This project studied the application of biodigestion on small farms to convert organic waste into bioenergy and biofertilizers. The first goal of this project was to measure and analyses potential feedstocks for biodigestion on small farms. These included organic wastes from a local small farm, biodiesel production byproducts, and food waste from local schools and restaurants. The second goal of this project was to demonstrate a functional biodigester to the small farming community. This included both demonstration of biodigestion, as well as biogas storage, cleanup, and usage. To complete this goal, a small-farm-scale biodigester was constructed for demonstration and usage.
The purpose of this project was to study the potential applications of bioenergy and biofertilizer production on small farms. The US EPA AgStar program outlines the bioenergy opportunities in the US for larger livestock operations (US EPA). Bioenergy options, however, are not just for large farms and cities. On the contrary, these emerging renewable energies must ensure economic benefits for family farms and rural communities (Wilkie, 2007). There are many small farms in the US that could produce bioenergy and biofertilizer from the variety of different organic wastes they produce. This project will study these different feedstocks and demonstrate the feasibility of biodigestion on small farms.
The process of anaerobic digestion, or biodigestion, has occurred naturally for millions of years. It is essentially the microbial decomposition of organic material in the absence of oxygen. As the material breaks down, methane is released. Under controlled conditions, this methane can be captured and used as an energy source (Wilkie, 2008). Biogas, as the gaseous product is termed, is composed largely of methane, and is a readily usable fuel that can be burned directly for cooking or heating water. Biogas can contain hydrogen sulfide that can cause problems for equipment using biogas. It may be necessary to remove this hydrogen sulfide prior to use. A simple technique is to use steel wool or iron-impregnated woodchips to scrub the hydrogen sulfide from the biogas. Biodigestion also produces a liquid and solid effluent. Because the bacterial metabolism consumes only the carbonaceous component of the material, the nutrients from the organic material remain within the effluent as a high-quality organic fertilizer (Arnott, 1985). Biodigestion captures both energy and nutrients from organic materials using a natural process that requires little to no input of energy and chemicals.
Nearly any type of organic material can be used as a feedstock for biodigestion. Small farms produce significant amounts of organic wastes, such as culled vegetables, crop residues, processing waste, and animal manure. Currently most of these wastes on small farms are composted, land applied, or hauled off-site. Through biodigestion of these wastes, both the energy and nutrients from the waste are captured and recycled for use on the farm. The variety of organic material available for biodigestion means that biodigestion can benefit every small farm. Along with plant and animal wastes, byproducts of biodiesel production, including glycerol and washwater, are potential feedstocks for biodigestion for small farms that produce their own biodiesel. In addition, organic wastes from the community can be brought onto the farm for additional production of biogas and biofertilizer, including food waste from schools or restaurants or biodiesel byproducts from community producers. The first goal of this project (Objective 1) is to study and analyze potential feedstocks for small-farm biodigestion. In order to accomplish this goal, waste audits were conducted at a variety of locations to determine the amount and type of organic waste that is generated. Samples of these materials were analyzed to estimate methane production potential.
Demonstrating the feasibility of on-farm biodigestion will make great strides towards the implementation of this sustainable technology on small farms in the region. Therefore, the second goal (Objectives 2 and 3) was to construct and demonstrate a functioning small-farm-scale biodigester with integrated biogas storage and clean-up to remove hydrogen sulfide. By giving small farmers the opportunity to see biodigestion with a reactor that can be replicated on their own farms, these farmers will be more likely to adapt this technology.
- Determine biogas potential of various organic wastes produced by small farms.
Demonstrate effective methods of biogas clean-up and storage.
Demonstrate a functioning biogas reactor and storage system to the small-farm community.