Process for the decolorization of pulp mill bleach plant effluent
 Pulp mill bleach plant caustic extraction effluent is decolorized using a primary or other sludge from a pulp and paper mill. The sludge is acidified and mixed with the effluent. After a short incubation period, the mixture of acidified sludge and effluent is raised to at least neutral pH, causing precipitation of most of the color in the effluent. The precipitated color may then easily be separated from the liquor by any conventional clarification technique. The method avoids the consumption of large quantities of expensive reagents or high transportation costs associated with the prior art decolorization techniques used on such effluent. 
The United States of America as represented by the Secretary of Agriculture
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inventional inventional additional additional inventional
David C. Hou-min Thomas K.
Eaton Chang Kirk