Water Washing WVO with Baking Soda



bsTim has been adding baking soda to his WVO wash water for the last six years. Most pretreatment methods work better with clean, dry oil, but this one works just as well, if not better, on nasty rancid WVO that most people avoid. Tim’s process involves three basic steps. First, he introduces the baking soda into the oil for a chemical reaction, second, he lets the products of the chemical reaction settle out, and third, he filters the oil in his filter cart.

To get the chemistry started, he adds one pound of baking soda to a cubie of fresh water. The mixture is poured into a clean drum after the baking soda has completely dissolved. Then, freshly collected oil is added to the drum stopping about 4 inches from the top. A paint stirrer powered by an electric drill mixes everything into a creamy peanut butter looking emulsion. At this point, the oil is heated to 100°F and kept there until it is time to transfer it to the filtration cart.

Baking soda neutralizes the acids in the oil, giving off CO2 gas as it does. The CO2 rises to the surface, taking bits of food particles and other trash along with it to form a doughy scummy mat on top of the oil. The bubbling keeps everything mixed while it is still neutralizing acids. After about 7-10 days, it stops bubbling, and the mat slowly settles to the bottom.

Once the bubbling stops and the scum layer goes away, watch for the water and oil to start to separate. A layer of clean oil should appear over the peanut butter colored mix after a day or so. If this separation has not begun by the second or third day after the bubbling stops, stir in 4 cups of dry all-purpose flour. The flour absorbs some water, and the separation should be underway by the next day. It takes another week for the water-soaked crud to settle to the bottom, and clean oil to rise to the top.

This clean oil on top is moved to the filtration cart, leaving the settled crud behind. Inevitably some of the scum from the bottom is transferred to the filtration cart, so Tim lets it settle overnight and drains the water from the bottom of the filter cart before starting the filtering. He moves the nasty stuff left behind in the wash tank to another drum for more settling. Once there is a full drum of the settled scum, it is put in cubies and taken to a landfill.

Tim buys his baking soda bulk to reduce expenses. Baking Soda and Flour together add just over a penny per gallon to the cost of processing, bringing his price for clean, dry, filtered oil to about ten cents per gallon. The baking soda process outperforms washing without baking soda. It removes bad odors from the oil, is less work, and filters last longer with the baking soda wash process. Not to mention clean up time is almost eliminated.


Tim's Filter Cart

The Filtration Cart

The filtration cart Tim has been using for the last eight years consists of a barrel, four whole-house plastic water filter housings, and a small 12-volt DC Shurflo diaphragm pump, all mounted on a cart with wheels. The pump moves oil through the filters at about 1/2 g/m. It has the dual purpose of final filtering and drying.

The first housing is just a strainer that uses one of the filter cores with about a half inch of dry paper towels wound around it, this catches the chunks, extending the useful life of the 20-micron filter next in line. The second, third, and fourth housings use 20, 10, and 5-micron filter inserts respectively. He circulates each barrel of oil through the filter bank for at least 72 hours.

The output of the last filter is discharged back into the top of the drum through a 3/16 reducing bushing to dry the oil. The restriction acts as a nozzle and speeds up the stream of oil and pulls a lot of air down into the oil. The bubbles increase the surface area of the oil and mix the oil, both of which increase evaporation (Headspace Desiccation) of the water. The top of the barrel has to be open to the air, so the water vapor can escape. Since it is outside, a lid is needed to keep out the rain. It is held up above the top of the barrel with a couple 2 X 4s set on edge.

The pump to run at about 30psi when the filters are new and clean. As the filters start to clog, the pressure rises on the pump. The pump automatically shuts down when the head pressure reaches 120 psi to prevent things from blowing apart. Once the pressure drops to 80 psi, the pump clicks back on, pressurizing the system again. The stock pump comes with a switch that cuts off the motor at 60 psi. Tim replaced it with a pressure switch salvaged from an air compressor to get the higher pressures he uses. Shurflo offers a similar pump that switches off at 100 psi. They are available on the internet for about $20 more than the 60-psi version. The 60-psi pump can be adjusted up to 75 or 80 psi, and the 100-psi pump can be adjusted up to almost 120 psi. Replace the micro-switches when they eventually wear out with something sturdier, like Tim's air compressor switch.

He heats the oil using two 240V 4400W water heater elements. They are wired in series and supplied with 120V power to give them 550W total power consumption. Tim has brazed a couple of water heater element adapters, low on the drums for mounting the elements. A water heater thermostat maintains the oil temperature at a constant 100°F the whole time the pump is running. An exercise mat wrapped around the drum holds up well to oil spills and helps keep the oil warm during filtering and drying.

  Click on the pictures to enlarge.


The Filter Bank

The filter bank is made of cheap whole-house plastic water filter housings made by "Omnifilter" (part no OB1), and are about $15.00 each at the local Menards home improvement store. They are a blue plastic with 3/4 inch pipe fittings for the in/out ports. The housings are pressure rated for up to 125 pounds. They start to leak past the plastic "O" ring seal in the screw-on housing threads at about 130 pounds pressure. They have survived filtering oil as hot as 200°F for days with no problem.

The plastic threaded in/out ports can crack or split when you tighten them enough to keep them from leaking at 120psi. So they need to be strengthened by adding a 3/4-to-1/2 inch plastic pipe reducers to the ports. They make the sidewall over 3/8 inch thick and eliminates all the cracking problems. Start by running a 3/4 pipe tap through the original threads of each filter such that the square shoulder at the bottom of the original threads is reamed away and replaced with deeper, NPT threads. Use epoxy glue as a thread sealer on the outer 3/4 inch threads of the adapter, this works as a sealer as well as adds a tiny bit of strength. The epoxy does not stick to the plastic, so there is no problem if you need to take things apart. To prevent deforming the adapter with a wrench or pliers, screw a short 1/2 inch steel pipe nipple in the adapter before starting. Remove the steel pipe nipple and saw off what sticks out and file everything smooth with the original housing to bring it back to its original width. Use 1/2 inch plastic pipe close nipples to couple the filters together.

The filters are a "depth" type filter media and are designed to operate under pressure, but oil leaks past the ends of the filter elements at pressures above about 30 pounds. So another modification is needed to seal the leak. Fabricate 2-1/4" O.D., 1" I.D., by 3/8 thick felt seals for both ends. These are quickly made using hole saws in a drill press. The felt seals should last indefinitely, so you only make them once. They do tend to get stiff with particulate so make several sets. When you change filters, drop the used seals into a jar of water that has as much baking soda as possible dissolved in it. Over a few days, the baking soda converts the hard stuff in the felt into soap. Just squeeze some fresh water into the seal, to make it as good as new.

Once the ends are sealed, some filters collapse under the high pressure as they get close to being fully clogged. To prevent collapsing a filter element, add plastic inserts down the center of each filter element. They are 8 1/2 inch long sections of 3/4 inch PVC plastic water pipe that are drilled full of 1/2 inch holes.

eBay is a cheap place to buy the filter inserts in bulk, 50 filters of mixed micron rating are available for around $1.50 each including shipping. Tim gets at least 500 gallons of washed oil through each set of filters. The filters only last for about 150 gallons without his baking soda and water wash.

Click on the pictures to enlarge.


Related Links:

infopop baking soda thread

Infopop thread detailing filter mods