The Economics of Enzyme Production

Novozymes makes the case for delivered enzymes, sharing results of studies on costs and effectiveness.
By Pamela Simms-Borre | October 14, 2010
Not long ago, you could ask any plant manager what the most costly part of cellulosic ethanol production was, and he or she would answer "Enzymes." Now enzyme costs have been reduced, but worries still abound about how much enzyme is needed and how best to source it. These worries are not as relevant anymore, says Cynthia Bryant of Novozymes.

"The discussion about on-site enzyme production versus a delivered enzyme solution has been going on for years, but we need to set the scene as it stands today," says Bryant, global business development manager, bioenergy for Novozymes. "In the past few years, the industry has made great strides within process development as well as enzyme development, so a lot has changed since the topic first surfaced."

The latest generation of cellulosic enzymes has finally moved the industry within the reach of commercialization. With the latest enzymes available to the industry, an average cellulosic ethanol plant of 55 MMgy will need to receive enzyme shipments only twice a week. This development significantly reduces the volume of enzymes a plant needs to be equipped to handle. Due to this reduction, the logistics, material handling, and delivery timeliness are no longer an issue, making plant operations a little less complex on a daily basis.

"We've moved beyond the barrier of multiple truckloads of enzyme deliveries per day," Bryant says. "We have reduced dosage and at the same time increased the percentage of cellulose converted. Now, using Novozymes Cellic CTEC2, we're talking enzyme delivery a couple of times a week."

Carbohydrate Sources not Equal
Besides the issue of enzyme volume, another much discussed topic is the ability of production facilities to employ the cheap carbohydrate sources that they already have at hand. Many plant managers think that these carbohydrates—coming from the distillate, stillage, hydrolysis, etc.—can be recycled and used as a sugar source during enzyme fermentation, effectively lowering the cost of enzymes. Unfortunately, although they can be used, these by-product carbohydrates are extremely inefficient ingredients for effectively growing enzyme-producing microorganisms.

"Being an enzyme producer, we were very interested in investigating the possibility of using lower-cost sources of carbohydrates, so we carried out a very intensive study into the possibility," Bryant says. "Unfortunately, we found that fungal fermentation yields are significantly lower when you use a lower-quality carbohydrate. It just doesn't pay off to switch to lower-cost sources." Although biomass carbohydrates are inexpensive, their heterogeneous nature can make them difficult to use in some fermentations. Each 5- and 6-carbon sugar possesses a different uptake rate in microorganism metabolism. Along with the crude biomass sugars there are also often significant inhibitors present, which can lead to lower fermentation yields and higher investment costs. "The industry's hope that lower-cost carbohydrate sources would be a cost improvement for enzyme production is just not true," she adds.

A Look into the Future
To explore the true economics of enzyme production, Novozymes investigated a set of scenarios that made it possible to objectively compare on-site and delivered production models. Novozymes developed production scenarios for an average-size plant producing 55 MMgy of cellulosic ethanol, looking ahead to the year 2013. The models anticipated the values for expression and dosage for three operational capabilities—novice, intermediate and advanced. "The dosing figures used in these scenarios are not guaranteed, but represent feasible benchmarks for our various partners, based on where we believe enzyme performance will be in 2013," Bryant explains.

The novice uses an inexpensive, royalty-free cellulase strain, but the expression rate (grams of enzyme protein per liter of broth) is low at 50 g/L, and the dosage of enzyme needed later during processing is very high at 14 percent wt/wt mg enzyme product per gram cellulose.

The intermediate uses a moderately expensive and more advanced cellulase strain. While the expression numbers are still low at 50 g/L, the dosage is much lower at 7 percent wt/wt mg enzyme product per gram cellulose.

The advanced, using a rather expensive, advanced cellulase strain with limited blending of other enzyme types, does even better with an expression of 70 g/L and a low dosage of 4 percent wt/wt mg enzyme product per gram cellulose.

In the analysis, Novozymes assumed technology that would result in the lowest possible capital cost for an on-site production setup and indexed the capital cost for building such a plant to the standard investment required to construct the ethanol facility. In fact, the setup for on-site production is one that has not been commercially proven yet, but offers the promise of the lowest possible capital costs. Likewise, the enzyme cost was calculated for the different models and indexed to the use cost of enzymes produced and delivered from Novozymes. In the scenarios, it is important to note that the Novozymes-delivered cost also includes the expense of transporting enzymes to the ethanol plant.

High Capital, Operating Costs
In all three on-site production scenarios, both the capital investment and the enzyme cost were significantly higher than for a standard ethanol plant. In an economy where it is already difficult to secure funding for a cellulosic ethanol plant, adding the expense of building an on-site enzyme production facility makes this challenge even more difficult.

The enzyme cost calculations for on-site production scenarios, when compared to a Novozymes-delivered baseline, showed substantial increases. The enzyme cost index value for a novice plant increased by almost four times, by more than two times at an intermediate plant, and by 68 percent for an advanced on-site production operation. Likewise, the capital investment required to incorporate on-site production increases by a factor of almost two.

As seen from the numbers in the table, none of the scenarios with on-site enzyme production are enabling the long-term viability of the cellulosic ethanol industry. And on top of the increased enzyme costs and capital investments needed for on-site enzyme production, there are also other reasons why on-site enzyme scenarios are not efficient.

Increasing Complexity
Novozymes believes that future developments within the industry will further decrease the viability of on-site enzyme production. Due to the complicated nature of biomass substrates, the enzymes needed to produce cellulosic ethanol are becoming increasingly complex. Higher-performing enzymes will be more multifaceted than those used today, and multiple-strain production as well as blending techniques will be required. Handling multiple-strain, complex enzymes will be more expensive, and additional capital investment will be required. These innovations will raise enzyme performance and reduce use cost, but will also make it much more difficult to produce the enzymes. This will result in higher capital costs, requiring larger facilities and more equipment, further decreasing the viability of on-site enzyme production.

"In most cases individual ethanol plants will not have the in-house expertise to drive development of these advanced enzymes, and those few that do will have to significantly increase their capital investments to accommodate these new production realities," Bryant says.

On-site enzyme production is not enabling the cellulosic ethanol industry today, nor will it be a competitive option in the future. Enzyme dosages have achieved a commercially relevant level, and some of the expected benefits from on-site production—such as using carbohydrate by-products—do not deliver on their promise. Cellulosic ethanol enzymes such as Cellic CTec2 are becoming more complex, and multiple-strain production will soon be required in order to achieve optimal performance levels. The increased complexity will require greater capital investments for on-site production facilities. Taking all of these things into consideration, the delivered enzyme model is the most cost-efficient solution for the industry.

Pamela Simms-Borre is a communication specialist for Novozymes. Contact Cynthia Bryant, global business development manager, bioenergy, Novozymes, at [email protected].