Methods and systems for digesting biosolids and recovering phosphorus

A process for digesting biosolids comprising:

• hydrolyzing insoluble organic polymers in a sludge derived from wastewater in an acidic hydrolysis environment having a pH between 5 and 6 to produce hydrolyzed biosolids;
• fermenting the hydrolyzed biosolids in an anaerobic digestion environment to produce anaerobically digested biosolids and biogas;
• optionally digesting the anaerobically digested biosolids in a thermophilic aerobic digestion environment to produce thermophilically digested biosolids;
• digesting the anaerobically digested biosolids or the thermophilically digested biosolids in a mesophilic digestion environment to produce mesophilically digested biosolids comprising nitrates at a concentration;
• transferring an amount of the mesophilically digested biosolids to the acidic hydrolysis environment;
• wherein the transferred amount is sufficient to (a) lower one or both of ammonia and pH in the anaerobic digestion environment in an amount sufficient to reduce precipitate formation potential;
• and/or (b) supply the nitrates from the mesophilic digestion environment to the acidic hydrolysis environment in an amount sufficient to inhibit activity of sulfate-reducing bacteria.