ABSTRACT
Increased Kraft pulp mill production generates increased solid wastes. In response, composting has emerged as an interesting alternative for disposal of these solid wastes. A central composite factor design was used to investigate the influence of incubation conditions (dregs addition and operation time) on chemical and biological parameters, determining the best in-vessel conditions in order to develop a correct composting design. Dregs helped reduce the pH drop that occurs at the beginning of the process. Biological activities presented high values during the active phase, followed by a decrease with stable final values along with N-NH(4)(+) and N-NO(3)(-) trend, which were indicative of mature compost. Dregs addition had not significant effect on the biological activities during composting of Kraft mill sludge. However, moderate amounts of dregs (between 5% and 8%) at operation time of 60-70 days would be the best compromise.