Interesting 22,00 litres for a voyage, looks to be a small feeder container ship, maybe 1590 NRT, 3,000 DWT, about 3,000 kW. Doesn't say what the length of voyage is, or if the fuel was used for everything or just the auxiliaries. They burnt 22,000 litres of Bio Fuel, maybe 19 tonnes in total and "saved" 40 tonnes of CO2 emissions. However the emissions still occurred from burning the Bio Diesel, it is just that they hope those emissions will be absorbed growing the oil crops for more Bio Diesel. I suppose they would have occurred "naturally" if the oi had been sent to landfill or a sewage treatment plant it would have been broken down to CO2 and Water by being eaten by Bacteria, without getting any useful work out of it.
My understanding is that you can mix up used cooking oil with water and then heat it, all the water soluble gunk settles out with the water and you can skim clean oil of the top that you can use this in older Diesel cars.
To get a fuel that you can use in Modern Diesel Cars you throw some Caustic Soda into the mix and that "saponifies" any long chain fatty molecules. (turns the caustic soda + fat into Sodium Stearate (Soap) and Glycerine. (remember the Fight Club? they were stealing Liposuction fat from the Dumpsters behind the plastic surgery clinics, and boiling it up with Caustic Soda to make fancy soap that the sold to finance everything and then mixing the Glycerine with Nitric Acid to make Nitro Glycerine, to make the bombs, and presumably following Alfred Nobel's idea of mixing the Nitro Glycerine with Fuller's Earth to make a more stable explosive, Dynamite.
I would expect that ships engines could run on that, most of the problems I have heard of have been with rubber seals and gaskets being attacked by the Veg Oil, but in the EU it is mandatory to add a % of Bio ethanol to all Petrol/ Gasoline sold at the pumps and Bio Diesel to all Road Diesel sold. I think there is a % of Bio Diesel in ship's Bunker fuels now.
It is all fascinating stuff, especially as they clear Tropical Rain Forests to plant Sugar cane to make Bio Ethanol or plant Palm Oil Palm trees for Bio Diesel, and by diverting farmland to Bio Fuels drive up the price of food beyond the reach of the Global poor, in order to save the environment, and make rich westerners feel good about themselves, we are pushing poor people round the world deeper into hunger and poverty.
It's a funny old world.
It is always better to ask a stupid question than to do a stupid thing.