Anaerobic digestion (AD) is another important process for recycling of organic waste streams. The technology is based in the natural digestive system of animals, utilizing anaerobic microbes that live in environments without oxygen. These are some of the same organisms what thrive in landfills, belching our methane gas, but in AD the process is controlled to maximize their productivity and capture the gases produced for further use. This process has been practiced in Asia for centuries as a source of cooking fuel, implemented widely at an industrial scale in Europe and more recently being adopted here in North America.
The valuable outputs of AD are:
· BIOGAS, a mixture of primarily Methane (CH4), Carbon dioxide (CO2) and Sulphur Dioxide (SO2). Methane is recovered to be used for energy production, by either burning it or passing it through a fuel cell. Carbon dioxide can be recycled as a biogenic source for use in industrial and beverage applications.
· LIQUID DIGESTATE, is used as a nutrient rich organic plant fertilizer
· DIGESTATE FIBER, is the solid portion of undigested material, mostly composed of cellulose and lignin, from plant fibers which decompose at a slower rate. This carbon-rich material is often used as animal bedding but can also be further composted.
There are two broad classifications of AD, the most common is the MESOPHILIC “wet” process that uses a concentration of water and takes place at lower temperatures, like an animal’s body temperature. This approach is often used to process animal manure, agricultural wastes and sewage.
The other approach is THERMOPHILIC “dry” digestion that occurs at higher temperatures with much lower moisture content. The process tends to have faster turn-over times, higher gas output, greater material decomposition and requires less space. This approach is more commonly utilized in municipal solid waste processing where it has been used to generate cleaner, renewable fuel for collection trucks.
Both composting and AD play important roles in organic waste mitigation and recycling though each has an advantage with different feed stocks. You can learn more about innovative companies providing AD solutions here:
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