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  • Maartje Sevenster

Dutch LCA Sheds Light on Preferred Waste Treatment Method

Fossil oil production can result in large amounts of excess water, with a wide range of geological elements, acids and salts as well as chemicals used in production mixed in. According to Dutch legislation the preferred treatment method for this stream, classified as waste, has to be based on LCA comparison of a range of alternatives, combined with risk and cost assessments. Sevenster Environmental performed such a life cycle assessment, together with CE Delft in the Netherlands, for Dutch oil company NAM.

Oil extraction in the North-East Netherland is controversial. The area is densely populated, certainly by Australian standards, and recent events involving leakage from transport pipelines as well as minor earth quakes due to natural gas extraction have resulted in an understandably negative public opinion when it comes to mining. The waste water is one of the aspects that leads to heated debates. So-called injection of the stream, with or without treatment, into a depleted (oil- or gas-) reservoir is clearly the preferred option from a cost perspective. Injection is widely seen by the community as a form of dumping waste, however, and as an emission into a “compartment” that is not covered by LCA. Therefore, LCA comparison has been viewed with suspicion, even though it is understood that potential containment issues should theoretically be covered by the parallel risk assessment.

It was deemed obvious that LCA would always favour this alternative over alternatives involving several intensive treatment steps, emission of the final effluent to surface water and storage of solid residues in landfill, given that the latter are all covered by LCA.

In practice, it turned out that LCA results are not as clear-cut as one might expect. The energy required for pumping and injection is significant and, depending on technical details, the addition of extra chemicals may be necessary in injection scenarios. Compared to a limited-treatment option, an initial scoping assessment showed that impacts may be comparable. However, the effluent from this treatment would need to be discharged to sea, given the remnant salt content, and this was not an acceptable options for other reasons.

A more detailed LCA comparison of injection and full treatment alternatives, with effluent to be discharged into fresh surface water, showed that the additional energy required for more extensive treatment did tip the balance in favour of injection. Nevertheless, scenario analysis involving technologies in early development showed that the balance may tip the other way once these become available. The indicator results in certain impact categories can be expected to become similar or higher in some of the injection scenarios, e.g. for toxicity and air pollution associated with upstream processes such as production of chemicals. Given that a six-yearly evaluation of available alternatives is part of the permit conditions for production at “Schoonebeek”, weighting will thus become an important issue in the next evaluation, because greenhouse-gas emissions of energy use in the primary processes are likely to be still considerably higher for the treatment-and-discharge alternatives.

In the current study, a single alternative showed the lowest impacts in all but one category. Still, several weighting sets were applied to indicator results to aid interpretation. For medium-ranking alternatives, the different perspectives highlight the trade-off between energy versus chemicals as inputs. While one of the community groups characterized the LCA, risk and cost assessments as “calculating the life out of the debate” - as might be expected in this post-truth era – the outcomes did shed some factual light on an emotional topic. In a letter to the House of Representatives on 12 February, the Minister of Economic Affairs announced his decision to extend the status of injection as preferred method for another six-year period.

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