Washing

After processing, settle for at least 12 hours, preferably 24 hours, before separating the glycerine by-product and starting with the wash.

Be careful separating the by-product layer from the biodiesel, it's very soapy stuff -- much rather have some biodiesel in the by-product than by-product in the biodiesel when you want to wash it.

If you do happen to get some by-product in the fuel when you're transferring it to the wash-tank, let it all settle again overnight in the wash tank, then add up to a quarter as much hot water, pour it over the surface of the fuel. Do a wash-test -- see Quality testing. If the fuel separates quickly from the water, continue with washing the batch as usual. If not, treat again with hot water, or use a gentle washing method.

We use standpipes to separate the glycerine by-product from the biodiesel (see caption) -- this is the best way, ensuring 100% separation, with all the by-product left behind.

The washing process

Transfer the biodiesel from the settling tank/processor, leaving ALL the glycerine by-product behind. Add water, wash.

Most people use 25% to 50% as much water as biodiesel or more for each wash. We use one-third as much, 20 litres of water and 60 litres of biodiesel.

Take no notice of advice that you have to pour the water in carefully and gently, that you mustn't pour it straight into the biodiesel, pour it against the side of the tank instead like you fill a beer mug or you might emulsify it. If you've used wash-tests to tune your processing and you test each batch before washing, just tip the water into the tank, it won't froth over like beer. Or pump it in through the lid.

The water sinks to the bottom. Proceed with the wash -- use the stir-washing method, see above.

Settle the fuel between washes for as long as you practically can before replacing the water and starting the next wash. Generally, the longer it settles, the more effective the next wash will be.

The first wash water turns white, like milk. Washing is completed when the water is clear after settling, with a pH of 7 (or the same as your tap-water), usually after the third or fourth wash.

Freshly washed biodiesel is often a bit cloudy. It should clear in a day or two. Leave it in a sealed container out in the sun, or heat it to 45-50 deg C (113-122 deg F) and let it cool in a vented container.

If the biodiesel goes cloudy again after it's cooled you probably haven't washed it thoroughly enough. Give it another wash, or if you're in a hurry, heating it to 45-50 deg C a second time might clear it. When it's clear go ahead and use it. See Drying the fuel, below.

If it doesn't clear, it probably needs reprocessing. Try the Reprocessing test and the Methanol test.

Recycling the wash-water

The counter-current method of re-using the washwater reduces water use for three washes by two-thirds.

The water doesn't become saturated with the contaminants it removes from the biodiesel. Instead an equilibrium is reached between the contaminants in the water and the contaminants still left in the biodiesel. Water from the first wash contains the most, with less in the second wash water and less again in the third. Water from the second and third washes can be re-used in washing your next batch of biodiesel. The second wash water is used for the first wash of the next batch, the third wash water for the second wash, with fresh water for the third wash. Only the water from the first wash is disposed of, and only when it has already been used for three washes in three successive batches of biodiesel.

Washing temperature

Washing is generally easier in summer than in winter, and the colder it gets the less effective the washing -- it takes longer and uses more water.

If your processor and wash-tank are in a heated room you shouldn't have any trouble. Otherwise, either heat the biodiesel or, easier, use hot water. Try to get the overall temperature to at least 30 deg C (86 deg F) or more. We use hot water in the winter. It's cheap for us, but it still uses energy, and energy isn't cheap no matter how little you pay for it. We have a Kyocera passive solar water heater, we just have to plumb it in, and then we'll use that.

Emulsions

Oil and water don't mix, and well-made biodiesel separates quickly and cleanly from the wash water when it settles.

But if the biodiesel isn't made properly and the reaction is incomplete it will contain half-processed oil molecules, monoglycerides and diglycerides (MGs and DGs), which are emulsifiers. Emulsifiers are used to make stable mixtures of oil and water, such as mayonnaise. If there's too much of it in your biodiesel, some of the biodiesel or all of it won't separate from the wash water, or at least not quickly, and in some cases maybe not for weeks. You have an emulsion problem.

In fact it's a quality test -- if it doesn't separate, you need to improve your processing (see Quality testing). Properly made biodiesel with good reaction completion will not emulsify.

The first thing to think about is why it happened so you can prevent it happening next time -- make good fuel!

The second thing is how to save the batch. One batch of sub-standard biodiesel won't hurt your motor (though constant use of it will), so rescue your bad batch and use it. Best to mix the bad batch in with better batches in your fuel tank.

A mild emulsion makes a third layer between the biodiesel and the wash-water after your first wash has settled. A paper-thin layer is fairly normal, just go on with the second wash. Thicker layers are not normal. Drain the layer off, with a bit of water and biodiesel on either side, and set it aside to settle, it will eventually separate. Heating it will usually separate it. Then leave it to dry, and add the top layer to your next batch of oil for reprocessing. Meanwhile continue with the second wash, which shouldn't produce an emulsion, or much less anyway.

A severe emulsion is when the entire tankful turns into a third-layer -- it looks like you have a tankful of chicken-soup or dirty-looking mayonnaise.

If you leave it overnight or for 24 hours it will usually separate, and again you'll be left with a third layer in the middle to deal with, as above. It might take longer to separate, several days or a week, especially in cold weather. Meanwhile your wash-tank is full of mayonnaise and you can't wash the next batch.

There are several ways of breaking the emulsion. Heating it will usually work -- 50-60 deg C (122-140 deg F) is usually enough. As with drying the oil before processing, if you use higher temperatures beware of causing steam explosions. Another way is to add hot water to the mix, if there's enough headroom in your wash-tank. The hotter the better. That should at least start the separation process: allow it to settle, drain off any water that's separated, add more hot water, and so on.

Another way is to add ordinary table-salt, sodium chloride. Dilute the salt in water first, add while stirring gently, keep adding until it starts to separate.

This works well to break the emulsion. But salt is an impurity that you should be washing out instead of washing in. It will take more washing than usual to get all the salt out and end up with clear, neutral water. And salty wash-water is not as innocuous as ordinary wash-water, so take care in disposing of it.

A third way is to use some acid to "quench" the wash, which will also break an emulsion. See next section.

Whichever method you used, once the emulsion is broken, continue with the rest of the washes until clear and dry as usual. Now you can use your rescued batch while pondering how to make better fuel next time.

Using acid

Some people say it's a mistake to "quench" the wash with acid. They say that while the acid will neutralize the alkali catalyst, it will also convert some of the soap to Free Fatty Acids (FFAs), which dissolve back into the biodiesel, and which you don't want in your fuel.

We don't use acid in the wash, but many people get good results using an acid quench. Some of them have had their biodiesel analysed, again with good results -- acid-quenched biodiesel can and often does meet and exceed standard specifications such as EN 14214 and ASTM D-6751. It's a normal procedure in commercial production.

Does it in fact convert soap to FFAs? Typical quantities of acid used are: 8 millilitres of 5% vinegar per litre of wash water used (usually a quarter to half as much water as the amount of oil used); 2 millilitres of 10% phosphoric acid per litre of washing water; enough ("not much") 5% phosphoric acid to bring the pH down to 7 (neutral). (Other acids used are sulphuric, citric or acetic, all well-diluted.)

This is how to convert soap to FFAs: Separating glycerine/FFAs. What it says is that for "average" WVO, titrating at 3 ml, you'd need 9.75 ml of 85% phosphoric acid per litre of oil used to convert the soap to FFAs, thus separating it from the glycerine. That's about 50 times as much acid as you'd use to quench the wash, and in the wash it's buffered by all that water too. FFAs? Naah.

But be sparing with the acid anyway.

An acid-quench will also break an emulsion or prevent it forming, which might disguise a processing problem that the emulsion would reveal. Always do a wash-test first! You can "break" an emulsion by slowly adding dilute acid (phosphoric, acetic, citric, or sulphuric, 10% concentration) until you see it start to separate (see "Emulsions", above).

NOTE: When diluting acid with water, always add the acid to the water, never add the water to the acid.

DudaDiesel Biodiesel Supply supplies concentrated acetic acid, citric acid, phosphoric acid and sulphuric acid, buy online: http://dudadiesel.com/.

Wash-water disposal

Wash-water is (or should be!) about as innocuous as the average family's laundry water.

Wash-water may contain the following:

Some biodiesel -- this is poor practice. The best way to avoid it is to use a standpipe in the wash-tank. Or, without a standpipe, when draining the wash-water, stop a few litres short of the interface with the first washes. With the final (3rd or 4th) wash, stop well short of the interface again, and drain the last of the water separately, along with some of the biodiesel. Let it settle in a separate tank. After a few batches' worth, syphon clean biodiesel from the top, dispose of the water.

Biodiesel is not an environmental hazard: US Environmental Protection Agency studies found that biodiesel is "more biodegradable than sugar and less toxic than table salt".

Some excess methanol -- most of the excess methanol is in the by-product, but some remains in the biodiesel and is removed with the wash-water.

The methanol can be reclaimed from the biodiesel, but it takes more energy than it recovers and it probably isn't cost-effective. For more information see Reclaiming excess methanol.

Methanol is poisonous, but only for humans and monkeys. Methanol is not viewed as an environmental hazard. According to the United Nations Environment Programme (UNEP), the International Labour Organisation (ILO) and the World Health Organization joint International Programme on Chemical Safety, methanol is readily biodegradable in the environment, it does not persist or bioaccumulate, it is not toxic to aquatic and terrestrial organisms and it does not have adverse environmental effects. See More about methanol.

The methanol in the biodiesel wash-water is not a problem for a waste-water treatment system -- in fact it might even be an advantage, some of the waste-water digester bacteria like it.

The lye catalyst -- potassium hydroxide (KOH) or sodium hydroxide (NaOH). See Soaps, below.

Sulphur (sulfur) -- if the acid-base process is used, the wash-water will contain some sodium sulphate or potassium sulphate salt. This is innocuous -- sulphur is one of the six plant "macro-nutrients" (nitrogen, phosphorous, potassium, calcium, magnesium, sulfur). It's essential for plant growth, all soils contain sulphur.

Soaps -- lye is commonly used as a drain-cleaner and presents no problems for waste-water treatment systems, and domestic waste-water contains much soap, also no problem for waste-water treatment.

Therefore, with good practices, wash-water can be disposed of as safely as domestic waste-water. Check with your local authority.

But this is treating the wash-water as a waste. There are better ways.

The wash-water can be treated with either magnesium sulphate (Epsom salts) or calcium hydroxide (both common chemicals), which will convert the water soluble soaps (sodium or potassium) in the water to insoluble magnesium or calcium soaps, which float to the top and can be collected. These soaps can be burnt as heating fuel.

The water should then be neutralised with dilute phosphoric acid. Now it contains potassium phosphates or sodium phosphates and can be diluted for use as irrigation water for pastures and fields (it needs more dilution with sodium than with potassium -- see Composting the by-product for more information on soil and plant nutrients).

The water can also be handled safely by means of a simple greywater system. There are many resources on the web to teach you how to do this.

Drying the fuel

When the fuel is clear -- not colourless but translucent, you can see through it, there's no haze or cloudiness -- then it's dry. Actually it's never dry: despite what the standards say, it always absorbs some water from the atmosphere, 1,200 ppm or more, but this is dissolved water, which is harmless, unlike suspended water, which must be removed.

It should clear by itself in a day or so after you separate the final batch of wash-water. Leaving it in the sun will help, or heat it to 45-50 deg C (113-122 deg F) and let it cool in a vented container. Most of the suspended water causing the cloudiness will evaporate off, and a little might settle out at the bottom. Water also condenses under the lid, careful when you take the lid off not to splash it back into the biodiesel. Or let it cool with the lid off.

If it goes cloudy again after it's cooled you probably haven't washed it thoroughly enough. Give it another wash. If you're in a hurry, heating it to 45-50 deg C a second time might clear it.

If it doesn't clear, it probably needs reprocessing. Try the Reprocessing test and the Methanol test. Work on improving your processing to achieve better process completion.

Another method is bubble-drying -- the same as bubble-washing but without the water. Drain the final batch of wash-water and use a bubble-stone and an aquarium air-pump to bubble air through the washed fuel. This will usually clear the fuel overnight. Sometimes it doesn't stay clear, in which case it might need another wash.

The disadvantage of bubble-drying is the same as with bubble-washing -- it oxidises the fuel, and you could have problems with the fuel polymerising unless you use it quickly. It won't pass the European EN 14214 standards requirements. We don't recommend bubble-drying for this reason. Our fuel is clear in a day or two anyway. Yours should be too.

Dry-washing