Biocides requirements

It is also important to consider the dose of biocide required to give the desired longevity in-use and compare this to the cost of the preservative. In many metalworking fluids, the preservative system can be the single most expensive component in the formulation. Getting the balance between cost and efficacy is key. 

The impact of each biocide on microbial populations, together with the compatibility studies, can be used to select the most effective biocidal treatment. The biocides are first evaluated for their ability to inhibit metabolic activity at the time of maximum growth activity this maximum time is determined from growth curves of the microbial populations of the formation and river wastes. Growth curves are then measured for the selected biocide(s) at different concentrations to determine the optimum level of biocide required and the period necessary for alternate slugging of the injection waters. The biocidal treatment is then determined from the growth-concentration curves and the compatibility studies. 

Safe handling of biocides. All chemicals should be handled cautiously (it is prudent to minimise all chemical exposures), but biocides require special caution because they are designed to be toxic to living organisms. 

The more complex the organism, the more likely it is that the biocides required for effective treatment could be harmful to higher forms of life. 

Chemical types of preservatives or biocides required in PO production are reflected in Table 1. 

Chlorine is desirable as a bulk pretreatment biocide for inlet water, but its subsequent removal upstream of the membrane is absolutely necessary ana difficult. NaHSO,3 is a common additive to dechlorinate before membranes. It is customarily added at 3-5 mg/1, an excess over the stoichiometric requirement. NH3 is sometimes added to convert the chlorine to chloramine, a much less damaging biocide. Heavy metals present in seawater seem to amplify the damaging effects of chlorine and other oxidants. 

The continuous recirculation and spraying results in dirty water building up in the sump. In order to reduce the incidence of infection to occupants and fouling of the nozzle, water treatment with biocides and softening of the water supply are required. The sump is complete with strainers in a position which allows easy access for cleaning. See Fig. 9.15. 

The Directive will operate by listing all active substances which can be used in biocidal products in a list (annex I to the Directive) and requiring that only those active substances listed can be used in biocidal products. Member states will then authorise biocidal products to a set of common principles (annex V of the Directive) with a system of mutual recognition of authorisations. 

The Directive, and implementing Regulations require that risk assessments are carried out on biocidal active substances and the products containing them. This requires the submission, and in many cases the generation of data and industry has to provide this. 

Biocides are added to the wet end process to prevent slime formation. Introduction of neutral or alkaline sizing instead of acidic papermaking, the closed water circuits, and the increasing proportions of recycled paper have required changes in biocide types in order to control different microbial populations. 

The types of biocides used in this application vary from the rest of the pulp and paper industry. These require to be longer lasting, i.e. sometimes up to 1 years protection is storage tanks and hence fall into the category of preservatives. 

Although there are many biocide alternatives available on the market, for example enzyme technology or bio-dispersants, there appears to be a continued requirement for the use of biocides in order to reduce the levels of microbiological contamination entering the paper making process. The increased awareness of environmental and safety aspects will continue to play an important role on the selection of biocides for paper making processes. The use of legislation to select biocides must be done in parallel with each plants internal risk assessment. No one biocide active will meet all the criteria set out by different European countries and hence the use of these actives must be carefully assessed on a plant by plant basis. 

Physical methods for the control of microbial biofilms, although often effective, are in many situations impractical. In this context it is notable that an almost universal feature of the biofilm mode of growth is their profound resistance to antibacterial compounds. Conventional chemical control methods, developed for use against fastgrowing planktonic cultures are only poorly effective against biofilm bacteria. Large doses of biocide or antibiotics, which are either environmentally undesirable or above toxic thresholds respectively, are required to eradicate biofilms in industry and medicine. 

The trend from heavy metal and phenolic based biocides, e.g. mercury and pentachlorophenol types, to more environmentally acceptable but less persistent organic types, requires more attention to plant hygiene (Figure 6, Briggs, 1980). 

However, because the growth requirements for bacteria and fungi are ideally found in water based paint formulations and because bacteria in particular reproduce so quickly, small numbers can rapidly reach problem proportions unless they are inhibited, e.g. by the use of a suitable biocide... 

Even if all of the above properties are fulfilled, the ideal biocide will not be used if it is prohibitively expensive. The ratio of required dosage to price (its cost effectiveness) is, therefore, crucial to the success of such a product. 

Although no single active agent meets all the requirements of the ideal wet-state paint antimicrobial, one biocide group stands out as being the "best we have" and those are products based on the isothiazolin-3-one structure (Figure 14). 

Biocides are by their nature intrinsically toxic, in this respect any adventitious release to the environment requires an assessment of the relative risk posed. The 5th Environmental Action Plan of the EU is committed to a substantial reduction in the use of biocides. In particular, the Biocidal Products Directive (98/08/EC) is concerned with controlling biocidal products in the market place. Compliance with this directive is required from all member states by 14th May 2000. In this context, a strategy to control the release of biocides is timely, if continued protection is to be afforded to industry and consumer alike. One approach to controlling the release of biocide is to encapsulate in an inert inorganic framework, prior to incorporation in the coating.1... 

This material shares many of the advantages of the triazine biocides. They are relatively cheap, compatible with most formulations and provide a source of reserve alkalinity. In addition, at the time of writing, there are no requirements for labelling R43 with this class of material. It shares similar disadvantages to the triazines, possessing poor thermal stability. Oxizolidines also need to be co-formulated with a fungicide to provide complete protection for a product. 

Secondly, customers are applying ever greater pressures on formulators to make less use of some chemistries, for example formaldehyde release biocides. Customers would prefer preservatives that are good for die environment and possess no adverse mammalian toxicity characteristics. This would require that new actives are developed. This is unlikely considering the new regulatory frameworks. 

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