FERMENTATIVE PRODUCTION OF LACTIC ACID AND BIOGAS FROM FOOD WASTE: PRELIMINARY TESTS

In the present work food waste was studied as nutrient source in fermentative lactic acid (LA) production and in biogas generation. LA was generated through simultaneous saccharification and fermentation (SSF) with only microorganisms, no enzymes and external nutrient sources were added. SSF was carried out in 2L-scale fermenters for investigation of bacteria performances at different solid-to-liquid ratios. Four microorganisms were tested; three thermophilic bacteria (Lactobacilli sp.) A211, A59 and A28a and one mesophilic strain (Streptococcus sp.) ATB620. ATB620 was the most promising one resulting in a LA concentration of 36.80 g/L, a yield of 85.46% and an optical purity of 99.95%. To further optimize LA production, SSF with ATB620 was carried out at four different solid-to-liquid ratios: 5, 10, 15 and 20% (w/v) under sterile conditions. The best results were achieved with 20% (w/v) resulting in 58.54 g/L LA, a yield of 76.73%, a maximal volumetric productivity of 3.24 g/L×h and an optical purity of 96.50%. Finally, anaerobic digestion (AD) of remaining solids and bacterial biomass was carried out under mesophilic conditions. The biogas productivity was 0.743 Nm3/kgVS containing 67.19% (v/v) methane.