Abstract
The present work evaluated the use of photo-Fenton process for the treatment of kraft pulp mill effluent. The photo-Fenton best operating conditions, such as pH, concentration, and H2O2: Fe2+ ratio were evaluated. The efficiency of the treatment was measured by COD (chemical oxygen demand) removal. The results showed that the optimum pH for the photo-Fenton process was equal to 3. The increase in H2O2 application resulted in an efficiency increase of the photo-Fenton process, although this was not a directly proportional relation. For most cases, the H2O2: Fe2+ proportion of 100:1 yielded the best results for COD removal. Solar radiation was more efficient than artificial UV to the COD removal. During the treatment the organic matter of the effluent was more oxidized than mineralized, showing a higher removal of COD than BOD (biochemical oxygen demand) and TOC (total organic carbon), respectively. So, photo-Fenton process increased the BOD/ COD ration but decreased the BOD/TOC ratio.
Highlights
Biological treatment processes are commonly used to treat pulp mill effluents and, in some cases, are not enough to meet regulations
The effluent used in the study showed typical characteristics of eucalyptus kraft pulp mill effluents (Table 1), as the high chloride content and the high ratio between organic matter (BOD or COD) and the nutrients nitrogen and phosphorus
The mixture of all currents of sectorial effluents of a mill generates a final effluent, the pH of which normally ranges from 5 to 8, which is more suitable for the biological treatment, but incompatible with the photo-Fenton reaction (Figure 1)
Summary
Biological treatment processes are commonly used to treat pulp mill effluents and, in some cases, are not enough to meet regulations In part, this is due to a fraction of recalcitrant organic matter present in the effluent, which is inert to biological oxidation. This type of treatment may fractionate complex molecules of high molecular mass into simpler intermediate compounds, such as acetic, maleic, and oxalic acids, acetone and chloroform. These new formed compounds are part of the bioenergetic cycle of living organisms and, they are compatible with the biological treatment [4]
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