Treatment of tannery effluents by a two step coagulation/flocculation process

A coagulation/flocculation method for the treatment of tannery effluents is described in which alkaline FeCl3 is used as flocculating agent and Ca(OH)2 as base/precipitant. Two cycles of the treatment reduced the chemical oxygen demand (COD) of the effluent by 87%, producing a colourless, odourless wastewater with no appreciable suspended solids. Further repetition produced no further reduction in the COD.