Treatment of direct red dye and free-formaldehyde sistem by electroflotation
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MOCANU, Larisa, GONTA, Maria, MATVEEVICI, Vera, PORUBIN-SCHIMBĂTOR, Veronica. Treatment of direct red dye and free-formaldehyde sistem by electroflotation. In: Achievements and perspectives of modern chemistry, 9-11 octombrie 2019, Chişinău. Chisinau, Republic of Moldova: Tipografia Academiei de Ştiinţe a Moldovei, 2019, p. 181. ISBN 978-9975-62-428-2.
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Achievements and perspectives of modern chemistry 2019
Conferința "International Conference "Achievements and perspectives of modern chemistry""
Chişinău, Moldova, 9-11 octombrie 2019

Treatment of direct red dye and free-formaldehyde sistem by electroflotation


Pag. 181-181

Mocanu Larisa, Gonta Maria, Matveevici Vera, Porubin-Schimbător Veronica
 
Moldova State University
 
Disponibil în IBN: 11 noiembrie 2019


Rezumat

The applications of electrochemical technologies based on electroflotation for removal of such pollutants as organic compounds expressed through Chemical Oxygen Demand (COD) from wastewaters are discussed [1]. Experiments were performed into an electroflotation cell with two electrodes: carbon anode and a stainless steel cathode which were placed on the bottom of the cell in order to establish the optimal operational conditions (e.g.: electroflotation time, electric current intensity) for removal efficiencies of more than 95% COD. The objectives were to (i) determine the chemical oxygen demand (COD) of mixtures containing direct red dye and free-formaldehyde (DR-FA) and (ii) establish the sequence of effluent treatment methods. COD (mgO/L) concentration was measured by potassium dichromate standard method using UV-Vis spectrophotometer T 80+. The laboratory research was focused on DR-FA systems with electrofloatation with different concentrations of dye and free-formaldehyde. Synthetic samples of wastewater which contain direct red dye (concentration ranges from 100 to 300 mg/L) and free-formaldehyde (concentration ranges from 20 to 800 mg/L) were introduced into the electroflotation cell. Experiments were carried out at the room temperature, at a steady rate, for 10 min. In all experiments 0.002 L NaOH (1M) was added to increase the conductibility. The pH value of synthetic wastewaters was 6.5. The solution current density was 0.5 Am-2. It can be considered favourable for electro flotation. It is to be noticed that the electroflotation method applied in the first step is effective only for the system which has 100 mg/L concentration of dye.At double dye concentrations, COD values increase in 3 times and when the system contains 300 mg/L of dye the COD values are 9 times higher than in the first system.According to the results (Fig. 1), the effect of removal depends largely on the concentration of the dye because the method is based on the principle of the electrochemical processes of oxygen and hydrogen evolution during electrolysis of wastewaters.The gas bubbles have raised the associated dye particles to the surface of the liquid. However, if the concentration of the dye grows, the molecular weight of the particles will also increase and will not concentrate the foam. Thus, it was necessary to combine physico-chemical methods to achieve CMA (6-8 mgO/L). The DR-FA system with a 200 mg/L concentration of dye and 20-80 mg/L of freeformaldehyde was treated by electro flotation and adsorption by active charcoal.The last system was treated by combining of 3 methods: electrofloating-oxidation with Fenton's reagent and adsorption of mineralized/ degraded compounds on active charcoal (Fig. 2).