Temperature-driven co-fermentation of waste activated sludge and food waste: process performance and microbial dynamics
Co-fermentation of waste activated sludge (WAS) and food waste (FW) was studied in continuous bioreactors at different temperatures, 25, 35, 45, and 55 ºC with a 3.5 day retention time. Solubilisation yield was highest at 45 ºC (575±68 mgCOD/gVS) and 55 ºC (508±58 mgCOD/gVS), compared to 396±32 mgCOD/gVS at 25ºC. Fermentation yield was higher at 55 ºC (425±28 mgCOD/gVS), followed by 35 ºC (327±17 mgCOD/gVS) and 45 ºC (326±19 mgCOD/gVS). Temperature significantly influenced the volatile fatty acids (VFA) profile. At 55 ºC, acetic (40%), butyric (40%), and propionic acid (5%) dominated, while at 35 ºC, acetic (37%), butyric acid (31%), and propionic acid (17%) were prevalent. Each temperature had a unique microbiota, where the original WAS microbiota played a crucial role. Notably, at 35 ºC, there is a risk of acetic acid consumption due to the proliferation of Methanosarcina, an mixotrophic methanogen imported from the WAS.