Static Washing

Static or gravity washing is the least aggressive and least likely to generate an emulsion. It is simply placing water and biodiesel in the same tank without any mixing. Contaminates migrate from the biodiesel to the water through the boundary layer over time. This process takes anywhere from 4 hours to 24 hours to saturate the water with contaminates. Most homebrewers will let the static wash continue over night before draining and starting a different technique. It is particularly effective as a first wash for biodiesel from high FFA oils.

The standpipe tank provides two drains at different heights. We make it out of a tight head or closed head drum and attach our plumbing to the bungs in the top of the drum. Then we flip it over so the plumbing is on the bottom and cut out what was the bottom for access to the wash tank.

Some have called it a poor man's cone bottom tank, but it is superior to the cone bottom tank. In fact, a common upgrade for cone bottom tanks is to add a second drain in standpipe tank fashion. The two different heights lets you get a cleaner drain than is possible with even a cone bottom tank. The lower drain lets you adjust the level of the water/biodiesel interface layer to just below the top of the upper drain. The upper drain then after purging will drain perfectly clean. One major advantage is that you can drain the biodiesel cleanly while leaving the wash water in the tank. This lets you reuse the wash water from the last wash again on the first wash of the next batch, thereby saving water.

A favorite wash tank for many is the plastic drum. If you choose the 'natural' color, you will be able to see the biodiesel and water through the drum. Poly drums are easy to find and dirt cheap.

Shown here is a plastic drum sitting on top of a wooden stand. The drains need to be attached to the stand to prevent them from loosening when the valves are operated. This stand has wheels but that is not required.

The typical plastic drum will have two 2" bungs. One bung will be a course threaded butress thread. The other will be standard 2"npt pipe threads. There are two styles of bungs, those with internal thread or "adapter bungs", and those without internal threads. Most drum will have the adapter bungs with 3/4" female pipe threads in them, but if they don't, you will need to aquire some for this washtank.

Washing has always been a bottleneck in making biodiesel. While you can make a batch in a few hours, it can take days to wash it. ProjectPurity from infopop overcame that bottleneck with this standpipe wash tank using a 275 gallon tote. He would make multiple 55 gallon batches loading them into the tote after settling. The tote can wash up to four batches reducing overall production time for the four batches by a week.

Pump washing is a harsh but very effective way to wash biodiesel. In this process the oil and water are broken into much finer particles than in other wash processes which results in a greater interface between the water and oil, and because of this the soap is quickly transferred from the biodiesel to the water. By following these simple steps, emulsions will be a thing of the past even with this aggressive wash method!

One word of caution: be sure your biodiesel is well made; i.e. pass 3/27 without any dropout. Under-reacted oil will contain an abundance of partially processed oil, monoglycerides and diglycerides. These are emulsifiers and will only cause problems, such as emulsions and poor or no water-oil separation.