. In the meantime, it also decreases the total sludge discharge, lessens the cost for sludge disposal, reduces the pressure for environment. It would be a highly potential method for energy conversion of industry waste. In this thesis, using pulp fiber as substrate, the adsorption of cellulase on cellulose fiber and the physical and chemical changes during the enzymatic hydrolysis process were discussed. These would provide the theoretical support for the enzymatic hydrolysis of paper sludge. Additionally, a new method for improving the efficiency of enzymatic hydrolysis by cationic polymer was also proposed, which could significantly reduce the cost of enzymatic saccharification.The adsorption of cellulase on cellulose fiber is the first step of the whole enzymatic hydrolysis process. It was found that the adsorption equilibrium was reached at the time of about 60 min. The kinetics of the adsorption process could be described by second order adsorption model, as the expression of(?). The adsorption equilibrium fits the Langmuir isotherm. The maximum adsorption amount was found in adsorption on short fiber, and the maximum Langmuir adsorption equilibrium constant in adsorption on long fiber, which indicated that cellulase shows the highest adsorption affinity on long fiber. Thermodynamics parameters were also calculated. The value of Gibbs energy change ?G ? was less than 0, value of enthalpy change ?H ? less than 0, value of entropy change ? S? higher than 0 , indicating that adsorption of cellulase on cellulose fiber is a spontaneous, exothermic and irreversible process. This adsorption process contains both physical adsorption and chemical adsorption. The highest enthalpy change ?H ? and entropy change ? S? were found in adsorption on 48 mesh fiber and 28 mesh fiber, respectively. Temperature, pH value and ionic strength in solution are the main factors affecting the activity of cellulase. For the industrial cellulase, it was found that temperature of 40～60℃, pH value of 3～7 and ionic strength of 20～100 mmol/L (expressed by concentration of citric acid) were the workable conditions. Response Surface Methodology was employed, to study the effects of temperature, cellulase dosage and pH on the efficiency of enzymatic hydrolysis of bleached pulp. At optimal conditions, the soluble sugar conversion could reach to 81.5%, and the glucose conversion to 54.3%. During the enzymatic hydrolysis process, the fiber configuration and quality change with reaction time. The changes were different for bleached softwood fiber and bleached hardwood fiber. In addition, the relative rate for glucose generation and soluble sugar generation in the hydrolysis was also not alike. The freeness and recycle times of pulp fiber also affect the enzymatic hydrolysis. With lower freeness, the efficiency was higher; with higher recycle times, the lower efficiency.The hydrolysis process of cellulose by cellulase is a combination of two process units, adsorption and catalytic step. The adsorption of the enzyme to cellulosic fiber is inversely dependent on temperature, while catalytic step is directly temperature dependent at the experimental conditions. The integration of these two effects causes the difference of temperature dependence of enzymatic hydrolysis for fibers with different length. The fines were high temperature dependent and easy to be affected by temperature, but the longer fiber shows the opposite performance. The activation energy for enzymatic hydrolysis was calculated through first order rate equation, which could confirm the proposed theory. The avoidance cost (capital and operational) of heating this material to 50oC for the enzymatic hydrolysis is significant.Cationic polyacrylamides(CPAM) could increase the adsorption of cellulase on cellulose fiber and then enchace the efficiency of enzymatic hydrolysis, by the mechanisms of charged patches or charged bridging. Cationic polyacrylamides with medium cationicity (40%), relatively low molecular weight (3.4～4.5 MDA) and dosage of 250 mg/L were found to have best efficiency-improving for enzymatic hydrolysis. Proper agitation could also enhance the efficiency, with the best Reynolds number of 298. It was found it had advantage to delay the addition of CPAM until the fiber was first shortened by the enzyme to a certain extent. The effect of CPAM in enzymatic hydrolysis system is universal, which could also be well used in the system of enzymatic hydrolysis of starch.After cellulase treatment, the fiber in paper sludge was cleanly cut into smaller units, cake consolidation would be improved because it would be easier to pack short fibers into a cake than longer ones. In other words, a lower void volume and a higher cake density would obtain. The highest improvement for cake solids could reach 6%. Cationic polyacrylamides could reduce the resistance in the dewatering process. The application of this method in industry is break even now, but will become more attactive as the cost:performace of cellulase increases and the cost of sludge disposal is trending higher.In the system of enzymatic hydrolysis of paper sludge, addition of small amount of Chloramine-T would restrain the growing of bacteria, and keep the cellulase active. Adjusting the initial pH value of the hydrolysis system is vital for controlling the whole process. The change of pH value during the hydrolysis would stay in the range suitable for cellulase. According to the mechanism of enzymatic hydrolysis, a kinetic model was proposed: (?). With varied intial enzyme loading and reaction time, precise conversion of hysrolysis could be expected. In the pilot scale of enzymatic hydrolysis of paper sludge, CPAM with dosage of 500 mg/L increased 32% of glucose production and 24% of soluble sugar production, respectively. It will highly benefit the industry.