Global Perspective on PFAS Immobilisation in Soil

A Global Perspective

Immobilisation is now an accepted option for the remediation of PFAS in soil worldwide. Below is a simple guide to the process, supported by recent presentations on the topic by global experts Jurgen Buhl, Cornelsen, Germany and Dr Richard Stewart, RemBind, Australia and a Case Study by Dr Ben Keet, Geo & Hydro-K8, New Zealand.

What is Immobilisation?

Immobilisation refers to the use of powdered sorbents to bind up PFAS contaminants in soil to prevent them leaching into groundwater where they can cause harm to human health and the environment.

How does it compare to other remediation options?

According to recent studies, immobilisation is considered the most viable, mature and cost-effective technology currently available for the remediation of PFAS in soil.

Other remediation options include soil washing, which involves removing the PFAS by washing the soil with water and then treating the PFAS contaminated water separately, and thermal destruction, which involves sending the soil to an offsite facility and heating it up to high temperatures to desorb and destroy the PFAS.

What are the practical steps involved in immobilisation?

Sorbent Selection

The first step in the immobilisation process is to select the right sorbent. The main classes of commercially available sorbents include mixed minerals (e.g. RemBind), activated carbon (e.g. FiltraSorb), and organoclays (e.g. FluoroSorb).

In choosing the right sorbent for your application, the following factors are important: price, dosage, and the ability to bind both short- and long-chain PFAS. The availability of credible long-term stability data to give you peace of mind that the PFAS will not re-leach over the longer term is also important.

Bench-Scale Testing

Once you have chosen your sorbents, the next step is to test them at bench-scale using specific soil from your site. This allows you to minimise the dosage rate (and therefore the cost) while also identifying any site-specific factors that may impact the sorbent performance.

The Mixing Process

Scaling up immobilisation to the field is simple – you will need your sorbent (delivered in bulk bags or pneumatic tankers), a water truck, and suitable mixing equipment. The process involves adding the sorbent to the soil at a dosage of 0.5% to 3% and adding water during the mixing process to manage dust and to assist in the binding process. The immobilisation process is then complete.

There are a wide range of mixing equipment options depending on your site requirements and the equipment at hand. These range from a simple loader or excavator with a sieve bucket through to more sophisticated equipment like a pug mill or specialised soil blender.

The key objective is to maximise the surface area contact between the sorbent and the soil for optimal remediation outcomes. Throughput rates are generally in the range of 250 to 1,000 m³ per day.

Validation

The mixing process can be validated using dye-based kits that assess the even spread of the sorbent across the soil stockpile. The ultimate validation of course involves assessing soil samples for PFAS leachability before and after treatment.