The test program described was designed to obtain the following basic information concerning the composting of a combination of primary and secondary dewatered sewage sludges: (1) effect of mixing; (2) effect of moisture content; (3) effect of recycling; (4) process capacity; (5) air requirements; (6) effect of chemicals used for conditioning the sludge for dewatering; (7) composition of off-gases; (8) destruction of pathogenic bacteria, fungi, nematodes, and viruses; and (9) chemical and physical composition of the final compost.