The invention relates to: a method of treating liquid waste (liquid agricultural or industrial effluents or aquatic sites) which is loaded or polluted with tributyl phosphate (TBP), modified bacterial strains which can be used in the aforementioned treatment method, a method for monitoring changes in TBP pollution, and the device which is used to perform said treatment method. According to the invention, the liquid waste-treatment or -purification method essentially comprises: steps (1) consisting in bringing said liquid waste into contact with at least one non-sulphur purple photosynthetic bacterial strain which is resistant to TBP and which is selected from the group containing Rhodopseudomonas palustris (Rp. palustris), Rhodospirillum rubrum (Rs. rubrum), Rhodobacter capsulatus (Rb. capsulatus) or Rhodobacter sphaeroides (Rb. Sphaeroides) as well as the aforementioned modified bacterial strains in order to overexpress cytochrome P450 in conditions that enable the degradation of the TBP present in said waste, regardless of the initial TBP concentration; and (2) the recovery of the purified liquid effluents.