Filtering waste vegetable oil
Preparation
Waste Vegetable Oil (WVO) contains different contaminants including food particles, water, Free Fatty Acids (FFAs) and animal fats. Many of these contaminants can be separated before the actual filtration stage in a settling tank. Oil is generally pre-treated in this way for about three weeks, though this settling process can be accelerated by pre-heating the oil to about 60°C. The animal fats, water and much of the food particle contamination will slowly sink to the bottom. The good oil can be extracted from the top of the tank and pumped into the filtration unit.
Note that filtration alone cannot remove Free Fatty Acids or other chemical or biological contaminants.
Filtration equipment
Home built filtration plants use cylindrical 5 or 10 inch filter cartridges, due to their low cost and easy availability. Several are placed in series, with gradually reducing micron filtration grades. These are described as 50/10/5/1 or similar, denoting an initial 50 micron filter followed by 10 micron all the way down to 1 micron. Such systems are usually driven by an electric pump such as the TAM105.
Industrial systems use much larger filter cartridges and even bank many filters in parallel to improve throughput, using an air driven pump to push the oil through.
Filter cartridges are typically rated at pressures of between 0.8 - 6 bar, so thus care must be taken not to exceed the pressure rating for the cartridges used in the system. This can be done by means of a bypass on an electric pump, or direct control of air flow to an air driven pump.
The waste oil can be also heated to about 40 degrees C for faster flow, but again, care should be taken as cartridges are even more prone to failure when hot.
