Formatted Title
Innovative Approach to Reutilize Resources and Remediate PFAS in Food Waste
Background/Objectives
Over 1.3 billion tons of food waste (FW) are disposed of in the world annually, representing a potentially utilizable source of nutrients and energy. Anaerobic digestion (AD) is a promising means of sustainably generating renewable energy and nutrient-rich compost from food waste while maintaining a net-negative global warming potential. However, poly- and perfluoroalkyl substances (PFAS) have been widely detected in food and food-contact materials, representing a substantial barrier to food waste re-utilization. PFAS are a class of synthetic chemicals that consist of a hydrophilic functional head group and a hydrophobic fluorinated carbon chain and are commonly incorporated into food contact materials for their grease-repellent properties. The carbon-fluorine bonds within the perfluorinated tail are exceptionally strong, making PFAS highly stable and resistant to degradation. Once PFAS enter the environment through releases to water and soil, they can go on to enter food chains and bioaccumulate to high levels in organisms. Moreover, PFAS are known to pose a risk to human health even at very low levels. In 2022, the U.S. Environmental Protection Agency (EPA) issued minimum recommended reporting levels as low as 4 ppt for perfluorooctanoic acid (PFOA) in drinking water. Consequently, compost derived from food waste could cause an unintended spread of PFAS to the environment if AD solids are not remediated. Most conventional PFAS treatment methods fall short of destructive remediation, instead capturing PFAS via adsorption. While thermal treatment processes such as hydrothermal treatment and pyrolysis have shown promise for destructive PFAS treatment, the effectiveness of these processes for PFAS treatment in food waste remain poorly understood. Sequential treatment of food waste by AD and thermal treatment could potentially enhance the efficiency of the overall resource recovery process while simultaneously remediating PFAS. The overall goal of this project is to evaluate PFAS remediation and resource recovery potential during food waste processing by sequential AD and thermal treatment.
Approach/Activities
The first part of the study is focused on the phase distribution of PFAS in model food waste before and after dry and wet (i.e., co-digestion with municipal sludge) AD at the laboratory scale. Preliminarily the AD has been performed in 1-L batch reactors filled with food waste and anaerobic sludge as inoculum. The FW recipe was based on the annual average of food received by the non-profit food bank Second Harvest Heartland in Minnesota. Ten typical foods that are commonly consumed by local people were selected as the representatives. Target PFASs, i.e., Perfluorobutanoic acid (PFBA), Perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS), were added to food waste to achieve consistent levels across experiments. Following AD, subsamples of solid, liquid, and oil AD products have been collected, extracted using the QuEChERS method, and analyzed for PFAS, and the distribution of PFAS between different phases has been studied. Methane production via headspace sampling was also monitored.
Results/Lessons Learned
Preliminary findings show that most PFAS partition substantially into the solid phase of the untreated food waste, while long-chain PFAS such as perfluorooctane sulfonic acid (PFOS) also partition into the oil phase. We hypothesize that breakdown of fatty acids during AD will cause long-chain PFAS to increasingly partition into the solid phase, such that subsequent treatment of the AD solids will be of interest. Future work will focus on PFAS fate during pyrolysis and hydrothermal treatment of digestate from dry and wet digestion, respectively. Finally, due to substantial concerns surrounding PFAS contamination, the impacts of this project will be global.