Preparing a heavy-metal adsorbent based on alginate-like extracellular polymers from conventional activated sludge via polyethyleneimine grafting

This paper describes the preparation of a novel heavy-metal adsorbent based on alginate-like extracellular polymers extracted from excess activated sludge. Typical extracellular polymeric substances obtained from activated sludge can adsorb heavy metals; however, their adsorption capacities are unsatisfactory. Although a gel-like recovery system can be formed, it still cannot be easily separated. By grafting polyethyleneimine, the adsorption capacities and recovery efficiencies of alginate-like extracellular polymers can be increased simultaneously. Fourier-transform infrared analysis of the changes in the functional groups of the modified samples showed a marked increase at 1238, 2923, and 1650 cm −1 , confirming successful grafting. Scanning electron microscopy and related analyses revealed the formation of a complex three-dimensional network and an increment in the specific surface area after grafting, which provided more active binding sites for Cu(Ⅱ) adsorption. The energy dispersive spectrum and X-ray photoelectron spectroscopy profile showed that the hydroxy, amino, and carboxyl groups in the adsorbent formed complexes with Cu(Ⅱ). The maximum adsorption capacity of the ALEC1-PEI adsorbent prepared in this study was 98.01 mg/g according to the Langmuir model, and the adsorption of Cu(Ⅱ) proceeded most efficiently at pH 5. Furthermore, the recycled adsorbent shows considerable potential for commercial application in wastewater treatment.