Process for removal of suspended solids from pulp and paper mill effluents

Abstract

A process is for removal of suspended solids including resin and fatty acids from pulp mill effluents including Chemi-Thermo-Mechanical Pulp (CTMP) mill effluents. The process involves filtration of untreated or primary treated effluents through a mat of primary sludge, pulp or woodroom sludge. A sludge mat is formed on a wire screen or punched drum and the effluent to be treated is filtered through the mat. Most of the suspended solids and a part of colloidal material and dissolved solids are retained by the mat. Following the filtration stage, the sludge is dewatered and removed. A portion of the sludge is recycled to form the mat for the next filtration cycle, while the excess sludge is purged. The filtration is achieved by the application of vacuum below the filter mat or pressure over mat. The process will produce treated effluent with low suspended solids and sludge at high solids consistency and eliminate the need not only for a clarifier but also for sludge thickening and filtration units often used in pulp mills. Calcium chloride may be added to the effluent prior to primary settling or before filtration, to enhance the removal of suspended and total solids.

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