Eka Chemicals' concept of ECF partial closure is based on keeping the alkaline and acidic filtrates from the bleach plant separate, reducing the alkaline efflunet volume wiht ultrafiltration, and purging chlorides and potassium from the recovery boiler ESP dust. The alkaline filtrates are recycled to te brownstock fiberline and the acidic filtrates are treatd in a biological waste treatment system. Mill pilot scale ultrafiltration trials on ECF alkaline bleach filtrate have been completed in an operating kraft softwood mill using oxygen delignification. The alkaline filtrate used was the combined EPO and EP filtrates in the bleachign sequence D(EOP)D(EP)D. Along with the traditional performance measurements of COD, AOX, color and hloride, the alkaline feed to the ultrafiltration unit, the ocncentrate and the permaeate were characterized for both inorganic and organic components. the alkaline feed, the permeate and the acidic filtrates, separate and in combination, were tested for their biological treatability and the environmenntal parameters were evaluated both prior to and after biological treatment.
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