REMOVING COLOR AND CHLORINATED ORGANICS FROM PULP-MILL BLEACH PLANT EFFLUENTS BY USE OF FLY-ASH

Color and chemical oxygen demand (COD) in bleach plant effluents are o f concern. Acidified flyash can effectively remove both color and COD from caustic bleach plant effluents. Equally effective, but quicker an d easier, is to acidify the effluent to approximately pH 1 and use unt reated flyash. Based on maximum color removal, the required contact ti me is short, about 10 min, and the optimum ash dosage is that amount w hich raises the pH of the final effluent to about 5. Sufficient color removal is obtained to easily meet Maine's color regulations. Prelimin ary tests on samples of deionized water spiked with two arochlors of P CB showed high removal efficiency. The major cost of implementing and operating the cleanup procedure will be the cost of the required acid. This might be minimized by using some of the acidic (chlorine) efflue nt to lower the pH of the caustic effluent. This will, however, lead t o less color reduction, and an unknown effect on the COD.