The decolorization of the effluent leaving chemical pulping mills
In order to produce, for example, paper for office or home use, lignin must be removed from pulp. This bleaching process generates a highly colored effluent that gets discharged into our waterways. Many pulp mills discharge 100 – 200 ML per day of this highly colored water. Currently no economically viable technology exists for this environmental and aesthetic issue. Through a uniquely collaborative research effort involving the Institute, Forest Research in New Zealand and graduate researchers in Professor L. James Wright’s group at the University of Auckland, Auckland, New Zealand, we have developed a first generation technology that can largely solve this problem for the mills. We are now probing more deeply into understanding how the chemistry works in terms of substrate oxidation pathways. This will lead us to the design of TAML activators that will make the process more efficient and more cost effective.
In February 2002, a field trial was conducted in New Zealand to assess the applicability of TAML activators for the decolorization of effluents from pulp mill bleach plants. The target of this trial was the treatment of roughly 50,000 L of effluent over a two week time frame. The pilot plant is shown in the figure. It basically consisted of tapping into the effluent stream line, passing this effluent into a barrel (Vessel 1) into which TAML activator and peroxide were added by metering pumps, allowing the reaction to take place for an average of 1 hour in this tank and then feeding it into a second tank (Vessel 2) for a 4 hour treatment. The field trial results were even better than the laboratory results in terms of color removal and we found that only 1 hour treatment was necessary. The results are shown in the figure by the difference in the color of the effluent sample before and after TAML treatment. This work is significant because we were able to give a practical demonstration of a technology for processing large volumes of material with very little modification to the existing plant. The New Zealand field trial thus constituted one of the largest field trials ever undertaken to prove the applicability of an AOP (Advanced Oxidation Process) to an industrial process. Additional field trials for this technology are going to be performed in the US when sufficient quantities of TAML activator become available.