Oxidation of the herbicides diuron and Alachlor by electrochemical advanced oxidation processes using anodes: Ti/IrO2, Ti/RuO2, Pt and BDD

Author(s)

Angelo Ricardo Fávaro Pipi

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2014-06-30

Examining board members

Adalgisa Rodrigues de Andrade; Carlos Alberto Martinez Huitle; Artur de Jesus Motheo; Paulo Olivi; Maria Valnice Boldrin Zanoni

• Advisor: Adalgisa Rodrigues de Andrade

Abstract

Commercial herbicide Diuron solution (Nortox SA) was degrated using Ti/RuxTi(1-x)O2 and Ti/IrxTi(1-x)O2 (x = 0.3, 0.5, and 0.7) anodes. Degradation was investigated in the presence and in the absence of chloride. In the absence of chloride, herbicide removal yielded 41 and 49% COD (chemical oxygen demand) removal, and 10 and 14% TOC (total organic carbon) removal at 100 mA cm-2, respectively. For a constant electrolysis time (4 h), Ti/Ru0.7Ti0.3O2 anode composition removed Diuron and its byproduct the most activelly. Addition of chloride doubled the removal ratio, and the Ti/Ru0.3Ti0.7O2 anode afforded 100% COD removal. Electrochemical advanced oxidation processes (EAOPs) quickly degraded and even totally mineralized the herbicide Alachlor in electrochemical cells equipped with a carbonaceous air-diffusion cathode that was able to electrogenerate H2O2 and with a Pt or boron-doped diamond (BDD) anode. The photoelectron-Fenton (PEF) process with BDD in the presence of 0.5 mmol L-1 Fe2+ performed the best in Alachlor solutions treatment (100 mL, 0.60 mmol L-1, 360 min.). According to GC-MS analyses, Alachlor degradation involved four different reaction pathways (dealkylation, cyclization, R-N bond cleavage and hydroxylation), to give nine byproducts, including the detected carboxylic. Different amounts of nitrogenated (NH4+ and NO3-) and chlorinated (Cl-, ClO3- and ClO4-) ions accumulated in the final solutions depending on the anode and the applied current. The herbicide Diuron (0.185 mmol L-1 and pH 3.0) was treated using different EAOPs like anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF), and solar PEF (SPEF). Experiments were performed in 100 mL electrochemical cells, and in a 2.5 L pre-pilot flow plant. In the electrochemical cells, the PEF treatment with BDD was the most potent, yielding 93% mineralization after 360 min at 100 mA cm-2. In the pre-pilot flow plant, the SPEF process furnished maximum mineralization of 70% at 100 mA cm-2. Oxalic and oxamic acids were detected as final carboxylic acids. Ammonium and chloride ions were also released; the latter ion was partially converted into chlorate and perchlorate ions at the BDD surface (AU)

• FAPESP's process: 10/08588-9 - Oxidation of herbicides through the electrochemical and photoelectrochemical process using dimensionally stable anodes: Ti/IrO2, Ti/RuO2 and BDD.
• Grantee: Angelo Ricardo Fávaro Pipi
• Support Opportunities: Scholarships in Brazil - Doctorate