This paper presents pilot-scale experiences on utilization of primary sludges from an integrated pulp and paper mill in the manufacturing of hardboard. The results have shown that the primary sludge added in 1/4 ratio yields the best result considering quality and operating aspects for the hardboard production. Lab-scale anaerobic treatability studies were carried out by an upflow anaerobic sludge blanket reactor (UASBR) with a volume of 10.351 using settled effluents from the related industry as the feed. Anaerobic treatability study results have shown that such an application prior to existing activated sludge system may provide 70 percent reduction in energy requirement for aeration and about 65 percent net reduction in excess biological sludge production.