Phosphorylated polyvinyl alcohol (PVA) gel is nontoxic and can be economically feasible for industrial scale applications. The use of PVA for cell immobilization has recently attracted much attention (1 –5 ). In this chapter, we provide details of a novel cell immobilization technique based on use of phosphorylated PVA as a support. PVA is first crosslinked with boric acid for a short time to form a spherical structure. This is followed by solidification of the gel beads by esterification of PVA with phosphate (phosphorylation). The short contact time with boric acid avoids severe damage to microorganisms. The phosphorylated PVA beads satisfy the requirements of supports having strong consistency, durability, and high cell viability as well as being of low cost (seeChapter 1 ). This method can be applied to immobilize cells of bacteria, yeast, or activated sludge. The characteristics of denitrifying sludge entrapped in phosphorylated PVA gel beads have been examined in our previous work (6 ). Furthermore, the PVA-immobilized denitrifying sludge has been found to have good stability over a long period of operation in a CSTR (6 ,7 ). However, the minuteness of the crosslinked gel structure results in a poor gas permeability of the PVA gel. This property can cause accumulation of gases inside the beads and force them to float up toward the surface of the bulk solution in the reactor. This would occur under circumstances in which an anaerobic fermentation process was operated and accompanied by gas production, such as carbon dioxide.
