Treatment of Fenton‐refractory olive oil mill wastes by electrochemical oxidation with boron‐doped diamond anodes

Abstract

In this work, the electrochemical oxidation of an actual industrial waste with conductive diamond anodes has been studied. The wastewater is the effluent of a wastewater treatment plant consisting of a Fenton reactor followed by a settler and a sand filter, in which the wastes generated in an olive oil mill are treated. These wastes contain a residual chemical oxygen demand of nearly 700 mg dm −3 which cannot be further oxidized with the Fenton process. The electrolyses were carried out under galvanostatic conditions, using a bench-scale plant equipped with a single-compartment electrochemical flow cell. Boron-doped diamond (BDD) and stainless steel (AISI 304) were use as anode and cathode of the cell, respectively. The complete mineralization of the waste was obtained with high current efficiencies limited only by mass transport processes. This confirms that besides the hydroxyl radical-mediated oxidation that occurs in the Fenton process, the electrochemical oxidation with conductive diamond electrodes combines other important oxidation processes such as direct electro-oxidation on the BDD surface and oxidation mediated by other electrochemically formed compounds generated in this electrode.

Electrochemical oxidation of succinic acid in aqueous solutions using boron doped diamond anodes

“…The small concentration of intermediates suggests that, once the electrochemical oxidation of succinic acid starts, this process proceeds to the complete mineralization of the molecule in a zone close to the anode surface. This behavior was previously reported for the oxidation of other organics on BDD anodes (Canizares et al 2006b;Louhichi et al 2008a;Martinez-Huitle and Brillas 2009;Rodrigo et al 2010;Saez et al 2007) and supports the hypothesis that the oxidation of the organics on these electrodes occurs directly on the anode surface or at a small distance very close to this surface, mediated by hydroxyl radicals generated by water oxidation. Figure 6 shows the influence of current density on COD and TOC destruction with specific electrical charge during galvanostatic electrolyses of succinic acid aqueous solutions (0.1 M Na 2 SO 4 ) containing 500 mg O 2 /L.…”

“…Mediated oxidation of succinic acid by hydroxyl radicals and other oxidants electrogenerated from supporting electrolyte oxidation on BDD appears to be more important than the direct oxidation mechanism in the case of succinic acid. Similar results were previously observed in several cases during galvanostatic electrolyses of organics on BDD anodes (Canizares et al 2006b;Louhichi et al 2008a;Martinez-Huitle and Brillas 2009;Rodrigo et al 2010;Saez et al 2007). Figure 4 presents the behavior of COD and TOC (Fig.…”

“…This could be due to the fact that succinic acid oxidation on BDD surface takes place at a potential, very close to that of the electrolyte oxidation. The absence of anodic peaks evidences that the succinic acid oxidation on BDD anodes is much more difficult than aromatic compounds' oxidation such as phenols, herbicides, dyes and surfactants (Bensalah et al 2009;Boye et al 2006;Canizares et al 2006b;Louhichi et al 2008b;MartinezHuitle and Brillas 2009;Rodrigo et al 2010;Sires et al 2006;Weiss et al 2008). Similar results were reported by other studies on aliphatic carboxylic acids and alcohols (Canizares et al 2003(Canizares et al , 2008Gandini et al 2000;Ivandini et al 2006;Louhichi et al 2008b;Martinez-Huitle et al 2008;Onofrio et al 2008).…”

“…This electrochemical method has been used at both laboratory and industrial scale to treat wastewaters contaminated with organic pollutants. Numerous previous studies focused on the treatment of wastewaters contaminated with toxic aromatic compounds such as phenol (Hagans et al 2001;Iniesta et al 2001;Panizza et al 2002;Weiss et al 2008;Yavuz et al 2008) and phenol derivatives (Bensalah et al 2009;Canizares et al 2004Canizares et al , 2005aPacheco et al 2007;Rodrigo et al 2001), herbicides (Brillas et al 2004(Brillas et al , 2007Boye et al 2006;Sires et al 2006), dyes (Ahmadi et al 2007;Butron et al 2007;Canizares et al 2006a;Chen and Chen 2006;Saez et al 2007) and others (Canizares et al 2006b(Canizares et al , 2007Carter and Farrell 2008;Kapalka et al 2008a, b;Kraft 2007;Louhichi et al 2008a, b;Martinez-Huitle and Brillas 2009;Panizza and Cerisola 2009;Prabhakaran et al 2009;Quiroz Alfaro et al 2006). Also, electrochemical treatment of other bioresistant organic pollutants such as aliphatic compounds was investigated by few researches using BDD anodic oxidation.…”

Electrochemical synthesis of peroxomonophosphate using boron-doped diamond anodes

“…In recent years, electrochemical oxidation with conductive-diamond anodes has become one of the most promising technologies in the treatment of industrial wastes polluted with organics [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and in the electrosynthesis of inorganic oxidants [13,[33][34][35]. Compared with other electrode materials, conductive-diamond has shown higher chemical and electrochemical stability as well as a higher current efficiency.…”