CA1092259A

CA1092259A - Installation for anaerobic purification of waste water

Info

Publication number: CA1092259A
Application number: CA281,279A
Authority: CA
Inventors: Robbert De Vletter; Evert Wind
Original assignee: Centrale Suiker Maatschappij NV
Current assignee: Corbion NV
Priority date: 1976-06-24
Filing date: 1977-06-23
Publication date: 1980-12-23
Also published as: SE425307B; ATA450377A; BE856081A; GB1579277A; NL166000C; NL166000B; FR2355783A1; DE2728585C3; DK147971B; NL7606904A; DE2728585B2; FR2355783B1; SE7707250L; DK147971C; DE2728585A1; DK279477A; AT356021B

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to an installation for anaerobic purification of waste or effluent water by means of a reactor, loaded with anaerobic sludge in which an after-settler device is provided, which separates a settling zone from an anaerobic decomposition zone, and means are provided for using the developed methane gas as a transport aid of the anaerobic sludge particles and for separating said gas from said particles.

Description

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The invention relates to an improved installation ~or the anaerobic purification of waste or effluent water comprising organic decomposable im-purities.
m e installation comprises a reaction or decomposition zone into which waste water comprising impurities is fed.
It is known, that waste water comprising decomposable organic sub-stances can be purified by an anaerobic microbial decomposition process, wherebymethane and carbon dioxide are being formed.
The use of this process for the direct purification of waste water, particularly of concentrated industrial effluent water has been tried, but it sho~-ed several disadvantages. A stable fermentation process can hardly be obtained, and a useful practice comparable with aerobic purification could not be realised in a technical scale. In the ~ournal ~'H20"(1974), Nr. 7, pp. 281-289 the state of the art has been given, with a comprehensive literature ; reference.
It has been described in said publication, page 281, that in using a methane-developing fermentation for the treatment of less concentrated waste -water (having 0.1 through 0.5% by weight of organic matter), one of the most important problems i3 to find a practically acceptable ~ay for separating the sludge. A stable methane-developing fermentation can be accomplished in a continuous way only if the total amount of active bacterial material in the reactor can be maintained at a constantly high level.
On page 283, Figure 1 of said publication an experimental device is shown, wherein a setting zone next to and at the top of a recipient for the - -interception of the gas is provided, said recipient at its lower side having a circular opening, which serves as the inlet as well as the outlet of the after-settler. With such a device a stable and continuous process cannot be achieved.
The problems reflected, which relate to the experiences as described with an experimental device having a contents of 16 liters are being still more severe with industrial reactors having a volume of dozens or several hundreds ~ .
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In the existing conventional sludge fermentation tanks e g. a reten-tion period of the entire mixture of about 30 days is a normal feature. For an efficient purification of waste water this sludge retention period (i.e.
life-time of the sludge) might not be made shorter (at least 10 days, see the above publication, page 287 at the bottom), while at the same time the rete~-tion period of the liquid should be reduced to several hours (viz. 3 through 6 hours). An effective purification can be achieved in such a short period only if relatively high concentrations of sludge are present in the reactor (i.e. dozens of grams per liter). In order to obtain this, an eff~ciently working system is necessary, wherein the following requirements are met-~1. The ascending gas bubbles are being collected, and the gas will be removed efficiently, such that no foam or liquid droplets will be entrained.

2. The liquid is separated from the mixture of sludge and liquid in such a way that a substantially sludge-free effluent will be produced.

3. me sludge separated from said liquid will be concentrated and be recycled into the reactor zone at the highest possible rate.
The separation of sludge and effluent in the conventional aerobic purification system is in general carried out by means of an after-settler separate from the aeration zone, and the concentrated sludge is recirculated into the aeration zone through a conduct by means of a pu p or by other means.
Since in aerobic systems considerable sludge formation is obtained, part of the concentrated sludge is cocurrently removed from the system (gutter sludge).
This is entirely different from anaerobic purification, for the followine reasons:
; a) In view of minor sludge formation only small amount of sludge has to be removed.
b) There is no need for using the underflow of the after-settler in order to obtain a concentrated gutter sludge, since at the bottom of the reactor there ~ .

exists a very high sludge concentration as a result of the good settling properties of the anaerobic sludee.
c) m e retention period of the sludge outside the reactor ought to be restricted to a minimum, because otherwise gas formation and flotation might -- -occur, such that the function of the settler device would become inefficient.
Several attempts to use anaerobic purification on industrial scale have failed, substantially for reasons of the issue mentioned in the last-above passage.
It is an ob~ect of the present invention to comply with the require-ments as mentioned in the above under 1 through 3, without occurrence offlotation and of other proble~s.
It is a further ob~ect of the present invention to obtain the following advantages:
- Simple construction - Easiness of access to all constructional parts - Absence of moving constructional parts, including recycling pump devices '''' '' ' i,--.. .... .

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- Possibility of an optimal adaptation of the installation to the typical properties of a certain envisaged type of waste water and of sludge, as well as to the input ch~rge, by a proper selPction of the mutual ratios of dimensions and by a control or adjustment of the inlet-opening or openings of the settler-device.
- A continuous process.
Still another object of the present invention is to provide a compact efficient installation for the anaerobic purification of industrial and/or domestic waste waters or effluents.
Other objects will be elucidated by the specification in detail of the invention, by the Figures enclosed and by the claims.
Detailed specification of the invention:
In order to comply with all the requirements mentioned in the above, use is made according to the present invention of the principle, that a column of a liquid in which gas-bubbles are present, will have a lower specific weight than a liquid without such bubbles.
This principle, upon which the known device of the mammoth pump is based, renders a number of specific advantages as well as disadvantages as compared with other types of pumps, and it is used only in special fields.
Surprisingly, it has been found according to the present invention that this principle can be used to transport the liquid from the anaerobic reactor zone into the after-settler compartment and to recycle the sludge back into the reactor, without an input of energy and without moving mechanical parts.
According to the present invention, there is provided an installation for the anaerobic purification of effluent or waste water by means of an anaerobic reactor, comprising a reactor tank or container with an after-settling compartment in an upper part thereof for separating sludge and liquid, characterized in that said after-sett~ng compartment comprises a supply open-ing for entry of a mixture of sludge and liquid from a reactor zone in the reactor tank and a lower-positioned outlet opening to said reactor zone, whereby the sludge, separated by settling in the after-settling compartment

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returns with liquid into said reactor zone, while deflecting means is provided in the reactor zone, which shields the supply opening and the outlet opening to and from said after-settling compartment respectively so that upward flow of developed gases is kept away from said openings, a shield for said supply opening being positioned much higher than said outlet opening so that developed rising gas entrains liquid and sludge upwardly to said supply opening in the reactor zone to cause circulation of liquid and sludge into and from the after-settling compartment and from and into the reactor tank respectively, separate interception and outlet means for said developed gases permitting an amount of anaerobic sludge to be continuously separated and recycled such that the purification process by fermentation proceeds continuously and equably.
In another aspect, the invention provides a pTocess for the anaerobic purification of effluent or waste water in a reactor tank, comprising having gas generated by fermentation of bacteria therein flow upwards so as to lift water and sludge to an inlet opening to an after-settling compartment in an upper part of the reactor tank, separating the gas from said water and sludge near said inlet opening so that the gas is guided away from said inlet open-ing and water and sludge flow through said opening into the after-settling compartment, withdrawing purified water from an upper part of said compartment and allowing sludge settled in the after-settling compartment to flow back into the reactor tank through a discharge opening in the bottom of the after-settling compartment at a distance below said inlet opening, deflecting rising gas below said discharge opening so as to prevent it from rising therethrough into said after-settling compartment, generating a circulation of water and sludge from the reactor tank into said after-settling compartment -and said sludge returning from said compartment into the reactor tank by means - of said gas flowing upwards in the reactor tank.
The installation is preferably provided with means for the control -and adjustment of the height of the inlet openings of the after-settler.
The inlet opening into the after-settler is positioned in top of a shielding bulkhead which conducts the ascending gas bubbles in a direction ' C '":
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at the side of the horizontal projection of said inlet opening into the interception zone for same, while the liquid with sludge is allowed to flow around said bulkhead to the inlet opening.
The outlet opening at the bottom of the after-settling compartment is positioned higher than the bulkhead which is placed oblique or horizontally in the reactor zone and which prevents the ascending gas bubbles to reach the outle~ opening.
Over the bulkhead is a vertical channel a vertical wall of which being substantially protruding into an overflow to the after-settler compart-ment, said wall under said overflow forming an intercepting zone with thewall of the after-settling compartment, wherein the gas is intercepted and from which the gas can be removed under controlled overpressure.

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ZZ~i9 The after-settline compartment is widening in a conical way in the upward direction and it has at its top a zone to collect foam which is open at its lower side, and delimited by a wall, into which protrude one or several tubings, leading from that wall of said after-settling compartment in an oblique way upward until said delimiting wall, such that inlet openings are formed for the mixture of sludge and water to pass into said after-settling compartment.
The installation comprises ad~ustable means for the control of the height of the inlet opening for the mixture of sludge and water to pass into the aM er-settling compartment.
One or several tubes may be constructed in a sliding way movable along their longitudinal axis such that the height of the inlet opening from the reactor zone into the after-settling compartment at the end of said tubes protruding into said reactor zone may be varied in a controllable way said sliding tubes are positioned in fixed tubes which extend from the wall of the after-settling compartment to the wall of the foam collecting zone.
From German Patent Specification 275,498 an installation is known for the treatment of waste water sludge, in which the fresh sludge is mixed with Permented sludge. In a reaction compartment a mixing funnel can be placed in such a position that the installation shows some resemblance to the instal-lation according to the present invention.
However, in this device according to German Patent Specification 275,498 the fresh sludge is directed into the mixing funnel, flowing out of same at the bottom and is mixed with fermented sludge, and the ascending gas is substantially directed to the bottom of said funnel in order to improve the sludge mixing.
The invention is further explained with reference to the en~losed drawings, which represent a schematic view of the installations with devices according to the present invention, and which are given only by way of example and should not be regarded as a limitation.
In these drawings, the following is depicted:
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, - ~09ZZ59 Figure 1 shows a radial sectional view of a cylindrical installation which is an embodiment of the invention.
Figure 2 shows a prespective view of a rectangular installation which is an embodiment of the invention.
Figure 3 shows a longitudinal sectional view of another rectangular embodiment of the installation according to the invention, wherein a gutter channel is positioned between the 2 compartments of the after-settling compartment.
In these figures the following parts are shown:
1 - reactor wall 2 - wall of the after-settler 3 - conducts forming the inlet openings into the after-settler 4 - zone for collecting foam

5 - bulkhead under inlet openings --

6 ~ bulkhead under outlet openings

7 - gas conveyance

8 - over flow drain

9 - gas collecting zone

10)- horizontal planes wherein between the liquid columns 12 and 13 are 113 positioned 12 - column of liquid in the after-settler with much sludge and without gas bubbles 13 - column of liquid outside of the after-settler having less sludge but with gas bubbles The after-settling compartment in Figure 1 has the shape of a circular funnel or knotted cone with an angle of slope of e.g. 45 having an opening 14 at its lower side. In said funnel openings 15 may be present at e.g. four positions, wherein the conducts 3, in this example cylindrical pipes, have been fixed. In Figure 1 also for this item a slope angle of 45 has been selected such that the axle of the pipes is perpendicular to the wall of said funnel. However, this is not obligatory for the function of the device. The ~! ~. .
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four pipes 3 reach into the central zone 4 which is open at it3 l~wer an~
upper sides.
Under each pipe 3 there is a bulkhead 5 e.e. consisting of a semi-cylindrical piece of pipe which prevents gas bubbles ascendine to reach into the pipes 3, since said bubbles during said ascending are directed into a direction outside the reach of the openings 15 by means of the bulkhead shield-ing.
Under the opening 14 of the funnel a shape 6 is positioned, which is made of two conical parts. By this shape ascending gas bubbles are directed to the s~de outside the reach of the opening 14; also the recycling of the sludge from zone 2 into the reactor is directed in a controlled way.
m e reactor wall ~ has not been depicted much lower than the bulkhead 5, however, this zone is extending lower in a distance of 2 to 4 meters, viz.
at least in a distance of the same height as that of the after-settling compart-ment 2. At the bottom of the reactor compartment there is an inlet for the waste water to be treated, which might be sub~ected to a prepurification, and furthermore there is an outlet for drawing off and cleaning of the installation,said outlet may be closed during normal function of the installation.
me function of the installation is as follows: -An amount of water with active sludge for anaerobic decomposition is fed into the Peactor zone of the tank and continuously waste water to be purified is added. By the fermentation reaction gas bubbles are being formed in the liquid and the impurities of the waste water are gradually decomposed into methane and some carbon dioxide and water. m e gas functions as a bubble pump, ; and around the after-settling compartment 2 an upward effect is carried out in the liquid. Thus said liquid is flowing with part of the sludge through open-ings 15 into the conducts 3 and therefrom into the foam collecting zone 4, where the foam is floating upon the liquid and may be removed either by skimming -means or by separate (not depicted) overflo~ or by chemical agents. Water and - 30 ~ludge drop into the funnel of the after~settling compartment, and at the bottom ;

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of the funnel a higher concentration of sludge is effected. The mixture leaves the funnel 2 through opening 14.
The ascending gas bubbles do not flow with the liquid into the open-ings 15 but are directed with liquid around the shielding bulkhead 5, such that the liquid can reach said opening but the gas bubbles rise till the zone 9 wherefrom the gas is carried off through the gas exit 7 under a certain over-pressure which is sufficiently high to have some gas remaining in the zone 9, ~n spite of the higher liquid level in the after-settling zone 2.
The circulation of the liquid and the sludge as described takes place mainly by the difference in specific gravity of the mixture of water sludge and ~-gas bubbles in the zone between the level lines 10 and 11, i~.e. over the column 12 ~ithin the after-settling compartment 2 and the column 13 outside of this compartment in the reactor~ Within the after-settling compartment an ascending liquid flow is superposed upon said circulation movement, whereby the liquid in the foam collecting zone 4 flows downward and splits into two flow streams in the lower part; this results in a descending flow to the opening 14 with the concentrated sludge and an ascending flow around the zone 4 to the overflow ô, and said fl~ i compensated by the waste water to be treated which is fed at the b~ttom of the installation.
The flow due to the overflow 8 will arrive in a zone which is gradual-ly widening in a direction to the top, and thus the flow rate is decreasing, with the result that the liquid will be stripped of sludge particles in an efficient way.
Into the conduct pipes 3 inner pipe 16 may be telescoped, which may be pushed in the conduct pipes and back, in order to vary the height of the inlet openings 18 at their lower ends, such that an inherent circulation in the natural manner can be ad~usted and controlled as described in the above.
In Figure 2 a rectangular reactor tank is depicted, in this figure the front and back walls are omitted, as well as the lower part of the reactor tank, for a better understanding of the invention.
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-` lO9ZZ59 In said lower part of the reactor tank there is an inlet for the waste water to be treated, and this lc~er part i8 about as hiBh as the part of the installation displayed.
In this embodiment as shown, the bulkheads 5 and 6 for directing the gas bubbles are made in the form of straight shaped beveled bodies of sheet material as shown in the drawing, said bulkheads shielding the rectangular openings 14 and 15 in top of them from ascending gas bubbles, such that said bubbles cannot reach the zone 9 and cannot ascend inside said openings 14 and -~
15. Another bulkhead 19 forms a separation between the surface of the foam collecting compartment 4 and the surface of the compartment from which the purified effluent is drained through the overflow gutter 8. Vertically ad~ust-able bulkheads 20 and 21 are used for the control of the supply into the after-settling compartment and the removal from the reactor zone through opening 15.
In Figure 3 two after-settling compartments 2 ad~acent to each other are depicted, which may have either circular or rectangular horizontal sectional shapes. At the ad~acent sides there are vertical conduct pipes 3, in the cen- ~ -tral part a mutual conduct channel 3 for both after-settling compartments, further this installation is in principle substantially equal to that as shown in Figures 1 and 2. -~, Further to these embodiments other types can be constructed, wherein the use of the same principle as the above is applied, since said principle may be used for general applications in several different kinds of constructions of after-settling installations.
The following example is described for the understanding of one particular embodiment of such an installation according to the present invention.
Example:
i In a cylindrically shaped reactor tank having a contents of 6 m3 an after-settling device according to Figure 1 had been assembled. The distance between both horizontal planes 10 and 11, which caused the effect of the sludge after-settling device, was 25 cm. Into this reactor sludge waste water was " " ~ ,................................................................. .
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10~'~2S9 supplied at the sump of the tank with a rate of 1 m3 per hour. m e chemlcal oxygen demand (C.O.D.) of the supplied fluid was 3000 gram per m3 The reten-tion time was 4 hours.
Initially into this reactor a sludge had been supplied as an inocu-lating material from a sludge fermentation tank of a municipal waste water purification installation. After a short period of adaptation the amount of gas developed was 1 m3 per hour comprising about 90% by volume of methane (natural gas).
me growth or increase of sludge was very small, which is inherent to anaerobic decomposition, it appeared to be practically possible to separate the sludge from the flow in such an efficient way that a concentration of 35 through 40 gram organic sludge material per liter fluid could be maintained in the reactor.
m ere were no disturbances in continuous operation, and the efficacy has been proven by the fact, that at a retention time of 4 hours of the liquid -a retention time of the sludge material of 25 days was observed.
mus, in a very economical way a purification of waste water has been obtained by means of the installation according to the present invention, while methane had been recovered, which could be used as an energy source.
me purified water showed the properties as required by environmental authorities.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An installation for the anaerobic purification of effluent or waste water by means of an anaerobic reactor, comprising a reactor tank or container with an after-settling compartment in an upper part thereof for separating sludge and liquid, characterized in that said after-settling compartment comprises a supply opening for entry of a mixture of sludge and liquid from a reactor zone in the reactor tank and a lower-positioned outlet opening to said reactor zone, whereby the sludge, separated by settling in the after-settling compartment returns with liquid into said reactor zone, while deflecting means is provided in the reactor zone, which shields the supply opening and the outlet opening to and from said after-settling compartment respectively so that upward flow of developed gases is kept away from said openings, a shield for said supply opening being positioned much higher than said outlet opening so that developed rising gas entrains liquid and sludge upwardly to said supply opening in the reactor zone to cause circulation of liquid and sludge into and from the after-settling compartment and from and into the reactor tank respectively, separate interception and outlet means for said developed gases permitting an amount of anaerobic sludge to be continuously separated and recycled such that the purification process by fermentation proceeds continuously and equably.

2. An installation as claimed in claim 1, characterized in that said supply opening to said after-settling compartment is positioned above a deflecting bulkhead, that directs the ascending gases sideward from the horizontal projection of said supply opening into the interception compartment for said gases, while the liquid with sludge is enabled to flow around said deflecting bulkhead into said supply opening.

3. An installation as claimed in claim 2, characterized in that a vertical channel is positioned in top of said deflecting bulkhead, a substantially vertical wall of which terminates at its upper side in an overflow to the after-settling compartment, said wall delimiting, together with a wall of said after-settling compartment, and beneath of said over-flow, an interception compartment for the gases, which is connected with an outlet for gas under some overpressure.

4. An installation as claimed in claim 1, characterized in that said outlet opening in a sump of the after-settling compartment is positioned over an oblique or horizontal bulkhead or shape in said reactor zone, preventing ascending gas bubbles to enter said outlet opening.

5. An installation as claimed in claim 1, characterized in that the after-settling compartment widens in upward direction and has at its upper inner side a compartment for collecting foam which is open at its lower side, and which is delimited by a raised border, into which one or several pipes are directed, which extend from the wall of the after-settling compartment in an oblique position upward to said raised border, thus forming supply openings intended for directing the mixture of sludge and liquid into the after-settling compartment.

6. An installation as claimed in claim 1, characterized in that adjustable means are present to vary the height of the supply opening of the mixture of sludge and water which is substantially freed of gas and directed into the after-settling compartment.

7. An installation as claimed in claim 6, characterized in that one or several pipes are longitudinally movable in a telescopic way in order to vary the height of the supply opening of the reactor zone into the after-settling compartment at the end of said pipes which protrudes into said reactor zone.

8. An installation as claimed in claim 7, characterized in that the telescopically movable pipes are pushed in fixed pipes which extend from the wall of the after-settling compartment to the raised border of the compartment for interception of foam.

9. An installation as claimed in claim 1, characterized in that said reactor zone has a rectangular horizontal section and that said after-settling compartment is delimited by one single oblique bulkhead extending entirely between two opposite walls of said reactor compartment, while a supply opening to the after-settling compartment is present at one end of said bulkhead and an outlet opening from the after-settling compartment is present at the other end of said bulkhead.

10. An installation as claimed in claim 1, characterized in that in the upper side of the reactor tank two or several after-settling compartments are positioned.

11. A process for the anaerobic purification of effluent or waste water in a reactor tank, comprising having gas generated by fermentation of bacteria therein flow upwards so as to lift water and sludge to an inlet opening to an after-settling compartment in an upper part of the reactor tank, separating the gas from said water and sludge near said inlet opening so that the gas is guided away from said inlet opening and water and sludge flow through said opening into the after-settling compartment, withdrawing purified water from an upper part of said compartment and allowing sludge settled in the after-settling compartment to flow back into the reactor tank through a discharge opening in the bottom of the after-settling compartment at a distance below said inlet opening, deflecting rising gas below said discharge opening so as to prevent it from rising therethrough into said after-settling compartment, generating a circulation of water and sludge from the reactor tank into said after-settling compartment and said sludge returning from said compartment into the reactor tank by means of said gas flowing upwards in the reactor tank.