The past investigations of PFAS defluorination were heavily invested in the treatment of model PFAS, with only a few studies that used electrochemical oxidation, plasma, advanced oxidation, and UV-sulfite photoreduction to treat diluted AFFF with total fluorine (TF) ranging between 0.1-27 mg F/L. All these technologies demonstrated structurally dependent reactivity in removing target PFAS, and none achieved near-complete defluorination. To date, only hydrothermal alkaline treatment realized ~100% defluorination of AFFF but demands high temperature (170-350°C), pressurized reactors (2-22 MPa), and alkaline addition (5 M of NaOH). Ball milling (BM) is an emerging technology for destroying PFAS chemicals at ambient conditions. Using potassium hydroxide (KOH) as a co-milling reagent destroys perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). However, the residual KOH in the media must be neutralized before discharge. Using quartz sand (SiO2) as a neutral reagent to destroy PFAS is possible. However, the degradation kinetics are slower, and the fluoride yield is low. Previously, we discovered that boron nitride (BN), a piezoelectric material, can be activated in the BM process to generate ~kV potential to destroy solid PFAS. Building upon this early success, this study reports unprecedented results that the BN-assisted BM (BN-BM) can achieve ~100% defluorination of undiluted liquid AFFF with a TF concentration of 9,080 ± 180 mg/L (vs. 0.1-27 mg/L reported previously ). We further developed a critical liquid film theory to guide the process scale-up. The critical insights of this study established a novel AFFF treatment paradigm and expanded the applications of piezoelectric BM from solid chemical destruction to liquid waste disposal.