Biocides system factors

System factors that affect efficiency of biocides... 

All release systems that liberate an immobilized biocide into the surroundings will exhaust rather quickly. Furthermore, the constant release is an environmental issue and supports the building of biocide-resistance in microbial strains. If a release system is the only possible option, then it would be desirable to release the biocide on demand, e.g., in cases of infection or the start of biofilm formation. This can be achieved by either degrading or swelling the matrix with an infection-specific enzyme or metabolite, or by cleaving the linker between biocide and surface with a biochemical factor. 

Each preservative has unique characteristics that might affect its suitability for a particular application. These include factors such as appearance, odour, toxicity, wood species compatibility and availability. The discussion that follows provides a basic background to a wide range of preservative systems. Some of these systems are still in use today, while others have been phased out and others are currently under development. Further discussion of preservative systems can be found elsewhere (Ibach, 1999 Nicholas, 1973b Richardson, 1993 Schultz and Nicholas, 2003). It will be readily apparent from this section that the transition away from traditional heavy metal broad spectrum biocidal compounds to organic chemistries has added significant complication to the wood preserving industry as a whole. 

The activity of a biocide will also be affected by other factors in the system in particular temperature and flow velocity will influence the biocidal efficiency in a heat exchanger (say a power station condenser). 

Although these data show the trends associated with changes in system variables the age and quality of the biofilm will also be a factor, i.e. whether the biofilm is open and "fluffy" or dense and compact. Diffusion of biocide into the biofilm will be facilitated by the existence of "pores" containing water within the biofilm matrix. The quality of the biofilm will be very much a function of the conditions under which it was laid down, particularly in terms of nutrient availability and flow rate (see Chapter 12). Apparent variations in biocidal efficiency reported in the literature may in fact be due to the different morphologies of biofilms of the same strain, but grown under different conditions. 

System variables that affect the efficacy of glutaraldehyde as a biocide include temperature, flow velocity, and glutaraldehyde concentration, but the most important factor is pH. 

Fig. 16.3 gives the flow sheet of a cooling water system commonly used in power generation that is also used in the process industries. Chemicals such as acids, biocides, scale and corrosion inhibitors and dispersants are added to control problems of fouling in the recirculating system (described elsewhere in this book). The technique is generally applicable where the make-up water is generally of low hardness and silica and low concentration factors are employed. 

The microbial infection of polymer emulsions is discussed, with reference to the sources of infection, causitive organisms, effects of microbial growth in polymer emulsions, prevention of microbial infection, and the use of biocides in polymer emulsions. These factors are considered with reference to redox initiated systems. The use of broad spectrum biocides, especially those based on isothiazolin-3-one derivatives is examined. 9 refs. 

Drug delivery systems have been developed for doxorubicin [51] (a drug used to treat leukemia but which has cardiac risk factors), and for flavors such as decanoic acid [52]. In both cases, the encapsulation efficiency as given by load, recovery speed and recovered quantity was assessed. In addition, the stabihty (shelf life) of such gel matrices in terms of stabihty of the pharmaceutically active ingredient was increased compared to their free form. Similar appHcations for coatings for the controlled release of biocides [53] and other pharmaceuticals such as vitamins [54] have also been made. Clearly, gel porosity, pore size distribution, temperature, pH all influence the release, and these parameters must be optimized. 

Chemical Techniques Numerous biocides have been used for biocontrol of membranes systems. The efficacy of a biocide depends on several factors, such as ... 

DBNPA is well rejected by RO membranes, up to 99.98% °, so on-line treatment is acceptable for most industrial applications. DBNPA can be used for potable applications if the treatment occurs offline (due to the limited passage of the biocide) , and the system is rinsed and monitored properly. The key factor for DBNPA effectiveness is to eliminate the active biological slime from the system via a cleaning process before using DBNPA, since DBNPA is a moderate electrophile, that does not attack the ESP. Thus, DBNPA is most effective on membranes that are relatively free of mature biological colonies and slime. At a pH above 8, the product tends to hydrolyze, so application at neutral pH is recommended The half life of DBNPA is 24 hours at pH 7,2 hours at pH 8, and 15 minutes at pH 9. 

However, Al-Hashem et al. [34] reported another example of dual biocide treatment where a high concentration batch treatment by a biocide was followed by a low concentration of continuos biocide treatment. The first step had been introduced to reduce the numbers of the bacteria (batch treatment) and keep it low (continuous treatment). Those authors, after not finding such treatments feasible enough both in terms of the extra time to be allocated for each treatment and the costs of the chemicals and facilities, prefer a batch dose of high concentration with special consideration of factors such as the frequency of biocide application and pre-treatment of the water entering into the system. 

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