ANAEROBIC CO-DIGESTEr 101
Myth Vs Reality
What is anaerobic digester (AD)? how is it different from a co-digester?
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ADs use microorganisms, heat, and oxygen-free conditions to break down organic material in order to stimulate methane production.
- The additional methane produced by ADs is trapped and used as either heat or energy from the farm (biogas) or is refined for use as a substitute for natural gas (biomethane or renewable natural gas).
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In the context of farms, most ADs take only animal manure. These are called manure-only digesters.
On-farm co-digesters mix manure with a number of inputs from outside the farm including food waste which can include various types of institutional food waste (expired food from grocery stores, scraps from schools, nursing homes, prisons and more) and industrial food manufacturing waste (pet food manufacturers, food processors, slaughterhouses, breweries, and more).
What is Digestate?
Digestate is the waste product from ADs. The nutrient content and quantity of the digestate will vary depending on the inputs used during the digestion process. The more inputs are added, the less predictable the impacts of digestate can be for crop production, the environment, and public health
If a“screw press” is used, the digestate can be separated into dry and liquid fractions.
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Liquid digestate- kept in lagoons until used for irrigation water on fields or immediately spread on fields as a "soil amendment"
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Solid digestate- stored in a solid form until it can be used as animal bedding or spread on fields