A biomass resource strategy for alginate-polyvinyl alcohol double network hydrogels and their adsorption to heavy metals

Alginate-based hydrogel adsorbents are being developed for removing heavy metals from wastewater. Activated sludges are a new source of low-cost alginate, and Pseudomonas species are dominant alginate-producing bacteria. In this work, polyvinyl alcohol/alginate (PVA/ALG) and polyvinyl alcohol/alginate/chitosan (PVA/ALG/CS) hydrogel beads were prepared by cross-linked blending P. aeruginosa alginate with polyvinyl alcohol and chitosan. The results show that PVA/ALG using bacterial alginate had better adsorption performance on Pb(II), Cd(II) and Cu(II) than that using commercial product. The maximum adsorption capacities of PVA/ALG and PVA/ALG/CS hydrogels for Pb(II) and Cr(VI) are 139.4 mg/g and 86.1 mg/g, respectively. The addition of chitosan greatly improved the specific adsorption of PVA/ALG/CS for Cr(VI). The adsorption processes of Pb(II) and Cr(VI) by PVA/ALG and PVA/ALG/CS are endothermic in nature, and mainly dominated by chemisorption and physisorption, respectively. After 5 cycles, the adsorption capacity of hydrogels for heavy metals maintains more than 85% of the initial adsorption capacity. The two hydrogels have good adsorption capacity for heavy metals in real water. Electrostatic interaction, complexation and cation exchange are involved in the adsorption of Pb, whereas the adsorption of Cr is related to electrostatic interaction, reduction, chelation and cation exchange. The results extend the application of alginate extracted from activated sludge microorganisms in pollutant removal.