5% Water Prewash
By Rick Da Tech
The concept is that you add water after the reaction is complete, but before settling has started. This helps the settling process, giving a faster more complete settling. Testing has shown a 30% to 50% reduction in soaps in the unwashed biodiesel. I have seen 95% settling in as little as 30 minutes. The disadvantage is that it introduces water into the processing tank.
The procedure came initially from the University of Iowa. Their process was further developed by a group effort on the internet to provide fine tuning that fit the homebrewing style. The highest yield came from adding 5% water by volume of the original amount of WVO. So for 100L veggie oil you would add 5L of water.
After the methanol / Lye solution is added, continue to mix for an hour before adding the water. You can use the Methanol test for Unwashed Biodiesel to determine when to add the water. Adding the water will stop further reactions and speed the settling process. One easy way to add the water is to put the water in a carboy and feed it in through the methanol/lye mixture input port using the same carboy lid and tubing used for the methanol/lye mixture. By partially closing the main tank valve, it is possible to suck all the water in the tank in just a few minutes. For best mixing it should take about 5 minutes. After the water has been introduced, continue to run the mixing pump for another 15 minutes.
After the mixing pump is finished, shut everything down and let settle overnight as usual. Some claim that since the water aides in separation and you can draw off the glycerin byproduct in just a few hours. You will have more byproduct using this method so be prepared with an extra bucket. The biodiesel will be hazier than biodiesel that has not had the pre-wash due to water in the biodiesel.
If you intend to do methanol recovery then this process will make it more difficult to obtain methanol of high enough purity in one pass through the still.