Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention relates to a process of converting in a reaction
vessel containing a movable bed organic materials in a microbiological way under
the formation of gas.
When using microorganisms for the manufacture of different types of
products it is essential that the contents of active microorganisms in the
reaction vessel is kep-t as high as possible.
In accordance with the prior art the content of organisms is control-
led by means of static sedimentation, floatation, centrifugation or filtration,
the microorganisms being separated from the discharged liquid phase and returned
to the reaction zone as biosludge. Limiting factors in this known technique
are, for example, the sedimentation properties or the centrifugation or filtra-
tion performance of the biosludge formed. Static sedimentation, which is the
technique most frequently used, involves the limitation -that the biosludge
cannot take up more than about 50% of the volume in a sedimented state in order
that static sedimentation shall operate in a satisfactory manner. This volume
corresponds to a concentration of biomass of 5 to 10 kgs DS (dry substance) per
m of reaction vessel.
In another type of known technique there is used a reaction vessel
containing a packing, the biomass being fixed to a solid surface structure, for
~ 20 example a bed of stone materials or plastics. A limiting factor in this case
; is the fact that no more than about 100 to 200 m surface per m of reaction
vessel can be obtained if blocking of -the cavities is to be prevented. Also
this specific surface corresponds to a concentration of biomass of 5 to 10 kgs
DS/m of reaction vessel. For such technique see for instance Swedish Patent
Specification Serial No. 7605005-3.
In a third variant of the known technique there is used a suspensible
bed in a reaction vessel, the bed being fluidized by means of an upward flow
of gases or liquid. (See for instance Swiss Patent Specification Serial No.
. ~ ~
~L6~66
612.655.) However, this system provides for a pronounced practical limi-tation,
in that the distribution oE the fluidization flow must be exactly uniform across
all of the lower part of the reaction zone cross section, which is very diffi-
cult to obtain in a large reaction vessel. Moreover, such fluid bed system calls
for careful selection of bed material with regard to grain size and distribution,
as is well known in the ar-t.
Thus, the object of the present invention is to provide a process and
an apparatus whereby organic materials in a microbiological way can be converted
under the generation of gas while avoiding the disadvantages associated with for
example the above-described conventional techniques.
To this end there is provided a process for subjecting organic mate-
rial to a microbiological conversion which involves generation of a gas, wherein
the conversion is carried out in a vessel containing a microorganism which is
grown on a movable bed of inorganic granular material and is present and freely
movable as microflocks in a continuous aqueous phase, substrate for the micro-
organism is supplied to the bed and mechanically stirred, gas generated by the
microorganism being used for expanding the bed, and the microflocks are extern-
ally separated from discharged liquid and returned to the reaction vessel.
The stirrer is suitably arranged so as to impart to the bed material
a downward movement, preferably all the way down to the bottom of the reaction
vessel, and it is preferred to in-troduce the subs-trate into the vessel within
the part of the bed subject to such downward movement. This results in effi-
cient fluidization of the bed due to the generation of gases therein. Thus,
- by the combined pneumatic and hydraulic mixing effects an optimized overall
process results.
In a preferred embodiment of the process of the invention there is
used a bed based on an organic granular material having a grain size lying
within the range about 0.05 to 5 mm. This material constituting the bed can be
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~i~lli2~3~6
sand, calcium carbonate, calcium hydroxide or dolomite or the like.
The invention also relates to an apparatus wherein this process can
be performed, ancl this apparatus includes a reaction vessel, a stirrer arranged
therein, means for supplying ]iquid containing substrate and means for discharg-
ing liquid and for recirculation of free active material. To obtain the object
of the invention the apparatus includes a movable bed of inorganic granular
material arranged in the reaction vessel, said bed being intended for supporting
growing microorganisms for conversion of the organic material.
The movable bed is preferably made of materials described above in
connection with the process.
The stirrer used is preferably constituted by a radial or axial tur-
bine or propeller placed at the lower end of the reaction vessel and suitably
positioned centrally therein.
At rest the movable bed suitably occupies 20 to 80% of the volume of
the reaction vessel, preferably about 40 to 60%.
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The reaction vessel of the apparatus of the invent-
ion is suitably provided with interior vertical ba~fles
over 20 - 100 % of the height of the vessel, and these
baffles can be present in a number of from 1 - 10.
The invention is generally applicable on a number
of different types of microbiological processes depending
on type of substrate and type of microorganism. As examp-
les there may be mentioned microorganisms of a monocult-
ure, such as Saccaromyces Services, to form ethanol from
- 10 carbohydrate substrates, or of a multiculture, such as
in the conversion of complex organic substrates to
methane gas and carbon dioxide. Another application of
the invention is in denitrification of nitrate-rich
aqueous substrates.
EXA~!IPLE
The invention will now be further described by a
non-limiting example in connection with the appended
drawing, wherein
Fig. 1 shows diagrammatically a vertical cross
section through an embodiment of the apparatus according
to the invention, and -
Fig. 2 shows diagrammatically the circulatory~eatures in the embodiment according to Fig. 1.
The embodiment of the apparatus according to this
invention shown in Fig. 1 of the drawings includes a
circular-cylindrical reaction vessel 1 having a planar
bottom and a curved top, the vessel being provided with
interior vertical baffles 2 which may be present in a
number of 1 - lO. It is pre~erred to use a l~lul.llity of
baffles evenly distributed around the inner wall of the
vessel. The reaction vessel is furthermore provided witll
a central stirrer 3 driven by an externally placed motor
through a gas-tight throughlet ~ at the upper end of
vessel 1.
Reaction vessel 1 contains a movable bed 5 of an
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inorganic granular material which at rest in the embodi-
ment shown occupies about half of the volume of the re-
action vessel. The reaction vessel furthermore contains
water as a continuous phase up to the level shown in
Fig. 1.
The supply of substrate, i.e. material to be treat-
ed, takes place through an inlet conduit 6 opening
directly under the stirrer 3. Treated liquid is removed
from the reaction vessel through an outlet conduit 7 and
- 10 is transferred to a separation device 8 wllereby separat-
ion bio sludge is separated and returned to the reaction
vessel to a place immediately below stirrer 3.
The fuction of the apparatus described above is
briefly as follows.
On the suspended bed material of inorganic material
which may be sand, calcium carbonate, calcium hydroxide
or dolomite having a grain size within the range 0.05 to
5 mm, present in the reaction vessel, a flora of anaero-
bic microorganisms will grow in a thin layer. Thereby,
the microorganisms will convert supplied organic com-
pounds to different types o~ products in dependence on
the type of substrate and the type of microorganisms.
For the purpose of transferring the substrate to
the microorganisms bound to the inorganic grains of the
bed material the substrate is transferred through inlet
conduit 6 to a place immediately below the stirrer 3
which is centrally positioned in the bed (Fig. l).
I~hen under operation stirrer 3 is brought into
rotation a flow of liquiLl and bed grains wil] be pumped
around in the rL~action vessel, t]lC sul-s~r;lte colnillg into
intilllate contact with the remai~ g contellts 0r the re-
;l c t i o ll v ~ c~ o~ ' ;l t C (I ~ .'; t i l' l' ~ s ~ c~ l~ i. z o l~ t -
al and downwaldly directed, in view of whicll a strong
flow will be obtained along the bottom of the reaction
vessel and upwarclly along tl~e walls of thL reaction
vessel. This flow means that the movable becl will extend,
6 ~L~16~66
the expansion being further increased by the generation
of a gas whic}l takes place when the substrate comes into
contact with the microorganisms supported by the bed. In
this manner a very even and homogeneous distribution of
the substrate in the bed will be obtained w}lereby effect-
ive utilization of the microorganisms will take place.
In Fig. 2 the flows provided by the mechanical mix-
ing by stirrer 3 and by the gases generated in the micro-
biological reaction are illustrated. In view of the
direction of the Elow created by the stirrer tllere is
obtained eEEicicnt clistribution of the substratc hori-
zontally at ~he bottom of thc reaction vessel. In view oL
the gas generation and the entrainment oE liquid phasc
wit]~ thc gas buhblcs tllcre is obtaincd a good mixillg in
vertical direction, as is clear from ~ig. 2.
The gas generation in the apparatus described is of
the order of 1 - 100 m3 of gas per m3 reaction vessel per
day, and the generated gases vary in dependence of type
of substrate and mic~oorganism and may be carbon dioxide,
methane gas or a mixture thereof, or nitrogen. By modi:Ey-
ing the height of the baffles and the rotation of the
mechanical stirrer the.movable bed can be brought to ex-
pand to the desired level. By discharging a liquid phase
from the surface at the upper end o:E the reaction vessel
~here the movable bed does not reach by the expansion the
microorganisms may to a great extent be maintained in the
system. The quantity of microorganisms maintained bound to
the bed material may vary from 1 - 50 g of DS/l volume of
reaction vessel.
~o r<~r-t Or tllc ]~I;crOOrg~ isllls ~lc rO.~ ll tllC Iorlll O~r
microflocks in thc liquid pllase. This part will not be
sep~r~te(l in the rcactio}l vcsse~ but is c~rlie~l along witl
the discharged liquid Elow. By mea}ls of separation device
8 they can be separated from the liquid and returned to
the reaction vessel. In this way the microor~anisms may be
maintained suspended in a quantity corresponding to
5 - 10 g TS/l (total suspen(led solids). In toto one can
obtain a total content of microorganisms bound to the
movable bed and suspended of about 60 ~ DS/l, which is
6 - 12 times of wllat can be obtaincd with.collventional
technique.
The invention is not delimited to the embodiment
described above. Thus, the ra.tio between height and dia-
meter of the reaction vessel may vary from 5:1 to 1:5.
Moreover, the details of the construction. described can
be varied and modified in a manner obvious to those
skilled in the art.
