JPH0355199B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for treating sewage sludge, and more particularly to a method and apparatus for preventing the bacterial production of sulfides, particularly hydrogen sulfide, and other malodorous sulfides in sewage water.

Municipal sewage typically contains oxygen-breathing bacteria and other microorganisms. They obtain oxygen for respiration from the dissolved oxygen normally present in the sludge. However, the sludge flows along the sewage system at a rate faster than the rate at which oxygen from the air in the head space of the gravity sewer(s) that forms part of the sewage system dissolves into the sewage. This tends to deplete the amount of dissolved oxygen for microbial growth in sewage. When there is no dissolved oxygen remaining in the sludge, certain bacteria known as facultative becteria obtain oxygen by decomposing oxygenated compounds, particularly sulfates, in the sludge, thereby producing hydrogen sulfide. and other sulfides,
This causes the sludge to rot. The produced sulfide exists in an equilibrium relationship of sulfide and disulfide as a function of the acidic pH of the putrid sludge, and hydrogen sulfide dissipates from solution into the atmosphere above the sludge. Gaseous hydrogen sulfide is oxidized to sulfuric acid by other bacteria that adhere to the wet walls and lids of the sewage system, and the sulfuric acid so produced rapidly corrodes concrete surfaces within the sewage system.

UK patent No.
No. 1452961) discloses a particularly effective method for solving the problem of preventing bacterial sulfide production. The method (typically) involves pressurized injection of commercial grade oxygen into the sewage water. Regarding gravity sewage, the above-mentioned British patent specification consists of removing a portion of sewage sludge, pressurizing the sewage, applying oxygenation to this pressurized sewage, and returning this oxygenated sludge to the sewage. The method is disclosed. UK patent No.1596246 by the applicant
No.) The specification discloses an improvement on the above technique, which is a technique in which sludge extracted from sewage is pumped into a storage tank installed above ground and oxygenated in this tank. . The oxygenated sludge from the storage tank is periodically released and falls into the sewer.

The above method of flushing oxygenated sludge to gravity sewers requires the use of pumps. The pump should be of a type capable of handling untreated sludge, which typically contains bulk materials such as rags. Although suitable pumps are commercially available, they are generally relatively expensive and require a power supply.

It is an object of the present invention to provide a method and apparatus for preventing hydrogen sulfide production by bacteria in gravity sewage by oxygenating sludge without requiring the installation of pumping equipment.

In accordance with the present invention, in order to prevent the production of hydrogen sulfide by bacteria in gravity sewage, a flow of untreated sludge is created in the sewage water and is directed along a channel having a long downward leg and a long upward leg. directing the outflow flow from the downward leg to the upward leg, and directing this outflow flow from the downward leg to the upward leg, at a point in the flow path spaced apart from the top of the upward leg, the lower of the upward leg and the downward leg A method is provided which includes the steps of introducing an oxygenating gas into the sludge in a monopod to oxygenate the sludge and returning the thus oxygenated sludge to the sewage.

The present invention also relates to a device attached to a gravity sewage system operable to prevent the production of hydrogen sulfide in sewage by bacteria, comprising an elongated upward leg and an elongated upward leg that directs sludge flow into the elongated upward leg. a first conduit directing sludge flow from the sewage to an oxygenator defining a flow path having a downwardly directed leg; means for introducing an oxygenating gas into the sludge of at least one of the legs, and a second conduit for directing the oxygenated sludge from the top of the upward leg so that it can be returned to the sewer. Provided is a device comprising:

The sludge flow from the sewage to the channel, the oxygenated sludge flow along the channel and returned to the sewage can be handled under gravity and bubbles of oxygenating gas in the upward leg of the oxygenator. Buoyancy effect of group
(i.e. gas lift effect)], thus obviating the need for the use of pumping equipment.

As a result of the prevention of bacterial production of hydrogen sulfide, the lining of sewer pipes with acid-resistant coatings is no longer necessary.

Oxygenators are typically buried underground. The apparatus of the present invention therefore does not include means for conveying sludge to an above-ground oxygenation plant (unlike on the apparatus disclosed in GB 1,596,246).

Both legs of the channel are placed in wells, the depth of which is sufficient to achieve a liquid head of typically at least 9 m, selected according to the amount of oxygen required for dissolution. It's the amount. The vertical hole has an inner tube, shaft or tube that defines the flow path. In such an arrangement, the downward leg of the channel may be defined by the space between the well shaft and the inner tube, shaft or tube, and the upward leg may be defined by the tube, tube or shaft. , or they could be the opposite. Typically, a suitable hole or shaft is dug in the ground and then a concrete shaft is placed or formed at that location in the hole. Next, an inner tube or cylinder made of a suitable material, such as ABS plastic resin or mild steel, is placed in this vertical hole shaft. Preferably, the inner tube or cylinder can be easily removed from the outer shaft to periodically wash the wells to facilitate removal of grit and to facilitate routine cleaning. Optionally, the outer shaft may have a curved bottom to eliminate the build-up of grit at the bottom of the well and to allow (in combination with sufficient liquid velocity) to transport the grit from the downward leg to the upward leg. In order to remove other or additional solids that may block the shaft, a pre-cleaning settling tank may be provided between the sewage and the shaft.

The oxygenating gas is typically commercial grade purity oxygen or oxygen enriched air. Preferably, the oxygenating gas is directed into the sludge along the flow path through at least one disperser or other means capable of dispersing the oxygenating gas as a number of bubbles. The distributor may include a porous gas distributor, typically of sintered material. This type of disperser is suitable for fine air bubbles (e.g.
It is generally possible to form bubbles (with diameters on the order of 0.1 mm or less). Preferably, at least two porous gas distributors are provided, which are spaced apart from each other so that the respective flows of bubbles emitted from each distributor do not immerse into each other in the vicinity of each distributor and disappear. It is. If immersed, the bubbles will associate with each other and prevent their dissolution.

Preferably, the oxygenating gas is introduced into the uplift leg from an area(s) close to the bottom of the uplift leg. By releasing a large number of bubbles to the liquid in the upward leg, the effective specific gravity of the liquid is reduced. This phenomenon facilitates retention of the flow of untreated mud down the downward leg of the channel and up the upward leg. Furthermore, the liquid head (hydraulic pressure) in the upward leg facilitates oxygen dissolution. Typically most, but not all, of the oxygen (approximately 90
%) is dissolved. Additionally, certain gases already dissolved in the incoming sludge (such as nitrogen) are driven out of solution by the dissolved oxygen in the sludge. The gas flow from the oxygenator toward the sewage ullage space has an oxygen concentration that is significantly higher than the atmospheric oxygen concentration anywhere within the sewage space. It is preferable that the effect not be so great as to achieve the desired results. If oxygen (or oxygen-enriched air) is bubbled into the flow path in an area remote from the top of the uplift leg, then a head of swage flowing from the uplift leg at an appropriate height (e.g. 9 m or more), it is believed that such oxygen enrichment to oxygen-deficient areas in the sewage water will not occur. However, if such enrichment occurs, additional sewer aeration may be provided or air or water curtains may be installed.
The oxygen-enriched area can be clearly distinguished from the rest of the atmosphere by water curtains.

Typically, the oxygen solubility for the sludge passing through the oxygenator under average flow conditions during the dry season is selected to be sufficient to achieve a dissolved oxygen concentration of at least 20 ppm. Typically, when the oxygenated sludge is returned to the sewage system (preferably in an area located downstream of the area where the sludge is taken up), the dissolved oxygen concentration of the sludge in the sewage is reduced to an oxygenator. 5 depending on the proportion of flow through the main sewer pipes which split towards
will increase to ~10ppm. Typically 1/4 to 1/3 of the flow is diverted to the oxygenator. A dam or similar structure may be installed within the sewer to ensure adequate sludge flow through the oxygenator under average conditions during the dry season. If the sludge is returned to the sewer in an area located downstream of the area where it is taken up, the dam is typically located intermediate between these areas.

The oxygenating gas is easily supplied under the pressure necessary to overcome the liquid head acting on the distributor(s) (or other gas distributors). For example, a conventional insulated storage tank for liquid oxygen with a vaporizer may be used, and the pressure within the oxygen-deficient area of this storage may be used to pass the liquid oxygen to the vaporizer, thus producing superatmospheric pressure. may be arranged to produce oxygen gas at

The method and apparatus of the invention will now be described with reference to the accompanying drawings for purposes of illustration.

The gravity water system 2 in the figure has a main drain 4 through which untreated sludge flows under gravity. The main sewer pipe 4 has a first conduit 6
are connected, and the sludge flows along this conduit 6 to the main sewer pipe 4.
to the oxygenator 10. This main sewer pipe 4
Also connected is a second conduit 8 which can lead oxygenated sludge from the oxygenator 10 to the main drain 4. The outlet of the second conduit 8 is located downstream of the inlet of the first conduit 6, and both conduits are typically separated by a distance of 2 to 10 meters along the main drain 4.

The oxygenator 10 has a first leg (downward leg) 12,
While descending this first leg 12 , the untreated sludge flows into the upward leg 14 and is discharged from the top of this upward leg 14 into the second conduit 8 . Both legs 12 and 14 have vertical holes 16
and an inner tube 18. The vertical hole 16 is formed by drilling into the ground and then lined by inserting a concrete pipe therein or by building a concrete pipe within the hole. The vertical hole 16 has suitable inlets and outlets and connects the outlet from the first conduit 6 and the inlet to the second conduit 8. Inner tube 18 is located coaxially within vertical bore 16 and is supported by support means (not shown). The bottom of the inner tube 18 is located approximately 15 cm higher than the bottom of the well 16, and the top or outlet of the inner tube 18 is located at the same level as the inlet to the second conduit 8. The downward leg 12 is defined by the annular space between the wall of the well 16 and the inner tube 18 and the upward leg is defined by the inner tube 18. The outlet of the inner tube 18 is typically at least 8 minutes from the inlet to the inner tube 18.
m (generally 9 m or more) above. During operation of the oxygenator, untreated sludge moves down the downward leg 12 and up the upward leg 14.

Oxygenator 10 also includes four peripherally located distributors 30 having cellular moldings of porous sintered material. Gaseous oxygen source 24
Oxygen is delivered to the distributor 30 from an annular tube 28 which connects to a tube 26 that connects to a tube 26 . Distributor 30 is inner tube 1
8 at or near the bottom of the inner tube 18. During operation, large numbers of microscopic bubbles (typically having an average diameter of 0.1 mm or less) flow into the rising sludge into the upper leg 14 of the oxygenator 10. The large number of air bubbles introduced into the sludge within the upward leg 14 assists in the upward flow of the sludge within the upward leg 14. This is based on the fact that the effective specific gravity of the liquid in the upward leg 14 is significantly reduced. This is evidenced by the fact that the level of liquid in the upward leg 14 is higher than the level of liquid in the downward leg 12, as shown in FIG. However, this is not an essential requirement of the present invention. The oxygen supply source 24 is located higher than the ground as shown in FIG. This source typically consists of a vacuum-insulated container containing commercial grade purity liquid oxygen under pressure of gaseous oxygen in an oxygen-deficient zone. As is customary, for liquid oxygen gas,
Means (not shown) is provided for directing liquid oxygen to the vaporizer under gas pressure in the oxygen-deficient zone. The gaseous oxygen thus reaching the distributor 30 from the oxygen source 24 via the tube 26 (which extends through the lid 20 which closes the well shaft 16 and keeps it level with the ground) is It can be supplied under a pressure that can overcome the hydraulic head (hydraulic pressure) of the facing leg 14.

Exhaust tube 18 has an outlet 32 extending into conduit 8 . A baffle 34 is provided at the inlet of the conduit 8 to prevent liquid from the conduit 8 from flowing into the oxygenator 10, and directs the jet through the buffle 34 to the oxygenator 10.
flow inward.

If desired, a dam 22 may be provided in the main drain 4 intermediate the inlet of the first conduit 6 and the second conduit 8 to facilitate the flow of untreated sludge from the main drain 4 to the conduit 6. . Typical height of dam 22 is sewer pipe 4
It is about 1/4 or 1/3 of the inner diameter of.

The apparatus shown in Figures 1 and 2 is located in an area of the sewage system upstream from where the sludge tends to be deficient in dissolved oxygen.

In operation, untreated sludge flows under weight from the sewer pipe 4 through the first conduit 6 to the oxygenator 10. When the sludge fills the shaft 16 to a suitable level, a sludge flow is established down the downward leg 12 and up the upward leg 14. This established flow is upward leg 1
4 is necessitated by the introduction of a large number of oxygen cells, which are introduced into the sludge via the disperser 30 at the bottom of the tube 18, which defines the sludge. This equipment can handle approximately 1/4 to 1/3 of the untreated sludge flow in gravimetric water under average flow conditions during the dry season.
is typically provided to the oxygenator 10. Typically, this sludge will have a dissolved oxygen concentration of no higher than 1 or 2 ppm as it enters the oxygenator 10. Oxygen is bubbled into the sludge rising up the uplift leg 14 at a rate sufficient to increase the dissolved oxygen concentration to 20 ppm as it exits the oxygenator 10.

The liquid head in the upward leg 14 provides a pressure that facilitates dissolution of the oxygen bubbles introduced into the sewage from the disperser 30. Immediately, as the liquid moves up the upward leg 14, the concentration of undissolved bubbles in the liquid decreases. Typically at least 90% of the oxygen introduced to the sludge will be dissolved in the sludge. It should be recognized that the sludge entering the oxygenator contains dissolved gases other than oxygen. Typically, the sludge will contain some amount of dissolved nitrogen and also some amount of dissolved carbon dioxide. Oxygen microbubbles introduced into the sludge in the oxygenator 10 displace some of the dissolved gases from the solution. The gas leaving the surface of the liquid in the upward leg 14 is therefore a mixture of oxygen and other gases displaced from the sludge. A certain amount of the gas has a tendency to flow back into the main drain 4. The gas will not significantly raise the oxygen concentration in the sewage water above that in the surrounding air.

The free flow of sludge through the oxygenator 10 into the gravimetric drain 4 takes place under gravity (with the aid of oxygen bubbles in the upward leg 14), thus eliminating the need for pumping equipment and the associated power supply. do not need. Furthermore, a pump is also unnecessary for supplying oxygen to the disperser 31.

Oxygenated sludge returning from conduit 8 to gravimetric sewer 4 can substantially increase the dissolved oxygen concentration in the downstream section of the sewer to which the sludge is returned. Typically the dissolved oxygen concentration increases to 8-10 ppm. As this sludge continues to flow through the sewage, microorganisms in the sludge and on the walls of the sewage pipe consume the dissolved oxygen concentration, but in oxygen-deficient areas of the sewage, contact between the surface of the sludge in the sewage and the oxygen-containing gas causes the sludge to sludge. More oxygen dissolves on the surface. If as a result of this process there is a tendency to produce sludge that does not contain any dissolved oxygen, additional equipment may be used downstream of the equipment shown in Figures 1 and 2 of the accompanying drawings of the present invention; One or more additional oxygenators may be installed and used at specific locations in the gravimetric sewage system. For example, a total stream of sewage can be oxygenated by dividing the total stream into four streams and passing each stream through its own oxygenator.

Maintaining a positive dissolved oxygen concentration in the sludge flowing through the sewer in accordance with the present invention obviates the need to line the sewer pipe with a protective coating. This fact is of particular advantage if the gravity drain diameter is, for example, 2.5 feet (0.76 m) or larger.

Preferably, the inner tube 18 is removable from the shaft 16 to facilitate cleaning of the shaft 16. Inner tube 18 may be removed periodically to clean the bottom of shaft 16.

[Brief explanation of drawings]

FIG. 1 of the accompanying drawings is a general schematic plan view of a heavy sewage system used in the present invention. FIG. 2 is a partial schematic side view of the sewage facility shown in FIG. 1. 2...Gravity type sewage, 4...Main sewage pipe, 6...First conduit, 8...Second conduit, 10...Oxygenator (oxygen addition) device, 12...Downward leg, 14...Upper Head leg, 1
6...Vertical hole (vertical hole shaft), 18...Inner pipe, 2
0... Lid, 22... Dam, 24... Gaseous oxygen supply source, 26... Conduit, 28... Annular pipe, 30... Distributor, 32... Outlet, 34... Batsuful.

Claims (1)

[Claims] 1. A method for preventing the production of hydrogen sulfide by bacteria in gravity-type sewage, in which a flow of untreated sludge is caused in sewage and the flow is made into a flow having a long downward leg and a long upward leg. Direct the flow from the sewage along the channel and direct the flow from the downward leg to the upward leg, and at a point in the channel spaced apart from the top of the upward leg, the upward leg and the downward leg oxygenating the sludge by introducing an oxygenating gas into the sludge in at least one of the legs;
The above method is characterized in that it includes the steps of returning the oxygenated sludge to sewage. 2 sludge discharge from the sewage into the channel and oxygenated sludge return to the sewage can be carried out without the aid of pumping equipment or the oxygenating gas in the sludge rising up the upward leg of the channel. Claim 1 carried out with the help of floating gas effect of a large number of bubbles
The method described in section. 3. A downward leg and an upward leg of the channel are provided in a vertical hole, an inner tube, shaft or tube is placed in the vertical hole, and the downward leg connects the inner tube, tube or shaft with the vertical hole shaft. Claims 1 or 2, in which the upward leg is defined by the inner tube, tube or shaft, or vice versa.
The method described in section. 4. A method according to claim 3, wherein the depth of the well is sufficient to provide a liquid head of at least 9 m. 5. The method according to any one of the preceding items, wherein the oxygenating gas is introduced into the sludge flowing along the flow path in the form of a large number of bubbles. 6. The method according to claim 5, wherein the diameter of the bubbles is 0.1 mm or less. 7. A method according to claim 5 or 6, wherein the oxygenating gas is introduced at the area(s) close to the bottom of the upward leg. 8. The gas flow flowing from the upward leg to the oxygen-deficient area of the sewage may affect the oxygen concentration in the oxygen-deficient area to the extent that the oxygen concentration in the oxygen-deficient area is significantly higher than the atmospheric oxygen concentration. The method described in any one of the preceding items, in which oxygenation is performed to prevent 9 1/4 to 1/3 of the sludge flow through gravity sewage is divided (converted) via the flow path (under average flow conditions in the dry season) as described in any one of the preceding items. Method. 10. The method of any one of the preceding clauses, wherein the rate of oxygen dissolution into the sludge passing along the flow path is selected to achieve a dissolved oxygen concentration of at least 20 ppm. 11. The method according to any one of the preceding items, wherein the oxygenating gas is oxygen of commercial grade purity. 12. A method according to claim 1, substantially as disclosed with reference to the accompanying drawings, for the prevention of hydrogen sulfide production by bacteria in gravity sewage. 13. In a device attached to a gravity sewage system operable for the prevention of hydrogen sulfide production in sewage by bacteria, an elongated upward leg and an elongated downward direction directing sludge flow into the elongated upward leg. a first conduit directing sludge flow from the sewage to an oxygenator defining a flow path having an upper leg and a lower leg at a point in the flow path spaced from the top of the upper leg; means for introducing oxygenating gas into the sludge of at least one of the legs, and a second conduit for directing the oxygenated sludge from the top of the upward leg so that it can be returned to the sewer. The above device characterized by: 14 by providing at least one gas distributor for introducing the oxygenating gas into the sludge in the form of a number of bubbles in the area(s) of the uplift leg close to the bottom of the uplift leg; Claim 13, characterized in that the at least one gas distributor enables the discharge of sludge from the sewage into the flow path and the return of the oxygenated sludge to the sewage without the aid of pumping equipment. The device described. 15. Apparatus according to claim 14, wherein the distributor comprises porous gas distribution means made of sintered material. 16. Both legs of the oxygenator are installed in a vertical hole, in which an inner tube, shaft or cylinder is placed, and the downwardly directed leg connects the inner tube, cylinder or shaft by means of the space between the vertical hole and the shaft. 17. A device according to any one of claims 13 to 16, in which the upward leg is defined by the inner tube, cylinder or shaft, and vice versa. 17. The device of claim 16, wherein the depth of the well is sufficient to provide a liquid head of at least 9 m. 18. Device according to claim 16 or 17, in which the inner tube, tube or shaft can be removed from the vertical hole. 19. Apparatus according to claim 13, which is attached to a gravity sewage system operable for the prevention of bacterial hydrogen sulfide production in sewage water, and which is substantially as disclosed with reference to the accompanying drawings.