Suitable materials for the anaerobic fermentation process have a high volume of organic substance. These products come not only from the livestock or agriculture industry but also from the food industry and the organic fraction of municipal waste. Some studies show that the transformation of all available waste into biogas/biomass could produce 8 billion m³ per year of bio-methane, equivalent to about 25 TWh of electricity per year.
The most common types of biomass used for energy production are the following:
Pig slurry: The solid substance in this manure is between 1-6%, depending on the type of breeding. The sewage of a pig of 100kg can produce approximately 25-35 m³ of gas per year.
Cattle slurry: The dry matter varies from 8-15%, depending on the type of farming, the amount of straw used, and the waste collecting system, with or without water use. The sewage of a 400kg dairy cow can produce 200-300 m³ of gas per year.
Poultry manure: This type of manure is difficult for production because it has aggregates that settle at the bottom of the digesters, and a high concentration of ammonia that inhibits the process. However, since chicken manure is easy to collect, some farms use such waste for the production of gas with excellent results. This biomass has a high total solids content of 18-20% and for this reason a horizontal digester is the most suitable to effectively treat the matter.
Energy crops: In recent years have been many studies on cultivation specifically for the production of energy in the anaerobic process. Some crops belonging to the grass family not only offer high yields but also grow and spread faster. These crops easily fit different types of soils and have a high percentage of dry matter. The use of these crops can reduce agricultural overproduction, which in recent years has led to a lowering of prices. Uncultivated, recycled, or water irrigated areas can be used to grow energy crops.
Crop residues: This category includes agricultural products such as fruits, vegetables, low-quality forage, and straw from silos. Crop residues are excellent components for the anaerobic process when added to animal manure in cogeneration.
Foods industry waste: Processing of agricultural products creates large quantities of reusable waste in anaerobic digestion, including whey, slaughterhouse waste, fats, fruit juices and liquid products of the distillery. These materials can be added to the slurry, increasing the energy yields and producing fertilizer.
Organic fraction of municipal waste: Business such as restaurants, wholesale markets, and retail stores result in 25-35% of the total wet component of all the municipal waste. This material has a high percentage of humidity (about 65%) and decomposes quickly. Thus it is suitable for the anaerobic process, producing a high economic return from the gas and fertilizer.