Wednesday, August 20, 2008

How to evaluate paper industry biocides?

The following post was sent to "" but I think that it may interest also the readers of BIOTOUCH blog (and comments, of course, are more than welcome!).

Before referring the originat text, I would like to add some ideas about evaluation of biocides.

As known by microbiologists, traditional plate count methods cause bias into the biocide test results. No matter the active compounds are added to the process samples for KILL tests, final results are still derived by colony count analyses.

To have faster and more reliable evaluation (no need to dose every alternative into the process for days..weeks) a novel test method, which performes the biocide evaluation in original samples all over the test, is needed. PMEU method seems, until now, definitely to be the best choose.

And then the original post:

What should an ideal biocide be like?

* effective against a variety of microbial species
* effective in different process environments (temperature, pH, RO potential, solid concentrations etc.)
* both fast and conserving type of action
* not harmful for employers of paper machine
* not harmful for paper machine
* not harmful for products of the paper machine
* not harmful for environment
* (something else?)

As far as I know, no such ideal biocide has been developed yet. "Tailored" biocide products shall therefore be combined to fight against raw material contamination, microbial activity in large process water and pulp systems, fiofilm producers...

The rapid development of fast-acting oxidative agents (chlorine-and bromine-based compounds, PAA, ClO2 and even O3) is very promising, but they have limited success as storing agents. Their broad-spectrum influence on even bacterial spores should be taken into account when planning biocide programs, which also should contain compounds to prevent biodegradation during storage periods and formation of biofilms on wet surfaces of the machine.

In some cases, activity of alternative biocides against certain hazardous bacteria are also worth to evaluate.
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