Volatile Fatty Acids Production by Anaerobic Fermentation of Urban Rganic Wastes

During six months of experimentation, a plug-flow system without recirculation was employed to study the volatile fatty acids (VFA) production by means of anaerobic fermentation of urban organic wastes. Results showed an important VFA production at mesophilic range of temperature (37°C). Particulary, VFA concentration in the outlet sludge went from 11.8 g/L at 2 days of retention time up to 23.1 g/L at 6 days of retention time. INTRODUCTION One of the biotechnologies developed in the last years to utilize municipal solid wastes (MSW) for useful energy and materials recovery is the anaerobic digestion. Paxticulary, the anaerobic fermentation of the organic fraction of the municipal solid wastes (OFMSW) mainly to acetic, propionic, butyric and valeric acids has been studied. The volatile fatty acids obtained can be recovered and used to produce methyl or ethyl esters which, considering their elevate Octane number (between 103-118), could be advantageously used as additive for gasoline (D’Addario et al., 1992). An alternative possibility would be the production of biogas in a second step of the anaerobic digestion. The resulting sludge from the fermentation could be converted in an optimal soil amendment after a composting step. All these possibilities makes the alternative particulary interesting. The main studies described in the literature about the steps for the production of esters from MSW are the ones made by Antonopoulos in the U.S.A and D’Addario and co-workers in Italy (Antonopoulos and Wene, 1989; D’Addario et al., 1992). However, further research is necessary in order to study the feasibility of the process. This work shows and discusses the results obtained using the OFMSW to produce volatile fatty acids in a tubular pilot-scale reactor at mesophilic temperature. The influence of operational parameters, such as hydraulic and solid retention time and organic loading rate, on the hydrolyticacidogenic phase of the anaerobic digestion has also been invesqgated.