Of these, burning is the leader by far, with some 86 percent of the collected used oil going up in smoke in space heaters, industrial kilns, boilers and furnaces. According to the U.S. Environmental Protection Agency, however, the preferred option is rerefining the oil for future use.

A California study last year went even further. Both the rerefining and distillation [reprocessing] methods and associated product markets should be strongly supported, it urged, because they are environmentally preferable to the combustion of unreprocessed used oil as fuel.

That position, however, is not shared by NORA, the Association of Responsible Recyclers, the Haymarket, Va., trade group which represents the used oil recycling industry. Earlier this year it approved a blunt statement by industry expert Alan Gressel, saying the California study was an unfair and factually unfounded attack on the use of used oil as a burner fuel alone or blended with virgin oil whose goal was to promote more extensive reprocessing.

Californias peer-reviewed study, authored by Bob Boughton of the state EPA and Dr. Arpad Horvath of the University of California, Berkeley, Department of Civil and Environmental Engineering, employed life cycle assessment (LCA) methodology to look at used oil. Their goal was to assess and compare the environmental impacts and benefit of each management method – rerefining, distillation and combustion.

Rerefining is actually a series of processes, the study pointed out, using flash evaporation to remove light petroleum parts and water, a defueling step to separate gas oils and lube distillate from heavy residual, and hydrofinishing as a final step. The output is a high-purity lubricating base oil suitable for manufacturing automotive engine oil and other lubricants.

Distillation reprocessing methods, on the other hand, include the removal of light petroleum parts and water, and the final separation of a heavy fuel oil from contaminants. The output includes a marine diesel oil with very low ash and sulfur content, and an asphalt flux residual.

More likely, used oil or blended used oil will be combusted. Blending used oil, which by itself is of poor quality, with other fuel oils lowers overall contaminants in the finished fuel to an acceptable level, to meet combustion equipment specifications and emissions limits.

Boughton and Horvath reviewed existing studies and assembled data from two major California recyclers representing over 75 percent of the collected used oil in that state. They employed an accepted LCA protocol, a systematic procedure for classifying and characterizing the types of environmental effects of each constituent, or contaminant, in used oil. From this, they assessed the potential environmental and human health impacts.

The researchers presented their results as ratios of potential environmental impacts on eight categories, comparing used oil combustion with no emission controls versus the alternative processing options (see below). The ratios of each case are near unity for many characteristics, Boughton and Horvath pointed out, [but] are especially high for terrestrial and human toxicity potentials, principally due to heavy-metal air emissions.

Consuming used oil as fuel, rather than rerefining or distillation, results in serious heavy-metals toxic effects, the study calculated. Zinc and cadmium releases to the environment and animals through burning were 150 times that of the other two methods, and the human toxicity impact potential from lead and chromium emissions was more than five times greater. And the potential impact on eutrophication – where a body of water, either naturally or from pollutants, becomes rich in nutrients and deficient in dissolved oxygen, making it less able to support marine life – climbed three times higher in the case of burning, thanks to the significant phosphorus content of used oil.

Given these results, Boughton and Horvaths conclusion was rather moderate in tone. [S]ource reduction and returning used oil to its original intended use are preferred over its use as a fuel, they stated.

Nevertheless, NORA took issue with the studys conclusions. Alan Gressel, facilities manager of Noble Oil Co., a Sanford, N.C., recycler of used oil, made several points on the trade groups behalf.

He applauded Boughton and Horvaths life cycle analysis. For those of us who have spent our working lives recovering lubricants and fuels from used oil, it is gratifying to read an articulate life cycle analysis of some of the available used oil management methods, he noted appreciatively.

That said, Gressel, who has more than 40 years experience in used oil recycling, charged that the report is sorely flawed. The most significant problem with [the study] is its reliance on obviously erroneous assumptions, he wrote.

For example, the California study said that all used oil that is used as burner fuel is burned in small heaters and boilers. This is simply incorrect, Gressel pointed out. In the U.S. over 40 percent of used oil is burned as paving aggregate dryers equipped with baghouses [large air pollution control devices that filter exhaust air through fabric bags]. Most of the rest is burned in lime, cement, light aggregate, and other kilns and in iron-making blast furnaces as well as utility and industrial boilers, all of which are permitted and equipped for the control of particulates and metals emissions.

Likewise, some 50 to 70 percent of the metals present in used oil fuel remain in the combustion unit, even in the absence of emissions control equipment, Gressel said. This condition, not high emission levels, is the prime reason that used oil fuel is not normally used in small package boilers. In the case of asphalt aggregate dryers, 99.5 percent of metals are removed before discharge.

He also pointed out that burning of used oil in small, oil-fired space heaters produces air emission in compliance with Vermonts air emissions regulations. Vermonts regulations are similar to those of other Eastern states.

Gressel added, The study assumes that all used oil is drained from internal combustion engines – which misses the 45 percent of the used oil supply that is generated by industry, and distorts the types and quantities of metals and other inorganics found in the total oil supply.

Responding, Boughton and Horvath reiterated their papers goal for readers to become more aware of the potential for environmental harm considering the large scale of the used oil management system and specific management methods employed.

And they defended their approach. Whether the emissions of a given technology are within given regulatory limits are immaterial to the conclusions of the paper, they argued. Using life cycle analysis methodology allows one to look beyond facility boundaries and account for the complete impact of a management method. It also allows one to compare management methods on a balanced and holistic perspective.

As for combustion, the authors noted, given 99 percent emissions control at large facilities, consuming used oil as fuel may not be a benign process from this overall perspective. Hazardous or not, the impacts from management and disposal of fly ash and baghouse ash or other wastes could be significant but were not included in the paper.

According to API, the two went on to point out, over 110 million gallons of used oil is consumed as fuel in small, used-oil-fired heating systems each year in the U.S. If the heavy-metal emissions are 50 percent controlled for these units, as Gressel states, the combined emissions of zinc from these units would be over 200 tons per year.

That amount, from 75,000 used-oil-fired heating systems in use today, equates to nearly 7 percent of the total zinc air emissions in the U.S., according to the U.S. EPAs Toxics Release Inventory for 2001, and would be dispersed over very large areas, primarily in the northern half of the continental U.S.

The bottom line for Boughton and Horvath? We believe that an important function of the used oil management system in use today is to ensure that the disposition of used oil leads to the lowest environmental and human health impacts. The cumulative impacts on the environment from the large volumes of used oil managed today should be of great concern.