Treatment of Cr(VI)-containing wastewater by addition of powdered activated carbon to the activated sludge process

Abstract

The effect of powdered activated carbon (PAC) on the removal of hexavalent chromium [Cr(VI)] and chemical oxygen demand (COD) and on oxygen uptake rate (OUR) by activated sludge microorganisms was investigated in batch and continuous flow reactors. The initial adsorption rate of Cr(VI) by PAC was greater than that by activated sludge flocs, and the equilibrium data could be described well by the Freundlich isotherm equation. The addition of PAC was an effective method to allow continuous operation of the biological process in the presence of Cr(VI) and increases in oxygen uptake rate as well as Cr(VI) and COD removal efficiencies were evident. The average COD and Cr(VI) removal efficiencies with PAC addition were 96 and 41%, respectively, while those without PAC addition were 85 and 9%, respectively. The kinetic constants of biological oxidation were determined on the two laboratory scale activated sludge units, one with PAC addition and the other without PAC addition, fed with synthetic wastewater containing Cr(VI). The addition of PAC to the aeration basin increased overall microorganism growth rate and biological removal rate of the substrate.