BIOFILM DEVICE FOR THE MONITORING OF MICROBIAL DISTURBANCES IN INDUSTRIAL PROCESS WATERS

Abstract: The invention relates to a device for the monitoring of microbes forming a biofilm on surfaces in industrial process waters consisting of a cylindrical, openable body (1), sample plates (2) placed symmetrically inside the body (1) parallel to its middle axis, and holders (4) placed inside the body (1) for the mounting and holding of the sample plates (2). The device furthermore comprises a valve for opening, closing and regulation of the flow-through.

Description: Biofilm device for the monitoring of microbial disturbances in industrial process waters The invention relates to a modern so-called biofilm device for the microbiological monitoring of industrial process waters. The device of this invention is particularly advantageous when microbial disturbances of paper industry are monitored. By means of the biofilm device it is namely possible to predict runnability problems caused by microbes. It can also be used for the selection of control methods in the paper mill itself. Biofilm is a term generally used in the field for a deposit formed by microbes on surfaces. The worst microbial problems in the paper and board manufacture are the runnability problems caused by microbial deposits i.e. the formations of holes and patches in the product, web breaks as well as drainage disturbances caused by blockages of machine felts. For the monitoring of these problems determination of the bacterial contents of circulation water samples is generally used. The freely floating common bacteria of the circulation waters cannot, however, give reliable indication of the runnability problems since especially the microbial deposits cause runnability problems - not separate bacteria in the circulation water - and, on the other hand, the deposits are formed on the surfaces, not in the circulation waters. Accordingly investigations of bacterial contents of the circulation waters are useless with respect to the prediction and monitoring of the runnability problems of paper and board machines. Essentially more useful than the foregoing is to determine in circulation waters certain microbes causing deposits, such as filamentous bacteria, filamentous yeasts and molds and slime-forming bacteria. In this way one can indirectly monitor biofilmforming microbes that possibly have come loose from surfaces to the circulation water. If there are plenty of such bacteria in the circulation waters, it might already be too late to control microbial problems and the runnability of the paper machine may already have weakened. Thus, the best way to avoid runnability problems is to monitor problem microbes directly from the biofilms formed on the surfaces. During the normal production of paper and board machines this is, however, difficult because the deposit samples can be handily taken only in the beginning of the shutdowns just before the washing of the machinery. The aim of the present invention is to remove the above-mentioned drawbacks and to develop a device with which it is possible to predict runnability problems caused by microbes particularly in paper and board mills. By the device of the invention the microbiological status of the surfaces of pipings and containers can be found out also during the normal production without stopping the run of the machines. The characteristic features of the invention are presented in the attached patent claims. The biofilm device of the invention consists of a cylindrical body and steel plates placed symmetrically in regard to each other and with respect to the flow of the circulation water inside the body, on the surfaces of which the microbes as well as other material, such as fibrils, fibers, pitch and pigment particles can attach from the side streams of the circulation water or a container. The symmetrical arrangement of the steel plates is an absolute prerequisite to make the steel plates comparable taken at various times into investigation. There has been biofilm devices in use previously. Pedersen, Appl. and Environ. Microbiol., vol. 43(1)(1982), p. 6-13, has developed a device for water research, in which small and easily breakable cover glasses are placed in a box above each other as "shelves". Hereby, the cover glasses are not in a symmetrical position with respect to the flow, and, thus, they are not equal with each other. Another disadvantage of the device is the fragility of the cover glasses. This type of a device cannot be applied for the biofilm examinations of process industry. The Robbins device (Ruseska I. et al., Oil & Gas Journal, vol. 80 (1982), p. 253264) does not fulfil the symmetry requirement either because removable sample plates are placed after each other along a pipe. The last plate is, in the theory, in the most disadvantageous position compared with the first plate as regards the flow. The size of the sample plates of the Robbins device is all too small to carry out microbiological analyses of the biofilms deposited on the plates. Conkey J., TAPPI Proceedings (1984), p. 115-120, has developed a tubular device, the principle of operation of which is fully different from that of the biofilm device of the present invention. The intention of the device is, namely, to indirectly monitor the amount of the material attaching on the surfaces of the pipe by measuring the flow resistance. The Conkey device does not contain detachable sample plates for laboratory investigations. The new device of the present invention is preferably prepared from acid-proof steel, which is a generally used pipe and container material in paper industry. This is important in a biofilm device because microbes attach differently for example to glass than to steel. To secure the reliability of the device the same material should be used in it as in the equipment to be investigated. The device of the invention and its steel plates tolerate fairly great pressures and strong flows contrary to, for example, the thin cover glass plates of the above-mentioned Pedersen device. The advantages of the biofilm device of the invention as compared with other devices are in summary the symmetric position of the sample plates made of steel in regard to each other and the flow-through, an adequate size of the sample plates for various microbiological analyses, the strength of the structure and in addition to this the suitability of the steel plates as such for epifluorescence microscopy. The biofilm device of the invention is also suitable to be used for testing the efficiency of biocides in the process of the mill. So far the testing and choice of biocides has taken place in laboratories, where it is difficult to simulate the dynamic conditions of circulation water. The device of the invention is also suitable both for testing biocides and for testing dispersing agents and washing chemicals. The device of the invention can be connected with any side stream of the circulation water or container in a paper or board mill or, for example, with a flow taken from the wet end. The flow-through of the device is preferably adjusted to the range of 0.5 to 100 liters/min. The sample plates are preferably kept in the flow to be investigated for about 1 to 90 days. In the following the invention is described in more detail by referring to a figure describing a biofilm device of the invention in a partial side section and a cutthrough of the biofilm device at point A-A of the steel plates perpendicularly against the vertical axis. The device consists of a cylindrical body 1 made of acid-proof steel, the ends of which have been formed conical. Sample plates 2 made of acid-proof steel have been placed inside the body so that they lie symmetrically around the middle axis of the body 1 parallel to the axis. The body 1 and the steel plates 2 can also be made of some other durable material. The body 1 of the device is hinged 3 in the middle or otherwise openable to install the sample plates and to remove them. Insi 'e the body 1 there is, for example, a hoop-formed holder 4, to which the lower end of the sample plates 2 can be placed for the symmetrical installing of the sample plates. The plates are fixed at their upper end of the sample plates 2 by a locking means (not shown) which can be, for example, a hoop-formed holder. As can be seen from the cross-section of the cylindrical body 1 the steel plates have been installed radially around the middle axis of the body parallel with the axis, whereby all plates are equal with each other. The number of the sample plates can be any number, provided the flow resistance will not grow harinfully high. The device comprises a valve (not shown) connected with the inlet for the opening, closing and regulation of the flow-through. In the following the operation of the device of the invention is described by means of examples. Experiments have been made both in laboratory and in industrial scale. Example 1 In laboratory, ground wood diluted with a very weak nutrient solution (MYGP) in the ratio 1:5 was circulated through two biofilm devices according to the invention. The composition of the MYGP solution was the following: Bacto malt extract 3g Bacto yeast extract 3g Bacto peptone 5g D glucose 10g distilled water 1000ml dilution in the ratio 1:40 with water. A yeast isolated from the broke of a paper mill was chosen as the microbe to be investigated. It was added into the mixture to be circulated to the concentration 10,000 cfu (colony-forming units) per ml. To the circulation of the first device 20 ppm of biocide Fennosan M 9 was added and the second biofilm device served as a control. The steel plates of the devices were taken for investigation after three and six days and the number of yeast cells per sq. cm was determined. The results are presented in Table 1. Table 1 Time Yeasts attached to steel plates (cfu/cm2) days Control Fennosan M 9 3 140 000 37000 6 1 600 000 11000 The results show that after 6 days lots of yeasts had attached to the steel plates of the control device and had grown there well so the device functioned according to expectations. In the presence of a biocide the attachment of yeast cells remained fractional i.e. at about 0.3%. Example 2 The laboratory experiment was carried out in the same way as in example 1. Yeast cells were added to a concentration of 290,000 cfu/ml. The yeast was from a board mill. Hydrogen peroxide (50ppm), which is known for its ability to prevent formation of a biofilm, was used as an inhibitive chemical. The results are presented in Table 2. Table 2 Time Yeasts attached to the steel plates (cfu/cm2) days Control Hydrogen peroxide 2 170 000 110 000 5 2 000 000 80 000 12 2000000 40 000 Also in this case the biofilm device functioned well. Lots of yeast cells (2 million cfu/cm2) had attached to the steel plates of the control device in 5 and 12 days, whereas the number of yeast cells in the presence of hydrogen peroxide remained, when lowest, at 2% of the control. Example 3 The idea of this ex.iple is to show the significance of the biofilm forming microbes harming the runnability of a paper machine. The head box and the wire tank of a paper machine were chosen as the sampling points. A biofilm device according to the invention was connected with the wire tank. Harmful molds were determined both from the biofilms of the surfaces and from the circulation water. The results are given in table 3. Table 3 Sampling Number of molds (cfu/ml) point Circulation water Biofilm Head box < 100 1400 Wire tank < 100 5400 The results show that molds harmful to the runnability could be found only in the biofilms of the surfaces, but not at all in the adjacent circulation water. Lots of molds could be found on the steel plates of the biofilm device connected with the wire tank. This experiment shows the utility of the biofilm device according to the invention in a mill. Example 4 In this test the biofilm device was connected with the white water tank of a paper mill. The aim was to test the function of the device and the possible attachment of harmful microbes on its steel plates. The steel plates were installed in the device on different days. The results are given in Table 4. Table 4 Time Bacteria (cfu/cm2) Fungi (cfulom2) days 12 3000 < 30 21 24000 270 22 140 000 5 400 34 730 000 32000 The results show that bacteria and fungi attached in the greater extent the longer the steel plates had been in the side stream of the white water tank. At a microscope the fungi were found to be filamentous i.e. potential deposit formers. Also some of the bacteria were filamentous. In summary, on the basis of the test results, it can be said that the function of the biofilm device according to the invention is reliable. By means of the device new information from the community structure and amount of microbes attaching to the surfaces may be obtained under production conditions. This information can be utilized in combatting microbes harmful to the runnability and in the optimization and scheduling of washings of the production machines.

Claims: Claims 1. Device for the monitoring of biofilm-forming microbes in industrial process waters, characterized in that the device consist of a cylindrical, openable body (1) made of acid-proof steel or other durable material, sample plates (2) made of acidproof steel or other durable material placed symmetrically inside the body (1) parallel to its middle axis, and holders (4) placed inside the body (1) for the mounting and holding of the sample plates (2). 2. Device according to claim 1, wherein the device further comprises a valve for the opening, closing and regulation of the flow-through. 3. Device according to claim 1 or 2, wherein it is connected with the circulation water of a mill or the side flow of a tank or, for example, with a flow taken from the wet end of a paper or board mill. 4. Device according to any of claims 1 to 3, wherein the flow-through of the device is adjusted to the range of 0.5 to 100 liters/min. 5. Device according to any of claims 1 to 4, wherein the sample plates are kept in the flow to be investigated for 1 to 90 days.

Inventors: VAEAETAENEN PENTTI, VAEAETAENEN, PENTTI
Applicants: KEMIRA CHEMICALS OY
Application year: 1995
Main classification: C12M1
IPC codes: C12M1, G01N33