Microbial processes attack

This chapter provides an overview of microbial processes involved in the degradation of natural and synthetic fibers, starting with an introduction of relevant terminology. It discusses the methods used to assess the microbial breakdown of fibers and gives examples of the sources of microbial communities and the methods of incubation that are used in these studies. Finally, it provides examples of the types of bonds that are susceptible to microbial attack. 

Through the contribution of these and many other constructive measures, the growth conditions for microorganisms on materials become unsuitable, and thus deteriorative processes can be prevented. Generally, all constructive measures that may change the growth influencing parameters mentioned in Sec. 4.3 are appropriate to reduce the importance of the microbially influenced attack on materials. 

In this process, which has been in existence as a concept for at least 30 years and is often referred to as a microbial process, chemolithiotrophic bacteria in aqueous suspensions in the presence of oxygen can be nsed to selectively attack the sulfur crosslinks in the snrface of waste rnbber crumb particles. The process can also be regarded as a type of biodegradation process, the by-prodncts of which can inclnde elemental sulfur, sulfates, sulfides and snlfnric acid. Specific examples of the bacteria that have been used to devulcanise rubber in this way inclnde species of Thiobacillus, e.g., T. thiooxidans. 

Emissions During Exterior End Use. When flexible PVC is used in exterior appHcations plasticizer loss may occur due to a number of processes which include evaporation, microbial attack, hydrolysis, degradation, exudation, and extraction. It is not possible, due to this wide variety of contribution processes, to assess theoretically the rate of plasticizer loss by exposure outdoors. It is necessary, therefore, to carry out actual measurements over extended periods in real life situations. Litde suitable data have been pubHshed with the exception of some studies on roofing sheet (47). The data from roofing sheet has been used to estimate the plasticizer losses from all outdoor appHcations. This estimate may weU be too high because of the extrapolation involved. Much of this extracted plasticizer does not end up in the environment because considerable degradation takes place during the extraction process. 

Reverse osmosis membrane separations are governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material, which is almost always a polymer, as well as its physical stmcture. Properties for the ideal RO membrane include low cost, resistance to chemical and microbial attack, mechanical and stmctural stabiHty over long operating periods and wide temperature ranges, and the desired separation characteristics for each particular system. However, few membranes satisfy all these criteria and so compromises must be made to select the best RO membrane available for each appHcation. Excellent discussions of RO membrane materials, preparation methods, and stmctures are available (8,13,16-21). 

I onsucrose Components from Storage or Damag e of Beets. Some nonsucrose components are associated with the conditions under which the beets have been stored prior to processing, as respiration products or products of microbial attack In either case they direcdy and indirectly reduce sucrose yield and may cause other processing problems. Glucose and fmctose have already been discussed and can derive from either source. 

Several processes often occur in lipids, including oxidation, hydration, dehydration, decarboxylation, esterification, aromatization, hydrolysis, hydrogenation and polymerization. In fact, the chemistry of these materials can be affected, for example, by heat (anthropogenic transformations), humidity, pH, and microbial attacks. 

Microbial vulnerability of polymers is often ascribed to enzyme activity, enzymes being crucial players in the biological biodeterioration process. As enzymes are macromolecular polymers, their attack on the polymer is usually only possible via superficially exposed polymer structures readily accessible via a microporous structure. Alternatively, the enzymatic attack works indirectly via... 

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