Environmental Science & Engineering - www.esemag.com - March 2004
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Contaminating oil in water is okay - as long as it’s not pollution

By Greg Reeves

Right: An on-line hydrocarbon monitoring unit installed on an oil platform in Indonesia.
Left: A benchtop unit to which users can bring a sample.

Industrial oil spills routinely make the news, but oil leaks from cars are far more routine and never make the news. What is it that defines oil contamination as a pollutant versus an acceptable by-product of our standard of living?

A little history may help. Petroleum based oils are a natural resource thanks to the evolution of the planet. Millions of years ago, plant and fish life decayed onto the ocean floor. As they decomposed they became covered with sediment and the natural decay process was eventually halted due to a lack of oxygen. This hydrogen and carbon mixture endured millions more years of temperature fluctuations and pressures within Earth’s crust and eventually formed as a thick goo we know as crude. The crude migrated throughout Earth’s crust and eventually found itself into pockets. Some of these reserves are conveniently located near Earth’s surface where they are readily tapped and used as a valuable energy source.

Under the right conditions, this natural resource will continue its decomposition and return to the eco-system as harmless by-products. If these conditions are monitored and controlled, contaminating oils are not an environmental hindrance and, therefore, by definition, not a pollutant. However, if the conditions are not right, oils can choke the process that is responsible for oil degradation. The result can be damaging to our environment and oil becomes labeled as a pollutant.

Defining oil types and their acceptable contamination levels in wastewater is not an easy task. Crude, in its natural form, is made up of thousands of compound variations. Once the crude is refined, the chemical structure changes which adds even more to the list. Often, these new man-made compounds do not break down as easily into the eco-system as their former structure as crude. There are many groups worldwide that contribute valuable research and data toward the oil contamination debate. The USEPA (www.epa.gov/waterscience), American Petroleum Institute (api-ec.api.org note: no www) and the International Association of Oil and Gas Producers, (www.ogp.org.uk) are three such organizations that offer valuable data on this topic.

Rather than attempt to define a polluting oil by its chemical structure, regulatory authorities tend to tag oil types by their character. Solvent extraction is one such approach to defining an oil’s character. By adding a solvent to a water sample, certain types of oil molecules will attract to the solvent when shaken. When left to stand, the solvent separates from the water, bringing these oils with it. For many years, this procedure was defined by USEPA Method 418.1 which used Freon as the extraction solvent to define contaminating oils. The Montreal Protocol (1992) phased out the production of Freon for this type of use and the new USEPA Method 1664 uses hexane as the extraction solvent.

The solvents are not identical and will draw out different hydrocarbons. As a result, the definition of a contaminating oil has changed. Industry is responsible for monitoring their wastewater contamination levels based on this definition and certain regulated procedures.

The solvent extraction method of measurement is to dry and weigh the oil sample through a lengthy gravimetric procedure. Since the gravimetric procedure is not practical for field use, regulatory authorities do allow correlation techniques. Gas Chromatographs (GCs) and Infrared Absorption (IR) instruments are the typical acceptable correlation methods. While these instruments offer a faster response, they still do not offer a simple and cost-effective approach to routine field measurements and for continuous online monitoring.

Industry tends to be diligent and environmentally responsible with regards to oil in water contamination, whether or not it is for economic, legal or ethical reasons. To meet this demand, instrument manufacturers offer additional alternative correlation techniques to monitor for oil in water contamination. For example, one such technique is fluorescence, which targets the aromatic hydrocarbons in a sample flow to give a relative reading of total oil. This technique does not require solvent extraction and can be used on-line.

These types of instruments do not replace required laboratory reporting requirements. They are designed to support industrial efforts by offering a cost-effective, easily maintained instrument for routine or on-line use.

Efforts to define and support environmental oil in water interests are ongoing. We are surrounded by oil leakage in our daily routine and have become complacent to it. Occasionally a catastrophic oil spill highlights the fact that, as a natural resource, oil quickly becomes a pollutant when mismanaged or altered by man.
Greg Reeves is President of Arjay Engineering Ltd. Contact, e-mail: greeves@arjayeng.com.

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