Portable reactor for carrying out gas-evolving biotechnological processes or gas consuming processes while maintaining a packed fixed-bed arrangement

The coalescence and release of bubbles from packing that supports the growth of microorganisms is promoted by mechanical action on the packed bed arrangement, in particular by continuous or intermittent vibrations, rotations, or by rocking motions. With particular advantage, a reactor vessel which is typically tubular is filled with packing upon which microbial growth is sustained, preferably leaving a free space of 10% to 35%, in particular 15% to 20%. The reactor vessel has an axis that is substantially horizontal but preferably inclined by at least about 3.degree., and is set continuously or intermittently, for example, by an axle drive or by means of friction wheel drive, into rotational or rocking motions about that axis. The gas can be discharged, for example, via valves and a cam mechanism. Alternatively, a vent pipe, taken through the hollow shaft on the discharge side and upwards, can be provided behind a screen plate. Pipes that are parallel to the axis and that have openings, which are protected by finlike rims with slots, feed liquid or gas to the biomass-containing system in the reaction vessel. In another embodiment, a vertical reactor is equipped with packing provided on vibrating plates which are set into vibration, preferably intermittently. For denitrification, a nitrate-nitrite degradation stage can be provided upstream of the reactor vessel.

BACKGROUND OF THE INVENTION 
The present invention relates to a procedure for carrying out 
biotechnological processes that involve the microbial evolution of gas and 
that take place in reactors containing granular carriers or particles 
which support growth of microorganisms. The present invention further 
relates to equipment for carrying out the procedure in a reactor vessel 
provided with liquid feed and discharge and with means for the taking off 
and, if appropriate, the feeding in of gas. 
Numerous biotechnological processes take place with the evolution of gas. 
Methane (CH.sub.4) is produced, for instance, in anaerobic degradation 
processes, and carbon dioxide (CO.sub.2) is formed in aerobic fermentation 
processes. Another example of bioreactions which proceed with gas 
evolution is bacterial denitrification, wherein nitrate is degraded in the 
presence of suitable bacteria and organic substances that act as indirect 
reducing agents under low-oxygen or oxygen-free reaction conditions. 
For carrying out these react columnar fixed-bed reactors are frequently 
used that permanently contain a particulate carrier ("packing") on which 
growth of bacteria is supported and on which the bacterial reaction takes 
place. But problems arise when these reactors operate, particularly with 
increasing reactor size, due to the evolution of gas associated with the 
bioreaction. The gas formed is released only with delay from the where the 
growth is sustained; as the reaction proceeds, the delayed release of gas 
can lead to partial blocking of the active surface occupied by bacteria, 
and to an increase in the filtration resistance, so that the throughput in 
the reactor is neither at its optimum level nor at constant rate. 
These phenomena have been investigated in more detail for denitrification 
in fixed-bed reactors where the organic substrate is metered into the 
nitrate-containing water flowing in or is made available by diffusion out 
of plastic packing. Nitrogen gas is evolved in the bacterial reaction, and 
problems arise with the release of the gas from the packed bed occupied by 
bacteria. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a procedure 
for enhancing the release of gas and, thereby, improving the gas-evolving 
microbial reaction(s), in a biological reactor. 
It is also an object of the present invention to provide a biological 
reactor wherein the release of gas formed in the course of a bioreaction 
is not delayed, avoiding the blocking problems encountered in conventional 
reactors. 
In accomplishing the foregoing objects, there has been provided, in 
accordance with one aspect of the present invention, a biological reactor 
comprising (i) a reactor vessel with a first end, a second end and a major 
horizontal axis that may be inclined at least 3.degree. to the horizontal, 
such that the first end is lower than the second end, the reactor having a 
liquid feed port at the first end and a liquid discharge port at the 
second end; (ii) a particle bed provided in the vessel for supporting 
microbial growth; (iii) means for introducing liquid into the vessel 
through the liquid feed port; (iv) means for removing liquid from the 
vessel through the liquid discharge port; (v) means for taking off gas 
from the vessel at the second end; and (vi) means for setting the vessel 
in motion relative to the major axis. In a preferred embodiment, the bed 
comprises packing which fills the vessel such that a free space above the 
packing is created, the free space corresponding to between about 10 and 
35% of the total volume of the vessel. 
In accordance with another aspect of the present invention, a biological 
reactor has been provided that comprises (i) a reactor vessel; (ii) a 
plurality of plates fixed in a predetermined arrangement within the 
vessel; (iii) granular material supported on the plates, which material 
can provide a carrier for microbial growth; and (iv) drive means for 
setting the plates into reciprocating motion. 
There has also been provided, in accordance with still another aspect of 
the present invention, a process comprising the evolution of gas via the 
action of microorganisms contained in or on a solid support in a 
biological reactor vessel, wherein the coalescence and release of the 
bioreaction gas from the support is promoted by setting the support in 
motion within the reactor vessel. In a preferred embodiment, the motion 
involved is cyclic, with a cycle time ranging e.g. between about 5 and 25 
minutes In another preferred embodiment, the motion comprise intermittent 
or continuous vibration of the support, preferably in a reciprocating 
motion with an amplitude of between 5 and 15 mm. 
Other objects, features and advantages of the present invention will become 
apparent from the following detailed description. It should be understood, 
however, that the detailed description and the specific examples, while 
indicating preferred embodiments of the invention, are given by way of 
illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the present invention, the coalescence and release of bioreaction gases 
from a solid/particulate carrier which supports the microbes is promoted 
by mechanical action on the substrate within the biological reactor. 
Typically, the substrate comprises a packed-bed arrangement of grains, 
plastic spheres or other material upon or within which microorganisms can 
be immobilized. The bed preferably fills most of the reactor volume, 
leaving a free space as described in greater detail below. Suitable 
mechanical action on the substrate in the reactor vessel includes rotation 
or rocking of the bed; continuous or intermitten vibration of the 
substrate can also be used, especially in reactors equipped with a series 
of superposed vibrating plates that provide a base for the packing which 
carries the bacteria. In any event, the effected displacement of the bed 
should not be so great as to create a shearing action sufficient to remove 
biomass that is affixed to the substrate material. 
A particularly preferred arrangement with the present invention comprises a 
generally horizontal packed bed with a longitudinal axis inclined by at 
least 3.degree., in particular about 5.degree. to 10.degree., to the 
horizontal, which bed is provided in a cylindrical vessel that has 
perforations for gas release in its upper region; that is not completely 
filled with packing but has a certain amount of free space above the 
packing, particularly 10% to 35%, especially 15% to 20%, of the total 
volume of the vessel; and that is set into a rotary or rocking motion 
about its longitudinal axis. The rotation or rocking motion (clockwise and 
anticlockwise by an angle, for example, of 350.degree., analogously to the 
motion of washing machine drums) can take place continuously or 
intermittently, that is, with appropriate pauses. Cycle times of about 5 
to 25 minutes, and speeds of rotation between about 0.2 to 10 rpm, are 
suitable, as is an axle or friction wheel drive which acts on the outer 
shell of the reactor vessel. 
A biological reactor within the present invention can also include suitable 
gas-discharge means, preferably in the form of at least one gas discharge 
opening, situated at the higher end of the reactor vessel, with a valve 
element (particularly a conical valve with a closing spring) for closing 
the opening, in combination with devices, such as a cam mechanism, for 
clearing the openings when they pass the highest points. 
A reactor of the present invention preferably has axial conduits or hollow 
shafts for liquid feed and discharge, with an outlet sufficiently raised 
beyond the reactor that the liquid level in the reactor vessel defines the 
gas-collection space. For gas discharge, a gas discharge pipe can be used 
that passes through the hollow shaft and that, in the reactor vessel, 
leads upwards behind a separating, end-face screen plate. Otherwise the 
liquid outlet could lead sufficiently far up into the reactor that gas 
could escape together with the liquid. 
In such a reactor, the packing of the fixed bed, which packing supports the 
microorganisms, while leaving a free space in the reactor, is moved by 
slow rotation in such a way that gas bubbles do not adhere for any length 
of time and the gas collects at the highest point in the reactor. The gas 
can then be discharged from that highest point, continuously or 
intermittently. 
Conduits which are parallel to the axis of the reactor and which have 
openings, slots or nozzles are preferably arranged along the inner wall of 
the reactor and are especially protected by fin-like projections equipped 
with slots. The conduits can also be arranged and protected behind a 
screen jacket in front of the packed bed. Through such conduits, the 
liquid to be treated can be fed in and distributed across the surface of 
the screen jacket. In a preferred embodiment, a rotary tube reactor within 
the present invention which is provided with protected pipes is used for 
carrying out gas-consuming biotechnological processes that consume oxygen, 
such as, for example, for conventional production of acetic acid from 
ethanol, for the production of amino acids using Corynebacterium 
glutamicum, and for aerobic effluent treatment. Surprisingly, it has been 
found that, by feeding oxygen in this way via conduits along the 
cylindrical wall, a particularly intensive introduction of oxygen can be 
achieved in a reactor of the present invention, an effect that is not 
achievable with other, known arrangements for efficiently stirring in or 
admixing oxygen. 
The liquid, delivered by means of a pump or via a suitable level 
difference, enters via the hollow axis at the lower end of the reactor, 
preferably through a screen, into the fixed bed in which the microbial 
conversion of material takes place. By virtue of the displacement 
(rotation or rocking) of the reactor vessel, which is preferably 
cylindrical, the bed within the vessel is in continuous or intermittent 
motion. This motion can be assisted, without slip, by longitudinal fins 
which confer increased stiffness to the inner wall of the reactor of the 
present invention. 
After a suitable residence time, which is adjusted to the desired degree of 
conversion or purification performance, the treated liquid leaves the 
reactor through the second hollow shaft via a screen. In a preferred 
embodiment, the two hollow shafts are rigid and joined to the reactor 
vessel by water-proof bearings, and are extended by the liquid feed and 
discharge lines. Of these lines, especially the discharge line reaches up 
to a height sufficient for setting the liquid level in the reactor vessel, 
while leaving a residual free volume in which the gas formed can collect. 
According to another preferred embodiment of the present invention, the 
reactor vessel is an inclined rotary tube that contains packing and is 
provided with a circle of gas discharge slots or openings at the higher 
end of the tube. The slots or openings preferably extend over about 5% to 
10% of the bed length and follow the generatrices of the rotary tube. The 
rotary tube of this embodiment is mounted at the end face in a somewhat 
larger, fixed cylindrical shell which has a gas discharge branch at the 
upper end and, on the same end face, a liquid outlet located below the gas 
outlet branch. In this way, the rotary tube containing the packed bed 
"floats" in a liquid shell, whereby the energy consumption for the 
rotation is reduced. 
With reference to FIG. 1, a tubular vessel 1 is largely filled by microbial 
growth-supporting packing 2, leaving a residual free volume 3 where there 
collects gas formed during the biological process effected by the 
microorganisms contained in and on the packing. The gas thus evolved can 
escape via a pipe 4 behind a screen 5 or alternatively via the liquid 
discharge pipe extending far up into the reactor as may be seen from the 
outline FIG. 1a. the screen must therefore permit the passage of liquid 
while retaining the carrier material (solid grains, spheres, etc.) of the 
bed. Screens produced from plates with apertures on the order of 5 mm have 
proved suitable in this regard; perforated sheets of sufficient mechanical 
strength can also be used. 
Line 6 indicates the liquid level in the inclined reactor, which level 
corresponds to outflow level 7, established in the upward-leading extended 
line 8 of conduit 9 on the outflow side. On the feed side, a conduit 10 is 
similarly connected rigidly to the reactor tube and, via a rotational 
joint (not shown), to a feed line. 
Optional screens 5 and 11, which in addition optionally may fulfill a 
deflecting function with regard to the entering liquid, close the tube 
space off from the hollow shafts, which are mounted in bearing blocks 12, 
13. A support bearing with drum drive is indicated by 14. 
The apparatus shown in FIG. 2 is similar to that of FIG. 1, but is provided 
with a circle of gated openings 15 for gas discharge. For each opening, a 
valve cone 16 is pressed against the valve seat (opening 15) by means of a 
valve spring, not shown. When passing its highest point, the valve cone 16 
is lifted from seat 15 by a cam mechanism 17, i.e., the stem of the valve 
cone is moved downward, allowing gas to escape via opening 15. In FIG. 2, 
moreover, screen 5 extends over the inlet to conduit 9 only, rather than 
across the entire cross section of the reaction vessel, as shown FIG. 1. 
The rotatable reactor vessel depicted in FIG. 1 or FIG. 2 can be provided 
on its inner wall with longitudinal fins which ensure that a quantity of 
material is taken along during the rotary motion. It is preferable that 
these fins be relatively flat, and that their extent not exceed 10% of the 
reactor radius. 
According to a preferred embodiment of the present invention which can be 
used in major installations, pipes 18 are provided (see FIG. 3) that have 
openings, distributed along their length, for feeding liquid or, when 
reactions with gas absorption are carried out, for feeding gas, 
particularly air. The pipes 18 are situated along the inner wall of the 
reactor vessel, and are screened from the packed bed, for instance, by a 
support screen 19 parallel to the reactor wall or by projections 20 that 
define slotted housing for each pipe, as indicated in FIG. 3. 
FIG. 4 depicts an embodiment of the present invention, suitable especially 
for smaller units, wherein reactor vessel 21 is combined with an upstream 
vertical column reactor 22. The latter reactor is continuously fed at 23 
with nitrate-containing water, by means of a feed pump 24, via a control 
valve 25 for precise regulation of the water flow rate. Between sieve 
trays 26, the column reactor 22 contains packing 27, for example, inert 
plastic granules such as Nitrex.RTM. filter material, or another suitable 
packing which, due to its porous or rough surface structure, provides 
favorable settlement zones for the denitrification bacteria. At the column 
reactor 22, the first degradation stage is initiated, in which the nitrate 
is largely reduced bacterially to nitrite or the water is freed of oxygen. 
The flow rate of the water is controlled such that a high nitrite content 
is measurable in the outflow 28 from the column reactor 22, and no 
formation of gas bubbles is observable in the upper third of the reactor. 
Via the connecting pipe 29, the water is passed on into the rotatable 
reactor 21. Through a hollow shaft 30 with a rotational joint and bearing, 
the water passes into the rotatable inner reactor vessel 31, about 75% of 
which is filled with granules 32, which provide a support for growth of 
denitrification bacteria. The second denitrification step takes place 
anaerobically, nitrogen gas (N.sub.2) and/or nitrous oxide (N.sub.2 O) 
being formed. Thus, mainly gaseous nitrogen is released as the final stage 
of the denitrification (nitrate-nitrite respiration) process, which gas 
escapes from the gas release slots 33, provided in the upper region of the 
inner vessel 31, into the air, which normally contains about 80% by volume 
of nitrogen. 
In order to avoid the adhesion of gas bubbles to the surface of the packing 
32, which adhesion inhibits the activity of the bacteria, the inner vessel 
31 is rotated continuously, or intermittently (at up to 15 minute 
intervals with about 3 minutes rotation), by means of the motor 34 at 0.2 
to 3 rpm. It is not absolutely necessary to move the rotatable reactor 
vessel continuously about it longitudinal axis. If maximum throughput is 
not important, the inner vessel 31 is set in rotation, for example, every 
15 minutes. This step is at the same time favored by the preferably 
inclined mounting of the reactor at an angle of at least 3.degree., 
especially 5.degree. to 15.degree.. The nitrogen gas can finally leave the 
apparatus via the gas discharge line 35. The water, low in nitrate, can 
then likewise be taken off from the apparatus via the water outflow 36 in 
the shell 37. 
In the operation of a reactor within the present invention, the continuous 
gas release from the pore spaces of the bed, or from the apparatus via the 
gas discharge openings, allows undisturbed bacterial growth on the matrix 
surface. Moreover, undisturbed water flow is ensured on the surfaces of 
the packing, where the degradation activity of the denitrification 
bacteria primarily takes place. Channeling within the reactor vessel, 
which would impede contact between water and the bacteria on the matrix 
surface, does not arise here. A particular technological advantage is 
realized with the substantial spatial separation of the nitrate 
degradation into two stages, with optimization of the residence times in 
the reactors 21 and 22 so that, preferentially, only the nitrate 
degradation to nitrite takes place in the column reactor 22, without 
bubble formation or reduction of the oxygen content to zero, whereas the 
nitrite is then degraded to in the rotatable reactor vessel 21. 
In the vibrating-plate column reactor shown in FIG. 5, nitrate-containing 
water is delivered into the reactor space, by means of a feed pump or a 
hydrostatic pressure difference under valve control, via the inlet 38. The 
reactor is fitted with a number of reactor chambers 39 (eight are shown) 
that avoids undue loading of the surface of individual vibrating plate, 
which are arranged one above the other and which function as a fixed bed. 
The vibrating plates are mounted to the central axis 41 by means of hollow 
bushes 40; the central axis is, in turn, guided in a bearing block 42. A 
solenoid 43 and a compression spring 44 enable the reactor chambers to be 
set into vertical vibrations via the central axis. 
In operating a reactor according to the present invention, the chambers of 
the reactor can be charged with suitable packing 45 which, due to its 
surface structure, provides an optimum settling zone for the 
denitrification bacteria. At the bottom of the chamber, in the section 46, 
openings extending radially from the center outward are provided, which 
allow the water that is to be denitrified to flow unhindered into the 
reactor chamber. 
The gas bubbles, formed in the course of the denitrification process on the 
active packing/bacteria contact surface, can escape along the gas 
discharge channel 48 via the gas outlet 47 from the reaction spaces. To 
avoid any possible adhesion of the gas bubbles to the packing, the reactor 
chambers are set into vibrations via the central axis, whereby the gas 
bubbles are led off without any problems along the obliquely arranged 
chamber covers 49. The gas bubbles rising in this way from the individual 
chamber spaces can then leave the reactor space via the opening 50. The 
treated water is taken off via the outflow 51. 
The bacterial denitrification in a movable, inclined packed bed which 
supports a growth of bacteria is also suitable for the regeneration of 
water, particularly seawater from aquaria or from intensive farming of 
aquatic animals.