Filtering Waste Oil Before Conversion To Biodiesel

Ways To Prefilter Oil When it comes to pre-filtering oil, the SVO folks are the experts, regularly filtering down to 5 and even 1 microns. If oil is first filtered to 10-30 microns then heated to about 80-90F and held there in an insulated drum for 8 hours, the top 2/3 will be water free. Co-ops tend to heat the oil first and filter while hot using pumps for speed. Some will use centrifugal separators, again for speed. Centrifuges may also hold promise for removing FFA’s. Most individuals, however, seem to be using gravity filtering the oil before heating and settling because of the ultra low cost and simplicity.

The Bag Filter
Bag filters are what they sound like, a bag used to filter fluids. They come in many materials, sizes and filtration rates. These filters are most commonly gravity feed. They can generally be found for under $5.00 each. There are numerous sources for bag filters, just search for them on the Internet.

The Cartridge Filter
Cartridge filters include both spin on filters and filter elements housed inside more permanent housings. A pump usually feed these filters. Most do not work well with gravity feeds. These units typically cost from $5.00 to $50.00. Racor and Goldenrod brands seem to be favorites among the SVO crowd for the final filter.

Blue Jean Filter
This one is for the packrats and scroungers. Take an old pair of jeans, sew up the bottoms of the legs. Cut two holes in the top of a drum and drop one pants leg in each hole. Each pant leg will hold about 5 gallons. Blue Jeans alone are not enough, but they get the big stuff that would quickly clog more expensive filters.

Filter in stages
To keep from clogging up your filters, filter through progressively finer filters. Start with 100 –200 micron, Then go to 50 micron and finally through a 10 micron filter. Some make these three different filtering stations, such a screen mesh then bag filter then cartridge filter. Others will put three bag filters together the coarse inside the fine for a single filtering station.

Bag Filter Housings
Commercial Bag Filter housings are rather expensive, but some have been lucky to find them second hand. Others wanting to use a separate housing will make their own from PVC pipe like the ones used in the original water heater processor by Dale Scroggins.
original water heater processor by Dale Scroggins.

The Water Cooler Method
The Water Cooler Method is a way to regulate the flow of WVO into a filter bag that allows unattended filtering. Cut a 6” diameter hole in the top of a 55-gallon drum. This is the “goes in” spot for the oil. Obtain a 5-gallon plastic water cooler bottle. Pour one cubee of room temperature WVO in it using a funnel. Remove the funnel and put the top of the bottle into the bag filter hole. This arrangement will feed the bag filter just exactly the right amount of oil, bubbling like a water cooler every time it feeds a little more oil.

This method works even using larger tanks separated by distance. The key is the exchange of air for oil at the top of the filter bag.

Bucket Bung
Unattended filtering is really big with the SVO folks and here is another way. Cut a hole in the bottom of a 5-gallon bucket about 2” from the edge. Insert a PVC pipe adapter (male threads /female slip fit) into the hole after removing the female half of the adapter leaving a shoulder. Slip an O-ring over the threaded part of the adapter sticking out the bottom of the bucket and secure that with a female threaded coupling. Apply some PVC glue on the inside of the bucket around the fitting to ensure a good seal. You now have a bung on the bottom of your 5 gal bucket. If your bung is small enough it will fit inside the bung on the top of a 55-gallon drum. Inlay a filter or use as a funnel.

The Cubee Drip
Cut a “V” notch in the spout of a cubee about ?” deep. Screw the lid back on to form a drip valve. Lay it on it’s front on the filter drum with the spout over the bag filter. Adjust for very slow drip. Tighten cap to slow drip. Loosen cap to open valve. A 55-gallon drum can hold 3 cubees over your filter(s). This method also keeps the crud in the bottom of the cubee out of the filter. It works best with cubee’s that have settled for a while.

All of the above tricks and tips and many more can be found in the Suggested Reading Links below.