Green liquor dregs effect on Kraft mill secondary sludge composting

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–NH4+ and N–NO3- 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.