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Moreira, Portugal

Rocha E.M.R.,Federal University of Ceara | Vilar V.J.P.,University of Porto | Fonseca A.,Efacec Ambiente SA | Saraiva I.,Efacec Ambiente SA | Boaventura R.A.R.,University of Porto
Solar Energy | Year: 2011

Sanitary landfill leachate resulting from the rainwater percolation through the landfill layers and waste material decomposition is a complex mixture of high-strength organic and inorganic compounds which constitutes serious environmental problems. In this study, different heterogeneous (TiO2/UV, TiO2/H2O2/UV) and homogenous (H2O2/UV, Fe2+/H2O2/UV) photocatalytic processes were investigated as an alternative for the treatment of a mature landfill leachate. The addition of H2O2 to TiO2/UV system increased the reduction of the aromatic compounds from 15% to 61%, although mineralization was almost the same. The DOC and aromatic content abatement is similar for the H2O2/UV and TiO2/H2O2/UV processes, although the H2O2 consumption is three times higher in the H2O2/UV system. The low efficiency of TiO2/H2O2/UV system is presumably due to the alkaline leachate solution, for which the H2O2 becomes highly unstable and self-decomposition of H2O2 occurs. The efficiency of the TiO2/H2O2/UV system increased 10 times after a preliminary pH correction to 4. The photo-Fenton process is much more efficient than heterogeneous (TiO2, TiO2/H2O2/UV) or homogeneous (H2O2/UV) photocatalysis, showing an initial reaction rate more than 20 times higher, and leading to almost complete mineralization of the wastewater. However, when compared with TiO2/H2O2/UV with acidification, the photo-Fenton reaction is only two times faster.The optimal initial iron dose for the photo-Fenton treatment of the leachate is 60mg Fe2+L-1, which is in agreement with path length of 5cm in the photoreactor. The kinetic behaviour of the process (60mg Fe2+ L-1) comprises a slow initial reaction, followed by a first-order kinetics (k=0.020 LkJUV-1, r0=12.5mg kJUV-1), with H2O2 consumption rate of kH2O2=3.0mmol H2O2 kJUV-1, and finally, the third reaction period, characterized by a lower DOC degradation and H2O2 consumption until the end of the experiment, presumably due to the formation of low-molecular-weight carboxylic groups. A total of 306mM of H2O2 was consumed for achieving 86% mineralization (DOCfinal=134mgL-1) and 94% aromatic content reduction after 110kJUV L-1, using an initial iron concentration of 60mg Fe2+ L-1. © 2010 Elsevier Ltd.

Vilar V.J.P.,University of Porto | Rocha E.M.R.,Federal University of Ceara | Mota F.S.,Federal University of Ceara | Fonseca A.,Efacec Ambiente SA | And 2 more authors.
Water Research | Year: 2011

A solar photo-Fenton process combined with a biological nitrification and denitrification system is proposed for the decontamination of a landfill leachate in a pilot plant using photocatalytic (4.16 m2 of Compound Parabolic Collectors - CPCs) and biological systems (immobilized biomass reactor). The optimum iron concentration for the photo-Fenton reaction of the leachate is 60 mg Fe2+ L-1. The organic carbon degradation follows a first-order reaction kinetics (k = 0.020 L kJUV -1, r0 = 12.5 mg kJUV -1) with a H2O2 consumption rate of 3.0 mmol H2O2 kJUV -1. Complete removal of ammonium, nitrates and nitrites of the photo-pre-treated leachate was achieved by biological denitrification and nitrification, after previous neutralization/sedimentation of iron sludge (40 mL of iron sludge per liter of photo-treated leachate after 3 h of sedimentation). The optimum C/N ratio obtained for the denitrification reaction was 2.8 mg CH3OH per mg N-NO3 -, consuming 7.9 g/8.2 mL of commercial methanol per liter of leachate. The maximum nitrification rate obtained was 68 mg N-NH4 + per day, consuming 33 mmol (1.3 g) of NaOH per liter during nitrification and 27.5 mmol of H2SO4 per liter during denitrification. The optimal phototreatment energy estimated to reach a biodegradable effluent, considering Zahn-Wellens, respirometry and biological oxidation tests, at pilot plant scale, is 29.2 kJUV L-1 (3.3 h of photo-Fenton at a constant solar UV power of 30 W m-2), consuming 90 mM of H2O2 when used in excess, which means almost 57% mineralization of the leachate, 57% reduction of polyphenols concentration and 86% reduction of aromatic content. © 2011 Elsevier Ltd.

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