Secondary treatment Secondary treatment, also called biological treatment: Use bacteria to break down organic compounds to Co2 A mixture of organisms- termed activated sludge- is added to the sewage effluent Air or oxygen is vigorously bubbled through pipes into the effluent The aerobic bacteria digest the organic material and break it down into co2 and water. The bacteria and any remaining undecomposed material are returned to the aeration tank and reusedSecondary treatment • Secondary treatment, also called biological treatment: Use bacteria to break down organic compounds to CO2. – A mixture of organisms – termed activated sludge– is added to the sewage effluent. – Air or oxygen is vigorously bubbled through pipes into the effluent. – The aerobic bacteria digest the organic material and break it down into CO2 and water. – The bacteria and any remaining undecomposed material are returned to the aeration tank and reused