Oil-in-Water Testing: The Controversy and its Effects on Produced Water Monitoring in Trinidad
Authors: Maharaj Utam S. , Roodalsingh R. 
Published: December 2007

The traditional method for determination of oil & grease in produced water effluents, ASTM D4281, has been reexamined to select alternatives to Freon, to assess its impact on technology selection, and evaluate its appropriateness as an indicator of polyaromatic hydrocarbons. MTBE/Hexane (15/85 by Volume) was found to be the best alternative to Freon. Analysis of the produced water effluents from our oilfields by ASTM D4281 indicated that high levels of oil & grease were often present; however, to select technology appropriately the physical forms of the crude oil needed to be quantified. In our installations, the major contributor to the oil & grease was the dissolved organics, which suggested that tertiary technologies would be required to reduce the levels.

By correlation of analytical results from sixteen (16) produced waters, the ASTM D4281 Method was found to be inappropriate as an indicator of polyaromatic hydrocarbons which are presumed to be the major toxic components in a crude oil. This was due to the large contribution of the dissolved organics to the determined oil & grease. The dissolved components were found to be largely non-hydrocarbon - phenols and naphthenic acids. These are predicted to have little or no toxicity at the levels present.

Introduction

The ASTM D4281 or its equivalents, such as ASTM D3921, USEPA Method 418.1 and Water and Wastewater Handbook Method 501 have been used internationally to determine levels of oil & grease in water and wastewater streams. This method involves the extraction of an acidified sample of wastewater with a fluoridated solvent such as 1,1,2 trichloro - 1,2,2 trifluoroethane (Freon) followed by determination of the weight extracted into the solvent. The oil & grease quantified is dependent upon the method used in the determination. The chemical species quantified are those which would dissolve in Freon and be non-volatile at 104 C. Compounds that would be accounted for are: paraffins&gt;C7 cycloalkanes, aromatics (excluding benzene and a few of its derivatives), acids, bases, amides, asphaltenes sulphur compounds and some organometallics.

According to Caudle, the USEPA had adopted ASTM D4281 and D3921 as easy-to-use methods which are indicators for the levels of polyaromatic hydrocarbons (PAHs) in a water. These compounds are of major concern due to their toxicity and status as priority pollutants in the environment. Accurate determination of the PAHs in water is quite complex, expensive and prohibitive on a routine basis.

Since the Montreal protocol which dictated the phase out of Freon as a laboratory reagent by the year 1995, ASTM D4281 and its equivalents are being reexamined. This is being done not only to seek alternative methods, but to evaluate its applicability as an indicator for PAHs. The method suffers from the deficiencies of not quantifying volatiles and its inability to identify the nature and quantities of the specific pollutants. It is well accepted that many waters that are described as off standard may not be as toxic as others that are considered within standard. This can lead to situations where operators may incur unwarranted costs in pollution control equipment or fines.

In Trinidad, our laboratory embarked upon the quest for an alternative method to ASTM D4281 and to address the question of the toxicity associated with the various produced waters being discharged into our waterways. In this paper we present the following:Evaluation of Alternative Solvents to Freon for use in ASTM D4281;Assessment of ASTM D4281 Impact on Technology Selection for Effluent Water Treatment;Assessment of ASTM D4281 as an Indicator of Polyaromatic Hydrocarbons and Toxicity of Produced Waters, andInitial work to Quantify and Identify the Dissolved Components in Water Effluents.

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