A drop-in treatment apparatus and system for PFAS-impacted liquids. The drop-in treatment apparatus and system may comprise one or more cartridges having a plurality openings; one or more mesh containers disposed within the one or more cartridges; one or more tethers; a submersible pump coupled to the cartridges via the tethers; and a power source electrically coupled to the submersible pump. The drop-in treatment apparatus may further comprise a plurality of prescribed masses of sorbent or resin filled within the mesh containers, such that the prescribed masses of sorbent or resin are disposed within the cartridges. The prescribed masses of sorbent or resin may be configured to remove PFAS compounds from a liquid and may be in the range of 0.1-50,000 milligrams per milliliter of liquid volume to be treated. The sorbent may be pyrogenic carbon, granular activated carbon, biochar, zeolite, aluminosilicates, and combinations thereof.