Microbiological Degradation of Materials - and Methods of Protection (EFC 9) PDF

Introduction

Microorganisms can grow on materials of construction which may be metallic, ceramic, or organic - both natural and artificial- and also on "auxiliary" materials, i.e. those, such as paints, adhesives, plasters, hydrocarbons, used in assembling, treating or decorating construction materials. This growth may result in undesirable changes in the properties of the materials, sometimes leading to their destruction. This study treats microbiological destruction of materials as a whole. The microorganisms involved include bacteria, fungi, algae and lichens but higher organisms are not included. Similarly, the microbiological deterioration of food, drugs (pharmaceuticals) and cosmetics is not an objective of this study.

However, materials and raw materials can also be improved or obtained by microbiological activities and these aspects as well as the destructiveeffects of microbial action will be discussed. Thus, besides the involvement of microorganisms in the deterioration of materials it is equally important to recognise their use in naturally occurring processes, e.g. copper production by oxidation of CuS in heaps of low grade copper-ore which would be unsuitable for metallurgical processing. Leaching of low grade ores is of growing interest at the moment after having been neglected apart from in a few operational plants for many years. Ceramic materials like kaoline for china (porcelain) are often brown-coloured by iron oxides. Successful attempts have been made to eliminate the iron by leaching using iron-reducing or complexing agents produced by microorganisms. Carbonaceous components can be partially liquefied by the action of surface active substances produced by microbial action. The costs of transporting coal can be reduced by transforming the coal microbiologically into a pumpable suspension (see 4.8.4.). Sulphur removal from coal by microorganisms is also possible.

Microorganisms are omnipresent in an active or a quiescent condition, although they can be detected visually only ifpresent in very high numbers. Their occurrence is restricted by lack of water or by temperatures below -IOoe or above 110°C.

The diversity of metabolism makes microorganisms indispensable for mankind, A long time before the era of biotechnology, bacteria and fungi were used for the production of foodstuffs, luxuries and antibiotics as well as for leaching of low grade ores and the degradation of wastes and noxious residues.

Only bacteria and fungi take part in the natural carbon and nitrogen cycles in which plants and animals are eventually transformed into carbon dioxide, water, nitrate, phosphate, sulphate, and humic compounds. By the diversity of their biological activities microorganisms are able to populate materials and auxiliary materials, although metals and ceramic materials do not act as nutrients. On the other hand, organic matter can be attacked directly and destroyed (e.g. wood, paper, leather, some plastics) or damaged as a result of attack of additives (e.g. plasticisers) etc. It is difficult to estimate the economic losses resulting from microbiological deterioration of materials since any evaluation must consider not only the deterioration per se but also the financial costs incurred in the protection of materials. Indirect damage caused by the shutdown of production in plants must also be considered.

Research and development in the field of destruction and protection of materials requires close cooperation of several disciplines. First of all, microbiologists interested in applied sciences are needed, and then cooperation is required. from all branches of the natural and technical sciences, e.g. physicists and engineers, chemists and architects with practical and research experience. They have to recognise and to explain microbiologically influenced corrosion, identify the causes and establish remedial measures. The education and professional experience of microbiologists have little in common with that of those workers in other disciplines and there is a lot of scepticism among the latter. The usual approach follows the route: corrosion damage appears, microorganisms are recognised to be the cause, biocides are put to work, the responsible factors are eliminated and the plant continues to run at reasonable cost. Some problems can be solved in this way but - without question - no systematic materials protection scheme taking into account all the particular environmental conditions will have been used.

As for other interdisciplinary fields, discussions organised by scientific-technical societies and research institutions are very valuable since only in this way is it possible to cover efficiently this very complex field.

Influenced by the evident economic importance of the subject, the Committee for Scientific Research of the OECD initiated a research program in 1962 on the biological deterioration of materials. Mr. G. Becker (Bundesanstalt fur Materialpriifung - BAM, Berlin) became leader of the German group. Between 1965 and 1970 five meetings were held supported by Deutsche Forschungsgemeinschaft (DFG) and these which led to the eventual production of the memorandum - "Applied Research: Organisms and Materials" - compiled by Mr. G. Becker and edited by DFG.

Since 1981 microbiologists in the field of microbiological deterioration of materials and materials protection have met regularly under the leadership of Prof. Dr. R. Schweisfurth. Their purpose was, and still is, to initiate advances in research and the awareness of biodeterioration of materials. At the occasion of a symposium supported by the VWfoundation and the BAM, this group was adopted as a subcommittee of DECHEMA's biotechnology working parties. The objective of this subcommittee was to achieve, by involving microbiologists, the advancement of research in this field as well as the spreading of knowledge regarding microbiological deterioration of materials. The International Biodeterioration Research Group (IBRG) - based in the UK - was founded in the nineteen sixties as a group of experts of the OECD. Scientists and technologists engaged in problems of biologically influenced deterioration of materials were brought together. At the present time IBRG includes a number of groups: "Taxonomy IEcology", "Constructional Materials (except wood)", "Problems of Industry", "Cooling & Lubricating Agents", "Corrosion by Microorganisms", "Painting Materials", and "Synthetic Materials". The International Research Group on Wood-Preservation (IRGWP) was founded in 1969 to continue the activies started in the OECD-working group on wood preservation. Initially IRGWP had 22 members from 9countries and the first chairman was G. Becker (BAM) from 1969to 1973. A number of subgroups exist, e.g. "Biologically important problems in the study of wood preservation", "Fundamentals of testing", "Methods of treatments" etc.

The working party "Microbial Corrosion" of the European Federation of Corrosion under the chairmanship of Ken Tiller, Teddington, was founded in 1987and has developed a number of activities in this field.

The National Association of Corrosion Engineers (NACE) from the USA has organised meetings and produced interesting publications in the field of biocorrosion of materials.

In Germany the journal Material und Organismen (i.e, "Materials and Organisms") first appeared in 1966; another, Dokumentation: Biologische Organismen und Werkstoffe (Documentation: Biological Materials testing - Organisms and Materials") appeared in 1981. Both are edited by Bundesanstalt fur Materialpriifung, Fachgruppe Biologische Materialpriifung, Berlin. Single papers on microbiological deterioration of materials are published from time to time as special reviews, e.g. in Werkstoffe und Korrosion. One review in that journal contains the results of the research program on "Corrosion and Corrosion Protection" of the BMFT, project management by DECHEMA, Frankfurt.

In the English speaking countries the review "Biofouling" (Harwood Academic publ.) has recently appeared. Contributions to microbiological materials deterioration appear also in the following: Advances in Applied Microbiology, Applied and Environmental Microbiology, Developments in Industrial Microbiology and Materials Performance (formerly Materials Protection and Performance), Microbiology Abstracts - Section A: Industrial and Applied Microbiology, Current Contents - Life Science, Agriculture, Biology Environmental Science also contain references.

Edited by: A.D. Mercer