There are many small projects using these oils. For example, McDonald's provides 500 tons of used cooking oil used each year to recycle companies and used to produce bio diesel.
It is quite possible, after settling and using filtration in 1 micron, to use used cooking oil (oil after frying for example) as fuel. These oils are highly oxidized and therefore have better combustion. The main advantage of this effort is to recycle waste from biomass to produce energy to replace fossil products.
However, these oils are highly acidic which presents a significant risk to the engine. Indeed engine oil is alkaline and when in contact with fuel oil, it neutralizes the engine oil and severely degraded its lubricating qualities which may lead to damaged engine. By way of comparison, crude permitted in Germany should not exceed 2% of oleic acid, while frying oils are between 5 and 10% (sometimes more).
It would suits often restaurants and other food companies, which often find it difficult to get rid of their waste oil and which will surely be pleased for this effort, although it is may be illegal according to the regulations on waste disposal which requires removal by a designated agency. However, this oil is in limited quantities, so it is certainly not a lasting solution.
A few factories produce biodiesel from fatty residues such as fish oil. Again, the sources are very limited quantity, but their use avoids local pollution (some of these wastes are otherwise released into the environment) and somewhat improves the profitability of industries.
