Shape stable poly(vinyl alcohol) hydrogels with immobilized activated sludge at repeated dry-rewet cycles

The poly(vinyl alcohol) (PVA) hydrogels can be used as a non-toxic and inexpensive immobilization matrix for microbial cells with capability of degrading organic or inorganic pollutants in wastewaters. This study for the first time produced the PVA hydrogels with immobilized cells by two-stage crosslinking which have high shape stability at dry-rewet cycles and, when recovered after sequentially three 24-hr cultivations, reveal high bioactivity in wastewater treatment. The [B(OH)₃][SO₄^2-] cores inside the PVA-boric acid-sulfate hydrogels are proposed to support the immobilized cells with sufficient structure flexibility and strength to maintain hydrogel structural integrity and of sufficient recalcitrance to biological attack. Conversely, neither the PVA-boric acid hydrogels nor the PVA-borate hydrogels can be applied as organic pollutant degraders with dry storage capability. The PVA-boric acid-sulfate hydrogels are proposed as ideal matrix that can be produced and stored in dry, massive quantity and then applied latter at the same or different sites.