Grantee Research Project Results
Final Report: Novel Co-Culture Process for Pretreatment of Food Waste for Alcohol Fuel Synthesis and Methanogenesis
EPA Grant Number: SU835304Title: Novel Co-Culture Process for Pretreatment of Food Waste for Alcohol Fuel Synthesis and Methanogenesis
Investigators: Bouldin, Ryan , Del Castillo, Pablo Aguilera , McElwee, Matthew , Critchfield, Maya , Harris, Nicholas , McAdam, Polly
Institution: College of the Atlantic
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2012 through August 14, 2013
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2012) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities
Objective:
Given the use of fossil fuels are having dramatic effects on our global climate, air quality, and food security there is a need for more carbon neutral and ecologically sustainable sources of energy. Localized energy production ensures significant efficiency advantages over more traditional centralized grid distribution systems due to the lack of transmission line losses. Localized energy production can also achieve efficiencies of nearly a 100% when production occurs at the site of generation, as is the case with residential solar and wind energy. Unfortunately, while solar and wind generated energy is considered sustainable and carbon neutral, due to their high capital cost they remain out of reach for many communities, particularly those in rural and developing regions of the world. An alternative eco-effective and environmentally benign approach that focuses on localized carbon neutral energy production could be developed from locally generated waste residues.
Therefore, to address the need for a cheap and local source of renewable energy and to lower the amount of municipal solid waste generated within a community, we proposed to develop a fungal co-culture system capable of digesting food scraps into fermentable sugars for liquid fuel synthesis. The integrated system would replace the need for an energy-intensive thermal pre- treatment to digest lignocellulosic material and generate onsite methane for cooking fuel or heating needs.
The initial stages of the work aimed to assess the viability of using food waste from various sources as suitable feedstocks for fermentation. A previous EPA funded grant (Production of Biobutanol from Biomass using Novel Membrane Reactor; EPA grant SU833927) demonstrated that cafeteria food waste was a viable feedstock for 1-butanol production.
Second, a new microbial strategy was developed to optimize digestion of food waste to fermentable sugars. Four different types of fungi, Pleurotus spp. (P. ostreatus and P. eryngii), Phanerochaete chrysosporium, and Ceriporiopsis subvermispora were cultivated and analyzed for their ability to digest food scraps into fermentable sugars. These organisms were selected because together they excrete a spectrum of extracellular laccases, cellulases and lignin peroxidases that are essential for degrading resilient carbohydrates in food waste; they can be easily obtained and cultured for inoculation of feedstock.
After the fungal culture driven hydrolysis and fermentation, there is expected to be material remaining (undigested or incompletely digested polysaccharides, proteins, and other natural compounds). Rather than create a new waste stream, an anaerobic digester was designed to transform any residual material (undigested or incompletely digested polysaccharides, proteins, and other natural compounds) into methane gas. This methane could be used for cooking fuel, to power a generator, or provide process heat. After methanogenisis, the undigested material can be composted.
Objectives:
It is the hope that this project can demonstrate the transformation of municipal solid waste into a local, carbon neutral, renewable energy system. The pathway toward this goal begins with the development of a novel fungal culture treatment to hydrolyze lignocellulose and other polysaccharides found in food waste to fermentable sugars while yielding a residue suitable for methane generation.
The following objectives were designated as milestones towards the realization of transforming food waste into a renewable, carbon neutral source of energy
- Determine effective sterilization and neutralization methods necessary for fungal cultivation
- Optimize fungal culture growth and saccharification efficiency utilizing mono and co- culture techniques
- Determine appropriate hydrolysate to support growth of clostridium spp. (hydrolysate may need to be diluted or concentrated)
- Design and build small-scale anaerobic digester for methane generation from food waste
- Optimize methanogenisis on residues from saccharification and fermentation
- Determine appropriate scale for food waste butanol facility (tons of food waste/day)
- Present findings and design pilot facility based on data
Summary/Accomplishments (Outputs/Outcomes):
All students working in the area of fungal cultivation have gained valuable experience working in an aseptic environment. They have learned basic sterilization techniques and proper procedures for handling and containing fungal species. The students have utilized these techniques to grow four different types of fungal species that were selected for their ability to degrade lignin, cellulosic, and other polysaccharide based materials. These species include two types of Pleurotus spp. (P. ostreatus and P. eryngii), Phanerochaete chrysosporium, and Ceriporiopsis subvermispora. The fungal species were initially grown on Yeast-Malt media in polystyrene petri dishes. Average growth rates (mm/hr) for the all species of fungi were determined by measuring the radial expansion (in mm) of mycelia along two perpendicular axes at various time points. Radial growth rates for the fungi on YM media were 0.43 mm/hr, 0.14 mm/hr, 0.11 mm/hr, and 0.00 mm/hr for Phanerochaete chrysosporium, Ceriporiopsis subvermispora, P. eryngii, and P. ostreatus, respectively. Alternative media is currently being investigated for the propagation of P. ostreatus. Additionally, it has been observed that all species of the selected fungi do propagate on sterilized food waste. At the current time, only qualitative observations of growth have been made. However, in stark contrast to that observed within YM growth media, it appears that the P. ostreatus propagates at the fastest rate on food waste. Experiments to determine both growth and saccharification rate are ongoing.
During our research of clostridial fermentation of organic waste, we came across a number of challenges; the inability of the organism to grow and be handled in the presence of oxygen, the control and induction of solventogenesis, the variance of nutrient composition of organic waste, and the separation and purification of target products. However, our biggest challenge has been ensuring complete conversion of butryric acid to 1-butanol. Proper pH control has been identified as the essential variable responsible for complete conversion. At the current time further research is necessary for us to continue to optimize the process when using organic waste as the feedstock.
To address the left over waste from fermentation, we have also constructed a small scale (20 L) three tank anaerobic digester. In our model, the first tank mixes food waste and methogenic bacteria to generate a mixture of methane and carbon dioxide biogas. The effluent gases from the digestion tank bubbles through reinforced tubing into the bottom of the second tank. The second tank is filled with water and designed as a filter to scrub the carbon dioxide from the methane rich gas stream produced in the first tank. To measure the rate of gas produced in the primary vessel, a third tank is utilized. As the biogas enters the second tank, the volume of the gas displaces water from the second to the third tank. The amount of water displaced into the third tank overtime determines the rate and volume of biogas production.
At the current time, we are in the process of filling the primary vessel and preparing for our initial attempt to produce methane. Initial qualitative results will be presented at the EPA Expo in April 2013.
Conclusions:
In the Phase I, we have successfully utilized aspectic technique to growth and propagate four species of fungal capability of digesting lignocelluloic material to fermentable sugars. The fungi have all been observed to propagate on food waste, which will serve as a starting point for an environmentally benign digestion process. This process alleviates the need for the more energy intensive and acid waste generating digestion process currently used to convert lignocellulosic material to sugar. It is the hope that the fungal co-culture system proposed will eventually produce enough sugars at a rate that is commercially viable for the production of biofuels. The fungal digestion process has been designed to be integrated into a system that utilizes the remaining waste after digestion and fermentation for the production of methane.
Supplemental Keywords:
food to fuel, fermentation, renewable feedstocks, fungi co-culture, biodigester, green chemistry, environment friendly chemical synthesis, alternative materials, pollution prevention, technology for sustainable environment.Relevant Websites:
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.