Case Study 9.5: Elimination of Dioxin and Furans by Alternative Chemical PI

In early 1988, a study of effluents from bleached pulp mills showed significant levels of dioxins and furans. As a result of these findings, the industry implemented a series of process changes including (i) eliminating the use of certain defoamers which contained dioxin and furan precursors, (ii) decreasing the use of chlorine as bleaching chemical, and (iii) increasing the use of chlorine dioxide for pulp bleaching. Between 1988 and 1996, there was a very significant reduction in effluent 2,3,7,8‐tetrachloro dibenzo‐p‐dioxin (TCDD) and 2,3,7,8‐tetrachloro dibenzo‐p‐furan (TCDF) concentrations. For example, in 1988 40% of the mill effluent samples contained less than 10 parts per quadrillion (ppq) of 2,3,7,8‐TCDD. In 1990, 70% of the samples contained less than or equal to 10 ppq of 2,3,7,8‐TCDD. By 1996, all but two mill effluent samples showed 2,3,7,8‐TCDD levels below 10 ppq. This record exemplifies how pollution prevention leading to Zero Discharge of dangerous environmental contaminants can be achieved at the source through process changes and substituting and intensifying chemical processes. Figure 9.12 shows a steady reduction of dioxin/furan formation to below detection level by substituting elemental chlorine to chlorine dioxide as a bleaching agent (Das and Jain 2001; NCASI 1993).