Environmental Science and Pollution Research

, Volume 25, Issue 28, pp 27783–27795 | Cite as

Mineralization of humic acids (HAs) by a solar photo-Fenton reaction mediated by ferrioxalate complexes: commercial HAs vs extracted from leachates

  • Ana P. F. Santos
  • Bianca M. Souza
  • Tânia F. C. V. SilvaEmail author
  • Rodrigo P. Cavalcante
  • Silvio C. Oliveira
  • Amílcar MachulekJr.
  • Rui A. R. Boaventura
  • Vítor J. P. VilarEmail author
New Challenges in the Application of Advanced Oxidation Processes


The mineralization of bio-recalcitrant humic acids (HAs) by a solar photo-Fenton (SPF) process was investigated in aqueous system, in order to understand its abatement in real high-HA content matrices, such as sanitary landfill leachates. SPF reactions were performed in tubular photoreactors with CPCs at lab-scale (simulated solar light) and pilot-scale (natural sunlight). Considering the experimental conditions selected for this work, the formation of insoluble HA-Fe3+ complexes was observed. Thus, to avoid HA precipitation, oxalic acid (Ox) was added, since Fe3+-Ox complexes present a higher stability constant. The effect of different process variables on the performance of SPF reaction mediated by ferrioxalate complexes (SPFF) was assessed with excess of H2O2 (50–250 mg L−1), at lab-scale: (i) pH (2.8–4.0); (ii) initial iron concentration (20–60 mg Fe3+ L−1); (iii) iron-oxalate molar ratio (Fe3+-Ox of 1:3 and 1:6); (iv) temperature (20–40 °C); (v) UV irradiance (21–58 WUV m−2); and (vi) commercial-HA concentration (50–200 mg C L−1). At the best lab conditions (40 mg Fe3+ L−1, pH 2.8, 30 °C, 1.6 Fe3+-Ox molar ratio, 41 WUV m−2), commercial HAs’ mineralization profile was also compared with HAs extracted from a sanitary landfill leachate, achieving 88 and 91% of dissolved organic carbon removal, respectively, after 3-h irradiation (8.7 kJUV L−1). Both reactions followed the same trend, although a 2.1-fold increase in the reaction rate was observed for the leachate-HA experiment, due to its lower humification degree. At pilot-scale, under natural sunlight, 95% HA mineralization was obtained, consuming 42 mM of H2O2 and 5.9 kJUV L−1 of accumulated UV energy. However, a pre-oxidation during 2.8 kJUV L−1 (12 mM H2O2) was enough to obtain a biodegradability index of 89%, showing the strong feasibility to couple the SPFF process to a downstream biological oxidation, with low chemicals and energetic demands.

Graphical abstract


Landfill leachates Solar-driven photo-Fenton Ferrioxalate complexes Biodegradability 


Funding information

This work was financially supported by project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under Portugal 2020 Partnership Agreement, through European Regional Development Fund (ERDF), and of Project POCI-01-0145-FEDER-006984—Associate Laboratory LSRE-LCM funded by ERDF through COMPETE 2020—Programa Operacional Competitividade e Internacionalização (POCI)—and by national funds through FCT—Fundação para a Ciência e a Tecnologia. Ana Santos acknowledges her Ph.D. fellowship (BEX 10029/13-3 process) supported by CAPES and CNPq. Bianca Souza acknowledges her Ph.D. scholarship by program Brazil/Portugal CAPES/FCT 308/11. Tânia Silva acknowledges her Ph.D. scholarship, reference SFRH/BD/73510/2010, supported by FCT. V.J.P. Vilar acknowledges the FCT Investigator 2013 Programme (IF/00273/2013).

Supplementary material

11356_2018_1561_MOESM1_ESM.doc (1.1 mb)
ESM 1 (DOC 1161 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Ana P. F. Santos
    • 1
    • 2
  • Bianca M. Souza
    • 1
  • Tânia F. C. V. Silva
    • 1
    Email author
  • Rodrigo P. Cavalcante
    • 2
  • Silvio C. Oliveira
    • 2
  • Amílcar MachulekJr.
    • 2
  • Rui A. R. Boaventura
    • 1
  • Vítor J. P. Vilar
    • 1
    Email author
  1. 1.Laboratory of Separation and Reaction Engineering-Laboratory of Catalysis and Materials (LSRE-LCM), Departamento de Engenharia Química, Faculdade de EngenhariaUniversidade do PortoPortoPortugal
  2. 2.Instituto de QuímicaUniversidade Federal de Mato Grosso do SulCampo GrandeBrazil

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