Hydrolytic-Acidogenic Fermentation of Organic Solid Waste for Volatile Fatty Acids Production at Different Solids Concentrations and Alkalinity Addition

Intermediate products from anaerobic fermentation, such as volatile fatty acids (VFA), are the preferred carbon sources for the production of added-value products, namely polyhydroxyalkanoates (PHA) or bioenergy. Organic fraction of municipal solid waste (OFMSW) can be valorized through the application of a hydrolytic-acidogenic stage, thus reducing its pollutant content and at the same time that it is obtaining high-value products (VFA). In this work, the anaerobic fermentation of OFMSW into VFA (production and profile) and the influence of both total solids (TS) content in the reactor and alkalinity addition were studied. The increase on TS content led to a decrease on the acidification degree whereas the increase on the alkalinity addition led to a higher degree of acidification. Hence, the highest degree of acidification (77.59 %) was obtained at the lowest TS content (5 %) and at the highest alkalinity addition (50 g CaCO3 L-1). However, depending on the ultimate use of the produced VFA, the acidified residue presenting the highest VFA content (98.96 %) with higher propionic acid concentration, which is a more suitable VFA mixture for the production of high-quality PHA, was obtained at an intermediate TS content (8 %). From the response surfaces obtained, it was observed that all response variables (VFA production, degree of acidification, and effluent quality) presented a higher dependency on TS content than on initial alkalinity addition.