Strategie per la digestione anaerobica degli oli alimentari esausti: messa a punto di un reattore gas-lift

Waste cooking oils (WCO) can be re-used for biogas production. Fatty materials, in anaerobic digestion, have the highest theoretical yields. However, the anaerobic digestion of fat-containing waste is often prolonged in time and problematic. To date, WCOs are mainly used for biodiesel production. An alternative use could be the anaerobic digestion, both in mono digestion and in codigestion, with for example pig slurry. I evaluated the best strategies that can reduce the problems related to the use of this substrate, trying to focus the attention on the biophysical factors involved. The main purpose was to bring microorganisms closer to the substrate, working in a two-phase system represented by the WCO and the hydrating medium. The strategies evaluated included: the reduction of the volume of hydration, to increase the probability of contact between microorganisms and substrate; the emulsion, which favors the stability of the micelles of oil in water, and therefore the maintenance of a greater surface of attack of the lipids by the microorganisms; the codigestion and the use of minerals such as sepiolite, in the hypothesis that they can reduce the latency phase and considerably speed up the digestion of fats. I worked in batch systems generally of 100ml, in strict anaerobiosis, in static conditions. I designed and developed a Gas-lift anaerobic reactor for the digestion of exhausted oils that could bring microorganisms closer to the substrate through a pneumatic stirring, favoring a rapid digestion of the substrate. The idea was born from the use of an Air-lift reactor, for the decontamination of hydrocarbon-rich wastewater, which actually favored the contact between aerobic microorganisms (Rhodococcus opacus) and oily substrate. The results obtained encourage a specific approach to fat degradation, compared to the currently used processes such as the Upflow Anaerobic Sludge Blanket Reactor (UASB) and the Continuous Stirred-Tank Reactor (CSTR).