Several times over the years, we have received requests for information about what can be done to recycle used motor oil. Though this is not an agricultural question, it is a common issue faced even in remote rural areas. The two-fold question is how to make use of a potential resource and how to avoid contaminating your environment.
After motor oil is used, there are three basic options 1) throw it away, 2) burn it for energy recovery and 3) re-refine it. Traditionally, used oil has often been dumped on the ground, put in the garbage for the landfill, or spread on roads to suppress dust. These are definitely not good options! One gallon of used oil can contaminate one million gallons of water and make it undrinkable—this is a year’s supply of water for fifty people! One pint of oil spilled in water can create an oil slick that can cover an acre.
Oil is regularly replaced in a vehicle because over time it obtains chemical or physical properties that hinder its use as a lubricant, and that can damage engine parts. If these impurities are removed, it can be used over and over again. The most common impurity in oil is water, which can come from leaky engine seals or condensation. Dirt also contaminates oil as it enters through bad seals and engine abrasion. Simple heating can drive off the water, and filtration can remove the dirt. However, the situation is not as simple as that. Chemical additives are included in motor oil to help prevent oil breakdown at high temperatures. Over time, these additives themselves will break down and can produce toxic substances such as xylenes, toluene and benzene. Heavy metals are also often found in used oil. For example, if leaded gasoline was used in the vehicle, there will be significant amounts of lead in the oil because of piston blow-by. Other heavy metals sometimes found in used oil include cadmium, chromium,
Burning used oil is a very feasible option. Both processed and unprocessed oil can be burned. The simplest processing method is to allow the oil to set. Settling and then decanting removes large particles and water so that the oil can more easily be burned (however, settling does not remove heavy metals and chemical additives). In the Middle East, used motor oil is collected and then sold to bakeries and industries (such as glass-making or pottery-making) to heat the ovens. The energy generated by burning used oil averages 144,000 BTUs per gallon. However, the presence of impurities in used oil means that burning it has the potential to produce hazardous air pollutants (metals and oxides). According to the Environmental Protection Agency regulations in the United States, “Used oil may be burned for energy recovery in used oil-fired space heaters provided that: 1) The heater burns only used oil that the owner or operator generates or used oil received from do-it-yourself oil changers who generate used oil as household waste; 2) The heater is designed to have a maximum capacity of not more than 500,000 BTU per hour; and 3) The combustion gases from the heater are vented to the ambient [outside] air.“
VITA (Volunteers in Technical Assistance) have two “howto” Technical Publications called “Waste Oil-Fired Kiln” (by Ali Sheriff and Bashir Lalji) and “Waste Oil-Fired Oven.” Both documents can be downloaded from the following website address: http://journeytoforever.org/farm_library/VITAlist.html
The technical bulletin “Waste Oil-Fired Oven” says that the oven is capable of maintaining a baking temperature of 160190°C (320-374°F) on 0.946 to 1.4 liters of waste oil per hour, depending on the chimney draft. The estimated cost for building the oven (in 1980) was US$25.00 to US$60.00. The design uses a drip-feed system. The oven should be in a semienclosed area with adequate ventilation for combustion.
Both Technical Bulletins contain warnings that we would do well to repeat. Waste engine oil might contain lead from leaded gasoline. The lead could be a hazard to people around the oven, because it would be released into the air as the oil burns. The warning continues: “Users of waste engine oil should have the oil tested to find out if it contains lead. [This is probably not going to happen in remote rural areas.] The baking chamber of the oven should be sealed tightly to keep combustion products away from the food being baked. The oven should be used outdoors or in a well-ventilated place. The chimney should be high enough to carry combustion products well away from the work area.
“Do not use engine oil to fire space heaters [i.e. small heaters not ventilated to the outside] or food dryers. Waste oil from electric transformers should not—repeat, not—be used as fuel in any circumstances. Transformer oil contains polychlorinated biphenyls compounds. PCB is highly toxic and should not be burned [or even handled] at all. If you think your waste oil supply might come from electric transformers, do not take chances. Do not burn the oil.”
Special space heaters can also be purchased specifically for burning used motor oil. This is usually done on a relatively large scale. Most such heating units are purchased by mechanics that collect oil from the engines they service. The uncle of one of our former technical staff has a unit which heats his home and water through the long cold winters of the northern US, so smaller-scale units are available, but expensive. Heaters for used motor oil cost US$2,000-15,000 and burn thousands of liters of oil a year. However they can be a good investment in certain cold climates. Savings on fuel can pay for the stoves within a year or two. If there are cool highland regions in your area and this idea is of interest to you, we suggest you contact:
North West Industrial Equipment, LLC 22023 70th Ave. South Kent, WA 98032 http://www.oilburners.com/
A third option for used oil is to re-refine it. In this process, the components of used oil are cleaned and separated into light hydrocarbons (used for fuel), a base lubricating oil, a heavy product sometimes used as an asphalt extender, and some waste. Re-refining oil requires one-third of the energy (compared to refining paraffinic crude oil) for an equivalent volume of oil. However, re-refining oil is definitely not a low technology means of cleaning motor oil. It is estimated that you need some 25 million gallons a year to justify the expense here in the United States.
More information online at http://www.recycleoil.org/ American Petroleum Institute.
Dunn, E. and D. Berkelaar 2006. Used Motor Oil. ECHO Development Notes no. 93