Microbial rating

Paris DF, JE Rogers (1986) Kinetic concepts for measuring microbial rate constants effects of nutrients on rate constants. Appl Environ Microbiol 51 221-225. 

Biotransformation second-order microbial rate constant k = 1.1 x lO L-organisms 1 Ir1 (Steen Collette 1989). Bioconcentration, Uptake (kj) and Elimination (k2) Rate Constants ... 

Murphy, E. M and Schramke, J. A., 1998. Estimate of microbial rates in ground-water by geochemical modeling constrained with stable isotopes. Geochim. Cosmochim. Acta, v. 62, pp. 3395-3406. 

The microbial rating is generally used for membrane filters that are used in the sterilisation industry and is expressed as the ability of the filters to sterilise liquids. The filter permeability is the expression of resistance to flow provided by the filter media. This direct method establishes the permeability and can provide flow and pressure drop data with respect to fluid temperature and viscosity, filter size, and time. The effect of pulsating flow is the loosening of fine particles by agitating the filter. 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

Water Activity. The rates of chemical reactions as well as microbial and en2yme activities related to food deterioration have been linked to the activity of water (qv) in food. Water activity, at any selected temperature, can be measured by determining the equiUbrium relative humidity surrounding the food. This water activity is different from the moisture content of the food as measured by standard moisture tests (4). 

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. 

For those pesticides which are utilized as microbial growth substrates, sigmoidal rates of biodegradation are frequentiy observed (see Fig. 2). Sigmoidal data are more difficult to summarize than exponential (first-order) data because of their inherent nonlinearity. Sigmoidal rates of pesticide metabohsm can be described using microbial growth kinetics (Monod) however, four kinetics constants are required. Consequentiy, it is more difficult to predict the persistence of these pesticides in the environment. 

Continuous chlorination of a cooling water system often seems most pmdent for microbial slime control. However, it is economically difficult to maintain a continuous free residual in some systems, especially those with process leaks. In some high demand systems it is often impossible to achieve a free residual, and a combined residual must be accepted. In addition, high chlorine feed rates, with or without high residuals, can increase system metal corrosion and tower wood decay. Supplementing with nonoxidizing antimicrobials is preferable to high chlorination rates. 

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