MODIFIED AND UNMODIFIED ALUMINA MEMBRANES IN ULTRAFILTRATION OF BOARDMILL WASTE-WATER FRACTIONS

The aim of the work was to study treatment efficiency and flux of vari ous, new ceramic membranes in the ultrafiltration of board mill wastew ater fractions. The wastewater fractions studied were the disk filtere d and flotation treated circulation wastewater and the overflow from t he clarification basin of coating colour wastewater. The membranes use d were flat sheet alpha- and gamma-alumina membranes and modified alph a-alumina membranes. The modifications were made in order to improve f lux and to decrease the fouling tendency of the membranes. The stabili zed fluxes achieved after 1 h of filtration were in the range of 80-90 l/m(2)h with the alpha-alumina membranes, about 60 l/m(2)h with the g amma-alumina membranes and about 100-160 l/m(2)h with the modified alu mina membranes. The treated circulation wastewater fouled the membrane s more than the treated coating colour wastewater. Ultrafiltration rem oved the suspended solids and colloidal material from the water. Both wastewater fractions studied had a fairly low CODCr content and hence the reductions in CODCr were low. Iron was removed from the treated co ating colour wastewater and odour from the treated circulation wastewa ter. Removal of odour and taste forming properties is important since the box board manufactured in the board mill is used for food, cosmeti cs and cigarette packings.