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Determination of a sugarcorn to ethanol and co-products value chain

Principal Investigator: Brandon Gilroyed

Research Institution: University of Guelph

Timeline: May 2015 – April 2018

Objectives:

  • Compare southwestern Ontario field trial of new sugarcorn varieties to sugarcorn grown in Ottawa for sugar (sucrose) yield from sugarcorn stalk under different harvest scenarios.
  • Evaluate sugarcorn as a substrate for bioconversion to ethanol.
  • Determine the best uses of sugarcorn press cake by evaluating: ensiling for animal feed; production of biogas via anaerobic digestion; and extraction of cellulosic sugars.
  • Evaluate storage of juice in ensiled intact stalks.
  • Calculate the economic potential of a sugarcorn crop to ethanol and co-products value chain.

 Impacts:

  • Identifying a farm management system for sugarcorn that will produce optimum biomass and sugar yield will help establish the on-farm viability of this proposed sugarcorn value chain.
  • The economic evaluation of sugarcorn utilized for ethanol and sugarcorn press cake co-product will help establish a market for Ontario growers by finding the best uses for the entire plant, such as ensiling for use as animal feed.

Scientific Summary:

The current model for sustainable biofuel production is the sugarcane sucrose to ethanol industry in Brazil. Ontario farmers cannot grow sugarcane but are adept at growing corn. Corn, like sugarcane, is a C4 grass, efficient in utilizing water, nutrients and CO2 to convert solar energy into sugar which is ultimately harvested as grain starch. This project evaluated the use of a new corn feedstock, termed sugarcorn, in biofuel and co-product applications. Sugarcorn are corn varieties yielding high sucrose concentrations in their stalks. Sugarcorn is being developed at AAFC to have high yields of sucrose in stalk juice. Sugarcorn also produces grain, and one of the objectives is to compare sugar yields when the crop is grown for grain or stalk juice. Stalk juice may offer potential advantages including ease of handling via pumping and reduced energy and enzymatic needs in preparation for fermentation to ethanol. Implementing usage of sugary corn in Ontario requires demonstration of crop and sugar yields, conversion processes and ultimately the yield; and determination of value of the final product and co-products.

Sugarcorn is potentially an excellent feedstock for the Ontario ethanol industry. Because sucrose is directly fermentable by yeast, several of the expensive and energy-intensive pre-treatment processes associated with conventional grain ethanol can be eliminated. Four genotypes of sugarcorn grown in Ridgetown and in Ottawa were evaluated for production of sugar, height, total biomass, moisture content, and juice yield. Juice obtained from crushing corn stalks was analyzed for sugar composition and concentration, and then used as the carbon source for ethanol fermentation. Ensiled corn was analyzed for feed properties and tested as a biogas production substrate. A final economic evaluation of sugarcorn was conducted to determine the value of ethanol and co-products compared against production costs.

Sugarcorn Genotype Comparison:

Four different inbred lines (referred to as genotypes) of sugarcorn were grown in a randomized complete block design with four replicates in the 2015, 2016, 2017 and 2018 growing seasons. Genotypes used included CO348XC103 (Genotype 1), CO384XC103 (Genotype 2), CO442XC103 (Genotype 3), and CO444XC103 (Genotype 4) (Reid et al., 2015). A conventional hybrid (DKC6189RIB; Genotype 5) was grown as a control for comparison. Crops were planted in early June, with harvest occurring approximately 10 days post-silking, which corresponded to an average of 1,955 crop heat units (CHU), in mid-August. At harvest, total fresh dry matter, dry matter, and moisture content were measured. Corn stalks were crushed using a three-roller press to extract juice, which was characterized using a refractometer (0Brx), HPLC, and/or spectrophotometer to assess sugar content.

Within each growing season, biomass yield was mostly similar between the four genotypes tested and the hybrid control, although genotype 4 had slightly lower (P<0.05) fresh matter yield than genotype 3. Biomass yield varied according to growing season (P<0.001), with the 2017 season producing significantly more biomass than the 2015 and 2016 seasons. Using oBrx, total biomass, and moisture content, an estimate of sugar yield was calculated according to the procedure used by Reid et. al. (2015).

Sugarcorn Population x Nitrogen Application Comparison:

For the 2016, 2017 and 2018 growing seasons, Genotype 2 (CO384XC103) was used to evaluate the impact of population density and nitrogen application rate on biomass and sugar yield. Three levels of nitrogen application and three levels of plant population density were tested in a Latin square design. Total fresh biomass yields were not statistically different based on treatment (P>0.05). Within nitrogen application rate, population density did not have a clear impact on total biomass yield. As described above, total sugar yield was estimated based on fresh matter yield, moisture content, and oBrx. Differences in sucrose yield were not statistically significant (P>0.05) although there appears to be a trend in the data suggesting lower nitrogen application rates and higher population density may increase overall sucrose yield.

Ethanol and Butanol Production from Sugarcorn Juice:

Our estimates for theoretical ethanol production from sugarcorn are lower than was reported previously by Reid et. al. (2015) in trials conducted at AAFC Ottawa in 2008 and 2009. In direct comparison between the two studies, differences in ethanol yield based on genotype varied as follows: Genotype 1: 2,157 L ha -1 in our study vs 2,996 L ha -1 in Ottawa; Genotype 2: 2,155 L ha -1 Ridgetown vs 2,697 L ha -1 Ottawa; Genotype 4: 2,070 L ha -1 Ridgetown vs 3,343 L ha -1 Ottawa. Several explanations for the differences in theoretical ethanol yield between Ridgetown and Ottawa may be applicable. The studies were conducted in different locations and in different growing years. The procedure for juice extraction varied between experiments. In Ottawa, juice was extracted using a hydraulic press from a 5 cm stalk section taken from an area between the internode above the primary ear to the second internode below the primary ear. In Ridgetown, juice was extracted using a modified 3-roller press from the entire corn plant. This difference in procedures may have contributed to the lower oBrix reported between the studies. However, the biggest difference affecting calculations relates to the fresh matter yield, which was reportedly far larger in Ottawa than Ridgetown. In the study at Ottawa, per hectare fresh matter was estimated by multiplying the mass of a single corn stalk by 75,000 plants ha -1. In Ridgetown, fresh matter was calculated by taking the total mass of each field plot at harvest, then calculating on a per-hectare basis. In Ridgetown, sugarcorn was planted at an estimated density of 90,000 plants ha -1 for the genotype trial.

For reference, USDA estimates for ethanol production from corn grain are 4,010 L ha -1 for a wet mill process and 4,162 L ha -1 for a dry mill process. In our study, sugarcorn had 52-57% of the theoretical ethanol potential compared to wet milled grain corn. As such, sugarcorn does not appear to be a direct competitor with grain corn for ethanol production. However, the short growing season requirements suggest that sugarcorn could be worked into novel crop rotations in ways that conventional corn currently cannot. Further, sugarcorn could be grown in regions where conventional grain corn cannot be grown. Looking at the prairie region of Western Canada, ethanol production uses wheat as a substrate instead of corn. Given that ethanol production from wheat is 9.69 L bu -1 and assuming a crop yield of 123.55 bu ha -1 (50 bu ac -1), ethanol yields are approximately 1,197 L ha -1 from wheat in Saskatchewan (Mohanty and Swain, 2019). The sugarcorn yields we have reported exceeded ethanol yields from wheat, though further direct comparison studies would be necessary to fully evaluate. Sugarcorn juice also requires far fewer processing steps than conventional grain ethanol, which should make the net energy ration more favourable while also reducing capital and operational costs. A full life cycle analysis of the sugarcorn in this context is necessary to quantify differences in economic return and environmental impact in comparison to grain ethanol production.

Succinic Acid Production from Sugarcorn Juice:

Beginning in 2017, our research group obtained additional funding from OMAFRA to explore fermentative production of succinic acid from sugarcorn juice. This research was not part of the original GFO funding application and did not use any of the funds provided by GFO. The objective of this project was to produce succinic acid, which is a platform chemical that can be used to synthesize a variety of high value compounds for use in a wide variety of industries (e.g., personal care products, fragrances, polymers, resins, plasticizers). To carry out this research, different concentrations of sugarcorn juice amended with yeast extract (a nitrogen source) and sodium bicarbonate (pH buffer) was fermented using Actinobacillus succinogenes in a Box-Behnken response surface method design. Optimal experimental conditions were determined to be 77.8% juice concentration, 16.5 g L-1 yeast extract, and 60 g L-1 sodium bicarbonate. These conditions were experimentally tested and resulted in a titer of 36.6 g L-1, a productivity of 0.51 g L-1 h-1, and a yield of 0.58 g g-1 sugar consumed. Using the estimates for sugar yield determined in the sugarcorn genotype experiments and the succinic acid yield determined in this study along with an estimated value for succinic acid of $5.50 kg-1, we estimated the value on a per ha basis. The value of sugarcorn being converted to succinic acid was estimated to be $10,133 ha-1 on average across all genotypes tested, which is far higher than the estimated value of ethanol per ha assuming an ethanol price of $1.50 L-1 ($857 ha-1). We estimated the value of grain corn at $2,910 ha-1 assuming a yield of 236 bu ac-1 and 10-year average corn price of $4.22 bu-1. These economic estimates do not factor in the cost of production, which will be significantly higher for succinic acid than conventional grain corn. However, there appears to be significant economic potential for a sugarcorn to succinic acid supply chain that warrants further investigation into both optimizing the fermentation process and determining the cost of production at full scale.  

Sugarcorn Silage for Animal Feed:

Sugarcorn biomass was chopped and ensiled (either fresh, or after juice pressing) using laboratory scale mini-silos in both the 2016 and 2017 growing seasons. Biomass was packed to a density of 180 kg m-3, stored for 4 months, and then opened and sent to a commercial laboratory for feed analysis. Feed analysis suggested that sugarcorn biomass, ensiled either fresh or after juice extraction, was a suitable feed that could be incorporated into a total mixed ration for dairy production.

As the juicing procedure used in our trials in Ridgetown were less efficient, the same calculation could not be used. In its place, we have estimated silage yield to roughly equal 30% of the fresh matter yield based on Reid et al. (2015).

Biogas Potential of Sugarcorn Biomass:

The biochemical methane potential of sugarcorn was assessed by incubating sugarcorn biomass with anerobic inoculum from the University of Guelph Ridgetown Campus’ biogas facility. Methane potential was assessed on biomass in both the 2016 and 2017 growing seasons, using either fresh biomass, biomass that had passed through a three-roller press to remove juice, or biomass that was ensiled for preservation. The methane production curve of all three substrates was very similar. As such, the overall biogas potential of sugarcorn biomass was similar regardless of treatment or genotype. The pressed material did not have as large a decline in biogas production as expected, which could be due to the relative inefficiency of the pressing process used on removing sugar from biomass. The sugarcorn substrates performed comparably to conventional corn silage in terms of methane yield.

Methane potential per hectare of land was calculated by determining yield of silage per hectare on a volatile solids (VS) basis. For reference, the estimated methane yield per hectare of whole crop maize silage is 1,660 – 12,150 m3 ha-1, though that data is reported from Europe and will vary according to crop yield (Murphy et al., 2011). It is not surprising that methane potential of sugarcorn is lower on a per hectare basis than for conventional corn silage given the significantly shorter growing period and inherent reduction in biomass yield.

External Funding Partners: OMAFRA/University of Guelph partnership funding

Project Related Publications:

Gomez-Flores R, Thiruvengadathan TN, Nicol R, Gilroyed B, Morrison M, Reid LM, Margaritis A (2018) Bioethanol and biobutanol production from sugarcorn juice. Biomass and Bioenergy 108:455-463.

Mohanty, S. K. and Swain, M. R. (2019). Chapter 3 – Bioethanol production from corn and wheat: food, fuel, and future. In Bioethanol Production from Food Crops, R. C. Ray and S. Ramachandran, Editors. Academic Press. P. 45-59.

Murphy, J., Braun, R., Weiland, P., Wellinger, A. (2011). Biogas from crop digestion. IEA Bioenergy Task 37 – Energy from Biogas.

Reid, L. M., Morrison, M.J., Zhu, X., Jindal, K.K., Ma, B. L. (2015). High stalk sugar corn: A potential biofuel crop for Canada. Agronomy Journal 107(2): 475-485.

 

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