We further investigated the performance of the BN-BM process in treating a doubled amount of AFFF (200 μL; TOF=95.6 μmol). Significant PFAS destruction was observed after 6 h (Figures and). More than 98% defluorination was still achieved after a prolonged treatment duration of 8 h (Figure and Table ). These results imply that the BM process has a high robustness toward AFFF loads. More importantly, it was noted that an "incubation period" was required before significant defluorination (arbitrarily defined as DeF>50%). Specifically, the destruction of PFAS and F -yield abruptly accelerated after 4 and 6 h for the treatment of 100 and 200 μL AFFF, respectively. This positive correlation between AFFF loads and the incubation period was not observed in the BM treatment of individual solid PFAS (Figure ), revealing mechanistic insights into the process as discussed below. As discussed in our previous study, the BM process is driven by the impact force provided by ball collisions. In general, BM of wet media yields a lower impact force than dry BM due to the presence of liquid phases that incur drag forces in the counter direction of impact. We hypothesize that due to its surfactant-like nature, AFFF should be uniformly coated on the surfaces of balls and jar walls at a certain liquid film thickness (Z). Further, we propose that there is a critical liquid film thickness (CLFT) so that when Z > CLFT (Figure -i), the drag force offsets the impact force enough to retard PFAS destruction. The delivery of impact energy to BN and the consequent PFAS destruction is only effective when Z < CLFT (Figure -ii).