Understanding the role of cellulose fiber on the dewaterability of simulated pulp and paper mill sludge

Abstract

Pulp and paper mill sludge (PPMS) mainly consists of primary sludge and secondary sludge (activated sludge). Before the disposal and utilization of PPMS, it is dewatered due to high water content. Cellulose fiber is a key and characteristic component in PPMS. In this paper, the role of cellulose fiber on the dewaterability of simulated PPMS (the mixture of cellulose fibers and activated sludge) was investigated, including the fiber content, fiber length and fibrillation degree. The results showed that the specific resistance to filtration (SRF) of simulated PPMS decreased with the increase of fiber content (0–30 w%) and also decreased with the decrease of average fiber length (0.597–0.303 mm) noticeably. However, the SRF increased dramatically when the average fiber length reduced further to 0.189 mm. The fiber fibrillation had no obvious effect on the sludge SRF. Besides, the addition of cellulose fiber had little impact on the sludge compressibility. The role of cellulose fiber in the PPMS is to form aggregates with high fiber-sludge adhesion and large floc size, which relieves the blinding effect and changes the permeability of sludge cake respectively, resulting in improving sludge filterability.