Note: Descriptions are shown in the official language in which they were submitted.
Description
The invention relates to a process for the
biological purification of sewage, with which sewage,
containing dissolved pollutants, and air are introduced
together under pressure, via at least one nozzle into a
reactor designed as a tank and are passed on in the
reactor as a two-substance mixture, as well as to an
apparatus for carrying out the process.
In the biological purification of sewage, pollutants
dissolved in the same are degraded by bacteria or micro
organisms. In order to increase their effectiveness or
to accelerate their multiplication, oxygen is fed to the
sewage . This can take place by supplying air or else pure
oxygen. Often, nutrients are also fed to the sewage. In
the case of known sewage treatment plants, this takes
place in so-called activated sludge tanks. The sludge
biologically produced thereby is separated from the
purified waste water in a downstream sedimentation tank.
The tanks used for this process have a large space
requirement. In spite of this, the biological degradation
rate is not satisfactory and the open design often leads
to a very disturbing odour nuisance for the surroundings .
Therefore, processes have been developed in which,
instead of the activated sludge tank, high-performance
reactors with significantly reduced space requirement and
increased biological degradation rate are used. Such a
process, described at the beginning, emerges from the
German journal "Chew. Ind. XXXVII/January 1985", pages 43
to 46. In this process, a compact reactor is used which
consists of a cylindrical tank, in which a cylindrical
insert tube, open at both ends, is arranged. A mixture
consisting of sewage and air is introduced into the
insert tube via a two-substance nozzle. The air fed via
the two-substance nozzle is dispersed into tiny bubbles
on account of great shearing forces in the region of the
two-substance nozzle, so that a large exchange surface is
produced and the charge of oxygen is favourably
influenced. With this known process, the biological
degradation rate can be increased considerably in com-
parison with conventional processes with activated sludge
2UU~~28
- 2 -
tanks. However, since the high substance exchange takes
place essentially in the region of the two-substance
nozzle and the turbulence in the insert tube is damped
relatively quickly by the sewage, this process also is
unsatisfactory in many cases.
The invention is based on the object of specifying
a process for the purification of sewage, with which the
substance exchange upon introduction of oxygen into the
sewage is significantly increased.
According to the invention, this object is achieved
by a process of the type described at the beginning by
- the sewage and the air being fed to the reactor via
at least two mutually separate nozzles,
- the streams of, the two-substance mixture emanating
from the nozzles being conducted in the reactor such
that they make impact with each other in the said
reactor in an impact zone and
- by the sewage being passed after de composition from
the reactor into a settling tank.
Due to the shearing field of the sewage in the
direct region behind the openings of the nozzles, on
leaving the nozzles, the air is divided into very small
bubbles. At the same time, the sewage jets emanating from
the nozzles suck in sewage or an air/sewage mixture from
the inside of the reactor. As~'a result, homogeneous two-
substance streams form downstream of the nozzles. The
two-substance streams are deflected, for example by
elbows, such that they collide within the reactor in the
impact zone, in which the air bubbles are divided
further. The kinetic energy of the flowing air/sewage
mixture is thereby dissipated. As a result, a high
turbulence and a large substance exchange surface in the
impact zone and in the other parts of the reactor above
and below the impact zone are produced. With the same
?5 energy charge as in tha case of the known process, the
substance exchange thus achieved is significantly higher.
Thus, with this process, in a simple way significantly
more oxygen is introduced into the sewage than was
previously possible. The process therefore makes possible
2a'~~ 128
- 3 -
a considerably increased biological degradation rate.
Advantageous developments of the invention, which
also concern in particular an apparatus for carrying out
the process, emerge from the subclaims.
Process and apparatus according to the invention are
explained in exemplary embodiments with reference to the
drawings in which:
Fig. 1 shows in diagrammatic representation an
apparatus for carrying out the process according to the
invention,
Figs. 2 and 3 show two apparatuses added to in
comparison with Fig. 1 and with different arrangement of
the nozzles,
Figs. 4 and 5 show two apparatuses modified in
comparison with Figs. 2 and 3,
Figs. 6 and 7 show two further developments of the
apparatus.
In a reactor 1, which is preferably designed as an
elongated cylinder, air LT and sewage AW, containing
dissolved pollutants, are to be mixed with each other. In
this process, as large a quantity as possible of oxygen
contained in the air LT is to be introduced into the
sewage AW. The reactor 1 opens out with its upper end, in
working position, into a compartment 2. Two nozzles 3 and
4, to which the sewage AW on the one hand and the air LT
on the other hand are fed, are arranged in the compart-
ment 2. The nozzles 3 and 4 are in this case arranged
such that the jets emanating from them pass into conduit
tubes 5 and 6, which for their part open out into the
reactor 1 at two diametrically opposite points.
The conduit tubes 5 and 6 may - as is evident from
the drawings - run substantially parallel to the reactor
1 and, after passing around an elbow, of preferably 90°,
are connected to the reactor 1. The two-substance
mixtures of sewage AW and air LT, conducted separately in
the conduit tubes 5 and 6, meet each other in the reactor
1 in an impact zone PZ outlined by broken lines. The
sewage can rise upwards according to the arrow 7, from
where it passes after decomposition via the compartment
200128
- 4 -
2 into a settling tank 8. The excess air (remaining
oxygen and atmospheric nitrogen) can escape as exhaust
gas according to the broken-line arrow 9 from the
compartment 2 via a filter 10. Exhaust gas escaping from
the settling tank 8 can also be passed via the filter 10.
In the compartment 2 there is a weir,ll fitted, by which
the decomposition necessary for the separate outflow or
discharge of sewage and exhaust gas is achieved. The
height of the weir 11 is variable.
Two nozzles 3 and 4 are in each case represented in
the drawings. However, more than two nozzles, mutually
separate in each case, may also be used. They are prefer-
ably made from two concentric tubes as two-substance
nozzles . As far as geometry and dimensions are concerned,
the nozzles 3 and 4 are preferably identically designed,
so that the reactor 1 is fed two or more uniform streams
of the two-substance mixture.
The arrangement of the conduit tubes 5 and 6 with a
substantially parallel run to the reactor 1 is not
obligatory. They could also run obliquely to the reactor
1': The conduit tubes 5 and 6 also do not have to open out
into the reactor 1 such that the emanating streams meet
each other frontally in the impact zone PZ. Rather, the
streams could also make impact with each other at an
angle other than 180°. In a preferred embodiment, however,
the streams make impact with each other frontally, that
is to say at an angle of 180°.
If more than two nozzles 3 and 4 are used, the
mouths of the corresponding conduit tubes 5 and 6 are
expediently arranged evenly offset on the circumference
of the reactor 1, thus, in the case of three nozzles,
there is for example an angle of 120° in each case between
the mouths. This also applies if the nozzles 3 and 4 open
out directly into the reactor 1 without conduit tubes 5
and 6.
The process and apparatus according to Fig. 1
operate for example as follows:
The reactor 1 is fed sewage AW and air LT separately
via the nozzles 3 and 4. For this purpose, the sewage AW,
~~~~j2a
- 5 -
laden with dissolved pollutants and microorganisms, is
delivered by means of a pump 12. On account of the
shearing field of the sewage AW at the outlet openings of
the nozzles 3 and 4 the air LT is dispersed. The gas
bubbles produced are entrained by the sewage AW and the
two-substance mixture thus produced makes impact with
each other in two streams in the impact zone PZ. As a
result, the gas bubbles are further dispersed, so that an
increased substance exchange takes place. Starting from
the impact zone PZ, two two-substance flows lead in
opposite directions within the reactor 1, according to
the arrows 7 and 13. It is achieved as a result that a
large part of the gas bubbles in the impact zone PZ
remains in suspension and is constantly dispersed
further. This leads to a further increase in the sub-
stance exchange. For this reason, in a preferred embodi-
ment, the impact zone PZ is created in the reactor 1 as
centrally as possible, that is to say approximately in
the middle.
~ For further improvement of the substance exchange,
the two-substance mixture within the reactor 1 may also
be conducted in an internal circuit, which is intended to
be indicated by the arrows 14. For this purpose, after
decomposition, the sewage may also be removed from the
reactor 1 in the direction of the arrow 13 and fed by
means of a pump 15 back to the nozzles 3 and 4, to be
precise together with the sewage AW delivered by the pump
12.
The sewage emanating from the reactor 1 upwards in
the direction of the arrow 7 passes into the compartment
2. From there, after decomposition, it is passed through
the weir 11 in the direction of the arrow 16 into the
settling tank 6, in which the bio sludge containing
microorganisms settles and separates from the purified
waste water. The waste water can be released into the
recipient in the direction of the arrow 17. The bio-
sludge can be removed as excess sludge in the direction
of the arrow 18 and fed to further processing.
In the case of the embodiments of the apparatus
2fl0~ ~ 28
- 6 -
according to Figs. 1 and 2, the nozzles 3 and 4 are
arranged in the upper region of the reactor 1. According
to Fig. 3, they may also be fitted in the lower region of
the reactor 1. This does not change the operating
principle of the apparatus.
The microorganisms required for the purification of
the sewage are contained in the bio-sludge settling in
the settling tank 8. It is therefore particularly
expedient if a part of the bio-sludge is conducted back
into the reactor 1 together with the sewage AW . A cor-
responding complete apparatus is evident from Figs. 2 and
3:
The sewage AW to be gurified, delivered by the pump
12, and bio-sludge delivered from the settling tank 8 by
means of a pump 19 are mixed with the sewage to be
returned into the reactor 1 (pump 15) and conducted into
the reactor 1 with oxygen-containing air LT via the
nozzles 3 and 4. The sewage streams emanating from the
nozzles 3 and 4 with the bio-sludge and the evenly
distributed gas bubbles are - as already described for
Fig. 1 - conducted through the conduit tubes 5 and 6 and
deflected by the elbows of the latter. They finally
collide within the reactor 1. In the impact zone PZ,
again a high substance exchange takes place, on the one
hand between the sewage AW and the air LT and on the
other hand between the sewage AW and the microorganisms.
The apparatuses according to Figs . 4 and 5 differ
from those of Figs. 2 and 3 in that the reactor 1 is
integrated with the settling tank 8, which is set on the
reactor 1 on the upper end, in working position of the
said reactor instead of the compartment 2. The separation
of the sewage in the reactor 1 from the sewage in the
settling tank 8 is performed by a rotating, preferably
cylindrical, partition wall 20. In Fig. 4, the gassing of
the sewage from above is represented and in Fig. 5 from
below. Since, in gassing from below, the nozzles 3 and 4
can suck in the sludge to be returned from the settling
tank 8 into the reactor 1, the use of the pump 19 for the
return of the bio-sludge can be dispensed with in the
~ou~~2
_,_
case of this apparatus.
The reactor 1 is distinguished by a very high
substance exchange rate. This means that only a small
reactor volume and a small average residence time are
required in order to achieve a certain oxygen concentra-
tion in the sewage. The space requirement for the degrad-
ation of the pollutants dissolved in the sewage to be
achieved by the microorganisms is higher than that for
the intensive gassing of the sewage AW in the reactor 1.
The separation of the reactor space into two zones can
therefore lead to a reduction in the energy requirement.
Fig. 6 shows such an apparatus for the case where the
gassing of the reactor 1 is performed from below.
The first zone corresponds to the reactor 1, into
which a high volume-related output is introduced. In this
zone, the oxygen concentration in the sewage AW is
greatly increased (>~ 2 mg/1) and very small bacteria
agglomerates with a large volume-related exchange surface
are generated by the bio-sludge in the sewage. The second
zone contains the volume of the sewage within the
partition wall 20 and above the reactor 1. In this space,
a cylindrical circulation tube 21 may preferably be fitted
concentrically to the partition wall 20. Due to the
pulsed stream of the two-phase flow emanating from the
reactor 1 and the upward force of the rising gas bubbles,
a sewage circulation takes place in this zone.
An oxygen exchange between the gas bubbles and the
sewage likewise takes place in the second zone. However,
compared with the first zone, this substance exchange
occurs with reduced intensity. In the annular gap between
the circulation tube 21 and the partition wall 20, the
sewage flows downwards. At the lower end of the annular
gap, a part of the downwardly directed sewage stream is
deflected back into the' circulation tube 21. The remaining
part of the sewage stream passes into the settling tank
8. The bio-sludge is sucked in by the settling tank 8 by
means of the nozzles 3 and 4, (or, if appropriate, by
means of a pump) and partially returned into the reactor
1.
2~~~128
_8_
The second zone may also be provided with a fixed
bed 22 in the form of a fill or an ordered pack. The
fixed bed 22 has the effect of immobilising the micro-
organisms contained in the sewage and increasing their
concentration in this zone. In order that the sewage
circulation in the second zone is not excessively damped
by the fixed bed 22, the said bed is preferably only
arranged in the annular gap between partition wall 20 and
circulation tie 21, as can be seen from Fig. 7.
By increasing the concentration of microorganisms
in the second zone by means of the fixed bed 22, the
requirement for bio-sludge to be returned from the
settling tank 8 can be dispensed with completely.
In the case of the apparatuses according to Figs. 6
and 7, the nozzles 3 and 4 can be fitted to the reactor
1 at the bottom. However, they may also be arranged at
the top, as emerges in principle from Figs. 1, 2 and 4.
