Apparatus for aerobic treatment of activated sludge

In an apparatus for the gasification of a biomass in an aqueous medium in the presence of organic substances degradable by the biomass, comprising a gasification tank, and a clearing chamber for the gasified water-containing biomass provided concentrically around the gasification tank, the gasification tank communicating with the clearing chamber through an inlet in the latter, the improvement wherein A. the gasification tank is from about 10 to 32 meters high, has a height/diameter ratio between approximately 40 and 0.2, is provided adjacent its floor with gas inlet points, and is connected via inlet pipes to at least one gas removal and flocculation cyclone; B. the same liquid level in all the clearing chambers is maintained by means of an overflow channel at about 0.1 to 2 meters below the liquid level of the gasification tank; and C. a sludge removal pipe connects each clearing chamber with a collector pipe. Advantageously the clearing chamber is funnel shaped.

With biochemical processes taking place aerobically, the quantity of oxygen 
required for the metabolism of the microorganisms (biomass) must be 
supplied and a specific oxygen concentration must be maintained. The 
oxygen necessary for waste water purification or fermentation is supplied 
to the liquid from the gas phase. This can be effected by means of surface 
aerators, jet nozzles, perforated floors or injectors. Jet nozzles are for 
example described in Chemie-Ingenieur Technik, 42, 474 (1970). 
Injectors are for example described in the journal Chemie-Ingenieur-Technik 
43 (1971) 6, 329-335. The injectors are similar in construction to water 
jet vacuum pumps, which produce a finely distributed air-water-mixture. 
Injectors are preferably arranged on the floor or directly above the floor 
of the activated sludge or fermentation tank (hereinafter termed 
gasification tank). This arrangement ensures uniform mixing in the entire 
gasification tank. 
As the motive water of the injectors it is preferable to use the 
biomass/water mixture present in the tank, and in the special case of 
water treatment a mixture of activated sludge/waste water. The biomass and 
water are generally separated from one another (clearing) subsequent to 
gasification. The greater part of the deposited biomass is continuously 
returned from the clearing stage into the gasification tank. After the 
concentration and filtration of the sludge the excess can for example be 
supplied to a storage or further processing stage. 
Known activated sludge tanks for waste water treatment generally take the 
form of ground level concrete tanks having a depth of up to 6 meters to 
which are connected spatially separated units for the separation of 
activated sludge and treated water. Suitable clearing units include in 
particular funnel tanks (so-called Dortmund wells). 
These Dortmund wells are generally made of concrete and are connected by 
pipes or channels laid on the ground to the activated sludge tank. By the 
spatial separation of the activated sludge tank and clearing units and the 
distributor systems thus becoming necessary, high pressure losses or 
differences of level are produced between the activated sludge tanks and 
clearing tanks. 
An apparatus is already known in which the aeration and clearing of the 
waste water takes place in a single tank. This apparatus consists of a 
preferably round tank having water depths of from approximately 3 to 5 
meters and an activated sludge tank diameter of approximately 8 to 20 
meters. Aeration is effected with surface aerators, gasification agitators 
or rotary devices. The clearing chamber is arranged concentrically about 
the activated sludge tank. 
Since the concentric partition between the gasification chamber and 
clearing chamber lies approximately from 0.2 to 0.4 meters below the 
common liquid level and since large perforations are arranged at the 
bottom of both chambers, the flow from the gasification chamber is readily 
provided. In addition, a return of activated sludge through the floor 
perforations to the gasification tank is ensured. Excess activated sludge 
can be removed continuously or periodically from the clearing chamber. 
The essential disadvantages of this known apparatus are that the turbulence 
which must necessarily be maintained in the gasification tank is also 
transmitted to the clearing chamber, as a result of which the conditions 
for the settling of the activated sludge are very unfavorable. Moreover, 
with this known apparatus the return of the activated sludge into the 
gasification tank takes place in a substantially uncontrolled manner. A 
further disadvantage is that in the case of the known apparatus, the flow 
moves horizontally through the clearing chamber which results in a lower 
surface load than in the case of a clearing chamber through which the flow 
moves vertically. 
The object of the present invention is to eliminate the disadvantages of 
known apparatus and to provide an apparatus for carrying out biochemical 
processes which in the smallest possible space permits both optimum 
gasification of the biomass and clearing. 
The present invention provides an apparatus for the gasification of a 
biomass in an aqueous medium in the presence of organic substances which 
can be degraded by the biomass in a gasification tank, comprising a 
clearing chamber for the gasified water containing the biomass provided 
concentrically about the gasification chamber, the gasification chamber 
and clearing chamber communicating with each other wherein 
a. a gasification tank which is about 10 to 32 meters high, whose 
height/diameter ratio is between approximately 40 and 0.2 and on whose 
floor or just above whose floor gas inlet points are arranged, having one 
or more concentrically suspended clearing chambers, is connected via inlet 
pipes to gas removal and flocculation cyclones, all clearing chambers 
having an equal liquid level; 
b. the liquid level in the clearing chambers is adjusted by means of one or 
more overflow channels so that it lies between about 0.1 and 2 meters, 
preferably between about 0.3 and 1 meter below the liquid level of the 
gasification tank; 
c. a number of sludge removal pipes corresponding to the number of clearing 
chambers leads into a collector pipe. 
The gasification tanks according to the invention are preferably 
cylindrical towers having a height/diameter ratio between approximately 
0.3 and 32, especially preferably between about 0.5 and 20. The 
height/diameter ratio can in its widest range lie between approximately 40 
and 0.2. The water level in the gasification tank lies between 
approximately 10 and 32 meters, preferably about 18 to 26 meters. The gas 
inlet points preferably comprise injectors; it is advantageous to arrange 
these on the floor or just above the floor of the gasification tank 
preferably equidistant from one another. 
If oxygen-containing gas in the gasification tank containing less than 
about 50% by volume is introduced into the water containing biomass which 
is under its own hydrostatic pressure, the individual inlet points are 
arranged at a distance of about 0.5 to 2 meters, measured from the center 
point of each gas inlet point, from one another. Each gas inlet point 
preferably has a cross-sectional area of from approximately 0.01 to 
0.1m.sup.2, each of which is loaded with about 100 to 1000 
effective-m.sup.3 gas per m.sup.2 cross-sectional area per hour. The gas 
pressure of the gas introduced is between about 0.01 and 0.5 bars above 
the hydrostatic pressure at the gas inlet point (effective-m.sup.3 is 
intended to mean the gas volume based on the gas pressure and gas 
temperature at the gas inlet point). 
If an oxygen-containing gas containing at least about 50% by volume oxygen 
is introduced into the gasification chamber, then the individual inlet 
points are preferably at a distance of about 2 to 10 meters, measured from 
the center point of each gas inlet point. Each gas inlet point has a 
cross-sectional area of approximately 0.1 to 0.5 m.sup.2, each of which is 
loaded with from 100 to 300 effective-m.sup.3 gas per m.sup.2 
cross-sectional area per hour. 
Here also the gas pressure of the gas introduced should be approximately 
0.01 to 0.5 bars above the hydrostatic pressure at the gas inlet point. 
Instead of injectors, single hole floors or jet nozzles can also be used. 
The gas containing oxygen is preferably supplied to the gas inlet point 
with a propellent liquid especially preferably with water containing 
biomass and/or unpurified waste water. The propellent liquid constitutes 5 
to 50% by volume, preferably about 10 to 30% by volume of the gas 
throughput.

Referring now more particularly to the drawings, in the prior art device of 
FIG. 1 the reference characters indicate the following elements; 
1. Funnel tank 
2. Inlet pipe 
3. Gas removal and flocculation cyclone 
4. Distributor arms 
5. Impingement plates 
6. Overflow channel 
7. Sludge discharge 
8. Purified waste water outlet. 
This apparatus functions as follows: 
Water flowing through one or more inlet pipes 2 from a gasification tank 
(not shown) flows tangentially into the gas removal and flocculation 
cyclone 3, the coagulation of the sludge being accelerated by the 
intensive rotational movement and at the same time the air still present 
being driven out. Above one or more distributor arms 4 there are located 
impingement plates 5, which impart a horizontal flow component to the 
issuing waste water containing activated sludge. Purified waste water can 
be supplied via the overflow channel 6 and the outlet 8 to the receiving 
stream, while the deposited sludge can be removed via the pipe 7. 
With reference to FIGS. 2 and 2a, the reference numerals have the following 
meanings: 
10 -- Gas removal and flocculation cyclone 
11 -- Distributor arms 
12 -- Impingement plates 
13 -- Inlet pipe for water containing biomass 
14 -- Clearing chamber 
15 -- Annular chamber floor 
16 -- Evacuation device 
17 -- Biomass, discharge pipe (not shown) 
18 -- Overflow channel 
19 -- Outflow pipe for cleared water 
20 -- Gasification tank 
21 -- Gas inlet points 
22 -- Cooling pipes for water 
23 -- Water level 
24 -- Sludge return 
25 -- Excess sludge pipe 
26 -- Feed pipes for gas containing oxygen 
27 -- Cover 
28 -- Pump. 
The liquid to be gasified is supplied to the gasification points 21 via 
pipes 22 with gas containing oxygen (e.g., air) supplied via 26. 
The water level 23 in the gasification tank 20 is higher than that in the 
clearing chamber 14 by the amount of the pressure loss in the inlet pipes 
13 and the gas removal and flocculation cyclones 10. The liquid to be 
cleared passes through one or more cyclones 10 and distributor arms 11 
with impingement plates 12 arranged above them into the clearing chamber 
14, which is arranged in annular manner around the gasification tank 20. 
The cleared liquid passes via the overflow channels 18 and outlet pipes 19 
and in the case of waste water can be supplied either directly to the 
receiving water or to a further biological or chemical/physical treatment. 
The biomass forms a sediment in the clearing chamber 14 and is evacuated 
pneumatically, hydraulically or mechanically by means of an evacuation 
device 16 which for example moves around on the annular chamber floor 15. 
The biomass is removed via the pipe 17 on the annular chamber floor 15 and 
can be returned via a pump (not shown) and the pipe 24 to the intake pipe 
of the pump 28 to the gasification points or via a distributor pipe (not 
shown) on the gasification tank floor into the gasification chamber 
uniformly distributed. The excess proportion is led away via the pipe 25. 
In the plan view of FIG. 2a, the overflow channels, cyclones and annular 
chamber floors extend over the whole circumference of the annular chamber; 
for the sake of clarity these parts are however only shown in segment. 
The reference numerals in FIGS. 3 and 3a have individually the following 
meanings: 
30 -- Gasification tank 
31 -- Gasification points 
32 -- Feed pipe for gasifying liquid 
33 -- Water level 
34 -- Inlet pipe for water containing biomass 
35 -- Gas removal and flocculation cyclone 
36 -- Distributor arms 
37 -- Impingement plates 
38 -- Clearing chambers (4 units) 
39 -- Feed pipes 
40 -- Biomass removal 
41 -- Overflow channel 
42 -- Discharge pipe 
43 -- Feed pipes for gas containing oxygen 
44 -- Pump 
45 -- Biomass removal 
46 -- Biomass return. 
In this arrangement the liquid to be gasified, introduced via the pump 44 
and the feed pipe 32 together with gas containing oxygen supplied via the 
pipe 43, is guided to the gasification points 31 and pumped and 
distributed into the gasification tank 30. The water level 33 in the 
gasification tank 30 is higher than in the clearing chamber 38 by the 
amount of the pressure loss (approximately 200 to 500 mm) in the inlet 
pipes 34 and the gas removal and flocculation cyclone 35. The liquid to be 
cleared passes through the cyclone 35 and the distributor arms 36 with the 
impingement plates 37 arranged above them into the clearing chamber 38. In 
this arrangement the clearing chamber is sub-divided into four funnel 
shaped chambers. The funnels have a wall angle of approximately 45.degree. 
to 75.degree. , preferably about 55.degree. to 65.degree. relative to the 
horizontal. The cleared liquid passes out via the overflow channel 41 and 
the outlet pipe 42 and can for example in the case of waste water 
purification be supplied either directly to the receiving water or to a 
further biological or chemical/physical treatment. The sludge forms a 
sediment in the clearing chamber 38 which is in the form of four sludge 
funnels and can be returned uniformly distributed via the four floor pipes 
39 and via a pump (not shown) and the pipe 46 into the intake pipe of the 
pump 44 into the gasification points or via a distributor pipe (not shown) 
on the gasification tank floor into the gasification chamber. The excess 
proportion of the biomass is removed via the pipe 40. (In FIG. 3a for the 
sake of clarity the overflow channel 41 is not shown). 
A variant of the embodiment shown in FIG. 3 has eight identical 
funnel-shaped clearing chambers. 
The reference numerals in FIGS. 4 and 4a individually have the following 
meanings. 
50 -- Gasification tank 
51 -- Gasification points 
52 -- Feed pipes for water containing biomass 
53 -- Water level 
54 -- Inlet pipes 
55 -- Gas removal and flocculation cyclones 
56 -- Distributor arms 
57 -- Impingement plates 
58 -- Clearing chambers (16 units) 
59 -- Feed pipes 
60 -- Biomass removal 
61 -- Overflow channels 
62 -- Discharge pipes for cleared water 
63 -- Feed pipes for gas containing oxygen 
64 -- Excess biomass outlet 
65 -- Biomass return 
66 -- Pump. 
The liquid to be gasified, introduced via the pump 66 and the feed pipe 52 
is supplied to the gasification points 51 together with gas containing 
oxygen introduced via the feed pipe 63 and pumped into the gasification 
tank 50. The water level 53 in the gasification tank 50 is higher than in 
the clearing chamber 58 by the amount of the pressure loss in the inlet 
pipes 54 and the gas removal and flocculation cyclones 55. The liquid to 
be cleared passes preferably via several cyclones 55 and distributor arms 
56 with impingement plates 57 arranged above them into the clearing 
chambers 58, of which 16 units are arranged in funnel form around the 
circumference of the gasification tank. The gas removal and flocculation 
cyclones can here as in the already described embodiments also be operated 
under a slight partial vacuum. Over each second saddle surface of 
consecutive clearing chambers there is arranged a gas removal and 
flocculation cyclone which can be supported on this saddle surface. At the 
point of each funnel there are short feed pipes 59, through which the 
deposited biomass can be returned uniformly distributed via a pipe 60, via 
a pump (not shown) and the pipe 65 to the intake pipe of the pump 66 to 
the gasification points or via a distributor pipe (not shown) on the 
gasification tank floor into the gasification chamber. The excess biomass 
proportion can be partially sluiced out via the pipe 64. 
The cleared liquid can be removed via the overflow channels 61 and 
discharge pipe 62. 
In FIG. 4a, overflow channels, cyclones and clearing chambers in 
communication via saddle surfaces are arranged over the whole 
circumference of the annular chamber. For the sake of clarity, these parts 
are only shown in segment in FIG. 4a. 
If waste water is purified in the apparatus according to the invention, the 
purified waste water can subsequently be supplied via the overflow 
channels to the receiving water or with the pressure drop present to a 
further biological or chemical/physical treatment. Preferably in the case 
of passing into the receiving water, the level difference existing between 
the water level in the clearing chambers and the water level of the 
receiving water is exploited in order to reinforce the diverted waste 
water with oxygen. For this purpose the cleared waste water is preferably 
supplied to the pressure side of an injector and to the low side air or 
oxygen enriched air or technical oxygen is supplied, in order to maintain 
a desired oxygen content in the waste water. 
With the apparatus according to the invention it is possible with space 
saving construction to undertake the optimum design and dimensioning of 
the gasification tank and of the clearing chambers. The apparatus 
according to the invention also permits excellent use of the pumping 
energy for all process stages and for the transport of the products 
formed. 
It will be appreciated that the instant specification and examples are set 
forth by way of illustration and not limitation, and that various 
modifications and changes may be made without departing from the spirit 
and scope of the present invention.