An ultrastructural approach has been attempted to study the surface features of 29 packing media reported in literature and a few more potential candidates for immobilizing micro-organisms. The electron micrographs reveal important features like degree of smoothness/roughness, microcrystals and fibres, ridges, macro and micro pores <196> their dimensions, depth and distribution and thereby the biomass accumulation capacity of the media. Based on microscopic observations the packing media have been classified as (i) smooth - polypropylene bead, glass bead, peristaltic tube, porcelain, powdered activated carbon, perspex, polyvinyl chloride and glass (ii) uneven - straw, paddy stem, nylon, sand, gravel and stone (iii) porous - jute, gravel, soil, granulated clay, limestone, ceramic, shell, refractory brick, diatomaceous earth, casuarina seed, granular activated carbon thermocol, sponge, pumice stone and polyurethane foam. The results clearly show that ultrastructural examination and image analysis can be a quick, effective and direct visual 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.

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