3-62: Leaching of Food Industry Residues to Improve Feedstock Quality and Resource Recovery

Food processing wastes and residues such as fermented grape pomace (FEGP) from wineries and sugar beet pulp (SBP) from sugar producers are potential feedstocks for biofuel and other bioenergy conversion using both thermochemical and biochemical approaches. However, high concentrations of alkali metals and chlorine in these feedstocks promote ash slagging and fouling as well as corrosion in high temperature conversion systems.  Residual ethanol and other organic compounds can be inhibitory to further microbial fermentation. Earlier research has shown leaching to be beneficial in reducing concentrations of deleterious constituents in biomass.  Leaching was studied for its application in extracting inorganic and organic constituents from FEGP and SBP. Samples of each feedstock were leached in water at ambient temperature for 30 or 120 minutes at dry solid-to-liquid ratios of 1/20 and 1/50 kg/L.  Leachates were analyzed for organic acids, water soluble carbohydrates, ethanol, potassium, sodium, and chloride. Leaching removed 82% of sodium, 86% of potassium, and 76% of chlorine from SBP. Leaching reduced total ash concentration in FEGP from 8.2% to 2.9% of dry matter, and from 12.5% to 5.4% in SBP.  Glycerol (7-11 mg/dry g), ethanol (131-158 mg/dry g), and acetic acid (24-31 mg/dry g) were also extracted from the FEGP. Propionic acid (89-100 mg/dry g) and glucose (27-33 mg/dry g) were extracted from the SBP. These results suggest that leaching is a beneficial pretreatment step for improving the quality of food processing residues for thermochemical and biochemical conversion. Some compounds in leachate may possibly be recovered for higher value uses.