System and method for treating wastewater and resulting primary and biological sludge

A method of treating wastewater and resulting sludge comprising:

• subjecting the wastewater to primary treatment and producing primary sludge;
• after subjecting the wastewater to the primary treatment, subjecting the wastewater to biological treatment and producing biological sludge;
• directing the biological sludge to a thermal hydrolysis unit and subjecting the biological sludge to a thermal hydrolysis process and producing thermally hydrolyzed biological sludge;
• mixing the primary sludge and thermally hydrolyzed biological sludge in a pressurized structure at a pressure greater than atmospheric pressure to form a sludge mixture;
• cooling the thermally hydrolyzed biological sludge in the pressurized structure by transferring sensible heat from the thermally hydrolyzed biological sludge to the primary sludge;
• transferring the sludge mixture of primary sludge and thermally hydrolyzed biological sludge from the pressurized structure to a pasteurization unit and subjecting the sludge mixture to a pasteurization process;
• and
• after pasteurizing the sludge mixture, transferring the sludge mixture from the pasteurization unit to an anaerobic digester and subjecting the sludge mixture to anaerobic digestion.