Analysis of the combination of adsorption technologies on granular activated carbon and electrochemical oxidation for the treatment of effluents contaminated with benzene

Author(s)

Rodrigo de Mello

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2023-02-24

Examining board members

Artur de Jesus Motheo; Eduardo Bessa Azevedo; Maria Valnice Boldrin; Carmen María Fernández Marchante; Manuel Andrés Rodrigo Rodrigo

• Advisor: Artur de Jesus Motheo

Abstract

Several classes of emerging contaminants (ECs) have already been discovered in water bodies, i.e., contaminants about whose effects on the environment and on humans are not yet fully understood. At the same time, concern about atmospheric air pollution has increased in recent years, with volatile organic compounds (VOCs) being the main contaminants. It is important to emphasize that ECs are present in the environment at low concentrations and that conventional treatment methods used in municipal wastewater treatment plants are not capable of removing them completely. Among the alternative methods, electrochemical processes are gaining ground. However, their efficiency decreases when the concentration of pollutants is low due to mass transfer limitations. For this reason, this thesis addressed the combination of adsorption and electrochemical oxidation technologies for the removal of pollutants in aqueous solutions and gas streams. First, the electrochemical treatment of the antibiotic tetracycline and benzene, toluene and xylene, examples of VOCs, in methanol medium was evaluated, as it is used to desorb the pollutants adsorbed on the surface of granular activated carbon (CAG). Different electrodes were used to evaluate the efficiency of the electrochemical treatment process: the electrodes made of mixed metal oxide, commercially known as DSA®, and anodes made of boron-doped diamond (BDD) in the presence of different supporting electrolytes (NaCl and H2SO4). Subsequently, the combination of adsorption and electrochemical oxidation technologies was evaluated in the treatment of a large volume of a solution with a low benzene concentration. Finally, a gas stream contaminated with benzene was generated to evaluate the combination of the above techniques in its treatment. In the electrochemical oxidation of the antibiotic used as probe molecule, DSA® in methanol and NaCl medium showed superior efficiency compared to BDD, with a removal of more than 90% after 10 minutes of experiment. When H2SO4 was used as the supporting electrolyte in methanol medium, the BDD showed greater removal of the contaminant. In the electrochemical treatment of benzene, toluene and xylene, the most interesting factor was the formation of value-added substances when the treatment was carried out in methanol, where BDD was more efficient than DSA®. In the treatment combining adsorption and electrochemical oxidation, the possibility of recovering CAG was evaluated and it was found that a drying step of the material was necessary for its adsorption capacity to remain constant. In addition, with regard to the sustainability of the system, the reuse of the treated methanol after the adsorption/desorption cycle was analyzed and it was found that the reuse in 3 cycles reduced the adsorption capacity of the CAG by less than 10%. Finally, the treatment of both aqueous solutions and air streams contaminated with benzene by combining adsorption and electrochemical oxidation techniques in methanol proved to be beneficial because the benzene concentration after the desorption step is high and anisole, a high added-value substance, is produced during the electrochemical treatment and its production is proportional to the initial benzene concentration. In this way, this thesis has contributed to a new point of view that can help to change the paradigm of wastewater treatment by electrorefinery techniques. (AU)

• FAPESP's process: 18/16308-8 - Production and characterization of hybrid nanomaterials from electrospun nanofibers and evaluation of their efficiency against the electrochemical oxidation of atrazine
• Grantee: Rodrigo de Mello
• Support Opportunities: Scholarships in Brazil - Doctorate