Biofilms, material surface conditioning with

Material surface conditioning in connection with microorganisms and biofilms... 

Material Surface Conditioning in Connection with Microorganisms and Biofilms... 

Like enzymes, whole cells are sometimes immobilized by attachment to a surface or by entrapment within a support. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for production of a secondary metabolite. A hollow-liber reactor, similar to those used for cross-flow filtration, can be used to entrap the cells while allowing input of the substrate and removal of products. Attachment of the cells to a nonreactive material such as alumina allows a great variety of reactor types including packed beds, fluidized and spouted beds, and air-lift reactors. Packed beds with a biofilm on the packing are commonly used for wastewater treatment. A semicommercial process for beer used an air-lift reactor to achieve reaction times of one day compared to five to seven days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavor profile that was attributed to mass transfer limitations. 

Under natural conditions, all surfaces are covered with microorganisms except for extremely clean rooms. Biofilm formation is the process by which a complex community of microorganisms becomes established on a surface. Biofilms can exist in many different forms and have many different compositions (O Fig. 12.1). They are ubiquitous on surfaces in soil and aquatic environments (Ford 1993) and are also present on materials exposed to humidity, particularly in tropical and subtropical climates. For example, microbial biofilms are common on surfaces of ancient archaeological limestone in Southern Mexico (O Fig. 12.2). This process of biofilm formation is prerequisite to... 

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