Dynamic reactors were used to study the effect of UAF on the raw fraction of MSW. UAF correlates positively with OUR and CO2 consumption rate and cumulative indices. A statistically significant correlation was found among O2 and CO2 dynamic indices. The effect of UAF depends on the biodegradability of each organic substrate. DRI24 above/below 1500/520 mg O2 kg−1 VS h−1 indicate fresh/stable MSW material.