Boosting Enzyme Performance During Cellulose & Starch Hydrolysis John Reye, Kendra Maxwell, Swati Rao, Jian Lu, Sujit Banerjee IPST, Georgia Tech October, 2009
Biofuels & c-pam Cellulases hydrolyze cellulose and amylases hydrolyze cornstarch to glucose. Enzymes are the most expensive consumable in these processes: potential for cost reductions. Our finding (accidental!): cationic polyacrylamides (c- PAMs) increase the rate of hydrolysis of both enzymes. Patent pending licensed to Akzo Nobel.
Cellulase reactions Endogluconases attack cellulose randomly. Exogluconases attack at the ends. ß-glucosidases hydrolyze cellobiose to glucose.
Effect on bleached fiber (FQA) fines (%) kink angle fiber length (mm) 32 24 16 40 30 20 1 0.7 0.4 HWD 0 4 8 12 time (hrs.) fines (%) kink angle fiber length (mm) 18 14 10 60 40 20 2.4 1.4 0.4 SWD 0 2 4 6 8 10 time (hrs.) Kink angle & fiber length track: fibers are first attacked at the kinked (weak) regions. Has mixing implications. Fines decrease for HWD: greater surface area, preferentially attacked. Fines increase for SWD; the fines population is initially low & increases as the fiber degrades.
Effect of c-pam on fiber length The rate of fiber length decrease is higher in the presence of c-pam. c-pam also accelerates the hydrolysis of fiber. fiber length (mm) 1 0.8 0.6 0.4 0.2 0 with c-pam control 0 10 20 30 40 50 time (h) 1% bleached HWD 500 ppm c-pam cellulase
1. Application to sludge dewatering Primary (fibrous) sludge treated with enzyme, conditioned with polymer & dewatered in a belt press simulator. The enzyme (cellulase) clips the fiber to smaller pieces. Cake solids increases because the shorter fibers pack better less void space. percent cake solids 40 38 36 34 32 4 hrs 6 hrs 2 hrs 4 hrs 0 0.01 0.01 0.03 0.03 enzyme (percent) high-ash sludge (TX)
Sludge dewatering (cont.) percent cake solids 41 40 39 38 1 hr 4 hrs percent cake solids 34 33 32 31 30 29 1 hr 2 hrs percent cake solids 42 41 40 39 1 hr 2 hrs 4 hrs 37 0 0.01 0.01 enzyme (percent) 28 0 0.01 0.01 enzyme (percent) 38 0 0.01 0.02 0.02 enzyme (percent) GA virgin SC virgin GA recycle Sludges from several mills were treated. Cake solids increased in all cases. Cost:benefits are presently ~ break-even. But enzyme costs are dropping. Could be useful where a mandatory cake solids value is required.
2. Dissolution of sludge Fibrous sludge is dissolved by cellulase. The sludge can be hydrolyzed to glucose or anerobically converted to methane. Adding c-pam (100-500 ppm by volume) with the enzyme increases the rate. TOC (ppm) glucose (ppm) 4000 2000 0 5000 2500 0 with c-pam with c-pam 0 5 10 15 20 25 hours Sludge - 43% ash, 5% consistency. Bleach initially added ph then adjusted to 4.7. Novozyme (Cellic Ctec, 0.03%) c-pam: 500 ppm
Economics of glucose production Basis: sludge containing 50 dry tpd of cellulose. Hydrolyze to glucose. Isolate glucose (membranes) & recycle water. Costs/day Enzyme: $6,000 Water treatment (RO): $1,100 (includes capital & O&M) Total: $7,100 Benefits/day Glucose: $13,000 Sludge disposal avoidance: $3,000 Total: $16,000 Other costs: transportation of glucose, acid, mixers, etc.
Benefits for the ethanol producer Corn-ethanol facilities have live yeast left at the end of their process that they have to discard because of limitations of solids. Injecting glucose at this stage utilizes this yeast without adding solids. Eventually they could start replacing their corn, which has both economic & political benefits. Also the price of glucose from sludge will be stable unlike the price of corn. They have the potential for taking glucose from the sludge output of several mills.
Economics of methane production The front-end costs dissolution of the fiber are roughly the same. Capital is required for the anerobic conversion of BOD to methane. The methane can be used onsite, e.g. at a lime kiln. Natural gas prices are low; sugar prices are high. Overall the glucose option is presently more attractive.
Issues Ash handling: do we drop out the ash early or later. Too much lime mud is a problem as it raises ph. Acid is required for neutralization; foaming is a problem. Sludge quality should be consistent. How do we concentrate the glucose. The corn-toethanol operation wants it as dry as possible.
3. Cornstarch hydrolysis Cornstarch: 1% α-amylase: 1% (v/v) Glucoamylase: 0.1% (added after 1 hr.) c-pam added initially Temperature 85 o C (1 hr) then 58 o C (5 hr) The c-pam acts on the glucoamylase. Too much c-pam is inhibitory
Issues The rate & timing of c-pam is important. It is a flocculant & it tends to increase the viscosity of starch & derived products. The c-pam can be added slowly or later in the process.
Screening c-pams Several c-pams catalyze both cornstarch & fiber hydrolysis. Glucose yields from cornstarch & fiber were each normalized to the maximum yield for each case. Controls are at (0,0) where no polymer is present; the best overall polymer is at (1,1). relative increase (starch) 1 0.5 0-0.5-0.5 0 0.5 1 relative increase (fiber) Biotech. Lett. 31, 1613, (2009)
Screening c-pams (cont.) Except for three instances where there was no effect, the c-pams provide a benefit for the corn starch application. For the fiber work, five of the polymers tested were inhibitory. Conclusion: the effect of the c- PAM is non-specific in that it boosts the performance of two completely different systems. relative increase (starch) 1 0.5 0-0.5-0.5 0 0.5 1 relative increase (fiber)
Binding to fiber Handsheets soaked in (a) enzyme & (b) enzyme + c-pam. Protein in solution measured & the enzyme on fiber calculated by difference. c-pam increases enzymefiber binding. (mg protein/g of dry fiber) 6 4 2 0 with c-pam without c-pam 0 0.1 0.2 0.3 0.4 0.5 enzyme (percent in water)
Enzyme-polymer binding Particle size measured by dynamic light scattering. Addition of polymer reduces the peak representing enzyme. Three different polymers show similar trends.
Possible mechanisms The c-pam could bind the enzyme to the fiber in a favorable configuration; form a loose fiber floc in which the enzyme may be trapped. The c-pam is inhibitory if binding reduces enzyme mobility. These are speculative.
Conclusions c-pams accelerate the rates of both cellulase & amylase hydrolysis by increasing enzyme-substrate binding, although excessive binding is unfavorable. They can potentially reduce enzyme dosage, which will reduce the overall cost of ethanol production. The c-pam can increase cake solids during primary sludge dewatering by reducing fiber length. Funded by State of Georgia, Georgia-Pacific, Akzo Nobel, New Page, Mead Westvaco, Bowater.