Process for tertiary treatment of waste waters from anaerobic digestion treatment process

Claim 1

A process for reducing BOD, nitrogen and phosphorus concentration from the effluent produced in the liquid-solid separation of anaerobically digested biochemical waste solution having in it ammonia and phosphorous, comprising the steps of: (1) anaerobically digesting biochemical waste having phosphorous and nitrogen to produce carbon dioxide gas and anaerobically digested biochemical waste and thereafter separating by solid-liquid separation the anaerobically digested biochemical waste into anaerobically digested sludge and effluent having ammonia and phosphorous, (2) adding lime to the effluent to render the pH of the effluent within the range of 10.3 to 11.0 and to form calcium phosphate with said phosphorus, (3) separating ammonia in the form of aqueous ammonia distillate from the effluent by reduced pressure distillation at a pressure of 200 mm Hg or lower, (4) adsorbing the separated ammonia in a weakly acidic ion exchange material, (5) desorbing the adsorbed ammonia by reacting said ion exchange material with an acid to form an ammonia salt and regenerate the ion exchange material, (6) blowing the carbon dioxide gas that was produced in step (1) into the effluent from which ammonia has been removed at the step (3), to form calcium carbonate, precipitate the calcium phosphate, formed in step 2, with the calcium carbonate, and separating said precipitate from the effluent, and (7) subjecting the effluent from which the precipitate has been separated at the step (6), to aerobic digestion treatment within a pH range of 6.0-7.5 for removing said BOD therefrom.