Reactive toughening of polyvinyl alcohol hydrogel and its wastewater treatment performance by immobilization of microorganisms

Abstract

In order to improve the hydraulic impact resistance of a polyvinyl alcohol (PVA) hydrogel as a microorganism immobilization material and meet the requirements of long-time aeration of sewage treatment, toughened PVA hydrogel beads were prepared by co-crosslinking with glycerol through the boric acid (H₃BO₃) – chemical crosslinking method. It was found that glycerol could increase the consumption of H₃BO₃ and decelerate the crosslinking reaction of PVA. Crosslinked structures of borate–PVA monodiol complex (abbreviation as BP) and PVA–borate–PVA didiol complex (abbreviation as BP₂) were formed, and the proportion of BP₂ increased by the introduction of glycerol. Moreover, the pores of the core and surface layers exhibited a similar size and the structure of the PVA/glycerol hydrogel was relatively uniform. With increasing glycerol content, the shear storage modulus (G′) and the effective network density (ν_e) increased first, then decreased, and reached a maximum in the presence of 1.5 wt% glycerol, indicating the formation of a dense network structure of the gel, resulting in an improvement in the tensile properties and crushing strength of the gel beads. PVA/1.5 wt% glycerol immobilized with and without a microorganism exhibited excellent hydrogel stability during long-term wastewater treatment process. The reactive toughening mechanism of glycerol on the PVA hydrogel was explored. The value of the oxygen uptake rate (OUR) and COD removal rate of the PVA hydrogel immobilized with activated sludge had no obvious difference with addition of glycerol, and a high microbial activity can be maintained.