Study on biosorption of humic acid by activated sludge

The biosorption performance of humic acid (HA) by activated sludge and the effects of inorganic metal ions as biosorption aid were investigated. It was confirmed that biosorption instead of biodegradation was responsible for HA removal. HA biosorption by activated sludge followed the Freundlich isotherm equation; however, biosorption of HA corresponded to the biosorption by a mixture of adsorbates. The removal efficiency improved when initial HA concentration was increased. While biosorption of HA can be suitably applied to treat high concentration HA wastewater because the HA concentration of blank sample was approximate to 1 mg/L. The total removal efficiency for HA improved when the quantity of adsorbent (activated sludge) was increased under constant contact time. The lower concentration of the adsorbent could realize the higher adsorptive capacity per gram activated sludge with a longer contact time, but the removal rate of pollutants was more important consideration in practice. Moreover, biosorption of HA was favored by addition of five metallic salts. The ionic strength increasing, cationic bridge, destabilization and precipitation are the main mechanisms to advance HA removal efficiency in solution after adding the salt (Na+), alkaline earth metallic (Ca2+, Mg2+) and hydrolyzing metallic (Al3+, Fe3+) ions, respectively.