Abstract: Method and apparatus are provided for the bioconversion of toxic substrates with increased yields of product. The invention makes use of immobilized cells as biocatalyst and complexing agent in either dissolved or solid form. The invention also employs various schemes and apparatus for separating immobilized cells and complexing agent for recycle and re-use in bioconversion reactions. A preferred embodiment of the invention produces improved yields and titers of L-phenylacetyl carbinol by the bioconversion of acetaldehyde using yeast cells.