Nonoxidizing biocides combinations

The biocide component will be tailored by a technical team, from a starting point of available products in a particular vendor s range. This biocide component is most usually a dual-alternating, nonoxidizer program, or an oxidizer/nonoxidizer combination, together with a suitable biodispersant. The selection process has been discussed in Chapter 6, and some starting-point selection charts provided (Tables 6.3 and 6.4). 

Combinations of newer nonoxidizing products (good biocidal potency but expensive) with some older materials (good penetrating ability and relatively low cost) may prove effective. Also, certain combinations of oxidizing biocides with nonoxidizers may prove suitable under many conditions. 

There are several biofilm cleaning and removal techniques in common use. They typically employ a program of several shock doses of various oxidizer/nonoxidizer biocide combinations, together with biodispersant, followed by heavy bleed. Particularly useful are the newer types of phosphonium salt biocides, which have an additional cleaning effect (e.g., THPS/TKHPS/TTPC). 

Effect of combination of non-oxidizing biocides. Experimental study shows that the combination of nonoxidizing biocides was more efficacious in biofilm control than biocides when used alone (Figure 9). Simultaneous use of isothiazolones (4 ppm) and quaternary ammonium compound (12 ppm) demonstrated better biofilm control than either isothiazolones or quat alone. This biocidal combination controlled biofilm (based on HTR data) for about 27, 30, and 32 hours after three consecutive treatments. The biofilm DO response was much more significant than any separately tested biocide and was similar to the test when isothiazolone was used together with oxidizing biocide. These laboratory results confirmed practical (field) evidence that combinations of biocides affect biofibns more effectively than biocides used alone. 

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