Valorization of sewage sludge for volatile fatty acids production and role of microbiome on acidogenic fermentation

This work explored the production of volatile fatty acids (VFA) through the anaerobic digestion of sewage sludge (SS). The first experiment took place at batch scale to evaluate the combined effect of using a thermal pretreatment (120 degrees C, 15 min) and different Substrate/Inoculum ratios (S/I) (1, 2, 4 and 6 g VS substrate/g VS inoculum) on the acidogenic potential of the SS. The results showed that the thermal pre-treatment influenced positively the degree of acidification of the SS at low S/I ratios, reaching maximum of 45%. Afterwards, a continuous lab-scale experiment, was set-up to study two ranges of organic loading rates (OLR): 1300-1600 mg COD L-1 d(-1) and 2400-3500 mg COD L-1 d(-1). The highest degree of acidification (22%) was achieved at the lowest OLR. Analysis of the microbial community in the reactor revealed that OTUs most abundant present genes related with amino acids and carbohydrates fermentation being crucial for VFA production.