WO1994009885A1

WO1994009885A1 - Bio filter

Info

Publication number: WO1994009885A1
Application number: PCT/DK1993/000357
Authority: WO
Inventors: Arne Kjaer Poulsen; Per Brock; Lars Brock; Olav Krogh Nielsen
Original assignee: Bbk Bio Air-Clean Aps
Priority date: 1992-11-02
Filing date: 1993-11-02
Publication date: 1994-05-11
Also published as: AU6280094A

Abstract

A method for deodorizing flue gas, in with the flue gas is conducted through a bio filter. Said bio filter consists of a carrier material, which includes an inorganic part and preferably also an organic part. At least the organic part is sterilized whereupon selected biological organisms with specific characteristics are added to the carrier material. By sterilizing the carrier material and subsequently adding biological organisms with specific characteristics, preferably microorganisms, a very high effectiveness is obtained in the bio filter since no undesirable organisms are present in the filter substance.

Description

BIO FILTER

BACKGROUND OF THE INVENTION

The present invention relates to a method for deodorization of flue gas through decomposition of gaseous components, in which the flue gas is conducted through a filter comprising an inactive carrier material which preferably consists of a combi¬ nation of inorganic and organic material, said filter also comprising a biologically active medium, preferably microorganisms.

The invention further relates to a filter substance for use by the method and the use of biological organisms with specific characteristics.

DK publication No. 144458 discloses a method for separating gaseous impurities from a gaseous medium. The separation takes place in a filter with a biologically active medium which consists of organic waste material and/or purification sludge and possibly compost. A biological medium consisting of these components will be able to absorb a wide range of different smells from waste gases. However, this biological medium will not be specifically applicable for a particular smell in a given waste gas in which case there will be many microorganisms present in the medium which are not necessary. Thus, in a biologically active medium of this kind there will be a large number of different microorganisms some of which are active, some decompose the active ones while still others are passive. The effectiveness compared to the filter size is consequently limited.

DE patent No. 3,345,944 discloses a method for separating gaseous organic pollutants through oxidization with bacteria. The bacteria comprise the species contained in purification sludge. Like in the method disclosed in the above-mentioned publication, this is a disadvantage since such a biological medium comprises a wide range of bacteria not all of which are active in the separation process. There is the additional disadvantage that bacteria contained in purification sludge are mostly anaerobic bacteria, which are less efficient than aerobic bacteria. EP patent application No. 0,464,661 discloses a bio filter for purification of polluting gases. The bio filter consists of a mixture of porous concrete granulate and a soil material in a given mixture proportion and with a given grain size. The composition of the soil material is not specified but, like the biological media discussed in the above publications, soil material such as humus or peat contains a variety of different bacteria, not nearly all of which are active in the separation process.

It is common for the prior art disclosed in the above publications that it fails to make any qualitative judgement of what kinds of biological organisms are most suitable for use in the disclosed methods or filters. This reduces the effectiveness of the filters as there will be organisms which are not active in the decomposition process.

Thus, it is the object of the present invention to present a method for purification of flue gases by means of a bio filter with much higher effectiveness than the prior art methods or bio filters.

This is achieved by a method of the kind mentioned in the introduction, which is characterized in that at least the organic part of the carrier material is sterilized, that biological organisms with specific characteristics are selected for biologically active medium, and that the biologically active medium is added to the carrier material.

The effectiveness of a bio filter is determined by the number of active biological organisms, including microorganisms such as bacteria and fungi, per volume unit, and the volume depends on the carrier material used and on the degree of concentration of microorganisms that can be contained in that carrier material.

With a method and a filter material according to the invention, very high effectiveness is obtained in a bio filter used in connection with the invention. The carrier material consists preferably of a mixture of inorganic and organic materials, e.g. vesicular clay products such as Fibo or Leca nuts, lava, vermiculite, plastic granulate, etc. , whereto is added for example compost, sludge, sphagnum, humus or other organic material. The addition of the organic material notably ensures that the microorganisms have something to feed on when the input of flue gas is reduced or when the content of nutrients in the flue gas is reduced.

Said carrier material, which consists of a specific combination of the above-mentioned or other suitable materials, is subjected to pasteurization, radiation, or other thermic, mechanical or chemical treatment in order to sterilize the carrier material. When the carrier material has been sterilized, there are no live organisms present in the material, primarily all microorganisms have been destroyed.

Thereupon selected microorganisms with specific characteristics are added, selected according to the flue gas or gases to be deodorized. The number of specific microorganisms added is sufficient for the filter to be saturated by them. This reduces the risk that other undesirable microorganisms will have a chance to oust the active microorganisms and establish themselves in the filter. In order to maintain the required population of active microorganisms it will be necessary, in periods when the flue gas does not contain sufficient nutrients for the microorganisms, to add supplementary nutrients so that the microorganisms may survive and multiply.

As the filter only contains selected microorganisms with specific characteristics and does not contain undesirable microorganisms which are either passive or feed on the active microorganisms, the effectiveness of the filter is consequently as high as it can be since all the microorganisms are active.

In order further to ensure high effectiveness of the filter, the microorganisms used are preferably aerobe bacteria and possibly fungi. The process velocity of the aerobe microorganisms for the flue gases in question is higher than the process velocity of the anaerobe microorganisms.

A preferred way of producing the filter is primarily to sterilize the organic part of the carrier material and, if possible, to avoid sterilizing the inorganic part since the latter will rarely contain any microorganisms. By only sterilizing the organic part, the costs of sterilization are minimized substantially. In some cases, however, it may prove necessary to sterilize the inorganic part as well. The mixture of the sterilized organic part and the optionally unsterilized or sterilized inorganic part of the carrier material is delivered to the user in tightly closed sacks or other kind of packaging which will prevent microorganisms from entering the carrier material.

At the application source the carrier material is added immediately before the installation is put to use. The carrier material is moistened through the addition of water, preferably in the shape of atomized water, in order to provide the correct humidity in the filter for the survival of the microorganisms. As mentioned previously, other nutritional substrates in addition to the organic part of the carrier material may be added in order to provide a sufficient amount of food for the microorganisms in periods when the content of nutrients in the flue gas is low.

Finally, the specifically selected microorganisms are added, which are given optimal life conditions by the combination of organic and inorganic carrier material without alien microorganisms. The amount of microorganisms to be added is determined by the bio filter being at least saturated, possibly supersaturated, so that other microorga¬ nisms will not be allowed to establish themselves.

During operation of the plant, it must constantly be ensured that the conditions of humidity and nutrition in the filter are sufficient for the microorganisms to survive and multiply for maintenance of the population of the specific active microorganisms. Therefore, the filter is equipped with a water atomizer equipment which is able to provide continuous and evenly distributed moistening of the plant. As the microorga- nisms added to the filter are primarily aerobe species, it is crucial not to add so big amounts of water that the oxygen is driven out and the microorganisms consequently suffocate. Furthermore, acid and base components are added in order to maintain the correct pH for survival of the microorganisms, for most microorganisms that is pH = 7.

The microorganisms added to the filter vary depending on the smell to be removed. Either bacteria or fungi or a mixture of these two types of microorganisms are added. The filter may also have macroorganisms in the form of live plants which may also have a decomposing effect on the smells of the flue gas.

A range of microorganisms that may be applied will be the following, which is in no way a complete list: Bacteria, such as nitrification bacteria, Myco bacteria, Chemo- lithotrophene bacteria, Coryne-shaped bacteria, Micromonospora and Hyphomicrobium sp. bacteria, Cromo and Flavo bacteria, Pseudomonas, Bacillus, Thiobacillus, Xanthobacter sp. Nocardia sp., Proteus, Streptomyces sp., and Actinomyces and others. Furthermore, a wide range of fungi may be applied, such as Penicillum sp. Cephalosprium sp., Mucor sp., Circinella sp., Cephalotecium sp. Ovularia sp. and

Stemphilium sp. and others.

The above-mentioned microorganisms only comprise the types bacteria and fungi. This does not rule out, however, that it may be possible also to use yeast for deodorizing the flue gas.

Below are a number of tables which show the effectiveness of various bio filters, both prior art filters and filters according to the present invention. Effectiveness has been measured for cleaning of hydrogen sulphide (H₂S), mercaptans, and ammonia (NH₃).

Explanation of the abbreviations and units used in the tables:

INL. Contents of the flue gas at the inlet into the bio filter.

BIO. Bio filter consisting of approx 4,000 sq.m of "bed type" filter containing among other things heather and sphagnum. PLT 1 Prior art plant consisting of a biosorp containing filter substance with pulverized lava and sphagnum from a purifying plant. PLT 2 Prior art plant consisting of a biosorp containing filter substance with sphagnum and Leca inoculated with sludge from a purifying plant. PLT 3 Plant for use by the method according to the invention and consisting of a biosorp containing filter substance according to the invention with 15 % by volume of 0-4 mm Leca, 35 % by volume of 4-10 mm Leca, 50% by volume of pasteurized compost (worm compost) and microorganisms of type A-92.

PLT 4 Plant for use by the method according to the invention and consisting of a biosorp containing filter substance according to the invention with 15 % by volume of 0-4 mm Leca, 35 % by volume of 4-10 mm Leca, 50% by volume of pasteurized compost (worm compost) and selected microorga¬ nisms with specific characteristics.

PLT 5 Plant for use by the method according to the invention and consisting of a biosorp containing filter substance according to the invention with 15% by volume of 0-4 mm Leca, 35 % by volume of 4-10 mm Leca, 50% by volume of pasteurized compost (worm compost) and microorganisms type B-92.

ODOUR Units/m³.

TEST 1.

OZONE added

New sample in stead of the one of 18th June

TEST 2.

TEST 3.

TEST 7.

TEST 11.

It appears from the test results that the plants according to the invention are substantially more able to reduce the number of Odour Units and that said plants also remove the ammonia component of the flue gas to 100%, unlike the prior art methods and types of filter substance.

All measurements on the bio filter and the various plants, respectively, have been taken at the outlet of the flue gas, i.e. after the flue gas has passed the whole filter substance. In order to examine the effectiveness gradient through the filter substance, a few additional measurements have been made 1 m. up inside the filter substance in the biosorp.

TEST 10.

Measurements at altitude 1 m ODOUR (Units/m³)

25,000

13,300 no measurement

10,800

4,500

% EFFECT (NH₃)

44.4 68.3 96.8 96.8

93.7

It is seen from this table that, as the flue gas passes through the filter substance, plants for use by the method according to the invention will decompose the ammonia component much faster than the prior art plants. This means that it will be possible to use much smaller plants to obtain the same effectiveness as in larger prior art plants. On the other it also means that it will be possible to achieve much higher effectiveness and thus a better purification rate with a plant at the same size as the prior plants.

DESCRIPTION OF THE DRAWING

The drawing illustrates how a bio filter 1 for use by the method according to the invention may be constructed. The bio filter comprises a biosorp 2 in which the filter substance 3 is contained. The filter substance 3 rests on a grid 4 so that a hollow space 5 is formed underneath the filter substance.

The filter substance comprises approx. 50% by volume of inorganic material, which is preferably porous and granulated in order to obtain a carrier material with a high water absorption capacity and a large surface relative to the volume. Said inorganic material may optionally be sterilized.

In addition the filter substance may secondarily comprise organic material intended for nourishment of biological organisms. Said organic material will preferably be sterilized in order to kill any undesirable microorganisms present in said material.

Finally, the filter substance comprises a biologically active medium consisting of one or more of the aforementioned bacteria or fungi. However, the biologically active medium may also consist in macroorganisms in the shape of plants which are able to absorb some of the flue gas components to be decomposed, possibly in symbiosis with fungi or bacteria. Thus, it will be possible to make the biologically active medium consist of a combination of micro- and macroorganisms.

The bio filter furthermore comprises inlet means 6 for the flue gas in the bottom 7 of the biosorp 2, and outlet means 8 for the deodorized flue gas in the top 9 of the biosorp. The bio filter also comprises an inlet 10 from a so-called "air-fog" equipment for moistening the filter substance with atomized liquid, preferably water, which may have substrates or other elements added that are suitable as nourishment for the biological organisms. To the atomized liquid there may be added acid or base components in order to adjust the pH value inside the biosorp. The lower part of the filter substance consists exclusively of Leca nuts or a similar material. In this manner any excessive acid or base residues are adsorbed before the atomized liquid is filled into the biosorp.

Claims

1. A method for deodorization of flue gas through decomposition of gaseous components, in which the flue gas is conducted through a filter comprising an inactive carrier material which preferably consists of a combination of inorganic and organic material, said filter also comprising a biologically active medium, preferably microorganisms, characterized in that at least the organic part of the carrier material is sterilized, that biological organisms with specific characteristics are selected for biologically active medium, and that the biologically active medium is added to the carrier material.

2. A method according to claim 1, characterized in that sterilization of the carrier material is effected through pasteurization.

3. A method according to claims 1 and 2, characterized in that aerobic microorganisms are used as biologically active medium.

4. A method according to any of the preceding claims, characterized in that only the inorganic material in the carrier material is sterilized before the biologically active medium is added.

5. A method according to any of the preceding claims, characterized in that water is added to the filter in the shape of atomized water, which is optionally mixed with an acid or base component.

6. A method according to any of the preceding claims, characterized in that sterilization of the carrier material is effected through irradiation.

7. A method according to any of the preceding claims, characterized in that the biologically active medium comsits of a mixture of one or more types of microorganisms such as various types of bacteria and/or fungi.

8. A method according to any of the preceding claims, characterized in that at least vegetable compost is added to the filter.

9. A bio filter for deodorization of flue gas through decomposition of gaseous components, in which the flue gas is conducted through a filter which comprises an inactive carrier material which preferably consists of a combination of inorganic and organic material, said filter also comprising a biologically active medium, preferably microorganisms, characterized in that at least the organic part of the carrier material is sterilized, and that biological organisms with specific characteristics, selected for biologically active medium, are added to the carrier material.

10. Use of selected biological organisms with specific characteristics in a bio filter.