Anerobic Digestion
Anerobic Digestion is a sequence of processes by which micro-organisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.
Key Concepts
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Hydrolysis: The first stage of anaerobic digestion, where complex organic molecules are broken down into simpler compounds by enzymes.
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Acidogenesis: The second stage of anaerobic digestion, where simple compounds are converted into volatile fatty acids and other organic acids by acidogenic bacteria.
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Acetogenesis: The third stage of anaerobic digestion, where organic acids are further converted into acetic acid, hydrogen and carbon dioxide by acetogenic bacteria.
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Methanogenesis: The final stage of anaerobic digestion, where acetic acid, hydrogen and carbon dioxide are transformed into methane and carbon dioxide by methanogenic archaea.
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Stillage: A colloquial term used to describe the spent grains and liquids that are present after distilling spirits. Distillery stillage has high levels of nutrients such as nitrogen, phosphorus, potassium, and also of total solids, total dissolved solids, total suspended solids, sulfate, and iron.
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Digestate: The solid and liquid material that remains after anaerobic digestion. It contains valuable nutrients and can be used as fertilizer or compost.
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Biogas: The gas produced when bacteria break down organic matter. It is mostly methane and carbon dioxide and can be used for various energy purposes.
Closed Loop Systems
The best way to explain what an Anerobic Digester does, other than produce methane, is that it creates a Closed Loop System. The term is slightly self-explanatory but to understand exactly what that means let's start at one of the steps in the food production process and work forwards.
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Crop fertilization is an important step to growing food, farmers use NPK (Nitrogen, Phosphorous, and Potassium) to increase the yield of their crops but the problem is that these minerals and others like Sulfur, Magnesium, and Zinc are disappearing from the ground that farmers use. This is the first solution that AD systems can solve; liquid fertilizer is a byproduct of AD which can then be used on crops instead of using commercial fertilizer that is often mined from the ground.
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The need for increased food production is imperative as our population reaches 8+ billion people, food scarcity is not that much of a problem in the United States but that is because our forebearers worked tirelessly to ensure such a reality. The changing climate is most certainly a threat not only to our country but to many others. But once you get that food into the hands of the general population, what happens? Well in the US, about 40% goes into the bin and the rest gets... "processed" before going into the sewer system.
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Anaerobic Digestors come to save the day, just add microbes and heat.
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Fertilizer and sterile solid waste are byproduct of AD systems which can be re-sold to farms or other businesses that find use for such products.
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Once that fertilizer is used to creates new feedstock for use at a distillery and the cycle repeats itself.
Ecological Impact
Methane is over 80 times more potent than carbon dioxide, dairy operations are abundant with producers of the gas, so we might as well use that resource to help the environment rather than harm it. Stillage produces less methane but also produces a number of other problematic compounds including CO2, Sulfur Dioxide, and a number of Oxides of Nitrogen.
The amount of methane that is removed from the air by anaerobic digestion depends on several factors, such as:
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The type and amount of organic waste that is digested.
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The design and efficiency of the anaerobic digester system.
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The quality and use of the biogas that is generated.
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The alternative fate of the organic waste if not digested.
According to one estimate, anaerobic digestion could reduce global greenhouse gas emissions by 1.3 percent by 2050. This would be equivalent to avoiding about 2.3 gigatons of carbon dioxide equivalent emissions per year.
Financial Impact
While Anerobic Digestion does not completely eliminate stillage it will allow distilleries to greatly reduce operational costs and waste production. There are plenty of other systems that can be integrated into the AD system in order to achieve complete elimination of waste. As great as sharing information is sometimes you have to keep some secrets if you want to know more about the financial impact of an AD system you are just going to have to talk to MegaWatt's team!
