Recipient Organization
UNIVERSITY OF VERMONT
(N/A)
BURLINGTON,VT 05405
Performing Department
Civil & Env Engineering
Non Technical Summary
Biorefining of renewable feedstocks to beneficial products is a cornerstone of circular bioeconomies.Farmers are key stakeholders in circular biorefining, providing substrates (e.g., manure, plant residues) and sites for processing facilities. Anaerobic digestion relies on microbial communities to convert organic materials into biogas, a mixture of carbon dioxide, methane, and other trace gasses. The biogas is either combusted to generate electricity or converted to pipeline-quality natural gas through a series of gas cleaning steps. While anaerobic digestion can recover energy and carbon from manure, the economic viability of on-farm anaerobic digestion is not guaranteed. While several fators impact the success of an anaerobic digestion project, a key determinant is the value of the final product. The long-term goal of the proposed project is to expand the products from anaerobic bioprocessing of agricultural wastes and enable farms to become sustainable hubs in circular bioeconomies.With the lack of natural gas infrastructure in rural areas throughout the United States, new products from biorefining of agricultural wastes could enhance the economic viability of agricultural systems. Propane is used as a fuel throughout much of rural America.The major driver for selecting either heating oil or propane as a fuel is cost. Prices for propane have increased in the past ten years and the current price in US average is currently $2.30 per gallon.Nearly all of the propane used in the United States is derived from fossil fuel refining. In the proposed work, we will investigate factors that increase the production of propane from combinations of cow manure and food waste and evaluate the life cycle impacts of this approach compared to conventional propane production.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Objective 1. Produce propane from cow manure and food wasteObjective 1.1 Ferment agricultural wastes to butyric acid with real-time butyric acid extraction.Objective 1.2 Upgrade butyric acid to propane with magnetic photoreforming.Objective 1.3 Generate propane in a batch fermentation-extraction-upgrading (FEU) system.Objective 2. Perform a technoeconomic and environmental life cycle assessment of propane production from agricultural wastes.Objective 2.1 Estimate the minimum selling price for propane.Objective 2.2: Assess the relative environmental impacts of propane production.
Project Methods
Objective 1.1 Our first objective is to construct the bioreactor and solvent overlay system. The fermentation to produce C4 will be done in a 2 L sequencing batch reactor (SBR). The SBR will operate through multiple stages and an extractant (trioctylamine dissolved in vegetable oil)will be added as an overlay to extract C4 from the fermentation broth. Trioctylamine has previously been used as an extractant for selective C4 removal from fermentation broth.Vegetable oil will be used as a solvent due to its low toxicity and anticipated low economic and environmental costs compared to other solvents.Maximizing C4 production relies on avoiding production of other carboxylates. To accomplish this, we will (1) inoculate the bioreactors with an inoculum rich in butyrate-producing organisms; and (2) perform selective extraction of C4. In ruminants, C4 is a primary product of fermentation. Therefore, we will recreate fermentation conditions similar to a rumen: the pH of the fermentation will be controlled between 5.5 and 7, the temperature will be controlled at 35 deg C, and an extractive layer will be provided to remove C4 from the fermentation broth (rather than being absorbed into the rumen wall, C4 will be absorbed into the extractant overlay).Feeding strategies impact C4 production in rumens and bioreactors.Co-digestion of food waste (FW) and cow manure (CM) to produce biogas is well studied, but the use of these substrates to produce C4 has not been studied. To determine an appropriate ratio of FW:CM, three ratios of FW:CM (0:1, 1:1, and 2:1) will be tested. After an initial stabilization period, we will monitor C4 production during the "Slow-Mix Ferment" stage to assess the rates and yields of C4 production. Each of the three FW:CM experiments is anticipated to last four months. Detailed analysis of the bioreactor performance will be conducted after two months of stabilization.Samples will be tested for chemical oxygen demand (COD), total carbohydrates (TC), total proteins (TP), total solids (TS), volatile solids (VS), and carboxylic acids. In addition, biomass samples will be collected for 16S rRNA gene amplicon sequencing throughout the reactor experiments to determine the taxonomy of abundant microbes enriched during each experiment. Objective 1.2 Concurrent with Objective 1.2, we will construct and test the catalytic upgrading system. This system will use a photoreforming process that converts C4 into propane, H2, and CO2 with ultraviolet light in the presence of a catalyst. A major advantage of this type of upgrading system is that it does not require an input of H2 and can be operated at standard pressures. The catalyst will be magnetic platinum-doped titanium dioxide@iron oxide nanocomposites (Pt-TNT@Fe3O4) and the Pt-TNT@Fe3O4 will be synthesized via sequential hydrothermal reactions as described by others.Morphology, composition, and doped Pt content of the nanocomposite will be characterized. We will construct a 1 L batch photoreactor consisting of a reaction vessel and UV-A LED lamps to perform the catalytic upgrading experiments. The Pt-TNT@Fe3O4 nanocomposites will be dispersed into the C4 solution prior to feeding into the batch photoreactor. After the completion of C4 to propane conversion reaction, the nanocomposite will be separated by a magnet and washed with deionized water and acetone to remove any attached organics and other impurities from the surface of the particles. The performance of the reusable photocatalytic nanocomposites will be evaluated through C4 to propane conversion efficiency based on the electron equivalents converted to propane. Initial experiments with a 100 mM solution of C4 will determine (1) the ideal mass ratios of catalyst to C4; and (2) the ideal reaction time. Liquid and gas samples will be collected from the bioreactor throughout the upgrading experiments, approximately once per hour. The aqueous phase will be analyzed for carboxylic acids and the gas phase will be analyzed for propane and H2. Characterization results will be used to perform a carbon and electron balance on the system and the different ratios of catalyst to C4 will be compared based on (1) the electron conversion efficiency to propane; (2) the electron conversion to H2; (3) the carbon conversion to propane; and (4) the total amount of C4 consumed. Based on past work performed by others, we will test mass ratios of 0.25, 0.50, 1.0, and 1.5 grams catalyst per gram C4. For each ratio, we will allow the reaction to run until C4 consumption stops. After determining an ideal ratio of catalyst to C4, we will conduct several photocatalytic experiments with fresh batches of 100 mM C4 solution and the Pt-TNT@Fe3O4 nanocomposites to determine how many times the catalyst can be reused.Objective 1.3 After optimizing bioreactor and photoreforming conditions, we will demonstrate the conversion of cow manure and food waste to propane using three steps: (1) fermenting the cow manure and food waste to produce C4, (2) extracting the C4 from the solvent; and (3) upgrading the extracted C4 to propane with photoreforming. These steps will be performed as sequential batches. Using optimal FW:CM ratio based on results of Objective 1.1, we will collect the organic phase for separation of C4 from the solvent by adding NaOH and water. Increasing the pH to 9 will cause the vast majority of C4 to lose a proton and re-enter the aqueous phase. The concentrated C4-water mixture will then be treated via photoreforming to produce propane (Objective 1.2).Objective 2.1Using TEA, we will determine a minimum selling price for propane to achieve a 10% rate of return. Capital, operations, and maintenance costs will be included in the TEA and the facilities will be sized based on Goodrich Farms in Vermont, a dairy operation with 900 milking cows. Capital costs will be included for reactors, piping, and equipment associated with (1) C4 fermentation; (2) conventional anaerobic digestion to produce biogas from the organics left in the aqueous phase of the SBR; (3) an alakine contactor to separate C4 from the extractant; (5) photoreforming of C4 to make propane; and (6) purification of propane. Operation costs will include extractant and catalyst replenishment and any thermal or electrical energy inputs in excess of that provided by biogas combustion. A process model (created with AspenPlus) will be used to size and cost equipment and reactors. One FW:CM ratio will be assumed, and performance of the C4 fermentation will be based on experimental results of Objectives 1.1 and 1.3. Photoreforming process performance will be based on Objectives 1.2 and 1.3, with one catalyst-to-C4 ratio assumed. Catalyst and solvent replenishment will be guided by experimental observations. Performance of the conventional anaerobic digestion process will be based on literature review and account for COD loss from upstream C4 production. Combined heat and power generation thermal and electrical efficiency will be based on typical performance of biogas heat and power generators.Objective 2.2We will also conduct LCA to compare the environmental impacts of the proposed propane production platform to conventional, fossil-fuel dependent propane production. The baseline will consist of two alternate scenarios: (1) propane production from natural gas refining; and (2) propane production from petroleum refining. The functional unit will be per gallon of propane. An inventory analysis will be performed based on the same system (including boundaries) used for the TEA, and SimaPro will be used to estimate the chemical and energy inputs and outputs using commercially available databases. The system will be compared to existing propane production platforms using the EPA Tool for Reduction and Assessment of Chemicals (TRACI) impact categories. The relative contributions of each step of the process will be analyzed to determine