Performance and mechanism of Pb(II) removal from water by the spent biological activated carbon (SBAC) with different using-time

Abstract

Aiming at preventing the production of a large amount of solid wastes (spent biological activated carbon, SBAC), while increasing their efficiencies as resources, this study was undertaken to explore the ability of SBACs with different lifespans to remove Pb(II) from water. SBACs with different using-time (5, 6 and 7 years) were collected in a full-scale BAC process, designated SBAC-5, SBAC-6, and SBAC-7, respectively. Although the content of metals (Ca(II) etc.) adsorbed on SBACs increases with using-time, FT-IR analyses confirmed the stability of surface functional groups on SBACs. Adsorption experiments showed that SBACs irrespective of using-time presented stable adsorption abilities (>99 %) for Pb(II) (2.0–8.0 mg/L) with the maximum uptake of 168.07 mg/g. Their adsorption properties were changed from Freundlich to Langmuir model over time. Adsorption processes were pseudo-second order kinetic and faster at a higher content of carboxyl groups. As a dominant adsorption mechanism, ion exchange with Ca(II) adsorbed on SBACs accounted for ∼60 % of the total adsorbed Pb(II). Water temperature, pH and coexisting ions have little effects on the removal of Pb(II). For the organics previously adsorbed on SBACs, almost no leaching was observed in the real river water, and application experiments verified SBACs’ ability to remove Pb(II) from actual water (>80 %). The findings will find a sustainable way out for a large amount of SBACs with different using-time, which not only prevent the production of large amounts of solid waste (spent biological activated carbon, SBAC), but also make the BAC process a more environmentally friendly and sustainable process.