Combined Reverse Osmosis and Freeze Concentration of Bleach Plant Effluents.

摘要

Reverse osmosis (RO) and freeze concentration (FC) were evaluated at three different pulp and paper mills as tools for concentrating bleach plant effluents. By these concentration processes,the feed effluent was divided into two streams. The clean water stream approached drinking water purity in some instances,and could potentially be recycled to the mill with minimal problems. The concentrate stream retained virtually all the dissolved material originally present in the feed. Typically,reverse osmosis removed 90% of the water from a stream containing 5 g/l of total solids to give a concentrated stream with 50 g/l solids. Freeze concentration further concentrated the reverse osmosis concentrate to about 200 g/l. Thus,each 100liters of feed resulted in about 98liters of clean water and 2liters of concentrate. Schemes for the ultimate disposal of this final concentrate were not tested. Based on data collected at the three mills,estimates of the process economics were made. Reverse osmosis alone,or combined with freeze concentration,is quite expensive. At curevels of water usage for bleaching,costs ranged from $18to $27per metric ton of bleached pulp (approximately $3.50/1000gallons (M gal) of bleach plant and increased membrane life could significantly lower these costs.