Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
A method for reducing the buildup of
slime and film in plant
The present invention relates to a method for reducing the
buildup of slime and film in plant that circulates water.
It is also based on a system for carrying out this method
and applications of this method.
Water circulation, in particular the increasingly
used closed circulation of the white water on paper machines
and cooling water circulation, always involves the problem
that and/or film builds up on solid surfaces and in the
liquid phase (cf. "Vortrage anla(3lich des 5. PTS-WAF-
Lehrgangs, Fortbildungskurs zur Wasser- and
Abwasseranalytik, Kontrolle des Einsatzes von mikrobioziden
finder Papiererzeugung". ("Lectures in the Fifth PTS-WAF
Course, Further Education on Water and Waste Water Anlysis,
Control of the Use of Microbiocides in Paper Production"),
organized by the "Papiertechnische Stiftung," Munich, and
Hans-Dietrich Held "Kuhlwasser" ("Cooling water") ,
Vulkan-Verlag Dr. W. Claussen, Essen, 1977, p. 70 to 73).
In the closed circulation of the white water
increasingly used for paper machines, microorganisms find
very good growth conditions due to the high organic and
inorganic nutrient offer present in the white water, and a
favourable environment, i.e. a high temperature, a pH value
close to the neutral point and a supply of oxygen. Since
many of the microorganism are not present in the circulating
water as free organisms but settle on the fibrous, filling
and fine material and the surfaces of the machine parts,
such as pipes, vessels and pumps, there is an undesirable
buildup of slime and film. When the slime or film is
detached from the surfaces this often leads to the formation
of lumps and thus possibly to holes in the paper web. This
weakens the paper web, i.e. cause it to tear, thereby
resulting in machine standstills. In order to prevent this
buildup of slime and film it is known to add biocides,
lignosulfonates or enzymes to the white water.
,~~
The use of biocides suppresses the growth of the
microorganisms and partly damages them. However, the use of
biocides is increasingly criticized. The greater the amount
of biocide is, the more damage is done to the environment to
which the white water is fed when the circulation is emptied.
Since microorganisms tend to become resistant to biocides it
is also necessary to change the biocide substances frequently
and/or increase their amount. This means a considerable
increase in pollution or considerable costs, e.g. for a
following adapted clarification plant or a drainage ditch.
Lignosulfonates are used as so-called "complexers"
which prevent the microorganisms from taking in food under
certain conditions. Sometimes a biocide must also be used
with the lignosulfonate, but in a much smaller amount then if
used alone (cf. German patent no. 34 47 686). The problems of
biocides thus continue to exist in a milder form.
Enzymes are added to the white water circulation in
order to convert the high molecular polymers, which promote
the build up of slime and film, into low molecular products
which are uncritical for the buildup of slime and film. This
method is environmentally safe but has not proved useful in
large scale application, presumably because it only allows for
a brief reduction of viscosity, while the hydrolysis or other
low molecular products formed by the enzymes may even be
preferred food for the slime forming microorganism.
Cooling water circulation involves the problem that
leaks or points of contact with the circulating product
stream, such as the condensation of gases in the cooling
circulation which arise during vaporization processes in the
circulating product stream, cause organic impurities to pass
into the circulating water in most cases. This again lead to
the growth of microorganism. Together with the organic and
inorganic impurities, these microorganism chiefly form
deposits on the surfaces of the heat exchanges, thereby
drastically reducing the heat transmission. This
necessitates frequent and expensive cleaning of the heat
exchangers to maintain the necessary removal of heat for the
particular process. In this case, too, biocides are mainly
used to reduce the buildup of slime and film on the
~,a.., , ...
~;0~35(~~9
3
heat exchanger surfaces.
The invention is therefore based on the problem of finding
an environmentally safe method for plant with water circulation
which reduces the buildup of slime and film in the water circu-
lation, thereby reducing the stop periods of the plant.
This problem is solved by a method of the type stated at
the outset whose characterizing feature is that microorganisms
are added to the circulating water.
Surprisingly enough, when the inventive method is carried
out and microorganisms are selectively added to the circulating
water in accordance with its organic load, there is a clear
reduction in the buildup of slime and film on solid surfaces
and in the liquid phase, although the addition of microorgan-
isms constitutes an increased organic contamination of the cir-
culating water.
The inventive method presents an environmentally safe way
of treating the most diverse types of circulating water in such
a way as to largely reduce the buildup of slime and film and
shorten the stop periods of the plant.
Microorganisms suitable for the inventive method have
proved to be in particular bacteria, mainly bacteria of the
following taxonomic groups: Aeromonas/Vibrio, Acinetobacter,
Alcaligenes, Enterobacteria, Pseudomonas, Bacillus, Lactobacil-
lus, Micrococcus, Staphylococcus and Streptococcus, in particu-
lar Aeromonas hydrophila, Acinetobacter calcoacetica, Alcalige-
nes eutrophus; Escherichia coli; Nitrosomonas, Nitrobacter,
Bacillus megaterium, B. macerans, B. polymyra, B. subtilis, B.
stearothermophilus, B. coagulans, B. circulans, B. cereus, B.
pasteurii; Chromatium; Pseudomonas arvilla, P. putida, P.
stutzeri, P. fluorescens, P. denitrificans, P. aeruginosa; Zoo-
gloea; Zymomonas; Leuconostoc; Proteus vulgaris; Sporosarcina
ureae; Rhodopseudomonas; Nocardia; Mycobacterium; Flavobacte-
rium; Agrobacterium; Cytophaga; Sporocytophaga; Streptomyces;
Micromonospora; Clostridium pectinovorum, C. felsineum; Azoto-
bacter: Streptococcus; Cellulomonas; Azomonas; Rhizobium; Thio-
bacillus, Thiothrix, Streptobacillus, Spaerothilus, Enterobac-
ter aerogenes; Serratia; Propionibacterium; Micrococcus; Ar-
throbacter, Corynebacterium, Brevibacterium; Photobacterium;
Xanthomonas, Chromobacterium, Vibrio, Acetotbacter,
Lactobacillus. In the following, bacteria will therefore be
primarily referred to.
However, other microorganisms can also be used in the
inventive method, such as fungi, such a fungi of the groups
Myxomycetes, Phycomycetes, Ascomycetes, Basidiomycetes,
Deuteromycetes, in particular Acrasiales, Asperigillus niger,
A. Oryzae, A. wentii; Candida lipolytica, tropicalis;
Saccharomyces; Chaetomium; Cryptococcus.
One can also use mixtures of bacteria or of fungi or
mixtures of bacteria with fungi.
The bacteria use according to the invention are
nonsessile bacteria, i.e. microorganisms or bacteria are
selected which show no, or only little, tendency to settle on
surfaces compared to the microorganism or bacteria forming
slime and film in the plant.
The tendency of the added microorganisms or bacteria
to settle on surfaces can be further reduced according to the
invention by adding tensides to the circulating water. A
suitable tenside has in particular proved to be a tenside
called "Konsan" available from KW Kalos & Wiechmann GmbH, Hude.
According to the inventive method the bacteria are
added in a relatively large quantity. Furthermore, they are
not used in lumps, flakes or colonies but preferably as single
bacteria. Due to their large quantity and their single form
the bacteria have a very large total surface, so that they
lead to strong absorption or intake of the nutrients existing
in the circulation. This results in a competition for the
food present in the circulating water, which is won by the
added nonsessile bacteria, due to their high food intake,
and lost by the slime and film forming microorganisms.
In order to allow the bacteria to be added to the
circulating water in an optimal single form, the invention
preferably assume dry bacteria or mixed cultures or dry
bacteria which are stirred by stirring means, well known in
the art, into a predetermined volume, whereby after an
activation period of e.g. one to ten hours the single
activated bacteria can be added to the circulating water.
Mixed cultures of dry bacteria have proven to be particu-
a
~ooso~s
~.-- 5
larly suitable for the inventive method Which are marketed
under the name "DBC plus" by Enviroflow Flow Laboratories,
Inc., A Flow General Company, McLean, Va., U.S.A.
The "DBC plus" mixed culture is selected in accordance with
the nutrient offer in the circulating water. The flora analysis
of the new "DBC plus" types of dry bacteria mixtures and the
main taxonomic group is as follows: Aeromonas, Acinotobacter,
Alcaligenes, Enterobacteria, Pseudomonas other gram-negatives,
Bacillus, Lactobacillus, Micrococcus, Staphylococcus, Strepto-
coccus and other gram-positives and those whose classification
is questionable.
Thus, "DBC plus type A2" is particularly suitable for the
circulating water of paper machines as well as for processes in
petrochemistry Where phenolic compounds may pass into the cool-
ing water.
Further, "DBC plus type L" is suitable for the cooling
water circulation in refineries where hydrocarbons can break
into the cooling water circulation, as well as in the cooling
circulation of oil mills, i.e. in the processing of vegetable
oils. Furthermore, "DBC plus type L1" is used in particular in
cooling circulations in the chemical industry, especially when
ketones must be expected in the cooling water.
The quantity of bacteria added to the circulating water
based on the quantity of organic substances in the Water is
preferably 1 to 101° bacteria per kg of the total organic car-
bon (TOC) of the organic substances, in particular 10 to 109
bacteria per kg of TOC and most preferably 102 to 108 bacteria
per kg of TOC.
In dry bacteria, in particular "DBC plus" bacteria, this
corresponds to about 10-6 to 50 g per kg of TOC, or 10-5 to 5 g
per kg of TOC, or 10-' to 0.5 g per kg of TOC.
Other additives are preferably also mixed into the circu-
lating Water along with the bacteria. The addition of tensides
was already referred to above for reducing the sessility of the
bacteria and other microorganisms on the surfaces of the ma-
chine parts. It is also advantageous to promote the growth of
the added bacteria by adding supplines (cf. Hans G. Schlegel,
"Allgemeine Mikrobiologie" ("General Microbiology"), 6th ed.
6
"""~" 1985, p. 174) .
The addition of lignosulfonates, as described in
German Patent No. 34 47 686, can also be advantageous although
no biocides at all are used in the inventive method.
It is also advantageous in the inventive method to
add enzymes which catalyze the breakdown of the organic
substances contained in the circulating water. The enzymes
used may, for example, be amylases, proteases, pectinases,
cellulases, acylases, aldolases, alcanoxygenases,
alkoholdehydrogenases, dehydrogenases, phosphatases,
dehydrases, dehydratases, oxygenases, oxidases, permeases,
kinases, carboxylases, lipases, phosphorylases,
decarboxylases, reductases, oxidoreductases and
hemicellulases.
The type of enzyme used depends on the application in
question. For example, cellulases and hemicellulases
preferably added to the white water of paper machines, while
proteases are added to the cooling circulation in food
processing, and lipases are added in particular to the cooling
circulation in oil mills and other food processing plant.
The quantity of enzyme or enzymes added is preferably
IU (International Units) to 500,000 IU per kg of TOC.
However, a quantity of maximally 10,000 or maximally 1000 IU
per kg of TOC is generally sufficient.
Further, a high content of dissolved oxygen in the
circulating water is advantageous in the inventive method.
This accelerates the breakdown of the organic substances,
thereby reducing the high load of these substances in the
circulating water.
The oxygen can be supplied by aerating the
circulating water with oxygen or by adding oxygen-releasing
compounds, such as H202 or peroxides.
In the inventive method, the bacteria and further
additives are preferably added continuously, which also
includes the addition of smaller portions over time. This
maintains the dominance of the added type of bacteria, thereby
ensuring the process stability.
The bacteria and other additives may be added in
time-proportional fashion, i.e. a certain amount preferably
added continuously for a certain time, e.g. one day. Instead,
they may also be continuously added in proportion to quantity.
That is, the TOC content is constantly analyzed ,possibly
automatically, and the amount of added bacteria and other
additives regulated in accordance with the analyzed TOC
content. Addition in proportion to quantity is preferable in
particular for processes involving great fluctuations of the
TOC content.
The invention is also based on a system for carrying
out the inventive method, comprising a feed area in which the
bacteria and/or other microorganisms and possibly the other
additives are continuously added to the circulating water.
The feed area is preferably provided with a dosing
means for automatically adding the microorganisms or bacteria,
and optionally one or more other dosing means for
automatically adding the other additives.
The individual components are fed in places as
separate as possible in the feed area. For example, if
proteases are used as the enzymes, they are added at a place
upstream of the place where the bacteria are added. This is
because the proteases are intended to settle with their active
centers on the organic substances in the circulation and
catalyze their breakdown. If the active centers of the
proteases came in direct contact with the added bacteria, they
would accelerate the breakdown of bacterioprotein and thus
damage the added bacteria.
For this reason. H202, for example, is added at a
place or at places located upstream of the place where the
enzyme and the bacteria are added, since H202 in excessive
concentration is a cellular poison and can damage the enzymes.
The addition of H202 is therefore preferably distributed over
the entire system.
The inventive method is suitable in particular for
reducing the buildup of slime and film in plant which
circulates the white water of paper machines, and in plant
which circulates cooling water.
