In this work, a new and economical way to prepare macroporous poly(vinyl alcohol) (PVA) foam was explored by adding calcium carbonate as a pore-forming agent and using epichlorhydrin as a chemical crosslinking agent to improve foam stability. The mixture for foam formation has been optimized to obtain macroporous PVA foam carriers with uniform apertures, narrow distribution of pore sizes, and good elasticity. The crosslinked PVA foam (CPVAF) carrier demonstrated better chemical and thermal stability, as well as larger specific surface area and diffusion coefficients than the traditional PVA (TPVA) carrier. Nitrifying bacteria were used to test the suitability of CPVAF and TPVA carriers for immobilized microorganisms. CPVAF carriers supported higher biomass density and microbial activity than TPVA carriers. At the same biomass density, the higher nitrification rate of CPVAF carriers was attributed to excellent mass transfer of the substrate (and oxygen) between the bulk solution and the immobilized microorganisms. (C) 2009 Elsevier Ltd. All rights reserved.