Grantee Research Project Results
Final Report: Biofuel and Bioenergy Production from Sugar Beets
EPA Grant Number: SU834729Title: Biofuel and Bioenergy Production from Sugar Beets
Investigators: Zhang, Ruihong , Rapport, Josh , Williams, Kelly , Nguyen, Lynn , Ong, Matthew , Lei, Nancy , Zicari, Steve
Institution: University of California - Davis
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2010 through August 14, 2011
Project Amount: $9,486
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2010) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities
Objective:
This P3 project is part of an overall effort at University of California, Davis for faculty and students to assist a farmer cooperative, the Mendota Advanced Bioenergy Beet Cooperative (MABBC), in California to develop an efficient and integrated bioenergy project, named Advanced Bioenergy Center Mendota (ABCM). When complete, ABCM will have five major components: The first component, an advanced ethanol production system, will process the roots of sugar beets gathered within a 50-‐mile radius of ABCM into advanced ethanol for transportation fuels. This component will be powered entirely using electricity and steam generated in the biomass gasification component. The second component, an Anaerobic Digestion (AD) system, will convert the beet tops and tails, and stillage from the ethanol production system, into biomethane and a high-‐grade soil amendment and fertilizer products. If necessary, MABBC will also be able to inject the biomethane into the natural gas pipeline. Our P3 efforts focused on the development of an engineering system for achieving ethanol and biomethane production from sugar beets, which is the critical part of ABCM. We aimed to accomplish the following four objectives in the Phase I of our project,
- Design an industrial scale system that will produce ethanol and biogas from ground sugar beet.
- Design, build, and test lab scale system based on industrial design.
- Determine optimal conditions for ethanol and biogas production.
- Develop engineering design and operating manual for the integrated ethanol and biogas production system.
When complete, it is estimated that each year the new bioenergy and biorefinery facility will:
- Process nearly 1 million tons of locally-‐sourced sugar beets
- Produce 33.5 million gallons of advanced ethanol and 1.6 million standard cubic feet (SCF) of renewable biomet
- Create up to 325 construction, engineering and design jobs; 50 bio-‐refinery operations positions, 40 to 50 feedstock operations jobs and 160 farm labor positions in a community which currently claims the highest unemployment rate in the United Stat
- Generate $90 million in direct economic activity
If such an integrated bioenergy and biorefinery system can be successfully developed, it is expected that such an engineering system and business model can be implemented in distributed scales from sugar beets and other biomass in other parts of the United States and world. The results and outcome of our P3 project will lead to development of a sustainable model and solutions for the people around the world promote local economy and prosperity and protect our planet with a sustainable future.
Summary/Accomplishments (Outputs/Outcomes):
Throughout Phase I of the project, the student design team, in collaboration with internal and external academic and industrial partners, applied their knowledge, conducted literature search and analyses, performed original research and development, developed computer modeling software and bench scale bioreactor systems, and obtained results and conclusions leading towards Phase II of the project. Major finding include:
Design and Analysis of an Industrial Scale System for Producing Ethanol and Biogas from Sugar Beets:
A spreadsheet based scalable model was developed to identify and quantify major material and energy inputs and outputs for an integrated ethanol and biogas production system. The model, implemented in MS-‐Excel™, expanded on a previous model for AD systems and is referred to as the Beet Ethanol and Anaerobic Phased Solids Integrated Design and Financial Model (BE-‐APS IDFM). The model envisions the following simplified processing steps and estimates preliminary materials and energy balances, as well as costs for the combined facilities:
- Beet-‐root reception and washing, size reduction, fermentation to ethanol, distillation and denaturation to final ethanol product specification, and delivery of whole stillage to downstream AD processing.
- Beet-‐leaf reception and washing, size reduction, mixing with whole stillage for anaerobic digestion, and biogas utilization for electrical and heat requirements on site.
The base case model indicates 1700 Tpd of unwashed beet roots can produce 82 Tpd (or approximately 9,000,000 gallon/year) of Ethanol. 1776 Tpd of whole stillage and 720 Tpd of beet tops are digested resulting in 118,872 Nm3/d of dry biogas at 61% methane. Total solids content entering the digester is approximately 10%. Combustion of 95% of the gas in the generator and <5% in a boiler satisfies the calculated heat load, and creates a surplus of 157,701 kWh/yr electricity (10.7MW generator size). Assuming a minimum attractive rate of return (MARR) of 15% is necessary, this project would only have a net present worth if feedstock costs did not exceed $16.69/ton (wet mass of combined root and leaves assumed). Capital costs are estimated at over $65M, and non-‐feedstock operating costs at over $4.4M/yr. Revenues totaling $33.8M/year (not including feedstock or co-‐product values) indicate that the majority of revenues are from ethanol sales (86% of total), but electricity sales also contribute significantly. These promising results should be interpreted cautiously as there are several assumptions in need of further refinement and this model is intended to serve as a framework for further development.
Sugar Beet Processing, Juice Extraction and Quantification:
Laboratory experiments were used to determine suitable methods for reducing the particle size of sugar beets, extraction of sugar juice from the beets and leaves and separation of juice from pulp with the objective of deciding the beet processing step and preparing the beets for later ethanol fermentation and anaerobic digestion experiments. Samples of previously frozen and thawed beet roots and leaves obtained from a local USDA-‐ARS research station (Albany, CA) were chopped and held at room temperature and 70°C for one hour prior to juicing using a commercially available centrifugal juicer. Samples released only a portion of the expected moisture as juice, the rest being retained in a wet pulp, even after squeezing with a handheld potato-‐ricer or Instron machine at pressures up to 1000 psig, with little difference between pretreatments or pressing regimes. Because of the very hygroscopic (water holding) capacity of sugar beets, likely due to the high natural pectin contents, direct mash utilization or water extraction methods were considered. It was found that water addition would increase the juice and sugar extraction but the economics of water addition and subsequent effluent management needs to be carefully evaluated. Based on our laboratory test results, we decided to use the ground beets (without juice and pulp separation) to be the feedstock for ethanol fermentation.
Ethanol Production from Sugar Beet Roots:
Both Saccharomyces cerevisiae and E coli KO11 were used to produce ethanol (EtOH) from sugar contained in the ground beet root . The fermentation was carried out at a loading of 10% solids for 48 hours and at 37°C. The results from E coli KO11 were not conclusive and need to be further investigated. Saccharomyces cerevisiae results showed final ethanol concentration from sugar beet mash was 25 g/L with a standard deviation of 0.4. Ethanol yields based on sucrose and total free sugars were almost complete, while based on volatile solids content were 0.26 g EtOH/g VS, leaving about half of the VS content to proceed to anaerobic digestion for biogas production. Yields were calculated by dividing the ethanol concentration by the initial concentration of each substrate, with the maximum theoretical ethanol yield as 0.51 g Ethanol/g sugar. Starches, cellulose and hemicellulose make up around 35% of the sugar beet volatile solids, and pectin, protein and other organic compounds are other constituents and are good substrate for AD. To determine the best conditions for ethanol recovery from fermentation broth, ongoing experiments are being conducted to recover ethanol from ethanol solution by laboratory distillation under different conditions.
Anaerobic Digestion of Sugar Beet Leaves:
Biogas and methane yields from sugar beet leaves were determined using batch AD tests. Digestion of fresh leaves and warm-‐water soaked leaves were tested to determine if water soaking for a period of time prior to anaerobic digestion would increase the biogas yield and/or rate of biogas production. The results show that there were no statistically significant differences in methane production rate or lag time between fresh leaves and water soaked leaves treated at different time and temperatures. The maximum methane yield, production rate, and lag time for all treatments averaged 267 mL/g (±18), 50 mL/g d (±6), and 0.8 d (±0.2), respectively. It was concluded that fresh beet leaves should be digested directly without any pretreatment.
Laboratory Bioreactors for Ethanol Fermentation and Anaerobic Digestion:
A considerable amount of effort was invested to design and build bioreactor systems to handle the ground beet roots and leaves that have high solids content (10-‐15%). New designs were created to achieve effective feed storage and pumping, mixing and effluent removal of bioreactors. Existing fermentors and anaerobic digesters were modified with new design features and tested and proven to be functional for carrying out continuous ethanol fermentation and anaerobic digestion. Specifications and operational manuals were prepared for guiding the use of these bioreactors for future experiments and teaching uses.
Conclusions:
Phase I objectives for evaluating scientific and engineering aspects of a California, beet-‐based bioethanol and biomethane project were accomplished by a multidisciplinary team of undergraduate, graduate, faculty, and industry partners. Preliminary process and economic modeling, based on laboratory data collected from processing, anaerobic digestion, fermentation, and distillation testing of local sugar beets, indicate promising results for achieving large scale, quantifiable benefits for beet growers, their communities, and the environment. A simple processing scheme whereby beets are collected, washed, ground and fermented with Saccharomyces cerevisiae appears capable of producing over 9,000,000 gallons per year of renewable bioethanol, supported by biogas production from anaerobic digestion of the beet leaves and leftover stillage from ethanol generation. Over 155,000 kWh/yr of surplus renewable electricity are also projected as possible. These results are promising and leave room for validation and optimization. Additional research and development focused on improving process design for ethanol and biomethane co-‐generation is needed which will include further investigation of optimum reactor design and organism selection for ethanol production, and continued process and economic design optimization. Our recommendations for necessary issues to be addressed on this project are detailed in the Phase II proposal to follow, which will be carried out in continued close collaboration with academic and industry partners to realize the maximum benefit of this project for people, prosperity, and the planet.
Journal Articles:
No journal articles submitted with this report: View all 4 publications for this projectSupplemental Keywords:
Agriculture, bioenergy, sugar beet, rural economyThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.