Apparatus for the biological purification of water

Apparatus for the biological purification of water with the separation of activated sludge by fluid filtration with the spontaneous returning of activated sludge into the activation area or zone, said separation area or zone being arranged above the activation area.

The present invention relates to an apparatus for the biological 
purification of water with the separation of activated sludge by fluid 
filtration with the spontaneous returning of activated sludge into the 
activation area, the separation area arranged above the activation area. 
The biological purification of water is performed by means of aerobic 
activation by urging air or oxygen into the water, followed by the 
separation of activated sludge wherein the activated sludge is separated 
from clarified water and returned back into the activation area. The 
up-to-date installations have both the separation area and the activation 
area integrated in one common tank. The most suitable separation for these 
units appears to be that in which the fluid filtration with activated 
sludge returns spontaneously into the activation. The separation area is 
arranged next to the activation area and can be located either side by 
side or above the activation area and is always connected with it by means 
of orifices for the inlet of water with activated sludge and for the 
returning of activated sludge. 
During fluid filtration, water in the separation area streams substantially 
upwards and consequently, the orifices for the inlet of activated sludge 
are always arranged in the bottom of the separation area in cases in which 
this type of separation is used. If, accordingly, the separation area is 
located side by side at the activation area, the orifice for the inlet of 
water with activated sludge into the separation is located in the bottom 
part of the activation area. If, however, the separation area is disposed 
above the activation area, such orifice is located in the upper part of 
the activation area. 
The arrangement of the separation area above the activation area offers 
advantages as compared with the arrangement of such areas side by side, 
particularly as concerns simpler design, better utilization of the 
surface, and more convenient shapes of the apparatus from the viewpoint of 
its transportation. 
Operational experience, however, shows the unfavorable effects of the 
flotation of activated sludge in the separation area. On the one hand, 
such flotation impairs the effectiveness of separation, and on the other 
hand it forms a layer of flotated sludge upon the surface of separation. 
The layer of flotated sludge hampers the operation of the unit by blocking 
the removal of clarified water from the separation area. The gradual 
blocking of this outlet causes an uneven distribution of water flow in the 
separation area, which is another cause of the deterioration of the 
separating effectiveness of separation. 
It has been further noted that the intensity of such unfavorable effect 
also depends upon the concentration of suspended solids in the water to be 
purified. In the case of organic feculent waters, a markedly deteriorated 
quality of clarified water, having a 5-times higher BSK.sub.5 average, has 
been noted due to this effect, as compared with the quality of water 
purified by other suitable means. In concentrated sewage, the above 
unfavorable effect can increase to the extent of causing the operation to 
break down. The described disadvantages can be so pronounced as to set 
practical limits to the use of installations with the separation area 
above the activation area. 
The above disadvantages are eliminated by the apparatus according to the 
present invention in which a bubble trap forming a cavity opened downwards 
is arranged above the passage for the transition of water from the 
activation area into the separation area. In a preferred embodiment the 
cavity of the bubble trap broadens in the downward direction. 
A further feature of the invention, which is particularly suitable for use 
in units of increased height, as well as for the purification of 
concentrated sewage, resides in that the activation area has a connecting 
channel linked up with the lower edge of the wall under said passage, said 
channel being oriented downwardly and having its lower end discharging 
into the lower part of the activation area. 
Another feature of the invention resides in that a guide element is 
arranged under the mouth of the connecting channel, said guide element 
consisting of skew walls creating a slot between themselves and the 
discharge mouth of said connecting channel. 
In the case of a more complex system in the area of the inlet of water into 
the separation area, as a rule the passage allowing the upward flow of 
water with activated sludge is considered as the above-mentioned passage 
for the transition of water with activated sludge from the activation to 
the separation, and directly at this passage the downward flow direction 
is turned upwardly.

In a vertical cylindrical tank 1, a funnel shaped partition 2 forms the 
activating area or zone 100 and above it the separation area or zone 15. 
The activating area 100 communicates with the separation area 15 by means 
of a passage 3 for the transition of water from the activation area 100 
into the separation area 15. 
The funnel shaped wall 4 under the partition 2 is fixed to brackets (not 
shown) on either the partition 2 or the wall of tank 1. The partition 2 
and the wall 4 create a ring channel 5 discharging at its lower end into a 
connecting conduit or channel 6 oriented in the direction of flow within 
the activation area 100 at its location. The connecting channel 6 extends 
down to the bottom part of the activation area 100. Under the lower, 
discharge end of the connecting channel 6 and spaced therefrom there is 
arranged a conical guide element 7 which is disposed coaxial of channel 6. 
Between the walls of the guide element 7 and the mouth of the connecting 
channel 6 there is formed a slot 8 which spouts an inclined stream of 
water from the channel 6 down to the bottom of the activation area 100. 
Passage 3 is defined as a passage allowing the upward flow of water with 
activated sludge, while the downward direction stream of the water in ring 
channel 5 is turned upwardly directly at passage 6. Over the passage 3 for 
the transition of water from the activation area 100 to the separation 
area 15 there is inserted a bubble trap 9 into the separation area 15, 
said bubble trap 9 forming a cavity which is preferably open at the 
bottom, with the lower brim of the bubble trap overlapping or projecting 
horizontally beyond the perpendicular projection of the passage 3. The 
bubble trap 9 is arranged so as to allow water to stream upwardly along 
its lower edge; the upper end of the bubble trap is connected to a pipe 10 
which constitutes an outlet 10 for trapped air leading outside the 
separation area 15. 
The separation area 15 is provided with a collecting flume 11 for 
discharging the clarified water; in the upper part of the tank 1 there is 
arranged an inlet 12 through which the water to be treated enters the 
activation area 100. The activation area 100 is provided with a pneumatic 
aeration system consisting of aerating elements 13. An air outlet 14 is 
arranged above the surface of the activation area 100. 
The described apparatus operates as follows: 
Water to be treated enters the inlet 12 of the activation area 100 where it 
becomes mixed with activated sludge. The aerating elements 13 serve to 
urge air into the activation area 100, yielding, on the one hand, oxygen 
required for the biologic processes of water purification and, on the 
other hand, the necessary streaming and turbulence within the activation 
area 100 indispensable for the said mixing and for maintaining the mixture 
of activated sludge. The air bubbles, which become partially deprived of 
oxygen, escape into the environment at the upper part of the activating 
area through the air outlet 14. During the flow of water through the 
activation area 100 some water with activated sludge is removed from the 
passage 3 and brought to the separation area 15 where the activated sludge 
is retained. The water from which activated sludge has been removed is 
then drained by the collecting flume 11 in the upper part of the 
separation area 15. The activated sludge retained in the separation area 
15 automatically returns into the activation area 100 through the passage 
3. 
The air bubbles penetrating through the passage 3 are caught at the oblique 
wall of the bubble trap 9 after passing through passage 3. Whereas both 
water and sludge stream along the lower edge of the wall of the bubble 
trap 9, the trapped air bubbles proceed to the upper part of the trap 9, 
from which they are discharged into the environment through pipe 10. The 
wall 4 under the partition 2 arranged in the activation area 100 in the 
direction of flow lines prevents the air bubbles rising upwardly within 
the activation area 100 from direct penetrating into the passage 3, thus 
reducing the amount of bubbles travelling through the passage 3, and 
consequently improving the operation of the air trap 9 above the passage 
3. The bubbles that have penetrated into the passage 3 in spite of that 
can trace their origin to the bubbles which are dragged away from the wall 
of the tank 1 by streaming and which are gathered during the flow of the 
liquid in the ring channel 5. 
The arrangement of the connecting channel 6 prevents the bubbles carried 
away by the downward stream of the liquid in the central region of the 
activation area 100 from penetrating into the area under the passage 3; 
this prevents the bubbles from entering the separation area 15, 
particularly in the case of highly concentrated and intensely aerated 
sewage, and also in the case of purifying plants or installations of 
considerable height. 
The above operation provides an effective protection against bubbles 
entering the separation area 15. From the above it can be seen that this 
penetration of bubbles and their agglomeration with the activated sludge 
in the separation area 15 is the cause of the flotation of activated 
sludge in the separation area 15. Consequently, the prevention of bubbles 
from entering the separation area 15 eliminates the unwanted flotation of 
sludge within the separation area 15. 
The described apparatus offers various advantages. The elimination of the 
flotation of sludge in the separation area approves the effectiveness of 
separation to the extent of achieving substantially better quality of 
water leaving the apparatus. Also, sewage waters with high concentrations 
of suspended solids can be treated without any problems. Purifying plants 
can be used having the separation area above the activation area, which 
offers advantages in numerous cases, especially as concerns the cost of 
construction and the area necessary for the construction of the purifying 
plant. 
Although the invention is illustrated and described with reference to one 
preferred embodiment thereof, it is to be expressly understood that it is 
in no way limited to the disclosure of such a preferred embodiment, but is 
capable of numerous modifications within the scope of the appended claims.