FI109091B - Method and arrangement for degassing activated sludge - Google Patents

Description

109091

Method and apparatus for degassing activated sludge - Förfarande och anordning for att avgasa aktivslam

The invention relates to a wastewater treatment method, in particular to a continuous treatment method, and to a wastewater treatment system, in particular for continuous treatment of wastewater.

In known wastewater treatment methods based on the utilization of activated sludge, the mixture of this activated sludge is kept in a suspended wastewater in a suspended state and aerated, and once it has emerged from the aeration tanks, it is led to post-clarification tanks where sediments are separated and thereby precipitated. The sediment separated by precipitation 10 is reused in the purification process and the liquid separated from the slag is discharged as purified waste water to the receiving site. The recyclable activated sediments recycled back to the purification process retain their purification properties when continuously or batchly re-fed to purify certain raw wastewater.

Such purification processes, which are carried out in particular in aeration rooms and carried out in deep tanks, for example more than five meters deep, have considerable disadvantages in their practical application. This is due to the fact that the activated sludge is characterized by a relatively poor sedimentation capacity and / or an unfavorable tendency to foam on the surface of the sediment blocks, which greatly complicates the sedimentation process in the post-clarification basin and renders the process quite impossible.

To eliminate this phenomenon, the use of an additional step in wastewater purification processes is known, whereby aeration wastewater is mixed by flocculating before being fed to a clarification basin, which results in an unnecessarily long purification process and often an irregular operation.

The invention is based on the finding that flocs of activated sludge during known purification processes have undesirable properties for waste water, which results in a limited efficiency and capacity of these processes.

As a result of this finding, the working steps and technical means of the invention are used which cause the flocs to become circulating sediments, whereby they act as an activated sludge in the recycling process with new properties that allow for significant increase in effluent treatment capacity and capacity.

2 109091 The wastewater treatment method, in particular the continuous treatment method, comprises mixing the effluent with the activated sludge and a of the mixture prior to transfer to a post-clarification basin.

Preferably the degassing is effected by sucking off the small gas particles.

Preferably, degassing is effected by producing a vacuum.

Prior to degassing, the aerated mixture is brought to a turbulent state and a flow controlled according to its direction of travel 10, preferably by introducing additional air into the mixture.

According to the invention, the wastewater purification system, in particular for continuous wastewater purification, comprising in principle a desired mixture of wastewater and an activated sludge aeration tank, in particular a cascade tank, connected to a post-clarification basin and into a chamber separated from it.

The form of the venting device is like an inverted U having one branch forming a collecting inlet pipe and another branch being a collecting collecting pipe, whereby the part connecting the upper parts delimits an intermediate chamber having a degassing chamber therefrom.

The lower end of the collecting feed pipe and the collecting outlet pipe is submerged or respectively connected to the aeration tank and post-clarification basin of the activated sludge mixture or also to a chamber separated from the tank and a post-clarification basin.

The collecting feed pipe has an orifice located above the surface of the aerated waste water, which fills the purified sewage tank or a chamber separated from it. Preferably, the collecting feed pipe has a suction transport pump or alternatively the suction transport pump is located in the collecting discharge pipe.

The surface of the mixture in the aeration tank or in the chamber separated from it is higher than the surface of the mixture in the post-clarification basin or chamber separated from it. The degassing space is connected to a vacuum source, preferably a suction pump.

The invention is based on the finding that flocs of activated sludge during known wastewater purification processes have undesirable properties which render these processes unsatisfactory.

, 109091 3

The object of the invention will be explained by an example of a model shown in the accompanying drawing, in which Fig. 1 schematically shows a small part of a wastewater purification device and Fig. 2 shows the same device when used in a cascade tank wastewater purification system 5.

The venting device 1 basically forms an inverted U-shaped tube, one arm being a collecting inlet pipe 2, the other arm being a collecting outlet 3, their upper end connecting portion delimiting the spacer chamber 4 to a separated degassing space 5. The collecting supply pipe 2 and collecting tube 10 the lower ends are submerged or respectively connected to an activated sludge mixture aeration tank and a post-clarification basin or are connected to a tank-separated chamber 7 and a post-clarification basin separated chamber 8 as shown in Figure 1.

The collecting feed pipe has an opening 6 located above the aeration surface "a" of the vented wastewater which fills the purified sewage tank or the chamber 7 separated from it.

The degassing space 5 is connected to a vacuum source, for example a suction pump, which is not shown in the drawing.

Fig. 2 shows a deaeration device 1 located at the top of the aeration cascade system of the activated sludge mixture in the purified wastewater and between the last chamber 20 and the post-clarification basin 10.

In the illustrated venting device 1, the mixture of pre-aerated waste water and activated sludge moves and flows compulsively and turbulently as a result of the additional air being sucked through the opening 6 located above the surface of the fluid filling chamber 7 in the aeration tank. In this case, the power of the mammoth pump is utilized to generate this flow. Further, the amount of air supplied, which desirably reduces the specific gravity of the mixture, is subsequently sucked off with the gases present in the mixture.

Example

In a typical urban wastewater treatment plant equipped with a mixture of wastewater 30 and activated sludge, the effluent is efficiently treated at a rate of 100 m3 per hour and an impurity load of 30 kg 02 / h. When the system was equipped with an exhaust system according to the invention, the sedimentation capacity of the activated sludge significantly increased, resulting in a 4109091 i! the associated sedimentation rates can be increased and the result is effluent treatment at least 50% more efficient without the need for any additional aeration tanks.

This result is achieved by pre-aerating the mixture of effluent and activated sludge and, under the reduced pressure conditions provided by the deaeration device of the invention, releasing from the gas the microbubbles contained in the gas which surround the activated sludge flocs and increase which results in these microbubbles being different from the flocs, and with the nearly complete disintegration of its 10 flock structures. With subsequent flow in the deaeration unit and under continuously decreasing vacuum conditions, the individual sediment blocks are rapidly and repeatedly interconnected, whereupon, after the deaeration operations, the flocs have a significantly higher specific gravity and their effective sedimentation capacity is significantly increased.

Thus, it becomes possible to carry out a purification process in which the activated sludge can retain significant and advantageous amounts of fibrous microorganisms for carrying out the process without affecting the sedimentation capacity of the sediment, which is impossible to achieve by conventional methods.

After being degassed, the flocs suspended in the activated sludge mixture filling the post-clarification basin, as a result of an internal flocculation process, produce gas which, however, is not related to the microbubbles in the sediment blocks but to the pre-degassed mixture.

It has been found here that activated sludge for vacuum evacuation, which accumulates in a post-clarification basin, which is then recycled to the aeration process as a circulating solvent and is characterized by an increased absorption capacity of impurities leading to its purification, accelerates the purification process and binds phosphorus.

It has been found within the scope of the invention that this sediment is much more resistant to the sudden loading caused by the deposition of impurities.

30

Claims (7)

1. Sewage treatment method, in particular continuous purification method, which consists partly of wastewater mixing with active sludge, this mixture is aerated in a basin, and then this aerated mixture is led to the subsequent post-sedimentation basin, using degassing, and partly in the return sludge, the post-sediment basin is re-used for aeration of wastewater, characterized in that the aerated wastewater and active sludge mixture to be directed to the post-sediment basin first pass through the under-degassing, whereby immediately before the above-mentioned under-degassing, heist by the addition of additional lute. 2. Design of the wastewater treatment plant, in particular for continuous wastewater purification, which generally comprises a selected type of aeration basin (7) for aeration of wastewater and active sludge mixture, in particular a multi-stage basin having a a one-way and recirculation coupling with the post-sediment basin (8) through a conduit in the form of an inverted U, one arm 20 of which is a collecting inlet pipe (2), and the other a collecting outlet pipe (3). characterized in that the design comprises elements for negative pressure degassing (1) consisting of an intermediate chamber (4) with a separate space (5) for gas suction, which at least partly coincides with the part connecting the upper ends of collecting pipes (2, 3). ) and whose cross-sectional area is larger than the cross-sectional area of these collection tubes which constitute an aeration basin coupling portion or its separated chamber (7) with the sedimentation basin (10) or its separated chamber (8), and furthermore possess such means (6) the wastewater and active sludge mixture added to the intermediate chamber (4) sets in turbulent motion, these means (6) being placed to create turbulent flow between the aeration basin and the vacuum degassing. Design according to claim 2, characterized in that the gas suction space (5) is coupled to the vacuum source, heist by means of a suction pump. 4. Design according to claim 2, characterized in that the lower ends of the inlet pipe (2) and the respective outlet pipe (3) like to fall into or are coupled with the aeration basin for active sludge mixing and the respective post-sedimentation basin 7, or with the separated chamber in the basin (7) and the separated chamber in the subsequent sedimentation basin (8). 5. A design according to claim 2 or 4, characterized in that the means which initiate turbulent movement are constituted by a shark (6) in the inlet pipe (2), placed above the level of the aerated wastewater in the wastewater treatment pool or over the separation of the basin. chamber (7). 6. Design according to claim 2 or 4, characterized in that a suction and pressure pump is installed in the inlet pipe (2). Design according to claim 2 or 4, characterized in that a suction and pressure pump is installed in the outlet pipe (3). i!