Optimization of conventional Fenton and ultraviolet-assisted oxidation processes for the treatment of reverse osmosis retentate from a paper mill

Abstract

1According to current environmental legislation concerned with water scarcity, paper 2 industry is being forced to adopt a zero liquid effluent policy. In consequence, reverse 3 osmosis (RO) systems are being assessed as the final step of effluent treatment trains 4 aiming to recover final wastewater and reuse it as process water. One of the most 5 important drawbacks of these treatments is the production of a retentated stream, which 6 is usually highly loaded with biorecalcitrant organic matter and inorganics; and this 7 effluent must meet current legislation stringent constraints before being ultimately 8 disposed. The treatment of biorefractory RO retentate from a paper mill by several 9 promising advanced oxidation processes (AOPs) -conventional Fenton, photo-Fenton 10 and photocatalysis-was optimized considering the effect and interaction of reaction 11 parameters; particularly using response surface methodology (RSM) when appropriate 12 (Fenton processes). The economical cost of these treatments was also comparatively 13 assessed. Photo-Fenton process was able to totally remove the COD of the retentate, and 14 resulted even operatively cheaper at high COD removal levels than conventional 15 Fenton, which achieved an 80% reduction of the COD at best. In addition, although 16 these optimal results were produced at pH = 2.8, it was also tested that Fenton processes 17 are able to achieve good COD reduction efficiencies (> 60%) without adjusting the 18 initial pH value, provided the natural pH of this wastewater was close to neutral. 19Finally, although TiO2-photocatalysis showed the least efficient and most expensive 20 figures, it improved the biodegradability of the retentate, so its combination with a final 21 biological step almost achieved the total removal of the COD. 22Keywords: Advanced oxidation processes; Fenton; photo-Fenton; photocatalysis; 23 reverse osmosis retentate; paper mill effluents; response surface methodology. 24 AOPs treatment of RO retentate from a paper millDaphne Hermosilla et al.3

The application of advanced oxidation technologies to the treatment of effluents from the pulp and paper industry: a review

“…In line with these results, Hermosilla et al (2012) also reported the photoFenton treatment as being able to totally remove the organic load present in the concentrate from a reverse osmosis installed in a recycled paper mill (Table 5).…”

“…Similarly, the treatment of reverse osmosis concentrate flowing out a specific pilot treatment train implemented in a recycled paper mill, consisting of anaerobic and aerobic biological stages followed by ultrafiltration and reverse osmosis membrane treatments, was also tested and optimized by surface response methodology by Hermosilla et al (2012), and an 80% COD removal was achieved at the best resulting treatment conditions (Table 5). …”

“…Consequently, the photo-Fenton alternative has generally been shown to be more efficient in the degradation of effluent components than its dark version (Karimi et al 2010), and improves both the total quantity and the rate of TOC abatement in comparison to the UV/H 2 O 2 system (Catalkaya and Kargi 2007;Hermosilla et al 2009b;Hermosilla et al 2012). …”

“…Considering the oxygen-equivalent chemical-oxidation capacity in order to properly compare these processes, Fenton's cost resulted to be 0.7-3.0 €/kg of equivalent O 2 , whereas electrochemical oxidation addressed 2.4-4.0 €/kg of equivalent O 2 , and ozonation raised its cost up to 8.5-10 €/kg of equivalent O 2 . In fact, Fenton processes (photo-Fenton particularly) were also considered by Hermosilla et al (2012) as the cheapest alternatives for the treatment of RO retentate from a paper mill.…”

“…Considering biological treatment is not able to remove bio-recalcitrant compounds (Balcioglu et al 2003;Bijan and Mohseni 2004), new trends are focused on incorporating other processes like advanced oxidation ones (AOPs) (Balabaniç et al 2012;Balcioglu et al 2003;Bijan and Mohseni 2004;Hermosilla et al 2012).…”