Poly(N-vinyl pyrrolidone)−Calcium Alginate (PVP−Ca-alg) Composite Hydrogels: Physical Properties and Activated Sludge Immobilization for Wastewater Treatment

Abstract

An alternative composite hydrogel material for cell immobilization is presented, and some of its important physical properties, such as weight swelling ratio (WSR) and cell viability, are evaluated. The hydrogel is prepared with cross-linked poly(vinyl pyrrolidone), PVP, and calcium alginate as the encapsulating rigid polymer. Composite hydrogels prepared with different proportions of sodium alginate lead to PVP/calcium alginate hydrogels with weight swelling ratios close to 11 (water content ≈ 90 wt %), higher than the WSR of PVP by a factor of 2. Low-vacuum SEM images reveal that the composite is made of PVP randomly distributed in a solid continuous cage formed by the rigid calcium alginate polymer. When cell viability of these composite hydrogels is evaluated from observations carried out using low-vacuum SEM, the images show that a concentrated bacterial population is attached to and growing on the surface of calcium alginate and entrapped PVP particles. In addition, when the composite hydrogels are used to entrap activated sludge and their efficiency to remove glucose from synthetic wastewater is evaluated and compared to the efficiency of a suspended activated sludge through kinetics studies, it is observed that the glucose depletion rate is practically the same for both systems, indicating that the composite materials have the right structure to allow the diffusion of substrate, byproducts, and oxygen for cell metabolism and may compete favorably with suspended activated sludge.