62ª Reunião Anual da SBPC

A. Ciências Exatas e da Terra - 4. Química - 2. Química Ambiental

APPLICATION OF ELECTROCHEMICAL TECHNOLOGY IN THE NORTHEAST BRAZILIAN REGION AS AN ALTERNATIVE DECOLORIZATION TREATMENT OF WASTEWATERS CONTAINING INDUSTRIAL TEXTILE DYES

Jéssica Horacina Bezerra Rocha 1 Juan Manuel Peralta-Hernandez 2 Djalma Ribeiro da Silva 1 Nedja Suely Fernandes 1 Carlos Alberto Martínez-Huitle 1

1. Universidade Federal do Rio Grande do Norte, Departamento de Química,UFRN-Brasil 2. Universidad Autónoma de Nuevo León. Facultad de Ciencias Químicas, UANL-México

INTRODUÇÃO:

Synthetic dyes are extensively used in many fields of up to-date technology, such as in various branches of the textile industry, leather tanning industry, paper production, food technology, etc. Due to large-scale production and extensive application, synthetic dyes can cause considerable environmental pollution and are serious health-risk factors. For the removal of dyes from wastewater a wide range of techniques, such as chemical precipitation, chemical oxidation or adsorption with subsequent biological treatment has been developed. However, the electrochemical processes for treating wastewater containing dyes have been recently proposed as an innovative alternative. Therefore, in this work, the electrochemical treatment of synthetic wastewaters containing Remazol Red BR (RRB) and Novacron Blue C-D (NB), dyes widely used in the Northeast Brazilian Textile industries, using boron doped diamond anodes (BDD) was investigated, in order to eliminate their strong color and their ecotoxicological consequences on aquatic environment. The influences of the main operating parameters, such as current density, pH, textile dye and temperature, on the color removal of a dye synthetic solution were investigated, in order to identify optimal experimental conditions.

METODOLOGIA:

The dyestuff solution was prepared dissolving textile dyes in distilled wastewater containing 0.25 M Na2SO4, adjusting pH value to 1, 4.5 and 8 using 0.5 M H2SO4 or 0.1 M NaOH. The textile dyeing industrial effluent generally has a pH 10, for this reason, electrochemical process was tested varying pH value in order to determine the pH influence in the removal efficiency. Initial concentrations of 190 mgL-1 of each dye were used. Bulk oxidations were performed in undivided electrochemical cell (400 mL) and these were performed under galvanostatic conditions using a potentiostat-galvanostat. BDD anode was supplied by Adamant Technologies (Neuchatel, Switzerland) and used as the anode, and titanium as the cathode (both electrodes with 10 cm2 of geometrical area). The temperature of the electrolyte was controlled using a water thermostat. Experiments were performed at 25 °C for studying the role of applied current density (20, 40 and 60 mAcm-2) and pH (1, 4.5 and 8), while the temperature effect (25 to 60°C) was studied under a current density of 40 mAcm-2. Color removal was monitored by measuring absorbance decrease; using a spectrophotometer. Hazen units were determined using the method 8025 (Pt-Co units). The energy consumption per volume of treated effluent was estimated.

RESULTADOS:

The absorbance was satisfactorily reduced during the treatment. The intensity of the visible band decreases continuously until its disappearance after about 60 min and 40 min of electrolysis, leading to complete solution decolorization for NB and RRB, respectively. Complete color removal, in all cases, was achieved; independently of the applied current density and pH. Although the elimination rate increase when the applied current density values were increased. However, at higher pH values (4.5 and 8) the decolorization time process increase about two times respect to obtained under lower pH values (1.0), probably due to that the electro-active species in more acidic medium are more easily oxidized than that of alkaline medium. According to Brazilian laws, the color in the residual effluents from textile industry must be lower than 300 Hazen Units, but inferior 300 HU values were achieved after short times or 50% of electrochemical treatment; in all cases. The increase of temperature from 25 to 60°C decreases the electrolysis-time required for the total color removal. The energy consumption seems to be proportional to the applied current density; it increases from 3.30 to 4.28 kWh per volume of treated effluent of RRB at pH 1, when the current density passes from 20 to 60 mAcm-2.

CONCLUSÃO:

The main conclusions of this work can be summarized in the following points: (i) Anodic oxidation using diamond films  (BDD) can be used successfully to remove completely all color from synthetic wastewaters polluted with textile dyes, considering the specific operating conditions (current density, pH and temperature), (ii) The influence of current density, temperature and pH as functions of time, during electrochemical experiments, showed that the oxidation by the electro-generated reagents from the anodic oxidation of supporting electrolyte (hydroxyl radicals) plays important role in the efficiency of the electrochemical process, (iii) Energy consumption measured during electrochemical treatment of synthetic dye wastewater solutions depends largely on the applied current density but modest influence of temperature on the energy requirements was observed and (v) Finally, these results allow to establish that the electrochemical treatment could be employed as an alternative for removing color from dye wastewaters, because after the application of electrochemical technology the wastewaters remaining into the Brazilian regulations to be discharged.

Instituição de Fomento: Universidade Federal do Rio Grande do Norte - UFRN and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES. Petrobras.

Palavras-chave: Electrochemical technology, Decolourization, Wastewater treatment.