Method of treating sludge

A method of treating sludge including solids containing phosphorus, ammonia and magnesium and enhancing the dewaterability of the sludge, comprising:

• directing the sludge to a biological fermenter;
• biologically treating the sludge in the biological fermenter which is operated under anaerobic conditions;
• causing the solids to release phosphorus, ammonia and magnesium into a liquid forming a part of the sludge by maintaining:
• (1) the temperature of the sludge in the fermenter to a temperature within the range of 50° C.-70° C.;
• and (2) controlling the hydraulic retention time of the sludge in the fermenter to approximately 6 to approximately 10 hours;
• directing the sludge from the fermenter to a solids-liquid separator;
• separating the solids from the liquid containing the released phosphorus, ammonia and magnesium;
• directing the separated solids to a thermal hydrolysis reactor and thermally hydrolyzing the separated solids;
• and
• after thermally hydrolyzing the separated solids, directing the hydrolyzed separated solids to an anaerobic digester and anaerobically digesting the hydrolyzed separated solids.