Sewage treatment

PCT No. PCT/AU87/00314 Sec. 371 Date Mar. 6, 1989 Sec. 102(e) Date Mar. 6, 1989 PCT Filed Sep. 15, 1987 PCT Pub. No. WO88/01985 PCT Pub. Date Mar. 24, 1988.The sewage treatment process combines physico-chemical clarification using fine material or clay particles with anaerobic digestion of a concentrated sewage. The particles are preferably magnetite. The sewage (10) is mixed with magnetite (12) having a hydroxylated surface layer in tanks (14, 16, 18, 20) in which acid, inorganic flocculant and polyelectrolyte may be added if necessary. The organic material in the sewage is adsorbed on the particles during the mixing contact and a clarified liquid effluent (28) is separated from the loaded particles in a clarifier (22). The organic material may be separated from the particles before or after treatment in an anaerobic digestion assembly (36). The particles are preferably cleansed and regenerated in a two stage countercurrent flow washing system (38, 40, 58, 60, 62) into which a dilute solution of caustic soda or lime (32) is introduced.