Method for treating organic sludge

A method for treating sewage containing organic sludge, comprising:

• subjecting the sewage to a solid/liquid precipitation treatment in an initial precipitation pond to obtain an initially precipitated sludge and an initially separated liquid;
• aerating the initially separated liquid in an aeration apparatus;
• subjecting the aerated initially separated liquid to a solid/liquid separation treatment in a solid/liquid separation apparatus to obtain an excessive sludge;
• subjecting the excessive sludge to an alkaline treatment to cause the excessive sludge to become alkaline with a pH of 8.0-9.8 while maintaining the temperature of the excessive sludge at ambient -100.degree. C. to solubilize organic matter in the sludge;
• subjecting the alkaline treated excessive sludge to a solid/liquid separation treatment in a solid/liquid separation apparatus to obtain alkaline treated solids and an alkaline treated liquid;
• and
• anaerobically digesting the alkaline treated liquid at a temperature of 20.degree.-60.degree. C. at a pH of 7.8-9.2 to obtain digested solids.

A method for treating sewage containing organic sludge by anaerobic digestion, comprising:

• subjecting the sewage to a solid/liquid precipitation treatment in an initial precipitation pond to obtain an initially precipitated sludge and an initially separated liquid;
• subjecting the initially precipitated sludge to an alkaline treatment at a temperature of ambient to an anaerobical digestion temperature at a pH of 7.5-10.5 to solubilize the initially precipitated sludge;
• aerating the initially separated liquid in an aeration apparatus;
• subjecting the aerated initially separated liquid to a solid/liquid separation treatment in a solid/liquid separation apparatus to obtain an excessive sludge;
• subjecting the excessive sludge to an alkaline treatment at a temperature of 50.degree.-100.degree. C. at a pH of 8.0-9.8 to solubilize the excessive sludge;
• mixing the solubilized initially precipitated sludge and the solubilized excessive sludge to obtain a second mixed sludge;
• and
• anaerobically digesting the second mixed sludge at a temperature of 20.degree.-60.degree. C. and at a pH of 7.8-9.2.