Electrocoagulation: Clarification of Residual Water From Chemistry Laboratories

Iago dos Santos Soares, Cleilson do Nascimento Souza, Libertalamar Bilhalva Saraiva, and Ana Mena Barreto Bastos

Federal Institute of Education, Science and Technology of Amazonas, Brazil

Abstract: This paper addresses the application of the electrochemical method to the treatment of chemical residues in the analysis and research laboratories in the areas of chemistry at Instituto Federal de Educação, Ciência e Tecnologia do Amazonas - IFAM, whose main objective was the removal of pollutants without adding chemicals. The acrylic reactor with a capacity of 40 L was divided into three tanks of 0.29 m high by 0.20 m long and 0.262 m wide (15.2 L per unit), with a ½ in. pipe for the waste inlet and outlet of treated water. The residues from the laboratory of physicochemical analysis - called residues 1, 2 and 3 — were characterized with analyzes of pH, conductivity, turbidity, alkalinity, COD and solids. The electrochemical cell was assembled with monopolar electrodes in parallel with an arrangement of 2 pairs of honeycomb electrodes, using a solid aluminum plate with a thickness of 3 mm and 200 mm high by 200 mm long, cut in one corner of each plate diagonally in order to place the fixing screw, with 400 cm² submerged in the residue. The direct current source was “Fonte de Alimentação ICEL Manaus PS – 3005”, with output voltage from 0 to 32 Volts, amp from 0 to 5A, input voltage of 110-220 Volts, without polarity inversion. Currents from 3A to 5A were used, depending on the chemical properties of the residue, with a reaction rate of 2 to 4 hours. The plates (sacrifice electrodes) were weighed before and after the electrocoagulation/flocculation with a 5.7 g mass loss. The pH and alkalinity showed an increase after the reaction for all residues, with a decrease in turbidity and color. The washout of the pollutant varied according to the increase in pH and the compounds formed with Al(OH)₃. In view of the results obtained in the experiments and analyzing the acceptable limits for legal disposal, issued by CONAMA Resolution 403/2011, it can be inferred that the system is efficient and removes most of the dissolved or suspended substances from the liquid effluents of the teaching and research laboratories.