Color Removal from Kraft Mill Effluents by Ultrafiltration

摘要

Color removal from kraft mill effluents by ultrafiltration (UF) has been examined during this program. A 3-stage, nominal 37.9 cu m (10,000 gpd) UF pilot plant was operated on caustic extraction filtrate for several months. Extensive evaluation of spiral-wound UF modules was carried out prior to staged system operation in single module tests. During these tests feed pretreatment and prefiltration options were investigated and the effects of a range of operating parameters on module flux performance were studied. A second module configuration, tubular assemblies, was also tested. All field tests were performed at the Canton, North Carolina Mill of Champion International. Non-cellulosic UF membranes were evaluated in laboratory tests before field trials were initiated. The preferred membrane was cast from a polysulfone formulation. Spiral modules were severely fouled by species present in white water recycle. Tubular modules, however, exhibited stable, economically-vialble flux performance. Color removal by the tubular UF membranes ranged from 97% to 99% when calculated on a concentrate basis. Projections based on process data indicate UF results in an overall color reduction of 91% (mass basis) for caustic extraction filtrate. Conceptual designs and economic analyses were developed for treatment systems with capacities of 3,790 cu m/day (1 MM gpd) and 7,980 cu m/day (2 MM gpd). Additionally, caustic extraction filtrate and decker effluent stream characteristics were monitored and qualitative assessments of ultrafiltrate and UF concentrate recycle within a kraft mill were made.