Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7b. Ex Situ PFAS Treatment Approaches

Formatted Title:

Lessons Learned from Treating over 900 Million Liters of Mine Water to <0.0002 µg/L for the Sum of PFAS: A Mining Site Case Study from Western Australia

Background/Objectives:

Decades of aqueous film-forming foam (AFFF) usage in mine sites across Australia in conjunction with limited access to water, forcing operators to rely on systems for reuse of surface and groundwater runoff, has expedited the plume expansion resulting in widespread contamination across vast areas of mining sites. As regulation has developed, local authorities and the mine operators have sought to ensure the runoff from these mine sites does not contaminate nearby drinking water catchments with per- and polyfluoroalkyl substances (PFAS).

Influent total PFAS levels were typically within range of 0.570 µg/L. This confidential mining client’s site exhibits a prime example of widespread PFAS contamination that poses a significant risk to ground water runoff, with the client operating a network of basins, sumps and storage ponds to effectively capture and contain all surface run off from the mine operations.

This risk profile has paved the way for the development of PFAS treatment systems capable of treating to the 99thpercentile level of protection set out by the PFAS National Environmental Management Plan (NEMP) 2.0, ensuring the reuse of effluent water from the system that is safe to be spread across the large expanse of the mine. The mine’s owners and the regulator nominated these stringent effluent criteria to ensure they operated far beyond the minimum requirements for the 99th percentile level of environmental protection.

Approach/Activities:

In 2020, SciDev constructed and commissioned a PFAS water treatment plant (WTP) designed to remove to <0.0002 µg/L for the sum of PFAS (based on 28 PFAS analytes).

By sampling for 28 PFAS analytes, as opposed to the three (3) regulated compounds in NEMP2.0. In doing so, SciDev was required to develop a system capable of treating water far beyond existing established treatment technologies that could remove PFAS to below the stringent criteria set out in NEMP2.0. The modular plant utilises a tailored water treatment approach, implementing multiple treatment concepts to create an efficient, effective and reliable process with proven capabilities. Clarification and chemical pretreatment are utilised for solids removal, reducing long chain PFAS, co-contaminants with the potential to foul downstream processes.

Measures were taken during the lab trials phase to ensure more than 300ML water treated per media change, to reduce operational costs to the client and overall environmental impact through a reduction in waste. The WTP used different configurations of highly sensitive ion exchange and adsorptive filtration media to remove contaminants. Efficient usage of this media is critical to maintaining performance and ensuring operational cost compliance.

Results/Lessons Learned:

To date the PFAS WTP based at the operator’s mine site in Western Australia has treated over 930 million liters of PFAS-contaminated water to <0.0002 µg/L for the sum of PFAS.

Reduction of waste outputs and improved operational costs were achieved via recycling spent ion exchange resin. Ion exchange resin despite reaching its capacity for short-chain PFAS removal still can offer very significant performance for long-chain PFAS removal if positioned upstream within the treatment train. This allows the maximum holding capacity for all media in the system to be achieved without compromising the overall performance.

Data monitoring and inter-stage sampling analysis enabled the operators to forecast and predict the breakthrough point so that maximum efficiency was achieved. The deployment of a robust pre-treatment clarification and chemical dosing stage upstream of the adsorptive media was critical and resulted in a significant removal of long-chain PFAS and other co-contaminants. Many PFAS removal sites have struggled with longevity of adsorptive media and ion exchange resin. The lessons learned from this project will demonstrate how to achieve the maximum potential from adsorptive media solutions.

The presentation will include a strong focus on the quantification of the effect of upgraded pre-treatment processes for the plant and will include correlated time and volume-phased evidence of the impact these treatment processes have. Reliable data was collected over several years of operation. Additionally, the presentation will discuss the advantages of multi-stage plant design and provide results on volume reduction and the PFAS loading throughout the life cycle of the adsorptive media and ion exchange resin.

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Dr. Adam Farahani