A combined electrocoagulation (EC) and electrochemical oxidation (EO) industrial textile wastewater treatment potential is evaluated in this work. A fractional factorial design of experiment showed that EC current density, followed by pH, were the most significant factors. Conductivity and number of electrooxidation cells did not affect chemical oxygen demand degradation (DCOD). Aluminum and iron anodes performed similarly as sacrificial anodes. Current density, pH and conductivity were chosen for a Box-Behnken design of experiment to determine optimal conditions to achieve a high DCOD minimizing operating cost (OC). The optimum to achieve a 70% DCOD with an OC of USD 1.47/m was: pH of 4, a conductivity of 3.7 mS/cm and a current density of 4.1 mA/cm. This study also shows the applicability of a combined EC/EO treatment process of a real complex industrial wastewater.

In this work, the Box-Behnken experimental design and the surface response methodology were applied for the optimization of the operational conditions of the electro-catalytic degradation of wastewaters, resulting from a local textile industry. The experiments were carried out in a laboratory scale batch cell reactor, with monopolar configuration, and electrodes made of boron-doped diamond (anode) and titanium (cathode). The multifactorial experimental design included the following variables: current density (i: 5-10 mA/cm 2 ), pH (3-7), and submerged cathode area (CA: 8-24 cm 2 ). To determine the process efficiency, the degradation percentage of: the chemical oxygen demand (%DCOD), the total organic carbon (%DTOC) and the color (%DC) were defined as response variables. The following optimal conditions for the electrooxidation (EO) process were obtained: i = 10 mA/cm 2 , pH = 3 and CA = 16 cm 2 , reaching ca. 92 % of DC, 37 % of DCOD and 31 % of DTOC. The electro-Fenton (EF) and photo-electro-Fenton (PEF) processes were also evaluated at EO optimal conditions. For the EF process, with addition of iron (0.3 mM), the %DC, %DCOD and %DTOC was enhanced to 95, 52 and 45 %, respectively. For the PEF process (UV = 365 nm), it was possible to reach 98 %DC, 56 %DCOD and 48 %DTOC.

ResumenEn la presente investigación se utilizó el proceso Fenton heterogéneo, con hierro cero valente (ZVI) en estado metálico, en un reactor de lecho fluidizado para el tratamiento de aguas residuales de una industria textil. El objetivo fue optimizar los siguientes parámetros de operación: concentración inicial de colorante, concentración de H2O2, pH, cantidad de ZVI, y radiación UV, para maximizar la eliminación de colorante y materia orgánica. Inicialmente, se usó un diseño de experimentos factorial fraccionado, con la finalidad de encontrar los factores más influyentes. Posteriormente, para su optimización, se empleó la Metodología de Superficie de Respuesta acoplado a un diseño experimental Box-Behnken. Las condiciones óptimas obtenidas fueron: concentración inicial del colorante: 881 mg/L, pH: 5, concentración de ZVI: 5,31 g/L, y concentración de H2O2: 0,86 mL/L. A estas condiciones se realizó un estudio cinético que demostró que es posible degradar el 100% colorante y el 80,83% de la demanda química de oxígeno en 150 minutos de reacción. Palabras clave: hiero cero-valente; Fenton; aguas residuales; optimización; diseño Box-Behnken Degradation of Yellow 12 Dye in Industrial Wastewater using Zero-Valent Iron, Hydrogen Peroxide and Ultraviolet Radiation AbstractThe Fenton heterogeneous process in a fluidized bed reactor using Zero Valent Iron (ZVI), in the metallic state, for the treatment of textile wastewater has been used an analyzed. The aim of this work was to optimize the following operating parameters: initial dye concentration, H2O2 concentration, pH, amount of ZVI, and UV radiation, for the removal of dye and organic matter. At first, a fractional factorial experimental design allows defining the most influential factors. After that, they were optimized using the Response Surface Methodology coupled to the Box-Behnken experimental design. The optimal conditions were found to be as follows: initial dye concentration, 881 mg/L; pH 5; ZVI concentration, 5,31 g/L; H2O2 concentration, 0,86 mL/L. At these conditions, the degradation kinetics was performed, reaching 100% and 80,83% of dye and chemical oxygen demand respectively, in 150 minutes of reaction.

ResumenSe efectuó la optimización estadística del costo de implementación y operación del tratamiento por electrooxidación de aguas residuales contaminadas con el colorante Amarillo 23. El objeto fue encontrar los valores de operación para la densidad de corriente, conductividad, y área de electrodos por unidad de volumen que minimicen el valor presente neto (VPN) de la operación mientras se mantiene una calidad de tratamiento establecida. Para alcanzar este objetivo se empleó la Metodología de Superficie de Respuesta acoplada a un diseño de experimentos Box-Behnken. Las condiciones óptimas encontradas fueron: Relación volumen tratado por área de electrodos: 9.076 mL/cm 2 , conductividad: 4000 µS/cm y densidad de corriente 20 mA/cm 2 , para las cuales el VPN predicho a 10 años es de 998636 USD y corresponde a un costo de 0.67 USD/m 3 de agua tratada. Palabras clave: tratamiento de aguas residuales; optimización; electroquímica; análisis de superficie de respuesta Optimization of the Operating Cost for the ElectrochemicalOxidation Process in a Water Treatment Plant Using Response Surface Statistical Analysis AbstractThe statistical optimization of the implementation and operational costs of an electrochemical-oxidation process for treatment of wastewater containing dye Yellow 23 was done. The aim was to optimize the operational parameters for the current density, conductivity, and area of electrodes per unit of volume in order to minimize the net present value (NPV) of the operation while maintaining a defined quality for the treated wastewater. To achieve this, the response surface methodology coupled to the Box-Behnken statistical design was used. The optimal conditions found were: a relationship of treated wastewater volume per area of electrodes of 9.076 mL/cm 2 , conductivity 4000 µS/cm, and current density 20 mA/cm 2 . At optimal conditions, the NPV for a 10 year operation is 998636 USD, which corresponds to a cost of 0.68USD/m 3 of treated water.

The elimination of total and fecal coliforms, from raw surface water, was carried out by electrochemical oxidation using either boron doped diamond (BDD/Ti) or graphite (GP) anodes, in a chloride-free medium. The optimal values of the operation parameters, maximizing the coliform elimination percentage, were determined using statistical experimental design. The current density (j: 2–20 mA/cm2), the conductivity (σ: 500–900 μS/cm) and the anode materials (An) were considered as variables to perform the Box-Behnken experimental design together with the response surface methodology analysis for optimization. The statistical analysis indicated that, in the evaluated range, the disinfection efficiency increased with an increase in j and decreased with an increase in σ. The following optimal conditions for the elimination of total and fecal coliforms were found: j: 10 mA/cm2, σ: 500 μS/cm and BDD/Ti used as anode material. The BDD/Ti electrode let to achieve complete coliform elimination after ca. 20 min of reaction while the GP one needed ca. 27 min. In water treated with both BDD/Ti and GP anode, after 7 days, any coliforms growth was observed. As a result of the oxidation process, the total organic carbon and nitrite concentration decreased while nitrate concentration increased.