Sulphate Reducing Bacteria (SRB) as harmful inhabitants of process waters

SRB is an interesting group of bacteria which can use sulphate as an electron acceptor for the respiration. Despite the chances of certain other bacteria to use sulphate as the sulphur source for their S-containing cell components, the "real" sulphate reducers transform SO4(2-) to S(-2) in their energy metabolism and oxygen actually inhibits their growth - they are therefore obligate anaerobes. Certain yield of energy may be achieved through fermentation by SRB's but this type of metabolism is regarded as relatively insignificant one for them.

These bacteria have first detected in waste waters of sulphite pulp mills but modern paper machine processes can also induce their growth if certain sulphur-containing compounds are available.

In addition to H2S production (which is a hazardous gas), colour problems can arise because the metal sulphides. FeS is an indicator compound in the analytical detection of SRB's but also a harmful agent of discolorization of paper and paperboard. Last but not least, SRB's have been shown to be conneceted to a certain type of iron corrosion and it is all possible to find those problems still today whenever technical structures with poor steel quality and certain types of organic deposits on their surfaces are combined.

SRB's have also other, peculiar features like the tendency to follow non-exponential growth curve. They have been the subject of firm microbiological research only since the middle of 20th century because their need of anaerobiosis was not understood earlier.

A new point of view shows the negative effects of high sulphate concentrations in lakes and rivers which receive waste water of bioleaching mining. If sediments of hypolimnion (lower water column of the lake) will be rich of sulphate and oxygen levels will simultaneously drop, the production of poisonous H2S is obvious. An article about the effects of sulphate in natural waters will be published soon by my fellow microbiologist and me. I will inform You when it happens.

A new beginning of P&P industry - in Africa?

I would like to share my new post (from www.industrymicrobiologist@blogspot.com) with the readers and participant of BIOTOUCH concept. Sometimes it is very refreshing to have some time for thinking about an utopia: "What if everything could be started again, taking into account the best, current knowledge of technical, physical, chemical, microbiological and energy topics in paper industry - what would the paper mills be like?"

- Here is my post:

"IM follows frequently the bright blog written by Jim Thompson (http://www.nipimpressions.com/).

His last post discusses about the dark future of Finnish P&P. In opposite, he gives an optimistic forecast: the promising region for the manufacture of pulp and paper could be Africa! After reading his points of view - short but comprehensive - I must agree. Everything could begin once more on this huge continent if only social and political confusions can be won there.

Sitting and thinking - what else? What about a new way to construct paper and board machines? To take into account not only technical issues, but also all chances to have machines which were easier to control and keep clean/safe than these old ones, we are still driving?

There are a lot of relatively simple solutions which can improve the hygiene of raw materials as well as keep wet end area, white water circulation, pulp towers and broke systems cleaner. These ideas were discussed during the professional career of IM and very many wise men (and women) agreed. It has been the question of reconstruction costs which has prevented the realisation of the progress in paper machine development towards cleaner production and processes.

But: what about starting everything once more? To build up machines with clever ON LINE process control and alarm systems? Machines which were easier to clean during production? Machines which even have self-cleaning constructions?

Ozzy Osbourne sings: " I'm a Dreamer" - but what we are lacking just now are the dreams, aren't we?"  

How to evaluate paper industry biocides?

The following post was sent to "industrymicrobiologist.blogspot.com" 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.