Influence of chlorine ratio and oxygen bleaching on the formation of PCDFs and PCDDs in pulp bleaching. I: A laboratory study

Previous studies had shown that polychlorinated dibenzofurans (PCDF) and polychlorinated dibenzo-p-dioxins (PCDD) were present in waste waters and sludges from pulp and paper mills, and that these compounds were formed during the chlorine bleaching process. Further laboratory studies had been carried out on factors affecting the formation of these compounds, and the results are summarized in tables and graphs, and discussed. The chlorine ratio was the most important factor. Lower amounts of PCDF and PCDD were found after oxygen bleaching of the pulp, but this was attributed to the efficient washing of the pulp in this process, which removed PCDF and PCDD precursors.