Which of the following is put into anaerobic sludge digester for further sewage treatment?

The sediment of secondary settling tank, having fungi and aerobic bacteria in the form of flocs, is put into anaerobic sludge digester for the degradation of flocs by anaerobic bacteria. Biogas is produced in this digester.

(1) Primary sludge is the sediment of primary settling tank, which consists of grit and sand. It is removed.

(2) Floating debris of sewage is removed by sequential filtration.

(3) Effluent of primary settling tank is put into aeration tank for the degradation of organic material by aerobes and to decrease BOD.