Effect of electrode material
The most widely used materials, as sacrificial anode for
electrocoagulation, are aluminium and iron. For comparative
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Polyphenol index COD Dark colour
Removal efficiency, %
Iron
Aluminium
Fig. 1. Effect of electrode material on the treatment efficiency (initial pH 4.96, current density 30 mA cm−2, electrolysis time 30 min).
purpose, electrocoagulation has been carried out with both
materials under exactly the same conditions. The compared
results of COD, polyphenol and dark colour removal, obtained with the same current density (30 mA cm−2) and
operating time of 30 min, are shown in Fig. 1. It appears
clearly that both materials are almost equally effective in
reducing COD and polyphenol index. However, aluminium
was found to be more effective in removing the dark colour
of OMW than iron. Indeed, the effluent treated with iron
as sacrificial anode appeared yellow first and then turned
brown. This behaviour was attributed to the excess of Fe(II)
and Fe(III) species generated during the electrolysis and
characterised by their yellow-brown colour. Another possible explanation is the occurrence of complexing reaction
between iron ions and polyphenol molecules leading to
brown soluble compounds. Thus, aluminium electrode was
selected as the most appropriate material for the present
application and was used for all subsequent experiments.