English: A schematic showing the design of a biodiesel reactor for making biodiesel from waste vegetable oil (WVO) or straight vegetable oil (SVO). The image was made based on an image in the book "Practical self-sufficiency by Dick and James Strawbridge"

Producing biodiesel so as to use it in an unmodifyied (modern) Diesel engine is much simpler than converting Diesel engines to run on SVO/WVO (requires changing to indirect injection, heating the fuel, ...) It involves following steps:

1. making the mixture by combining the catalyst with ethanol or methanol. When using potassium hydroxide as the catalyst, you need about 3g per litre of WVO. For the alcohol: when using methanol, you need about 20% of the volume of WVO
2. adding mixture to SVO/WVO in biodiesel reactor
3. heating SVO/WVO + mixture to 60°C using an immersion heater and circulate it (done in a biodiesel reactor)
4. leave to stand for 6 hours (no circulation)
5. drain the glycerol which has formed and sunk to the bottom
6. wash the SVO/WVO + mixture with water in a tank with a fish tank aerator (bubble washing). This is done by adding 1 part water to every 2 parts biodiesel and then turning on the aerator. The washing needs to happen for 2 to 4 hours
7. heat the SVO/WVO in a tank with an immersion heater