Flocculation and Precipitation of the pulp Mill Effluent with Magnesium Hydroxide

Abstract

It is usual that the pulp mill effluent is treated by means of Fe (OH)3 or Al (OH) 3 flock flocculation and sedimentation. In testing the effluent, only COD, BOD and chromaticity are measured in many cases, and the influence of the components in the effluent is nearly left alone. The authors, however, used magnesium components in treating the pulp mill effluent, and measured anionic colloid contents in the effluent by means of a colloidal titration method, and also made measurement of saccharide. The relationship among the added magnesium content, the removal ratios of the COD, colloid and saccharide concentration, the sedimentation rate of sludge, and the sludge volume was carefully investigated, and as a result, the authors were able to have a prospect of putting an effluent treatment method into practical use. Stated below is the information obtained from the tests carried out by the authors. (1) The magnesium hydroxide method is relatively superior in the sedimentation and filtration rates to the aluminum hydroxide or the ferric hydroxidemethod. (2) The anionic colloid in the effluents of Kraft Pulp (KP), Sulfite Pulp (SP), Semichemical Pulp (SCP) and Fermentation Pulp can be completely removed by means of magnesium hydroxide. (3) The removal of the COD in magnesium hydroxide method is about 70% in the cases of the KP and SCP effluents, and about 55% in the cases of the SP and Fermentation Pulp effluents. (4) Residual COD loading components are estimated to be lower in molecular weight of organic compounds in the pulp mill effluent.