Due to the low concentration of resveratrol specified within the Japanese knotweed rhizome used to simulate the base case model, approximately 6,000 kg of Japanese knotweed rhizomes is needed per batch. While ethanol is widely used across the simulated facility, a large quantity of ethanol at an approximate 1:1 ratio is required during the extraction process, largely attributing to the high cost for ethanol. To demonstrate the relationship between resveratrol concentration and the quantity and cost of ethanol in the process, we calculated ethanol consumption as we increased the concentration. Here, Figure 4.2 illustrates the change in the total cost of ethanol and amount of ethanol used when the concentration of resveratrol per knotweed rhizome is increased up to 3 mg/g.The increase of resveratrol found within the rhizomes led to an exponential decrease in the quantity of ethanol needed for processing. In comparison to the base case model, there’s a reduction of $1.6 million to the overall cost of ethanol when the concentration of resveratrol is increased an order of magnitude to 1mg/g. When resveratrol concentration is as high as 3 mg/g, ethanol cost decrease by $2.1 million, a 53% decrease from the base case model results. When the cost of total ethanol used is compared between 1 mg/g and 3 mg/g models, wholesale grow bags the difference is only about $575 thousand or a 23% decrease.
A simple method to evaluate the effect of the concentration in rhizomes, we measured the mass of knotweed rhizomes needed for processing as concentration was varied. As expected, an increase in knotweed concentration results in fewer knotweed rhizomes needed for processing. Figure 4.3 shows the change in mass of knotweed rhizomes needed and ethanol consumption per increasing concentration of resveratrol within the knotweed.Notably, ethanol is a commodity which has experienced some volatility in price during the last few years. A commodity tracker provided by trading economics.com tracks the cost of ethanol per gallon in USD daily . Trading Economics demonstrates that the price of ethanol per gallon reached a low of about $0.95 in April of 2020 and a high of $3.43 on November of 2021, with a current price of about $2.65 per gallon during the time this report was written 2 . The initial jump in ethanol price was over 260% in only a time span of one year and seven months. The price has since dropped about 23% since its peak in a span of 4 months with financial analysts at Trading Economics forecasting a further reduction in price in the near future. This fluctuation in price ultimately limits the ability to effectively assess the effect that the cost of ethanol has towards resveratrol production and similar bio-manufacturing facilities utilizing large quantities of ethanol.
In effort to assess the effect the ethanol price has on the OPEX, the price of ethanol was varied by increments of $0.50 from $1.00 to $3.00. The corresponding OPEX values for each scenario is demonstrated in Figure 4.4 below.In the scenario where ethanol was priced towards its low price of $1.00 per gallon, the annual operating cost to produce 100 MT of resveratrol is reported to be $13.2 and $9.2 million, with and without depreciation, respectively. In the same simulation file, where ethanol is now priced at $3.0 per gallon, the annual operating cost increases to $17.0 and $13.2 million, with and without depreciation, respectively. The base case scenario was performed using a price of $2.00 per gallon of ethanol. The annual operating cost for the base case model is $15.0 and $11.2 million, with and without depreciation, respectively. The difference in annual operating cost is roughly 16% when compared to the $1.00 per gallon scenario and 11.5% when compared to the $3.00. With each increment of $0.50, the annual operating costs steadily increases an average of 6.8% from the last. To assess the cost of ethanol to the COGS, the COGS values was plotted against the change in ethanol price, shown below in Figure 4.5.As expected, the COGS was shown in increase in a linear fashion, in a similar trend to that shown in the relationship between OPEX and ethanol price. An incremental increase of $0.50 from $1.0 to $3.0 per gallon of ethanol increased the COGS an average value of $10.
The COGS value for the optimistic case of $1.0 per gallon case is reported to be $131 and $92 including and not including depreciation, respectively. The variation in price is about $20 for both COGS values and a percentage difference of 13.5% and 18.1%, includingand not including depreciation, respectively. While ethanol is understood to change in price due to many unprecedented factors, it is recommended that the price of ethanol be discussed and be agreed upon for long periods of time with commercial supplies in efforts to hedge against the variation in price in the global market.Another commodity deemed essential to produce 100 MT of resveratrol is the cellulase enzymes used for hydrolysis in the process. Patents released by three resveratrol manufacturers in China detail steps on how to utilize ß-glucosidase for hydrolyzing polydatin into resveratrol to increase production . Here, the simulation for the base case model was designed in a similar fashion to incorporate the utilization of ß-glucosidase found in cellulase. As a result, the annual cost of cellulase enzymes was expected to be $71,436 or 1.3% of the annual operating cost. However, the price of cellulase enzymes used within the model was retrieved using literature values derived from a techno-economic analysis on enzymes costs for bio-fuel production3 . This value was not discussed or confirmed with a large-scale commercial manufacturer of industrial enzymes. The use of industrial enzymes remains a challenge as prices remain inconsistent due to enzymes being reported in terms of dollars per gallon of biofuels3,4. These prices often account for factors beyond the cost of enzymes themselves, such as overall bio-fuel yield, feedstock choice, and enzyme loading 3 . Consequently, a wide range of prices for industrial cellulase enzymes exists. Notably, an analysis performed by scientists at the United States National Renewable Energy Laboratory mention retrieving a Multi-Year Program Plan from the Office of the Biomass Program, Energy Efficiency and Renewable Energy, U.S. Department of Energy where the price of cellulase enzymes was anticipated to be within the range of $0.35/gal in 2007 and $0.12/gal by 2012. The same authors at the NREL performed a techno-economic analysis on thedesign and economics for conversion of lignocellulosic biomass to ethanol and concluded they were able to retrieve a price of $0.34/gal when using their own on-site enzyme production section, aligning their cost with the expectations of the DOE. Novozymes, an industry leader in industrial enzyme production, released a press release titled “New enzymes turn waste into fuel” in February of 2010 mentioning they can offer cellulase enzyme at a competitive price of $0.50 per gallon of cellulosic ethanol5 . Using the pricing information retrieved by the techno-economic analysis on cellulase enzymes for industrial applications mentioned above3 , grow bags for gardening a range of prices for cellulase enzymes per gallon of ethanol can be found to be between $0.68-$1.47. The difference in price is understood to be attributed to using the maximum theoretical yields of sugar consumption and if yields were based on saccharification and fermentation yields found in literature3 .
Since the price of enzymes are another variable cost which attribute to the cost of production, a sensitivity analysis was performed to assess the impact of such a large spread between enzyme cost. A scatter plot demonstrating the relationship between the COGS and enzymes cost is shown below in Figure 4.6.The range of ethanol used for this analysis were chosen from the values retrieved during our search for enzymes costs and a case where the enzymes are supplied at no additional cost. The list is as follows, $0.00/gal, $0.12/gal, $0.35/gal, $0.50/gal, $0.68/gal, $0.85/gal, and $1.47/gal. A large change in COGS values was not seen. The largest change in COGS when comparing to the base case occurred when the price of enzymes increased an order of magnitude to $1.47/gal. Here, the change in total cost was 188%, or a price increase of $134,000 a year when compared to the base case model. The low cost of enzymes for resveratrol production can be expected since the amount of enzymes being loaded to the reaction vessel is relatively small compared to the total mass also entering the reactor . To ensure the model was appropriately modeled, the percentage of enzyme costs was measured as the enzyme cost was varied, shown in Figure 4.7. As expected, as the cost of enzymes increase, as did the percentage of total enzymes cost to the total raw material costs.An alternative to single use enzymes highlighted in other Rsv production patents and scientific literature is the use of fermentation. Rather than purchasing and mixing pure enzymes with plant tissue, this approach mixes plant tissue with microbial cultures, utilizing the enzymes secreted within the solution, ultimately reducing operating costs and raw material cost associated to the addition of water for mixing. This method’s feasibility has already been demonstrated by Wang, H. et al., who effectively compares hydrolyzing P. cuspidatum herbs using fermented fungi versus using acid hydrolysis was performed and dubbed using fungi as an effective and feasible alternative6 . Arguably, applying this method for large scale production might not be practical, as one patent reports the time for fermentation ranges from 10 to 15 days7 , significantly reducing processing time and annual production throughput. Additionally, other researchers argue that the activity of the β-glucosidase enzyme responsible for converting polydatin to Rsv does not perform optimally under fermentation conditions 8 . Another alternative which can be utilized to address high enzyme costs was demonstrated in the analysis performed by the U.S. NREL. Design a bio-processing facility with its own on-site enzyme production section4 . This approach is one that has already been utilized in Rsv literature where the feasibility of fermenting Aspergillus oryzae and separating the β-glucosidase enzyme from solution to hydrolyze P. cuspidatum plant tissue was demonstrated8 . The use of on-site enzyme production is expected to reduce purchasing costs and provide a consistent supply of enzymes available for industrial use.As described above, the most utilized approach when extracting resveratrol from Japanese knotweed is the use of an enzymatic hydrolysis step to convert any existing polydatin to resveratrol. However, data surrounding large scale processing of Japanese knotweed is limited, therefore, bioprocessing parameters such as percent conversion was retrieved using literature on laboratory scale experiments. It should be noted that literature describes an efficient process where conversions can yield values as high as 100%9 . Rather than initializing 100% conversion within the simulation, another conservative approach was taken, and 90% conversion was specified within the base case model. To evaluate the impact that the percent conversion had on the CAPEX and COGS, the percentage was varied from 90 to 100 by increments of two, shown in Figure 4.8.Increasing the enzymatic conversion led to a reduction in both CAPEX and COGS. Utilizing the 90 and 100 percent conversion results for comparison, the difference in COGS is $3.1 and a $200 thousand difference in CAPEX. The largest drop in CAPEX among the different percent conversions occurred between 92 and 94 percent conversion, yielding a decrease in CAPEX of 55 thousand . Here, the reduction in price is attributed to 3 factors: the reduction in equipment size, the reduction of units needed for processing knotweed, and lastly, the reduction in raw materials such as water and ethanol entering the process at a 1:1 mass ratio with the mass of knotweed. The relationship between Japanese knotweed and COGS to increasing enzymatic conversion percentages is shown in Figure 4.9. One specific example where the reduction in CAPEX is seen is the reduction of reactor size needed to perform the enzymatic hydrolysis. The size of the reactor in the base case model is 13,621 L but the reactor is resized to 12,925 L when the conversion was increased to 94%. While there is a price decrease in both the CAPEX and COGS when 100% conversion is initialized, the author would advise against expecting to replicate similar values as 100 percent conversion may not be practical at large scale.