Ashley Belle

Ashley Belle

Several weeks ago, I had a conversation with a farmer about turning organic waste materials into value-added products, and we landed upon the topic of anaerobic digestion.

Anaerobic digestion is a microbial based process where organic waste, such as manures, crop residues, or food waste, is decomposed in an oxygen-free environment to produce methane enriched biogas.

The captured biogas can be used in multiple ways as a renewable form of energy. On the farm, the biogas can be used as a fuel in furnaces or boilers to heat water and barns.

Additionally, biogas can be used to generate electricity to provide barn lighting or sold to the local electric grid. Some farms even clean and upgrade their biogas to remove impurities and carbon dioxide so that it can be injected into the natural gas grid. There is also the option of compressing the methane gas for use as a vehicle fuel.

Besides biogas, there are other products of anaerobic digestion. Post digestion, effluent is discharged from the digester. Effluent consists of undigested solids and liquid.

After solids separation, the liquid can be used as a fertilizer, thus reducing the need for fossil fuel-derived fertilizers. Additionally, the solids can be composted and sold as a soil amendment or reused as bedding material.

With anaerobic digesters capturing methane gas, the technology helps to reduce greenhouse gas emissions associated with the handling of liquid manures.

This is especially important considering methane has a global warming potential 28 times greater than carbon dioxide. When properly operated, a digester can also reduce odors from liquid manures, allowing for homes and farms to co-exist.

One may wonder if anaerobic digestion is a feasible option for their farm operation. Several factors should be taken into consideration. The farm should ensure that a constant year-round supply of manure is available for digestion.

Ideally, the manure should be relatively free of excessive straw and sand bedding, which not only creates clogging in digestion piping, but it also decreases the working volume of the digester.

If one is concerned with being limited by their animal waste capacity, then co-digesting the manure with additional organic feedstocks located in close proximity to the farm can be a solution for making digestion technology viable for smaller farming operations.

Some common co-digestion feedstocks include crop residues and used cooking greases. Some operations even charge tipping fees to receive organic materials, such as food waste.

When properly operated, digesters can produce large quantities of biogas. The farm should survey their energy needs and determine the best usage of the biogas year-round.

In the United States, biogas is most often used for combined heat and power. To ensure digesters function optimally, the farm should also have staff who can devote the time and have the technical expertise.

There are multiple ways to generate revenue streams with anaerobic digestion technology. To learn more about digestion, resources are available through U.S. Environmental Protection Agency AgSTAR, the Natural Resources Conservation Service, or your local Extension office.

Ashley Belle is a University of Illinois Extension environmental and energy stewardship educator.

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