Acidogenic Fermentation Towards Valorisation of Organic Waste Streams into Volatile Fatty Acids

F. C. Silva, L. S. Serafim, H. Nadais, L. Arroja and I. Capela

Abstract
Anaerobic acidification of eight organic streams (cheese whey, sugarcane molasses, organic fraction of municipal solid wastes (OFMSW), glycerol, soapy slurry, winery wastewater, olive mill effluent, and landfill leachate) was evaluated in batch experiments to determine their acidogenic potential and examine the composition of the produced volatile fatty acids (VFA). Cheese whey, molasses and OFMSW presented the highest acidogenic potentials (0.3 to 0.4 gVFA per g of chemical oxygen demand fed, CODfed) with the predominance of acetic, n-butyric and propionic acids. A further experimental set was applied to cheese whey, by varying food-to-microorganism ratio (F/M) and initial alkalinity. Maximisation of VFA production (up to 0.63 gVFA g–1CODfed) was obtained for an initial alkalinity of 5 – 7 g L–1 as CaCO3 and F/M ratios of 2 – 4 gCOD g–1VSS. Moreover, it was demonstrated that low F/M ratios combined with high alkalinity supply can shift the VFA profile by increasing the production of propionic and n-valeric acids. The results are useful towards optimal designs for acidogenic processes based on the composition of the VFA produced, since the control of the acidification products is crucial for valorisation in some applications.

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Keywords
Anaerobic acidogenesis, volatile fatty acids (VFA), cheese whey, sugarcane molasses, OFMSW