Grantee Research Project Results
Final Report: Using Waste to Clean Up the Environment: Cellulosic Ethanol, the Future of Fuels
EPA Grant Number: SU834325Title: Using Waste to Clean Up the Environment: Cellulosic Ethanol, the Future of Fuels
Investigators: Wyman, Charles , Garong, Ramon Joshua , Turgman, Anthony , Kwon, Christine , Shi, Jian , Tam, Kawai , Nguyen, Vu
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2009 through August 14, 2010
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2009) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities , Pollution Prevention/Sustainable Development
Objective:
The proposed research investigated the conversion of final alternative daily cover–green (ADC-green) into ethanol through a three-step process of pretreatment, enzymatic hydrolysis, and fermentation. Bench-scale experiments were conducted to maximize the production of ethanol from the cellulosic material by investigating several parameters. It was anticipated that varying reaction time and temperature in the pretreatment process, and addition of bovine serum albumin (BSA) loading during the enzymatic hydrolysis step would result in higher yields of glucose. This bioconversion process of an ADC-green waste stream to produce ethanol can potentially supplement the use of other cellulosic materials such as corn stover. Furthermore, increased use of cellulosic ethanol in fuels has a net reduction in the carbon footprint as an opportunity to recycle carbon exists in the very nature of the cellulosic feedstock; unlike the continual build-up of carbon in the atmosphere through fossil fuel combustion.
Summary/Accomplishments (Outputs/Outcomes):
In the process of converting municipal solid waste (MSW) into ethanol we optimized the first two major steps of pretreatment and enzymatic hydrolysis stages to enhance the sugar yield and to reduce the cost. For the pretreatment process, we tested different parameters of reaction time (ranging from 5 – 80 minutes) and temperature (ranging from 140 - 180°C) designed for dilute acid pretreatment. The best yield resulted from pretreatment experiments conducted at 160°C for 20 minutes with the highest glucan yield of 38%. As the reaction time and temperature are increased, degradation of glucan and xylan to unusable sugars is more pronounced. In converting ADC-green to biofuel it is important to have a high glucan composition and high sugar recovery, as this correlates to a greater potential yield of ethanol.
Due to the high cost, cellulase enzyme use must be minimized; however, in the ADC-green waste stream, many components can potentially inhibit the enzymatic hydrolysis reaction and thus lead to high enzyme use. To lower the overall costs, the addition of BSA to detoxify the enzymatic process was investigated. In addition to blocking non-specific binding of cellulases, BSA or other proteins also may help stabilize enzymes during the course of hydrolysis and reduce possible inhibition by other impurities in pretreated MSW. By changing the different concentration levels of enzyme loading (ranging from 5 - 60 FPU/g glucan) as well as using protein detoxification it was possible to improve the enzyme digestibility to optimize time and cost. Our results indicate that pre-incubation of pretreated ADC-green with BSA positively augmented the performance of enzymatic hydrolysis by ~5-20% at low enzyme loadings of 5-15 FPU/g glucan. These results demonstrated that cellulose hydrolysis was improved significantly by over 20% for pretreated ADC-green in comparison to results from previous lower glucan-to-glucose conversions at low enzyme loadings.
Based on our experimental data, we further modeled a larger-scale batch process of approximately 500,000 gallons/year capacity to determine economic feasibility. Using SuperPro 7.2 modeling software from Intelligen, the process plant model consisted of unit operations for collection and preparation of ADC-green, presoaking and pretreatment, enzymatic hydrolysis, fermentation, distillation, and ethanol storage. The theoretical economic parameters were calculated using modeling software and Excel programming. The estimated initial capital investment is $12.3M and annual operating costs are $1.5M. It was determined that our ethanol selling price must be $1.93 per gallon in order to start generating a profit.
Conclusions:
For the implementation of bioconversion of ADC-green on a larger scale, we must find a way to maximize the efficiency of all of the processes. Our research has demonstrated that pretreatment conditions and protein detoxification of ADC-green show promise of increasing the sugar yields while decreasing enzyme usage. Modeling a batch process of approximately 500,000 gallons/year capacity based on the results of this work, we determined that our ethanol selling price must be $1.93 per gallon in order to generate a profit. Further research in equipment design and use of alternative proteins may improve the economics and is proposed for the Phase II segment.
Proposed Phase II Objectives and Strategies:
Municipal solid waste (MSW) is one of the lowest cost feedstock sources for cellulosic ethanol production. Clearly, MSW-ethanol can help address waste disposal challenges, augment the diversity of the domestic energy resource base, and help mitigate the impact of potential fuel supply disruptions, reduce greenhouse gas emissions, and improve energy security. Through the support of Phase I, we have demonstrated some very promising initial outcomes regarding the conversion of ADC-green to biofuels, i.e., ethanol. For instance, the lab research results indicated that low cost ADC-green was among the best feedstock for fuel ethanol production because of high sugar yields at low enzyme loadings supplemented with bovine serum albumin (BSA). We believe that the further development of this technology through continual Phase II support is essential for the potential commercial application of our technology. In Phase II we plan to address three key questions that bridge the gap between lab-scale demonstrations to pilot scale to real world commercial practices.
- Steam gun pretreatment of ADC-green
- Design of a new steam gun pretreatment reactor
- Optimization of steam gun pretreatment
- The mass/energy balance of pretreatment
- Seeking alternative inexpensive protein sources to BSA
- Market analysis/survey for potential cheap protein sources
- The performance of cheap protein sources on enhancing enzymatic hydrolysis yields
- Simultaneous saccharification and fermentation of pretreatment ADC-green to ethanol
- Batch vs. continual mode
- Effect of adding BSA or BSA substitutes on ethanol yield
Based on the experimental data, the Phase II award also is sought to design a pilot-scale plant with a more reasonable target production rate of 50,000 gallons/year of ethanol. We will design the plant in more detail using SuperPro software and determine the economics and design features required to make the plant efficient and code compliant. In addition to the design and capital investment costs, we also will take into account the cost of utilities, materials, personnel, insurance, and finally, the sales price of our ethanol.
The Phase I award also was an integral educational tool for undergraduates for a senior design project and for high school students for their Science Fair projects. The high school students presented their work entitled "An Analysis between ADC-green and Wood Waste Using the Processes of Post-Hydrolysis Versus Enzymatic Hydrolysis and K-lignin" to peers, judges, and the public at the Riverside Unified School District Science Fair competition and won first prize. We have presented the findings in the form of the Senior Design Project. Furthermore, we plan to present our current data at the Sustainable Expo. Finally, the data from the experiment will be published in a research paper.
Supplemental Keywords:
chemicals, toxics, ethanol, solvents, organics, pollution prevention, life-cycle analysis, alternatives, sustainable development, clean technologies, innovative technology, renewable, waste minimization, public good, adsorption, transportation,Relevant Websites:
UCR Newsroom: http://newsroom.ucr.edu/news_item.html?action=page&id=2195
Targeted News Service: http://targetednews.com/pr_disp.php?pr_id=2441187
Web Newswire: http://www.webnewswire.com/node/474866
High School Students take home gold at the Riverside Unified School District Science Fair: http://www.cert.ucr.edu/
The 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.