IMMOBILIZATION IN FIXED-FILM REACTORS - AN ULTRASTRUCTURAL APPROACH

An ultrastructural approach has been attempted to study the surface fe atures of 29 packing media reported in literature and a few more poten tial candidates for immobilizing micro-organisms. The electron microgr aphs reveal important features like degree of smoothness/roughness, mi crocrystals and fibres, ridges, macro and micro pores <196> their dime nsions, depth and distribution and thereby the biomass accumulation ca pacity of the media. Based on microscopic observations the packing med ia have been classified as (i) smooth polypropylene bead, glass bead, peristaltic tube, porcelain, powdered activated carbon, perspex, polyv inyl chloride and glass (ii) uneven - straw, paddy stem, nylon, sand, gravel and stone (iii) porous - jute, gravel, soil, granulated clay, l imestone, ceramic, shell, refractory brick, diatomaceous earth, casuar ina seed, granular activated carbon thermocol, sponge, pumice stone an d polyurethane foam. The results clearly show that ultrastructural exa mination and image analysis can be a quick, effective and direct visua l technique for selecting support media for bioreactors. An example of application of quantitative image analysis for providing quantitative geometric description of surface features is also presented. Copyrigh t (C) 1996 IAWQ. Published by Elsevier Science Ltd.