In this study, decolorization and degradation of aqueous nickel phthalocyanine reactive dye solutions was comparatively studied by electrochemical methods, such as electrocoagulation, electrooxidation and electro-Fenton processes. In the electrocoagulation process with aluminum electrodes the colored aqueous solutions containing 100 mg/L nickel phthalocyanine and 6 g/L NaCl were treated at initial pH 7.5 and applied current densities of 5, 10 and 20 mA/cm 2 , where fast and 100% decolorization was achieved in 10, 5 and less than 2.5 minutes of electroprocessing respectively. The electrooxidation process was conducted in acidic electrolyte solutions containing 100 mg/L nickel phthalocyanine and 6 g/L Na 2 SO 4 with Ti/Pt and graphite plate electrodes at the applied current density of 5 mA/cm 2 . Even after 60 minutes of electrolysis time the dye remained undegradable by 17 and 40%, respectively. Substituting Na 2 SO 4 with the same concentration of NaCl, complete degradation of the dye was achieved in 30 and 20 minutes with Ti/Pt and graphite electrodes respectively. In the electroFenton process with Fe electrodes and added amounts of H 2 O 2 at pH 3 and an applied current density of 5 mA/cm 2 complete degradation of nickel phthalocyanine occurred in 20 minutes.
In the present work, the decolorization treatment of colored wastewaters produced from polyamide textile dyeing is studied using the electrocoagulation process with sacrificial aluminum electrodes. The electrical energy is obtained from a solar photovoltaic array by directly connecting it to the electrocoagulator without batteries. The photovoltaic electrocoagulation (PV-EC) system is made versatile according to the instantaneous solar irradiation by adjusting the wastewater flow rate to the current intensity supplied by the photovoltaic array. All the PV-EC experiments were performed in Kavala Institute of Technology (latitude 40˚55´, longitude 24˚22´, and altitude 138 m above the sea level). The purpose of this paper is to investigate all parameters affecting the efficiency of the process, such as initial wastewater pH, conductivity, operating time, flow rate, and solar irradiation. The efficiency of the EC process was followed by measurements of turbidity and chemical oxygen demand (COD). According to the obtained experimental results, fast and effective decolorization of the treated wastewater occurred in a few minutes of electroprocessing. Turbidity was quantitatively reduced from 103 to 0.2 NTU, amounting to a removal percentage of over 99%, whereas COD was reduced by 65%. The proposed process is appropriate for decolorizing colored textile dye wastewaters and especially for small applications in remote and isolated locations without connection to public electric grid.
In this work the performance of electrocoagulation in the treatment of acid lead battery manufacturing wastewater was studied. Both iron and aluminum sacrificial electrodes remove lead effectively. However, pH of the treated wastewater depends on the electrode material and the supporting electrolyte used. Iron electrocoagulation with KCl as supporting electrolyte reduces the initial Pb 2+ ion concentration of 8.6 mg L-1 to 0.2 mg L-1 in 20 minutes of electrolysis time. At the same time, however, the initial wastewater pH of 2.96 rises sharply to 12.24 exceeding by far the upper legal limit for effluent discharge to the environment. On the contrary iron electrocoagulation with Na 2 SO 4 as supporting electrolyte does not increase pH sufficiently to the appropriate range. Aluminum treatment with KCl and Na 2 SO 4 electrolytes need 35 minutes of electrolysis time for effective lead removal. Effective removal of both, acidity and lead in a single step was achieved in only 25 minutes of electrolysis time with iron electrodes and a mixed supporting electrolyte solution containing 0.03 M Na 2 SO 4 and 0.003 M KCl.
Small and insular communities are sometimes not served by an efficient Wastewater Treatment Plant, and this is a hazard for both the environment and public health. A wastewater treatment apparatus based on the electrocoagulation process (EC) was tested with municipal wastewater from a small community in Northern Greece with a maximum of 6500 population equivalents. COD decrease was assessed under various parameters: current intensity, time duration, pH and use of Fe or Al electrodes. A simulation of meeting the community’s electricity needs with this apparatus was tested through RETScreen software. The results showed a satisfactory COD decrease through electrocoagulation which was affected by all the parameters mentioned; Fe electrodes could efficiently be used at 300 mA for 60 min for 55% COD removal. It was also shown that a photovoltaic panel system covers the electricity needs of the apparatus, thus no external electricity source is needed for its use. This apparatus could be used effectively by this community, so that the running costs are minimal.
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