Degradation of inorganic polyphosphates (polyP). Releases orthophosphate processively from the ends of the polyP chain. Prefers long-chain length polyphosphates as substrates (By similarity). Can also hydrolyze ATP and ADP substrates, but lacks GTPase activity. Cannot hydrolyze pppGpp to ppGpp (PubMed:22880033). [phosphate](n) + H2O = [phosphate](n-1) + H(+) + phosphate kcat is 4.4 sec(-1) with ATP as substrate. Homodimer. Belongs to the GppA/Ppx family.