초록
<P><B>Abstract</B></P> <P>The problem of waste disposal has recently focused on practices for waste recycling and bio-resources valorization. Organic waste produced in urban context together with biological sludge produced in wastewater treatment plants (WWTPs) can be used as renewable feedstock for the production of building blocks of different products, from biopolymers to methyl esters. This paper deals with the optimization of the fermentation process in order to transform urban organic waste (a mixture of pre-treated food waste and biological sludge) into added-value volatile fatty acid (VFA) rich stream, useful for biological processes within a biorefinery technology chain. Different temperatures, pH, hydraulic retention times (HRTs) and organic loading rates (OLRs) were tested both in batch and continuous trials. Batch tests showed the best working conditions at 37 °C and pH 9, using the bio-waste feedstock thermally pre-treated (76 h at 72 °C). These conditions were applied in continuous process, where higher HRT (6.0 d) and lower OLR [7.7 kg VS/(m<SUP>3</SUP> d)] gave the best performances in terms of process yield and maximum VFA level achieved: 0.77 COD<SUB>VFA</SUB>/VS<SUB>(0)</SUB> and 39 g COD<SUB>VFA</SUB>/L. An optimized fermentation process is crucial in a biorefinery perspective since it has to give a final stream of constant composition or tailored products suitable for further applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Acidogenic fermentation process was optimized for urban bio-waste valorisation. </LI> <LI> Thermal pre-treatment favoured the urban bio-waste organic matter solubilisation. </LI> <LI> Mesophilic alkaline fermentation enhanced VFA production yields. </LI> <LI> Higher HRTs and lower OLRs gave the best performance in a CSTR with 39 g COD<SUB>VFA</SUB>/L. </LI> <LI> Alkaline urban bio-waste fermentation increased the HV precursors concentrations. </LI> </UL> </P>