Biomass is considered anything of organic origin (dead or alive). When biomass is used as fuel is essentially combusted to produce what we call biomass energy. Biomass fuels range from burning wood, wood pellets, biofuels (ethanol or biodiesel), animal manure, corn, municipal solid waste and landfill gases.
There are two ways we can use biomass in order to become energy producing fuel:
The burning of wood for meeting our heating or cooking needs is the most ancient way of using biomass as fuel and the most known that is still used in households even today. For example fireplaces were quite common in houses in the past and can still be found nowadays in many houses.
Another method is incineration. In this case, the most popular biomass fuel used is municipal solid waste (garbage collected by local authorities produced from schools, household, commercial building etc) to get heat and electricity. The problem with incinerating Municipal Solid Waste is that it is not a 100% organic hence it is not a 100% biomass. Thus the MSW has to be properly presorted in order to eliminate harmful non-organic materials from being used as fuel. In addition, various pollutants that might be produced have to be filtered out and the ash left should be disposed properly. On the other hand, there are cases where a plant can use 100% biomass fuel such as the New Hope Partnership plant located in Florida (which is the largest biomass energy plant in the US and has a production capacity of 140 MW) that uses as fuel mainly sugarcane.
Municipal solid waste can also be thermally treated (>700 c) instead of being incinerated to get energy. This waste to energy process, which is called gasfication, causes the waste molecules to break apart and creates syngas which is similar to natural gas thus can produce electricity and a number of consumer products.
The evolution of traditional fireplaces is biomass stoves. Biomass stoves use as fuel various organic materials but the most popular ones are wood pellets and corn (corn does not really go any processing). In the case of wood pellets they are a byproduct of leftover wood materials that cannot be used to produce anything else i.e. branches, bark, leftover paper, sawdust etc. These materials, that can be usually found in sawmills, are processed to create wood pellets that are small in size (typically a twentieth of an inch in diameter with an inch length). The small size of pellets is what makes them easy to be used by the automated feeding system inside the stove.
Finally there are bio-fuels used in motor vehicles where we have two categories ethanol and biodiesel. Ethanol can be produced from corn and it is a form of alcohol that gets mixed with gasoline to produce a greener fuel. Biodiesel can be produced from animal fats and vegetable oils (new or used).
Above is a list of the most common biomass fuels. What should be noted as a great advantage for biomass energy that is produced from these biomass sources is renewable and thus sustainable if used properly (i.e. deforestation to get burning wood is considered harmful biomass energy). Thus proper usage can help us reduce our fossil fuel dependency which has a taken a token on our economy over the past years.