Microbiological slime

Crevice corrosion also develops under deposits or fouling, e.g. under the basalt plates of barnacles. The microbiological slime often observed on the surface of stainless steels can shift the free corrosion potential in the positive direction so that the pitting potential of the steels is exceeded [108]. Pipes made of a chromium steel with 26% Cr and 1% Mo failed within a brief period with biological deposits, but remained resistant in deaerated and sterile seawater in desalination plants [109]. 

R. Johnsen and E. Bardal, The effect of microbiological slime layer on stainless steel in natural seawater, CORROSION 86, paper No 227, NACE, Houston, 1986. 

TABLE 6.5 Typical Microbiological Evaluation of Slime Layer in Fig. 6.13 and Typical Counts in Cooling Water Contacting Heavily Slimed Surfaces ... 

Sand filters usually provide efficient SS removal for suspended matter above 30 x particle size, but they may need to be periodically sanitized using chlorine, formaldehyde, or similar substances (especially filters with very fine grain media). It is not uncommon for filters to contain microbial slimes and therefore act as a source of microbiological reinfection. 

In the past, copper was believed to be toxic to most microbiological species. Although this may be true in a test tube under laboratory conditions, it is not generally true in the real world. In this real world, microbial communities excrete slime layers which tend to sequester the copper ions and prevent their contact with the actual microbial cells, Aus preventing the copper from killing the microbes. Many cases of MIC in copper and copper alloys have been documented, especially of heat-exchange tubes, potable water, and fire protection system piping. 

This demand will reduce the amount of chlorine available for microbiological control and lead to slime growth, especially in the tower basin and water distribution system, with biofilms and under-deposit corrosion being common effects of this problem. 

Waterside problems that lead to decreases in efficiency and material deterioration can be caused by a variety of mechanisms, such as electrochemical corrosion and deposition of foulants. These problems can be exacerbated by low flow, poor operational practice, process contamination, or specific stresses. It is also important to try to determine cause and effect relationships in order to provide a logical and practical water treatment solution. Such a solution will usually involve some form of cleaning, plus a combined engineering and chemical action plan. Inspection may be made easier by the use of a Boroscope or similar optical/video recording device. The color, texture, and quantity of all deposits should be noted, measurements of pits taken, and microbiological contaminants analyzed. It may be useful to conduct biocide efficiency tests on bacterial slimes. The period when a heat exchanger is open for inspection may be an opportune time for the permanent installation of ports for corrosion-monitoring probes. 

Microbiological flora load, including slimes, SRBs, biofilms, etc. 

The chemistry of chlorine is such that it generally succeeds in oxidizing and breaking down only the surface of slime masses. It is often poor at penetrating and dispersing heavy anaerobic infestations and is completely indifferent to what it will oxidize, attack, or corrode, so there is a fundamental need for chlorine alternatives in the service industry s microbiological control armory. 

Microbiological growth inc. planktonic sessile bacteria. Andformation of biofilms, slimes biomass... 

The moleciilia dimensions of bacterial endotoxins are too large to pass through reverse osmosis membranes, and therefore the process is permitted by the pharmacopoeias for production of Water for Injection. However, the outlet water from reverse osmosis units can easily become microbiologically contaminated by formations of films or slimes downstream of the membranes. At least two micraterfogical problems may be encountered with reverse osmosis. First, micit iological films may slough off into the water at unpredictable intervals or... 

In the case of microbiological oiganisms which cause slime and subsequent breakaways, microbicides are used. These have changed in the last 10-20 years in order to comply with recent legislation. Products used today, e.g. chlorine dioxide, have to break down into non-toxic chemicals after they have killed the miao-organisms. 

Microbiological deposits may be formed in many different places in the papermaking process. However, the closer to the wet-end the more detrimental the deposits will be for the papermaking process. Mio-obiological deposits may form on submerged surfaces as well as surfaces above the water line of the paper machine. In the latter case it is a requirement for slime formation that a surface is kept moist by splashes or aerosol formation. Examples of such surfaces are the frame of the wire section and the frame of the press section. 

An inorganic material, like filler, can be incorporated into an organic deposit or microbiological deposit, hi these cases the organic material or the microbiological material (slime) will act as a binder, and without this binder the inorganic material would not normally deposit. 

Microbiological forms, including various types of algae and slime-forming bacteria... 

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