1a. Objectives (from AD-416)
Our overall goal is to develop a productive, efficient, and sustainable biomass feedstock supply system using perennial grasses and legumes as a primary feedstock. This project addresses critical needs for feedstock development using perennial grasses and legumes by developing innovative ways to fractionally harvest and store these feedstocks. Specific objectives are: 1) design and fabricate new harvesting mechanisms to separate the high-protein and high-fiber fractions from these crops at harvest; 2) quantify the machine's field performance using a controlled set of operating variables; 3) use this information to improve the mechanisms through re-design during the off-season; and 4) collaborate to develop on-farm storage and pretreatment systems to preserve and add value to both the high-protein and high-fiber fractions. Additional objectives in the extended project include: 5) determine storage characteristics of switchgrass & reed canarygrass stored under anaerobic conditions in bunker & bag silos at different moisture contents; 6) quantify packing density, porosity & temperature profile of biomass materials during storage; 7) determine aerobic stability of stored feedstocks; 8) assess composition & bioconversion potential of feedstocks before & after storage under various conditions; & 9) estimate storage costs under different conditions, taking into account storage losses & changes in quality, as well as bioconversion potential of the stored material.
1b. Approach (from AD-416)
Design and fabricate equipment for field-fractionation of bioenergy crops during harvest. Test equipment on established fields of alfalfa, switchgrass, and reed canarygrass. Determine yield and quality of fractions obtained, along with power requirements and operating costs. Improve design of equipment to improve performance, reliability, and operating costs. Store harvested materials under different conditions, and determine dry matter losses and quality changes resulting from storage under these methods. We will also compare the yield and quality of switchgrass and reed canarygrass when stored at different moisture levels in either bag silos (a widely adopted storage technology) or in bunker silos (a potentially lower-cost method that does not generate plastic waste). Conventional measures of silage preparation (packing density, porosity, temperature profiles) will be combined with measures of microbial conversion in the silo (fermentation acid production), and of subsequent bioconversion potential of feedstock after storage to fuels and fuel precursors. Because exposure of anaerobically stored feedstocks to air can cause undesirable spoilage by microorganisms, we will conduct aerobic stability tests to determine if storage method affects the rate and extent of feedstock spoilage, and if different microbial agents are responsible for spoilage of different feedstocks stored under different conditions. We will estimate costs of storage of each feedstock that will take into account the dry matter losses and quality change of each feedstock during storage, and the bioconversion potential after storage.
3. Progress Report
This project provides data on the optimum methods of fractionating, harvesting, and storing biomass materials that are required for meeting sub-objective 2A of the in-house parent project. Research conducted for this period concentrated on anaerobic storage and aerobic stability of moist perennial grasses. Our approach was to direct-cut perennial grasses in the late fall when they are at 35-45% wet basis (w.b.) moisture and conserve by anaerobic storage. This technique offers many advantages over the traditional bale system. Direct cutting eliminates the mowing, raking, and baling operations. The system is less weather-dependent because no field drying must take place. Use of a forage harvester to chop the material produces a value-added, size-reduced product at the time of harvest. Anaerobic sealed storage produces a consistent product at removal from storage. Reed canarygrass and switchgrass were harvested at two moisture contents (~54 and 43% w.b.) in the fall of 2010 and stored in pilot-scale silo bags until late spring 2011. Loss of dry matter (DM) during storage ranged from 2.3% to 3.4%, with an average across all treatments of 2.3%. There was no significant difference in storage losses between high- and low-moisture treatments. Both grasses were removed from storage with uniform moisture through the cross-section and length of the bag. Moisture content at removal only varied 1 to 2 percentage units from the harvest moisture. Aerobic stability was determined during 2- and 7-day aerobic exposure after removal from storage. For the two exposure durations, losses of 1.6% and 2.3% of DM were determined. Lactobacillus buchneri was applied as a bacterial inoculant at the time of harvest to improve the aerobic stability of the grasses. The inoculant was successful in reducing the heating degree days and temperature rise above ambient in both grasses during aerobic exposure. Lactobacillus buchneri also produced significantly lower yeast and mold counts than the control. Inoculation did not have a significant effect on DM loss during storage or aerobic exposure. The harvest and anaerobic storage of moist perennial grasses has been a success thus far. The system offers a longer harvest window, produces a size-reduced material at the time of harvest, conserves feedstock DM well, and is aerobically stable, especially when inoculated with L. buchneri. Progress was monitored through frequent telephone conversations and face-to-face meetings with the cooperator.