GB2165831A

GB2165831A - Effluent purification installation

Info

Publication number: GB2165831A
Application number: GB08523556A
Authority: GB
Inventors: Botho Bohnke; Bernd Diering
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-10-18
Filing date: 1985-09-24
Publication date: 1986-04-23
Also published as: ATA278485A; IT8522352A0; GR852512B; BE903441A; DE3438198C2; ES547807A0; NL8502833A; CN1015885B; IT1185987B; FR2572067A1; CH671570A5; ES8608451A1; CN85108394A; FR2572067B1; GB8523556D0; DD237646A5; TR24358A; AT393263B; DE3438198A1; GB2165831B

Abstract

An effluent collector (1) precedes the mechanical purification stage. The mechanical purification stage possesses a preliminary purification contrivance (2) such as a rake, a sand-trap tank (3) with aeration equipment (4), and subsequent intermediate clarifier equipment (5) with a sludge offtake (6). Before erection of the subsequent biological purification stage (8) it can be independently operated by itself as a basic constructional stage, and after erection of the subsequent biological purification stage it can be operated in combination with the latter. <IMAGE>

Description

SPECIFICATION Effluent purification installation This invention relates to an effluent purification installation functioning in more than one stage, that can be erected and put into operation in several constructional stages, with a mechanical purification stage and, in the fully constructed state, at least one subsequent biological purification stage, in which an effluent collector precedes the mechanical purification stage and in which the mechanical purification stage possesses a preliminary purification contrivance in the form of a rake or the like, a sand-trap tank with aeration equipment and a subsequent intermediate clarifier equipment with sludge offtake, and which also can be independently operated by itself as a basic constructional stage before erection of the subsequent biological purification stage, and after erection of the subsequent biological purification stage can be operated in combination with the latter.

In the known similar effluent purification installation the sand-trap tank possesses a volume corresponding to a volume requirement of a maximum of four litres per inhabitant ("inhabitant" here and in the following also standing for "inhabitant equivalent".) The aeration does not convert the sand-trap into a definite activation tank. Controlled withdrawal of activated sludge for the purpose of bringing about specific biological operating conditions in the aerated sand-trap does not take place.

Although the basic stage forms the first constructional stage it nevertheless remains collectively a mechanical purification stage. The purification efficiency that can be achieved is meagre and well below 30%. The use of the mechanical purification stage as basic constructional stage is more of a stop-gap measure than a feature that is to be recommended in effluent treatment. If a biological purification stage or several of them are added as a further constructional stage, then the full cost of building is necessary for the combined operation, having for example a volume requirement of about 179 litres per inhabitant with a purification efficiency of some 93%. As part of the known practice the first biological purification stage that follows the above-described mechanical purification stage is a low-load stage.

On the other hand effluent purification plants with a plurality of biological stages are known (cf.

German Patents 26 40 875 and 3117 805) in which the first biological stage is operated as an adsorption stage at very high load with a sludge loading of 2 to 12 and the second biological stage is operated at low load (the sludge loading here and in the following is expressed as kg. BOD5 per kg. of dry substance per day.) In the adsorption stage the sludge is maintained in the initiation phase. The initiation phase is as it were the phase preceding substrate respiration in which the enzymes necessary to decomposition of the substrate are formed.

The initiation phase is consequently the boundary area in which substrate respiration is just starting but is not yet fully effective. In order to maintain the sludge of the first activation stage in this condition a low sludge age and a correspondingly controlled removal of excess sludge from the intermediate clarifier are necessary. In conjunction with the stated volume requirement of the first activation stage it results that the principal action in that stgage is adsorption or flocculation of high molecular weight compounds and these compounds, without decomposition, are discharged with the excess sludge in the intermediate clarifier. This saves the considerable energy that would otherwise be necessary for the decomposition of these compounds.Subsequently the low molecular weight and easily decomposable compounds can be biologically decomposed very easily and rapidly in the second activation stage if this is operated with a sludge loading of about 0.15. Accordingly quite different operating mechanisms are active in the two activation stages. A preliminary mechanical purification stage is used as before.

The invention is based on the realisation that this adsorption technology can contribute considerably, both in construction and in operation, to the further development of effluent purification installations that can be erected that brought into operation in several constructional stages. Hitherto effluent purification installations have not been installed and operated in accordance with the freatures of adsorption technology.

The object of the invention is to develop an installation of the type initially described that even when the basic construction stage is operated on its own a considerable purification efficiency of some 30% and considerably more can be achieved, and that after further construction and with a total volume requirement of merely 100 litres or less per inhabitant purification efficiency can be achieved in combined operation that is at least equal to or even considerably greater than that of the known methods.

According to the present invention, the sand-trap tank has a volume corresponding to a volume requirement of at least 6 litres and preferably 8 litres per inhabitant and is equipped to serve as an adsorption stage i.e., as an activation stage, that is operated in the aerobic and/or optionally anaerobic region with a sludge loading L55 equal to or greater than 2, (LDS = LJDS with Lv representing the volume loading in kg. BOD5 per cubic metre per day and DS representing the dry substance content in kg. per cubic metre) and in which the sludge can be maintained in the initiation stage by means of the intermediate clarifier and the sludge offtake therefrom. The oxygen content in the adsorption stage is to be maintained within the range of from 0.5 to 1.0 mg. per litre.

The invention makes use of the fact that by the means described the sand-trap tank of the known installation of this kind can operate as an adsorption stage. It thereby achieves, with increase of building cost of merely some 2% relatively to the whole effluent purification installation, a purification efficiency of 30% and more when operated by itself. If the design is so arranged that sludge recycling facilities are connected to the intermediate clarifier equipment or to the sludge offtake and fed into the effluent collector of a minimum of 20%, and preferably about 40% to 65%, of the sludge withdrawn from the intermediate clarifier then when the equipment is operated by itself it can attain a purification efficiency as great as 60% at small additional cost.The sludge return takes place at an adequate distance in advance of the mechanical purification stage, in any case before the sandtrap tank. When the equipment is operated by itself the excess sludge can, as is normal, be conveyed to a septic tank. The possibility however also exists that when the equipment is operated by itself the sludge that is not recycled can for further treatment without a septic tank be conveyed to equipment for the addition of calcium salts or iron salts (or other conditioning materials) and subsequently to a chamber filter press. Also when the equipment is operated by itself the outflow from the intermediate clarifier can be directly conveyed to equipment for the irigation and/or fertilization of agricultural crops.

If the basic stage is erected in -accordance with the invention, then further construction can be installed in various ways. One of these possibilities is characterized in that in combined operation the subsequent biological purification stage is installed as the second constructional stage and as an activation tank for sludge loading LDS in the range of 0.15 to 1, is connected to the outlet of the intermediate clarifier equipment and is equipped with a final clarifier equipment with sludge offtake. Then a trickle filter stage with a volume lodding of 0.2 to 2 or more, according to its filling, can as a further constructional stage be located between the intermediate clarifier and the activation tank of the second constructional stage.If the filling is of chippings a volume loading of 2 will not be exceeded, but if it is of plastics a volume loading as great as 6 is possible. Another possibility is characterized in that in combined operation the subsequent biological purification stage is constructed as the second constructional stage and as a trickle filter stage with a subsequent activation tank equipped for sludge loading of 0.05 to 1 and the activation tank is attached to a final clarification equipment with sludge offtake. It is within the scope of the invention to connect the trickle filter stage directly to final clarification equipment.In all cases the effluent in the basic constructional stage or adsorption stage does not only undergo the purification described but additionally, so far as concerns the discharge that is directed into the subsequent stages, an effective treatment or preparation for further purification, similar in its nature to "cracking".

The basic constructional stage works particularly effectively with high sludge loading when bacteria alone dominate the situation. The is preferably ensured (cf. German Patent 33 17 371) in that the adsorption stage is operated with procaryotic cells as working biomass and that procaryotic cells that per cubic metre amount to at least 1% by weight of the working biomass in a cubic metre of the adsorption stage are continuously introduced into the adsorption stage with the inflowing crude effluent as make-up biomass, preferably in a quantity of 5% to 15% by weight per cubic metre. In this connection strict separation of the bacterial colonies between the basic constructional stage/adsorption stage and the subsequent stages can be advantageous.Good results however are also achieved if in combined operation at least a part of the excess sludge removed from the final clarification equipment can be re-introduced, via suitable feedback equipment, into the sand-trap tank acting as adsorption stage.

Tests have in fact shown that the high sludge loadings Lids, as specified for the adsorption stage, the bacteria alone dominate the situation. Sludge production in the adsorption stage is then seven to ten times greater than in the subsequent lowloaded activation stages. The proportion of eucaryotes, which devour bacteria, in the adsorption stage and accordingly in the basic construction stage of the purification installation according to the invention is relatively low. The bacterial population in the subsequent activation stages has approximately the same composition as that in the adsorption stage, but as a rule the bacteria in the subsequent activation stages exhibit markedly less activity.These characteristics, particularly the high bacterial sludge production with a sludge yield increased by seven to ten times leads, as it were, in spite of the recycling of the excess sludge from the final clarification equipment, to a dilution of the eucaryotes population and thereby to considerable weakening and washing-out of the eucaryotes from the bacterial colonies of the adsorption stage. The chances of survival of eucaryotes in these so markedly bacterialy-orientated colonies of the adsorption stage are very small, so that by the indicated supply of procaryotic cells with the inflowing raw effluent the sludge feedback described can be carried out.

In summary, the advantages achieved are to be seen in that with an effluent purification installation according to the invention, even when the basic construction stage is operated on its own as first construction stage, a considerable purification efficiency of some 30% or more can be achieved, and this with minimum additional constructional expense. Merely by re-cycling the sludge the purification efficiency can in this case be increased to about 60%. After further extension one can obtain in combined operation with a total volume requirement of merely some 100 litres per inhabitant, or less, a purification efficiency that is at least equal to or even greater than that of the known type of installation (with a volume requirement of 179 litres per inhabitant). Further advantages may be summarized as follows: First of all, at the expenditure for mechanical purification the purification efficiency of the first construction stage is practically doubled, compared with the known methods. A further biological stage can be built later without difficulty, so that the final purification efficiency can be made practically as great as desired by this subsequent building or building-on, coupled with combined operation. If one works merely with the first construction stage, i.e. with the basic stage designed according to the invention, an addition of calcium salts or iron salts is however carried out, or other precipitating agents are applied, so that the sludge can be further processed in a chamber filter press.It is possible to produce combustible filter cakes which enable twice as much energy to be derived from the sludge as is possible with methane gas extraction from septic tanks. Even the basic construction stage allows use to be made of all microbiological reaction mechanisms, which lead to continuous improvement by mutation of strains of bacteria and thereby also ensure markedly better stability of the process under sudden peak loads. In agriculturally-based countries, and particularly in areas where there is a shortage of effluent water, such well-prepared, nutritous water is produced by the basic constructional stage of the invention alone that it can be used both for fertilization and for irrigation purposes. In addition to this, methane gas is produced and by use of a septic tank a nourishing sludge for agriculture is accumulated.

An embodiment of the invention and a modification thereof will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a fully constructed effluent water purification installation according to the invention; Figure 2 shows the basic constructional stage of the installation of Figure 1, on an enlarged scale; Figure 3 shows an extended basic constructional stage according to Figure 2; Figure 4 corresponds to Figure 1, but shows a known effluent water purification installation; and Figure 5 also corresponds to Figure 1, but shows another form of construction of an effluent water purification installation according to the invention.

The effluent water purification installations represented in Figures 1, 4 and 5 can be erected and put into service in several stages of construction and operate in a plurality of functional stages. The fundamental construction consists of a mechanical purification stage and, in the fully-developed condition, at least one subsequent biological purification stage. An effluent water collector, indicated by the thick line 1, precedes the mechanical purification stage. The mechanical purification stage possesses preliminary purification equipment in the form of a rake 2 or the like, a sand-trap 3 with aeration equipment 4 and subsequent intermediate clarifier equipment 5 with sludge offtake 6. The expression "intermediate clarifier equipment" is used because this clarifier equipment functions as an intermediate clarifier 5 in the fully constructed state of the installation.The mechanical purification stage can be operated independently and on its own as the basic constructional stage, i.e., before the subsequent biological purification stage is erected. After erection of the subsequent biological purification stage it can be operated in combination with the latter.

Figures 1 and 5 show fully-built installations according to the invention. Figure 4 on the other hand shows the known form of construction. By comparative examination of the sand-trap tank 3 of the installation according to the state of the art on the other it is seen that sand-trap tank 3 of the in stallation according to the invention is larger. In Figures 1 and 5 the sand-trap tank 3 possesses a volume corresponding to a volume requirement of at least 6 litres and preferably 8 litres per inhabit ant. In Figure 4 this volume requirement is about 4 litres per inhabitant. The sand-trap tank 3 in Figure 1 to 3 and 5 is equipped to serve as an adsorption stage.This means that sand-trap tank 3 works as an activation stage in the aerobic and/or optionally annaerobic range, this being with a sludge loading LDS equal to or exceeding 2, whilst in this sand-trap tank 3 which works as an adsorption stage the sludge can be maintained in the initiation phase by means of the intermediate clarifier 5 and the sludge offtake 6 that forms part of it. Thus a purification efficiency of some 33% is obtained if the basic stage is operated on its own. This corresponds in practice to a doubling of the purification efficiency that can be obtained by operation on its own of the basic constructional stage of an installation according to the state of the art (see Figure 4). The building cost is however, increased by only 2% compared with the total cost.Figure 3 shows the possibility that with small additional cost an improvement of the purification efficiency up to about 60% can be achieved. It can be seen that here where the basic stage is operated on its own sludge recycling equipment 7 is provided at the intermediate clarifier equipment 5 (or its sludge offtake 6) for the introduction of at least 20%, but preferably from some 40% to 65%, of the sludge withdrawn from intermediate clarifier 5 into the effluent collector 1 that precedes the sand-trap tank 3. The feedback may take place at a distance of 800 to 1000 metres before sand-trap tank 3.

Figure 1 shows that in combined operation the subsequent biological purification stage is arranged as the second constructional stage with an activation tank 8 for a sludge loading in the range of 0.15 to 1 which is connected in the outlet 9 of the intermediate clarifier equipment 5 and is provided with a final clarifier equipment 10 with sludge offtake 11. It has not been shown that as a further constructional stage a trickle filter could be located between intermediate clarifier equipment 5 and the activation tank 8 of the second construction stage. Figure 5 show that in combined operation the subsequent biological purification stage is produced as the second constructional stage and as a trickle filter 12 followed by an activation tank 8 equipped for the above-stated sludge loading, the activation tank 8 being connected to a final clarifier equipment 10 with sludge offtake 11. In the form of construction according to Figures 1 and 5 a strict separation of bacterial colonies is in this respect maintained between the basic constructional stage operating as an adsorption stage and the subsequent activation stages. This is not absolutely necessary. In combined operation a portion of the sludge withdrawn from the final clarifier equipment 10 could indeed be re-introduced into the sand-trap tank 3 operating as an adsorption stage, via suitable re-cycling equipment 13, as has been indicated in Figure 5 by a chain-dotted line. In the form of construction according to Figure 5 the outflow beyond final clarifier equipment 10 could be supplied via a separate feedback pipe to effluent collector 1, up to five times the inflow quantity this being for the purpose of denitrification and or dilution.

Claims

1. An effluent purification installation functioning in more than one stage, that can be erected in several constructional stages, with a mechanical purification stage and, in the fully constructed stage, at least one subsequent biological purification stage, in which an effluent collector precedes the mechanical purification stage and in which the mechanical purification stage possesses a preliminary purification contrivance in the form of a rake or the like, a sand-trap tank with aeration equipment and a subsequent intermediate clarifier equipment with a sludge offtake, and which also can be independently operated by itself as a basic constructional stage before erection of the subsequent biological purification stage, and after erection of the subsequent biological purification stage can be operated in combination with the latter, the sand-trap tank having a volume corresponding to a volume requirement of at least 6 litres and preferably 8 litres per inhabitant and being equipped to serve as an adsorption stage.

2. An effluent purification installation according to claim 1, wherein when operated alone and in combined operation sludge recycling equipment to feed into the effluent collector at least 20% and preferably some 40% to 65% of thg sludge withdrawn from the intermediate clarifier is connected to the intermediate clarifier equipment or to its sludge offtake.

3. An effluent purification installation according to claim 1 or claim 2, wherein when operated alone the sludge that is not recycled can be conveyed, for further treatment without a septic tank, to equipment for the addition of calcium salts or iron salts and to a chamber filter press.

4. An effluent purification installation according to any one of claims 1 to 3, wherein when operated alone the outflow from the intermediate clarifier can be conveyed to equipment for the irrigation andlor fertilization of agricultural crops.

5. An effluent purification installation according to any one of claims 1 or 2, wherein when operated in combination the subsequent biological pu rification stage is installed as the second constructional stage for sludge loading Lns in the range of 0.15 to 1, is connected to the outlet of the intermediate clarifier and is equipped with a final clarifier with a sludge offtake.

6. An effluent purification installation according to claim 5, wherein in a further construction stage a trickle filter stage with a volume loading of 0.2 to 2 or more, according to its filling, is located between the intermediate clarifier equipment and the activation tank of the second constructional stage.

7. An effluent purification installation according to claim 1 or claim 2, wherein when operated in combination the subsequent biological purification stage is produced as the second constructional stage and as a trickle filter stage followed by an activation tank equipped for a volume loading equal to or greater than 0.15, and the activation tank is connected to final clarifier equipment with a sludge offtake.

8. An effluent purification installation according to any one of claims 1 to 7, wherein when operated in combination at least a part of the sludge withdrawn from the final clarifier equipment can be re-introduced into the sand-trap tank operating as an adsorption stage, via suitable re-cycling equipment.

9. An effluent purification installation according to any one of claims 1 to 8, wherein the adsorption stage is operated with procaryotic cells as working biomass, and that procaryotic cells that amount to at least 1% by weight of the working biomass in a cubic metre of the adsorption stage are continuously introduced into the adsorption stage with the inflowing crude effluent as make-up biomass, preferably in quantity of 5% to 15% by weight per cubic metre.

10. An effluent purification installation according to any one of claims 1 to 7 and 9, wherein a strict separation of bacterial colonies is maintained between the adsorption stage and the subsequent stages.

11. An effluent purification installation substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 5 of the accompanying drawings.