The present invention provides methods for the reduction and recycling of papermaking sludge. Papermaking sludge is incinerated in a rotary heater, typically a rotary cement kiln, asphalt dryer, or specially designed rotary kiln or incinerator. Aggregate may be combined with the sludge to provide better dispersion of the sludge within the heater, and to facilitate heat transfer. Once in operation, the heat of sludge combustion is added to the process heat, resulting in markedly reduced energy requirements. Papermaking sludge is typically fed continuously into said rotary heater while temperatures in the combustion zone are maintained in the range of approximately 800.degree. to 3500.degree. F. During incineration, mixing catalysts (typically casein or soy protein) and wood fibers are burned, while moisture is evaporated. The resulting product consists essentially of carbonate particles which are collected for subsequent use.