Activated Sludge Process

ACTIVATED SLUDGE PROCESS

Activated Sludge Process is an aerobic biological sewage treatment process. It consists of the following units

• Aeration tank
• Secondary settling tank
• Sludge return line
• Excess sludge waste line

• Raw sewage is given primary treatment in primary sedimentation tank with a short detention time of 1 to 1.5 hours.
• Primary sedimentation tank removes less settleable solids.
• Raw sewage is mixed with activated sludge (return sludge). This mixture is called mixed liquor
• Mixed liquor is  aerated and mixed for 4 to 10 hours depending on degree of purification required and strength of sewage
• Aerated mixed liquor is sent to final settling tank where sludge settles
• Effluent from final settling tank is disposed off
• A portion of effluent from final settling tankis mixed with raw sewage before sending it into primary settling tank
• Part of settled sludge is sent back in aeration tank for seeding the raw sewage and excess quantity is treated and disposed off