PFAS
PFAS are a persistent recalcitrant family of compounds, characterized by long, fluorinated carbon chains.
Remediation of PFAS-contaminated soil and water has had limited success due to the chemical stability of PFAS, although thermal treatment options are currently being explored as the best option for achieving substantial destruction of PFAS. Due to the high thermal stability of PFAS, however, temperatures greater than 700°C are required to destroy PFAS and temperatures above 1000°C are necessary to minimize production of short-chained volatile organic fluorines (VOFs) and fluorinated dioxins and furans (PFDD/F).
Self-sustained smoldering is a low-cost/energy thermal technique for the treatment of contaminated soils. Temperatures in excess of 700°C or even 1000°C are possible, depending on the conditions of the system and the fuel being combusted.
Savron is currently conducting proof-of-concept laboratory studies to explore the application of smoldering combustion to treat PFAS-impacted soils and media. Results to data demonstrate that:
Granular activated carbon (GAC) can be used to support smoldering combustion to achieve temperatures that destroy PFAS when added to soils at ~40 to 60 g/kg.
PFAS absorbed to GAC or soils can be treated via smoldering combustion resulting in non-detectable levels in soils, sand and ash.
- Hydrogen fluoride (HF) is generated suggesting that complete decomposition of PFAS via smoldering combustion is possible.
Laboratory work continues and opportunities for a field demonstration of the technology are being evaluated.
BIOSOLIDS
Managing organic sludge and biosolids, the major by-products from wastewater treatment plants (WWTPs), persists as a widespread challenge that often constitutes the majority of WWTP operating costs.
Self-sustained smoldering combustion is a new approach for organic waste treatment, in which the waste – the combustion fuel – is destroyed in an energy efficient manner after mixing it with a porous matrix.
Laboratory proof-of-concept testing and large-scale prototype testing using Savron’s STARx Hottpad systems have been conducted to evaluate the conditions under which smoldering can be used to treat WWTP sludge and biosolids. It was found that a self-sustaining reaction is achievable using WWTP sludge and biosolids with water content as high as 80% and that at larger scales, using a solid organic waste product (such as wood chips) as the porous matrix greatly enhances the uniformity of treatment and expands the range of WWTP sludge and biosolids materials that can be successfully treated. The higher temperatures achievable using a solid organic matrix material may also allow for the treatment of emerging recalcitrant contaminants sometimes found in WWTP sludge and biosolids.
Prototype testing continues and opportunities for a field demonstration of the technology are being evaluated.
ACID MINE DRAINAGE
Acid mine drainage (AMD) and acid rock drainage (ARD) present a significant environmental challenge due to the oxidation of metal sulfides in waste rock or mine tailings.
The removal of sulfide from mine waste (e.g., tailings) can be achieved using thermal treatment technologies with highly elevated temperatures (e.g., in the range of 600 to 1000°C for removal of sulfide from pyrite). Savron’s ex-situ smoldering (STARx) systems are a low cost, energy efficient process, which have demonstrated potential for remediating AMD/ARD-generating wastes. Temperatures sufficient for complete sulfide removal (i.e., in excess of 1000°C) can be generated via smoldering with the use of a surrogate fuel.
Savron is currently conducting proof-of-concept laboratory studies to explore the application of smoldering combustion to treat mine tailings and other mining waste materials. Results to date demonstrate that:
Successful smoldering treatment of tailings with a vegetable oil amendment can achieve temperatures in the range of 600°C and 77% reduction in total sulfur.
Granular activated carbon (GAC) can be used to support smoldering combustion to achieve higher temperatures (i.e., >1000°C) when added to tailings at ~40 to 60 g/kg.
On-going laboratory development work continues and opportunities for a field demonstration of the technology are being evaluated.