Abstract
In a joint Industry program, the composition and the environmental risk of produced water discharges on the Dutch Continental Shelf was investigated, along with the investigation of existing heavy metal removal technology potentially suitable for offshore application. On fifteen gas platforms and four oil platforms on the Dutch Continental Shelf samples have been taken of produced water, which subsequently were analyzed for general physical/chemical waste water characteristics, oil and oil related compounds, mono- and poly-cyclic-hydrocarbons, other organics, heavy metals and radionuclides. The environmental risk of produced water discharges was evaluated on the basis of acute toxicity data from bio-assays, of data of individual compounds, fate determination and bio-accumulation. Finally, existing/proven technology capable of reducing volatile hydrocarbons (BTEX) and/or heavy metal content from produced water and that was potentially suitable for offshore application was investigated.
The following conclusions can be drawn from the program results:
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the general composition is presented in table 1;
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the concentrations of chemical constituents in gas produced water are considerably higher than those in oil produced water;
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gas produced water may be considered as moderately to practically non-toxic, according to the GESAMP* classification;
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acute toxicity expressed as median lethal or effect concentration may vary over more than three orders of magnitude;
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a dilution of 3.000 is required for gas platform produced water to attain the lowest 96-hr no-effect-concentration for the acute toxicity for the most sensitive species;
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for gas platform produced water the dilution of 3.000 will be reached within 7 mins. at a distance of 50-300 m from the point of discharge.
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no existing suitable technology for heavy metal removal was identified;
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for removal of BTEX, air stripping seems to be a promising method.
* Joint Group of Experts on the Scientific Aspects of Marine Pollution.
