In 2018 alone, the US generated 292 million tons of municipal waste according to the US EPA. Roughly 50% of this waste was landfilled, while less than a third was put toward recycling or composting. Food waste alone makes up about 24% of the annually landfilled mass at 35.3 million tons per year. In addition to the negative impacts, landfills have demonstrated on the environment and human health in general, some states have begun to outlaw and dissuade the disposal of food waste and sewage sludge into landfills altogether. An urgent need has thus been created for the development of alternative disposal strategies. Although a variety of industrial-scale anaerobic digestion processes can convert landfill wastes into valuable products like biogas. This production is limited, however, by the co-production of volatile fatty acids (VFAs). However, the separation of VFAs from the fermenter broth may cost up to 50% of the entire cost of product. Cost aside, liquid-liquid extractions (LLE) of VFAs typically produce low separation efficiency, and distillation columns—while they may achieve greater separation efficiency—tend to have prohibitively high installation and operational costs. In this work, we present a highly efficient method for removing and extracting VFAs from a real food waste feedstock using gravity-only energy input . We obtain over an order of magnitude better separation of VFAs as compared to literature that studied comparable processes. The impact of varying the pH of the fermentation broth, the composition of the organic extractant, and the aqueous-to-organic flowrate ratio are also determined. Heretofore unknown, the aqueous-to-organic flowrate ratio is found to be particularly crucial for achieving optimal extraction. An aqueous broth feed pH of 2.5, an organic extractant consisting entirely of tri-n-octylamine, and a 10:1 ratio of aqueous broth to organic extractant are identified as yielding K_D = 44.5+7.9, single-pass recovery = 81.3+2.5%, and EF = 8.1+0.3. Furthermore, our separation demonstrates excellent reproducibility and scalability from the benchtop (100mL) to the pilot (5L) scale. The economic and environmental implications of this work are also discussed.

Meltem Urgun-Demirtas

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