Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste and/or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.
The digestion process begins with bacterial hydrolysis of the input materials. Insoluble organic polymers, such as carbohydrates, are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.
These bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogens convert these products to methane and carbon dioxide. The methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments.
It is used as part of the process to treat biodegradable waste and sewage sludge. As part of an integrated waste management system, anaerobic digestion reduces the emission of landfill gas into the atmosphere. Anaerobic digesters can also be fed with purpose-grown energy crops, such as maize.
Anaerobic digestion is widely used as a source of renewable energy. The process produces a biogas, consisting of methane, carbon dioxide and traces of other ‘contaminant’ gases. This biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. The nutrient-rich digestate also produced can be used as fertilizer.
Let’s Start With Anaerobic Digestion!
Turning Food Waste Into Fuel Takes Gumption And Trillions Of Bacteria!
Using anaerobic digestion technologies can help to reduce the emission of greenhouse gases in a number of key ways:
- Replacement of fossil fuels
- Reducing or eliminating the energy footprint of waste treatment plants
- Reducing methane emission from landfills
- Displacing industrially produced chemical fertilizers
- Reducing vehicle movements
- Reducing electrical grid transportation losses
- Reducing usage of LP Gas for cooking
How to Make a Biogas Plant at Home!
Over the coming winter months I will be experimenting with the building of my own Biogas Plant following the many how-to instructions on both YouTube and the many other sites. We must find out if this small digester can create a usable gas from the water hyacinth.
Here is what I will be attempting:
Cut the top of the larger water tank completely off. This will serve as the digester tank to hold the feedstock. Cut the top from the smaller barrel and fit it, upside down, inside of the larger jug for a telescoping effect. This will act as the dome to capture the methane gas. This barrel system should be fitted on a frame with a flat, horizontal base and a cross-beam at the top to hold the dome in place once it reaches its maximum methane capacity.
Fit the flexible pipe to the bottom of the large tank. This pipe should be a few centimeters longer than the height of the barrel itself. Attach a funnel to the open end. This will be used to pour the slurry, which is the mixture of feedstock and water that ferments to produce the methane gas. The funnel end will be loosely attached to the top of the tank and can be used in case of an overflow.
Fit the outlet valve to the upper section of the larger waste barrel. This valve determines the amount of waste the digester is capable of holding. The spent feedstock can be used in various ways, including as fertilizer for gardens, in compost piles and as a supplement in livestock feed.
Attach the gas outlet to the top section of the smaller, inner tank. This should be placed so it can be attached conveniently to a stove or oven. The outlet valve can be attached to the stove using a flexible pipe. Determine the correct fitting for the stove by consulting the manufacturer’s suggestions.
Load the system with 20kg of waste slurry composed of water and cattle dung. It is especially important that the first load of feedstock is cattle dung because the bacteria in the dung breaks down organic matter to produce the methane gas.
After waiting about two weeks, gas production should begin and be noticeable as the dome begins to rise up from the larger tank. Test the gas to be sure it is combustible. If so, you can begin using other types of feedstocks such as municipal and food waste.