No Excuses: BP-funded Study Suggests Mercury Limits Are Attainable

In the policy arena, politics often dictate the execution of policy. In 2007, the US Environmental Protection Agency (EPA) set a threshold for mercury in wastewater discharge at 1.3 parts per trillion (ppt) as a part of the Great Lakes Initiative (GLI). The low threshold reflected the EPA’s position on the harmfulness of mercury in water supplies.

Despite the federal limit, Indiana regulators granted British Petroleum (BP) a permit to discharge mercury at 23.1 ppt at its Whiting, Indiana refinery in 2007 due to expansion and technological concerns. As part of the permit, BP was required to conduct research on mercury removal technologies. The oil giant funded Argonne National Laboratory to conduct the required study. In a comprehensive analysis of 11 technologies, the authors find that most methods could achieve the GLI threshold on a lab-scale (i.e. very small scale) with varying levels of efficiencies and highlight three methods that warrant greater study. This demonstrates that the 1.3 ppt threshold is physically and chemically achievable by current technology. The study’s results likely led Indiana regulators to reduce the discharge level to 8.75 ppt last September when the company renewed its permit.

In order to conduct a thorough comparative assessment of the mercury removal technologies, the authors designed a strict experimental protocol. All of the technologies were tested on wastewater from one discharge channel at BP’s Whiting refinery. All of the experiments were done in a clean room using a standard testing procedure designed by the EPA. Additionally, prior to testing the efficacy of the technologies, the authors sent samples to an independent laboratory to measure pre-removal mercury concentrations daily for each sample and compared post-removal concentrations to this value.

The wastewater from the refinery contained primarily particulate mercury that can be adequately removed through simple filtration. The authors find that using a filter of size 45 micrometers is sufficient to reduce the level of mercury in the refinery’s wastewater to the 1.3 ppt level. They do caution that the experiments are all done on a small scale within a laboratory and that this method of filtration is effective because of the predominance of particulate mercury (versus dissolved mercury) in this particular wastewater stream.

Since mercury can potentially be present in particulate and dissolved form, the authors measure the effectiveness of the technologies across both forms. They find that varying levels of removal efficiency depend on the ratio of particulate to dissolved mercury in the sample. The authors also highlight three technologies for further study on their potentials for scale-up—ultrafiltration, adsorption or the adhesion of molecules to a surface, and an emerging reactive filtration technology. Ultrafiltration effectively achieved the 1.3 ppt threshold for particulate mercury while adsorption was the most effective at removing dissolved mercury. The most promising of the three is the emerging reactive filtration, which achieved the threshold for both forms of mercury.

Although the entire study focuses on one type of wastewater from a single refinery, there are broad implications for improved wastewater treatment technologies in all industries with mercury discharge such as coal-fired plants and municipal waste streams.

In this single comprehensive study, the authors demonstrate that in the current technological landscape, a 1.3 ppt threshold is achievable, at least on a small-scale. Although no studies have been conducted on the efficacy of fully scaled mercury removal processes, BP and other industrial companies can no longer use technological infeasibility as a justification for pollution. This study adds a new dimension to the conversation between BP and Indiana regulators and will likely impact the requirement of future permits.

Feature Photo: cc/(Dana)