Phosphorous ions are extracted (210) from solutions by adsorbing phosphorous ions in a scavenger and by releasing the phosphorous ions into an eluate during regeneration (230) of the scavenger. The regeneration (230) is performed by ammonia. Phosphate anions are precipitated (262) in form of tri-ammonium phosphate upon introduction (260) of excess amounts of ammonia. The ammonia remaining in solution after the precipitation of tri-ammonium phosphate is reused (266) for regenerating the scavenger.