Photodegradation of high molecular weight kraft bleachery effluent organochlorine and color

Previously it was shown that the high molecular weight (HMW) fractions of C and E-stage kraft bleachery effluents are very resistant to microbial degradation but are decolorized and dechlorinated by abiotic sunlight-dependent and sunlight-independent processes. In this work, to better understand the importance and mechanisms of this light-mediated effluent decolorization and AOX mineralization, two artificial light sources with defined outputs and spectra were used to irradiate hardwood and softwood HMW effluent fractions. Both longwave u.v. and blue-green visible light were effective in mineralizing a large fraction of the AOX to chloride ions, and in decolorizing the effluent over several days. Photo-decolorization showed a strong oxygen dependence while AOX mineralization did not. Visible light at an intensity comparable to the sun at the Earthʹs surface in northern latitudes mineralized a substantial proportion of the “stable” HMW AOX, in both fresh and salt water, and at low and high effluent dilutions. Such light also mineralized an appreciable fraction of the HMW carbon to CO2 by abiotic mechanisms. The hardwood HMW fraction showed insignificant toxicity as measured by a bacterial toxicity test, both before and after extensive photolysis.