Electrocoagulation is an electrochemical technique with many applications, in which a variety of unwanted dissolved particles and suspended matter can be effectively removed from an aqueous solution by electrolysis. Thus, for example, it is used to clarify food wastewater, 1 tar-sand and oil-shale wastewater, 2 as well as potable water. 3 It can remove phosphate from sewage, 4,5 cyanide and chromate from industrial wastewater, 6 and fluoride from drinking water. 7 Several heavy metal ions can also be efficiently removed from industrial waste. 8,9 Electrocoagulation can also be used to decolorize dyecontaining solutions, such as textile wastewater 10,11 and crude aqueous plant extracts.
12-17The main advantages of the electrocoagulation method over coagulation by the addition of chemicals, such as salts of aluminium and iron, are simple equipment and easy operation, a shortened reactive retention period, a reduction or absence of equipment for adding chemicals, and a decreased amount of precipitate or sludge. Moreover, and perhaps most important of all, during electrocoagulation the liquid is not enriched with anions, and its salt content does not increase, as is the case of a chemical treatment. 6 In this study, we decided to investigate the electrocoagulation of certain phenolic compounds in a systematic manner, in view of the fact that phenolic substances often occur in many industrial wastes, especially textile and paper mill effluents, and also in many plant extracts, e.g. flavonoids and tannins. Additionally, we also report on a simple method for recovering these phenolic substances from coagulated sludge.
ExperimentalTwo aluminium plates (dimension 30 × 10 × 0.05 cm) were used as electrodes. These were dipped 3 cm apart and 9 cm deep into a magnetically-stirred aqueous solution (1 litre) of a phenolic compound (0.1% w/v) in a glass jar (diameter 11 cm, height 23 cm). Sodium chloride (2 g) was added as an electrolyte. Direct current (0.5 A, 22 V) from a DC power supplier was then passed through the solution via the two electrodes. At every 15-min interval during a 2-h period of electrolysis, a 10-cm 3 aliquot sample of the solution was drawn, filtered, and taken for an absorbance measurement at an appropriate wavelength of the absorption maximum for each phenolic compound, as follows: phenol 250, resorcinol 272, pyrocatechol 252, pyrogallol 243, phloroglucinol 233, n-propyl 3,4,5-trihydroxybenzoate 243, orcinol 241, hydroquinone 243, and tannin 242 nm. The measured absorbance was then converted to the residual weight percentage of the compound by a calibration curve obtained from a plot between the absorbance versus the concentration for each compound. All of the phenolic compounds used were of standard reagent grade, and were used as such.Phenol and resorcinol (1,3-dihydroxybenzene) were purchased from Fluka Chemie AG, Buchs, Switzerland; pyrocatechol (1,2-dihydroxybenzene) and pyrogallol (1,2,3-trihydroxybenzene) were purchased from E. Merck, Darmstadt, Germany; phloroglucinol (1,3,5-trihydroxybenzene) an...
