Waste-activated sludge (WAS) as Cr(III) sorbent biosolid from wastewater effluent.

A biological sludge--waste-activated sludge (WAS)--from a dairy filtering station was investigated for the removal of trivalent chromium from aqueous solution. Kinetic results revealed that chromium adsorption was instantaneous. The removal rate increases up to pH 4 for contact times beyond 20 min. The equilibrium state is attained in 30 min in all the considered systems. The reaction orders as well as the diffusion rate constant were determined. Values adsorption isotherms measured at pH 3 generally followed the Langmuir model. The maximum uptake capacity was 25.64 mg/g. Values of thermodynamic parameters show that chromium (III) sorption on WAS is an exothermic process. This study provides an opportunity for the removal of heavy metals such as chromium from aqueous solutions using a low-cost biosolid as adsorbent support.