Document Type : Article
Authors
Dept. of Civil & Environmental Engineering Tarbiat Modares University
Abstract
Due to the potential contamination of groundwater and surface water in the vicinity of the consumer dye industry, removal of this dyestuff waste is an environmental priority. Water clarity and solubility of gases in the presence of even a small amount of dye is reduced. If there are colored substances toxic to lower layers light penetration in the water is low. In addition, photosynthesis of aquatic plants and the amount of dissolved oxygen is so low that aquatic animals are destroyed. Dyes are stable compounds that are not easily biodegradable, and azo dyes are considered especially carcinogenic. Dye removal via various methods of physical, chemical, biological or a combination of them is possible that can be noted on physical methods such as adsorption, membrane filtration and ultrasonic waves, chemical methods, such as ion exchange, electrolysis, coagulation and flocculation, canonical and advanced oxidation, and biological methods, using algae, fungi and bacteria.Chemical coagulation is a common method of wastewater containing dye. High levels of dissolved solids and sludge in purified effluent are the disadvantages of chemical coagulation. In recent years, because of the versatility and compatibility with the environment, the electrochemical method
as an effective method for treating wastewater of containing dye industries is taken into consideration. In the electric coagulation, production happens in the place of coagulant materials that are the result of dissolution metal anode (steel) by passing an electric current.If we put sewage between the positive anode and negative cathode that are plugged to electricity, an electric field is established because of the electrical conductivity of the solution. By electrolysis of water, tiny bubbles of oxygen and hydrogen are produced and they move upwards and form a blanket on the surface. Bubbles bring suspended particles to the surface and form a sludge layer that is mechanically collected.Expected use of electric flotation process simultaneously with electric coagulation eliminates the requirement of gravity sedimentation unit for the separation of the clots, resulting in the separation of both emissions and reducing the cost of the filtration.Studies in the field of electrochemical dye degradation based on electric coagulation and flotation property of the produced bubble are rarely used. In this study, reactors designed in a manner intended to electric coagulation properties and electric flotation can be used simultaneously. In addition, this study is a used innovation, such as the use of grille stainless steel electrodes with horizontal arrangement.In this research, the electrode-related parameters affecting the performance of the electric coagulation and flotation system, including the surface, distance, type, and shape of electrodes, were investigated. In addition, the influences of each of these parameters on the removal efficiency of Acid Red 14 from synthetic wastewater, energy and the anode consumption were determined and their values were optimized.The surface of electrode equal to 20.5 cm2, the distance between the electrodes equal to 0.5 cm, and stainless steel as type of electrode and a grid shape electrode (mesh generator) were chosen as optimized.Under optimal conditions in about 20 minutes, 100\% dye removal efficiency with special energy consumption equal to 6.2 kWh/kg was obtained. Dye removal with the anode consumption equal to 4.4 kg Fe/kg and sludge TSS 17000 mg/L was also obtained.According to electric coagulation and flotation benefits such as the ability to fully automatic exploit, easy control of parameters involved in the process, safe operation conditions and very high tolerance to organic, hydro and toxins shocks and considering the importance of reducing the cost using systems with less material and energy and TSS consumption, use of this method for filtrating or pre- filtrating is suggested prior to supplementary filtration of industrial wastewater containing dye. The advantages of this method compared to other methods of dye removal are as follows: simple equipment, high speed and short retention time to remove pollutants, easy navigation, and low amount of chemicals, and low produced sludge which has high sedimentation or floating rate with low amount of water.
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