Formatted Title
Tackling the Complexities, Challenges and Impact of Heavy Rainfall on PFAS Treatment in Landfill Leachate
Background/Objectives
With Australia experiencing the La Niña phase of the El Niño -Southern Oscillation (ENSO) climate cycle for the last three years, landfills across Australia have been experiencing large volumes of rainfall. Although per- and poly-fluoroalkyl substances (PFAS) are not a new contaminant to the Australian landfill industry, the increased rainfall has presented many landfills with the requirement to treat large volumes of leachate and surface water runoff contaminated with PFAS. Cleanaway was faced with this complex problem for a landfill facility they operate in Queensland, Australia. The inundation of rain onto the site caused leachate to build-up in the landfill cells and they identified a potential environmental risk if rain was to continue to fall in extremes. Cleanaway, like many landfills in similar conditions, only had one discharge option available to them and that was to discharge directly into the sewer network under a trade waste agreement. This meant that not only was treatment required to bring PFAS concentrations from 30 µg/L down to 0.2 µg/L, but the treatment of salt, nutrients, metals and hydrocarbons was required as well. All of these contaminants have their own difficulties, but the removal of salts and total dissolved solids (TDS) without the use of expensive process equipment such as membrane technologies posed an interesting challenge. As for many landfills faced with this same problem, there was no need to construct an expensive, permanent solutions for PFAS and leachate treatment. Once Australia moved into a new ENSO climate cycle there will have no requirement for the treatment and release of surface water from the facility. This eliminates many of the traditional forms of leachate treatment (such as biological reactors) that are expensive and have long commissioning times. The final design needed to be modular, temporary, have a short lead-time and fast treatment rates.
Approach/Activities
There are a number of options for temporary PFAS treatment, however very little of them can handle the high level of co-contaminants present in leachate, whilst still achieving a <0.2 µg/L concentration for the sum of PFAS. An extensive bench-top evaluation was undertaken to determine the appropriate treatment technologies to trial in a laboratory setting. This bench top evaluation showed that very little research had been produced to investigate the behavior and efficacy of typical PFAS treatment technologies when high levels of co-contaminants are present. After benchtop technology selection was complete a number of laboratory trials were undertaken to investigate the use of air stripping, lime softening, struvite precipitation, adsorption and ion exchange for the treatment of the PFAS contaminated leachate. These technologies were trial in isolation and in combination to identify the best outcome for the site.
Results/Lessons Learned
The laboratory trials provided some great insight into the efficacy of adsorption and ion exchange technologies for the removal of PFAS with high levels of co-contaminants present. The use of powdered activated carbon (PAC) was trialed at a variety of dose rates and with a variety of TDS and electric conductivity (EC) concentrations in the feed water. A removal efficiency of up to 93% for PFAS was observed with PAC dosing of 3.5 g/L and in TDS concentrations as high as 4,440 mg/L. However, concentrations still remained above 0.2ug/L even will doses as high as 6 g/L. The ion exchange process easily achieved the discharge criteria at flow rates of 7 bed volumes (BV)/hr. However, we did see some hindering of the ion exchange process at high TDS concentrations of 10,600 mg/L, with removal efficiency reduced to 98.6% and a final concentration of 0.3 µg/L of total PFAS. After lab trials were complete, the following process was determined optimal and designed as the temporary PFAS treatment plant:
- Struvite precipitation for the removal of nutrients
- PAC dosing for the removal of hydrocarbons and PFAS reduction
- Clarification followed by hydrated lime softening for TDS and metals reduction
- Clarification
- Adsorptive filtration – for the removal of fine precipitates and PFAS reduction
- Ion exchange filtration- for final scrubbing of PFAS
This temporary WTP has now been fabricated and commissioned at the Cleanaway facility in Queensland. We are collecting long-term data on the performance of both adsorption and ion exchange media on the removal of PFAS in a leachate matrix. We will be collating this data and comparing it to projects of a similar design with less co-contaminants present in the feed water.