Development of Biorefinery Schemes for the Production and Recovery of Volatile Fatty Acids from Agro-Industrial Wastes

Volatile fatty acid (VFAs) represent the final product of anaerobic acidogenic fermentation and can be exploited as precursors for the production of added-value chemicals. The biotechnological conversion of agro-industrial wastes into VFAs can be considered a valuable alternative to waste disposal. However, the productivity of processes, which refer to the carboxylation platform are affected by the purity of produced VFAs. Biosphere SRL (Forli, Italy) had started to valorize wastes to obtain biogas. VFAs were produced using maize silage (MS), vegetable waste (VW) and cheese whey (CW) as feedstock. The co-digestion of VW (70%) MS (30%) (VMW) under continuous operation with hydraulic retention time (HRT) of 6 days and a controlled pH 7 resulted in a VFAs rich solution of 30 g.L-1. The fermentation of CW was performed in a packed bed bioreactor where Vukuopor was the supported material. The HRT, organic loading rate (OLR) and pH were parameters tested under continuous operation. By a HRT of 6 days, ORL of 4.2 g.L-1.d-1, and pH 5.8−6, 16 g·L-1 of total VFAs were produced, with a yield higher than 75%. Electrodialysis (ED) process was studied for the concentration of VFAs from the two acidogenic effluents resulted from the previous mentioned anaerobic acidogenic digestions. Under potentiostat operation the VMW concentration stream was concentrated from 29 g.L-1 to 50 g.L-1. Thought it is expected that a concentration of 100 g.L-1 can be achieved by performing sequential batch. With CW acidified effluent the concentration achieved was similar however the initial solution was poor in VFAs. Experiments with Nanofiltration were performed for the separation of ferulic acid (FA) and sugars from an enzymatic hydrolysate of wheat bran. Eight different membranes were screened at different pressures and solution pH. The best condition was found be membrane NT7450 operated at pH 9 and 16 bar.